Citation
A multiple tracer approach to determine the ground and surface water relationships in the western Santa Fe River, Columbia County, Florida

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Title:
A multiple tracer approach to determine the ground and surface water relationships in the western Santa Fe River, Columbia County, Florida
Creator:
Hisert, Richard A., 1965-
Publication Date:
Language:
English
Physical Description:
xiii, 212 leaves : ill. ; 29 cm.

Subjects

Subjects / Keywords:
Aquifers ( jstor )
Bathroom sinks ( jstor )
Groundwater ( jstor )
Karsts ( jstor )
Limestones ( jstor )
River water ( jstor )
Rivers ( jstor )
Streams ( jstor )
Surface water ( jstor )
Tracer bullets ( jstor )
Dissertations, Academic -- Geology -- UF
Geology thesis, Ph. D
O'Leno State Park ( local )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.) -- University of Florida, 1994.
Bibliography:
Includes bibliographical references (leaves 199-211).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
Richard A. Hisert.

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University of Florida
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A MULTIPLE TRACER APPROACH TO DETERMINE THE GROUND AND SURFACE WATER RELATIONSHIPS IN THE WESTERN SANTA FE RIVER,
COLUMBIA COUNTY, FLORIDA









By

RICHARD A. HISERT


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


1994













ACKNOWLEDGEMENTS


I would like to thank my committee members for

encouraging and supporting me throughout this endeavor and especially Dr. Ellins for providing me the initial funding and impetus for pursuing this study as well as her numerous editorial comments. In addition, I would like to acknowledge that many of the tools and methods in this work closely follow the guidelines and advice, both written and verbal, of Dr. K.K. Ellins. I am forever indebted to Todd Kincaid for all of his help in the lab and in the field with this project. His friendship and efforts are truly genuine. Thanks are also extended to the numerous students who lost many hours of sleep and helped with the field experiments in this study. My sincere thanks go to the excellent staff at O'Leno State Park, especially its manager Mr. Dale Kendrick for all of his help. I also thank the National Science Foundation, Geological Society of America and Sigma Xi for providing funds for this project. Also, I would like to thank Tim Aydt of the University Athletic Association for his funding through this project.

Finally, I thank my sisters Tonia, Melissa, Jill and

Tara and my parents Gerald and Nancy for their never ending support and encouragement in all my endeavors. Hopefully








they think, this will be my last academic one. Lastly I would thank my wife, Nicohl, for helping me through all the tough times and laughing with me during all the good ones.


iii















TABLE OF CONTENTS

P~gn

ACKNOWLEDGEMENTS ................... ....... * ii

LIST OF TABLES. . . ........ ....... . ..... ... .. ...... vii

LIST OF FIGURES ................ ......... .... ......... . ix
ABSTRACT ................................. ........... . xii

CHAPTER

1 INTRODUCTION ... ............. .... . . . ... 1

Purpose ........................ . ........... 2
significance ...... ............. ............. 3
Study Area........ ...................... 4
Physiography........ ......... . ............. . . 10
Climate .... ..... o...... ....... .......... ... 14
Geology ... o -... o..... o.... o ...... .. . .. . ...... 14
Karst Development ........ . ..... ...... .. .o 28
Regional Ground Water Flow ................. 33
Wetland Environment. ............ ... ... ..... 34

2 BACKGROUND ....... ..... ... ............ ........37
Radon-222 ..... ....... . .o - -o o . .. 3
Sulfur Hexafluoride....... .. . . . o . ..... . 39
Rhodamine WT ... ... . .... . . .......... oo 44
Oxygen Isotopes.. ... ...... ...... . ..... . ..... 46
Cation Concentrations........................ 48
Previous Hydrogeological Investigations ...... 50 Reaeration Coefficients................-..... 53

3 MATERIALS AND METHODS .... ... .................. 56

Gas Chromatography and the Injection Port
System ....... ... ..o....................... 56
SF6 Injection System. ......................... 57
Thermometry ......... ..... .......... ... 57
Sampling Techniques.. ..... . ........ ..... . 58
SF6 Sampling............... ...... . .... . .. 58
Rhodamine Wt Sampling..................... 59








Radon Sampling... ........................ . 61
Oxygen-18 Sampling ..................... 61
Cation Sampling .............................. 63
Quality Control ............................ 63
Reaeration Methods ........................... 63
Analytical Techniques ........................ 66
Gas Chromatography ........................... 66
Fluorometric Procedures .................... 67
Radon Analysis .................... ......... 68
Atomic Adsorption Spectrometry ............. 69
Computer Modeling ......................... 69
Numerical Models ........................... 70

4 RESULTS AND DISCUSSION ............ . .......... 74

Mixing Experiments ........................... 74
Introduction ....................... ........ 74
Radon-222 .................................. 75
Sulfur Hexafluoride ........................ 76
Process of Dilution and Mixing ..........7.. 77
Injection at Wilson Springs... ............... 79
Hollingsworth Bluff ........................ 80
River Rise to Two Kilometers ............... 84
Rum Island to Ginnie Springs ............... 84
Summary of Mixing Experiments ................ 86
Wilson Springs ............... ............ 86
Hollingsworth Bluff ........................ 91
River Rise to Two Kilometers ............... 94
Rum Island to Ginnie Springs ............... 96
Discussion ............................ o 96
Water Tracing Experiments .................... 99
O'Leno Sink to River Rise .................. 99
Results .... ... . . . . . . . . . . . . . . 0
Sweetwater to Santa Fe River Boils ........ 113 Jim's Sink to Santa Fe River Boils ......... 114 Summary of Water Tracing ................... 123
Flow Component Analysis ...................... 126
Radon-222 Transect ......................... 126
0-18 Transect ..................... ......... 129
Cation Concentrations ...................... 131
Temperature Transects ...................... 136
Computer Modeling .......................... 141
Reaeration Studies .........o................. 145
Gas Transfer ... ........................... 152
Reaeration Coefficients .................... 155

5 SUMMARY AND CONCLUSIONS ........................ 163

Mixing....................................... 163
Tracing...................................... 164
Flow Component ........................................ 164
Reaeration ................................... 165









Sulfur Hexafluoride .......................... 166
Karst Development in O'Leno State Park....... 167


APPENDECIES

A GAS CHROMATOGRAPHY AND THE INJECTION
PORT SYSTEM ................ .................. 171

B SF6 INJECTION SYSTEM ......... ............. 192

C CATION BOTTLE PREPARATION......o............... 197

REFERENCES. ..... .... * * .. .. . .. .. .. . .. .. .. . 199

BIOGRAPHICAL SKETCH ............................. 212














LIST OF TABLES


Table page

1 Regional Stratigraphy in Northeastern Alachua
County, Florida (after Biddlecomb, 1993) .......... 20

2 Hydraulic Conductivity of Wetland Soils Compared
to Other Mineral Soils .............................. 36

3 Statistical Data for Radon Distribution throughout
the Stream Cross-Section .......................... 92

4 Estimated time Until Leading Edge of Tracer
Reaches Sink ...................................... 108

5 Estimated Passage Time for the Tracer Cloud
at Each Sink ...................................... 108

6 Travel Times for SF6 a Sinks in O'Leno State
Park .............................................. 111

7 SF6 Travel Times for Jim's Sink to Santa Fe
River Rise Experiment ............................... 120

8 Cation Concentrations for Locations in O'leno
State Park ........................................ 133

9 Stream Gaging data for the Santa Fe River ......... 153

10 Values of k in Meters per day for Intervals
Between the Stream Gaging Locations in the First
Reaeration Experiment ............................. 156

11 Values of k in Meters per day for Intervals
Between the Stream Gaging Locations in the Second
Reaeration Experiment ............................. 157

12 Comparison of Schmidt Numbers for SF6,
Rn-222, and 02 at Selected Temperatures .......... 159

13 Comparison of Selected Stream Reaeration
Coefficients Determined Through the use of
Volatile Tracers .......... ........................ o 161


vii








14 Comparison of Stream Reaeration. Coefficients
YK, (day-1) Determined Through the Use of SF6
with Values Derived from Predictive Models......... 162


viii














LIST OF FIGURES


FIGURE

1 Santa Fe River Basin in north central Florida
(after Hunn and Slack, 1983) ...................... 5

2 Springs found in western Santa Fe River Basin.
(after Hunn and Slack, 1983) ......................... 8

3 Potentiometric surface of the Florida Aquifer
and direction of ground water flow in the study
area (from Meadows, 1991) ........................... 9

4 Physiographic provinces in the study area (from
Kincaid, 1994).................................... 11

5 Structural features in peninsula North Florida
(after Biddlecomb, 1993) .......................... 16

6 Geology of western Santa Fe River Basin
(after Briel, 1976) ............................... 17

7 Cross section through the western Santa Fe River
Basin (after Briel, 1976) ......................... 18

8 Hydrogeologic units of the western Santa Fe
River Basin (after Hunn and Slack, 1983) .......... 28

9 Rio Grande de Manati Rn-222 concentration
(from Ellins et al., 1990) ........................ 40

10 Ichetucknee River Rn-222 concentrations ........... 41

11 Charcoal packets used in rhodamine WT dye
tracing experiment ................................ 60

12 Sampling device and graduated cylinder for SF6
and Rn-222 ........................................ 62

13 Rise to plateau for SF6 in the Santa Fe River ..... 65 14 A. Finite difference grid. B. Computer
notation for finite difference grid
(after Hisert, 1990) .............................. 73








15 Lower Santa Fe River Basin near Wilson Springs
(from Ellins et al., 1993) ........................ 81

16 Sample locations at Hollingsworth Bluff
(from Ellins et al., 1993) ........................ 83

17 River Rise to 4 km on Lower Santa Fe River
(from Ellins et al., 1993) ........................... 85

18 Rum Island to Ginnie Springs on
Lower Santa Fe River (from Ellins et al., 1993)... 87 19 SF6 concentrations response curves
0.5 to 1.0 km ..................................... 88

20 SF6 concentrations response curves
1.5 to 2.0 km ................... ............... 89

21 Contoured cross-sections of 222Rn
concentrations in river near Hollingsworth Bluff
(dimensions in meters, contour interval equals
10 dpm/L ................................. ......... 93
22 Mixing results at 0.5, 1.0, 1.5 km downstream
of the River Rise . . ............................. 95

23 Plan view of mixing in Ginnie Springs area ........ 98 24 O'Leno State Park with numbered sample
locations for O'Leno tracing experiment
(from Ellins et al, 1993) ......................... 100

25 Bathymetry of O'Leno Sink ......................... 105

26 Bathymetry of River Rise .......................... 106

27 Concentration response curves for Ogden Pond,
Ravine Sink, Pareners Branch Sink and Small Sink.. 109 28 Concentration response curves for New Sink,
Jim's Sink, Two Hole and Sweetwater Lake .......... 110 29 Concentration response curves for Sweetwater
experiment ............................... ........ 115

30 Concentration response curves for Jim's Sink
experiment ........................................ 118

31 Concentration response curves for Jim's
sink injection ........... . . ....................... 119









32 Flow Pattern of the underground Santa Fe River
through O'Leno State Park .......................... 124

33 Sample locations for 222Rn, "80, major
cations and Temperature ............................ 127
34 Radon-222 concentrations for karst features found
throughout the park ................................. 128
35 80O Values for Karst Features in O'Leno
State Park .......................................... 132

36 Cation Concentrations in O'leno State Park ........ 135 37 Temperature Readings Recorded in O'Leno State
Park ................................................ 138

38 Computer model set up for the western Santa Fe
River region between O'Leno Sink and Rum Island... 142 39 Sampling locations for the first reaeration
experiment .......................................... 146

40 Sulfur hexafluoride and radon profiles for
the first reaeration experiment ................... 147

41 Sampling locations for the second
reaeration experiment ............................... 149

42 Sulfur hexafluoride and radon profiles for
the first reaeration experiment ................... 150

43 Gas chromatograph setup for SF6 analysis .......... 175 44 Cross section of dreirite tube used in
SF6 analysis ........................................ 177

45 Multi port injection system for SF6 analysis ....... 179 46 Glass syringe used for injecting SF6 sample ....... 186 47 SF6 field injection system used throughout all
injection experiments ............................... 194














Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy


A MULTIPLE TRACER APPROACH TO DETERMINE THE GROUND AND SURFACE WATER RELATIONSHIPS IN THE WESTERN SANTA FE RIVER, COLUMBIA COUNTY, FLORIDA

By
Richard A. Hisert

December 1994

Chairman: Douglas L. Smith
Major Department: Geology


This project characterized the complex karstic

groundwater/surface water relationships of the Santa Fe River in north-central Florida while further developing the use of the new geochemical tracer sulfur hexafluoride (SF6) and naturally occurring radon-222 (222Rn) as well as relatively established hydrologic techniques. To accomplish the objectives, mixing, water tracing, flow component and reaeration experiments were completed along several reaches of the Santa Fe River and within O'Leno State Park.

The mixing experiments revealed the effects of incoming springs and syphons within the stream cross section and suggested more detailed sampling strategies in order to accurately evaluate stream parameters. In addition, these experiments established newly developed SF6 injection


xii








techniques. Water tracing experiments established two things: 1) SF6 is an excellent alternate method of ground water tracing and 2) the relationships among water sources in O'Leno State Park.

Flow component analysis further described the complex water balance within O'Leno State Park while comparing several techniques. Finally, reaeration studies confirmed the usefulness of SF6 in determining gas exchange in karstic riverine studies.

A consequence of the research was the establishment of a first-rate SF6 analytical laboratory; one of only a handful in North America. SF6 has become a viable alternative to the presently used dyes and harmful gases, in perhaps one of the most complicated ground water and surface water regions in the world. In addition, because this study was undertaken successfully in such a hydrologically complicated environment, future use of SF6 in simpler environments promises to be successful as well.


xiii














CHAPTER 1
INTRODUCTION

The nature of active karst regions is complex and hydrogeologically difficult to describe. Clues to the historical development of a karst region are also hard to evaluate. Past studies of karst regions employ a variety of hydrologic tracers that were often scientifically inadequate or had negative side effects (White,1990). As karst regions, in general, become increasingly populated the need to develop a reliable and environmentally safe ground and surface water tracer is obvious (Dennis Price, personal communication, 1994). Sulfur hexafluoride, a newly developed artificial tracer, provides a means to interpret ground and surface water interactions in a dependable, nontoxic manner.

Wetland areas found within this region of Florida may provide some insight to the geological development of karst, both past and present. The careful study of karst and wetland areas together may aid in the future planning of active karst regions. The Santa Fe River Basin in northcentral Florida provides the unique opportunity to assess the relationships between ground water and river water and wetlands within a complex karstic setting.










Purpose

The primary purpose of this project was to accurately characterize the complex karstic ground water/surface water relationships of the Santa Fe River while continuing to develop the use of the new geochemical tracer SF6 and naturally occurring 222Rn. The relationships between the two primary water resources, ground water and surface water, were assessed in terms of their distribution using SF6, 222Rn and other tracing techniques. The wetlands in the region were also addressed in terms of their chemical signature and connection between ground and surface water. In order to accomplish this task several goals were outlined. They included

1) designing and developing an efficient laboratory,
injection system and collection system for the
dispersal and analysis of SF6;
2) understanding the temporal changes of the Santa Fe
River system;

3) understanding the mixing aspect of the river;

4) characterizing ground water, surface water and
spring water Rn concentrations in the study area;

5) locating most if not all sub-surface flow sources
and sinks of ground water to the Santa Fe River
within the O'Leno State Park region;

6) measuring river discharge and stage during high and
low flow sampling periods.


Significance

This work provides valuable information on the ground

water/surface water relationships of the Santa Fe River. It










first describes the complex interactions between ground and surface water within the stream and describes how to accurately address river sampling in a karstic environment. Surface and ground water data, used in conjunction with the river reaeration data gained in this study, can assist future planners and developers of the Santa Fe River basin in managing their surface and ground water resources. This work also documents a method of interpretation for active karst regions. Wetland areas studied in conjunction with intensive ground and surface tracing experiments may provide a means to interpret historical and future developments of karst features.

The research also expanded the application of SF6 as a workable tracer in a number of complicated ground water and surface water situations. Propane, ethylene and fluorescent dyes currently in use to predict ground water flow paths, flow rates, reaeration coefficients, and stream mixing, are toxic or have negative side effects such as water discoloration (Aley, 1990; Quinlin, 1990). In contrast, SF6 and 222Rn are nontoxic in low concentrations, have no color or odor and 222Rn occur naturally. For these reasons, the measurement of SF6 and 22Rn together may gain in popularity in reaeration and tracer studies and possibly replace the presently used toxic gases in sensitive environments (Ellins, 1989).










An important consequence of the research effort is the establishment of a state-of-the-art SF6 analytical laboratory. At present, only a few institutions in North America have developed the analytical capability to utilize SF6 as a water tracer. The tracer, SF6, has become a viable alternative to the presently used dyes and harmful gases in perhaps one of the most complicated ground water and surface water regions in the world. The techniques and ideas learned from this study will enable future researchers to study ground water in a more efficient and less harmful manner to the environment. In addition, because this study was undertaken successfully in such a hydrologically complicated environment, future use of SF6 in a simpler environment may have high success rates as well.



Study Area

The Santa Fe River, located in north-central Florida, is a principal tributary of Florida's second largest river, the Suwannee River, which is classified as an Outstanding Florida Water (OFW) (Fernald and Patton, 1984). The Santa Fe River originates in Lakes Santa Fe and Altho and flows westward until it goes underground at O'Leno Sink. It returns to the surface five kilometers farther south and continues to flow sinuously south and west until it joins with the Suwannee River (Figure 1). Elevations within the drainage basin of the river range from 85 m in the eastern



































SUWANNEE RIVER WATER MANAGEMENT
DISTRICT
I - x


Figure 1. Santa Fe River in north central Florida (from Hunn and Slack, 1983).








6

sub-basin to 10 m in the western part of the basin (Hunn and Slack, 1983).

The Santa Fe River basin is underlain by several

hundred meters of sand, clay, marl, dolomite and limestone which unconformably overly a Paleozoic basement. The lower sedimentary rocks (Cretaceous to early Eocene) consist primarily of marine limestone and some evaporites and clays, which have very low permeabilities. The sedimentary rocks (middle Eocene to middle Miocene) overlying the low permeability layer are predominantly porous limestones that comprise the Floridan Aquifer. The limestones of the Eocene Ocala Group underlie the study area and provide the source for many of the springs feeding the Santa Fe River (Figure 2; Briel, 1976; Hunn and Slack, 1983).

The karstic hydrology of the Santa Fe River is

extremely complex. The ground and the surface water systems in the region do not have the same geographical boundaries within this region. Although surface water does not cross the Santa Fe River basin boundary, the ground water system in the area does not coincide with the stream drainage system. Accordingly, the flow of the Santa Fe River is not consistently related to the size of the drainage basin and the amount of rainfall over the basin as a whole. Both the topography and the geology are responsible for these conditions in the Santa Fe basin (Briel, 1976; Hunn and Slack, 1983). Because of these circumstances, relationships










between surface water and ground water have not yet been completely resolved (Hunn and Slack, 1983; Ellins et al., 1993; Hisert and Ellins, 1993; Kincaid, 1994).

Below the River Rise in O'Leno State Park there is a noticeable absence of surface water flowing into the Santa Fe River from tributaries. From the River Rise to the point of confluence with the Suwannee, approximately 22 known springs are visible along the banks of the lower Santa Fe (Figure 2). Numerous sinkholes bordering the Santa Fe provide the conduits by which precipitation flows underground to recharge the aquifer and eventually discharge into the Santa Fe River.

The potentiometric surface of the Floridan Aquifer in the Santa Fe basin is shown in figure 3. The upstream bending of the equipotential contours indicates a leakage of ground water into the lower reach of the Santa Fe River. Water normally flows from the aquifer to the river when the surface of the river lies lower than the potentiometric surface of the aquifer. The direction of flow is reversed when the surface of the river rises above the potentiometric surface. In periods of drought the water in the lower Santa Fe River channel consists primarily of discharge from the Floridan Aquifer; while at times of heavy rainfall, the










































Figure 2. Springs found in western Santa Fe River Basin (from Hunn and Slack, 1983).










83 rIEI 45'


EXPLANATION
-10- POTENTKI*MEIRIC CONTOUR-Shows aloude at
which W I level slands m tay cased wels m
I*e Upp fbidan aqudem Conk" inlmval I10
NlW. Dalmn is sea level
GENERAL DIRECTOR OF GROUND WATER FLOW M MONITORED DAIRY FARM


5 t0 Is 20 25 MILES
I I I I 25 I I I I I I )5 .t0 IS 20 25 KILOMETERS


Figure 3. Potentiometric surface of the Florida Aquifer and direction of ground water flow in the study area (from Meadows, 1991).


WI"









is,














%nor5


W 82,i1-i'


83*15"










"surface water" in the river recharges the aquifer via the springs through a process, which is known as "backflow" (Hunn and Slack, 1983; Kincaid, 1994). The spring that normally feeds the river with ground water is now acting as a conduit by which the aquifer is being fed with river water.
Phvsiogra~hy

This study area lies within the Western Valley and Marginal Zone physiographic provinces (White, 1970) and forms the boundary between Alachua and Columbia counties (Figure 4). To the east of Western Valley province lies the Northern Highlands Marginal Zone which is the boundary between the Western Valley Lowlands and the Northern Highlands, as described by White (1970). The Northern Highlands are poorly drained and plateau-like with elevations generally greater than 30 m above mean sea level (msl). The eastern boundary of these highlands is Trail Ridge, a sinuous, elongate feature that runs through the central part of peninsular Florida. The Cody Scarp is the topographic marker that separates the highlands from the lowlands. This "scarp", although one of the most prominent features in peninsular Florida, can often be graded and difficult to identify through the undulating topography of the Marginal Zone.

O'Leno State Park lies within the eastern extent of the Marginal Zone. The Marginal Zone has also been described by










































LEGEND
a- Chiefland and b- Columia Lamestone Plains Wacasassa Flats - c- Bel and d- Brookisle Ridges High Spnngs Gap
r Suwannee and Santa Fe Ri-er Valley Lowands River



Figure 4. Physiographic provinces in the study area (from Kincaid, 1994);










other authors as the Transitional Zone, the hydrologic and topographic transition between highlands and lowlands (Ceryak et al., 1983) and the Perforated Zone, the zone throughout which sinkholes have breached the western extent of the Northern Highlands (Macesich, 1988). Although, the terminology represents about the same physical area, there are subtle differences between the many terms Marginal Zone, Cody Scarp, Perforated Zone and Transitional Zone. The eastern boundary of the Marginal Zone is sinuous due to differential erosion produced by various streams and delineated by the point to which headword eroding streams have dissected the Northern Highlands (Williams et al., 1977). Its western boundary is also variable and generally depicted as the western edge of the Hawthorn Group of sediments. The width of the Marginal Zone ranges from 2 to 11 km and elevations within this zone range from about 15 to 30 m above msl.

Within the Marginal Zone numerous streams disappear into the top of the Floridan Aquifer, including Clay Hole Creek and Rose Creek (Columbia County), and Turkey Creek and Mill Creek (Alachua County). The Santa Fe River that borders both Alachua and Columbia counties also disappears within this zone. The Suwannee River is the only stream that passes from the highlands to the lowlands without disappearing underground.








13

The Western Lowlands, bounding the western edge of the Marginal Zone, is a weathered limestone plain. There is a noticeable absence of surface streams as most runoff infiltrates directly to the subsurface due to extremely permeable nature. Sand and thin soil form a veneer over the Ocala and Suwannee Limestones which were formerly covered by the Hawthorn Group sediments (Pirkle, 1956). Williams et al. (1977) and Williams (1983) acknowledged the difficulty in assessing the cause of the denudation of the limestone plain. These workers suggest that the limestone plain may be the result of marine planation which removed subsequent sand deposits or fluctuating ground water levels activating karst erosion processes. Remnants of the Alachua Formation and Hawthorn Group covering the older limestone are present as outlier hills and sinkhole fill. The remnants, especially the outlier hills, are evidence that the younger units covered the Western Plain at previous times. Except for the outlier hills, most of the Western Valley has a maximum elevation of 10 to 15 m (Pirkle, 1956). White (1970) named the portion of the Western Valley between the Northern Highlands and the Brooksville Ridge the High Springs Gap. The lower Santa Fe River (below the River Rise) meanders through the High Springs Gap and separates Alachua and Gilchrist Counties from Columbia County.

This karstic limestone plain was subsequently terraced by the Wicomoco, Penholoway, Talbot, and Pamlico seas of










Pleistocene interglacial periods (Pirkle, 1956; Clark et al., 1964). During this time period accumulations of clastic material were deposited over low lying hills and cavernous limestone (Clark et al.,1964).


Climate

The average temperatures at Lake City and Gainesville are about 190C and 200C respectively. The dependence of average annual rainfall on three different types of storms explains, at least in part, the high variability in annual rainfall. Annual rainfall for the period 1900-1976 ranged from 76 cm in 1908 to 213 cm in 1964 in Lake City, and from about 84 cm in 1917 to 195 cm in 1964 in Gainesville (Hunn and Slack, 1983). Monthly rainfall is usually greatest from June to September. Rainfall in the basin is derived from weather fronts, local thunderstorms, and seasonal tropical storms.

Geologv
The following discussion of the geology of the Santa Fe basin was compiled from numerous sources, among which there is not complete agreement on the nomenclature and age of some of the formations. For more detailed discussions pertaining to the geology of parts of the basin the reader is referred to Vernon (1951), Puri (1957), Meyer (1962), Clark et al. (1964), White (1958; 1970), Faulkner (1973) and Scott (1988).










The dominant large scale structural features in northpeninsular Florida are shown in Figure 5. These features include; the Peninsular Arch, Ocala Platform, Jacksonville Basin and Appalachicola Embayment (Brooks, 1981; Ceryak et al., 1983; Miller et al., 1978; Scott, 1988; Opdyke et al., 1984). Of these, the Peninsular Arch dominates the distribution of Mesozoic sedimentary rocks throughout this study region.

The Santa Fe River basin is underlain by several hundred meters of partially consolidated marine and nonmarine deposits of sand, clay, marl, gravel, limestone, dolomite, and dolomitic limestone. The interpretation of electric logs of test wells indicates that 0.85 to 1.05 km of sediments, ranging in age from early Cretaceous to Holocene, unconformably overlie structurally high, complex basement rocks of Paleozoic age (Figure 6 and 7). The lower sediments (Cretaceous to early Eocene) consist primarily of marine limestone, some evaporites and clay, and they have very low permeability. These rocks form a basal aquiclude which effectively prevents the further downward movement of ground water.

The sedimentary rocks (middle Eocene to middle Miocene) overlying the basal aquiclude are predominantly porous marine limestones which serves as the principal waterbearing units in the area that comprise the Floridan


























Appalachicola Embayment






A.


Jacksonville Basin


-F0 0


Figure 5. Structural features in peninsular-north Florida (after Biddlecomb, 1993).

































Ocala Limestone


Figure 6. Geology of the western Santa Fe River Basin (after Briel, 1976).

















Alaohua ormtoon'l
8uwannnee Lleeto ne
-a



I o Avon Park Limestone



,, Lake City Limestone


0 1 4 6 4 0
.. . L Oldsmar Limestone


Figure 7. Cross section through the western Santa Fe River Basin (after Briel, 1976; L-LI refer to figure 6).










Aquifer. The Floridan Aquifer underlies all of the Santa Febasin and it is the principal source of many of the springs on the lower Santa Fe River.

An upper aquiclude of sand and clay sediments overlies the limestone units in the eastern half of the basin. These sediments are early-to-middle Miocene in age and they generally have low permeability, serving to confine the water in the Floridan Aquifer under artesian pressure. Locally, some limestone beds within the unit are tapped for domestic water supplies.

Above this unit, sediments of coarse sand and clay (late Miocene to Holocene) serve as a temporary storage reservoir for water which seeps slowly into the semiconfining beds of the aquiclude. This secondary, or watertable aquifer, is usually under non-artesian conditions and is recharged directly by local rainfall which percolates quickly through the topsoil. The water-table aquifer yields moderate quantities of water to shallow wells in those areas of the Northern Highlands where it exists.

The Tertiary strata which compose the Floridan Aquifer in the Santa Fe basin have been divided into several series on the basis of their age and their position in the stratigraphic column (Table 1). The lowest series (Eocene) includes the Oldsmar Limestone, Lake City Limestone, Avon Park Limestone, and the formations of the Ocala Group.










Table 1. Regional Stratigraphy in Northeastern Alachua County, Florida (after Biddlecomb, 1993).


Formation
Era Period Epoch or Characteristics
El I I Group I


Recent

to
Pleisto. and Plio.


Terrace
Deposits
and

residuum


- S - S U


Pleisto.
to

Miocene


Alachua Formation


Sinkhole fill, fluvial terraces, and thin surficial sand (2); fine to medium grain sands with minor organics and heavy minerals


Gray to blue-gray clayey sand that weathers red-brown (1); sinkhole fill and residuum from postEocene deposits, with limestone boulders and phosphate
(3)


Phosphatic clayey sandsandy clay with varying amounts of Fullers Middle to Hawthorn Earth and carbonate (1); Lower Group three formations described but difficult Miocene to map locally (4); two lithologic types mapped in study area (6)
ery pale yellow, Suwannee oderately indurated,
Limestone orous, fossil-rich
Lalcarenite (2); Rhynholampus gouldii


Eocene


Ocala Limestone


- I - I - a a


White to cream, soft & granular, massive, fossil rich limestone, locally well indurated (1); Lepidocyclina sp.








21
The oldest unit which bears fresh water is probably the Oldsmar Limestone (early Eocene), but its permeability isgenerally low and the sulfate concentration is high. The high sulfate content of the Oldsmar Limestone causes it not to be considered an important contributor to the Floridan Aquifer. The top half of the unit is a moderately porous brown limestone with some gypsum and anhydrite. The bottom of the Oldsmar, however, is strongly dolomitized, and the water therein is highly mineralized and unsuitable for domestic use. Over most of the Santa Fe basin, the Oldsmar lies at relatively great depths (400 meters to 500 meters below the surface).

The Lake City Limestone (middle Eocene) is the oldest formation in the area from which supplies of fresh ground water may be obtained. This unit is about 150 meters thick and is composed of alternate layers of dark brown dolomite and chalky white limestone, both of which contain chert and gypsum. The permeability of the unit varies from low near its base to high at the top, and the entire formation is considered a part of the Floridan Aquifer, but very little is being pumped from the Lake City Limestone because of its high sulfate content.

The Avon Park Limestone (late-middle Eocene)

disconformably overlies the Lake City limestone, and is a creamy, chalky deposit which is 52-82 meters thick and has a distinctive and abundant fauna of foraminifera. The Avon










Park Limestone is a highly permeable part of the Floridan Aquifer, but it is not extensively tapped as a potable water supply because of its high sulfate content. The Oldsmar, Lake City and Avon park Limestones do not out-crop within the Santa Fe basin.

The Ocala Group (late Eocene) disconformably overlies the Avon Park Limestone. The group consists of three formations of very similar lithology. From oldest to the youngest they are the Inglis, Williston and Crystal River formations. The limestones of the Ocala Group vary from a porous, cream-white, loose coquina of large foraminifera and shells to a brown, solution ridden, echinoid-rich limestone. The total thickness ranges from 46 to 76 meters. Locally, limestone at the top of the Ocala has been replaced with chert. The permeability of these formations is extremely high and the Ocala Group serves as the principal source for many of the springs and large capacity wells in the Santa Fe basin.

Limestones of the Ocala Group, the oldest rocks exposed in the Santa Fe basin, are commonly found at the surface west of High Springs along the channel of the lower Santa Fe River; the outcrop is covered in the area only by a veneer of loose sand. A well developed karst topography, which includes such features as filled open sinks, sinkhole lakes, solution pipes, basins and prairies, is typical of areas underlain by the Ocala Group. The intricate fracture










pattern of the limestone has produced a one-meter water rapid on the river near Fort White. The strike of the falls is approximately N. 600 E., which conforms to the general fracture pattern of northern Florida.

The Oligocene Series, represented by the Suwannee Limestone, unconformably overlies the Crystal River Formation. The Suwannee Limestone is very permeable and porous and is lithologically similar to the members of the Ocala Group. The Suwannee is composed of hard and soft beds of white, tan, or cream-colored limestone that are partly dolomitic and coquinoid; some sand and silicified layers of chert are also present. The Suwannee is a residual material which is generally absent in the western half of the Santa Fe basin; it occurs locally north and northeast of Gainesville, and appears to be continuous in a narrow outcrop northwest of O'Leno State Park. Its thickness in this area reaches 15 meters.

The Miocene Series is represented by the Hawthorn Group and Alachua and Choctawatchee formations (Scott, 1988). The Hawthorn Group, in the study area, consists of three formations, (the Coosawhatchie, Marks Head and Penny Farms). The Hawthorn Group is composed of marine sands, clays, marls and sandy limestones, all of which may be phosphoritic. The lower part of the Hawthorn contains beds of hard dolomitic limestone and interbedded clays, and the contact with the underlying formations is probably disconformable. The main










deposit reaches a thickness of 75 meters and consists chiefly of thick clays that range in color from yellow-green to blue-gray. Layers or lenses of sand and soft white limestone and phosphatic limestone are interbedded with clays; large pebbles of phosphate having brownish-black color are disseminated throughout the formation.

Though the Hawthorn is continuous over much of the Santa Fe basin, the main body of the deposit lies in the Northern Highlands province along the upper course of the river. The outcrop in this area is often covered by a relatively thin layer of loose sand, sandy clay, and organic humus. Remnants of the Hawthorn have filled sinks and lake basins and have formed a mantle of sediment over the outcrop of the Ocala Group in some parts of the western basin. The relatively thick and impermeable Hawthorn sediments serve as the principal confining beds to contain the waters of the Floridan Aquifer under artesian pressure. In addition, these semi-confining beds serve as a basal aquiclude for the shallower water-table aquifer, retarding the movement of this water into the aquifer below. The Hawthorn Group is itself an aquifer and yields small quantities of water to domestic wells in the eastern sections of the Santa Fe basin, but its permeability is generally low and the chemical quality of the water it produces is usually poor at depth.








25
The Choctawatchee Formation overlies the Hawthorn along the extreme eastern parts of the Santa Fe basin, but it does not crop out anywhere within the area. Thin beds of sand and limestone are interlayered with soft yellow fossiliferous clay and partly-indurated marl. Pebbles of phosphate and silica are disseminated in these beds, and mollusk shells are abundant throughout the formation. The thickness of the Choctawhatchee Formation in the basin is only about four meters, and it is of minor importance as a hydrologic unit.

The Alachua Formation (late Miocene to early

Pleistocene) is a terrestrial deposit of reddish-white sands interbedded with various colored clays, sandy clays, and pebbles of phosphate. Siliceous limestone and phosphate boulders are scattered throughout the formation, as are organic materials and the fossils of various types of land vertebrates. The sandy clay and sand beds of the Alachua Formation are not as calcareous and phosphatic as similar beds in the Hawthorn, though phosphate deposits are mined in the Fort White area near the confluence of the Santa Fe and Ichetucknee Rivers. The Alachua Formation reaches a thickness of 30 meters and crops out near the south bank of the river along the Alachua/Gilchrist county line. The Alachua acts in conjunction with Hawthorn as a semiconfining unit to retain water in the Floridan Aquifer, although the aquifer is often exposed in the area of the










outcrop due to the collapse of caverns in the underlying Ocala Group. In areas where this sinkhole development has been extensive, direct recharge to the Floridan Aquifer from local rainfall is common.

