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 Title Page
 Letter of transmittal
 Acknowledgement
 Table of Contents
 Abstract
 Introduction
 Geology
 Hydrogeology
 Back Matter


FGS



Reappraisal of the geology and hydrogeology of Gilchrist County, Florida, with emphasis on the Waccasassa Flats
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 Material Information
Title: Reappraisal of the geology and hydrogeology of Gilchrist County, Florida, with emphasis on the Waccasassa Flats
Physical Description: ix, 76 p. : ill., maps ; 29 cm.
Language: English
Creator: Col, Nolan
Florida Geological Survey
Publisher: Published for the Florida Geological Survey in cooperation with the Suwannee River Water Management District
Place of Publication: Tallahassee, Fla.
Publication Date: 1997
 Subjects
Subjects / Keywords: Geology -- Florida -- Gilchrist County   ( lcsh )
Hydrogeology -- Florida -- Gilchrist County   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Nolan Col ... et al..
Bibliography: Includes bibliographical references (p. 68-70).
General Note: At head of title: State of Florida Department of Environmental Protection, Division of Administrative and Technical Services, Florida Geological Survey.
General Note: Florida Geological Survey report of investigation 99
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: oclc - 39740670
lccn - 99164899
issn - 0160-0931 ;
System ID: UF00099451:00001

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Table of Contents
    Title Page
        Page i
    Letter of transmittal
        Page ii
        Page iii
    Acknowledgement
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
    Abstract
        Page viii
        Page ix
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Geology
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
    Hydrogeology
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
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        Page 61
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        Page 63
        Page 64
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        Page 66
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        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
    Back Matter
        Page 78
        Page 79
Full Text










STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
Virginia Wetherell, Secretary





DIVISION OF ADMINISTRATIVE AND TECHNICAL SERVICES
Nevin G. Smith, Executive Services Director





FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief





REPORT OF INVESTIGATION NO. 99





REAPPRAISAL OF THE GEOLOGY AND HYDROGEOLOGY
OF GILCHRIST COUNTY, FLORIDA, WITH
EMPHASIS ON THE WACCASASSA FLATS

By

Nolan Col, Frank Rupert, Meryl Enright, and Glenn Horvath


Published for the
FLORIDA GEOLOGICAL SURVEY
Tallahassee
in cooperation with the Suwannee River Water Management District
1997
















LETTER OF TRANSMITTAL


Florida Geological Survey
Tallahassee
1997


Governor Lawton Chiles
Tallahassee, FL 32301

Dear Governor Chiles:

The Florida Geological Survey, Division of Administrative and Technical Services,
Department of Environmental Protection, is publishing as its Report of Investigation No. 99,
Reappraisal of the Geology and Hydrogeology of Gilchrist County, Florida, with Emphasis
on the Waccasassa Flats. This report summarizes the results of a cooperative project
between the Suwannee River Water Management District and the Florida Geological
Survey. It presents needed data on the stratigraphy and ground-water resources of this
unique geomorphic region in a format useful to other agencies, planners, and the citizens
of Florida.



Respectfully yours,




Walter Schmidt, Ph.D, P.G.
State Geologist and Chief
Florida Geological Survey

































Printed for the
Florida Geological Survey

Tallahassee
1997

ISSN 0160-0931



iii












ACKNOWLEDGEMENTS


The authors wish to thank a number of individuals for their input, help, advice and
review of this study. Special thanks are due to the staff of the Florida Geological Survey
(FGS) for their critical review of the data and manuscript. The authors wish to thank the
following individual and corporate land owners/managers for their interest in water
resources and cooperation in granting access to private property: Ms. Terri Newman and
Mr. Randy Wiggins, Dr. J. Clayton Pruitt, Lloyd and Ray Thomas, Mrs. E.B. Turner and
family, Mr. and Mrs. A.L. Tuten, Mr. J.H. Hill, Mr. Bryan Olmert and the Loncala Phosphate
Company, Mr. Mike Conlon, Mr. Ed Montgomery and ITT Rayonier, Mr. William McArthur
and Wade Investments, Larry Studstill and Johnny Parrish.
The authors also wish to extend our thanks and appreciation to: Dr. Sam Upchurch,
ERM-South, Inc., for sharing ideas, notes and geochemistry software; Wes C. Skiles, Karst
Environmental Consultants, Inc., for sharing field work results and notes on karst
hydrology; Doug Smith, Hydro Tech, Inc., for stratigraphic and ground-water level data.
We wish to extend our appreciation and thanks to our colleagues for their individual and
collective efforts and contributions. Thanks to John Morrill and Albert Phillips of the FGS
for the installation of monitor wells. At SRWMD we want to thank Ron Ceryak for critical
review, support, and sharing ideas and experience, Jana F. Col for support, inspiration, and
sharing ideas and notes on water quality, Martin Gabriel and Willie Ray Hunter for datum
surveys and data collection, Donald Munroe and Cindy Boyette for GIS and database
support, and Teri Smith for data input and management. Thanks also are due Dennis Price
for field support with monitor well construction, Tom Brown for legal work on easements,
Bud Bennett for piloting a fly-over of the study area, Marvin Raulston for statistical data
and Rob Mattson for field assistance. Special thanks are also extended to Mr. Tom Miller
of the FGS for his countless tedious hours of CAD work editing and digitizing figures for
the text.











CONTENTS

Acknowledgments ........................................................... ....................................... iv
Abstract ................................................................................................................. viii
Introduction ................................................................................................ ......... 1
Purpose ................................................................ ..................... ............. 1
Location .......................................................................................................... 1
W ell Numbering System ....................... ........................................................ 1
Metric and Volume Conversion Factors ............................................................... 4
Methods ............................................................................................................... 4
Monitor W ell Construction ................................................................................ 6
W ater Quality Sampling ............................................................................... 6
Permeameter Analyses ................................................................................ 6
Sieve Analyses .............................................................................................. 8
Climate ...........................................................................................................13
Modified Future Land Use ..................................................................................13
Geology ...................................................................................................................... 18
Geomorphology ............................................................ ....................................18
Stratigraphy .....................................................................................................23
Middle Eocene Series ..................................................................................24
Avon Park Formation.............................................................................24
Upper Eocene Series ................................................................................... 24
Ocala Limestone .................................................................................. 24
Pliocene to Holocene Series .........................................................................32
Undifferentiated Sands and Clays .................................................. ............32
Soils................................................................................................................35
Hydrogeology .........................................................................................................35
Surficial Aquifer System ....................................................................................37
Extent .......................................................................................................37
Hydraulic Conductivity.................................................................................37
Ground-water Levels .................................................................................. 37
Ground-water Quality ..................................................................................43
Ground-water Drinking W ater Standards.......................................................49
Exceedance of Primary Drinking W ater Standards....................................49
Exceedance of Secondary Drinking W ater Standards ............................... 49
Development ..............................................................................................50
Floridan Aquifer System .........................................................................................50
Extent .......................................................................................................50
Properties ......................................................................................................50
Ground-water Levels .................................................................................. 50
Recharge ............................................................................................. 56
Discharge ............................................................................................56
Ground-water Quality ..................................................................................59
Exceedance of Primary Drinking W ater Standards........................................59
Exceedance of Secondary Drinking W ater Standards ................................... 59
Development ......................................................................................... 62
Surface W ater .............................................................. ....................................66
W ater Quality .............................................................................................66


v










References ............................................................... ..........................................68