Coarse clastic sediments, the Cypress Head Formation,

of late Miocene age were deposited in the Northern Highlands of the Santa Fe basin as terraces at different stages of sea level. These deposits comprise the prominent topographic features of the region, and they overlie most of the older sediments in the area. Two lithologic units are discernable; one predominantly sand and the other predominantly clay. The sand unit is mostly fine grained and argillaceous at the surface but coarsens with increasing depth, and large pebbles of phosphate quartz are found at its base. The sands are dark brown or black due the presence of organic humus and iron-bearing materials. This unit ranges from 6 to 15 meters in thickness. The clay unit is mottled red to yellow-gray and ranges from two to five meters in thickness. The clays are generally in the upper part of a sequence of beds which overlie cream-colored sands and sandy clays. The total thickness of these sediments reaches 15 meters in the northeastern parts of the basin.

Pleistocene and Holocene fluvial deposits of clay, sand and gravel usually occur beneath the flood plains of the Santa Fe and its tributaries. The stream bed of the lower Santa Fe, however, is primarily exposed limestone veneered









with coarse sand. Deposits of peat and muck are being formed in the bottom of plugged sinkholes, lakes and swamps in the basin. Eolian dunes of fine sand generally mantle the higher topographic elevations, and thicker lenses of wind blown sand mantle the valley floors and form the principal shallow surficial aquifer in the Northern Highlands.

The western part of the Santa Fe River consists of a

well developed karst plain with exposed Tertiary limestones, comprising the Floridan Aquifer. The Floridan Aquifer is mostly unconfined here because the Hawthorn Group has been removed by erosion (Puri, 1957, Briel, 1976; Fernald and Patton, 1984; Figure 8). Except for the Santa Fe and Ichetucknee Rivers, and Cow Creek (intermittent), the western sub-basin lacks surface discharge. Several large springs contribute baseflow to the lower Santa Fe River (Figure 2). Ground water influx also occurs within river bottom seeps that are controlled by large joint features found within the aquifer. Unfortunately, the detection of such sources of ground water delivery to the river is very difficult due to the depth of the river and the dark color of the water (Hunn and Slack, 1983). Ground water from the Floridan Aquiferadding to the lower Santa Fe River modifies the chemical parameters of the river and is indicated by increasing pH, alkalinity, specific conductance, and decreasing temperature (Fernald and Patton, 1984).




















82045' 82015,


3000




ALAC UA COp

GILCHRIST CO


29 046'


LE=
SATURATED UNIT NEAREST TO LAND SURFACE m surnam aquif
0 5 0 Conqn be � " i KILOMETERS P FdaeWW








Figure 8. Hydrogeologic units of the western Santa Fe River
Basin (after Hunn and Slack, 1983).










Karst Development

Because karst dominates in this study region, a brief description of its evolution and type is necessary to understand the ground water and surface water interactions. The Florida Platform encompasses the Florida Peninsula and parts of the Southeastern Atlantic and Gulf Coastal Plain. Including the encircling continental shelves, the Florida Platform has been primarily a carbonate platform on which thousands of meters of dolomites and limestones have been deposited with relatively minor amounts of evaporite and clastic sediments for much of the Mesozoic and Cenozoic periods (Clark et al., 1964; Beck, 1986).

The carbonate rocks of the Florida Platform have been variously subjected to repeated cycles of sea level fluctuations (White, 1958; Hanshaw and Back, 1979; Randazzo and Bloom, 1985; Ford and Williams, 1989). Sea level and its changing position is considered to be the keystone in the development of karst processes due to its repeated shift from vadose to phreatic zones (Back et al., 1984). The origin of numerous submarine karstic features on the Florida Platform is also attributed to glacio-eustatic sea level changes (Jordan, 1954; Jordan et al., 1964; Malloy and Hurley, 1970; Gomberg, 1977; Doyle et al., 1985; Hebert 1985; Popenoe, 1985; Mullins et al., 1986; Twichell and Parson, 1986; Paull et al., 1987).








30
There are primarily two types of karstic evolutionary schemes (Ford and Ewers, 1978). The first theory employs generalized models of the origin and sequence development of karst landforms. The second theory describes regional denudation chronologies in which the history of karst landform is reconstructed (Gunn, 1986).

Grund (1914) and Powell (1975) based their early

theories of karst on the geographical cycle concept and the sequential development of both surface (exokarst) and underground (endokarst) landforms. This type of development is in contrast to more recent author's theories such as Ford and Ewers (1978) who consider the development of exokarst and endokarst landforms separately. By doing so, Ford and Ewers (1978) have resolved most of the contradictions in development found the earlier papers of Grund (1914) and Powell (1975). Waltham (1981) supports Ford and Ewers and their theories of karstic environments that suggest separating the exokarst and endokarst development. To support these authors, numerous studies of closed depressions (dolines) have showed that since dissolution proceeds from the surface downward, there is little, if any, genetic relationship between the surface karst and the underground landforms (Williams, 1972; Jennings, 1975; 1983; Palmquist, 1979).

Within the western Santa Fe River basin, both exokarst and endokarst interactions as well as paleokarst phases








31
affect the development of karst in the region. Stringfield and others (1979) concluded that the vertical movement of water from the surface through joints, fractures and other openings in the Tertiary carbonate rocks of Florida, to discharge areas initiated the formation of lateral dissolution channels causing a circulation system below the water table. As base level and the top of the saturation zone were lowered, accompanying sinkholes developed in the initial stage of karstification because of the previously karstified underlying carbonate rocks (Stringfield et al., 1979).

In contrast to these sinkhole laden areas there are

subregions within the western river basin where previously existing dolines and dissolution shafts extended many meters below present day sea level. These sinkhole regions are now buried because of the present higher water table. This higher water table is the result of increase in sea level caused by Pleistocene deglaciation. This increase in sea level resulted in the zone of saturation to rise to water levels in the limestone at or above the bottom of the dolines that form in the zone of aeration (LeGrand and LaMoreaux, 1975).

White (1958) believes that the karst topography created by previous emergent episodes has been buried by the sands deposited during interglacial times of high sea level. These karst features, although sometimes difficult to










identify and analyze due to the brevity of glacial stages compared to the interglacial stages, can be attributed to ground water circulation in the Florida Platform which is the product of several cycles of subaerial exposure.

Fewer and smaller solution openings should be

encountered with increasing subaerial exposure of the continental shelf. The decrease in solution openings occurs because surface elevation decreases. This surface decrease in turn causes the total length of time as well as number of times the area will be emergent and exposed to subaerial conditions to decrease. Thus, during interglacial stages of warmer climate, sea levels were higher, and solution was probably retarded in the lower coastal areas because the openings were largely filled with sediments and salt water which has less capacity to dissolve limestone. White (1958) states that the coastal plain karst should be most mature on the highest land surfaces. White's theory of more developed karst on higher regions is represented in this study area. The most active karst regions in the western Santa Fe River basin are found along the marginal zone marking the boundary between the coastal lowlands and the central highlands physiographic province, where elevations are generally above 30 meters in elevation.

With prolonged re-emergence of the Florida Platform the reactivation of the karst cycle slowly opened new avenues of underground discharge and the piezometric surface gradually










dropped. This seems to have occurred in the western Santa Fe River basin where disappearing lakes, disappearing rivers, and abandoned spring heads all suggest such a drop (White, 1958).
The karst development and evolution on the Floridan peninsula was a complicated and intricate interaction of surface and ground water interactions as well as the overriding influence of the karst base level, sea level. The karst's complicated nature is evident today in the surface and ground water interactions found within the western Santa Fe River Basin.



Regional Ground Water Flow
The general trend of ground water flow in the western portion of the Santa Fe River Basin is in a westerly to south westerly direction (Hunn and Slack, 1983; Fernald and Patton, 1984; Beck, 1986). The Floridan Aquifer discharges to the Santa Fe and Ichetucknee Rivers, via springs near the rivers where the potentiometric surface is near land surface. Discharge from the Floridan Aquifer also occurs through wells and evapotranspiration. Recharge to the Floridan Aquifer occurs via syphons within the Santa Fe River and through predominant point recharge regions or sink holes found throughout the lowlands physiographic province (Hunn and Slack, 1983; Fernald and Patton, 1984). Because there is a lack of surface streams other than the Santa Fe










and Ichetucknee rivers, almost all the water that reaches the ground surface flows as ground water through this region.

Based on a survey completed by the Suwannee River

Management District (1990), the potentiometric surface of the Floridan Aquifer is approximately 10 m National Geodetic Vertical Datum (NGVD) near O'Leno State park and drops to less than 5 m NGVD where the Santa Fe River and Ichetucknee rivers join.



Wetland Environment

The hydrologic component of wetlands is considered to be the most important component to the wetland environment because it ultimately controls the type of soil that will form and the type of vegetation that will grow in an area. However, it is often the least understood and the most difficult to determine. For example, water flow rates through the soil in wetlands vary several orders of magnitude (Table 2).

Most of the wetlands that border the Santa Fe River have been classified as bottomland hardwood wetlands or riparian wetlands (Mitsch and Gosselink, 1986) or a palustrine forest (Cowardin et al., 1979). Some cypress domes are found in the study area especially throughout O'Leno State Park. These areas have a different type of hydrochemical regime than the riparian wetlands that control








35
their existence. For the most part, the chemical composition of these wetlands will be addressed in order to better establish the wetlands' possible connections with other water sources in the region. In actuality, very little is known about the quantity and quality of wetland water added to the riverine environment in many areas (Mitsch and Gosselink, 1986).












Table 2. Hydraulic Conductivities of Wetland Soils Compared to Other Mineral Soils (from Mitsch and Gosselink, 1986).


Wetland or Soil Type


Hydraulic conductivity
cm/sec x lo-'


Northern Peatlands


Highly Humified
Blanket Bog, U.K.

Fen, U.S.S.R.
slightly decomposed
moderately decomposed
highly decomposed

Carex fen, U.S.S.R.
0-50 cm deep
100-150 cm deep

North American Peatlands
(general)
fibric
hemic
sapric

Coastal Salt Marsh

Great Sippewisset Marsh, MA
(vertical conductivity)
0-30 cm
high permeability zone
sand-peat transition zone

Non-Peat Wetland Soils


Cypress Dome, FL
clay with minor sand
sand

Okeefenokee Swamp
Watershed, GA

Mineral Soils (general)

Clay
Limestone
Sand


0.02-0.006


500 80
1


310
6



>150 1.2-150
<1.2


1.8 2,600
9.4


0.02-0.1
30


2.8-834


0.05 5.0 5000













CHAPTER 2
BACKGROUND


Radon-222 (222Rn)
Radon is an inert, volatile gas occupying the final

place in the noble gas group of the periodic table. It is the heaviest known gas with an atomic number of 86 and atomic mass of 222. 222Rn, with a half-life of 3.823 days, is the most abundant of the three predominant alpha emitters and is naturally derived from radium-226 (226Ra half-life=l.6 x 103 years). Both 226Ra and 222Rn are part of the uranium238 decay series. Uranium-238 and 226Ra are common constituents in continental sedimentary rocks and sediments (Key, 1981; Ellins et al., 1989, 1990). As 226Ra decays naturally to 222Rn, in a closed system, 99 percent equilibrium between 226Ra and 222Rn concentrations will be established within approximately 25 days (Rogers, 1958; Ellins 1988; 1989; Asikainen, 1981).

Because 222Rn is highly soluble in water and a volatile gas it will remain in the aquifer to decay to lead-206 or once released to the surface, will be absorbed in the atmosphere where it exists in low concentrations (Elsinger and Moore, 1983; Rogers, 1958). Three physical properties, the short time duration required to establish equilibrium 37









between 222 Rn and its parent nuclide 226Ra, the ubiquity of 226Ra in continental sedimentary material, and the volatility of naturally occurring gaseous 222Rn, make 222Rn a commonly used natural tracer with many applications (Broecker et al., 1967; Key, 1981; Ellins, 1988).

Rogers (1958) was the first to use 222Rn to investigate the relationship between ground water and surface water. Rogers determined that 222Rn concentrations in a Wasatch Mountain, Utah, flowing stream will be low due to the volatility of the gas and the slow decay rate of the radium source that may be contained in rock and sediment in the stream channel. Furthermore, he demonstrated that 222Rn concentrations in ground water from springs were much higher than those in surface water. Also, the spring water was identified as the source of 222Rn in the streams.

Rogers initial study has led to many advances in the usefulness of 222Rn in hydrogeological problems (Broecker, 1965; Broecker et al., 1967; Jacoby et al., 1979; Fanning et al., 1987; Ellins, 1985; 1986; 1988; Ellins et al., 1990). Subsequent studies by Ellins (1989) and Ellins and others (1990) corroborated Rogers work. They described the low levels of 22Rn in a Jamaican and Puerto Rican stream as a function of the loss of 222Rn to the atmosphere and the high levels of 222Rn due to the input of 222Rn enriched ground water. Figure 9 depicts the relationship between surface and ground water 222Rn levels in a Puerto Rican stream.








39

Initial measurements of background 222Rn concentrations of about 10 dpm/L in the Santa Fe River have been performed. Also, spring 222Rn concentrations were measured at levels around 1000 dpm/L for the lower Santa Fe River basin (Figure 10). Using these values, the ratios of ground water 222Rn concentrations to stream levels is 100:1 (Ellins et al., 1993). Because this ratio is so high, 222Rn provides a sensitive means of detecting ground water influx to surface flow that no other naturally-occurring chemical in ground water and surface water can compare (Ellins, 1990).



Sulfur Hexafluoride (SF.)

Wanninkhof (1986) employed SF6 as a gaseous tracer. to study the gas-exchange rates across the air/water interface in three lakes. In addition, he included an in depth discussion of the physical properties of SF6 and its analysis. To date, his work is the most thorough and detailed employing SF6 in the hydrologic field. The following will provide a summary of his data pertinent to this investigation. The interested reader is directed to read Wanninkhof (1986) for more detailed information.

SF6 is a volatile, artificial, nontoxic, inert gas,

that can be detected by electron capture detection methods down to 5x10"17 moles following the procedures of Wanninkhof (1986) and (Ellins, 1989). The molecular weight of SF6 is



























7143 X)


eo- LOWER MANATI (MAY 1985)
- 10- O esISD CONCUITmNAIONS Or

C 0 ISTIM&T [O COW1011ltllo" or
.: 150.- 31R,,, STMAM. OJUStO rOe
Z 140o. LOSS OuC TO GAS U"Naf
0 (w GnOu"D*T aI n'lrL u
130- 9 f % I
120-1
0
I.- 110
ZS

Z 100. 4tllXl
0
(' 90-, 2, J
01 3 (7 %
N





./ 3.5 3.0 2.5 2.0 1.5 1.0 0
GAUGING HWY 2
STATION 6 GAUGING
(4.OM3Is) STATION 7
(4.OrmI)













Figure 9. Rio Grande de Manati 22Rn concentrations (Ellins, et al., 1990).








500

-450
E
-a 400

6350 Gauging Station 40 July spring@ 300 I Hollingsworth Bluff
C
o250
0
C
o200 ,13 5
150

100

50

0 , i i I i a
11 13 15 17 19 21 23 25 Distance Irom Rise (kin)


Figure 10. Ichetucknee River 222Rn concentrations.










146.05 g. It has a vapor pressure at 210C of 22.8 atm and has an extremely low solubility in water at 5.4 cm3 SF6/kg (Wanninkhof, 1986). Wanninkhof (1986) reports that SF6 has an atmospheric background level of about 1.5 parts per trillion by volume. This value has not significantly changed over the past eight years (Wilson and McKay, 1993). Water in equilibrium with air will have a concentration of 5x1016 mol/L (Ellins, 1989). SF6 is not considered dangerous because a maximum limit of 1000ppm is considered harmful to humans and spiked samples usually contain less than 0.5ppb of SF6 (Wanninkhof, 1986).

The difficulties associated with SF6 as a tracer are its affinity for certain porous substances, its ease of contamination and contamination of SF6 with other gases during analyses (Ellins, personal communication, 1993; Wanninkhof, 1986). Materials such as rubber, plastic, grease, and teflon cannot be used in lines, containers, and extraction and analyses equipment because of their affinity for SF6 (Wanninkhof, 1986). Steel, copper, glass and nylon tubing were used exclusively in these experiments and are not prone to adsorb SF6 (Wanninkhof, 1986). Because small amounts of SF6 were used in this study, 99.99% pure SF6, standards of SF6 (lppt, 49ppt, 222ppt) and experiment samples were kept in different rooms at all times, except during analyses of water samples, to avoid crosscontamination of the SF6. Contamination with some aerosols










and synthetic lubricants can pollute air to such an extent that analyses becomes impossible (Wanninkhof, 1986). Because of this, no aerosols, lubricants, or petroleum products were allowed in the analysis lab or near sample containers.

The Schmidt number (kinematic viscosity of water

divided by the diffusion coefficient of the gas) is about the same for both SF6 and 222Rn (Wanninkhof, 1986; Ellins et al., 1994). Because these Schmidt numbers are similar, gas transfer velocities for both gases in a stream will be the same (Ellins et al., 1993). Therefore, the dual application of 222Rn and SF6 allows for the more accurate description of surface and ground water interactions. Details of their application can be found in Ellins and others (1993) and Ellins and others (1994). Briefly, the dual tracer work allows for the accurate detection of ground water springs or seeps and the quantification of its input to the stream.

Most recently SF6 has been shown to be "conservative" tracer in simple laboratory experiments revealing its inert properties with respect to adsorption to saturated sandy material (Wilson and Mackay, 1993). In this experiment however, the SF6 can only be labelled conservative because the sandy material through which the SF6 was pumped was enclosed within an acrylic tube. Essentially the experiment was run under closed conditions with respect to the atmosphere, depicting SF6 as being conservative.










Rhodamine WT

Perhaps the most widely used tracers in karst terrane are fluorescent dyes. These dyes are commonly used because they are readily available, and they all, to some degree, are absorbed on activated coconut charcoal or unbleached cotton. Fluorescent dyes are generally superior to nonfluorescent dyes because they can be detected at concentrations ranging from one to three orders of magnitude less than those required for visual detection. Thus, traces with fluorescent dyes usually can be completed without the aesthetically unpleasant probability of discoloring a private or public water supply.

Because tracing karst ground water flow frequently involves either private or public water supplies, the problem of toxicity of the tracers must be considered. There is a relatively large amount of information available on the toxicity of the most common tracers. Smart (1984) presents a review of the toxicity of 12 fluorescent dyes used for water tracing that includes the tracers discussed in this manual, namely, rhodamine WT, optical brighteners, Direct Yellow 96, and fluorescein. As reported by Smart, three dyes present minimal carcinogenic and mutagenic hazard: Tinopal CBS-X (brightener), fluorescein, and rhodamine WT. Douglas and others (1983) reported that rhodamine WT is non-carcinogenic but found a small but statistically significant dose-related, mutagenic effect.










However, they concluded that the use of rhodamine WT does not appear to represent a major genotoxic hazard.

Steinheimer and Johnson (1986) have shown that, under customary dye study practices in surface waters, the possible formation of carcinogenic nitrosamines from the use of rhodamine WT should not constitute an environmental hazard. In ground water, which may be enriched with nitrite, nitrosamines could form, but high-nitrite concentrations in ground water are uncommon (Hem, 1985). Therefore, the possible formation of nitrosamines is not likely to be a problem (Mull et al., 1988). Quinlan (1987) points out that numerous investigators (Anliker and Muller, 1975; Lyman et al., 1975; Ganz et al., 1975; Burg et al., 1977; Smart, 1984) have found optical brighteners to be nontoxic, non-carcinogenic, and non-mutagenic and therefore safe for use a tracer. It should be pointed out the one dye, rhodamine B, which was earlier approved by the EPA for use as a tracer in potable water (Cotruvo, 1980), is no longer recommended because impurities within it are known to be carcinogenic and possibly mutagenic (Smart, 1984).

Although many different fluorescent dyes are used as ground water tracers, present usage is centered on four: rhodamine WT (CI Acid Red 388), fluorescein (CI Aid Yellow 730), optical brighteners and Direct Yellow 96. In general rhodamine WT is not used for qualitative tracing because of the difficulty of visually distinguishing the pink color of










the dye from that of other organic compounds that can be easily be sorbed by activated coconut charcoal (Mull et al., 1988). However, it is considered an ideal tracer in quantitative settings under specific hydrologic conditions, even though no fluorescent tracer is 100 percent conservative because some dye is lost to sorption or chemical decay (Mull et al., 1988). Therefore, dye loss must be considered during quantitative analysis of the dyerecovery data. Its advantages are that it is photochemically stable and can be used in low pH waters. Its disadvantages include the following problems: its detection may require fluorometric analysis, it is moderately adsorbed to clay particles and is difficult to distinguish in qualitative tracing. The dyes detectable limit is about 0.01 micrograms per liter, in most natural settings, with a fluorometer which is about one to two orders of magnitude lower than the other popular used tracers.



Oxygen Isotopes
Naturally occurring oxygen is composed of the stable isotopes 160, 170, and 180. The ratio of 160 to 180 in air is about 1:489; however, in nature this ratio can vary by about 10%. Many chemical and physical processes in nature are accompanied by oxygen isotope fractionations.








47

During phase changes between liquid and gas the heavier water molecules tend to concentrate in the liquid phase, which fractionates the oxygen isotopes. Water that evaporates from the ocean is isotopically lighter than the water remaining behind, and precipitation is isotopically heavier; that is, precipitation contains more 180 than the vapor left behind in the atmosphere.

The use of mass spectrometry can determine the ratio of isotopes in a water sample. These isotopic ratios from an environmental water sample can be compared with the isotopic ratio of standard mean ocean water (SMOW). The comparison is made by means of the parameter (6), which is defined as

(1)

6180 (0/00) = r (8o/16o) (--180/160)J x l03 (18o/160) M

(Fetter, 1988).

Ground water in this region within the Floridan Aquifer has a relatively constant value of about -4 parts per mil, relative to (SMOW) (Paul Gremillion, personal communication, 1993). In shallow ground water systems with normal temperatures, the concentration of isotopes are little affected by chemical processes. Once the water moves below the upper part of the soil zone, the 180 concentration becomes a characteristic property of the subsurface water mass. Surface water, on the other hand, has varying concentrations of 180 due to the addition or mixture of










precipitation with different 180 concentrations and evaporation affects can change the overall nature of the 180 signal. Because of differences in the 180 content observed in ground water and surface water, mixing between the two water masses can be estimated.

Stable oxygen isotopes of the water samples were

analyzed using an initial process of equilibration of CO2 gas in a shaker bath at 300C. This CO2 gas was then distilled off line using a methanol and dry ice slush mix and liquid nitrogen trap. The CO2 gas was then sealed in six millimeter vacuum-pyrex glass tube for transfer to the VG-Isogas Prism Series 2 mass spectrometer for analysis. Precision of internal standard was 0.1 per mil (Dave Hodell, personal communication, 1993).



Cation Concentrations

As precipitation reaches the ground in a watershed, it will either infiltrate into the ground, pass back to the atmosphere through evapotranspiration or flow on the surface as runoff. When enough runoff comes together, possibly combined with ground water flow its mineral content is already different from that of the original precipitation.

Because of the differing geologic, atmospheric, and human environments there is no typical water quality for surface and subsurface flows (Mitsch and Gosselink, 1986). Wetland environments, however, are the sources, sinks and










transformers of elements for various trace metals, particularly iron, manganese and sulfur, which make their chemical signature distinct from other water environments (Mitsch and Gosselink, 1986).

Due to the fact that elements should differ from one water environment to the next, and the fact that there are multiple water sources in the region, cation concentrations were measured in water samples taken from the two major water components of the area, stream flow, and ground water. Wetland/riparian water was also sampled throughout O'Leno State Park. Primarily aluminum, calcium, sodium, potassium, and magnesium were analyzed by atomic absorption techniques to distinguish between environments. These elements were analyzed because there is abundant background information on them and they typically are used in conjunction with one another to distinguish between different water bodies or sources (Fetter, 1988). For example trilinear diagrams with Mg', Ca', and Na +K , as their corner points are used to classify magnesium, calcium, and sodium or potassium type natural waters (Fetter, 1988).

The major cation species in most natural waters are Na , K, Ca', and Mg". The ground water chemistry of the Floridan Aquifer in this region has been well established as has the chemistry of the Santa Fe River (Hunn and Slack, 1983; Katz, 1992). The two bodies are chemically distinct at the sinking point of the Santa Fe River at O'Leno Sink










because the river at this point is a surface fed stream, driven by precipitation events. Because the Floridan Aquifer material is primarily limestone, the ground water chemistry reflects the dissolution of the aquifer material. The dominant cation in ground water is Ca*, which has a concentration about 10 times that of the upstream Santa Fe River (Hunn and Slack, 1983; Katz, 1992).

Because there are at least two chemically distinct water bodies, mixing of these water masses through the region will indicate sources and sinks of ground water, river water and possibly wetland water to and from the river system.


Previous Hydrogeological Investigations

Records of stream flow in the basin have been collected by the U.S. Geological Survey at various points in the area since 1927. These records were published annually in a series of water-supply papers, and a summary of these records through 1950 is published in Water Supply Paper 1304 (1951). Black and Brown (1951) gave information about the chemical quality of water in the area and other parts of Florida.

Skirvin (1962) provided the most detailed description of the O'Leno State Park area as he attempted to determine the location of the underground flow path of the Santa Fe River. Although his work never conclusively determined the








51
underground path, it did make some significant contributions to understanding this karst. The focus of the work was topographical mapping of the state park. Also included in his work were the first published bathymetric maps of the park's numerous sinks. Skirvin's major contribution to the hydrogeological aspects of the park was the observation that water remained flowing from the River Rise even though the upstream section of the Santa Fe River was damned due to construction. This piece of information is significant because it reveals that the under ground flow path of the Santa Fe River through O'Leno State Park has ground water contributing to its flow before it reaches the River Rise. He also noted a significant "clearing up" of the water found within the sinks and at the River Rise during this damming period.

Briel's (1976) application of 23U/23U to the

characterization of water sources in the lower Santa Fe River basin permitted the identification of three different water types within the basin. Using this finding he characterized the springs along the Santa Fe River as being one or a combination of many water types and thus identify different source regions for the Santa Fe River. His work has recently been disputed because springs which he believed to be unconnected have since been directly linked through cave diving excursions (Kincaid, 1994). Kincaid (1994) was










able to swim through conduits that directly linked the two adjoining caverns Devil's Ear and July Springs.

The next phase of investigation into this region was undertaken by Hunn and Slack (1983). This comprehensive report characterized nearly every aspect of the water resources within the Santa Fe River basin. It revealed the quantity and quality of the surface and ground water in the region as well as their distribution. The paper concluded by discussing the potential for future development in the region from both a surface and ground water prospective.

Even though this paper was detailed and extensive it did not make connections between hydrologic aspects and geologic characteristics. Beck (1986) provided some insight to the connections between karst and the geologic nature within the northern peninsular region. His guidebook indicates numerous exposures within karst features as well as interpretive relationships between stratigraphy and the surrounding karst.

Biddlecomb's (1993) research into the Robinson's Sink region just north of O'Leno State Park also gives general background information on the region. In addition he provides an in-depth probe into the relationships among surface water, ground water (the multiple aquifers) and precipitation along the Cody Scarp found in this active karst region.










Reaeration Coefficients

Streeter and Phelps (1925) defined the reaeration coefficient as a first order rate constant in the basic absorption equation for water. The reaeration coefficient in a natural stream is a general measure of gas exchange capacity and includes the effects of molecular diffusion and mechanical dispersion (mixing) (Hampson and Coffin, 1989; Ellins et al., 1994). Although the reaeration coefficient is generally reported as a single constant, the single value actually represents an average of many individual values within the stream reach (Tsivoglou, 1967).

Water quality managers use these reaeration values and dissolved oxygen (DO) models to estimate the capacity of a stream to sustain organic loadings from natural or unnatural sources. The self-cleaning capacity of a river is directly related to the DO levels and the ability to replace oxygen removed by the reduction of organic wastes. The reaeration process is primary in controlling the negative effects oxygen-demanding substances (Hampson and Coffin, 1989; Parker and Gay, 1987; Yotsukura et al. 1984). Methods for the accurate and dependable evaluation of stream reaeration capacities are a valuable tool in the determination of waste-load allocations and waste-treatment requirements.

A variety of methods for the determination of stream reaeration coefficients have been proposed. These include the dissolved oxygen balance technique, the disturbed










equilibrium method, gas tracer techniques, and various predictive mathematical models (Hampson and Coffin, 1989; Rathbun et al., 1978; Parker and Gay, 1985; Yotsukura et al., 1984). All of these methods have limitations. For example predictive models sometimes yield unreliable results and gas tracer measurements may be expensive and logistically difficult to carry out (Bennett and Rathbun, 1972). Since its development, however, the gas tracer method has been considered the most promising and reliable method (Tsivoglou and others, 1965; Rathbun et al., 1978; Ellins et al., 1994). This method had gained further acceptance since the introduction by Rathbun and others (1978) of a modification of the method which uses hydrocarbon gas tracers instead of the radioactive tracer krypton-85 (Tsivoglou et al., 1965).

To find reaeration coefficients, other workers have experimented with a variety of gaseous tracers, including natural 222Rn (Ellins et al., 1990; and Elsinger and Moore, 1983) freon-12 (Duran and Hemond, 1984; Wilcock, 1984; 1988), and SF6 (Wanninkhof et al., 1990; Ellins et al., 1994). The currently accepted technique for measuring reaeration involves the deliberate injection of a suitable gaseous tracer into a stream. The tracer is subsequently carried downstream and the rate at which it is lost to the atmosphere from the water is measured and expressed as a gas transfer coefficient, k. The rate of gas transfer that









55
occurs between the stream and the atmosphere is dictated by the gradient of gas concentrations across the air/water surface (Ellins et al., 1994). In tracer experiments, the values of k for a suitable tracer can be related to the rate of oxygen uptake and expressed as a reaeration coefficient

(K2). The gas transfer velocities of the two gases in a stream should be approximately the same because 222 Rn and SF6 have approximately the same Schmidt number (Ellins et al., 1994).














CHAPTER 3
MATERIALS AND METHODS


Gas Chromatography and the Injection Port System

The gas chromatograph was the instrument used to

analyze the SF6 and the general procedures followed those of Wanninkhof (1986). The entire chromatographic system consists of several pieces of equipment which have numerous components (Kaiser, 1963; Keulemans, 1957). The details for the entire system can be found in Appendix A. In general the SF6 saturated water sample is fed into an injection port system that first separates the SF6 gas from the carrier gas and sends both downstream to the gas chromatograph to be analyzed. Once the SF6 has reached the electron capture detector (ECD) within the gas chromatograph it passes through a beam of emitted electrons (6Ni). Because SF6 is a halogenated compound it has a high affinity for electrons and thus will disrupt the flow of electrons passing in front of its passage. This disruption in electron flow is translated into an electrical pulse which is read by the integrator. The integrator displays the time at which the SF6 reached the ECD and an SF6 area versus time curve. The area under this curve is compared to a previously








57
established standards curve and finally the concentration of SF6 is calculated.



SF, Iniection System

The injection system used to transport the SF6 from its tank to the water consists of two major components. The details of the entire system can be found in Appendix B. These components are a 220L barrel and a two stage peristaltic pump. Basically, SF6 is forced under its own pressure into a the water barrel. Once saturation is achieved, the water is then pumped via tygon tubing into the study region. The ends of the tygon tubing are held in place with two pound lead weights.


Thermometry

Thermometry is a simple tool that has been used to

distinguish between ground water and surface water features in numerous aquifer settings (Pitty et al., 1979; Larson et al., 1987; Lobmeyer, 1985). To further distinguish between the Santa Fe River and water filled karst features in the area, temperature readings were taken in many of the surface and stream water features. Locally, the ground water temperature remains at about 20-210C year-round whereas surface water temperature varies depending upon local air temperature (Fernald and Patton, 1984). Temperature readings were taken on January 11, and 14, 1992, during the










coldest part of the year, to identify differences between surface features and ground water fed features. On March 24, 1992 temperature readings were again taken to confirm these data. A thermometer, cased in perforated metal, was lowered into the features to a depth of one meter until the temperature had reached equilibrium between the water and the thermometer. The thermometer was quickly removed and the temperature was recorded. This procedure was repeated three times at each location and an average temperature was then recorded. The precision of the technique was less than

0.50C, determined by the 0.10C divisions on the thermometer.



SamDling Technigues

SF, SamDling

For all mixing, flow component, water tracing and gas exchange experiments SF6 was collected in either 50 ml biological oxygen demand (B.O.D.) pre-labelled glass bottles or 50 ml glass syringes. For each sample, the bottle was conditioned once with the river or sink water and then the sample was drawn. Samples collected in the B.O.D. bottles were capped underneath the water to prevent air from entering the sample and thus allowing SF6 to come out of solution. Samples collected in the glass syringes were filled to the 50 ml mark underneath the water and then any air found in the syringe was discharged at the surface. A minimum of 30 ml was needed for each analysis.








59

Samples were stored on ice in a cooler and transported to the U.F. hydrology lab for analysis. The purpose for storing the samples on ice is to keep the SF6 from coming out of solution at higher temperatures.



Rhodamine WT Sampling

Samples collected for the rhodamine WT analysis were captured on activated charcoal packets following the procedures of Aley (1990). These pre-labelled packets consisted of about 4.25 grams of activated charcoal surrounded by a 10 cm long by 10 cm wide fine fiberglass mesh attached to a wire connected and a weight. The wire was fastened to the weight so that when the charcoal packet was attached it would remain suspended above the floor of the river or sink (Figure 11). The packet was placed at the immediate opening of spring where possible to maximize rhodamine WT adsorption. This suspension of the packet also decreased the amount of debris that would become entangled on the packet thereby reducing the adsorbing capacity.

These samples remained in the water for 3.5 to 4 hours so that a definite rhodamine WT signal could be recorded (Pete Butt, personal communication, 1992). After collection, the sample was lightly rinsed with water, placed in a plastic bag, removed from sunlight and placed on ice until analyzed.






















Line
to
Surface


Charcoal Packet


=l i


Wire




Weight








Figure 11. Charcoal packets used in rhodamine WT dye tracing experiment.








61
The standard elution solution used was a mixture of 5% aqua ammonia and 95% isopropyl alcohol solution. The isopropyl alcohol was 70% alcohol and 30% water. The aqua ammonia solution was 29% ammonia. Twenty millimeters of the eluting solution was poured over the washed charcoal, capped and then allowed to stand for 60 minutes. The liquid was then carefully poured off the charcoal for analysis (Aley, 1990).



Radon SamplinQ

Radon water samples were collected in pre-labelled

plastic 250 ml graduated cylinders specifically fitted for 222Rn extraction (Figure 12). The pre-evacuated graduated cylinders were attached to tygon tubing fastened to a two inch diameter by three meter length of poly-vinyl chloride (pvc) tubing (Figure 12). This tubing was held at the desired depth, the inlet valve was opened and the water then flowed under pressure into the cylinder. A 150 to 190 ml sample was collected, the inlet valve was closed and then the cylinder was placed back into the cooler for later analysis.



Oxvyen-18 Sampling

Water samples for isotope analysis were collected in pre-labelled 30 ml pyrex glass bottles with screw on displacement caps. Each sample bottle was first






















PVC tubing


Clamps


_ -" Rubber Stopper


Evacuated
Graduated Cylinder






Rubber Tubing


Figure 12. Sampling device and graduated cylinder for SF6 and 21Rn.6










conditioned, by rinsing the bottle with the river or sink water, and then collected at approximately 0.5 m depth in the water body. The cap was then secured while the bottle remained beneath the water surface.



Cation Sampling

The major cation sampling used glass (BOD) bottles. The bottles were cleansed following the procedures in Appendix C.



Ouality Control

Duplicate samples were taken at intervals of about 15% of the total number of samples. In addition, duplicate analysis of the same sample were performed at 10% intervals of the total number of samples taken. Duplicate analysis of the same sample were impossible because the total volume of each sample was needed in the analysis for the gas chromatograph (SF6), the fluorometer (rhodamine WT) and the radon extraction system 222Rn. However, duplicate sampling was executed whenever the number of sample containers allowed.


Reaeration Methods

During the Summer of 1991, two twelve-hour long

reaeration experiments were carried out on the Santa Fe River which required the continuous injection of SF6 over a









certain time period. A two-channel peristaltic pump was used to inject 220 liters of SF6 saturated stream water at two points across the river at a rate of 15L/hour. The governing restraint, in determining the length of reach used in each of the experiments, was the time required for SF6 to reach plateau concentrations in the stream. It took about five hours for plateau concentrations to be reached in the Santa Fe River (Figure 13).

Heavy sampling over the entire length was carried out after plateau concentrations were reached. From fifty to 250m downstream of the injection point, samples were collected based on predictive equations and the results of the mixing study (Yotsukura et al., 1984). Lateral and vertical mixing problems in the river channel were minimized by collecting integrated samples 1/3 depth of the stream by direct suction into bottles. In addition, SF6 grab samples were also collected at two points across the stream in the second reaeration study. Immediately following the experiments both 222Rn and SF6 samples were analyzed on a 24 hour schedule. The margin of error for sample analyses was calculated by analyzing river water samples during plateau levels at three locations. The SF6 concentrations were within an average of 7% of each other.







1500


-j 1250
E
0501000

z
0750


t- 500
z
w
0
z
0 250

(0
0 50 100 150 200 250 300 350
TIME PAST INJECTION (MINUTES)

- 3.5km -+- 2.0km - 1.5km


Figure 13. Rise to plateau for SF6 in the Santa Fe River.









Analytical Techniaues



Gas Chromatogra~hv

Gas chromatography is a physical method of separation, in which the components to be separated are distributed between two phases. One of these phases constitutes a stationary bed of large surface area (the column packing material), the other being a fluid that percolated through the stationary bed (the carrier gas and sample gas) (Keulemans, 1957; Kaiser, 1963).

In the case of SF6 analyses, a sample was injected into the separating column filled with a micro-sieve mesh, with ultra high pure (UHP) grade nitrogen gas. The carrier gas, nitrogen, and SF6 were then separated and sent to the gas chromatograph where each was analyzed with an electron capture detector (ECD). The ECD is a device that basically consists of cathode an anode and a recording device. The radioactive 6Ni emits electrons (beta particles) across a nitrogen carrier stream onto an anode. There a recording device records the resistivity of the passing electrons. If the stream is interrupted by a substance absorbing electrons, like (SF6), the output signal will change. Interpretation of this analysis is then recorded by an integrator which graphically and quantitatively indicates the presence of SF6 in each sample. This method is highly sensitive, rapid and simple in execution. Accurate,







67

quantitative information can be obtained using small amounts of sample (20ml).



Fluorometric Procedures

A fluorometer's method of detection is completed by interpreting a sample's amount of light reflectance. A sample is quickly passed through a port that continuously reads the light reflectance property of the fluid. In order for a fluorometer to accurately read a sample it must remain in the sample loop for at least 15 seconds (Aley, 1990). Some Turner Designs Model 10 Fluorometers can be modified to analyze the standard three millimeter sample that is typically used in lab fluorometers. The fluorometer used in this study was not modified because of lack of funding to complete the process. Because the sample taken was the same volume as the sample loop, the continuous running of the fluorometer passed the sample very quickly through the sample loop and therefore did not allow sufficient time to quantitatively determine the sample's rhodamine concentration. However, relative measurements of the strength of the solution passing through the loop could be determined by recording the degree to which the fluorometer's needle was deflected. Values such as strong

(4), moderate (3), weak (2), very weak (1) and none (0) were recorded for each of the samples.










Radon Analysis
222Rn was stripped from water using a small extraction system and transferred to an airtight chamber. The radioactive disintegrations of the 222Rn trapped in the chamber, a modified Lucas-type scintillation cell, were measured and recorded by an alpha-scintillation counter. The scintillation counting material is mounted on the face of a photomultiplier tube, the pulse of light produced by the radiation is converted to an electrical pulse which in turn may be amplified and counted. For work with short range, densely ionizing radiations like alpha particles, the scintillator is finely crystalline zinc sulfide coated in a thin layer on the face of the photomultiplier. The technique and analytical equipment are fully described in Ellins (1988).

The error reported for the radon analyses is a

composite of the errors associated with sample counting, cell background counting, channel noise, volume, cell efficiency, and operator error. The precision of the entire procedure was determined by running duplicates of 25 samples in the lab. The level of uncertainty associated with precision of the method does not exceed 14% (Ellins, 1988).


Atomic Absorption Spectrometry

Two water samples were taken at 0.5 m depth, in B.O.D. glass bottles previously cleaned in nitric acid and triple










distilled water from 23 locations throughout the park. Water samples from the adjacent Santa Fe River was also analyzed for major cation chemistry. The samples were then analyzed for the major cations Ca', Mg4, Al , K, and Na on a Perkin Elmer model 3100 atomic adsorption spectrometer using the acetylene flame ionization techniques outlined in the Perkin Elmer manual (Perkin Elmer, 1990).

The basic technique involves developing a standard curve using lab standards for each of the elements being analyzed and then analyzing samples which fall along the standard curve. In concept the sample is ionized by an acetylene flame in the presence of a light beam emitting the frequency of absorbance for the element in question. Once the sample has been ionized the amount of absorption of this light is recorded. This absorption is then compared to the standard and statistically plotted along the standard curve which calculates its actual concentration. In the University of Florida lab, software that accompanies the spectrometer automatically calculates the concentration of cation within the sample. Each sample was analyzed twice and an average value was recorded.


Computer Modeling

A model is a tool designed to represent a simplified version of reality. In general, mathematical models use governing equations limited by boundary conditions to










simulate the flow of ground water (Luckner and Schestakow, 1991). Using calculus, it is sometimes possible to calculate the heads at given points as a function of space coordinates and thus generate an analytical solution. To obtain this solution several simplifying assumptions about the aquifer must be made, including: 1) homogeneous stratigraphy, 2) isotropic conditions, 3) a linear water table configuration, and 4) approximation of the problem by a rectangle (Wang and Anderson, 1982).

For many modeling problems these assumptions are

unrealistic and require use of numerical methods to solve the mathematical model. Governing equations are approximated by algebraic statements, boundary conditions, and by programming techniques. Finite difference models are based on rectangular grids whereas finite element models use grids made of triangular elements. Iterative calculations produce estimates of hydraulic head at nodal points that eventually converge to values of acceptable accuracy. Models are calibrated by matching computer-generated head values with field measured head values within reasonable limits (Mercer and Faust, 1981).


Numerical Models

Finite-difference methods used to solve partial

differential equations use a grid of rectangular cells to represent the region of interest. For two-dimensional










problems a grid system is overlain on a map view or crosssection of the aquifer (Mercer and Faust, 1981). At each grid node the head will be calculated based on equation 2:

(2)

d/dx (TX dh/dx) + d/dy (TY dh/dy) = S dh/dt Q (xy,t)

where

T = transmissivity, LT"1,

h = head, L, t = time, T,

S = storativity,

Q = net ground water withdrawal, L3T",

x,y = rectilinear coordinates,

for which there is no general solution. But through the finite-difference approximation a numerical solution can be obtained by replacing the derivations in equation 3 by differences taken between nodal points (Wang and Anderson, 1982). At each finite-difference node the form of equation

2 at each i,j is equation 3:

(3)

Ti-1,j,2 (hj.lj-h,,j)/dxI + T1,1,2 (h1 1,-hi,)/dx2 + T,j,2 (h1,j.1-h1,j)/dy2 + T,,11 (h1,,+.-hij)/dy2 = S(hf j-hoj )/t = Q1j'/dxdy,

where

ho1,1 = the calculated head at the end of the

previous time increment, t,

T,-.,0,I and T,,.-,, = aquifer transmissivity within








72

the vector volume between node i,j and i-l,j; i+l,j; i,j+l; i,J-1 (Figure 14).

Because nodes throughout the entire grid have equations in the same form as equation 3, these equations are solved simultaneously for the unknown hij variable (Luckner and Schestakow, 1991). By allowing T (transmissivity) to vary with time as the thickness of the aquifer varies, equation 3 can be used in unconfined cases (Wang and Anderson, 1982).

A model based upon the two-dimensional PLASM (Prickett and Lonnquist Aquifer Simulation Model) and MOC (method of characteristics) program was used to simulate ground water flow conditions around the O'Leno State Park and western Santa Fe River region (Luckner and Schestakow, 1991). These models were chosen because their computer requirements corresponded to the facilities available. Also, they were accessible and relatively powerful with respect to the kinds of data needed as input.















(x-deltx, y-delty)





(x-deltx, y)






(x-doltx, y+delty)


(x, y-delty)





(Xy)


(x, y+delty)


(x+deltx,y-delty)





(x+deltx,y)





Y


(x+deltx,y+delty)


(+1,j-1)


U+1,) r �
I


(i+l, i+j)


Figure 14. Computer difference grid. B. grid (after Hisert,


modeling coordinates. A. Finite Computer notation for finite difference 1990).


-1)


(,J-1)


(i-i, j(i-lJ+


(Lj)

del1ti
jdeltY


1)


(i,j +)


I: deltx -














CHAPTER 4
RESULTS AND DISCUSSION

Mixing Experiments


Introduction

The measurement of mixing characteristics, longitudinal and transverse dispersion, has been studied in detail in order to address the streams capacity of handling pollution and to determine alternative tracing techniques and tracer types. Previous procedures have employed saline solutions, rhodamine dyes, ethylene, propane and radioactive tracers to measure these mixing attributes (Luk et al, 1990; Jobson and Rathbun, 1982; Yotsukura et al., 1970). Mathematical models have been derived to calculate the concentrations of a tracer under certain stream conditions over time and distance to understand mixing processes (Fischer, 1966; O'Loughlin and Bowmer, 1975). However, these models have often made several assumptions about stream parameters (i.e. bed roughness, wetted perimeter, chemical degradation and diffusion). By making these assumptions they allow for greater error in their prediction. More importantly the models do not easily offer the flexibility of additional sources and sinks for river water and or ground water in








75
complicated riverine conditions which can greatly affect the stream's mixing capabilities.

In the karstic terrane of the western Santa Fe River basin assessing mixing parameters of the stream is made difficult by the numerous springs, seeps, syphons and boils found within the Santa Fe River. In order to accurately obtain a representative sample of river water for analysis, three detailed mixing experiments were devised to address the cross sectional distribution in the volatile dissolved gases, natural radon-222 (222Rn) and artificial sulfur hexafluoride (SF6).


Radon-222

The use of radon-222 (222Rn) in monitoring the

relationship between ground water and surface water has been employed in a variety of hydrologic and geologic ground water settings (Rogers, 1958; Broecker et al., 1967; Jacoby et al., 1979; Elsinger and Moore, 1983; Ellins 1985, 1986; 1988; 1990; Lee and Hollyday, 1987). Although these authors have described the concentrations of 222Rn throughout a reach of a river they neglect to address the lateral and vertical variations of radon concentrations throughout the water column which may be significant.

Because 222Rn is inert, naturally occurring, reaches

equilibrium with the host aquifer within a short time period (about one month), and is often found in a much higher










concentration in ground water versus surface water and remains in solution in the aquifer until the ground water is discharged, it can be used to identify pulses of ground water to many surface features. This process has been described in Ellins and others (1993).



Sulfur Hexafluoride

SF6 has been used in the medical field as a dense

displacement gas, in atmospheric tracer experiments, ocean circulation experiments, to monitor gas exchange in lakes and rivers and as a ground water tracer (Lovelock and Ferber, 1982; Ledwell, 1984; 1986; Ledwell et al., 1986; Ledwell and Watson, 1988; Wanninkhof et al., 1987; Wanninkhof et al., 1990; Hisert and Ellins, 1993).

The artificial tracer, sulfur hexafluoride, (SF6) was

selected for this study over other tracers propane, ethylene and rhodamine WT because it is inert, non-biodegradable, nontoxic and can be detected in extremely low concentrations (femtamoles per liter). Also, it does not have some of the associated problems that rhodamine WT has with organic acids that are commonly found throughout many southeastern U.S. states, including Florida (Fernald and Patton, 1984). The major problem of using rhodamine in Florida streams is that the naturally tannin streams create a high background fluorescence, thus making rhodamine identification difficult. In addition, SF6 is relatively inexpensive










compared to rhodamine and samples can be analyzed quickly, approximately 25 samples per hour, following the procedures of Wanninkhof (1986). As part of this study the refinement of injection and sampling procedures for riverine environments was also completed.



Processes of Dilution and Mixing

When soluble material is injected into a flowing

stream, its eventual fate is determined by the physical process of diffusion, convection, chemical degradation, adsorption and evaporation. If a tracer is injected at a point in a flowing channel, it is immediately subjected to the process of turbulent diffusion and dispersion, and its concentration tends to become uniform in the cross-section (O'Loughlin and Bower, 1975; Plate and Friedrich, 1984). The distance required for near uniformity to be achieved may typically be on the order of hundreds of times the channel width (O'Loughlin and Bower, 1975). The events in this stage are three-dimensional and the actual spread rate of dilution depends on the channel geometry and the large-scale turbulence structure of the flow. At this point in the evolution of mixing and dispersion theory, it is difficult to predict the length of this initial phase (O'Loughlin and Bower, 1975). However, it does appear that the mixing length is determined by the same physical parameters which determine the later dispersion phase in the dilution of the








78

tracer. Attempts to characterize the behavior of the tracer in the initial stage by using one-dimensional formulations are suspect and lead to erroneous predictions of tracer attenuation.

During the dispersion phase, the tracer behaves as a one-dimensional slug of material in the channel; the only significant concentration gradient is that in the direction of flow. A more detailed description of the mathematical derivation of the one-dimensional dispersion equation can be found in O'Loughlin and Bower (1975). Concentrations for a given time period can be predicted for a non-conservative tracer using the following equation:

(4)
C(X,t)= N exp (-]Kt) exp[C-"x-Ut)2]
(4piDt)1/2 4Dt

where
U = mean velocity, m/s
D = longitudinal dispersion coefficient,
K = first order decay constant for the tracer,
x = distance, m, and
t = time, s, (O'Loughlin and Bower, 1975).

According to Graf (1986) the distance needed in order

to achieve complete transverse mixing within a stream can be calculated using the equation:

(5)

0.1 V W2

Ez










where
V = mean reach velocity, m/s
W = stream width, m
Ez= transverse mixing coefficient (equal to
c*d*u), where;
c = dimensionless constant, 0.2 for straight streams 0.4-0.6 for more irregular stream sides and bottoms,
d = mean depth, m,
u = shear velocity, m/s.


Using this equation, estimates of length of mixing for three reaches of the Santa Fe were calculated. Because of the uniformity of slope and discharge along the river reaches sampled, the average length of stream needed for complete mixing was calculated to be 1.4 km. This estimate was tested in an earlier experiment on the Santa Fe and revealed a complete mixing between 1.0 and 1.5 km, as the equation had predicted.

Because of the river's complex hydrologic character, four separate mixing experiments over three different reaches of the Santa Fe River were completed.



Injection at Wilson SprinMs

The initial injection experiment took place on June 5, 1991 between Wilson Springs and 2.0 km downstream of Wilson Springs. This site was chosen because of its relative ease of access to the Santa Fe River and its close proximity to our working base camp (Figure 15).

The goals of this experiment included 1) determination of the average stream velocity, 2) testing the SF6










injection design, 3) determination the river's lateral mixing component, the length at which an injected tracer would become completely laterally mixed, 4) testing the sampling strategy, 5) testing the analytical procedures and equipment with field drawn samples.



Experiment Design

Samples were obtained at four sites located 0.5 km apart and at the SF6 injection site, which was located approximately 20 m downstream of the Wilson Springs boat ramp. Samples were collected from a stationary canoe at a depth of 0.3 m in BOD (biological oxygen demand) bottles. In some instances, 50 ml glass syringes equipped with threeway tips were used instead of the BOD bottles, but the general sampling strategy was the same. The sample was taken and capped at depth. The bottle was then transferred to the cooler and stored until analysis took place. A predetermined time at which to start the sampling and the SF6 injection was relayed to the volunteers before they were stationed at their sampling points.



Hollingsworth Bluff

The second experiment was carried out at Hollingsworth Bluff. This site was chosen because no known springs or fissures have been identified in the area, it is relatively straight and has a constant depth and width, and thus 222Rn


























* I.u.tn~


2.5 !- Wetlands Z9'54'



2 a


North
0 0.5 1. h m ~1 lan




82046'










Figure 15. Lower Santa Fe River near Wilson Springs (from Ellins et al., 1993).










was assumed to be being well mixed in this reach (Figure 16). In addition, because the reach is relatively straight a uniform velocity profile can be assumed. Three cross sections spaced 100 meters apart were sampled for 22n. Twenty samples were taken at each of the locations labeled Mix 1, Mix 2 and Mix 3 on figure 16. Four water samples were collected at equally spaced intervals across the width and depth of the stream. Water samples were collected via rubber tubing secured to 5 cm PVC piping, previously marked in 0.5 meter intervals, with an open end in the water and the other end attached to a previously evacuated 250 ml graduated cylinder. The graduated cylinder was opened once the tubing reached the appropriate depth and the vacuum created within the cylinder sucked water up from depth filling the graduated cylinder to about 150 ml. Samples were then stored in a cooler and then taken back to the lab to be analyzed. In addition, two integrated samples were taken, one across the width of the stream at 0.5 meters depth and the second taken vertically mid-stream throughout the top three meters of the water column.

Six stream velocity measurements were also taken at each of the three locations using a Weathertronics Flow Meter, to monitor the total discharge over the sampling area. 222Rn measurements were made using Lucas-type scintillation cells with alpha scintillation counters. A small portable extraction system was used to strip the 222Rn












































I I I a L II
Ikm 0o0m 0N
SCALE UNPAVED ROADS






Figure 16. Sample locations at Hollingsworth Bluff (from Ellins et al., 1992).








84

from water samples collected in the field into scintillation cells.


River Rise to Two Kilometers

The third experiment evaluated the mixing

characteristics from the River Rise of the Santa Fe River to

2 km downstream using a continuous injection of SF6 from a point source located in the middle of the river (Figure 17). This reach was investigated to examine the effects of the known boils located within the river between 0 and 0.25 km and 0.75 and 1.0 km. SF6 was continuously injected into the river until plateau levels were reached, approximately two hours. About twenty water samples were taken across the width of the three locations, at 0.5, 1.0, and 1.5 km downstream of the River Rise, using a similar method to that employed in the first mixing experiment. Subsequent sampling locations at 2.0, 3.0 and 4.0 km were sampled but samples became unusable after transportation because they became aerated or they were sampled incorrectly. Discharge measurements were taken before and after the samples were taken to ensure constant river flow.


Rum Island to Ginnie SDrings

The fourth mixing experiment was carried out in an area characterized by several springs and river syphons approximately 15.75 km downstream of the River Rise, near













































2%r~


-I


1.0kM
I


h -
'A


0.5
I I


,0


-- I i I S


M A.ILS


Figure 17. River Rise to four kilometers on lower Santa Fe River (from Ellins et al., 1993).










Ginnie Springs (Figure 18). Sulfur hexafluoride was injected near Rum Island Spring in the middle of the river through a single point source. Water samples were taken at three points across the width of the stream at 0.5 m depth at 13 locations downstream of Rum Island. Between 15.5 km to 16.50 km water samples were taken every 250 m and from 16.50 km to 17.00 km, every 50 m. Sample spacing was altered in this area in order to evaluate an experiment that was being carried out beneath the river, within the Devil's Ear Cave system, in conjunction with the SF6 mixing experiment. Discharge measurements were taken at four locations throughout the length of the experiment.


Summary of Mixing Experiments



Wilson Springs

Stated goals of the mixing experiment were

accomplished. The lateral mixing component was described in this experiment. Using equation 5, the distance needed for complete lateral mixing was calculated to be 1.4 kilometers under the flow conditions of the experiment. This value also agrees well with the concentration response curves found in figures 19 and 20. A concentration response curve that shows a typical rising and falling peak with one central peak describes a location where there is complete lateral mixing. At 0.5 km the mixing is incomplete due to

























































Figure 18. Rum Island to Ginnie Springs on lower Santa Fe River (from Ellins et al., 1993).




Full Text

PAGE 1

A MULTIPLE TRACER APPROACH TO DETERMINE THE GROUND AND SURFACE WATER RELATIONSHIPS IN THE WESTERN SANTA FE RIVER, COLUMBIA COUNTY, FLORIDA By RICHARD A. HISERT A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1994

PAGE 2

ACKNOWLEDGEMENTS I would like to thank my committee members for encouraging and supporting me throughout this endeavor and especially Dr. Ellins for providing me the initial funding and impetus for pursuing this study as well as her numerous editorial comments. In addition, I would like to acknowledge that many of the tools and methods in this work closely follow the guidelines and advice, both written and verbal, of Dr. K.K. Ellins. I am forever indebted to Todd Kincaid for all of his help in the lab and in the field with this project. His friendship and efforts are truly genuine. Thanks are also extended to the numerous students who lost many hours of sleep and helped with the field experiments in this study. My sincere thanks go to the excellent staff at O'Leno State Park, especially its manager Mr. Dale Kendrick for all of his help. I also thank the National Science Foundation, Geological Society of America and Sigma Xi for providing funds for this project. Also, I would like to thank Tim Aydt of the University Athletic Association for his funding through this project. Finally, I thank my sisters Tonia, Melissa, Jill and Tara and my parents Gerald and Nancy for their never ending support and encouragement in all my endeavors. Hopefully ii

PAGE 3

they think, this will be my last academic one. Lastly I would thank my wife, Nicohl, for helping me through all the tough times and laughing with me during all the good ones. iii

PAGE 4

TABLE OF CONTENTS Page ACKNOWLE DGEMENTS i i LIST OF TABLES vii LIST OF FIGURES ix ABSTRACT xii CHAPTER 1 INTRODUCTION 1 Purpose 2 Significance 3 Study Area 4 Physiography 10 Climate 14 Geology 14 Karst Development 28 Regional Ground Water Flow 33 Wetland Environment 34 2 BACKGROUND 37 Radon-222 37 Sulfur Hexafluoride 39 Rhodamine WT 44 Oxygen Isotopes 46 Cation Concentrations 48 Previous Hydrogeological Investigations 50 Reaeration Coefficients 53 3 MATERIALS AND METHODS 56 Gas Chromatography and the Injection Port System 56 SF6 Injection System 57 Thermometry 57 Sampling Techniques 58 SF6 Sampling 58 Rhodamine Wt Sampling 59 iv

PAGE 5

Radon Sampling 61 Oxygen-18 Sampling 61 Cation Sampling 63 Quality Control 63 Reaeration Methods 63 Analytical Techniques 66 Gas Chromatography 66 Fluorometric Procedures 67 Radon Analysis 68 Atomic Adsorption Spectrometry 69 Computer Modeling 69 Numerical Models 70 4 RESULTS AND DISCUSSION 74 Mixing Experiments 74 Introduction 74 Radon-222 75 Sulfur Hexafluoride 76 Process of Dilution and Mixing 77 Injection at Wilson Springs. 79 Hollingsworth Bluff 80 River Rise to Two Kilometers 84 Rum Island to Ginnie Springs 84 Summary of Mixing Experiments 86 Wilson Springs 86 Hollingsworth Bluff 91 River Rise to Two Kilometers 94 Rum Island to Ginnie Springs 96 Discussion 96 Water Tracing Experiments 99 O'Leno Sink to River Rise 99 Results 103 Sweetwater to Santa Fe River Boils 113 Jim's Sink to Santa Fe River Boils 114 Summary of Water Tracing 123 Flow Component Analysis 126 Radon-222 Transect 126 0-18 Transect 129 Cation Concentrations 131 Temperature Transects 136 Computer Modeling 141 Reaeration Studies 145 Gas Transfer 152 Reaeration Coefficients 155 5 SUMMARY AND CONCLUSIONS 163 Mixing 163 Tracing 164 Flow Component 164 Reaeration 165 v

PAGE 6

Sulfur Hexafluoride 166 Karst Development in O'Leno State Park 167 APPENDECIES A GAS CHROMATOGRAPHY AND THE INJECTION PORT SYSTEM 171 B SF6 INJECTION SYSTEM 192 C CATION BOTTLE PREPARATION 197 REFERENCES 199 BIOGRAPHICAL SKETCH 212 vi

PAGE 7

LIST OF TABLES Table page 1 Regional Stratigraphy in Northeastern Alachua County, Florida (after Biddlecomb, 1993) 20 2 Hydraulic Conductivity of Wetland Soils Compared to Other Mineral Soils 36 3 Statistical Data for Radon Distribution throughout the Stream Cross-Section 92 4 Estimated time Until Leading Edge of Tracer Reaches Sink 108 5 Estimated Passage Time for the Tracer Cloud at Each Sink 108 6 Travel Times for SF6 a Sinks in O'Leno State Park Ill 7 SF6 Travel Times for Jim's Sink to Santa Fe River Rise Experiment 120 8 Cation Concentrations for Locations in O'leno State Park 133 9 Stream Gaging data for the Santa Fe River 153 10 Values of k in Meters per day for Intervals Between the Stream Gaging Locations in the First Reaeration Experiment 156 11 Values of k in Meters per day for Intervals Between the Stream Gaging Locations in the Second Reaeration Experiment 157 12 Comparison of Schmidt Numbers for SF6, Rn-222 , and 02 at Selected Temperatures 159 13 Comparison of Selected Stream Reaeration Coefficients Determined Through the use of Volatile Tracers 161 vii

PAGE 8

Comparison of Stream Reaeration Coefficients K, (day' 1 ) Determined Through the Use of SF6 with Values Derived from Predictive Models.. viii

PAGE 9

LIST OF FIGURES FIGURE Page 1 Santa Fe River Basin in north central Florida (after Hunn and Slack, 1983) 5 2 Springs found in western Santa Fe River Basin. (after Hunn and Slack, 1983) 8 3 Potentiometric surface of the Florida Aquifer and direction of ground water flow in the study area (from Meadows, 1991) 9 4 Physiographic provinces in the study area (from Kincaid, 1994) 11 5 Structural features in peninsula North Florida (after Biddlecomb, 1993) 16 6 Geology of western Santa Fe River Basin (after Briel, 1976) 17 7 Cross section through the western Santa Fe River Basin (after Briel, 1976) 18 8 Hydrogeologic units of the western Santa Fe River Basin (after Hunn and Slack, 1983) 28 9 Rio Grande de Manat i Rn-222 concentration (from Ellins et al., 1990) 40 10 Ichetucknee River Rn-222 concentrations 41 11 Charcoal packets used in rhodamine WT dye tracing experiment 60 12 Sampling device and graduated cylinder for SF6 and Rn-222 62 13 Rise to plateau for SF6 in the Santa Fe River 65 14 A. Finite difference grid. B. Computer notation for finite difference grid (after Hisert, 1990) 73 ix

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15 Lower Santa Fe River Basin near Wilson Springs (from Ellins et al., 1993) 81 16 Sample locations at Hollingsworth Bluff (from Ellins et al., 1993) 83 17 River Rise to 4 km on Lower Santa Fe River (from Ellins et al., 1993) 85 18 Rum Island to Ginnie Springs on Lower Santa Fe River (from Ellins et al., 1993)... 87 19 SF 6 concentrations response curves 0.5 to 1.0 km 88 20 SF 6 concentrations response curves 1.5 to 2.0 km 89 21 Contoured cross-sections of 222 Rn concentrations in river near Hollingsworth Bluff (dimensions in meters, contour interval equals 10 dpm/L 93 22 Mixing results at 0.5, 1.0, 1.5 km downstream of the River Rise 95 23 Plan view of mixing in Ginnie Springs area 98 24 O'Leno State Park with numbered sample locations for O'Leno tracing experiment (from Ellins et al, 1993) 100 25 Bathymetry of O'Leno Sink 105 26 Bathymetry of River Rise 106 27 Concentration response curves for Ogden Pond, Ravine Sink, Pareners Branch Sink and Small Sink. . 109 28 Concentration response curves for New Sink, Jim's Sink, Two Hole and Sweetwater Lake 110 29 Concentration response curves for Sweetwater experiment 115 30 Concentration response curves for Jim's Sink experiment 118 31 Concentration response curves for Jim's sink injection 119 x

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32 Flow Pattern of the underground Santa Fe River through O'Leno State Park 124 3 3 Sample locations for 222 Rn, 18 0, major cations and Temperature 127 34 Radon-222 concentrations for karst features found throughout the park 12 8 35 18 0 Values for Karst Features in O'Leno State Park 122 36 Cation Concentrations in O'leno State Park 135 37 Temperature Readings Recorded in O'Leno State Park 12 8 38 Computer model set up for the western Santa Fe River region between O'Leno Sink and Rum Island. . . 142 39 Sampling locations for the first reaeration experiment 146 40 Sulfur hexafluoride and radon profiles for the first reaeration experiment 147 41 Sampling locations for the second reaeration experiment 149 42 Sulfur hexafluoride and radon profiles for the first reaeration experiment 150 43 Gas chromatograph setup for SF6 analysis 175 44 Cross section of dreirite tube used in SF6 analysis I 77 45 Multi port injection system for SF6 analysis...... 179 46 Glass syringe used for injecting SF6 sample 186 47 SF6 field injection system used throughout all injection experiments 194 xi

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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy A MULTIPLE TRACER APPROACH TO DETERMINE THE GROUND AND SURFACE WATER RELATIONSHIPS IN THE WESTERN SANTA FE RIVER, COLUMBIA COUNTY, FLORIDA By Richard A. Hisert December 1994 Chairman: Douglas L. Smith Major Department: Geology This project characterized the complex karstic groundwater/surface water relationships of the Santa Fe River in north-central Florida while further developing the use of the new geochemical tracer sulfur hexafluoride (SF 6 ) and naturally occurring radon-2 2 2 ( 222 Rn) as well as relatively established hydrologic techniques. To accomplish the objectives, mixing, water tracing, flow component and reaeration experiments were completed along several reaches of the Santa Fe River and within O'Leno State Park. The mixing experiments revealed the effects of incoming springs and syphons within the stream cross section and suggested more detailed sampling strategies in order to accurately evaluate stream parameters. In addition, these experiments established newly developed SF 6 injection xii

PAGE 13

techniques. Water tracing experiments established two things: 1) SF 6 is an excellent alternate method of ground water tracing and 2) the relationships among water sources in O'Leno State Park. Flow component analysis further described the complex water balance within O'Leno State Park while comparing several techniques. Finally, reaeration studies confirmed the usefulness of SF 6 in determining gas exchange in karstic riverine studies. A consequence of the research was the establishment of a first-rate SF 6 analytical laboratory; one of only a handful in North America. SF 6 has become a viable alternative to the presently used dyes and harmful gases, in perhaps one of the most complicated ground water and surface water regions in the world. In addition, because this study was undertaken successfully in such a hydrologically complicated environment, future use of SF 6 in simpler environments promises to be successful as well. xiii

PAGE 14

CHAPTER 1 INTRODUCTION The nature of active karst regions is complex and hydrogeologically difficult to describe. Clues to the historical development of a karst region are also hard to evaluate. Past studies of karst regions employ a variety of hydrologic tracers that were often scientifically inadequate or had negative side effects (White, 1990) . As karst regions, in general, become increasingly populated the need to develop a reliable and environmentally safe ground and surface water tracer is obvious (Dennis Price, personal communication, 1994) . Sulfur hexafluoride, a newly developed artificial tracer, provides a means to interpret ground and surface water interactions in a dependable, nontoxic manner. Wetland areas found within this region of Florida may provide some insight to the geological development of karst, both past and present. The careful study of karst and wetland areas together may aid in the future planning of active karst regions. The Santa Fe River Basin in northcentral Florida provides the unique opportunity to assess the relationships between ground water and river water and wetlands within a complex karst ic setting. 1

PAGE 15

2 Purpose The primary purpose of this project was to accurately characterize the complex karstic ground water/ surface water relationships of the Santa Fe River while continuing to develop the use of the new geochemical tracer SF 6 and naturally occurring 222 Rn. The relationships between the two primary water resources, ground water and surface water, were assessed in terms of their distribution using SF 6 , 222 Rn and other tracing techniques. The wetlands in the region were also addressed in terms of their chemical signature and connection between ground and surface water. In order to accomplish this task several goals were outlined. They included 1) designing and developing an efficient laboratory, injection system and collection system for the dispersal and analysis of SF 6 ; 2) understanding the temporal changes of the Santa Fe River system; 3) understanding the mixing aspect of the river; 4) characterizing ground water, surface water and spring water 222 Rn concentrations in the study area; 5) locating most if not all sub-surface flow sources and sinks of ground water to the Santa Fe River within the O'Leno State Park region; 6) measuring river discharge and stage during high and low flow sampling periods. Significance This work provides valuable information on the ground water/surface water relationships of the Santa Fe River. It

PAGE 16

3 first describes the complex interactions between ground and surface water within the stream and describes how to accurately address river sampling in a karstic environment. Surface and ground water data, used in conjunction with the river reaeration data gained in this study, can assist future planners and developers of the Santa Fe River basin in managing their surface and ground water resources. This work also documents a method of interpretation for active karst regions. Wetland areas studied in conjunction with intensive ground and surface tracing experiments may provide a means to interpret historical and future developments of karst features. The research also expanded the application of SF 6 as a workable tracer in a number of complicated ground water and surface water situations. Propane, ethylene and fluorescent dyes currently in use to predict ground water flow paths, flow rates, reaeration coefficients, and stream mixing, are toxic or have negative side effects such as water discoloration (Aley, 1990; Quinlin, 1990). In contrast, SF 6 and 222 Rn are nontoxic in low concentrations, have no color or odor and 222 Rn occur naturally. For these reasons, the measurement of SF 6 and 222 Rn together may gain in popularity in reaeration and tracer studies and possibly replace the presently used toxic gases in sensitive environments (Ellins, 1989).