FIGURES
1. Location of Study Area................................................................................... 2
2. Location of Ground-water Monitor Wells in Gilchrist County, Florida ...........................
3. Typical Four-Inch Diameter Schedule 40 PVC Monitor Well .....................................7
4. Permeameter Set-Up Diagram .......................................................................... 9
5. Average Annual Rainfall at Trenton, Florida, 1976 1993.........................................14
6. Departure from Mean Annual Rainfall at Trenton, Florida, 1976 -1993 .......................16
7. Gilchrist County Modified Future Land Use .......................................... .............. 17
8. Location of Waccasassa Flats in Gilchrist County, Florida.................................... 19
9. Geomorphology of Gilchrist County, Florida ...........................................................20
10. Hydrologic Basins and Location of Surface Water Features in Gilchrist County, Florida ..22
11. Geologic Map of Gilchrist County, Florida ...........................................................25
12. Hydrogeologic Cross Section Location Map..............................................................26
13. Hydrogeologic Cross Section A A' ......................................................................27
14. Hydrogeologic Cross Section B B'.......................................................................28
15. Hydrogeologic Cross Section C C' ........................................................................29
16. Hydrogeologic Cross Section D D'........................................................................30
17. Hydrogeologic Cross Section E E' ..........................................................................31
18. Top of the Floridan Aquifer System in Gilchrist County, Florida................................33
19. Isopach of Undifferentiated Sands and Clays Unit, Gilchrist County, Florida ................34
20. Soils Map of Gilchrist County, Florida.......................................................................36
21. Surficial Aquifer System Ground-water Levels Network, Gilchrist County, Florida ........38
22. Comparative Ground-water Levels at Sites 4 and 5, July 1991 through June 1993 ..39
23. Comparative Ground-water Levels at Sites 6 and 7 July 1991 through June 1993 ......40
24. Comparative Ground-water Levels at Sites 8 and 9 July 1991 through June 1993 ....41
25. Ground-water Levels at Sites 31 and 32 vs. Rainfall at Bell, Florida, July 1991 through
June 1993 ......................................... ................... .......................................42
26. Ground-water Quality Network, Gilchrist County, Florida...........................................44
27. Range and Median of Select Water Quality Parameters.............................................46
28. Piper Diagram and Associated Stiff Diagrams for Surficial Aquifer System in Gilchrist
County, Florida..............................................................................................47
29. Key to Predominant Water Types in Gilchrist County, Florida....................................48
30. Potentiometric Surface of the Floridan Aquifer System in Gilchrist County, Florida,
June, 1993 ................................................................. .............. ................... 51
31. Generalized Total Fluctuation of the Floridan Aquifer System in Gilchrist County,
Florida, July 1991 to June 1993.....................................................................52
32. Floridan Aquifer System Ground-water Levels Network, Gilchrist County, Florida..........54
33. Ground-water Levels at Site 36 vs. Rainfall near Trenton, Florida,
July 1991 through June 1993.............................................................................55
34. Recharge Potential of the Floridan Aquifer System in Gilchrist County, Florida............57
35. Piper Diagram and Associated Stiff Diagrams for Unconfined Floridan Aquifer System...60
36. Piper Diagrams and Associated Stiff Diagrams for Confined Floridan Aquifer System ....61
37. Gilchrist County Water Well Permits Issued by Section, January 1976 June 1993......63
38. Gilchrist County Permitted Water Use in Million Gallons per Day (MGD) by Section,
October 1, 1982- June, 1993 .......................................................................64










TABLES


1. Hydrogeologic Sites in Gilchrist County, Florida..................................... ............. 3
2. Metric and Volume Conversion Factors ............................................................ 4
3. Coefficient of Hydraulic Conductivity Values for Study Samples ...............................10
4. Average Range of Hydraulic Conductivity for Various Geologic Materials ..................11
5. Possible Paleoenvironments of the Waccasassa Flats Based on Grain Size Data............12
6. Thiessen Polygon Weighted Rainfall Averages for Gilchrist County, Florida..................15
7. Background Ground-water Quality Network Parameters ............................................45
8. Springs of Gilchrist County, Florida........................................................................58
9. Permitted Water Use in Gilchrist County, Florida .................................................65
10. Physical Water Quality Parameters of Select Surface Water Features in Gilchrist
County, Florida..............................................................................................67

APPENDICES

I. Geologic Summary of Wells Drilled During Study......................................... ............71
II. Monitor Well Data..........................................................................................72
II. Ground-water Levels ......................................................................................73
IV. Gilchrist County Background Ground-water Quality................................................74
A. Descriptive Statistics .................................................................................74
B. Notable Ground-water Quality Values.................................................................76










ABSTRACT


Gilchrist County is an inland county, situated in northwestern peninsular Florida. It
is bounded by the Suwannee River on the west, the Santa Fe River on the north, and by
Alachua and Levy Counties to the east and south, respectively. Gilchrist County has a
humid, subtropical climate. Average annual temperatures are 82 degrees F in the summer
and 58 degrees F in the winter. Rainfall averaged 61.78 inches for the 18 years between
1976 and 1993. Agriculture and silvaculture are the primary industries.
The Waccasassa Flats is a geomorphic subprovince of the broad Gulf Coastal
Lowlands. It occupies approximately 102 square miles, extending from the Santa Fe River
in north central Gilchrist County southward to the vicinity of Trenton, then southeastward,
terminating in north-central Levy County. As its name implies, the area comprising the
Flats is generally flat-lying and characterized by gentle sand hills, pine flatwoods, wetlands,
cypress ponds, and small scattered lakes. The near-surface geology consists of
undifferentiated Pleistocene-Holocene sands, clayey sands, and clays resting on Eocene
carbonates of the Ocala Limestone and Avon Park Formation. The undifferentiated unit is
generally less than 50-feet thick over most of the Flats. Clays within the undifferentiated
sediments form local perched ponds and lakes.
In an effort to better understand this unique hydrogeologic region, a series of 16 study
well sites were selected, drilled, and monitor wells installed as part of the state's Ground-
water Quality Monitoring Program. Well cores and cuttings obtained during drilling were
described lithologically and analyzed for hydraulic conductivity and grain size. The wells
drilled during this study were used in conjunction with existing Ambient Ground-water
wells in Gilchrist County to construct a series of five cross sections across the Flats.
Water level and quality data obtained from the wells through 1993 are summarized in the
text and appendices.
There are two aquifer systems in Gilchrist County. The Floridan aquifer system (FAS)
which underlies the entire county is the primary ground-water resource accounting for
99% of the permitted water use in the county. A limited Surficial aquifer system (SAS)
occurs only in the Waccasassa Flats (Flats) where agriculture accounts for more than 99%
of the permitted water use. The Waccasassa Flats as mapped using GIS is a 102 square
mile mosaic of sand hills, pine flatwoods, wetlands, cypress ponds and small scattered
lakes. In the Flats unconsolidated sediments both support a Surficial aquifer system and
serve as a semiconfining unit for the underlying FAS. In general, hydraulic conductivity
appears to decrease in the SAS (from 1.74 ft./day to very low or no permeability) with
depth. The SAS water table ranges from at or near land surface to 15 feet below land
surface. Fluctuations in the SAS during the study period ranged from three to seven feet.
The primary drinking water standard for turbidity was exceeded in eight of ten SAS
samples; and all SAS samples had pH values below the minimum standard of 6.5. SAS
water quality may be characterized as low in pH, dissolved solids and specific
conductance.
In Gilchrist County the largest ground-water fluctuations in the FAS occur along the
outer margin of the Waccasassa Flats, near rivers and where an unconfined FAS is overlain
by an appreciable thickness of unconsolidated sediments. The FAS in Gilchrist County is
karstic both east and west of the Flats as well as along its margins. In the Flats cavities
were encountered near the top of rock during well construction drilling, while low rock
permeabilities were reported with depth. Ground-water level data show that at most sites
where the surficial and FASs are monitored there is one foot or less difference between
the SAS water table and the potentiometric surface of the FAS. The greatest difference