PAGE 17

4 An important consequence of the research effort is the establishment of a state-of-the-art SF 6 analytical laboratory. At present, only a few institutions in North America have developed the analytical capability to utilize SF 6 as a water tracer. The tracer, SF 6 , has become a viable alternative to the presently used dyes and harmful gases in perhaps one of the most complicated ground water and surface water regions in the world. The techniques and ideas learned from this study will enable future researchers to study ground water in a more efficient and less harmful manner to the environment. In addition, because this study was undertaken successfully in such a hydrologically complicated environment, future use of SF 6 in a simpler environment may have high success rates as well. Study Area The Santa Fe River, located in north-central Florida, is a principal tributary of Florida's second largest river, the Suwannee River, which is classified as an Outstanding Florida Water (OFW) (Fernald and Patton, 1984) . The Santa Fe River originates in Lakes Santa Fe and Altho and flows westward until it goes underground at O'Leno Sink. It returns to the surface five kilometers farther south and continues to flow sinuously south and west until it joins with the Suwannee River (Figure 1) . Elevations within the drainage basin of the river range from 85 m in the eastern

PAGE 18

5 Figure 1. Santa Fe River in north central Florida (from Hunn and Slack, 1983) .

PAGE 19

6 sub-basin to 10 m in the western part of the basin (Hunn and Slack, 1983). The Santa Fe River basin is underlain by several hundred meters of sand, clay, marl, dolomite and limestone which unconformably overly a Paleozoic basement. The lower sedimentary rocks (Cretaceous to early Eocene) consist primarily of marine limestone and some evaporites and clays, which have very low permeabilities. The sedimentary rocks (middle Eocene to middle Miocene) overlying the low permeability layer are predominantly porous limestones that comprise the Floridan Aquifer. The limestones of the Eocene Ocala Group underlie the study area and provide the source for many of the springs feeding the Santa Fe River (Figure 2; Briel, 1976; Hunn and Slack, 1983). The karstic hydrology of the Santa Fe River is extremely complex. The ground and the surface water systems in the region do not have the same geographical boundaries within this region. Although surface water does not cross the Santa Fe River basin boundary, the ground water system in the area does not coincide with the stream drainage system. Accordingly, the flow of the Santa Fe River is not consistently related to the size of the drainage basin and the amount of rainfall over the basin as a whole. Both the topography and the geology are responsible for these conditions in the Santa Fe basin (Briel, 1976; Hunn and Slack, 1983) . Because of these circumstances, relationships

PAGE 20

7 between surface water and ground water have not yet been completely resolved (Hunn and Slack, 1983; Ellins et al., 1993; Hisert and Ellins, 1993; Kincaid, 1994). Below the River Rise in O'Leno State Park there is a noticeable absence of surface water flowing into the Santa Fe River from tributaries. From the River Rise to the point of confluence with the Suwannee, approximately 22 known springs are visible along the banks of the lower Santa Fe (Figure 2) . Numerous sinkholes bordering the Santa Fe provide the conduits by which precipitation flows underground to recharge the aquifer and eventually discharge into the Santa Fe River. The potentiometric surface of the Floridan Aquifer in the Santa Fe basin is shown in figure 3. The upstream bending of the equipotential contours indicates a leakage of ground water into the lower reach of the Santa Fe River. Water normally flows from the aquifer to the river when the surface of the river lies lower than the potentiometric surface of the aquifer. The direction of flow is reversed when the surface of the river rises above the potentiometric surface. In periods of drought the water in the lower Santa Fe River channel consists primarily of discharge from the Floridan Aquifer; while at times of heavy rainfall, the

PAGE 21

8 Figure 2. Springs found in western Santa Fe River Basin (from Hunn and Slack, 1983) .

PAGE 22

,tl.?8 JK ,t> (Hi t 8 SI-«8 9 <4-1 o c o -H •p o 0) u TJ c <0 • P H 1 <4H T3 P 3 3 -P ID W O d) •H £ P -P P 0 ) c 6 *H O •H £ P O C rH d) dH P o p fa d) •p • (d m J d) TJ P C 3 3 S' O •H P fa CP

PAGE 23

10 "surface water" in the river recharges the aquifer via the springs through a process, which is known as "backflow" (Hunn and Slack, 1983; Kincaid, 1994). The spring that normally feeds the river with ground water is now acting as a conduit by which the aquifer is being fed with river water. Physiography This study area lies within the Western Valley and Marginal Zone physiographic provinces (White, 1970) and forms the boundary between Alachua and Columbia counties (Figure 4) . To the east of Western Valley province lies the Northern Highlands Marginal Zone which is the boundary between the Western Valley Lowlands and the Northern Highlands, as described by White (1970) . The Northern Highlands are poorly drained and plateau-like with elevations generally greater than 30 m above mean sea level (msl) . The eastern boundary of these highlands is Trail Ridge, a sinuous, elongate feature that runs through the central part of peninsular Florida. The Cody Scarp is the topographic marker that separates the highlands from the lowlands. This "scarp", although one of the most prominent features in peninsular Florida, can often be graded and difficult to identify through the undulating topography of the Marginal Zone. O'Leno State Park lies within the eastern extent of the Marginal Zone. The Marginal Zone has also been described by

PAGE 24

11 LEGEND a* Chiefland and bColumbia Limestone Plains cBell and dBrooks vtile Ridges Suwannee and Santa Fe River Valley Lowlands E3 Wacasassa Flats High Springs Gap River Figure 4. Physiographic provinces in the study area (from Kincaid, 1994) *

PAGE 25

12 other authors as the Transitional Zone, the hydrologic and topographic transition between highlands and lowlands (Ceryak et al., 1983) and the Perforated Zone, the zone throughout which sinkholes have breached the western extent of the Northern Highlands (Macesich, 1988) . Although, the terminology represents about the same physical area, there are subtle differences between the many terms Marginal Zone, Cody Scarp, Perforated Zone and Transitional Zone. The eastern boundary of the Marginal Zone is sinuous due to differential erosion produced by various streams and delineated by the point to which headword eroding streams have dissected the Northern Highlands (Williams et al., 1977) . Its western boundary is also variable and generally depicted as the western edge of the Hawthorn Group of sediments. The width of the Marginal Zone ranges from 2 to 11 km and elevations within this zone range from about 15 to 30 m above msl. Within the Marginal Zone numerous streams disappear into the top of the Floridan Aquifer, including Clay Hole Creek and Rose Creek (Columbia County) , and Turkey Creek and Mill Creek (Alachua County) . The Santa Fe River that borders both Alachua and Columbia counties also disappears within this zone. The Suwannee River is the only stream that passes from the highlands to the lowlands without disappearing underground.

PAGE 26

13 The Western Lowlands, bounding the western edge of the Marginal Zone, is a weathered limestone plain. There is a noticeable absence of surface streams as most runoff infiltrates directly to the subsurface due to extremely permeable nature. Sand and thin soil form a veneer over the Ocala and Suwannee Limestones which were formerly covered by the Hawthorn Group sediments (Pirkle, 1956) . Williams et al. (1977) and Williams (1983) acknowledged the difficulty in assessing the cause of the denudation of the limestone plain. These workers suggest that the limestone plain may be the result of marine planation which removed subsequent sand deposits or fluctuating ground water levels activating karst erosion processes. Remnants of the Alachua Formation and Hawthorn Group covering the older limestone are present as outlier hills and sinkhole fill. The remnants, especially the outlier hills, are evidence that the younger units covered the Western Plain at previous times. Except for the outlier hills, most of the Western Valley has a maximum elevation of 10 to 15 m (Pirkle, 1956) . White (1970) named the portion of the Western Valley between the Northern Highlands and the Brooksville Ridge the High Springs Gap. The lower Santa Fe River (below the River Rise) meanders through the High Springs Gap and separates Alachua and Gilchrist Counties from Columbia County. This karst ic limestone plain was subsequently terraced by the Wicomoco, Penholoway, Talbot, and Pamlico seas of

PAGE 27

14 Pleistocene interglacial periods (Pirkle, 1956; Clark et al., 1964). During this time period accumulations of clastic material were deposited over low lying hills and cavernous limestone (Clark et al.,1964). Climate The average temperatures at Lake City and Gainesville are about 19°C and 20°C respectively. The dependence of average annual rainfall on three different types of storms explains, at least in part, the high variability in annual rainfall. Annual rainfall for the period 1900-1976 ranged from 76 cm in 1908 to 213 cm in 1964 in Lake City, and from about 84 cm in 1917 to 195 cm in 1964 in Gainesville (Hunn and Slack, 1983) . Monthly rainfall is usually greatest from June to September. Rainfall in the basin is derived from weather fronts, local thunderstorms, and seasonal tropical storms. Geology The following discussion of the geology of the Santa Fe basin was compiled from numerous sources, among which there is not complete agreement on the nomenclature and age of some of the formations. For more detailed discussions pertaining to the geology of parts of the basin the reader is referred to Vernon (1951), Puri (1957), Meyer (1962), Clark et al. (1964), White (1958; 1970), Faulkner (1973) and Scott (1988).

PAGE 28

15 The dominant large scale structural features in northpeninsular Florida are shown in Figure 5. These features include; the Peninsular Arch, Ocala Platform, Jacksonville Basin and Appalachicola Embayment (Brooks, 1981; Ceryak et al., 1983; Miller et al., 1978; Scott, 1988; Opdyke et al., 1984) . Of these, the Peninsular Arch dominates the distribution of Mesozoic sedimentary rocks throughout this study region. The Santa Fe River basin is underlain by several hundred meters of partially consolidated marine and nonmarine deposits of sand, clay, marl, gravel, limestone, dolomite, and dolomitic limestone. The interpretation of electric logs of test wells indicates that 0.85 to 1.05 km of sediments, ranging in age from early Cretaceous to Holocene, unconformably overlie structurally high, complex basement rocks of Paleozoic age (Figure 6 and 7) . The lower sediments (Cretaceous to early Eocene) consist primarily of marine limestone, some evaporites and clay, and they have very low permeability. These rocks form a basal aquiclude which effectively prevents the further downward movement of ground water. The sedimentary rocks (middle Eocene to middle Miocene) overlying the basal aquiclude are predominantly porous marine limestones which serves as the principal waterbearing units in the area that comprise the Floridan

PAGE 29

16 Figure 5. Structural features in peninsular-north Florida (after Biddlecomb, 1993).

PAGE 30

17 Figure 6. Geology of the western Santa Fe River Basin (after Briel, 1976).

PAGE 31

13A31 ns NT3« ox Q3MM343M SM3X3N Ni NOUYA313

PAGE 32

19 Aquifer. The Floridan Aquifer underlies all of the Santa Febasin and it is the principal source of many of the sprinqs on the lower Santa Fe River. An upper aquiclude of sand and clay sediments overlies the limestone units in the eastern half of the basin. These sediments are early-to-middle Miocene in age and they generally have low permeability, serving to confine the water in the Floridan Aquifer under artesian pressure. Locally, some limestone beds within the unit are tapped for domestic water supplies. Above this unit, sediments of coarse sand and clay (late Miocene to Holocene) serve as a temporary storage reservoir for water which seeps slowly into the semiconfining beds of the aquiclude. This secondary, or watertable aquifer, is usually under non-artesian conditions and is recharged directly by local rainfall which percolates quickly through the topsoil. The water-table aquifer yields moderate quantities of water to shallow wells in those areas of the Northern Highlands where it exists. The Tertiary strata which compose the Floridan Aquifer in the Santa Fe basin have been divided into several series on the basis of their age and their position in the stratigraphic column (Table 1) . The lowest series (Eocene) includes the Oldsraar Limestone, Lake City Limestone, Avon Park Limestone, and the formations of the Ocala Group.

PAGE 33

20 Table 1. Regional Stratigraphy in Northeastern Alachua County, Florida (after Biddlecomb, 1993) . Formation Era Period Epoch or Characteristics Group > Terrace Sinkhole fill, fluvial CO Recent Deposits terraces, and thin c surficial sand (2); fine k1 a) to and to medium grain sands with minor organics (0 ! D 1 Pleisto. residuum and heavy minerals o and Plio. Gray to blue-gray clayey sand that Pleisto. Alachua weathers red-brown (1); sinkhole fill and to Miocene Formation residuum from postEocene deposits, with o limestone boulders and — phosphate 1 ° (3) N Phosphatic clayey sandsandy clay with varying c Hawthorn amounts of Fullers a) CO Middle to Earth and carbonate (1); O £ \ Lower Group three formations described but difficult Miocene to map locally (4); two lithologic types mapped in study area (5) Oligocene Suwannee Limestone Very pale yellow, moderately indurated, porous, fossil-rich calcarenite (2); Rhyncholampus gouldii White to cream, soft & Eocene Ocala Limestone granular, massive, fossil rich limestone, locally well indurated (1); Lepidocyclina sp. 5

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21 The oldest unit which bears fresh water is probably the Oldsmar Limestone (early Eocene) , but its permeability isgenerally low and the sulfate concentration is high. The high sulfate content of the Oldsmar Limestone causes it not to be considered an important contributor to the Floridan Aquifer. The top half of the unit is a moderately porous brown limestone with some gypsum and anhydrite. The bottom of the Oldsmar, however, is strongly dolomitized, and the water therein is highly mineralized and unsuitable for domestic use. Over most of the Santa Fe basin, the Oldsmar lies at relatively great depths (400 meters to 500 meters below the surface) . The Lake City Limestone (middle Eocene) is the oldest formation in the area from which supplies of fresh ground water may be obtained. This unit is about 150 meters thick and is composed of alternate layers of dark brown dolomite and chalky white limestone, both of which contain chert and gypsum. The permeability of the unit varies from low near its base to high at the top, and the entire formation is considered a part of the Floridan Aquifer, but very little is being pumped from the Lake City Limestone because of its high sulfate content. The Avon Park Limestone (late-middle Eocene) disconformably overlies the Lake City limestone, and is a creamy, chalky deposit which is 52-82 meters thick and has a distinctive and abundant fauna of foraminifera. The Avon

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22 Park Limestone is a highly permeable part of the Floridan Aquifer, but it is not extensively tapped as a potable water supply because of its high sulfate content. The Oldsmar, Lake City and Avon park Limestones do not out-crop within the Santa Fe basin. The Ocala Group (late Eocene) disconformably overlies the Avon Park Limestone. The group consists of three formations of very similar lithology. From oldest to the youngest they are the Inglis, Williston and Crystal River formations. The limestones of the Ocala Group vary from a porous, cream-white, loose coquina of large foraminifera and shells to a brown, solution ridden, echinoid-rich limestone. The total thickness ranges from 46 to 76 meters. Locally, limestone at the top of the Ocala has been replaced with chert. The permeability of these formations is extremely high and the Ocala Group serves as the principal source for many of the springs and large capacity wells in the Santa Fe basin. Limestones of the Ocala Group, the oldest rocks exposed in the Santa Fe basin, are commonly found at the surface west of High Springs along the channel of the lower Santa Fe River; the outcrop is covered in the area only by a veneer of loose sand. A well developed karst topography, which includes such features as filled open sinks, sinkhole lakes, solution pipes, basins and prairies, is typical of areas underlain by the Ocala Group. The intricate fracture

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23 pattern of the limestone has produced a one-meter water rapid on the river near Fort White. The strike of the falls is approximately N. 60° E., which conforms to the general fracture pattern of northern Florida. The Oligocene Series, represented by the Suwannee Limestone, unconformably overlies the Crystal River Formation. The Suwannee Limestone is very permeable and porous and is lithologically similar to the members of the Ocala Group. The Suwannee is composed of hard and soft beds of white, tan, or cream-colored limestone that are partly dolomitic and coquinoid; some sand and silicified layers of chert are also present. The Suwannee is a residual material which is generally absent in the western half of the Santa Fe basin; it occurs locally north and northeast of Gainesville, and appears to be continuous in a narrow outcrop northwest of O'Leno State Park. Its thickness in this area reaches 15 meters. The Miocene Series is represented by the Hawthorn Group and Alachua and Choctawatchee formations (Scott, 1988) . The Hawthorn Group, in the study area, consists of three formations, (the Coosawhatchie, Marks Head and Penny Farms) . The Hawthorn Group is composed of marine sands, clays, marls and sandy limestones, all of which may be phosphoritic. The lower part of the Hawthorn contains beds of hard dolomitic limestone and interbedded clays, and the contact with the underlying formations is probably disconformable. The main

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24 deposit reaches a thickness of 75 meters and consists chiefly of thick clays that range in color from yellow-green to blue-gray. Layers or lenses of sand and soft white limestone and phosphatic limestone are interbedded with clays; large pebbles of phosphate having brownish-black color are disseminated throughout the formation. Though the Hawthorn is continuous over much of the Santa Fe basin, the main body of the deposit lies in the Northern Highlands province along the upper course of the river. The outcrop in this area is often covered by a relatively thin layer of loose sand, sandy clay, and organic humus. Remnants of the Hawthorn have filled sinks and lake basins and have formed a mantle of sediment over the outcrop of the Ocala Group in some parts of the western basin. The relatively thick and impermeable Hawthorn sediments serve as the principal confining beds to contain the waters of the Floridan Aquifer under artesian pressure. In addition, these semi-confining beds serve as a basal aquiclude for the shallower water-table aquifer, retarding the movement of this water into the aquifer below. The Hawthorn Group is itself an aquifer and yields small quantities of water to domestic wells in the eastern sections of the Santa Fe basin, but its permeability is generally low and the chemical quality of the water it produces is usually poor at depth.

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25 The Choctawatchee Formation overlies the Hawthorn along the extreme eastern parts of the Santa Fe basin, but it does not crop out anywhere within the area. Thin beds of sand and limestone are interlayered with soft yellow fossiliferous clay and partly-indurated marl. Pebbles of phosphate and silica are disseminated in these beds, and mollusk shells are abundant throughout the formation. The thickness of the Choctawhatchee Formation in the basin is only about four meters, and it is of minor importance as a hydrologic unit. The Alachua Formation (late Miocene to early Pleistocene) is a terrestrial deposit of reddish-white sands interbedded with various colored clays, sandy clays, and pebbles of phosphate. Siliceous limestone and phosphate boulders are scattered throughout the formation, as are organic materials and the fossils of various types of land vertebrates. The sandy clay and sand beds of the Alachua Formation are not as calcareous and phosphatic as similar beds in the Hawthorn, though phosphate deposits are mined in the Fort White area near the confluence of the Santa Fe and Ichetucknee Rivers. The Alachua Formation reaches a thickness of 30 meters and crops out near the south bank of the river along the Alachua/Gilchrist county line. The Alachua acts in conjunction with Hawthorn as a semiconfining unit to retain water in the Floridan Aquifer, although the aquifer is often exposed in the area of the

PAGE 39

26 outcrop due to the collapse of caverns in the underlying Ocala Group. In areas where this sinkhole development has been extensive, direct recharge to the Floridan Aquifer from local rainfall is common. Coarse clastic sediments, the Cypress Head Formation, of late Miocene age were deposited in the Northern Highlands of the Santa Fe basin as terraces at different stages of sea level. These deposits comprise the prominent topographic features of the region, and they overlie most of the older sediments in the area. Two lithologic units are discernable; one predominantly sand and the other predominantly clay. The sand unit is mostly fine grained and argillaceous at the surface but coarsens with increasing depth, and large pebbles of phosphate quartz are found at its base. The sands are dark brown or black due the presence of organic humus and iron-bearing materials. This unit ranges from 6 to 15 meters in thickness. The clay unit is mottled red to yellow-gray and ranges from two to five meters in thickness. The clays are generally in the upper part of a sequence of beds which overlie cream-colored sands and sandy clays. The total thickness of these sediments reaches 15 meters in the northeastern parts of the basin. Pleistocene and Holocene fluvial deposits of clay, sand and gravel usually occur beneath the flood plains of the Santa Fe and its tributaries. The stream bed of the lower Santa Fe, however, is primarily exposed limestone veneered

PAGE 40

27 with coarse sand. Deposits of peat and muck are being formed in the bottom of plugged sinkholes, lakes and swamps in the basin. Eolian dunes of fine sand generally mantle the higher topographic elevations, and thicker lenses of wind blown sand mantle the valley floors and form the principal shallow surficial aquifer in the Northern Highlands . The western part of the Santa Fe River consists of a well developed karst plain with exposed Tertiary limestones, comprising the Floridan Aquifer. The Floridan Aquifer is mostly unconfined here because the Hawthorn Group has been removed by erosion (Puri, 1957, Briel, 1976; Fernald and Patton, 1984; Figure 8). Except for the Santa Fe and Ichetucknee Rivers, and Cow Creek (intermittent) , the western sub-basin lacks surface discharge. Several large springs contribute baseflow to the lower Santa Fe River (Figure 2). Ground water influx also occurs within river bottom seeps that are controlled by large joint features found within the aquifer. Unfortunately, the detection of such sources of ground water delivery to the river is very difficult due to the depth of the river and the dark color of the water (Hunn and Slack, 1983). Ground water from the Floridan Aquifer adding to the lower Santa Fe River modifies the chemical parameters of the river and is indicated by increasing pH, alkalinity, specific conductance, and decreasing temperature (Fernald and Patton, 1984) .

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28 3 0 ° 0 0 ’ 29 ° 45 ’ 82 ° 45 ’ 82 ° 15 ’ Figure 8. Hydrogeologic units of the western Santa Fe River Basin (after Hunn and Slack, 1983) .

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29 Karst Development Because karst dominates in this study region, a brief description of its evolution and type is necessary to understand the ground water and surface water interactions. The Florida Platform encompasses the Florida Peninsula and parts of the Southeastern Atlantic and Gulf Coastal Plain. Including the encircling continental shelves, the Florida Platform has been primarily a carbonate platform on which thousands of meters of dolomites and limestones have been deposited with relatively minor amounts of evaporite and clastic sediments for much of the Mesozoic and Cenozoic periods (Clark et al., 1964; Beck, 1986). The carbonate rocks of the Florida Platform have been variously subjected to repeated cycles of sea level fluctuations (White, 1958; Hanshaw and Back, 1979; Randazzo and Bloom, 1985; Ford and Williams, 1989). Sea level and its changing position is considered to be the keystone in the development of karst processes due to its repeated shift from vadose to phreatic zones (Back et al., 1984). The origin of numerous submarine karstic features on the Florida Platform is also attributed to glacio-eustatic sea level changes (Jordan, 1954; Jordan et al., 1964; Malloy and Hurley, 1970; Gomberg, 1977; Doyle et al., 1985; Hebert 1985; Popenoe, 1985; Mullins et al., Parson, 1986; Pauli et al., 1987). 1986; Twichell and

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30 There are primarily two types of karstic evolutionary schemes (Ford and Ewers, 1978) . The first theory employs generalized models of the origin and sequence development of karst landforms. The second theory describes regional denudation chronologies in which the history of karst landform is reconstructed (Gunn, 1986) . Grund (1914) and Powell (1975) based their early theories of karst on the geographical cycle concept and the sequential development of both surface (exokarst) and underground (endokarst) landforms. This type of development is in contrast to more recent author's theories such as Ford and Ewers (1978) who consider the development of exokarst and endokarst landforms separately. By doing so. Ford and Ewers (1978) have resolved most of the contradictions in development found the earlier papers of Grund (1914) and Powell (1975) . Waltham (1981) supports Ford and Ewers and their theories of karstic environments that suggest separating the exokarst and endokarst development. To support these authors, numerous studies of closed depressions (dolines) have showed that since dissolution proceeds from the surface downward, there is little, if any, genetic relationship between the surface karst and the underground landforms (Williams, 1972; Jennings, 1975; 1983; Palmquist, 1979) . Within the western Santa Fe River basin, both exokarst and endokarst interactions as well as paleokarst phases

PAGE 44

31 affect the development of karst in the region. Stringfield and others (1979) concluded that the vertical movement of water from the surface through joints, fractures and other openings in the Tertiary carbonate rocks of Florida, to discharge areas initiated the formation of lateral dissolution channels causing a circulation system below the water table. As base level and the top of the saturation zone were lowered, accompanying sinkholes developed in the initial stage of karstif ication because of the previously karstified underlying carbonate rocks (Stringfield et al., 1979) . In contrast to these sinkhole laden areas there are subregions within the western river basin where previously existing dolines and dissolution shafts extended many meters below present day sea level. These sinkhole regions are now buried because of the present higher water table. This higher water table is the result of increase in sea level caused by Pleistocene deglaciation. This increase in sea level resulted in the zone of saturation to rise to water levels in the limestone at or above the bottom of the dolines that form in the zone of aeration (LeGrand and LaMoreaux, 1975) . White (1958) believes that the karst topography created by previous emergent episodes has been buried by the sands deposited during interglacial times of high sea level. These karst features, although sometimes difficult to

PAGE 45

32 identify and analyze due to the brevity of glacial stages compared to the interglacial stages, can be attributed to ground water circulation in the Florida Platform which is the product of several cycles of subaerial exposure. Fewer and smaller solution openings should be encountered with increasing subaerial exposure of the continental shelf. The decrease in solution openings occurs because surface elevation decreases. This surface decrease in turn causes the total length of time as well as number of times the area will be emergent and exposed to subaerial conditions to decrease. Thus, during interglacial stages of warmer climate, sea levels were higher, and solution was probably retarded in the lower coastal areas because the openings were largely filled with sediments and salt water which has less capacity to dissolve limestone. White (1958) states that the coastal plain karst should be most mature on the highest land surfaces. White's theory of more developed karst on higher regions is represented in this study area. The most active karst regions in the western Santa Fe River basin are found along the marginal zone marking the boundary between the coastal lowlands and the central highlands physiographic province, where elevations are generally above 30 meters in elevation. With prolonged re-emergence of the Florida Platform the reactivation of the karst cycle slowly opened new avenues of underground discharge and the piezometric surface gradually

PAGE 46

33 dropped. This seems to have occurred in the western Santa Fe River basin where disappearing lakes, disappearing rivers, and abandoned spring heads all suggest such a drop (White, 1958). The karst development and evolution on the Floridan peninsula was a complicated and intricate interaction of surface and ground water interactions as well as the overriding influence of the karst base level, sea level. The karst's complicated nature is evident today in the surface and ground water interactions found within the western Santa Fe River Basin. Regional Ground Water Flow The general trend of ground water flow in the western portion of the Santa Fe River Basin is in a westerly to south westerly direction (Hunn and Slack, 1983; Fernald and Patton, 1984; Beck, 1986). The Floridan Aquifer discharges to the Santa Fe and Ichetucknee Rivers, via springs near the rivers where the potentiometric surface is near land surface. Discharge from the Floridan Aquifer also occurs through wells and evapotranspiration. Recharge to the Floridan Aquifer occurs via syphons within the Santa Fe River and through predominant point recharge regions or sink holes found throughout the lowlands physiographic province (Hunn and Slack, 1983; Fernald and Patton, 1984). Because there is a lack of surface streams other than the Santa Fe

PAGE 47

34 and Ichetucknee rivers, almost all the water that reaches the ground surface flows as ground water through this region. Based on a survey completed by the Suwannee River Management District (1990), the potentiometric surface of the Floridan Aquifer is approximately 10 m National Geodetic Vertical Datum (NGVD) near O'Leno State park and drops to less than 5 m NGVD where the Santa Fe River and Ichetucknee rivers join. Wetland Environment The hydrologic component of wetlands is considered to be the most important component to the wetland environment because it ultimately controls the type of soil that will form and the type of vegetation that will grow in an area. However, it is often the least understood and the most difficult to determine. For example, water flow rates through the soil in wetlands vary several orders of magnitude (Table 2) . Most of the wetlands that border the Santa Fe River have been classified as bottomland hardwood wetlands or riparian wetlands (Mitsch and Gosselink, 1986) or a palustrine forest (Cowardin et al., 1979). Some cypress domes are found in the study area especially throughout O'Leno State Park. These areas have a different type of hydrochemical regime than the riparian wetlands that control

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35 their existence. For the most part, the chemical composition of these wetlands will be addressed in order to better establish the wetlands' possible connections with other water sources in the region. In actuality, very little is known about the quantity and quality of wetland water added to the riverine environment in many areas (Mitsch and Gosselink, 1986) .

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36 Table 2. Hydraulic Conductivities of Wetland Soils Compared to Other Mineral Soils (from Mitsch and Gosselink, 1986). Wetland or Soil Type Hydraulic conductivity cm/sec x 10' 5 Northern Peatlands Highly Humified Blanket Bog, U.K. 0.02-0.006 Fen, U.S.S.R. slightly decomposed moderately decomposed highly decomposed 500 80 1 Carex fen, U.S.S.R. 0-50 cm deep 100-150 cm deep 310 6 North American Peatlands (general) f ibric hemic sapric Coastal Salt Marsh >150 1.2-150 <1.2 Great Sippewisset Marsh, MA (vertical conductivity) 0-30 cm high permeability zone sand-peat transition zone Non-Peat Wetland Soils 1.8 2,600 9.4 Cypress Dome, FL clay with minor sand sand 0.02-0.1 30 Okeefenokee Swamp Watershed, GA Mineral Soils (general) 2.8-834 Clay Limestone Sand 0.05 5.0 5000

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CHAPTER 2 BACKGROUND Radon-222 f 222 Rn) Radon is an inert, volatile gas occupying the final place in the noble gas group of the periodic table. It is the heaviest known gas with an atomic number of 86 and atomic mass of 222 . 222 Rn, with a half-life of 3.823 days, is the most abundant of the three predominant alpha emitters and is naturally derived from radium-2 2 6 ( 226 Ra half-life=l. 6 x 10 3 years) . Both 226 Ra and 222 Rn are part of the uranium238 decay series. Uranium-238 and 226 Ra are common constituents in continental sedimentary rocks and sediments (Key, 1981; Ellins et al., 1989, 1990). As 226 Ra decays naturally to 222 Rn, in a closed system, 99 percent equilibrium between 226 Ra and 222 Rn concentrations will be established within approximately 25 days (Rogers, 1958; Ellins 1988; 1989; Asikainen, 1981). Because 222 Rn is highly soluble in water and a volatile gas it will remain in the aquifer to decay to lead-206 or once released to the surface, will be absorbed in the atmosphere where it exists in low concentrations (Elsinger and Moore, 1983; Rogers, 1958). Three physical properties, the short time duration required to establish equilibrium 37

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38 between 222 Rn and its parent nuclide 226 Ra, the ubiquity of 226 • • Ra in continental sedimentary material, and the volatility of naturally occurring gaseous 222 Rn, make 222 Rn a commonly used natural tracer with many applications (Broecker et al., 1967; Key, 1981; Ellins, 1988). Rogers (1958) was the first to use 222 Rn to investigate the relationship between ground water and surface water. Rogers determined that 222 Rn concentrations in a Wasatch Mountain, Utah, flowing stream will be low due to the volatility of the gas and the slow decay rate of the radium source that may be contained in rock and sediment in the stream channel. Furthermore, he demonstrated that 222 Rn concentrations in ground water from springs were much higher than those in surface water. Also, the spring water was identified as the source of 222 Rn in the streams. Rogers initial study has led to many advances in the usefulness of 222 Rn in hydrogeological problems (Broecker, 1965; Broecker et al., 1967; Jacoby et al., 1979; Fanning et al., 1987; Ellins, 1985; 1986; 1988; Ellins et al., 1990). Subsequent studies by Ellins (1989) and Ellins and others (1990) corroborated Rogers work. They described the low levels of 222 Rn in a Jamaican and Puerto Rican stream as a function of the loss of 222 Rn to the atmosphere and the high levels of 222 Rn due to the input of 222 Rn enriched ground water. Figure 9 depicts the relationship between surface and ground water 222 Rn levels in a Puerto Rican stream. \

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39 Initial measurements of background 222 Rn concentrations of about 10 dpm/L in the Santa Fe River have been performed. Also, spring 222 Rn concentrations were measured at levels around 1000 dpm/L for the lower Santa Fe River basin (Figure 10) . Using these values, the ratios of ground water 222 Rn concentrations to stream levels is 100:1 (Ellins et al., 1993) . Because this ratio is so high, 222 Rn provides a sensitive means of detecting ground water influx to surface flow that no other naturally-occurring chemical in ground water and surface water can compare (Ellins, 1990) . Sulfur Hexafluoride fSF^ Wanninkhof (1986) employed SF 6 as a gaseous tracerto study the gas exchange rates across the air/water interface in three lakes. In addition, he included an in depth discussion of the physical properties of SF 6 and its analysis. To date, his work is the most thorough and detailed employing SF 6 in the hydrologic field. The following will provide a summary of his data pertinent to this investigation. The interested reader is directed to read Wanninkhof (1986) for more detailed information. SF 6 is a volatile, artificial, nontoxic, inert gas, that can be detected by electron capture detection methods down to 5xl0' 17 moles following the procedures of Wanninkhof (1986) and (Ellins, 1989) . The molecular weight of SF 6 is

PAGE 53

222 40 (4.0m J /t> Figure 9. Rio Grande de Manati 222 Rn concentrations et al. , 1990) . (Ellins,

PAGE 54

400 in CM o o o o o O o o in o in o m O m CO CO CM CM (1/tudp) uoi JBJJU 9 0UOQ uopea •H 0)
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42 146.05 g. It has a vapor pressure at 21°C of 22.8 atm and has an extremely low solubility in water at 5.4 cm 3 SF^kg (Wanninkhof, 1986). Wanninkhof (1986) reports that SF 6 has an atmospheric background level of about 1.5 parts per trillion by volume. This value has not significantly changed over the past eight years (Wilson and McKay, 1993). Water in eguilibrium with air will have a concentration of 5xl0' 16 mol/L (Ellins, 1989) . SF 6 is not considered dangerous because a maximum limit of lOOOppm is considered harmful to humans and spiked samples usually contain less than 0 . 5ppb of SF 6 (Wanninkhof, 1986). The difficulties associated with SF 6 as a tracer are its affinity for certain porous substances, its ease of contamination and contamination of SF 6 with other gases during analyses (Ellins, personal communication, 1993; Wanninkhof, 1986) . Materials such as rubber, plastic, grease, and teflon cannot be used in lines, containers, and extraction and analyses equipment because of their affinity for SF 6 (Wanninkhof, 1986) . Steel, copper, glass and nylon tubing were used exclusively in these experiments and are not prone to adsorb SF 6 (Wanninkhof, 1986) . Because small amounts of SF 6 were used in this study, 99.99% pure SF 6 , standards of SF 6 (lppt, 49ppt, 222ppt) and experiment samples were kept in different rooms at all times, except during analyses of water samples, to avoid crosscontamination of the SF 6 . Contamination with some aerosols

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43 and synthetic lubricants can pollute air to such an extent that analyses becomes impossible (Wanninkhof , 1986) . Because of this, no aerosols, lubricants, or petroleum products were allowed in the analysis lab or near sample containers . The Schmidt number (kinematic viscosity of water divided by the diffusion coefficient of the gas) is about the same for both SF 6 and 222 Rn (Wanninkhof, 1986; Ellins et al., 1994). Because these Schmidt numbers are similar, gas transfer velocities for both gases in a stream will be the same (Ellins et al., 1993). Therefore, the dual application of 222 Rn and SF 6 allows for the more accurate description of surface and ground water interactions. Details of their application can be found in Ellins and others (1993) and Ellins and others (1994). Briefly, the dual tracer work allows for the accurate detection of ground water springs or seeps and the quantification of its input to the stream. Most recently SF 6 has been shown to be "conservative" tracer in simple laboratory experiments revealing its inert properties with respect to adsorption to saturated sandy material (Wilson and Mackay, 1993) . In this experiment however, the SF 6 can only be labelled conservative because the sandy material through which the SF 6 was pumped was enclosed within an acrylic tube. Essentially the experiment was run under closed conditions with respect to the atmosphere, depicting SF 6 as being conservative.

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44 Rhodamine WT Perhaps the most widely used tracers in karst terrane are fluorescent dyes. These dyes are commonly used because they are readily available, and they all, to some degree, are absorbed on activated coconut charcoal or unbleached cotton. Fluorescent dyes are generally superior to nonfluorescent dyes because they can be detected at concentrations ranging from one to three orders of magnitude less than those required for visual detection. Thus, traces with fluorescent dyes usually can be completed without the aesthetically unpleasant probability of discoloring a private or public water supply. Because tracing karst ground water flow frequently involves either private or public water supplies, the problem of toxicity of the tracers must be considered. There is a relatively large amount of information available on the toxicity of the most common tracers. Smart (1984) presents a review of the toxicity of 12 fluorescent dyes used for water tracing that includes the tracers discussed this manual, namely, rhodamine WT, optical brighteners, Direct Yellow 96, and fluorescein. As reported by Smart, three dyes present minimal carcinogenic and mutagenic hazard: Tinopal CBS-X (brightener) , fluorescein, and rhodamine WT. Douglas and others (1983) reported that rhodamine WT is non-carcinogenic but found a small but statistically significant dose-related, mutagenic effect.

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45 However, they concluded that the use of rhodamine WT does not appear to represent a major genotoxic hazard. Steinheimer and Johnson (1986) have shown that, under customary dye study practices in surface waters, the possible formation of carcinogenic nitrosamines from the use of rhodamine WT should not constitute an environmental hazard. In ground water, which may be enriched with nitrite, nitrosamines could form, but high-nitrite concentrations in ground water are uncommon (Hem, 1985) . Therefore, the possible formation of nitrosamines is not likely to be a problem (Mull et al., 1988). Quinlan (1987) points out that numerous investigators (Anliker and Muller, 1975; Lyman et al., 1975; Ganz et al., 1975; Burg et al., 1977; Smart, 1984) have found optical brighteners to be nontoxic, non-carcinogenic, and non-mutagenic and therefore safe for use a tracer. It should be pointed out the one dye, rhodamine B, which was earlier approved by the EPA for use as a tracer in potable water (Cotruvo, 1980) , is no longer recommended because impurities within it are known to be carcinogenic and possibly mutagenic (Smart, 1984) . Although many different fluorescent dyes are used as ground water tracers, present usage is centered on four: rhodamine WT (Cl Acid Red 388), fluorescein (Cl Aid Yellow 730), optical brighteners and Direct Yellow 96. In general rhodamine WT is not used for qualitative tracing because of the difficulty of visually distinguishing the pink color of

PAGE 59

46 the dye from that of other organic compounds that can be easily be sorbed by activated coconut charcoal (Mull et al., 1988) . However, it is considered an ideal tracer in quantitative settings under specific hydrologic conditions, even though no fluorescent tracer is 100 percent conservative because some dye is lost to sorption or chemical decay (Mull et al., 1988). Therefore, dye loss must be considered during quantitative analysis of the dyerecovery data. Its advantages are that it is photochemical ly stable and can be used in low pH waters. Its disadvantages include the following problems: its detection may require fluorometric analysis, it is moderately adsorbed to clay particles and is difficult to distinguish in qualitative tracing. The dyes detectable limit is about 0.01 micrograms per liter, in most natural settings, with a fluorometer which is about one to two orders of magnitude lower than the other popular used tracers. Oxygen Isotopes Naturally occurring oxygen is composed of the stable isotopes 16 0, 17 0, and 18 0. The ratio of 16 0 to 18 0 in air is about 1:489; however, in nature this ratio can vary by about 10%. Many chemical and physical processes in nature are accompanied by oxygen isotope fractionations.

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47 During phase changes between liquid and gas the heavier water molecules tend to concentrate in the liquid phase, which fractionates the oxygen isotopes. Water that evaporates from the ocean is isotopically lighter than the water remaining behind, and precipitation is isotopically heavier; that is, precipitation contains more 18 0 than the vapor left behind in the atmosphere. The use of mass spectrometry can determine the ratio of isotopes in a water sample. These isotopic ratios from an environmental water sample can be compared with the isotopic ratio of standard mean ocean water (SMOW) . The comparison is made by means of the parameter (5), which is defined as ( 1 ) 5 18 o (°/oo) = -LLH Q/ . 16 0) s affpl c zX.. 8 0/ 16 0) SM0M ] x 10 3 ( 18 °/ 16 o) SHOW (Fetter, 1988). Ground water in this region within the Floridan Aquifer has a relatively constant value of about -4 parts per mil, relative to (SMOW) (Paul Gremillion, personal communication, 1993) . In shallow ground water systems with normal temperatures, the concentration of isotopes are little affected by chemical processes. Once the water moves below the upper part of the soil zone, the 18 0 concentration becomes a characteristic property of the subsurface water mass. Surface water, on the other hand, has varying concentrations of 18 0 due to the addition or mixture of

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48 precipitation with different 18 0 concentrations and evaporation affects can change the overall nature of the 18 o signal. Because of differences in the 18 0 content observed in ground water and surface water, mixing between the two water masses can be estimated. Stable oxygen isotopes of the water samples were analyzed using an initial process of equilibration of co 2 gas in a shaker bath at 30°C. This C0 2 gas was then distilled off line using a methanol and dry ice slush mix and liquid nitrogen trap. The C0 2 gas was then sealed in six millimeter vacuum-pyrex glass tube for transfer to the VG-Isogas Prism Series 2 mass spectrometer for analysis. Precision of internal standard was 0.1 per mil (Dave Hodell, personal communication, 1993). Cation Concentrations As precipitation reaches the ground in a watershed, it will either infiltrate into the ground, pass back to the atmosphere through evapotranspiration or flow on the surface as runoff. When enough runoff comes together, possibly combined with ground water flow its mineral content is already different from that of the original precipitation. Because of the differing geologic, atmospheric, and human environments there is no typical water quality for \ surface and subsurface flows (Mitsch and Gosselink, 1986) . Wetland environments, however, are the sources, sinks and

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49 transformers of elements for various trace metals, P a ^"t icularly iron, manganese and sulfur, which make their chemical signature distinct from other water environments (Mitsch and Gosselink, 1986) . Due to the fact that elements should differ from one water environment to the next, and the fact that there are multiple water sources in the region, cation concentrations were measured in water samples taken from the two major water components of the area, stream flow, and ground water. Wetland/riparian water was also sampled throughout O'Leno State Park. Primarily aluminum, calcium, sodium, potassium, and magnesium were analyzed by atomic absorption techniques to distinguish between environments. These elements were analyzed because there is abundant background information on them and they typically are used in conjunction with one another to distinguish between different water bodies or sources (Fetter, 1988) . For example trilinear diagrams with Mg ++ , Ca ++ , and Na + +K + , as their corner points are used to classify magnesium, calcium, and sodium or potassium type natural waters (Fetter, 1988) . The major cation species in most natural waters are Na + , K 1, Ca ++ , and Mg ++ . The ground water chemistry of the Floridan Aquifer in this region has been well established as has the chemistry of the Santa Fe River (Hunn and Slack, 1983; Katz, 1992). The two bodies are chemically distinct at the sinking point of the Santa Fe River at O'Leno Sink

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50 because the river at this point is a surface fed stream, driven by precipitation events. Because the Floridan Aquifer material is primarily limestone, the ground water chemistry reflects the dissolution of the aquifer material. The dominant cation in ground water is Ca ++ , which has a concentration about 10 times that of the upstream Santa Fe River (Hunn and Slack, 1983? Katz, 1992). Because there are at least two chemically distinct water bodies, mixing of these water masses through the region will indicate sources and sinks of ground water, river water and possibly wetland water to and from the river system. Previous Hydrogeological Investigations Records of stream flow in the basin have been collected by the U.S. Geological Survey at various points in the area since 1927. These records were published annually in a series of water-supply papers, and a summary of these records through 1950 is published in Water Supply Paper 1304 (1951) . Black and Brown (1951) gave information about the chemical quality of water in the area and other parts of Florida. Skirvin (1962) provided the most detailed description of the O'Leno State Park area as he attempted to determine the location of the underground flow path of the Santa Fe River. Although his work never conclusively determined the

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51 underground path, it did make some significant contributions to understanding this karst. The focus of the work was topographical mapping of the state park. Also included in his work were the first published bathymetric maps of the park's numerous sinks. Skirvin's major contribution to the hydrogeological aspects of the park was the observation that water remained flowing from the River Rise even though the upstream section of the Santa Fe River was damned due to construction. This piece of information is significant because it reveals that the under ground flow path of the Santa Fe River through O'Leno State Park has ground water contributing to its flow before it reaches the River Rise. He also noted a significant "clearing up" of the water found within the sinks and at the River Rise during this damming period. Briel's (1976) application of 234 U/ 238 U to the characterization of water sources in the lower Santa Fe River basin permitted the identification of three different wate ^ types within the basin. Using this finding he characterized the springs along the Santa Fe River as being one or a combination of many water types and thus identify different source regions for the Santa Fe River. His work has recently been disputed because springs which he believed to be unconnected have since been directly linked through cave diving excursions (Kincaid, 1994). Kincaid (1994) was

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52 able to swim through conduits that directly linked the two adjoining caverns Devil's Ear and July Springs. The next phase of investigation into this region was undertaken by Hunn and Slack (1983) . This comprehensive report characterized nearly every aspect of the water resources within the Santa Fe River basin. It revealed the quantity and quality of the surface and ground water in the region as well as their distribution. The paper concluded by discussing the potential for future development in the region from both a surface and ground water prospective. Even though this paper was detailed and extensive it did not make connections between hydrologic aspects and geologic characteristics. Beck (1986) provided some insight to the connections between karst and the geologic nature within the northern peninsular region. His guidebook indicates numerous exposures within karst features as well as interpretive relationships between stratigraphy and the surrounding karst. Biddlecomb's (1993) research into the Robinson's Sink region just north of O'Leno State Park also gives general background information on the region. In addition he provides an in-depth probe into the relationships among surface water, ground water (the multiple aquifers) and precipitation along the Cody Scarp found in this active karst region.

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53 Reaeration Coefficients Streeter and Phelps (1925) defined the reaeration coefficient as a first order rate constant in the basic absorption equation for water. The reaeration coefficient in a natural stream is a general measure of gas exchange capacity and includes the effects of molecular diffusion and mechanical dispersion (mixing) (Hampson and Coffin, 1989; Ellins et al., 1994). Although the reaeration coefficient is generally reported as a single constant, the single value actually represents an average of many individual values within the stream reach (Tsivoglou, 1967). Water quality managers use these reaeration values and dissolved oxygen (DO) models to estimate the capacity of a stream to sustain organic loadings from natural or unnatural sources. The self-cleaning capacity of a river is directly related to the DO levels and the ability to replace oxygen removed by the reduction of organic wastes. The reaeration process is primary in controlling the negative effects oxygen-demanding substances (Hampson and Coffin, 1989; Parker and Gay, 1987; Yotsukura et al. 1984). Methods for the accurate and dependable evaluation of stream reaeration capacities are a valuable tool in the determination of waste-load allocations and waste-treatment requirements. A variety of methods for the determination of stream reaeration coefficients have been proposed. These include the dissolved oxygen balance technique, the disturbed

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54 equilibrium method, gas tracer techniques, and various predictive mathematical models (Hampson and Coffin, 1989; Rathbun et al., 1978; Parker and Gay, 1985; Yotsukura et al., 1984). All of these methods have limitations. For example predictive models sometimes yield unreliable results and gas tracer measurements may be expensive and logistically difficult to carry out (Bennett and Rathbun, 1972) . Since its development, however, the gas tracer method has been considered the most promising and reliable method (Tsivoglou and others, 1965; Rathbun et al., 1978; Ellins et al., 1994). This method had gained further acceptance since the introduction by Rathbun and others (1978) of a modification of the method which uses hydrocarbon gas tracers instead of the radioactive tracer krypton-85 (Tsivoglou et al., 1965). To find reaeration coefficients, other workers have experimented with a variety of gaseous tracers, including natural 222 Rn (Ellins et al., 1990; and Elsinger and Moore, 1983) freon-12 (Duran and Hemond, 1984; Wilcock, 1984; 1988), and SF 6 (Wanninkhof et al., 1990; Ellins et al., 1994) . The currently accepted technique for measuring reaeration involves the deliberate injection of a suitable gaseous tracer into a stream. The tracer is subsequently carried downstream and the rate at which it is lost to the atmosphere from the water is measured and expressed as a gas transfer coefficient, k. The rate of gas transfer that

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55 occurs between the stream and the atmosphere is dictated by the gradient of gas concentrations across the air/water surface (Ellins et al., 1994). In tracer experiments, the values of k for a suitable tracer can be related to the rate of oxygen uptake and expressed as a reaeration coefficient (K 2 ) . The gas transfer velocities of the two gases in a stream should be approximately the same because 222 Rn and SF, have approximately the same Schmidt number (Ellins et al., 1994) .

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CHAPTER 3 MATERIALS AND METHODS Gas Chromatography and the Injection Port System The gas chromatograph was the instrument used to analyze the SF 6 and the general procedures followed those of Wanninkhof (1986). The entire chromatographic system consists of several pieces of equipment which have numerous components (Kaiser, 1963; Keulemans, 1957). The details for the entire system can be found in Appendix A. In general the SF 6 saturated water sample is fed into an injection port system that first separates the SF 6 gas from the carrier gas and sends both downstream to the gas chromatograph to be analyzed. Once the SF 6 has reached the electron capture detector (ECD) within the gas chromatograph it passes through a beam of emitted electrons ( 63 Ni) . Because SF 6 is a halogenated compound it has a high affinity for electrons and thus will disrupt the flow of electrons passing in front of its passage. This disruption in electron flow is translated into an electrical pulse which is read by the integrator. The integrator displays the time at which the SF 6 reached the ECD and an SF 6 area versus time curve. The area under this curve is compared to a previously 56

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57 established standards curve and finally the concentration of SF 6 is calculated. SF 4 Injection System The injection system used to transport the SF 6 from its tank to the water consists of two major components. The details of the entire system can be found in Appendix B. These components are a 220L barrel and a two stage peristaltic pump. Basically, SF 6 is forced under its own pressure into a the water barrel. Once saturation is achieved, the water is then pumped via tygon tubing into the study region. The ends of the tygon tubing are held in place with two pound lead weights. Thermometry Thermometry is a simple tool that has been used to distinguish between ground water and surface water features in numerous aquifer settings (Pitty et al., 1979; Larson et al., 1987; Lobmeyer, 1985). To further distinguish between the Santa Fe River and water filled karst features in the area, temperature readings were taken in many of the surface and stream water features. Locally, the ground water temperature remains at about 20-21°C year-round whereas surface water temperature varies depending upon local air temperature (Fernald and Patton, 1984) . Temperature readings were taken on January 11, and 14, 1992, during the

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58 coldest part of the year, to identify differences between surface features and ground water fed features. On March 24, 1992 temperature readings were again taken to confirm these data. A thermometer, cased in perforated metal, was lowered into the features to a depth of one meter until the temperature had reached equilibrium between the water and the thermometer. The thermometer was quickly removed and the temperature was recorded. This procedure was repeated three times at each location and an average temperature was then recorded. The precision of the technique was less than 0 . 5°C, determined by the 0.1°C divisions on the thermometer. Sampling Techniques SF^ Sampling For all mixing, flow component, water tracing and gas exchange experiments SF 6 was collected in either 50 ml biological oxygen demand (B.O.D.) pre-labelled glass bottles or 50 ml glass syringes. For each sample, the bottle was conditioned once with the river or sink water and then the sample was drawn. Samples collected in the B.O.D. bottles were capped underneath the water to prevent air from entering the sample and thus allowing SF 6 to come out of solution. Samples collected in the glass syringes were filled to the 50 ml mark underneath the water and then any air found in the syringe was discharged at the surface. A minimum of 30 ml was needed for each analysis.

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59 Samples were stored on ice in a cooler and transported to the U.F. hydrology lab for analysis. The purpose for storing the samples on ice is to keep the SF 6 from coming out of solution at higher temperatures. Rhodamine WT Sampling Samples collected for the rhodamine WT analysis were captured on activated charcoal packets following the procedures of Aley (1990). These pre-labelled packets consisted of about 4.25 grams of activated charcoal surrounded by a 10 cm long by 10 cm wide fine fiberglass mesh attached to a wire connected and a weight. The wire was fastened to the weight so that when the charcoal packet was attached it would remain suspended above the floor of the river or sink (Figure 11) . The packet was placed at the immediate opening of spring where possible to maximize rhodamine WT adsorption. This suspension of the packet also decreased the amount of debris that would become entangled on the packet thereby reducing the adsorbing capacity. These samples remained in the water for 3.5 to 4 hours so that a definite rhodamine WT signal could be recorded (Pete Butt, personal communication, 1992) . After collection, the sample was lightly rinsed with water, placed in a plastic bag, removed from sunlight and placed on ice until analyzed.

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60 Wire Figure 11. Charcoal packets used in rhodamine WT dye tracing experiment.

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61 The standard elution solution used was a mixture of 5% aqua ammonia and 95% isopropyl alcohol solution. The isopropyl alcohol was 70% alcohol and 30% water. The aqua ammonia solution was 29% ammonia. Twenty millimeters of the eluting solution was poured over the washed charcoal, capped and then allowed to stand for 60 minutes. The liquid was then carefully poured off the charcoal for analysis (Aley, 1990) . Radon Sampling Radon water samples were collected in pre-labelled plastic 250 ml graduated cylinders specifically fitted for 222 Rn extraction (Figure 12) . The pre-evacuated graduated cylinders were attached to tygon tubing fastened to a two inch diameter by three meter length of poly-vinyl chloride (pvc) tubing (Figure 12). This tubing was held at the desired depth, the inlet valve was opened and the water then flowed under pressure into the cylinder. A 150 to 190 ml sample was collected, the inlet valve was closed and then the cylinder was placed back into the cooler for later analysis. Oxygen-18 Sampling Water samples for isotope analysis were collected in pre-labelled 30 ml pyrex glass bottles with screw on displacement caps. Each sample bottle was first

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62 Figure 12. Sampling device and graduated cylinder for SF and 222 Rn.

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63 conditioned, by rinsing the bottle with the river or sink water, and then collected at approximately 0.5 m depth in the water body. The cap was then secured while the bottle remained beneath the water surface. Cation Sampling The major cation sampling used glass (BOD) bottles. The bottles were cleansed following the procedures in Appendix C. Quality Control Duplicate samples were taken at intervals of about 15% of the total number of samples. In addition, duplicate analysis of the same sample were performed at 10% intervals of the total number of samples taken. Duplicate analysis of the same sample were impossible because the total volume of each sample was needed in the analysis for the gas chromatograph (SF 6 ) , the fluorometer (rhodamine WT) and the radon extraction system 222 Rn. However, duplicate sampling was executed whenever the number of sample containers allowed. Reaeration Methods During the Summer of 1991, two twelve-hour long reaeration experiments were carried out on the Santa Fe River which required the continuous injection of SF 6 over a

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64 certain time period. A two-channel peristaltic pump was used to inject 220 liters of SF 6 saturated stream water at two points across the river at a rate of 15L/hour. The governing restraint, in determining the length of reach used in each of the experiments, was the time required for SF 6 to reach plateau concentrations in the stream. It took about five hours for plateau concentrations to be reached in the Santa Fe River (Figure 13) . Heavy sampling over the entire length was carried out after plateau concentrations were reached. From fifty to 250m downstream of the injection point, samples were collected based on predictive equations and the results of the mixing study (Yotsukura et al., 1984). Lateral and vertical mixing problems in the river channel were minimized by collecting integrated samples 1/3 depth of the stream by direct suction into bottles. In addition, SF 6 grab samples were also collected at two points across the stream in the second reaeration study. Immediately following the experiments both 222 Rn and SF 6 samples were analyzed on a 24 hour schedule. The margin of error for sample analyses was calculated by analyzing river water samples during plateau levels at three locations. The SF 6 concentrations were within an average of 7% of each other.

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1250 65 o o O o o o m O n o in
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Analytical Techniques Gas Chromatography Gas chromatography is a physical method of separation, in which the components to be separated are distributed between two phases. One of these phases constitutes a stationary bed of large surface area (the column packing material) , the other being a fluid that percolated through the stationary bed (the carrier gas and sample gas) (Keulemans, 1957; Kaiser, 1963). In the case of SF 6 analyses, a sample was injected into the separating column filled with a micro-sieve mesh, with ultra high pure (UHP) grade nitrogen gas. The carrier gas, nitrogen, and SF 6 were then separated and sent to the gas chromatograph where each was analyzed with an electron capture detector (ECD) . The ECD is a device that basically consists of cathode an anode and a recording device. The radioactive 63 Ni emits electrons (beta particles) across a nitrogen carrier stream onto an anode. There a recording device records the resistivity of the passing electrons. If the stream is interrupted by a substance absorbing electrons, like (SF 6 ) , the output signal will change. Interpretation of this analysis is then recorded by an integrator which graphically and quantitatively indicates the presence of SF 6 in each sample. This method is highly sensitive, rapid and simple in execution. Accurate,

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67 quantitative information can be obtained using small amounts of sample (20ml) . Fluorometric Procedures A fluorometer ' s method of detection is completed by interpreting a sample's amount of light reflectance. A sample is quickly passed through a port that continuously reads the light reflectance property of the fluid. In order for a fluorometer to accurately read a sample it must remain in the sample loop for at least 15 seconds (Aley, 1990) . Some Turner Designs Model 10 Fluorometers can be modified to analyze the standard three millimeter sample that is typically used in lab fluorometers. The fluorometer used in this study was not modified because of lack of funding to complete the process. Because the sample taken was the same volume as the sample loop, the continuous running of the fluorometer passed the sample very quickly through the sample loop and therefore did not allow sufficient time to quantitatively determine the sample's rhodamine concentration. However, relative measurements of the strength of the solution passing through the loop could be determined by recording the degree to which the fluorometer 's needle was deflected. Values such as strong (4), moderate (3), weak (2), very weak (1) and none (0) were recorded for each of the samples.

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68 Radon Analysis 222 Rn was stripped from water using a small extraction system and transferred to an airtight chamber. The radioactive disintegrations of the 222 Rn trapped in the chamber, a modified Lucas-type scintillation cell, were measured and recorded by an alpha-scintillation counter. The scintillation counting material is mounted on the face of a photomultiplier tube, the pulse of light produced by the radiation is converted to an electrical pulse which in turn may be amplified and counted. For work with short range, densely ionizing radiations like alpha particles, the scintillator is finely crystalline zinc sulfide coated in a thin layer on the face of the photomultiplier. The technique and analytical equipment are fully described in Ellins (1988) . The error reported for the radon analyses is a composite of the errors associated with sample counting, cell background counting, channel noise, volume, cell efficiency, and operator error. The precision of the entire procedure was determined by running duplicates of 25 samples in the lab. The level of uncertainty associated with precision of the method does not exceed 14% (Ellins, 1988) . Atomic Absorption Spectrometry Two water samples were taken at 0.5 m depth, in B.O.D. glass bottles previously cleaned in nitric acid and triple

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69 distilled water from 23 locations throughout the park. Water samples from the adjacent Santa Fe River was also analyzed for major cation chemistry. The samples were then analyzed for the major cations Ca~, Mg ++ , Al +++ , K*, and Na + on a Perkin Elmer model 3100 atomic adsorption spectrometer using the acetylene flame ionization techniques outlined in the Perkin Elmer manual (Perkin Elmer, 1990) . The basic technique involves developing a standard curve using lab standards for each of the elements being analyzed and then analyzing samples which fall along the standard curve. In concept the sample is ionized by an acetylene flame in the presence of a light beam emitting the frequency of absorbance for the element in question. Once the sample has been ionized the amount of absorption of this light is recorded. This absorption is then compared to the standard and statistically plotted along the standard curve which calculates its actual concentration. In the University of Florida lab, software that accompanies the spectrometer automatically calculates the concentration of cation within the sample. Each sample was analyzed twice and an average value was recorded. Computer Modeling A model is a tool designed to represent a simplified version of reality. In general, mathematical models use governing equations limited by boundary conditions to

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70 simulate the flow of ground water (Luckner and Schestakow, 1991) . Using calculus, it is sometimes possible to calculate the heads at given points as a function of space coordinates and thus generate an analytical solution. To obtain this solution several simplifying assumptions about the aquifer must be made, including: 1) homogeneous stratigraphy, 2) isotropic conditions, 3) a linear water table configuration, and 4) approximation of the problem by a rectangle (Wang and Anderson, 1982) . For many modeling problems these assumptions are unrealistic and require use of numerical methods to solve the mathematical model . Governing equations are approximated by algebraic statements, boundary conditions, and by programming techniques. Finite difference models are based on rectangular grids whereas finite element models use grids made of triangular elements. Iterative calculations produce estimates of hydraulic head at nodal points that eventually converge to values of acceptable accuracy. Models are calibrated by matching computer-generated head values with field measured head values within reasonable limits (Mercer and Faust, 1981) . Numerical Models Finite-difference methods used to solve partial differential equations use a grid of rectangular cells to represent the region of interest. For two-dimensional

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71 problems a grid system is overlain on a map view or crosssection of the aquifer (Mercer and Faust, 1981) . At each grid node the head will be calculated based on equation 2: ( 2 ) d/dx (T, dh/dx) + d/dy (T„ dh/dy) = S dh/dt Q (x,y,t) where T = transmissivity, LT' 1 , h = head, L, t = time, T, S storativity, Q = net ground water withdrawal, L 3 T' 1 , x,y = rectilinear coordinates, for which there is no general solution. But through the finite-difference approximation a numerical solution can be obtained by replacing the derivations in equation 3 by differences taken between nodal points (Wang and Anderson, 1982) . At each finite-difference node the form of equation 2 at each i,j is equation 3: (3) where ho, , = the calculated head at the end of the * t i previous time increment, t, T, . ; . and T, , . . = aquifer transmissivity within * * • J # * 'fJ'#'

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72 the vector volume between node i,j and i+l,j; i,j+i; i,J-l (Figure 14). Because nodes throughout the entire grid have equations in the same form as equation 3, these equations are solved simultaneously for the unknown h ( ] variable (Luckner and Schestakow, 1991) . By allowing T (transmissivity) to vary with time as the thickness of the aquifer varies, equation 3 can be used in unconfined cases (Wang and Anderson, 1982) . A model based upon the two-dimensional PLASM (Prickett and Lonnquist Aquifer Simulation Model) and MOC (method of characteristics) program was used to simulate ground water flow conditions around the O'Leno State Park and western Santa Fe River region (Luckner and Schestakow, 1991) . These models were chosen because their computer requirements corresponded to the facilities available. Also, they were accessible and relatively powerful with respect to the kinds of data needed as input.

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73 A (x-deltx,y-delty) (x,y-delty) (x+deltx,y-delty) deltx B (i-i, j-D (i-l, j) (i, j) deity deltx (i+1 r 1 ,j> t (i-l,j+l) (i, j+l) (i+l# i+j ) Figure 14. Computer modeling coordinates. A. Finite ^ff erence grid. B. Computer notation for finite difference grid (after Hisert, 1990) .

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CHAPTER 4 RESULTS AND DISCUSSION Mixing Experiments Introduction The measurement of mixing characteristics, longitudinal and transverse dispersion, has been studied in detail in order to address the streams capacity of handling pollution an d to determine alternative tracing technigues and tracer types. Previous procedures have employed saline solutions, rhodamine dyes, ethylene, propane and radioactive tracers to measure these mixing attributes (Luk et al, 1990; Jobson and Rathbun, 1982; Yotsukura et al., 1970). Mathematical models have been derived to calculate the concentrations of a tracer under certain stream conditions over time and distance to understand mixing processes (Fischer, 1966; O'Loughlin and Bowmer, 1975). However, these models have often made several assumptions about stream parameters (i.e. bed roughness, wetted perimeter, chemical degradation and diffusion) . By making these assumptions they allow for greater error in their prediction. More importantly the models do not easily offer the flexibility of additional sources and sinks for river water and or ground water in 74

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75 complicated riverine conditions which can greatly affect the stream's mixing capabilities. In the karstic terrane of the western Santa Fe River basin assessing mixing parameters of the stream is made difficult by the numerous springs, seeps, syphons and boils found within the Santa Fe River. In order to accurately obtain a representative sample of river water for analysis, three detailed mixing experiments were devised to address the cross sectional distribution in the volatile dissolved gases, natural radon-2 2 2 ( 222 Rn) and artificial sulfur hexafluoride (SF 6 ) . Radon-222 The use of radon-2 2 2 ( 222 Rn) in monitoring the relationship between ground water and surface water has been employed in a variety of hydrologic and geologic ground water settings (Rogers, 1958; Broecker et al., 1967; Jacoby et al., 1979; Elsinger and Moore, 1983; Ellins 1985, 1986; 1988; 1990; Lee and Hollyday, 1987). Although these authors have described the concentrations of 222 Rn throughout a reach of a river they neglect to address the lateral and vertical variations of radon concentrations throughout the water column which may be significant. Because 222 Rn is inert, naturally occurring, reaches equilibrium with the host aquifer within a short time period (about one month) , and is often found in a much higher

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76 concentration in ground water versus surface water and remains in solution in the aquifer until the ground water is discharged, it can be used to identify pulses of ground water to many surface features. This process has been described in Ellins and others (1993) . Sulfur Hexafluoride SF 6 has been used in the medical field as a dense displacement gas, in atmospheric tracer experiments, ocean circulation experiments, to monitor gas exchange in lakes and rivers and as a ground water tracer (Lovelock and Ferber, 1982; Ledwell, 1984; 1986; Ledwell et al. , 1986; Ledwell and Watson, 1988; Wanninkhof et al., 1987; Wanninkhof et al., 1990; Hisert and Ellins, 1993). The artificial tracer, sulfur hexafluoride, (SF 6 ) was selected for this study over other tracers propane, ethylene and rhodamine WT because it is inert, non-biodegradable, nontoxic and can be detected in extremely low concentrations (femtamoles per liter) . Also, it does not have some of the associated problems that rhodamine WT has with organic acids that are commonly found throughout many southeastern U.S. states, including Florida (Fernald and Patton, 1984) . The major problem of using rhodamine in Florida streams is that the naturally tannin streams create a high background fluorescence, thus making rhodamine identification difficult. In addition, SF 6 is relatively inexpensive

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77 compared to rhodamine and samples can be analyzed quickly, approximately 25 samples per hour, following the procedures of Wanninkhof (1986) . As part of this study the refinement of injection and sampling procedures for riverine environments was also completed. Processes of Dilution and Mixing When soluble material is injected into a flowing stream, its eventual fate is determined by the physical process of diffusion, convection, chemical degradation, adsorption and evaporation. If a tracer is injected at a point in a flowing channel, it is immediately subjected to the process of turbulent diffusion and dispersion, and its concentration tends to become uniform in the cross-section (O'Loughlin and Bower, 1975; Plate and Friedrich, 1984). The distance required for near uniformity to be achieved may typically be on the order of hundreds of times the channel width (O'Loughlin and Bower, 1975). The events in this stage are three-dimensional and the actual spread rate of dilution depends on the channel geometry and the large-scale turbulence structure of the flow. At this point in the evolution of mixing and dispersion theory, it is difficult to predict the length of this initial phase (O'Loughlin and Bower, 1975) . However, it does appear that the mixing length is determined by the same physical parameters which determine the later dispersion phase in the dilution of the

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78 tracer. Attempts to characterize the behavior of the tracer in the initial stage by using one-dimensional formulations are suspect and lead to erroneous predictions of tracer attenuation. During the dispersion phase, the tracer behaves as a one-dimensional slug of material in the channel; the only significant concentration gradient is that in the direction of flow. A more detailed description of the mathematical derivation of the one-dimensional dispersion equation can be found in O'Loughlin and Bower (1975). Concentrations for a given time period can be predicted for a non-conservative tracer using the following equation: (4) c(x,t)= M exp(-Kt) expr(x-Ut) 2 ! ( 4piDt) 1/2 4Dt where U = mean velocity, m/s D = longitudinal dispersion coefficient, K = first order decay constant for the tracer, x = distance, m, and t = time, s, (O'Loughlin and Bower, 1975). According to Graf (1986) the distance needed in order to achieve complete transverse mixing within a stream can be calculated using the equation: (5) 0.1 V W 2 L Ez

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79 where V = mean reach velocity, m/s W = stream width, m Ez= transverse mixing coefficient (equal to c*d*u) , where; c = dimensionless constant, 0.2 for straight streams 0.4-0. 6 for more irregular stream sides and bottoms, d = mean depth, m, u = shear velocity, m/s. Using this equation, estimates of length of mixing for three reaches of the Santa Fe were calculated. Because of the uniformity of slope and discharge along the river reaches sampled, the average length of stream needed for complete mixing was calculated to be 1.4 km. This estimate was tested in an earlier experiment on the Santa Fe and revealed a complete mixing between 1.0 and 1.5 km, as the equation had predicted. Because of the river's complex hydrologic character, four separate mixing experiments over three different reaches of the Santa Fe River were completed. Injection at Wilson Springs The initial injection experiment took place on June 5, 1991 between Wilson Springs and 2.0 km downstream of Wilson Springs. This site was chosen because of its relative ease of access to the Santa Fe River and its close proximity to our working base camp (Figure 15) . The goals of this experiment included 1) determination of the average stream velocity, 2) testing the SF 6

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80 injection design, 3) determination the river's lateral mixing component, the length at which an injected tracer would become completely laterally mixed, 4) testing the sampling strategy, 5) testing the analytical procedures and equipment with field drawn samples. Experiment Design Samples were obtained at four sites located 0.5 km apart and at the SF 6 injection site, which was located approximately 20 m downstream of the Wilson Springs boat ramp. Samples were collected from a stationary canoe at a depth of 0.3 m in BOD (biological oxygen demand) bottles. In some instances, 50 ml glass syringes equipped with threeway tips were used instead of the BOD bottles, but the general sampling strategy was the same. The sample was taken and capped at depth. The bottle was then transferred to the cooler and stored until analysis took place. A predetermined time at which to start the sampling and the ^^6 injection was relayed to the volunteers before they were stationed at their sampling points. Hollingsworth Bluff The second experiment was carried out at Hollingsworth Bluff. This site was chosen because no known springs or fissures have been identified in the area, it is relatively straight and has a constant depth and width, and thus 222 Rn

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81 82*46' 29 * 54 ' Figure 15. Lower Santa Fe River near Wilson Springs (from Ellins et al., 1993).

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82 was assumed to be being well mixed in this reach (Figure 16) . In addition, because the reach is relatively straight a uniform velocity profile can be assumed. Three cross sections spaced 100 meters apart were sampled for 222 Rn. Twenty samples were taken at each of the locations labeled Mix 1, Mix 2 and Mix 3 on figure 16. Four water samples were collected at equally spaced intervals across the width and depth of the stream. Water samples were collected via rubber tubing secured to 5 cm PVC piping, previously marked in 0.5 meter intervals, with an open end in the water and the other end attached to a previously evacuated 250 ml graduated cylinder. The graduated cylinder was opened once the tubing reached the appropriate depth and the vacuum created within the cylinder sucked water up from depth filling the graduated cylinder to about 150 ml. Samples were then stored in a cooler and then taken back to the lab to be analyzed. In addition, two integrated samples were taken, one across the width of the stream at 0.5 meters d®pth and the second taken vertically mid-stream throughout the top three meters of the water column. Six stream velocity measurements were also taken at each of the three locations using a Weathertronics Flow Meter, to monitor the total discharge over the sampling area. 222 Rn measurements were made using Lucas-type scintillation cells with alpha scintillation counters. A small portable extraction system was used to strip the 222 Rn

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83 -U t | 1km I 300 m SCALE N UNPAVED R0A0S Figure 16. Sample locations at Hollingsworth Bluff (from Ellins et al., 1992).