recorded between the SAS water table and the potentiometric surface of the FAS was
3.49 feet. The relatively small difference in elevation between the SAS water table and
the potentiometric surface of the FAS, the mirror fluctuation patterns, the reversal of the
hydraulic gradient in some wells, and water quality data, underscore the significance of
hydraulic communication between aquifers. FAS water quality is alkaline with high specific
conductance and high dissolved solids.
In the FAS, primary ground-water drinking water standards were only exceeded for
turbidity. Recharge potential in the Waccasassa Flats is low. The ground-water mounding
in the Flats results from a high water table in the semi-confining SAS and low aquifer
permeabilities in the FAS as estimated from field observations and lithologic logs.
Recharge potential increases along the edge of the Flats where the semi-confining
overburden is thin or breached. Where the FAS is unconfined in the county recharge
potential is high. FAS ground-water discharges primarily to the 16 known springs or spring
groups which outcrop in the river corridors along the northern and western boundaries of
the county. Gilchrist County is hydrologically divided into the Suwannee River, Santa Fe
River, and the Waccasassa River surface water basins. There are numerous small lakes
and wet prairies perched in poorly drained soils on the Waccasassa Flats. Most of the
lakes are perched along the margins of Flats. These lakes are generally shallow, acidic,
dark colored water bodies with low dissolved solids content.









REPORT OF INVESTIGATION NO. 99


REAPPRAISAL OF THE GEOLOGY AND HYDROGEOLOGY
OF GILCHRIST COUNTY, FLORIDA, WITH
EMPHASIS ON THE WACCASASSA FLATS

By

Nolan Col, P.G. #198, Frank Rupert, P.G. #149, Meryl Enright, and Glenn Horvath

INTRODUCTION

PURPOSE

In 1983, the Florida Legislature mandated the establishment of an Ambient Ground-water
Quality Network to aid in the prediction and detection of contamination of the state's ground-
water resources. Funded and coordinated through the former Florida Department of
Environmental Regulation (now Florida Department of Environmental Protection, FDEP), the
legislation provided the funding for construction of a background ground-water well network
statewide. Included within the scope of the mandate are provisions for defining aquifer
systems based on new and existing hydrogeologic data and water quality sampling and
analysis. These monies have allowed state agencies to work on cooperative data acquisition
and analysis projects.
The present study represents a cooperative project between the Florida Geological Survey
(FGS) and the Suwannee River Water Management District (SRWMD) to obtain hydrogeologic
data on the Waccasassa Flats (Flats) in Gilchrist County. Funding was provided through the
Florida Department of Environmental Protection Ground-water Quality Monitoring Program. The
primary purposes are threefold: First, to obtain geologic core data from the Flats and define the
geology of the Waccasassa Flats in light of modern stratigraphic nomenclature. Second, the
project attempted to better delineate the geographic extent of the Flats based on
geomorphology, soils, structure, and topography. Finally, the project provided for the
installation of aquifer monitoring wells to obtain baseline data on ground-water levels and
geochemistry, and to serve as future monitor wells in the Flats area. Such information is vital
to formulating effective ground-water policy, assessing water quality, and understanding the
regional ground-water systems.

LOCATION

The Waccasassa Flats extend from near the Santa Fe River, in north-central Gilchrist
County, Florida, southward to the vicinity of Trenton, then southeastward, terminating in north-
central Levy County (Figure 1). In Gilchrist County, the Flats comprise approximately 102
square miles.
The name Waccasassa Flats first appeared on the 1953 General Highway Map of Gilchrist
County, published by the Florida Department of Transportation (FDOT). Yon and Puri (1962)
attribute the name's origin to Dr. Robert 0. Vernon, at that time State Geologist of Florida, who
suggested it to the FDOT.

WELL NUMBERING SYSTEM

The wells utilized in this study are identified by two well numbering systems: the FGS
accession number, consisting of a "W", a dash, and a one to five digit number unique to each










FLORIDA GEOLOGICAL SURVEY


SUWANNEE
COUNTY

LAFAYETTE
COUNTY







o
^ 4
^ f


SUWANNEE
RIVER
WATER
MANAGEMENT
DISTRICT


GILCHRIST COUNTY


0 50 MILES
0 80 KILOMETERS
SCALE


FGS080197


Figure 1. Location of Study Area.









REPORT OF INVESTIGATION NO. 99


Table 1. Hydrogeologic Sites in Gilchrist County, Florida


SITE NO. FGS NO. WELL ID DATUM AQUIFER ACTIVITY
1 D-3 -071401005 33.45 F 1,2& 5
2 -071515001 85.35 F 1
3 W-16549* -071525001 43.69 F 1, 2, 3, 4 & 5
4 W-16599* -071526001 72.72 F 1, 2, 3 & 5
5 W-16598 -071526002 72.60 S 1, 2, 4 & 5
6 W-16547* -071528001 75.35 F 1,2, 3 & 5
7 -071528002 75.35 S 1, 2, 4 & 5
8 W-16537* -071529003 68.19 F 1, 2,3&5
9 -071529004 69.01 S 1,2& 5
10 -071532001 70.93 F 1
11 -071630002 42.64 F 1, 2 & 5
12 W-16550* -071630004 47.70 F 1, 2, 3, 4 & 5
13 -081412001 83.68 F 1
14 -081416001 37.54 F 1
15 -081425001 67.83 F 1
16 -081513001 67.56 F 1, 2,3& 5
17 W-16604* -081515002 74.61 F 1, 2, 3 & 5
18 -081515003 74.53 S 1,2,4&5
19 -081517003 85.98 S 1, 2, 3, 4 & 5
20 -081518005 69.30 F 1
21 -081535001 84.86 S 1, 2,4 & 5
22 W-16613' -081535002 84.96 F 1, 2, 3 & 5
23 -081536001 82.36 S 1, 2, 4 & 5
24 W-16624* -081536002 83.30 F 1, 2, 3 & 5
25 -081605003 N/A F 3
26 -081618001 63.68 F 1
27 D-28 -081624004 86.48 F 1
28 -081631001 69.03 F 1, 2 & 5
29 W-16636* -081632001 N/A F 3
30 -091420001 34.26 F 1
31 W-16635* -091504001 88.53 F 1, 2, 3&5
32 -091504002 88.12 S 1,2,4& 5
33 -091530005 51.80 F 1,2&5
34 W-16680* -091534001 69.29 F 1, 2, 3 & 5
35 -091534002 67.35 S 1, 2, 4&5
36 -091607001 87.31 F 2
37 W-16646* -091628005 87.72 F 1, 2, 3, 4&5
38 W-318 -101516001 55.74 F 2
39 D-50 -101601002 88.14 F 1, 2&5
40 W-16663 -101634001 69.56 F 1,2,3&5
41 W-16662 -101634002 69.92 S 1,2,4&5
*vf=iroai oL riw luGVD F Flu~am id 4~ if


W#= lithologic log; D = drillers log;
S = surficid aquifer syste n; Activities: 1


UdLUll- 1= VLJ
= Water Quality; 2


r = rlUilu aln4Ulll a y1ICIII
= Ground Water Levels; 3 = Core


4 = Permeability and 5 = Wells constructed.
Wells with after number were drilled during this study.