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84 from water samples collected in the field into scintillation cells. River Rise to Two Kilometers The third experiment evaluated the mixing characteristics from the River Rise of the Santa Fe River to 2 km downstream using a continuous injection of SF, from a point source located in the middle of the river (Figure 17) This reach was investigated to examine the effects of the known boils located within the river between 0 and 0.25 km and 0.75 and 1.0 km. SF 6 was continuously injected into the river until plateau levels were reached, approximately two hours. About twenty water samples were taken across the width of the three locations, at 0.5, 1.0, and 1.5 km downstream of the River Rise, using a similar method to that employed in the first mixing experiment. Subsequent sampling locations at 2.0, 3.0 and 4.0 km were sampled but samples became unusable after transportation because they became aerated or they were sampled incorrectly. Discharge measurements were taken before and after the samples were taken to ensure constant river flow. Rum Island to Ginnie Springs The fourth mixing experiment was carried out in an area characterized by several springs and river syphons approximately 15.75 km downstream of the River Rise, near

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85 Figure 17. River Rise to four kilometers on lower Santa Fe River (from Ellins et al., 1993).

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86 Ginnie Springs (Figure 18) . Sulfur hexafluoride was injected near Rum Island Spring in the middle of the river through a single point source. Water samples were taken at three points across the width of the stream at 0.5 m depth at 13 locations downstream of Rum Island. Between 15.5 km to 16.50 km water samples were taken every 250 m and from 16.50 km to 17.00 km, every 50 m. Sample spacing was altered in this area in order to evaluate an experiment that was being carried out beneath the river, within the Devil's Ear Cave system, in conjunction with the SF 6 mixing experiment. Discharge measurements were taken at four locations throughout the length of the experiment. Summary of Mixing Experiments Wilson Springs Stated goals of the mixing experiment were accomplished. The lateral mixing component was described in this experiment. Using eguation 5, the distance needed for complete lateral mixing was calculated to be 1.4 kilometers under the flow conditions of the experiment. This value also agrees well with the concentration response curves found in figures 19 and 20. A concentration response curve that shows a typical rising and falling peak with one central peak describes a location where there is complete lateral mixing. At 0.5 km the mixing is incomplete due to

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87 Figure 18 . Rum Island to Ginnie Springs on lower Santa Fe River (from Ellins et al., 1993).

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6/6/91 SF6 injection 0.5 km 0 10 20 30 40 SO 60 TIME BAST INJECTION (MINUTES) 6/6/91 SF6 INJECTION 1.0KM Thousands Figure 19. SF 6 concentration response curves 0.5 to 1.0 km

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Thousands 6/6/91 SF6 INJECTION 1.5KM 89 6/6/91 SF6 INJECTION 2.0KM Thousands Figure 20. SF 6 concentration response curves 1.5 to 2.0 km.

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90 the multiple peaks and random distribution of SF 6 throughout the sample period of 55 minutes. At 1.0 km mixing is not yet complete as two peaks are easily recognizable at this local. At 1.5 km mixing is complete as indicated by a rising and falling curve with one central peak. The velocity of the river was also calculated using the centroid of mass of the tracer curve. Using the concentration response curves at locations 1.5 and 2.0 km (Figure 20) , the velocity calculated over these two distances was 0.279 m/s and 0.301 m/s, respectively. These values corresponded well with velocity measurements taken with a Weathertronics flow meter which revealed average stream velocities of 0.275 m/s at 1.5 km and 0.295 m/s at 2 . 0 km. This experiment established a reliable, field worthy injection system, used repeatedly over the last threeyears without any major changes. The system described in Appendix A was used with only minor adjustments throughout this and all other SF 6 injections described in this dissertation. Secondly, the sampling design using BOD bottles and glass syringes in conjunction with canoes and coolers to store samples in ice was also effective. Sampling times and intervals based upon equation eight accurately captured the rising and falling edges of the tracer as it made its way downstream. Thirdly, the analytical techniques and gas chromatograph system described in Appendix A was also

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91 productive in analyzing SF 6 samples efficiently, expediently and with a high degree of precision. Hollingsworth Bluff Table 3 provides the 222 Rn statistical data calculated for the three stream cross sections sampled. At 100 m the concentrations vary the most across the width and depth of the river, from 83 dpm/L found along the stream bottom, to 321 dpm/L recorded in the middle of the stream. The three cross sections in figure 21 show the contoured distribution of 222 Rn concentrations at 100, 200 and 300 meters from the reference point at Hollingsworth Bluff. Radon-222 values recorded at 200 meters ranged from 112 dpm/L to 286 dpm/L. Variability in 222 Rn values diminished with distance downstream of the injection point. At 300 meters all values appeared to increase over the 100 m distance and the variability between sample locations decreased to its lowest level. The increase in concentration is probably due to a diffuse influx of ground water between the last sampling site and 300 m and its dispersion throughout the water column. The standard deviation suggests that all values fall within 15% of the average, the precision of the radon-222 analysis. The contoured data also reflects this homogeneous trend. Horizontal and vertical samples taken across the width of the stream at 0.5 meters depth and at mid-stream from

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Table 3. Statistical data from mixing experiment #2 , 222 Rn data reported in dpm/L. 92 Parameter 100 m 200 m 300 Average of all samples 162 151 283 Standard Deviation 52 47 36 Number of Samples 20 20 19 Horizontal Sample 180 125 271 Vertical Sample 165 175 260 High 321 286 399 Low 83 112 235

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93 Radon Cone, at 100m Radon Cone, at 200m Raoon Cone, at 300m Figure 21. Contoured cross-sections of 222 Rn concentrations in the river near Hollingsworth Bluff, dimensions are in meters, contour interval equals 10 dpm/L.

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bottom to top reveal nineo Se approximations to the overall -erage of all samples taken the stream ^ ”° b ° th lnt£9rated sampling methods were within approximately 10* o f the stream average. Because the horizontal and vertical samples reflect mpies reflect an overall stream average it is suggested that this type of sampling procedure the mam river channel. 94 River Ri.se to Twq K -[ 1 nmofare sulfur hexafluoride was sampled at 20-25 looations -thin each of the three cross-section at 0.5, l.o, and km using the same techniques of infection, sampling and analysis as in the first mixing experiment at Wilson Springs, A wen-mixed pattern was recorded heyond the i.o dlStanc e from the injection point. The SF 6 concentrations were lower than expected <^ure 22) . In each of the three sample locations sf concentrations were about an order of magnitude lower Ln previous experiments and the third mixing experiment. This rs probably due to the continuous influx of assumed non-SF sa urated water to the river system throughout the upper reaches, between n ^ orz-v 0 and 250 m and between 750 m and looo m coming from boils and seeps in the river In addif boils in the river furth addition, the water t , “"** the Water causes the ose SF 6 faster to the atmosphere than a stream

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95 SF6 Cone, at 0.5 km SF6 Cone, at 1 0 km SF6 Cone, at 1.5 km Figure 22. Mixing results at 0.5, 1.0, and 1.5 km downstream of the River Rise, dimensions are in meters, contour interval varies.

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96 without this boiling feature (Wanninkhof, 1986) . The results of this study are useless due to their values being close to the detection limit of the procedure. Rum Island to Ginnie Springs In this relatively straight reach of the river covering about 2.25 km, 39 SF 6 samples were collected after plateau levels of SF 6 were reached in the stream about 2.5 hours at three equally spaced locations stretched across the width of the Santa Fe River. Figure 23 shows the contoured SF 6 concentrations and locations of major springs along this reach. The continuous input of Blue Springs water greatly depresses the plume of SF 6 as it moves in a downstream direction. Along the southern bank of the river. Blue Spring which discharges greater than 1.15 x 10 5 m 3 /s of water keeps the SF 6 from thoroughly mixing throughout the 1.5 km reach of the river, and in effect creates a plumelike wedge of ground water into the Santa Fe River. Discussion The application of SF 6 allowed for the characterization of stream parameters such as velocity, mixing (lateral, vertical and horizontal) , and spring influence on the distribution of river dissolved gases. That is, by injecting SF 6 into a riverine environment with known spring influxes, the effect of these springs on the dispersion of

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97 water within the stream water column can now be assessed. In addition, the injection of SF 6 into a region with no prior knowledge of springs or syphons may also indicate the location of such features. Field methods including equipment, injection setup, water sampling and analytical methods for SF 6 have also been established. This work provides the foundation for future riverine experiments employing SF 6 as its water tracer. Moreover, naturally occurring 222 Rn can also be used to interpret spring influence and mixing characteristics throughout a stream cross section. The distribution of 222 Rn gas throughout a cross-section of the Santa Fe River is dependent on several variables, dispersion, stream roughness, stream depth, stream velocity, stream profile, and the location of the ground water source (Yotsukura et al., 1984). These experiments show that in this karstic setting, concentrations of 222 Rn decreased with depth and appear to be dependent upon source area. The overall average cross section concentrations correlate well to both the vertical and horizontal samples taken at the midpoint of the stream. On the basis of these experiments, future river water sampling should be done in an integrated fashion to account for concentration variabilities that may exist in the stream cross section, even though complete mixing is assumed in the reach of the river.

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98 E a o o o o — a cm N — — o o o o CD M <0 <0 V Figure 23. Plan view of mixing in Ginnie Springs area.

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99 Water Tracing Experiments O'Leno Sink To River Rise At the request of O'Leno State Park managers, a gaseous tracer experiment was conducted during July 1991. This request came forth because a rapidly opening sink hole "New Sink" had opened apparently overnight within O'Leno State Park boundaries. Their purpose was to determine the relationships among the Santa Fe River, surface water and sink holes along the five kilometers underground portion of the Santa Fe River within O'Leno State Park, Columbia County, Florida. A gaseous tracer, SF 6 , was introduced into O'Leno Sink for two hours. After this injection, seven sinks between O'Leno Sink and the resurgence of the Santa Fe River were monitored over a four to 30 hour period to determine ground water flow paths and travel times and duration of the gaseous tracer within the sinks and the River Rise. O'Leno State Park is located on the borders of Columbia and Alachua Counties in north central Florida (Figure 24) . Within the park, the Santa Fe River flows southward and is diverted underground for approximately five kilometers. The Santa Fe River rises and continues to flow in a westward direction. Within the park there are numerous karstic features: sink holes, water filled sinks, springs, and water filled

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100 Figure 24. O'Leno State Park with sample locations for O'Leno tracing experiments.

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101 fractures. The features range in size from a few meters across to two or three kilometers in length. It has been observed that some of the features have flowing water, (New Sink) , while others appear to be stagnate (Two Hole) . In addition, some features have clear water similar to that of "pure ground water" while others contain the typical tannin stained, dark waters of the Santa Fe River and surrounding wetlands. Initial reconnaissance of the O'Leno State Park began in early July, 1991. Topographic and park maps along with aerial photos were interpreted to determine possible connections between sinks in the park. A tracer experiment was designed to determine the connections and travel times between O'Leno Sink, several sinks within the park and the River Rise. Sinks were chosen based on four criteria: 1) visual observations of water movement through the sink, 2) accessibility, and 3) potential connection to underground and 4) lack of alligators! Discharge measurements and bathymetric surveys of O'Leno Sink and the River Rise were completed. Discharge measurements were needed to get a rough estimate of the amount of water flowing through the region in order to determine the injection rate of the tracer. The bathymetric surveys at O'Leno Sink and the River Rise were carried out

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102 to locate the best depth for injecting the tracer and sampling for the tracer. The injection system was set up over O'Leno Sink following these measurements. Twine was strung above the sink and centered over the deepest area within the sink so that floating debris would not entangle the injection tubing. The SF 6 injection system used in the previous experiments was set above the eastern edge of the sink. Injection of the river water was completed using a peristaltic pump and two lengths of tygon tubing as previously described in the Wilson Springs experiment. The injection tubing extending out from the drum was placed over the center of the sink. Two injection points, one midway in depth (about 15m) and the second at the bottom of the sink (about 30m) were put in place to ensure that the tracer would enter the conduit system. Injection of the tracer occurred over a two hour time period so that an adequate sampling window would be available downstream of the injection site. Sampling the sinks and River Rise was limited by the: 1) number of volunteers, 2) number of sample containers, 3) number of sinks sampled, 4) sampling interval, and 5) total sample time. Where possible one end of the sink was designated the "sampling end" based on the observance of flow coming up from depth creating a boiling appearance at the surface.

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103 Where this feature was not visible a sample was simply collected from a canoe from the middle of the sink. Samples were collected as a grab sample of water at arms depth (about 0.5m) in a glass B.O.D. bottle or glass syringe. After collection, the samples were stored in coolers filled with river water and then transported back to the University of Florida for gas chromatographic analysis. Initial minimum estimates of tracer travel times from the injection site to individual sinks were determined using the discharge measurements determined at O'Leno Sink and straight line distances between sinks (equation 6) : ( 6 ) TL = 5.88 * Q' 0 34 * X 1,33 where TL = travel time to leading edge of tracer Q = discharge, m 3 /sec X = distance downstream of injection, m (from Rathbun, 1979) . The maximum time allowed for sampling for a two hour injection was determined using equation 7. (7) P = 1.41 * T 0 72 where P = passage time for tracer "cloud” T = travel time estimated from previous calculations, peak travel times (from Rathbun, 1979) . Results Eight sinks (Ogden Pond, Ravine Sink, Pareners Branch Sink, Small Sink, New Sink, Jim's Sink, Two Hole and

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104 Sweetwater Lake) and the River Rise were sampled over a four to 30 hour period depending on the location along the rivers interpreted underground path. An average discharge of 42m 3 /s was recorded above O'Leno Sink two days prior to the injection of tracer. Bathymetric surveys of O'Leno sink revealed that the deepest part of the sink was located along the eastern edge of the sink (Figure 25) . Its maximum depth was approximately 34 meters, confined to two points along this edge. The Rise was much shallower, maximum depth 16.5 meters, and broader along its banks (Figure 26) . It was determined that a relatively unknown amount of water may be entering the underground system at any time. Also, several conduits may be taking the tracer downstream, dividing and then recombining the same and different waters further diluting the tracer. In addition, exposure of the tracer to the atmosphere would also cause a loss in SF 6 concentration. Based on these assumptions the tracer was injected at the pump's maximum rate, approximately 110 liters per hour. Based on initial travel time estimates and total passage time of the tracer cloud, it was determined that a two hour injection would be sufficient to sample downstream sinks. After the completion of this slow injection the remaining contents of the barrel were dumped into the sink to see if it could be detected as a spike in the downstream sinks.

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105 44 40 36 CO 28 24 0J cS 2 20 16 12 9 Cl 2m North a 12 i 6 20 24 28 Meters 32 36 40 44 Figure 25. Bathymetry of O'Leno Sink.

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106 Meters Figure 26. Bathymetry of River Rise. /T\ j.

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107 Utilizing as many samples as possible within the shortest sampling interval, about 200 samples were taken over the 30 hour time period at eight locations. Minimum travel times were calculated using equation 6 (Table 4) . Passage times for the tracer cloud are more difficult to determine because mathematical equations predicting these times do not take into account residence time of the tracer within the sink itself. However, they can be used to give a minimum estimate of the sampling window at each sink. Using equation 7 estimates of passage times were determined (Table 5). Note that T hours is not the time calculated in the first equation but rather a time calculated as the travel time of peak concentration. Sulfur hexafluoride was detected in all but one of the locations, River Rise. In all but one of these locations, Two Hole, the initial peak was detected to within about a half-hour time period. The concentration response curves for Ogden Pond, Ravine Sink, Parener's Branch, Small Sink, New Sink Jim's Sink and Sweetwater Lake are shown in figures 27 and 28. Table 6 provides the arrival times for the leading edge of the tracer (TL) , the travel time of the centroid of SF 6 (T) , and the total tracer passage time for those sinks monitored for a sufficiently long interval. The mid-point of the two hour injection (one hour) was used to calculate the centroid of the mass (T) , except for SF 6 slug injection which was

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108 Table 4. Estimated time until leading edge of tracer reaches sink. Minimum Location Distance (km) Travel Hours Time Minutes Ogden 0.1 0.01 0.7 Ravine 0.7 0.16 9.7 Pareners 0.95 0.24 14.5 Small 1.0 0.26 15.6 New 1.1 0.29 17.7 Jim's 1.2 0.33 19.9 Two Hole 1.9 0.61 36.6 Sweetwater 2.8 1.02 52.1 River Rise 4.75 2.06 123.9 Table 5. Estimated passage sink. time for the tracer cloud at each Minimum Location Distance (km) T Hours Passage time for 2 hr. inject, (min) Ogden 0.1 0.02 126 Ravine 0.7 0.24 150 Pareners 0.95 0.34 159 Small 1.0 0.36 160 New 1.1 0.40 163 Jim's 1.2 0.44 166 Two Hole 1.9 0.72 187 Sweetwater 2.8 1.11 211 River Rise 4.75 1.97 258

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Oflden Pond Ravine Sink Thousands 109 C •H CO (0 03 T 3 C o PU c 0 ) T 3 O' o p o e p CO c o •H P «3 P C Q) O c o u f'
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Thousands no 2 UJ 2 o O *0 * a (I/IOU^OL) NOliValNSONOO’JS X C •H co 10 s H h 3 * c •H CO * 0 ) 2 P O co T 3 c m o p a 3 &> O ss

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Ill Table 6. Travel times for SF 6 at sinks in O'Leno State Park. Site Distance from 0 ' Leno Sink (m) (min) T P. (min) Passage (min) T (min) Ave. Vel . (m/s) Ogden 190 16 125 120 54 0.06 Ravine 857 193 * * * Pareners 1333 300 560 600 480 0.04 Small 1476 366 590 434 510 0.04 New 1571 370 600 480 535 0.04 Jim's 1761 400 * * * Two Hole 3237 440 * * * Sweetw. 4361 670 1167 * 1590 0.04 Rise 6011 ** ** * * Ogden
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112 be monitored at Ogden Pond. In this case, (T) was calculated from the point in time when the SF 6 solution remaining in the barrel was dumped into O'Leno Sink. Table 6 also provides the average travel velocities calculated using the centroid of mass travel times and the straight line distance between the sinks. Using these data, an average underground flow velocity of 4.3 km/day between O'Leno Sink and Sweetwater Lake was determined for July, 1991, a period of unusually high flow ^Omj/s, during July 1991 versus 25m 3 /s normal; Hunn and Slack, 1983). The entire passage of the tracer cloud was recorded at four of the eight sampling locations: Ogden Pond, Parener's Branch Sink, Small Sink, and New Sink. Sampling did not occur long enough at Ravine Sink nor the three most distant sinks from the injection point (Jim's Sink, Two Hole and Sweetwater Lake) . During 30 hours of monitoring, SF 6 was not detected at the Santa Fe River Rise. One possible explanation for not detecting any SF 6 is that the duration of the sampling period required to monitor the tracer was underestimated and sampling was stopped before the leading edge of the SF 6 front arrived at the Santa Fe River Rise. Another possibility is that the tracer became diluted by ground water, added along the flow path, so that the concentrations were to low to detect. Another possibility is that the River Rise was not the primary resurgence of the underground Santa Fe River.

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113 A significant decrease of about 50% in SF 6 concentration noted between Jim's Sink and Two Hole Sink raised the possibility of tracer dilution by mixing with ground water. Discharge measurements obtained during the experiment, however, did not reflect a gain but rather a loss of about 4 m 3 /s between O'Leno Sink (31.3 m 3 /s) and the River Rise (27.4 m 3 /s) . Sweetwater To Santa Fe River Boils Because SF 6 was not detected at the River Rise in the first tracing experiment, a subsequent study was carried out between the point of last SF 6 detection, Sweetwater Lake and River Rise. In this experiment SF 6 was injected into Sweetwater Lake in the downstream end of the sink. The injection process was the same as the one used in the O'Leno Sink injection with a two hour injection period of 220 L of SF 6 saturated, Sweetwater Lake water. A sampling schedule based on equations ten and eleven was also produced for the three downstream locations at the River Rise, and 50 m and 250 m downstream of the River Rise. In addition, ground water travel velocities were also estimated based upon the earlier tracing experiment, which further determined when sampling was to begin and end for this experiment. In this trace, SF 6 was detected at River Rise providing evidence of a link between Sweetwater Lake and River Rise. Since the connection between O'Leno Sink and Sweetwater Lake

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114 was established in the first trace, the data from the second trace confirms that the River Rise is a point of resurgence for some portion of the Santa Fe River flow diverted into O'Leno Sink. SF 6 was also detected at two locations 50 m and 250 m downstream of the River Rise, revealing two possible resurgence points of diverted Santa Fe River water. The tracer response plots for the locations sampled, (shown in Figure 29) , are not "ideal" smooth response curves such as those associated with the sinkholes monitored in the first tracer study. Instead, they are characterized by multiple peaks indicating the sporadic arrival of the tracer at all three locations. These data suggest that the underground flow of the Santa Fe River between Sweetwater Lake and the River Rise does not take a singular path, but possibly multiple pathways. Jim's Sink to Santa Fe River Boils As a result of the first two water tracing experiments, a connection between all the sinks monitored in the park was established. However, beyond Jim's Sink it appeared that there was some ground water augmentation or underground Santa Fe River water diverted in this complex system. To better establish the relationships between ground water and underground Santa Fe River water downstream of Jim's Sink, another water tracing experiment was undertaken. In addition, this tracing experiment provided the opportunity

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Rlvor Riaa 115 50 m Oownatream from River Rise 2 SO in Oownatream from Rher fllaa Figure 29. Concentration response curves for Jim's Sink experiment.

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116 to compare rhodamine WT dye, the most frequently used ground water tracer, and SF 6 the newly developing ground water tracing technique. The tracer solution was prepared as described previously and a 20% solution of pure rhodamine WT was added to this barrel. The SF 6 and rhodamine WT solution was introduced to Jim's Sink via tygon tubing at approximately 1.75-2 L/m. The mid-depth injection of this SF^rhodamine solution into the sink was continuous over the next two hours. Two hours prior to tracer injection, packets filled with activated charcoal were placed at obvious upwelling points in Two Hole Sink, Sweetwater Lake, the River Rise and boils in the Santa Fe River 250 m downstream of the River Rise, in order to establish background readings for rhodamine WT. After completing the injection, these packets were collected and replaced. These packets were rinsed with water and stored on ice until their analysis. Based upon the results of the two earlier water tracing experiments, a sampling scheme was established at each of the four locations. SF 6 water samples were collected about every half-hour beginning about 16 hours after injection at Two-Hole and ending about 37 hours after injection at the boils in the lower Santa Fe River. The rhodamine WT packets were changed at about four hour intervals over that same sampling period.

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117 SF. was detected at Two Hole Sink, Sweetwater Lake, the 6 Santa Fe River Rise, and at the boils 250 meters below the River Rise. The concentration response curves for these locations are shown in figure 30 and 31. Arrival times for the leading edge of the tracer (TL) , the travel time of the centroid of the SF 6 mass (T) , and the total tracer passage time are shown in Table 7. The average SF 6 travel velocities calculated from the travel times of the centroid of the SF 6 mass and the straight line distance between the sinks are also shown in Table 7. Rhodamine WT dye was also detected at all the sampling sites. These results also are shown in Figures 30 and 31. Values were recorded as "no response", "weak", "moderate", "strong" and "very strong" as only relative values of intensity could be obtained due to the limitations of the analytical equipment. The rhodamine sample packets were collected at four hour intervals which imposes a delayed peak response curve over that of the SF 6 sample curve. This delay in rhodamine is in response to the sampling interval not the travel rate of the tracer. The arrival of the tracer front and the most discerning peak occurred 33 and 65 minutes later 250m downstream than at the Santa Fe River Rise. SF 6 detected at the boils possibly represents the same slug of tracer detected at the river's resurgence. The quantity of tracer recovered at the boils is 80% of the volume of the tracer recovered at the rise, which is a consequence of gas exchange between the

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Conciliation (10 mol/i) Concentration (10 mol/L) 118 Two Holt SF6 — Two Holt Rhod WT 0 500 1000 1600 2000 2600 Time put Infection (min) Swtttwtttr 8F6 Swtttwtttr Rhod WT Figure 30. Concentration response curves for Jim's Sink experiment. Relative Rhodamlne Strength Relative Rhodamlne Strength

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Conc«nti *tlon (10 mol/L) Conctntntlon (10 mol/L) 100 6 Tim* out Injection (min) Boils -sBoils Rhod WT — Rivsr Riss SF6 Rlvsr Riss Rhod WT Figure 31. Concentration response curves for Jim's Sink experiment . Rolatlv* Rhodamln* Strength Relative Rhodamln* Strength

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120 Table 7. SF 6 travel times for Jim's Sink to Santa Fe River Rise Experiment. Distance below Ave. Jim' s Sink T k T R (min) Passage T Vel . Site (m) (min) (min) (min) (m/s) Two Hole 1476 480 690 480 610 0.04 Sweetw. 2600 720 1050 660 1020 0.04 River R. 4250 870 1440 1020 1320 0.05 Boils 4500 930 1500 1020 1410 0.05 T. = time to leading edge of tracer; T p = travel time of centroid of the SF 6 mass. T, travel times were calculated from the mid-point of the two hour SF 6 injection (60 min) . Estimated mean underground flow velocity between Jim's Sink and the Santa Fe River Rise is 3.9 km/day.

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121 river and the atmosphere between the two sampling locations. A rough estimate of gas transfer was determined of SF 6 over the 250 m distance, according to equation 8: ( 8 ) k=h v/x ln{[SF 6 ]up Qup/ ( [SF 6 ]down(Qdown) ) } where k is the gas transfer velocity; h is the mean depth (1.1 m) ; v is the stream velocity (0.124 m/s); x is the interval under investigation (250 m) ; Qup is the discharge at the River Rise (5.8 m 3 /s) ; Qdown is the discharge at the boils (6.3 m 3 /s) ; [SF 6 ] up is the peak concentration of SF 6 at the River Rise (90 x 10' 13 mol/L) ; and [SF 6 down is the peak concentration of SF 6 at the boils (35 x 10' 13 mol/L) . The calculation yielded a gas transfer coefficient of 17.6 m/d, which is lower than the value of 27.5 m/d obtained in an earlier gas exchange experiment carried out along a 5 km section of the Santa Fe River below the River Rise. At that time stream discharge exceeded 30 m 3 /s (Ellins et al., 1993) . Examination of the SF 6 concentration response curve at the boils (Figure 31) reveals two additional peaks on the trailing limb of the response curve, suggesting that some of the subterranean flow of the Santa Fe River is discharged to the main stem of the river at this point. This finding is supported by discharge measurements obtained during the experiment, which reflect an increase of 0.5 m 3 /s from 5.8 m 3 /s at the Santa Fe River Rise to 6.3 m 3 /s at the boils.

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122 Examination of the SF 6 response curves for each sampling location reveal some interesting points (Figure 30 and 31) . Two Hole Sink and Sweetwater Lake curves are characterized by a single sharp peak. The curve for the Santa Fe River Rise, however is characterized by a sharp rise to a peak and than a more gradual concentration increase to a second peak. This second shape suggests that two partially overlapping response curves are depicted at the Santa Fe River Rise. At the boils, 250 m downstream, peak separation is more pronounced and two peaks are noticeable in the concentration response curve. Most of the underground river flow resurfaces at the River Rise, but a small flow may be diverted via minor pathways to a discharge point 250 m below the rise. Additional support for a two conduit flow route is provided by comparing the total mass SF 6 recovered at each of the sampling sites. If there is equivalent discharge at Two Hole Sink, Sweetwater Lake, and the River Rise, the quantity of SF 6 recovered is 15.7 x 10‘ 4 mol (229 x 10‘ 3 g) , 12.0 x 10' 4 mol (175 x 10' 3 g) , and 19.3 x 10' 4 mol (282 x 10‘ 3 g) , respectively. Since the mass of the tracer at the Santa Fe River Rise is greater than at either sink alone, the underground flow of the river must follow more than one flow path. Discharge at the three sampling locations would not be constant but less at Two Hole Sink and Sweetwater Lake than at the River Rise, if this the case. Moreover,

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123 the estimates of the quantity of tracer recovered at Two Hole Sink and Sweetwater Lake would be too high in such a scenario. The mass of tracer recovered at the Santa Fe River Rise, however, would still be greater than at either Two Hole Sink or Sweetwater Lake. Thus the conclusion that the subterranean flow of the Santa Fe River follows more than one route between Jim's Sink and the River Rise is still valid. Summary of Water Tracing The artificial tracer SF 6 was used successfully in three water tracing investigations in the Santa Fe River Basin to track the subterranean pathway of the Santa Fe River between O'Leno Sink and the River Rise of the Santa Fe River. The results of the water tracing experiments carried out indicate that the subterranean flow path of the Santa Fe River follows a single corridor flow conduit from its sinking point at O'Leno Sink to Jim's Sink. After Jim's Sink, the underground flow path splits following one conduit at Two Hole Sink and then to the Santa Fe River Rise, and a second pathway to Sweetwater Lake and then the River Rise. The sub-surface flow pattern that is tentatively proposed is shown in Figure 32. These data confirm that (1) the Santa Fe River Rise is the primary resurgence of the underground flow of the Santa Fe River and (2) suggest that a small portion of the underground river enters the main stem of the

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124 Figure 32. Flow pattern of the underground Santa Fe River through O'Leno State Park.

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125 Santa Fe River about 250 m below the River Rise at a spot marked by boils in the River. Average flow velocities calculated ranged from 1.0 to 3.4 km/day. Such rapid ground water movement renders the water resources of the santa Fe River basin vulnerable to contamination and underscores the urgent need for careful managements practices. The results of this research further confirms that SF 6 , which is safe, chemically and biologically inert, and capable of being detected in extremely low concentrations, is well suited for water tracing applications in karst terranes. In comparison to fluorescent dye tracers, such as rhodamine WT, SF 6 has the advantages of detectability at low concentrations and none of the interference problems associated with organic acids, dissolved particulates, and aquifer material that can occur with fluorescent dyes. This is particularly helpful in hydrologic settings such as the Santa Fe River with high organic acid concentrations. SF 6 is a volatile compound so gas exchange occurs when ground water is exposed to the atmosphere in karst windows. In hydrologic settings where there is no contact between ground water and the atmosphere, however, SF 6 may have potential as a quantitative tracer. SF 6 may also have value in determining whether a hydrologic flow network is completely developed in the vadose zone or in a partially flooded setting, as is sometimes the case in alpine or steep

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126 gradient systems. Further research is needed to properly evaluate the performance of SF 6 in comparison to other proven tracers and to develop additional hydrologic applications for this compound. Flow Component Analysis After the completion of the tracing experiments within O'Leno State park it appeared that the subterranean flow path of the Santa Fe River had been characterized. However, its relationship with the ground water along its course had remained unresolved. In order to further establish the link between the two sources of water in the park several flow component analysis experiments were completed. The experiments used both relatively simple techniques such as water temperature readings and more complicated techniques such as 18 0 , 222 Rn, and major cation concentration analysis. These techniques were employed because of their relative ease of use and their potential to separate or indicate different water types. Radon-222 Transect Water samples were taken from 18 different water filled features throughout the park and from the parks main office faucet which taps the Floridan Aquifer in the region (Figure 33; Dale Kendrick, personal communication, 1991). Samples were drawn into graduated cylinders as previously described

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127 Figure 33. Sample locations for 222 Rn, temperature . 18 0, major cations and

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009 128 ^ CO CM (1/Ludp) 8 uo;;ej)U 83 uoo uopey o o o co o to CM lO o o to o in hco o o o CO o in CM CM O o in o in f'o o in K E C W o c V -I o o E 03 0) k. ++ CO c 5 o o o o c (0 eo 5 Figure 34. Radon-222 concentrations for Karst features

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129 and analyzed as before (see Materials and Methods Chapter 3 and Figure 17) . The results of this transect show the 222 Rn levels at each location (Figure 34) . The tap water sample in this transect reflects that of typical ground water conditions in the area (Ellins, personal communication, 1993) . The 222 Rn concentrations found throughout the park in its upstream section (eg. O'Leno Sink, Ravine Sink/linear features. New Sink group including Jim's Sink) are essentially zero to atmospheric background levels. However, beyond Jim's Sink (eg. Two Hole, Sweetwater Lake and River Rise) the 222 Rn levels steadily increase towards the ground water levels. This increase in radon levels suggests an influx of ground water into these sinks along the subterranean path of the Santa Fe River. The surface features, (cypress dome and meander scar, having low 222 Rn levels, downstream of Jim's Sink) also confirm that the surface water is not directly, hydrologically connected to the ground water in this region of the park. 18 0 Transect Two water samples were collected from 17 different water filled features located throughout O'Leno State Park (Figure 33) . Each sample was collected at a depth of about 0.5 m where possible. Samples were collected and analyzed

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130 as previously described. In theory, the oxygen isotope value for the ground water and the surface water should be different because of the evaporative and precipitation effects on the composition of the surface water. The ground water value will have a characteristic signature value based primarily upon the source of the ground water and any mixing the water has had with other ground water. The surface water on the other hand will have a signature value based primarily upon the 18 0 value of the precipitation, and any subsequent or previous rain events and the evaporative effects on the surface water body. The surface water, if it has undergone substantial evaporation will relinquish the lighter isotope 16 0 to the atmosphere making the residual water heavier or more enriched in 18 0 (Fetter, 1988) . The process causes the 18 0 value to increase relative to standard mean ocean water values (SMOW) . Because this water has remained at the surface and has not been mixed with either pure ground water or with new precipitation it can easily be distinguished from ground water. Figure 35 shows the 18 0 values for the water features sampled in O'Leno State Park. In this figure there are three distinct groups of water. The first group appears to be pure ground water and is represented by the tap water, which is drawn from the Floridan Aquifer. The second group is surface water and is represented by the cypress dome, meander scar and to some degree the drainage ditch. The

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131 third group is a mixture of the surface water and the ground water and is represented by essentially all other features labelled on the figure. These results suggest that there are three different types of water within O'Leno State Park and that there is a contribution of ground water to the underground Santa Fe River water beyond Sweetwater Lake. Cation Concentrations Total cation concentrations as well as cation ratios were evaluated. Al +++ , Ca ++ , Mg ++ , K*, and Na* were detected at all 21 locations (Figure 33) . Of these, Ca ++ appeared to be the element that best separated ground water and surface water components. All other elements appeared to give inconsistent results. Several element ratios were also evaluated in order to separate water types (Table 8) . According to Fetter (1988) ratios of Mg/Ca, Na/K and (Ca+Mg)/ (K+Na) have been used to establish water properties. Mg/Ca ratios of 0.5-0. 7 indicate a limestone source, 0.7-0. 9 ratios indicate dolomite and ratios >0.9 indicate a silicate source rock (Fetter, 1988; Katz, 1992). Na/K ratios equalling 47 indicate seawater, ratios equal to 10 indicate rainwater and those between 15 and 25 indicate water that is close to its recharge area. In addition, (Ca+Mg)/ (K+Na) values greater than 1.0 also indicate that water is close to its recharge area. The Na/K ratio and (Ca+Mg)/ (K+Na) ratio

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Cypress Dome 132 O o o (0 o 10 CM in o o m TT O n k co o o o CO o in CM CM O o in o m o 0 in 1 J£ C 55 o c ® E «s 9 e J o •o 9 O c
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Table 8. Cation ratios for locations throughout O'Leno State Park. 133 Location meq/L Mg/Ca meq/L Na/K meq/L (Ca+Mg)/ (K+Na) Tap water 0.029 53.855 188. 204 O'Leno Sink 1.092 15.225 9. 317 Drainage Ditch 1.413 13.435 4 . 059 Ogden Pond 1.175 13.908 9. 008 Ravine Sink 0.996 14.788 11. 132 Linear Feature #1 0.702 26.455 35. 266 Linear Feature #2 0.690 24.903 33. 570 Linear Feature #3 0.754 18.518 21. 709 Pareners Branch 0.998 14.641 11. 410 Small Sink 1.031 14.345 11. 182 New Sink 1.004 13.983 11. 996 Jim's Sink 0.943 14.396 13. 295 Cypress Dome #1 0.364 3.779 79. 593 Two Hole Sink 0.473 28.830 75. 129 Meander Scar #1 1.839 60.090 3. 028 Black Lake 0.176 14.881 104. 929 Cypress Dome #2 0.620 28.468 23. 314 Sweetwater Lake 0.697 14.711 24. 077 River Rise 0.697 15.778 28. 533 River Rise + 50m 0.715 15.967 27. 842 River Rise + 250m 0.689 16.618 30. 433 Precipitation 0.020 0.015 0 . 041 Average Std. Dev. 0.895 0.462 23.572 17.455 34. 41. 076 407 Mg/Ca = 0.5 0.7, limestone Mg/Ca = 0.7 0.9, dolomite Mg/Ca = > 0.9, silicate Na/K = 47, seawater Na/K = 10, rainwater Na/K = 15-25, close to rain water (Ca+Mg)/ (K+Na) = > 1.0, near recharge (ratios from Fetter, 1988)

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134 yielded varying results with no apparent trends or correlations . Using the Mg/Ca ratio, ground water and surface water groupings of water bodies can be delineated. Those features having a ratio of greater than one reflect the water chemistry of surface water fed bodies. These include: O'Leno Sink, drainage ditch, Ogden Pond, Small Sink, and the meander scar. Those features having a Mg/Ca ratio of less than one reflect a ground water influenced feature. These features include: tap water, linear features 1, 2, and 3, Two Hole Sink and the River Rise sampling locations. Ternary diagrams also reveal distinct types of water groups (Fetter, 1988; Katz, 1992). When plotted, the cation concentrations of Mg ++ , Ca ++ and Na^+K* show three distinct types of water, calcium dominated type, a sodium or potassium type and a non-dominate ion type which constitutes the largest number of samples in O'Leno (Figure 36). Those features that are dominated by the calcium ions are the downstream features: Two Hole Sink, Black Lake, Cypress Pond #1 and the upstream tap water site that was taken from the ranger house at the park's northern entrance. The nondominant ion features included the three linear features, the three River Rise samples, and the upstream sinks (Ravine Sink, Sweetwater Lake, Jim's Sink, New Sink, Pareners Branch Sink) . The sodium and potassium dominant features primarily

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135 100 * Figure 36. Cation concentrations at all locations throughout O'Leno State Park (top), groupings of selected features through the park (middle) and dominant ion areas within ternary diagram (bottom, after Fetter, 1988 and Katz, 1992).

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136 include the surficial features, such as the meander scars and the drainage ditches. The middle diagram in figure 36 reveals a trend of increasing Ca ++ (ground water) influence with increasing distance through the park. The surficial features represent the surface end member water type and the tap water sample represents the ground water end member. The upstream sinks, those above Jim's Sink, more closely resemble the chemical signature of the surface water in the area. The downstream sinks, namely Sweetwater Lake and the three River Rise locations more closely resemble the chemical signature of the ground water (tap water sample) . The linear features which lie within 100m of Ravine Sink more closely resemble the nature of the ground water as well. Temperature Transect In a previous study, Skirvin (1962) reported that it was possible to detect ground water in all the sinks monitored in this study during a period when Santa Fe River discharge to O'Leno State Park was temporarily, but completely dammed due to construction in the upper reaches of the Santa Fe River. To determine the extent that the underground Santa Fe River flow is augmented by ground water, temperature measurements were utilized to calculate the relative proportions of ground water found in those sinks hydraulically connected to the underground pathway of

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137 the Santa Fe River. Five additional water-filled karst features in O'Leno State Park were also monitored for comparison purposes. The first set of 13 water temperature measurements was taken on January 11, 1992. The air temperature was 11°C and the water in O'Leno Sink was 15°C. Ground water was assumed to be 22°C (Fernald and Patton, 1984; Florida Geological Survey, 1992) . The temperature measurements revealed that those sinks in hydraulic contact with the underground flow of the Santa Fe River between Ogden Pond and Jim's Sink were warmer that the Santa Fe River by about 2.5°C, suggesting some ground water mixing with the underground flow of the Santa Fe River (Figure 37) . The most noticeable increase in water temperature, however, occurred at Two Hole Sink. The water temperature in Two Hole Sink was 3.5°C greater than the previous sink measured, Jim's Sink. Black Lake was measured because it had a maximum depth of only three meters making it a surficial feature not in hydraulic contact with the underground flow of the Santa Fe River. Black Lake recorded a temperature much lower than ground water, 14°C. Two additional temperature readings were taken on January 14 and March 24, 1992. The ambient air temperature was warmer, however, so the temperature gradients were diminished and the results, although similar, are less dramatic. On January 14, a significant averaging of temperatures may have taken place due to a previous night's

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138 legend 1 Up river 2 Oleno Sink 3 Ogden Pond 4 Ravine Sink 5 Linear #1 6 Linear #2 7 Linear #3 3 Pareners Sink 9 Small Sink 10 New Sink 11 Jims Sink 12 2-Hole Sink 13 Sweetwater 14 Black lake 15 River Rise 16 River Rise»50m Figure 37. Temperature readings taken throughout O'Leno State Park.

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139 rainfall in the area of 3.2 cm (personal communication. Dale Kendrick, 1992) . Because the Santa Fe River follows a subterranean flow path for at least five kilometers before resurfacing at the River Rise, some factors in addition to mixing with warmer ground water may result in elevated temperatures. These include: the type of flow, the surface area of the underground water in contact with the walls of its conduit and exposure of ground water to the atmosphere. The least important of these is the transfer of heat from the limestone aquifer to the underground stream across the rock/water boundary. This is because limestone has a very low heat conductivity (0.0052 gram calories per centimeter degree second, Plummer and Sargent, 1931; Lobmeyer, 1985; Luckner and Schestakow, 1991) . In fact, more often the surrounding rocks act as insulators to the ground water system (Lobmeyer, 1985) . Assuming that the warming could not have been achieved by contact with the limestone aquifer, and a relatively short time period which ground water is exposed to the atmosphere (about 48 hours) , it is suggested that mixing of surface water with warmer ground water offers the best explanation for the increased temperatures observed. Calculations of ratios in percent between ground water and Santa Fe River water measured at each sink can be accomplished by assuming that the measured temperatures of

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140 O'Leno Sink (15°C) and River Rise (22°C) are respectively the minimum and maximum temperatures attainable by the water in this region. Therefore, a one degree increase in the measured sink water temperature would be equal to about a 15% contribution of ground water. For example, at Ravine Sink, the temperature increase of 3°C to 18°C represents a 45% ground water influx to the underground flow of the Santa Fe River. Based on the temperature measurements, this ratio of about 40/60 or 45/55 (ground water/underground Santa Fe River water) remains fairly uniform through Jim's Sink, a distance of 1.2 km. At Two Hole Sink, however, the water temperature rises 6°C from 15°C at O'Leno Sink to 21°C, suggesting 85% ground water augmentation. The water temperature at the River Rise is 22°C, which is the same as local ground water temperatures. This finding suggests that there is no original Santa Fe River water left at this point and that is has dispersed or continued elsewhere in its underground path. However, this can not be true because the SF 6 tracing experiments revealed measurable amounts of SF 6 at the River Rise, and demonstrated a hydraulic connection between O'Leno Sink and the River Rise. Temperature measurements confirm that Black Lake, which remains colder than the other downstream sinks, is only a surficial feature with no ground water or Santa Fe River water component. This finding is corroborated by the fact that its maximum depth is only three meters (Skirvin, 1962) .

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141 Computer Modeling Computer modeling of an aquifer requires making several assumptions about aquifer parameters. These assumptions include: isotropic conductivities, constant head or constant flux boundaries, relatively homogeneous aquifer material, and workable ranges of hydraulic conductivity values (cm/s or m/d) . Numerous scenarios were attempted to model the area based on the water flow velocities calculated from the tracing experiments. Because of the anisotropic conditions that exist and the complex interactions between ground and surface water the area, it was impossible to model with the current software packages available. The initial model setup shows the distribution of the discretized area, boundary conditions, water table elevations and surface water features (Figure 38) . This model set up was completed using ModelCad™ (Geraghty and Miller, 1990) a computer aided design software package for ground water modeling. Because there is no confining layer in the modeled area a two dimensional model setup was produced. A three dimensional model is normally setup when two or more aquifers are found within a specific area. This pre-processed input file was then sent to the main computer program MOC™ (Method of Characteristics, Konikow and Bredehoeft, 1987) for interpretation.

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No Flow Boundary # Spring 142 C o -H 0 > a) u u a) > a) b tO •P C (0 CO c u a) •p w a> s a> 42 P P O • C CU (0 d H w P h a) to a) T3 O e B « T3 C (0 P X a) c p -h d w a e o o c U 0 ) a • • oo O ci C a) a> p a) d 5 &>-P •H QJ b 13 iug*6 ;b AjBpunog peen jubjsuoq o z

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143 In theory the constant head boundaries at the western and eastern edge of the mapped area act as the driving forces of water flow. A default head elevation is assigned to all other gridded areas and the computer then calculates the predicted head values over a certain time interval based upon the aquifer's physical properties (thickness, hydraulic conductivity, storativity, leakance, recharge) . In most non-karstic aquifer settings this process is relatively straight-forward . In this karst ic region hydraulic conductivities of the aquifer may vary by several orders of magnitude within the same aquifer (Hunn and Slack, 1983) . Moreover, these trends in conductivities have no obvious geologic or topographic boundaries. To further complicate this karstic setting, numerous springs are located in the area which creates another modeling challenge. This challenge is created because the computer model does not have a "spring" parameter which allows for the accurate depiction of a spring in the model. Instead, the springs were modelled as recharging wells to the river with their recharge values equivalent to each springs output. The river, however, as previously noted, is directly connected to the underlying aquifer and in reality may fluctuate with the top of the potentiometric surface of the Floridan Aquifer. Because of the complexity of the model and the abnormally high hydraulic conductivities the computer

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144 program was unable to process the data. The program failed for several reasons. The reasons include first, the computer program has a built-in mass balance system that allows for only a 10% error in the amount of water going into and coming from the aquifer. The abnormally high conductivities of the aquifer and the numerous springs lining the stream caused a gross imbalance in the water exiting the aquifer. Second, the recharging wells to the surface effectively elevated the ground water levels to unrealistic levels. These unrealistic levels created "mounds" of water surrounding each spring. Third, because surface water and ground water are one in the same in many cases, they can not be quantitatively described and accounted for in the model. This third problem again results mass-balance errors in the model. Fourth, the anisotropic conditions of the aquifer were not reproducible in computer modeling format because of the general lack of knowledge of the three dimensional location of conduit patterns surrounding the Santa Fe River. This fourth problem lead to an unrealistic homogeneous aquifer setting. Numerous attempts were made to adjust the model to produce some output, however all were unsuccessful. It is now understood that even with all the data collected from this report and many others, the area in many ways is still perplexing. These results are corroborated by several authors that have suggested that no current ground water

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145 computer model can accurately characterize karstic conditions (James Quinlan, personal communication, 1994; Paul Laymen, personal communication, 1994) . Reaeration Studies Sampling locations along the Santa Fe River for the first experiment are shown in Figure 39. Figure 40 shows the SF 6 , 222 Rn and stream-flow profiles for this reach. Hornsby Springs is the only documented major contributor of ground water to the Santa Fe River along this reach. However, distinct peaks in the 222 Rn profile reveal locations of unrecorded ground water influx. The stream flow data indicate that the Santa Fe River flow is increased by as much as 13 m 3 /s upstream of Hornsby Springs. SF 6 concentrations decline downstream of the injection point due to gas exchange, where increases in the SF 6 concentrations are noted except at 2.75 km and 4.5 km (Columbia Springs). The increase in SF 6 concentration may reflect incomplete lateral mixing in the stream or the return flow previously diverted from the main stream channel to conduits in the limestone aquifer further upstream. At 2.75 km and 4.15 km, two large syphons where stream flow is diverted underground are clearly visible. Stream water lost to sub-channel conduit flow results in no change in tracer concentrations in the stream at the point of flow loss. Downstream of the flow loss point, SF 6 concentrations continue to decline in

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146

PAGE 160

100 147 Radon (dpm/D/Discharge (m*3/s) 4) CD CO 0) I S + O CO u. CO p 0 ) (0 p p 3
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148 the stream-flow due to gas exchange. SF 6 laden stream flow diverted underground, however, is removed from the atmosphere's contact and gas exchange no longer occurs. SF 6 concentrations therefore remain the same in the underground flow, except where dilution due to mixing with ground water takes place. The influx of return flow of previous surface water to the Santa Fe River is indicated by SF 6 concentrations that are higher than concentrations in samples collected in the river upstream, which will have a declined due to gas exchange. Columbia Spring discharges to the Santa Fe River and represents the return of stream flow drawn underground by means of a syphon in the Santa Fe River at 4.15 km is shown by elevated SF 6 concentrations at 4.5 km. Sampling locations for the second reaeration experiment are shown in figure 41 and the SF 6 , 222 Rn and stream flow profiles are shown in figure 42. Both types of SF 6 profiles are shown in order to represent the integrated and grab sampling results. A number of springs add to stream flow along this reach of the Santa Fe River. The 222 Rn peaks in figure 42 match the locations of known springs. Unlike the first reaeration experiment, SF 6 concentrations do not decline as expected (figure 42). The SF 6 profiles are instead characterized by many spikes possibly caused by poor mixing of ground water with stream flow. Some locations of the SF 6 peaks, however, closely correspond with the 222 Rn

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SANTA FE RIVER 149 41. Sampling locations for the second reaeration experiment Ellins et al., 1992).

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150 35 30 25 20 15 10 5 0 15.75 16 16.25 10.5 16.75 17 17.25 17.5 17.75 10 10.25 Distance from Rise (km) SF6 Radon Discharge Figure 42. Sulfur hexafluoride and radon profiles for the first reaeration experiment. Discharge (m‘3/s)

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151 peaks and known springs. For example, the SF 6 peak at 17.2 5km matches the 222 Rn peak that represents ground water delivery from the Devil's Ear, Devil's Eye and Little Devils springs. Another SF 6 peak centered around 17.85 km corresponds to Ginnie Spring. The occurrence of 222 Rn and SF 6 concentrations together suggests that discharge from the Devil's Ear, Devil's Eye, Little Devil and Ginnie Springs is not pure ground water, but a mixture of ground water and Santa Fe River water, which was diverted underground at locations upstream. Work completed by Kincaid (1994) supports this theory. Although there is no direct evidence of syphons in the Santa Fe River along this reach, the stream flow profile indicated loss between 17.00 km and 17.75 km (Figure 42). An extensive cave system, the Devil's Ear Cave System, extends beneath the Santa Fe River along the second reaeration experiment. Several springs, including July, Little Devil and Devil's Ear are physically connected by a network of conduits to the cave system (Kincaid, 1994) . Cave divers have reported intrusions of tannin colored water from the Santa Fe River to the Devil's Ear Cave. The observations coupled with the 222 Rn and SF 6 data provides evidence of the influence of the Devils 's Ear Cave system of interactions between ground water and stream flow in this part of the Santa Fe River (Kincaid, 1994) . A more detailed description of the reaeration coefficients calculated and the relationship

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152 between the Santa Fe River with ground water along this reach of river is discussed in Kincaid (1994) . Gas Transfer The gas transfer velocity (k) for SF 6 during plateau concentrations for each continuous injection was determined according to equation 8. Ground water influx along the study reaches increased stream-flow and diluted the tracer. In addition, there is discharge from riparian wetlands to the Santa Fe River. Naturally occurring 222 Rn was used to locate of ground water delivery along each reach. Adjusted stream-flow values, based on the stream gaging effort, accounted for the dilution by ground water in calculating the gas transfer velocities using SF 6 . Table 9 provides the stream gaging data for the Santa Fe River. The gas transfer velocity of 27.5 m/d was calculated for the River Rise reaeration experiment between 0.25 km and 3.75 km. This length of reach was used to avoid possible mixing problems at the beginning of the reach and the influence of returning SF 6 -labelled stream flow at Columbia Springs. The Devil's Ear cave system exerts a controlling influence over interactions between ground water and stream flow along the Santa Fe River based on the 222 Rn and SF 6 data. Also, in this region of study the spring discharge should be regarded as a dynamic mixture of ground water and

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Table 9. Stream gaging data for the Santa Fe River. First Reaeration Experiment, River Rise 153 Distance from River Rise (km) Discharge (m 3 /s) Depth (m) Velocity (m/s) 0.25 27.4 1.76 0.445 1.0 32.4 1.90 0.506 1.5 35.4 2.80 0.379 2.0 43.6 2.03 0.540 3.75 40.1 2.45 0.527 4.13 47.4 1.24 0.720 Second Reaeration Experiment, Rum Island to Ginnie Springs Distance from River Rise (km) Discharge (m 3 /s) Depth (m) Velocity (m/s) 15.75 22.8 1.66 0.260 16.00 23.1 1.50 0.280 17.00 30.7 1.66 0.340 17.35 22.8 0.74 0.460 17.60 29.2 1.96 0.300 17.90 32.5 2.44 0.240 18.25 33.9 2.62 0.250

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154 Santa Fe River water rather than pure ground water (Kincaid, 1994) . Because this reach involves complicated interactions of surface and ground water it was not possible to determine the extent to which stream flow entered conduits of the Devil ' s Ear Cave nor to accurately address the quantity of pure ground water discharge along the reach. In an accompanying study by Kincaid (1994) a more detailed investigation of the reaeration and gas exchange values for this reach of river was completed. His work revealed an average k value of 6.90 m/d and an average value of 2.70 day' 1 for this reach of river. Corrected discharge values (shown in Table 9) were used in the gas exchange calculations in an attempt to take into account stream flow loss and the degree to which tracer concentrations are decreased by dilution resulting from ground water augmentation. This method produced gas transfer velocities of -17.3 m/d and 1.0 m/d for the integrated and grab sampling SF 6 data, respectively. These negative values suggest that gas exchange is negligible along this short reach and that the decline in concentrations observed is due entirely to dilution by ground water. Based on the measured stream flow values for the reach gas exchange calculations do not adequately account for dilution by ground water and thus over estimate the value of k. On the other hand, the adjusted stream flow values do not account for the mixing of Santa Fe River water

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155 with pure ground water in the Devil's Ear Cave and the subsequent discharge of some mixture of the two water types along the reach. Table 10 and 11 show the calculated values of k in m/d for intervals between the stream gaging stations in the Santa Fe River. As previously mentioned comparisons of k values between stream segments underscores the degree of variability induced by the non-uniformity of the stream channel and incomplete mixing of ground water with stream flow. Although 222 Rn was used to estimate gas exchange in the river, no attempt was made in the Rum Island reach of the Santa Fe River because of the close proximity and great number of ground water influxes to the Santa Fe River. These factors made it impossible to determine the rate of gas exchange between pulses of 222 Rn in the stream. The interested reader is referred to Kincaid (1994) for a more detailed discussion of factors involved in estimating gas exchange in this portion of the Santa Fe River. Reaeration Coefficients Santa Fe River gas transfer velocities determined using SF 6 were related to the rate of oxygen uptake and expressed as reaeration coefficients (I^) . Temperature strongly controls the gas transfer coefficient determined for these gaseous tracers used in the stream reaeration studies. The

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156 Table 10. Values of k in meters per day for intervals between the stream gaging locations in the first reaeration experiment. Distance from Transfer Station Injection (km) Interval (km) Discharge (m 3 /s) SF $ (pmol/L) Velocity k (m/d) 1 0.28 27.43 369 8 1.00 0.72 32.43 277 33.3 14 2 . 05 1.05 34.65 255 1.5 27 3.7 1.65 40.12 69 72.7

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157 Table 11. Values of k in meters per day for intervals between the stream gaging locations in the first reaeration experiment. Distance Sta. from Inject. (km) Int . (km) Disch. (m 3 /s) (pmof/L) Transfer Velocity k(m/d) Mes. j Adj .“ Int. ] BOD Int. ] BOD 2 0.25 23.1 1266 [ 1108 6 1.25 1.25 30.7 811 | 780 5.5] 2.2 13 1.60 0.35 22.8 | 30.7 699 ] 763 1.7] 2.6 17 1.85 0.25 29.2*37.1 673 ] 580 -26.8 ] 15.0 21 2.15 0.30 32.5] 40.4 **l i 622 24 2.5 0.35 33.9 [ 41.4 233 ] 653 *The measured stream flow data reflect the loss of flow along the second reaeration experiment at point 17.35 km, which corresponds to 1.6 km below the SF 6 injection. The adjusted stream flow values take tracer dilution by the influx of ground water into consideration in estimating gas transfer velocities, using the integrated and grab sampling SF 6 data with measured stream flow data, the gas exchange transfer velocities calculated for the second experiment between Rum island and Ginnie Springs area are 9.2 m/d and 19.0 m/d, respectively. When the adjusted discharge values are used in the calculation, however, negative gas transfer velocities of -17.3 m/d and -1.0 m/d are estimated for the integrated and grab sampling SF 6 data, respectively, not available due to questionable data.

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158 higher the temperature, the faster the gas exchange process. In order to compare gas exchange coefficients for different gases or to use one gas exchange coefficient to predict another a dimensionless ratio, the Schmidt number (Sc) , was used (Ledwell, 1984; Wanninkhof, 1988; Kincaid, 1994). The schmidt number is defined as the kinematic viscosity of water (v) divided by the molecular diffusivity of the gas (D) . Since both v and D are temperature dependent, the Schmidt number corrects for the temperature and species dependence of the gas under consideration (Jahne et al., 1987; Wanninkhof, 1990). The Schmidt numbers for SF 6 , 222 Rn and 0 2 for temperatures ranging between 15 and 27 degrees Celsius are found in Table 12. There are many models available to describe the relationship between the gas transfer velocity (k) and the Schmidt number (Sc) (Kilpatrick et al., 1989). In this work, the correction of the exchange coefficient is based upon equation 9 . where k = transfer velocity, Sc = Schmidt number, n = -0.5 and depends on the turbulence at the air/water interface.

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159 Table 12. Comparison of at selected temperatures Schmidt • numbers for SF 6 , 222 Rn, and 0. Temperature °C SF 6 ~~ zzz Rn~ °2 15 1288 1089 689 20 950 839 531 25 741 678 418 27 683 607 378 The reaeration coefficient was calculated using the following equation (from Ellins et al., 1993). ( 10 ) K2 = k (SF 6 )/ h (Sc0 2 /ScSF 6 )-°5 where K 2 = reaeration coefficient, day' 1 ; k = gas transfer velocity, m/d; h = average stream depth, m; Sc = Schmidt number for the indicated gas at 23°C (water temperature of the river) . The Santa Fe River's gas transfer velocity and corresponding reaeration coefficient is 27.5 m/d and 16.7 day' 1 , with v= 0.53 m/s, h = 2.1 m, Q = 40.0 m 3 /s, and t = 23 °C in the eastern reaches of the river. Table 13 provides a comparison of reaeration coefficients from Florida and other streams using volatile tracers. Using a variety of tracers the reaeration coefficients based on SF 6 measurements are within the same order of magnitude as Kj

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160 values given for other streams with the exception of the West Fork of the Walker Branch, Oak Ridge TN. The typical K 2 values range from 118 to 139 day' 1 , using SF 6 , propane and ethane as gaseous tracers (Wanninkhof et al., 1990; Genereux et al., 1992). Therefore the Kj values for this stream are about an order of magnitude greater than other published values for different streams. Many predictive equations have been developed for specific streams that permit estimation of gas transfer and reaeration coefficients. These equations typically relate reaeration coefficients to several easily measurable physical and hydraulic parameters of a stream. Table 14 shows reaeration coefficients (Kg) values determined for the two river reaches based on different predictive models available in the literature. The calculated K 2 values vary considerably. None of the equations reference in Table 14 were suitable indicators of the reaeration coefficient determined for the first Santa Fe River experiment, through experimentation. The basic statistics for the predicted values for this reach were a mean of 2.69 day' 1 a standard deviation of 2.08 day' 1 , and a median of 2.25 day' 1 . If these statistics are compared to the value estimated from the SF 6 tracer experiment (16.7 day' 1 ), it can be concluded that all these models underestimate Kj for this reach of the Santa Fe River.

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161 Table 13. Comparison of selected stream reaeration coefficients determined through the use of volatile tracers (from Ellins et al. 1993). Stream V (m/s) h (m) Q ( m 3 / s ) *2 (d 1 ) k (m/d) tracer °C t Ref. Waitoa 1.89 0.4 0.70 14.0 5.52 CHjCl 12 1 Waipa 2.40 4.1 36.0 0.3 1.22 CHjCl 12 1 Bonner 3.05 0.3 0.05 7.4 2.21 propane 25 2 N. River 2.26 0.45 0.62 12.0 5.40 ethylene 27 3 Jackson River St. 1.33 0.69 3.3 2.28 85 Kr 25 4 W. Fork/ Walker Br. 0.69 0.10 0.02 134 13.9 sf 6 25 4 W. Fork/ Walker Br. 0.2 118 propane 7 W. Fork/ Walker Br. 0.2 139 ethane 7 Assabet River 0.23 0.51 0.08 2.4 1.7 Freon-12 5 6 Alligator Creek, FL 0.28 0.21 4.1 propane 8 John Rowe Br. FL 0.46 0.02 3.8 propane 8 Country Clb Creek, FL • 0.33 0.07 19.5 propane 8 Peace R. FL 0.98 9.90 2.8 propane 8 References 1 Wilcock, 1984 2 Grant and Skavroneck, 1980 3 Kwasnik and Feng, 1979 4 Tsivoglou, 1967 5 Wanninkhof et al., 1990 6 Duran and Hemon, 1984 7 Genereux et al., 1992 8 Hampson and Coffin, 1989

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162 Table 14. Comparison of stream reaeration coefficients Kj (day' 1 ) determined through the use of SF 6 with values derived from predictive models (from Ellins et al . , 1993) . Reference Santa River Rise Fe River Rum Island O'Conner and Dobbins, 1958 3.1 2.9 Krenkel and Orlob, 1963 8.3 6.2 Cadwallader and McDonnell, 1969 4.7 2.3 Issac and Gaudy, 1968 1.0 1.1 Negulescu and Rojanski, 1969 2.7 2.5 Padden and Gloyna, 1971 1.3 1.6 Bansal, 1973 00 • o 1.0 Bennett and Rathbun, 1972 2.4 3.6 Bennett and Rathbun, 1972 5.0 4.9 Parkhurst and Pomeroy, 1972 1.6 1.5 Churchill et al., 1962 (1) 0.1 0.0 Churchill et al., 1962 (2) 1.1 1.4 Langbein and Durum, 1967 1.0 1.1 Owens et al., 1964 (1) to • 3.5 Owens et al., 1964 (2) 2.1 3.3

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CHAPTER 5 SUMMARY AND CONCLUSIONS Mixing In the karstic terrane of the western Santa Fe River basin, assessing mixing parameters of the stream is made difficult by the numerous springs, seeps, syphons and boils found within the Santa Fe River. Three detailed mixing experiments were devised to address the variability in the volatile dissolved gases, natural radon-2 2 2 ( 222 Rn) and artificial sulfur hexafluoride (SF 6 ) . These experiments revealed that 1) sulfur hexafluoride is an efficient and useful stream tracing agent that allows for the characterization of stream parameters such as velocity, mixing (lateral, vertical and horizontal) , and spring influence; 2) the injection of SF 6 into a region with no prior knowledge of springs or syphons may also indicate the location of such features; 3) naturally occurring 222 Rn can also be used to interpret spring influence and mixing characteristics throughout a stream cross section; 4) concentrations of 222 Rn decreased with depth and appear to be dependent upon source area; 5) the overall average cross section concentrations correlate well to both the vertical and horizontal samples taken at the midpoint of the stream 163

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164 and 6) future river water sampling should be done in an integrated fashion to account for concentration variabilities that may exist in the stream cross section, even though complete mixing is assumed in the reach of the river. Tracing A previously untested ground water, gaseous tracer, SF 6 , was introduced into O'Leno Sink, Jim's Sink and Sweetwater Lake on three different occasions in order to establish travel rates through the park and detect possible points of input from ground water. The tracing experiments demonstrated that 1) the underground Santa Fe River moved through a single conduit in the top one-third of the park; 2) the river flows at a constant rate through the park and intersects sinks consecutively and continuously downstream of O'Leno Sink to the River Rise; 3) mathematical equations used normally to predict the rate at which surface water moves within a stream are applicable to estimate the rate at which ground water has moved through the park, supporting the idea of non-Darcian flow conditions. Flow Component The multiple application of various natural tracers revealed the location of a significant source of ground water to the system beyond Jim's Sink. In addition, it was

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165 found that 1) the temperature data provided as much useful information as the other more complicated techniques and it was also useful in a conservative nature to estimate the relative mixing of surface and ground water; 2) temperature, geochemical, radon and oxygen isotope data show identify the distribution of and connections among ground water, surface water and wetland water; 3) because of the rapid nature that the Santa Fe River and ground water moves through O'Leno State park (about 3 km/day) and the depth at which the water appears to be moving, about (30 m below land surface) the wetlands located throughout O'Leno State Park do not largely contribute to the underground system of the Santa Fe River. Reaeration Utilizing the decrease in SF 6 concentrations along the two reaches, a gas transfer velocity of 27.5 m/d and a Kj value of 16.7 day' 1 were calculated. These values are within the same order of magnitude as other streams reported. It was determined that 1) 222 Rn is unacceptable as a gas exchange tracer in these reaches because of complex and incomplete mixing of 222 Rn enriched ground water delivered by numerous springs and seeps creating complex cross-stream and vertical concentration gradients in the river; 2) stream channel characteristics caused the rate of gas transfer, along short intervals of a few hundred meters between

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166 sampling locations in the river, to have a high degree of variability; 3) gas exchange experiments should be completed in river length long enough to average in channel morphology as well as hydrologic characteristics; 4) since existing predictive eguations to estimate gas transfer and reaeration coefficients are site specific, it is difficult to apply them in different hydrologic settings. Computer Modeling An attempt to devise a computer model of the study area was completed. It was determined that due to the complex hydrogeologic nature of the basin and the inability of current computer models to address specific hydrologic parameters, computer models are not suited to accurately characterize ground water and surface water conditions. Sulfur Hexafluoride The results of this research confirmed several aspects of SF 6 . Most importantly they include that 1) SF 6 is chemically and biologically inert, capable of being detected in extremely low concentrations, and is well suited for water tracing and mixing applications in karst terranes; 2) in comparison to fluorescent dye tracers, such as rhodamine WT, SF 6 has the advantages of detectability at low concentrations and none of the interference problems associated with organic acids, dissolved particulates, and

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167 aquifer material that can occur with fluorescent dyes; 3) SF 6 has the potential as a quantitative tracer under specific closed conditions; 4) SF 6 may also be applied to geotechnical problems such as well competency tests, and detecting upward leakance through a confining layer. The draw backs of SF 6 are that 1) contamination of the analytical equipment is a easy; 2) it is a volatile tracer and is lost quickly to the atmosphere and 3) sampling SF 6 is often time consuming and labor intensive. Karst Development in the O'Leno State Park The landscape within the western Santa Fe River Basin is a snapshot in time. The time scale of the park's evolution is many orders of magnitude slower than that of our human observation. Some landforms in the park are relatively young, such as New Sink. Others are vastly older, formed perhaps by the slow sculpturing of limestone since the early Tertiary. Determining the time at which events occurred to develop the park is difficult. Historical factors such as: temperature, sea level, carbon dioxide levels, rainfall and depositional environment have varied drastically since the deposition of the Eocene limestones that underlie the park and house the conduit system for the Santa Fe River. Caves and surface landforms record some of the history; the difficulty is unraveling the record (White, 1990) . The conduit system within the park

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168 has not been explored and described in detail and thus leaves many questions unanswered about its nature. Based on these experiments and surface features it has been determined that O'Leno Sink is the initial sinking point of the Santa Fe River. The river travels at about 3.5 km/day, underground, in a single conduit and periodically returns to surface and then disappear at several points along its upper reach. Up to Jim's Sink there appears to be little ground water augmentation to this flow. Downstream of Jim's Sink there is more ground water mixing with the Santa Fe River and its flow becomes more diffuse. The river eventually reappears at the River Rise with a geochemical and temperature signal much more like that of ground water rather than surface water. The age of the surface sinks may be estimated by the age of the surrounding wetlands that surround the sinks. For example, where New Sink opened there are now small cypress saplings, an obligate wetland species, taking root. In contrast, surrounding Jim's Sink, there are many cypress trees with eight foot diameter trunks making this sink a much older feature. Also, if the trunks of the cypress trees appear to be falling into the sink this may indicate that either the sink is migrating in the trees direction or that the sink opened after the establishment of the cypress tree. Using these two ideas it may be possible to establish an age relationship among the various sinks in the park and

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169 thus a relationship between the conduit system and the wetlands found within the park. That is, the older wetlands would indicate the older karst landforms and describe how; in what direction, and at what rate the park developed. The general abundance of sinks and karst features in the upper reach of the park verses the downstream end of the park indicates that the upper reach is more active. The reason for this higher activity in this part of the park may be due to two things. First, the upper reach has only one conduit for the Santa Fe River. If there is only one conduit for the same volume of water that flows through the lower reach of the park, it must be larger, and is therefore more likely to intersect the surface causing a collapse and sink formation. Second, the nature of the water in the upper reach is that of surface water. This water is more undersaturated with respect to Ca ++ , and is more capable to erode the underlying limestone. New Sink has migrated to the north about 5m over the past two years. This process will continue as the small sinks converge into large sinks and new sinks continue to appear along the pathway of the underground Santa Fe River. The upper reach of the park will more quickly become a surface feature for the Santa Fe River and perhaps Jim's Sink will eventually appear to be the sinking point of the Santa Fe River in the future. Accompanying the development of the karst surface feature, wetlands will also coalesce

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170 lining the banks of the new portion of the river and appear much like that of the eastern part of the Santa Fe river Basin.