FLORIDA GEOLOGICAL SURVEY


well, and the SRWMD site identification number, based on township, range and section
information and a unique three digit number. The SRWMD well ID number is a nine digit
code indicating Township, Range, Section and a unique three digit designation for each
well; the negative sign indicates south, e.g., -071401005 =T07S, R14E, section 1, with
005 = the fifth well to be located in the section. This number is used to access well data
in the District database, and is provided in the tables, along with the FGS accession
number, where available. Table 1 provides a summary of the wells used in this study, and
their identification numbers.
Wells are located on maps according to the township, range, and section rectangular
coordinate system. The location coordinates assigned to each well consist of five parts: the
township number, the range number, the section number, and two letters representing the
quarter/quarter location within the section. The basic unit of this coordinate system is the
township, which is six miles square. Townships are numbered consecutively in tiers both north
and south of the Florida Base Line, an east-west survey line passing through Tallahassee. The
township rectangle is also numbered both east and west of the Principle Meridian, a north-
south survey line also passing through Tallahassee. Each township square is equally divided
into 36 one-square-mile pieces called sections. Sections are numbered 1 through 36 in rows
within the section.

METRIC AND VOLUME CONVERSION FACTORS

To prevent duplication of parenthetical conversion of units in the text of reports, the Florida
Geological Survey has adopted the practice of providing a tabular listing of conversion factors.
For those readers who may prefer to use metric units rather than the customary English units,
the conversion factors for terms used are given in Table 2.

Table 2: Metric and Volume Conversion Factors

MULTIPLY BY TO OBTAIN
feet 0.3048 meters
inches 2.540 centimeters
inches 0.0254 meters
miles 1.609 kilometers
sq. miles 2.590 sq. kilometers
gallons 3.785 liters
gallons 0.003785 cubic meters
cubic feet/sec 0.02832 cubic meters/sec
cubic feet/sec 7.481 gallons/sec


METHODS

A series of 16 study well sites were selected in Gilchrist County based on access and
limitations of field time. These wells are situated to provide four east-west transects across
the flats and to augment the existing well network adjacent to the flats. Figure 2 shows all the
study well locations, including previously-existing Ground-water Quality Monitoring Program
wells which were sampled during this study. Table 1 summarizes the location information for
each well. At least one continuous core was drilled at each study site using the FGS drill rig.
Multiple holes were drilled at most sites for installing monitor wells, obtaining additional core,









REPORT OF INVESTIGATION NO. 99


A SUWANNEE COUNTY
-N-


I el


LAFAYETTE















z
o
0
L)
a


COLUMBIA COUNTY


T8S



0


U
-l-
T9S 4







T10S


LEVY COUNTY


* WELL LOCATION


MILES
0 1 2 3 4 5
0 2 4 6
KILOMETERS


FGS080297


Figure 2. Location of Ground-water Monitor Wells in Gilchrist County, Florida.








FLORIDA GEOLOGICAL SURVEY


and for obtaining 1.375-inch diameter, 24-inch long split spoon samples at selected intervals
for sediment permeability studies.
The cores and split spoon samples were boxed on site, and sent to the FGS offices for
lithologic description and coding into a digital geologic database (Well Log Data System Version
2.0, Geologic Information Systems, Inc., Gainesville, FL). A geologic summary for each well
drilled during this study is provided in Appendix I.

Monitor Well Construction

Twenty-three monitor wells were constructed as part of this study to sample ground-
water quality and record ground-water level measurements in Gilchrist County's
Waccasassa Flats. The new monitor wells, which augment an existing county network,
were constructed under SRWMD supervision by the FGS. The boreholes were drilled with
a Failing 1500 drill rig using the mud rotary method. The basic monitor well design (Figure
3) includes a four- inch diameter threaded flush joint Schedule 40 PVC casing (riser) with
centralizers and four- inch diameter, threaded, factory slotted 0.010 inch (#10) Schedule
40 well screen. Well screens were set below the estimated minimum water table. The
screens were filter packed with a clean, well sorted sand. Above the screen, the filter
pack was topped with a bentonite seal. The remaining portion of the annulus, from the
bentonite seal to land surface, was grouted with neat cement. Wells were terminated (as
conditions permitted), with an 18 inch stick-up above land surface and sealed with a
locking cap. Upon completion monitor wells were developed using a combination of surge
block, air blowing, and pump-off methods. Ground-water monitor wells were instrument
leveled to second order of accuracy. Ground-water levels are reported in reference to
National Geodetic Vertical Datum (NGVD). Core samples to describe lithology and
stratigraphic relationships were taken at the new monitor well sites. Split spoon samples
to determine confining bed permeabilities were taken at 12 sites. Monitor well data are
provided in Appendix II.

Water Quality Sampling

Water quality sampling to assess background-water quality conditions was done by
SRWMD in accordance with the Florida Department of Environmental Protection (FDEP)
recommended protocol (Maddox et al., 1993). Water quality laboratory analysis was
performed by FDEP, Tallahassee, and United States Geologic Survey (USGS), Ocala,
Florida. The physical water quality parameters, temperature, specific conductivity and pH
were field measured using a YSI 3500 Water Quality Monitor.

Permeameter Analyses

Falling head permeameter tests were conducted on split-spoon core samples from selected
wells to characterize the hydraulic conductivity of the sediments. The split spoon samples
were taken from selected intervals at 11 of the sites. At all sites sampled, a separate hole was
drilled adjacent to the continuous core hole for recovery of the split spoon samples. The split-
spoon samples were recovered in 1.375-inch diameter clear plastic core tubes, placed inside
the core barrel. The tubes were capped on site and shipped to the FGS lab in a vertical
orientation to minimize sediment disturbance. In the lab, a hacksaw was used to cut one 2-
inch-long segment from each 24-inch tube containing sediment. The portion of original sample
from which the 2-inch segment was taken varied from sample to sample; care was taken to









REPORT OF INVESTIGATION NO. 99


Vented PVC Cap

Protective Steel Casing

Concrete
Pad


. ck


J Two Inch
Neat Grout


Ground Water Level

Centralizer


Bentonite Seal


Four Inch Schedule 40
PVC Riser




Filter Pack





Sediment Trap


Slotted 0.010 PVC
Screen


Not to Scale


FGSO00387


Figure 3. Typical Four-Inch Diameter Schedule 40 PVC Monitor Well









FLORIDA GEOLOGICAL SURVEY


select the least disturbed section of each original split spoon core for sampling. This involved
visual inspection of each section of core tube for defects which would bias the tests (e.g., air
pockets in the sediment, voids, dried or cracked sediment). Polyurethane mesh was placed
over the cut ends of each 2-inch sample to keep the sediment from escaping.
Each cut segment was then placed on a permeameter, and tested for a period of time
sufficient to conduct three falling head permeability tests. Figure 4 illustrates the permeameter
setup used in this study. In each test, the initial head, final head, total elapsed time of test,
volume of sample, volume of water passing through the sample, and water temperature were
measured. Flow data obtained from the permeameters was plugged into a simple FGS
computer program designed to calculate hydrologic conductivity (K), and the resulting
conductivity values for each split spoon sample were tabulated. Table 3 summarizes the
results obtained. Values obtained for the coefficient of hydraulic conductivity give only a
relative measure of sediment permeability. In general, the larger the negative exponent
obtained from testing, the poorer the respective sediments are as an aquifer. Table 4 illustrates
some comparative K values for various soil and rock types.
Hydraulic conductivity values for the tested samples ranged from a low of 1.66(10") cm/s
up to 8.98(104) cm/s, which qualify as poor aquifers. In general, the highest conductivities
occurred in the shallowest sediments. Several of the wells (W-16547, W-16550, and W-
16599) showed a general decrease in conductivity with depth. The lowest conductivity values
were measured in sediments with a high percentage of silt and clay size particles, which lie at
depth in the wells, often directly over the limestone bedrock. No area pattern to the hydraulic
conductivity is apparent.

Sieve Analyses

Sediment grain size analyses were conducted on the unconsolidated sand and clayey sand
portions of each of the 16 continuous cores. Approximately 100 gram samples were taken
from each core at 10-foot intervals. Each of these was then split in half (approximately 50
gram samples). One split set was set aside, and the other used in laboratory analyses.
Samples in the test set were dried slowly at a constant temperature of 35 degrees Celsius
and weighed. Some samples contained organic material; in most, the organic content was
minimal, but was nonetheless effective in causing coagulation of the silt and clay present. All
samples were therefore treated with a hydrogen peroxide bath, which removed organic.
Each sample was then placed in a beaker with a known volume of dispersing agent
(sodium hexametaphosphate) and stirred vigorously in order to disperse the clay fraction and
facilitate wet sieving of the sample to remove the clays. Following this bath, the sample was
run through a 4 phi wet sieve in order to remove the silt and clay fraction.
The screen fraction (greater than 4 phi) was carefully rinsed from the sieve into a beaker
and dried. The weight of this coarse fraction was calculated and subtracted from the total dry
weight of the sample. The resultant loss upon wet sieving was assumed to be the combined
organic, silt and clay weight.
The sand fraction of each sample was placed in a nest of 1/4 phi interval sieves, ranging
from -1.25 phi to 4.00 phi. The stacked sieves were then placed on a Ro-Tap machine for 30
minutes.
Next, the sieves were removed from the Ro-Tap and the individual screens were cleaned.
The weight of the sand fraction on each sieve was measured and recorded. The pan fraction
(that fraction of the coarse sample finer than 4 phi) was saved and added to the beaker which
contained the fine fraction. The totals of both the fine and coarse fractions were then
mathematically adjusted (the pan fraction weight was subtracted from the "coarse" fraction









REPORT OF INVESTIGATION NO. 99


WINGNUT



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FLORIDA GEOLOGICAL SURVEY













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REPORT OF INVESTIGATION NO. 99





Table 4. Average Ranges of Hydraulic Conductivity for Various Geologic Materials
(Adapted from Freeze and Cherry, 1979, and Davis and DeWiest, 1966).


ROCK TYPE








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FLORIDA GEOLOGICAL SURVEY


weight, and added to the "fine" fraction weight). This allowed for a more accurate
representation of the percentage of organic, sand and silt-clay fraction for each sample.
Sieve data were analyzed with GRAN-7, a computer program (designed by Dr. W.F.
Tanner, Florida State University) that calculates mean, standard deviation, skewness, kurtosis,
the fifth and sixth moment measures and relative dispersion. The mean particle size in all
samples studied ranged from very fine sand (3.444 phi) to medium sand (1.728 phi). The
largest grains in most samples were coarse to very coarse sand. Very coarse sand-granule size
grains (-1.00 phi) were present at 130 feet in W-16621. Particle sizes less than 4.0 phi were
also present in all samples tested, in percentages ranging from 0.43 to 42.26 percent. In
general, the samples display an overall decrease in grain size down-hole, with a corresponding
increase in the fines (< 4.00 phi). This is in large part due to the increase in clay content of
the undifferentiated sediments with depth. This fining-downwards correlates well with the
general decrease in hydraulic conductivity with depth observed in the permeameter results
(Table 3). For example, well W-16547 shows an overall increase in percentage of fines down-
hole from 10 to 78-feet deep. Permeameter results from the same well show a down-hole
decrease in average hydraulic conductivity in the samples between 7 and 39 feet; similar
results are observed in the other study wells in which both grain size and permeabilities were
tested.
In an attempt to ascertain the environment of deposition for the undifferentiated sediments
in the Flats, the grain-size results produced by the GRAN-7 program were used in SUITES, a
computer program designed to derive possible paleoenvironments based on sediment grain size
(Tanner, 1991a; 1991b; Balsillie, 1995). This program potentially enables samples to be
placed in a general environmental setting: dune, mature beach, river, settling or closed basin
(lake, lagoon, estuary, etc.), tidal flat and glaciofluvial.
The output from the SUITES program allows broad paleoenvironmental interpretations,
based on given sets of sediment particle size data. Table 5 represents the environmental
summary derived by the SUITES program. Rows with only one "X" give a better indication of


Table 5: Possible Paleoenvironments of the Waccasassa Flats Based on Grain Size Data.


Environment DUNE MATURE RIVER SETTLING TIDAL GLACIO-
BEACH FLAT FLUVIAL
Parameter
Mean of Skewness X X
Mean ofS.D. X X
Variability Diagram X X
Relative Dispersal of Mean
vs. X
Relative Dispersal of S.D.

Mean of the Tail of Fines X
S.D. of the Tail of Fines X
Tail of Fines Diagram X X
S.D. (Skewness) vs.
S.D. (Kurtosis) X
Inverted Relative Dispersal
(Skewness vs. Kurtosis) X









REPORT OF INVESTIGATION NO. 99


the actual environment of deposition, with the tail-of-fines measurement (a plot of the grain
size suite means and standard deviations for grains 4 phi and higher) indicating the last or most
recent agent of transportation. Rows with two" X's" cannot, with any certainty, indicate either
environment of deposition as the correct one. Samples taken from wells drilled in the
Waccasassa Flats region were broadly identified to be from a closed basin or settling
environment with possible river influences.
SUITES also identified dune, mature beach and glaciofluvial as potential environments,
however, the program cannot properly distinguish between the environment of deposition and
environment of source material, (i.e., whether the sample was originally beach, dune or
glaciofluvial material and later placed in a river or settling environment). Also, there were not
sufficient examples of either the surf break or the dune hump to warrant labeling the sediments
beach or dune. The surf break and dune hump are inflections on a probability plot curve that
suggest beach or dune, respectively. A glaciofluvial environment can also be eliminated due to
the extreme southern location of the samples relative to any glacial environments in the recent
or geologic past.

CLIMATE

Gilchrist County's climate is humid subtropical. Summers are hot and humid with winter
temperatures influenced by cold air masses moving into Florida from the interior portion of
the continent. The average annual maximum temperature at the nearest climatological
station (Gainesville, Florida) is 82 degrees F; the average annual minimum temperature is
58 degrees F (Winsberg, 1990).
Precipitation in Gilchrist County is associated with convective and convergent
atmospheric lifting during the warmer months and frontal systems in the winter. Average
rainfall at Trenton, Florida (Figure 5) for the 18 year period January 1976 through
December, 1993 was 61.78 inches. At Trenton, Florida, 56 percent of the average
annual rainfall was recorded between May and September for the period of record.
Rainfall for the three year study period July 1991 through June 1993 at Trenton, Florida,
was 2.58 inches below average.
Annual rainfall for the County was estimated for comparative purposes using the
Thiessen polygon method (Gilman, 1964). The weighted annual average based on 18
years of record from four sites: Trenton, Bell, Forest Grove and High Springs, Florida, is
61.23 inches (Table 6 ).
Departure from mean annual rainfall at Trenton, Florida, for the period 1976 to 1993 is
shown in Figure 6. Graphing departures from the normal or average rainfall for the 18
years of record illustrates wet and dry years.