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APPENDIX A GAS CHROMATOGRAPHY AND THE INJECTION PORT SYSTEM

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Gas Chromatography and the Injection Port System Introduction This section provides the basic instructions to operate the Shimadzu gas chromatograph (GC) equipped with an electron capture detector (ECD) for the analyses of sulfur hexafluoride. It gives a brief overview of the component parts of the system but does not go into detail about their construction, design and specific functions. This section will provide the user with a basic working knowledge of the equipment but the user should at no time attempt to "fix", or "repair" the instruments without further consultation or assistance from someone who is more capable of doing so. The equipment is expensive and extremely sensitive, therefore even the slightest wrong adjustment or contamination of the system can render the system out of commission for months and require expensive repair. It is also important to read all of the instructions before attempting to run the system. At no time should there be any type of petroleum product in the lab, even if the GC is not being used. This especially holds true for WD-40 and other aerosol products. Smoking is also strictly prohibited from the lab at any time. Also, because of the sensitivity of this system the setup of the system may take one or more days to accomplish, 172

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173 therefore if planning an experiment, make sure to start the system running at least 36 hours before analysis is to occur. Purpose of the GC system The GC system has been designed so that repetitive SF 6 analyses can be completed efficiently and relatively quickly. If the system is operated properly, approximately 15-20 samples can be analyzed in one a hour period. The analysis can detect SF 6 in concentrations as low as single parts per trillion with a precision of 3%. Equipment There are six component parts of the entire gas chromatographic system. All parts must be in excellent working order or the analyses will not be able to be completed accurately, if at all. With reference to figure 43, the system consists of: 1) 2 (UHP) ultra high pure grade nitrogen tanks, 2) electric-heat gas purifier, 3) multi-port injection system, 4) gas chromatograph, 5) integrator, and 6) 3 SF 6 standard tanks. Equipment: functions 1) Nitrogen Tanks. A) This tank acts as the source of the carrier gas for the sample of gas injected into the GC. This gas will

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174 essentially push the sample gas through the system to be first separated and then analyzed. B) This tank acts as the source of gas which is used to fill the headspace of the syringes which holds the water samples. Once shaken the SF 6 will diffuse into the headspace of the syringes and then be injected into the system. 2) Electric-Heat Gas Purifier. This component removes any contaminants that may be in the carrier gas. 3) Multi-port Injection System. This component first separates individual gas components in the sample gas and then consistently delivers equal amounts of injected sample gas to the GC for analysis. 4) Gas Chromatograph. This component measures the amounts of individual gases found in the injected sample gas. 5) Integrator. This component interprets the data gained from the GC and provides a printout of the relative amounts of gases found in the injected sample gas. 6) SF 6 Standards. The standards are known concentrations of SF 6 . They are used to generate a calibration curve by which sample

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Nitrogen Tanks, N 175 Figure 43. Gas chromatograph setup for SF 6 analysis.

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176 data will be compared to, to obtain actual concentrations of sf 6 . General Procedure Before beginning to turn anything on there are several items that should be checked. Also take a minute to familiarize yourself with the individual components of the system. The items that need to be checked include: 1) that there is enough paper in the integrator, 2) that there is ink in the ink jet printer on the integrator, 3) that there is nitrogen, at least 200 psi in each tank, 4) the glass purifier, it should be black with some brown at each end. If it is totally brown it needs to be replaced, 5) that all equipment is plugged in properly, 6) that there is a dreirite tube hanging from the injection port, if it is not there one will have to be made. It consists of dreirite, glass wool and tygon tubing (Figure 44) , 7) make sure that there is water in the beaker set next to the multi-port system and push the tygon tubing to the bottom of the glass.

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Top Glass wool Drierite Glass wool — tygon tubing Bottom Figure 44. Cross section of dreirite tube used in SF analysis.

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178 Step-wise procedure 1) Turn on the N 2 tank ("A" in Figure 43) that is connected to the GC system and adjust a flow rate to about 20 psi on the left dial of the regulator. To turn the tank on, simply turn the top tank handle counter-clockwise until it is all the way open then turn it back one-half of a turn. Watch the needles on the two dials to see if they respond, to set the pressure going out of the tanks turn the brass handle on the regulator clockwise to increase the amount of gas leaving the tanks, the left pressure gauge should be set between 20-23 psi. 2) Turn on electric-heat gas purifier. 3) Check, using "Snoop”, around any steel or copper connections for leaks in the system. 4) Open all capped areas on the multi-port injection system. 5) Purge the system for one hour. 6) Multi-port Injection System: Figure 45, adjust flow rates using knobs marked A and B on the multi-port system so that the flow meter on the left of the multi-port system is equal to the 5 ml bubble meter on the right side of the multi-port system. Once they have been adjusted to the same

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179 Figure 45. Multi port injection system for SF 6 analysis.

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180 flow rate adjust the regulator on the nitrogen tank so that they read 20 ml/sec. It is important to move the switch from load to inject on the multi-port system and recheck in each location that the flow rates are the same. Note, this may take some time, be patient! The flow rate on the flow meter is determined by comparing the number to which the floating ball rises up to, to the pink sheet of paper posted on the wall behind the system. The number on the flow meter is not the flow rate, the flow rate is the number written on the pink sheet under the "flow" column. The flow rate on the bubble meter is determined by squeezing the lower tube filled with snoop and timing how long it takes to rise to the 5 ml mark on the tygon tubing. Then, by using the blue slide rule determine the flow rate through the tube. 7) GC Adjustments (the entire manual is located in the GC box located to the left of the system) : Turn on the GC and set the upper temperature dial, (inject temp) to 320 by rotating the black dial to the left of the setting and set the lower dial (column temp) to 70, using the same procedure. Always make sure that there is nitrogen going through the GC when it is running. 8) Leave entire system running for about 1 hour. 9) Recheck flow rates on both meters and adjust if needed. 10) On the front of the GC, the lower most silver knob (marked attenuation) should be set on 1, the current knob

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181 should be set on 1.0, the blue button should be set on 1 (pressed in) . 11) Integrator adjustments (a copy of the first page of the manual is found in the appendix, the entire manual is located in the GC box located to the left of the system) : turn on integrator, the switch is located on the back right of the machine near the plug into the machine. First the machine will go through its own system check and give a relatively blank screen. Once it stops it will now wait for your command. Hit the LCD STATUS button, this will bring up a new display on the screen. This is the screen that you almost always want to have displayed. At the top of the screen several letters will be displayed similar to: CH FI BIN PLOT CS ATTEN RUNTIME LEVEL The meaning of each symbol is: CH = channel, should be set on A FI = file name, PLOT = whether the system will plot automatically (AUTO) , on (ON) or off (OFF) CS = chart speed, (in cm of paper printed per minute) it should be set on 1 ATTEN = attenuation, this is basically a filter adjustment of the signal transmitted into the integrator from the GC, set at 32,

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182 RUNTIME = keeps a running time of how long the integrator has been working, LEVEL = the relative strength of the signal being transmitted to the integrator, 12) Depress the ATTEN button on the integrator and then type "32" and hit the ENTER button and then hit the LCD STATUS button. 13) Now basically, if everything is going right, all major adjustments have been made. 14) Read the level on the integrator, it should be reading quite high at first and may take several minutes to hours to days to adjust to a level of 1000 which is what you want. If it is not at 1000 or even close try adjusting the coarse adjustment knob on the GC, to get the level down to 1000. If that succeeds then switch the load/inject button on the multi-port system to the opposite position, you will notice that the level will jump probably significantly and may stay there for again minutes, hours or days? If you are lucky and the level responds quickly back to around 1000, try using the fine adjustment knob to get it to be exactly 1000 and have it remain there. If this happens, then again switch the load/inject button to the opposite position and watch the levels. It should eventually come down to 1000. AGAIN this procedure has been known to take days to reach equilibrium so do not expect any miracles and be patient. 15) If the levels do not come down within a day or so

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183 or are erratic the system has a problem and should not be used any further. 16) If the levels have equilibrated to 1000 on both the inject and load modes and the flow rates remain consistent in both inject and load modes the system is now ready for use. One final step before continuing is to hit the PT EVAL button on the integrator. So now hit the PT EVAL button, this will evaluate the amount of "noise" coming through the GC, the integrator is now thinking and is averaging out the amount of noise going to the integrator, this process takes a couple of minutes. You will know when it is finished when it prints out something like PT = 50 . The PT value should be less than 100, if not then the system is not ready to be used. This procedure should be repeated for both the load and inject modes of the multi-port system. Now assuming all is well, i.e. levels at 1000, flow rates good, PT = <100, you can proceed with an injection. Injection of a gas sample occurs via a glass syringe, this is true for all samples but glass syringes are not used for analysis of standards. 17) Injection techniques. First make sure the inject/load switch on the multi-port system is set on load. 18) To complete a series of standards begin with standard one, this should be marked on the tag on the tank. 19) Turn on the standard tank, by turning the knob on the top of the tank. Next open the three-way-stop-cock on

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184 the end of the standard tank hose. Now insert the end of the stop cock into the tygon tubing of the drying column which should be fastened to the multi-port injection system at the location labelled "sample inject". 20) Now slowly bend the tip of the hose and watch the glass filled with water to see if excess standard is exiting the system. This should be a slow and gradual process and not last more than a second or two. In other words do not blast gas through the system let it escape slowly. What you are doing is filling up the sample loop with a specific amount of gas and excess gas is exited to the water. 21) Wait 10 seconds, then simultaneously switch the load/ inject button to inject and hit the INJECT A button on the integrator. If done correctly the printer should be going and begin plotting a relatively straight line. 22) At about 0.60 to 1.1 minutes into the injection the plotter should be printing a large peak on the graph, once the peak has been completed and returns to base level hit the INJECT A button again and switch the load/inject switch back to load. At this point the integrator will begin to print out the information needed from the sample and will also temporarily store it in its memory. At this point write on the printed paper the sample number where the print out occurs. 23) If all has gone well, the levels should re-adjust back down to around 1000. If they do not do so immediately

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185 let the machine run in the load mode until it does occur (about 5 minutes) , if it does not come back on line then obviously there is a problem in the system, most likely it is some type of contamination, and no further use of the machine is recommended. 24) Repeat steps 19-23 until the area printed out on the paper is reproducible to 5%, then move on to standard 2 and then 3 following the same procedures. 25) Injection of samples with syringes (Figure 46) . The syringes should be filled with a water sample in excess of 30ml. Only the samples that are filled to greater than 30ml and have no air bubbles in them should be used, but do not throw out samples with air bubbles or ones having less than 30ml of water because they may be able to provide some qualitative data for the experiment. 26) The first step in the process is to remove the excess water in the syringes by slowly opening the three-way stop cock are pushing the water out the end up to the 30ml mark on the syringe. Next, open nitrogen tank "B" and allow some excess nitrogen flow out so that you can just barely hear it escaping. Now fill the top 20ml of the syringe with nitrogen. Carefully, insert the tip of the syringe into the tygon tubing attached to the nitrogen hose, and very slowly open the three-way stop cock to allow nitrogen to push the sample and syringe piston down ward. Be careful not to open the stop cock too quickly, you may blast the sample and

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186 headapaca filled with gaa water sample 20ml 50ml Figure 46. Glass syringe used for injecting SF 6 sample

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187 piston on the floor. Now allow the nitrogen to fill up the top 20ml in the syringe, so that the top of the piston should be at the 50ml mark on the syringe. Shut the stop cock and then turn off the nitrogen tank. 27) Now shake the syringe carefully but vigorously for 2 and 1/2 minutes. This procedure causes the SF 6 to enter and mix in the headspace of syringe. 28) Next, make sure the load/insert switch is set on load, insert the tip of the syringe into the drying column, open the stop cock to allow only the gases in the headspace to enter the drying column. At this time you should have some support of the bottom of the piston so that it DOES NOT drop. Now slowly and steadily push the gas and only the gas in through the system. There should be some excess gas exiting into the glass beaker to the left. Once you have pushed the gas through the system close the stop cock and take it out of the drying column. Wait 10 seconds and then as before, simultaneously hit the INJECT A button on the integrator and switch from load to inject on the multi-port injection system. 29) Follow the same procedures in steps 22 and 23. 30) Repeat with more sample syringes following steps 25-29. Consistency on filling the headspace exactly to the same level with each syringe, injecting at the same rate, shaking the syringe for the same length of time are all crucial in obtaining accurate results.

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188 31) After 5 to 10 samples have been run, run any standard once, and make sure it coincides with the standards run earlier. If it does not coincide run it again or run another standard. If still nothing is reproduced correctly, do not proceed any further. 32) Shut down of system. Once all of the samples have been run and standards have been run at the end of all the samples, now its time to shut the system. The system should only be shut down if no samples are going to be run over the next weeks time. If more samples are scheduled to be run the next day or even within a week or so it is best to leave the system running with all equipment left on. 33) However if no samples are to be run, follow these steps strictly. First, turn off the GC and the integrator. Allow the GC to cool for at least three hours or preferable over night. Second, remove the drying column from the sample inject port, and cap the port with a swage cap. Third, turn off the nitrogen tank "A" and the electrical heat purifier, and allow the nitrogen too bleed off all excess gas. Fourth, remove the hose exiting from the bottom left side of the GC and cap the GC port with a swage cap. Fifth, put all tools, papers, and sample sheets away, and wash all bottles and syringes and place them back in their appropriate place.

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189 Trouble Shooting Tips There are many things that can go wrong with this system, but fortunately if the system is set up properly and great care is taken for the system, especially where contamination is concerned it does not break down often. However when something does go wrong, months can go by trying to solve the problem. Many "small" problems can be fixed often with little effort. A comprehensive guide to trouble shooting is provided in the GC notebook holder located to the left of the system. It is entitled "Troubleshooting Guide: How to Locate Gas Chromatography Problems and Solve Them Yourself", Guide 792C, by Supleco. By looking through this guide many small problems can by located and taken care of. A copy of its front page is found in the appendix. Bake Out Procedure The bake out procedure is the technique used on the GC and separating column to recondition the column to enhance its performance. The procedure takes place in the GC oven. It is completed by following these steps: 1) If the GC has been running turn it off, and open the GC oven door, but continue to let the nitrogen gas flow through the system. Let the GC cool for about two hours or more. 2) Once it has cooled, disconnect the column from the

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190 multi-port injection system, and cap the openings left on the multi-port system. 3) Disconnect the main nitrogen gas line from the injection board and re-attach it so that gas is flowing directly into the GC and bypassing the injection board completely. 4) Inside the oven disconnect the fitting upstream of the larger steel tubing and insert the column in this gap in flow. Reconnect the column in this area and tighten all fittings. Check for leaks using snoop and correct them if needed. 5) Close the oven door and lower the flow rate of nitrogen to 15 psi, by adjusting the top handle on the nitrogen tank. 6) Set the Inject temp to 320. a) set the oven/column temp to 95 and let run for one hour. b) next set the oven/column temp to 105 and run for one hour. c) finally set the oven/column temp to 230 and let run for two hours. 7) Now turn off the GC and open the oven door let the system cool for at least two hours. 8) Remove the column and replace it on the injection system, reconnect the steel tubing in the oven, and

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191 reconnect the copper tubing to its original location on the injection system. 9) After all connections have been made recheck everything on the system with snoop and begin the startup procedure for running the GC System.

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APPENDIX B sf 6 INJECTION SYSTEM

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SF C Injection System Numerous attempts were made by R. Hisert and T. Kincaid to efficiently design an injection system that would deliver at a consistent rate the SF 6 -saturated river water to the river. The design had to be field sturdy, easy to transport, relatively inexpensive, and most importantly reproducible. The final design was reached after numerous attempts and was only sightly modified after nearly two years of continued use. The design included: A) a 701b. SF 6 tank, B) a two stage regulator, C) 220 liter plastic barrel, D) a peristaltic pump, E) a 12 volt battery, F) 120m of 0.633cm tygon tubing, and several 2 pound lead weights (Figure 47) . Its general theory was to saturate water with SF 6 and then inject the water into the river or sink. Previous experiments that injected the SF 6 directly into a water had problems of gas loss immediately to the atmosphere (personal communication, R. Wanninkhof, 1991) In most cases the injection system would be set up and tested in the field the evening before the experiment was to take place. The general set up procedure involved first filling the 220L barrel with river water by hand dumping 193

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194 Figure 47. SF 6 field injection system used throughout all injection experiments.

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195 five gallon buckets of river water into the top opening of the barrel. The next step would be to connect a one meter piece of tygon tubing to the copper tubing that already was fitted with a diffusion stone at its end. The end containing the diffusion stone was first threaded through a rubber stopper and then into the barrel, where it lay nearly at the bottom. The opposite end of the this piece of tygon was connected to the two stage regulator that is controlling the outflow of SF 6 to the barrel. Next, another two meter piece of tygon tubing was threaded through the same rubber stopper and placed also at the bottom of the barrel. The opposite end of this tygon tubing was attached to a "T" fitting which created two lines going into the peristaltic pump. On the out flow side of the peristaltic pump, two separate, appropriate length pieces of tygon tubing were then stretched out into the water, and held on the bottom with lead weights. The peristaltic pump was then connected to the 12 volt battery and the system is complete for injection. The initial phase of injection involved saturating the river water in the barrel with the SF 6 . The SF 6 would vigorously be injected into the airtight barrel for about two minutes. After this, the two stage regulator would be turned down so that the back pressure on the regulator read about 1-2 psi. By continually allowing SF 6 to enter the barrel, it assured complete saturation of the river water

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196 throughout the injection. Often times the plastic barrel even swelled with the increasing pressure so that the SF 6 had to be turned down. Once the water was saturated, after approximately five minutes, the peristaltic pump was turned on and the water would then begin to flow from the barrel to the river. During most occasions particulate matter that had been transferred into the barrel would be seen moving through the clear tygon tubing reassuring that the water was actually being injected. The injection rate for the experiments was approximately two liters per minute, which allowed for at most a two hour injection.

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APPENDIX C CATION BOTTLE PREPARATION

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The cleansing process consisted of first rinsing the bottles in deionized water, second the bottles were then filled with three normal nitric acid and left standing overnight. Next the nitric acid was emptied and then the bottles were rinsed thoroughly with triple distilled water. These bottles were left to air dry, capped and then ready for sampling. Water samples were again taken at about 0.5 m where permissible. The fifty milliliter collected sample was then packaged for transport back to the lab for analysis. 198

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REFERENCES Aley, T., 1990. Procedure for Analysis of Fluorescein and Rhodamine WT Dyes in Water or Charcoal Samplers. Ozark Underground Laboratory Circular, Little Rock, AR. Anliker, R. and G Muller., eds., 1975. Fluorescent Whitening Agent, Environmental Quality and Safety, Supplement v. IV, New York, Academic Press, 319 p. Asikainen, M. , 1981. State of disequilibrium between 238 U, 226 Ra and 222 Rn in groundwater from bedrock. Geochem. Cosmochim Acta, 45:201-206. Back, W. , Hanshaw, B.B., and van Driel, J.N., 1984. Role of groundwater in shaping the Eastern Coastline of the Yucatan Peninsula, Mexico. In Groundwater as a Geomorphic Agent, R.G. LaFleur (ed.), Boston, Allen & Unwin, p. 280-293. Bansal, M.K., 1973. Atmospheric reaeration in natural streams. Water Research, 7 (5) : 769-782 . Beck, B.F., 1986. A generalized genetic framework for the development of sinkholes and karst in Florida, USA. : Environmental Geology Water Science, 8(1/2): 5-18. Bennett, J.P., and R.E. Rathbun, 1972. Reaeration in openchannel flow: U.S. Geological Survey Professional Paper 737, 75 p. Biddlecomb, A.H., 1993. Hydrogeology and karst development of the Robinson Sinks Area, Alachua County, Florida. M.S. Thesis, University of Florida, Gainesville, 122 p. Black, A. P . and E. Brown, 1951. Chemical character of Florida's waters — 1951 Florida State Board Conservation Division, Water Survey and Research Paper 6 . Briel, L. , 1976. An investigation of the U 234 /U 238 disequilibrium in the natural waters of the Santa Fe River basin of north central Florida, Ph.D. Dissertation, Florida State University, Tallahassee, FL. 199

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200 Broecker, W.S., 1965. An application of natural radon to problems in ocean circulation. Symposium on Diffusion in Oceans and Fresh Waters. New York, Lamont-Doherty Geological Observatory, Palisades, p. 116-145. Broecker, W.S., Y.H. Li, J. Cromwell, 1967. 226 Ra and 222 Rn: Concentrations in Atlantic and Pacific Oceans. Science, 158:1307-1311. Brooks, H.K., 1981. Physiographic divisions of Florida and accompanying guide. Institute of Food and Agriculture Sciences, University of Florida, Gainesville, Florida. Burg, A.W. , Rohovsky, M.W., and C.J. Kensler, 1977. Current status of human safety and environmental aspects of fluorescent whitening agents used in detergents in the United States, Critical Review in Environmental Control, 7:91-120. Cadwallader, T.E. and A.J. McDonnell, 1969. A multivariate analysis of reaeration data, Water Research, 3:731-742. Ceryak, R. , Knapp, M.S. and T. Burnson, 1983. The geology and water resources of the Upper Suwannee River Basin, Florida. Florida Geological Survey, Report of Investigation 87. Churchill, M.A., Elmore, H.L., and E . A. Buckingham, 1962. The prediction of reaeration data. Journal of Sanitation Engineering Division American Society of Civil Engineers, 88 (SA-4) : 1-46 . Clark, W.E., Musgrove, R.H., Menke, C.G., and J.W. Cagle, 1964. Water Resources of Alachua, Bradford, Clay, and Union Counties. Florida Geological Survey, Report of Investigation 35, 170 p. Cowardin, L.M., Carter, V. , Golet, F.C., and LaRoe, E.T., 1979. Classification of wetlands and deepwater habitats of the United States. FWS/OBS-79/31, U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC, 120 p. Cotruvo, J.A., 1980. Memorandum of April 10, 1980, from the Director of the Criteria and Standards Division, Environmental Protection Agency, to P.J. Traina, Director of the Water Management Division, Region IV of the EPA concerning rhodamine WT and B (text available, with 2-page discussion, as Fluorometric Facts, Bulletin 102, from Turner Designs, Inc., 247 Old Middlefield Way, Mountain View, CA 94943) .

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201 Douglas, G.R., Grant, C.E., Bell, R.D.L., Salamone, M.F, Heddle, J.A., and E.R. Nestmann, 1983. Comparative mammalian in vitro and in vivo studies on the mutagenic activity of rhodamine WT. Mutation Research, 118:117125. Doyle, L.J., Brooks, G., and J. Hebert, 1985. Submarine erosion and karstif ication on the West Florida continental margin: disparate environments and similar features: Geological Society of America Abstracts with Programs, 17:565. Duran, A.P., and H.F. Hemond, 1984. Dichlorodif luoromethane (freon-12) as a tracer for nitrous-oxide release from a nitrogen enriched river. In: Brutsaert, W. and G.H. Jirka, (eds.), Gas Transfer at Water Surfaces. Hingham, Mass.,D. Reidal, p. 293-302. Ellins, K., 1985. The application of 222 Rn in measuring groundwater discharge to the Martha Brae River, Jamaica. In: Proceedings of the International Symposium on Tropical Hydrology sponsored by the American Water Resources Association, Miami, FL, May 1985. Ellins, K. , 1986. Estimating groundwater influx to a portion of the Rio Grande de Manati River Basin in Puerto Rico through the measurement of 222 Rn. In: Proceedings of the third Caribbean Islands Water Resources Congress, U.S. Virgin Islands, Miami, FL, July 1986. Ellins, K.K., 1988. Isotope hydrology of karst drainage basins in Jamaica and Puerto Rico. Ph.D. Dissertation, Columbia University. Ellins, K.K., 1989. Tracing ground water and surface water in the western Santa Fe River basin using SF 6 and 222 Rn. Proposal to the National Science Foundation. Univeristy of Florida, Gainesville, FL. Ellins, K.K. and R. A. Hisert, 1994. Tracing subterranean flow patterns in the Santa Fe River Basin, Florida, with SF 6 . Hydrologic Processes, In press. Ellins, K.K., Hisert, R.A., and T.R. Kincaid, 1992. Hydrogeology of the western Santa Fe River Basin. Field Trip Guide, South Eastern Geological Society Spring Meeting, Gainesville, FL. Ellins, K.K., A. Roman Mas, and R. Lee, 1990. Using 222 Rn to examine groundwater/ surface discharge interaction in the Rio Grande de Manati in Puerto Rico, Journal of Hydrology, 115:319-341.

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202 Ellins, K.K., Wanninkhof, R.H., Quinones-Aponte, V. and R.A. Hisert, 1994. Using SF 6 and 222 Rn to determine reaeration rates in streams. Journal of Environmental Pollution, In press. Elsinger R.J. and W. Moore, 1983. Gas exchange in the Pee Dee River based on 222 Rn invasion. Journal of Geophysical Research Letters, 10:443-446. Fanning, K.A., Breland, J.A. Ill, and L. Torres, 19 8 7 . 226 Ra and 222 Rn in Florida's Rivers and Estuaries, unpublished. Faulkner, G.L., 1973. Geohydrology of the cross-Florida barge canal area with special reference to the Ocala vicinity: U.S. Geological Survey WRI 1-73, p. 117. Fernald, E.A. and D.J. Patton, 1984. Water Resources of Florida, Tallahassee, Florida. Fetter, C.W., 1988. Applied Hydrogeology. Columbus, OH: Merrill Publishing Co. Fischer, H.B., 1966. A note on the one-dimensional dispersion model. International Journal Air Water Pollution, 10: 443-452. Florida Geological Survey, 1992. Florida's water quality monitoring program background hydrogeochemistry. Florida Geological Survey Special Publication 34, Tallahassee, FL, 364 p. Ford, D.C., and R.O. Ewers, 1978. The development of limestone cave systems in the dimensions of length and depth. Canadian Journal Earth Science, 15:1783-1789. Ford, D.C., and P.W. Williams, 1989. Karst Geomorphology and Hydrology: London, Unwin Hyman, p. 601. Ganz, C.H., Schultz, J., Stensby, P.S., Lyman, F.L., and K. Macek, 1975. Accumulation and elimination studies of four detergent fluorescent whitening agents in Bluegill (Lepomis Macbrocbirus) , Environmental Science and Technology, 9:738-744. Genereux, D.P. Hubbard, E.F., and H.F. Hemond, 1992. Determination of gas exchange rates for a small stream on Walker Branch Watershed, Tennessee. Water Resources Research, 28 (9) : 2365-2374 .

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203 Geraghty and Miller, Inc. 1990. ModelCad, Computer Aided Design Software for Ground-Water Modeling, J.M. Geraghty, Jacksonville, FL. Gomberg, D.N. , 1977. Neogene karst in the Florida Straits, In: Tolson, J.S., and F.L. Doyle, eds., Proceedings of the 12th International Congress on Karst Hydrogeology Huntsville, AL, University of Alabama at Huntsville Press, p. 213-226. Graf, J.B., 1986. Transverse mixing of dye slug injected into center of flow, U.S.G.S. Water Supply Paper 2269. Grant, R.S., and S. Skavroneck, 1980. Comparison of tracer methods and predictive equations for determination of stream reaeration coefficients on three small streams in Wisconsin. U.S. Geological Survey Water Resources Investigation 193642: WRI 80-19. Grund, A., 1914. Der Geographische Zyklus in Karst. Z. Ges. Erdk. Berl., 52:621-640. (partly translated in Sweeting (1981), p. 54-59. Gunn, J., 1986. Solute processes and karst landforms, In: Trudgill, D. ed., Solute Processes: New York, John Wiley & Sons Ltd., p. 363-437. Hampson, P.S. and J.E. Coffin, 1989. Measurement of reaeration coefficients for selected Florida streams, U.S. Geological Survey Water Resources Investigations Report 87-4020, 81 p. Hanshaw, B.B. & Back. W. , 1979. Major geochemical processes in the evolution of carbonate-aquifer systems. Journal of Hydrology, 43:278-312. Hebert, Jean A., 1985. A Miocene karst drainage system: seismic stratigraphy of the continental shelf west of Florida. Geological Society of America Abstracts with Programs, 17:606. Hem, J.D., 1985. Study and interpretation of the chemical characteristics of natural waters. U.S. Geological Survey Water Supply Paper 2254, 264 p. Hisert, R.A., 1990. Hydrogeology and water budget analysis of two interdunal ponds, Nags Head Woods Ecological Preserve, Dare County, North Carolina. M.S. Thesis. Old Dominion University, 194 p.

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205 Key, R.M., 1981. Examination of abyssal sea floor and nearbottom water mixing processes using Radium-226 and Radon-222. Ph.D. Dissertation, Texas A&M University. Kilpatrick, F.A., Rathbun, R.E., Yotsukura, N. , Parker, G.W., and L.L. De Long, 1989. Determination of stream reaeration coefficients by use of tracers. Techniques of water resources investigations of the United States Geological Survey, Chapter A18. Kincaid, T.R., 1994. Groundwater and surface water relationships in the Ginnie Springs Area, High Springs, FL. Masters Thesis, Gainesville, Florida. Konikow, L.F. and J.D. Bredehoeft, 1987. U.S.G.S. Twodimensional solute transport model MOC, Holocomb Research Institute, Butler University, Indianapolis, IN. Krenkel, P.A., and G.T. Orlob, 1963. Turbulent diffusion and the reaeration coefficient, Transactions of the American Civil Engineers, 128:293-334. Kwasnik, J.M. and T.H. Feng, 1979. Development of a modified tracer technique for measuring stream reaeration rates, PB 296317. National Technology Information Service, Springfield, VA. Langbein, W.B., and W.H. Durum, 1967. The reaeration capacity of streams. U.S. Geological Society Survey Circular 542. Larson, G.L., Mathews, R.C. and R. Herrmann, 1987. Limestone influences on physical and chemical features of a mountain stream. Groundwater, 24:166-72 Ledwell , J.R., 1984. The variation of the gas transfer coefficient with molecular diffusivity. In: Gas Transfer at Water Surfaces, Brutaert, W. and G.H. Jirka, (eds.), Hingham MA, D. Reidel, p. 293-302. Ledwell, J.R., 1986. Mixing experiments. U.S. WOCE Planning Report No. 8, U.S. Planning Office for WOCE, College Station, Texas, 35 p. Ledwell, J.R. , and A.J. Watson, 1988. The deliberately injected tracers for the study of diapycnal mixing in the ocean. In: J.C.J. Nihoul and B.M. Smart (eds.) Small Scale Turbulence and Mixing in the Ocean, Elsevier, Amsterdam.

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207 Meyer, F.W., 1962. Reconnaissance of the geology and groundwater resources of Columbia County, Florida. Florida Geological Survey Report of Investigations no. 30, 74 PMiller, J.A., Hughes, G.H., Hull, R.W. , Vecchioli, J., and P.R. Seaber, 1978. Impact of potential phosphate mining on the hydrology of Osceola National Forest, Florida. United States Geological Survey, Water Resources Investigation 78-6. Mitsch, W.J., and J.G. Gosselink, 1986. Wetlands Ecology. New York, Van Nostrand Press. Mull, D.S., Liebermann, T.D., Smoot, J.L.,and J.H. Woosley, Jr., 1988. Application of dye-tracing techniques for determining solute-transport characteristics of ground water in karst terranes. Environmental Protection Agency Report 904/9-88-001, 101 p. Mullins, H.T., Gardulski, A.F., and A.C. Hine, 1986. Catastrophic collapse of the West Florida Carbonate Platform Margin. Geology, 14:67-170. Negulescu, M. and V. Rojanski, 1969. Recent research to determine reaeration coefficients. Water Research, 3(3) : 189-202. O'Conner, D.J., and W.E. Dobbins, 1958. Mechanisms of reaeration in natural streams. Transactions American Civil Engineers, 123:641-684. 0 ' Loughlin, E.M. and K.H. Bowmer, 1975. Dilution and decay of aquatic herbicides in flowing channels. Journal of Hydrology, 26:217-235. Opdyke, N.D., Spangler, D.P., Smith, D.L., Jones, D.S., and R.C. Lindquist, 1984. Origin of the epeirogenic uplift of Pliocene-Pleistocene beach ridges in Florida and development of the Florida karst. Geology, 12:226-228. Owens, M. Edwards, R.W.,and J.W. Gibbs, 1964. Some reaeration studies in streams. International Journal Air and Water Pollution, 8 (819) :469-486. Padden, T.J., and E.F. Gloyna, 1971. Simulation of stream processes in a model river. Rep. EHE -70-23, CRWR-72. University of Texas at Austin. Palmquist, R. , 1979. Geologic controls on doline characteristics in mantled karst. Z. Geomorph., N.F., Suppl. Band 32, p.90-106.

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211 Wilcock, R. J. , 1984. Reaeration studies on some New Zealand rivers using methyl chloride as a gas tracer. In: Brutsaert, W. and G.H. Jirka (eds.), Gas Transfer at Water Surfaces, Hingham, MA, D. Reidel, p. 413-421. Wilcock, R.J., 1988. Study of river reaeration at different flow rates, Journal of Environmental Engineering, 114:91-105. Williams, K.E., Nicol, D. , and A. F. Randazzo, 1977. The geology of the western part of Alachua County, Florida. Florida Geological Survey, Report of Investigation 85. Williams, P.W. , 1972. Morphometric analysis of polygonal karst in New Guinea. Bulletin Geological Society America, 83:761-796. Williams, P.W., 1983. The role of subcutaneous zones in karst hydrology. Journal of Hydrology, 61:45-67. Wilson, R.D., and D.M. Mackay, 1993. The use of sulfur hexafluoride as a conservative tracer in saturated sandy media. Ground Water, 31 (5) : 19-724 . Yotsukura, N., H.B. Fischer, and W.W. Sayre, 1970. Mixing characteristics of the Missouri River between Sioux City, Iowa, and Plattsmouth, Nebraska, U.S. Geological Survey Water Supply Paper 1899-G, 28 pp. Yotsukura N. , Stedfast, D.A., and G.H. Jirka, 1984. Assessment of a steady state propane-gas tracer method for determining reaeration coefficients, Chenango River, New York, U.S. Geological Survey Water Resources Investigations Report 84-4368, 69 p.

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BIOGRAPHICAL SKETCH Richard A. Hisert was born to Gerald H. Hisert and Nancy M. Hisert on December 15, 1965 in the small, upstate town of Cobleskill, New York. He graduated from Cobleskill High School in 1984. He attended Marietta College in Marietta, Ohio, where he received his Bachelor of Science degree in Geology in 1988 while lettering and captaining the soccer team for four years . He then obtained his Masters of Science degree at Old Dominion University in Norfolk, Virginia, in the Fall of 1990. While attending Old Dominion University he worked at the University's Applied Marine Research Laboratory as a wetland investigator and hydrogeologist. In addition, he worked with The Nature Conservancy on his masters thesis in the Outer Banks of North Carolina. In the Fall of 1990 he attended the University of Florida. While attending the University of Florida he worked as a teaching assistant, research assistant, and athletic tutor. Over the last two years he has worked with consulting firms in Jacksonville, Florida, as a hydrogeologist. He was married to Nicohl T. Tobey on September 11, 1992 and July 31, 1993. 212

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of poctor of PhLtoSdphy. Douglas L. Smith, Chair Professor of Geology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. £' Janes L. Eades A^ociate Professor of Geology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy'* P. Snancrler 7 \ P. Spangler Associate Professor of Geology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree G. Ronnie Best Scientist of Environmental Engineering Sciences I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.

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This dissertation was submitted to the Graduate Faculty of the Department of Geology in the College of Liberal Arts and Sciences and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. Dean, Graduate School