MODIFIED FUTURE LAND USE

Gilchrist County's modified future land use is shown in Figure 7. Rural residential at
approximately 228 square miles is the predominant future land use. The second largest
land use is agriculture with approximately 90 square miles. Most of the Waccasassa Flats
is in agriculture but there is some rural residential usage. Urban development
(approximately 6 square miles) is generally confined to the communities of Trenton,
Fanning Springs and Bell with some strip development occurring along SR 26.
Conservation and recreation lands (approximately 3 square miles) are located in both the
Suwannee and Santa Fe River corridors with approximately 20 square miles of
environmentally sensitive lands mapped in the riverine flood plains.








FLORIDA GEOLOGICAL SURVEY















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SUrban
[ Rural Residential
[ Agriculture
3 Conservation/Recreation
[ Environmentally Sensitive
SWater MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS

FGS080797


Figure 7. Gilchrist County Modified Future Land Use (Central Florida Regional Planning
Council, 1991a).








FLORIDA GEOLOGICAL SURVEY


GEOLOGY

GEOMORPHOLOGY

The Waccasassa Flats in Gilchrist County (Figure 8) is a 102 square mile mosaic of
sand hills, pine flatwoods, wetlands, cypress ponds and small scattered lakes. The Flats
trend north-south through the center of the County. Dominant vegetation types on the
Flats include deciduous turkey oak (Quercus laevis), loblolly (Pinus taeda), slash (Pinus
elliottii) and long leaf pine (Pinus palustris), cypress (Taxodium), titi (Cyrilla racemiflora),
red maple (Acer rubrum) and sweet gum (Liquidambar styraciflua). The natural habitat
supports white tail deer (Odocoileus virginianus), bobcat (Lynx rufus), raccoon (Procyon
lotor), wild turkey (Meleagris gallopavo), gopher tortoise (Gopherus polyphemus), alligator
(Alligator mississippiensis), water birds such as egrets and herons (Ardeidae) and migratory
fowl such as sandhill cranes (Grus canadensis). The Waccasassa Flats in limited land use
development supports pine plantations, cattle grazing and some row crops (e.g., corn and
watermelons).
The Waccasassa Flats in Gilchrist County (Figure 9) comprise a subzone of the more
extensive Gulf Coastal Lowlands zone of White (1970). This region is characterized by
generally flat to gently rolling terrain that was inundated by transgressive Plio-Pleistocene
seas. Characteristically the Flats terrain consists of Quaternary sand hills underlain by
Eocene carbonates and Plio-Pleistocene siliciclastics. Vernon (1951) described the
Waccasassa Flats as a poorly drained linear feature of approximately 125 square miles
trending north-south from the vicinity of the Santa Fe River in north-central Gilchrist
County, southward to near Trenton, then southeastward into northern Levy County.
Brooks (1981) described the Waccasassa Flats as an area of flatwoods, mostly in Levy
County, that lies at less than 56 feet (MSL) in elevation and features surficial plastic
sediments over limestone. Brooks (1981) termed the area that approximates Vernon's
Waccasassa Flats the Bell Sand Hills and Williford Flats. Rupert (1988) described the
Waccasassa Flats in Gilchrist County as on average about 60 feet in elevation, including
isolated sand hills with elevations between 90 and 100 feet. The overall area was
described as underlain by a structural low filled with Miocene and younger siliciclastics.
The Waccasassa Flats defined here using basic physiographic principles generally
conform to Vernon's (1951) description. These principles (Brooks, 1981) include the
evaluation of: 1) Rock and soil type, 2) Geologic structure of the underlying rock, 3)
Geomorphic processes that constructed or shaped landscape and; 4) Relief. The
Waccasassa Flats were mapped using Geographic Information System (GIS) topographic,
hydrographic and soils databases. As defined and mapped in this study the area of
Waccasassa Flats in Gilchrist County is approximately 65,070 acres or 102 square miles.
Elevation in the Waccasassa Flats is greater than 55 feet (ft.) NGVD except where
karst has apparently lowered the land surface. Several isolated sand hills (possibly relict
marine features associated with the Bell and Brooksville Ridges) reach 90 to 100 feet
NGVD. The Flats are bounded on the east by the Central'Highlands. This zone is locally
subdivided into two features, the Brooksville Ridge and the High Springs Gap. The
northern terminus of the Brooksville Ridge borders the east-central and southeastern edges
of the Flats. The ridge is composed primarily of Pleistocene sediments resting on Eocene
limestone. Land surface elevations on the crest of the ridge are about 100 feet NGVD. A
distinct erosional escarpment at approximately 70 to 75 ft. NGVD is the line of
demarcation between the Waccasassa Flats and the Brooksville Ridge. The escarpment
has been extensively modified by dissolution of the underlying limestone in the










REPORT OF INVESTIGATION NO. 99


SUWANNEE COUNTY





LAFAYETTE COUNTY .A


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FGS080897


SCOLUMBIA COUNTY







47





T8S


LEVY COUNTY


Waccasassa Flats


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TIOS
T10S


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( STATE/COUNTY ROAD



Figure 8. Location of Waccasassa Flats in Gilchrist County, Florida.


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS







FLORIDA GEOLOGICAL SURVEY


SUWANNEE COUNTY


.- COLUMBIA COUNTY
'


LAFAYETTE


-N-t

I


TOWN
ESTATE ROAD
GEOMORPHIC ZONES
CENTRAL HIGHLANDS GULF COASTAL LOWLANDS
BROOKSVILLE RIDGE W WACCASASSA FLATS
HIGH SPRINGS GAP 3 BELL RIDGE
MILES CHIEFLAND LIMESTONE PLAIN
01 2 3 4 5 SANTA FE RIVER VALLEY LOWLANDS
0 2 4 6 SUWANNEE RIVER VALLEY LOWLANDS
KILOMETERS
FGS080997

Figure 9. Geomorphology of Gilchrist County, Florida (after White, 1970).








REPORT OF INVESTIGATION NO. 99


south-central portion of the Flats. The High Springs Gap, a topographic lowland at the
northern terminus of the Brooksville Ridge, borders the northeastern edge of the
Waccasassa Flats. The western edge of the Flats is bounded by flat sandy terrain,
underlain by highly karstic Eocene limestone. Vernon (1951) named this feature the
Chiefland Limestone Plain. Surficial sediments in the plain generally consist of well drained
Pleistocene sands averaging less than 20 feet in thickness. The land surface is gently
rolling terrain with elevations from 25 to approximately 65 feet NGVD.
In the Waccasassa Flats, surface water (Figure 10) occurs in wetlands, in isolated
lakes in the interior and in lakes along the outer margins of the Flats. There are small
intermittent creeks associated with Lakes Joppa and Jennings, but there are no perennial
streams in the Waccasassa Flats. Cow Creek and other small streams in northern Gilchrist
County occur at elevations equal to or less than 60 ft. NGVD. These streams are not
considered features per se of the Waccasassa Flats. Rainfall on the Flats may evaporate,
be transpired by plants, or locally recharge the Surficial aquifer system. During periods of
high ground-water levels and/or when rainfall rates are too high for soil infiltration, sheet
flow runoff occurs. Sheet flow may move laterally across the Flats until intercepted by
surface water features and/or karst depressions. Depressions on the margins of the Flats
serve as sinking points for runoff recharging the Floridan aquifer system.
The origin of the Waccasassa Flats has been a source of speculation. The name
Waccasassa is from the Creek American Indian language (Simpson, 1956). In Creek,
wakka = cow or cattle and sase = there are; which roughly translates to "cow range".
Vernon (1951) proposed that the broad valley of the Flats represents a former stream course,
which was beheaded by stream capture; Vernon believed that Cow Creek at the northern end,
and the Waccasassa River at the southern end of the Flats, may be remnants of the former
large stream which once traversed the area. He also cited the presence of what he termed
deltaic sediments, at the southern end of the flats in central Levy County, as further evidence
for the existence of a larger paleo-stream emptying out of the Flats. Clayey sediments
deposited by such a stream would thus be responsible for shielding the underlying carbonates
from dissolution and supporting the generally swampy, standing water conditions within the
flats.
Yon and Puri (1962) and Puri et al. (1967) conducted detailed studies of the Waccasassa
Flats area, and based on adjacent topographic features, concluded the flats were marine in
origin. They hypothesized the following paleoenvironmental scenario: the escarpment
extending along the western edge of the Brooksville Ridge was the paleo-shoreline during
Waccasassa Flats deposition time (probably Pleistocene Penholoway sea based on elevation);
the remnant sand features associated with the Bell Ridge were likely once offshore barrier
islands lying to the west, and the siliciclastic sediments comprising the Flats were deposited in
a low energy setting between these barrier islands and the mainland paleo-shoreline.
As part of their studies, Yon and Puri (1962) and Puri et al. (1967) conducted a series of
auger-hole transects across the flats, and constructed several stratigraphic cross sections in
Gilchrist County. These authors concluded that a graben was present under the southern
portion of the Flats, which was filled with low-permeability Miocene and Pliocene siliciclastic
sediments. These sediments, they believed, retarded downward percolation, minimizing karst
dissolutional lowering and creating swampy conditions within the Flats area.
The present study, with its relatively wide well spacing, could not confirm the presence of
a graben under the Flats. Geologic cross sections numbers one and four (Figures 13 and 16)
indicate a possible elevational low in the top of the underlying limestone under the south central
portion of the Flats. Whether the lower surface is actually the result of a structural feature, or
simply reflects drilling in paleokarst features, cannot be determined from the available data.









FLORIDA GEOLOGICAL SURVEY


EXPLANATION

A SPRINGS
1 Pleasant Grove
2 Townsend
3 Siphon Creek Rise
4 Ginnie Springs Complex
Ginnie Spring
Deer Spring
Devils Eye
Dogwood Spring
Twin Spring
5 Blue
6 Lilly
7 Rock Bluff
8 Lumber Camp
9 Sun
10- Hart
11- Otter
12- Bell

OTHER SURFACE FEATURES


13-
14-
15-
16-
17-
18-
19-
20-
21-
22-
23-
24-


Bagget Lake
Cow Creek at CR138
Cow Creek at CR340
Dinner Pond
Fourmile Lake
Franklin Sink
Jennings Lake
Joppa Lake
Waccasassa Lake
Sevenmile Lake
Threemile Lake
Waters Lake


LEVY COUNTY


BASINS

SSanta Fe River Basin

l Suwannee River Basin

Wacasassa River Basin

FGS081097


Figure 10. Hydrologic Basins and Location of Surface Water Features in
Florida.


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MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS

U.S. HIGHWAY

STATE/COUNTY
ROAD
H TOWN



Gilchrist County,









REPORT OF INVESTIGATION NO. 99


Sediment size analyses conducted during the course of this study suggest the plastic
sediments underlying the flats were deposited in quiet water conditions. Mean sediment
particle size in the study well intervals tested ranged from fine sand (3.44 phi) to medium sand
(1.73 phi). The samples also display an overall decrease in grain size down-hole, with a
corresponding increase in clay-size sediments. Such clays are typically deposited under low-
energy conditions which, in Florida, could include streams and marine embayments.
An attempt was made in the present study to identify the origin of the Waccasassa Fats.
Paleoenvironmental analyses of selected intervals in the study cores, using the SUITES
computer program, broadly identified the sediment regime of the Waccasassa Flats to be from
a closed basin or settling environment with possible fluvial influences (Table 5). Other possible
environments derived from the data include dune, mature beach, and glaciofluvial; the latter
possibility can be disregarded due to the lack of glacial activity in Florida. As shown on Table
5, seven of the parameters indicate a quiet, settling environment and three parameters suggest
a fluvial component. Only one example each of dune and beach environment was found,
strongly suggesting that the latter were not the predominant paleoenvironments. Since the
SUITES program looks only at grain size parameters, it cannot distinguish between the
environment of deposition and the environment of the source material; at least some of the
marine paleoenvironments identified on Table 5 may represent reworked material originally
eroded from dune or beach deposits and transported into the area.
An important consideration in this analysis is the time-transgressive nature of the sampling
method. Each core selected for grain size analyses was sampled at approximately 10-foot
intervals down-hole, with each sample representing a different period of Quaternary time. It is
possible that the area of the modem Flats was influenced by more than one paleoenvironment
during the time span represented in these samples. High-standing Pleistocene seas likely
flooded the region, at least sporadically, during the Pleistocene interglacials, as Yon and Pui
(1962) suggested. However, no data exists to rule out Vernon's (1951) paleostream scenario
as at least a contributing factor to the local sediment column. Perhaps a continuous stream
connecting Cow Creek on the north and the Waccasassa River on the south once flowed
through the Flats during a Pleistocene sea level lowstand. As later Pleistocene seas
transgressed over the region, the precursor Waccasassa River was inundated and Cow Creek
flowed into the resulting marine embayment from the north. Subsequently, perhaps through
sediment infilling, the connection between the two streams was destroyed, leaving the two
distinct overland streams we see today. Such a multi-phase concept for the evolution of the
Flats cannot be proven or discredited with the existing data. However, since both fluvial and
marine paleoenvironments remain as possibilities, neither can be completely eliminated as the
possible origin of the surficial sediments in the Flats.

STRATIGRAPHY

The oldest rocks penetrated by drilling in Gilchrist County are Lower Ordovician sandstones
and shales, generally occurring at depths in excess of 3,400 feet below land surface (Puri et
al., 1967; J. Duncan, personal communication, 1997). These sediments are in turn overlain by
approximately 2,000 feet of Mesozoic Erathem marine sands, shales and carbonates (Applin
and Applin, 1944; Vernon, 1951; Puri et al., 1967). The majority of the overlying Cenozoic
sediments are comprised of marine limestones and dolostones. These carbonates are locally
overlain by marine and terrestrial siliciclastic sediments, which generally average less than 50-
feet thick.
The Eocene limestones and dolostones are important freshwater bearing units, and
comprise the Floridan aquifer system. Most local wells draw from these units from depths of








FLORIDA GEOLOGICAL SURVEY


less than 200 feet below land surface. For the purposes of this report, the following discussion
of the geology and hydrogeology of the Waccasassa Flats area will be restricted to these
important Eocene and younger units.
Figure 11 is a geologic map of Gilchrist County, showing the mappable stratigraphic units
at or within 20 feet of the surface. The predominant near surface units are Eocene Ocala
Limestone, weathered Miocene-Pliocene siliciclastics, and Quaternary undifferentiated
sediments. Shallow, karstic, Eocene limestone occurs under the High Springs Gap and undel
the karst plain region west of the Waccasassa Flats. Quaternary sediments, composed largely
of undifferentiated quartz sands, clayey sands, and sporadic, thin, clay beds, overlie most oi
Gilchrist County. The thickest Quaternary sediments (>20 feet) occur in the Waccasassa
Flats and in a series of sand hills situated in the High Springs Gap. The core of the Brooksville
Ridge is comprised of weathered, highly leached Miocene-Pliocene sands and clayey sands,
resting on Eocene limestone.
Figures 12 17 depict a series of hydrogeologic cross sections through the Waccasassa
Flats, illustrating the shallow stratigraphy. Cores recovered during the course of this study
(Appendix I) were used along with other water well data in Gilchrist County to construct the
geologic cross-sections.

Middle Eocene Series
Avon Park Formation

The oldest rock unit locally penetrated by water wells is the Middle Eocene Avon Park
Formation (Applin and Applin, 1944; Miller, 1986). The lithology of the Avon Park Formation in
the study area is typically a light yellowish-gray to yellowish olive-gray to light gray dolostone.
It generally has a muddy appearance to the matrix, which differentiates the Avon Park from the
more skeletal framework and calcirudite matrix of the overlying Ocala Limestone. Fossils,
when present, consist of recrystallized miliolid foraminifera and rare mollusks and echinoids.
Several cores contained peat-like organic flecks, and one core (W-16547) contained what
appeared to be a terrestrial tree or possibly mangrove leaf impression and Lepidodendron
seagrass leaf impressions. The porosity is largely moldic.
The top of the Avon Park Formation is typically irregular due to karstification. Gilchrist
County lies over the eastern flank of the Ocala Platform, a structural high in post-Paleocene
sediments which brings the Avon Park sediments to anomalously shallow depths relative to the
rest of the state. Cores taken during this study encountered the top of Avon Park Formation
sediments at depths ranging from 114.5 feet below land surface (W-16636) in the
Waccasassa Flats in southern Gilchrist County, to 183 feet below land surface (W-16680) just
west of the flats in the northwestern part of the county.
The Avon Park Formation is a unit within the Floridan aquifer system. It is unconformably
overlain by sediments of the Upper Eocene Ocala Limestone. Near the Avon Park Formation -
Ocala Limestone contact, there is commonly a mixing of the two lithologies, with Ocala
Limestone material filling what were probably voids and cavities in the surface of the Avon
Park Formation.

Upper Eocene Series
Ocala Limestone

The Ocala Limestone (Dall and Harris, 1892) is a biogenic marine limestone comprised
largely of foraminifera and whole and broken fragments of molluscs, echinoids, and bryozoans.
It is informally subdivided into upper and lower units based primarily on lithologic differences
(Scott et al., 1991); the upper unit characteristically is a packstone to wackestone, comprised










REPORT OF INVESTIGATION NO. 99


-N- SUWANNEE COUNTY


NY

LAFAYETTE COUNTY Trn


EXPLANATION

QUATERNARY
Qu- UNDIFFERENTIATED SURFICIAL SANDS,
CLAYEY SANDS, CLAYS, AND PEATS >20
FEET THICK. NO FORMATIONS RECOGNIZED.
TERTIARY
To- OCALA LIMESTONE. WHITE TO GRAY,
FOSSILIFEROUS. MOLDIC LIMESTONE.
VARIABLE FROM PACKSTONE TO GRAINSTONE.
Twh- WEATHERED HAWTHORN GROUP SEDIMENTS,
HIGHLY LEACHED SANDS AND CLAYEY SANDS
OF THE BROOKSVILLE RIDGE.


COLUMBIA COUNTY


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS

i TOWN


ESTATE / COUNTY ROAD

FGS081197


Figure 11. Geologic Map of Gilchrist County, Florida (from Rupert and Campbell, 1993).








FLORIDA GEOLOGICAL SURVEY


k SUWANNEE COUNTY
-N-

E C Y
LAFAYETTE COUNTY A


COLUMBIA COUNTY
- .COLUMBIA COUNTY


7 WELL LOCATION AND NUMBER MILES
0 1 2 34 5
CROSS SECTION LOCATION
0 2 4 6
Wells Identified with a one or two digit number are keyed to
text Figure 2 and Table 1. Auxilllary wells and KILOMETERS
driller's logs used to construct sections are
Identified by the FGS accession number (W-) and
"0-" numbers, respectively. FGS081297




Figure 12. Hydrogeologic Cross Section Location Map.











REPORT OF INVESTIGATION NO. 99


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FLORIDA GEOLOGICAL SURVEY


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VERTICAL EXAGGERATION IS 200 TIMES TRUE SCALE.


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FGS081497


Figure 14. Hydrogeologic Cross Section B B'.


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REPORT OF INVESTIGATION NO. 99


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FOSOuIS7


Figure 15. Hydrogeologic Cross Section C C'.


C
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FLORIDA GEOLOGICAL SURVEY


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VERTICAL EXAGGERATION IS 200 TIMES TRUE SCALE.


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Figure 16. Hydrogeologic Cross Section D -D'.





















30


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REPORT OF INVESTIGATION NO. 99


E
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Mus VERTICAL XAGGERATION IS 200 TIMES TRUE SCALE.
o i


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Figure 17. Hydrogeologic Cross Section E E'.


w a
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30 -100

-80
20-
S60

-40
10-
-20

0--0
NGVD
--20
-10 -
-40








FLORIDA GEOLOGICAL SURVEY


of large foraminifera commonly attaining 0.25 to 0.5 inch in diameter, bryozoans, and
echinoids. The lower unit contains fewer large skeletal fragments, and is generally a grainstone
composed primarily of miliolids and other small foraminifera, bryozoans, and molluscs. It is
often dolomitized. Differentiating the two units is generally based on the grain size differences.
The Ocala Limestone underlies all of Gilchrist County, and is the uppermost limestone of
the Floridan aquifer system. Figure 18 illustrates the top of the Floridan aquifer system in
Gilchrist County.
In the study cores, the Ocala sediments were altered to various degrees by groundwater.
Coloration varied from white to gray to tan. The state of preservation varied from highly
recrystallized, to rotten, crumbly, marl-like material, to relatively well preserved limestone or
dolomitic limestone. In some cases, picking specific units was difficult, and subjective at best.
For the purposes of this study, the Upper Eocene sediments were simply categorized as Ocala
Limestone.
The study cores penetrated the top of the Ocala Limestone at depths ranging from 10.7
feet below land surface (W-16636, north of the town of Bell and just west of the flats) to
103.3 feet below land surface (W-16680, in the southern part of the flats). One well (W-
16621, located in the central part of the flats) drilled 247 feet of undifferentiated sediments
without reaching the top of Ocala; this anomalous well may have been drilled in a
paleosinkhole.
In the study area, the lithology of the Ocala Limestone is typically a white to very light
orange to yellowish-gray skeletal limestone. Portions of some cores are dolomitized, but the
Ocala is generally less recrystallized and less indurated than the underlying Avon Park
Formation. The Ocala is also easily differentiated from the Avon Park by its distinct fossil
assemblage, particularly the presence of the large foraminifera Lepidocyclina and Nummulites,
and by the pelecypod Amusium ocalanum. It is generally a very porous unit, characteristically
exhibiting extensive secondary porosity, and makes an excellent aquifer rock.
The top of the Ocala is regionally high under the Waccasassa Flats due to the structural
influence of the Ocala Platform. In addition, the surface of the unit is highly karstified, with
numerous sinks and other dissolution features. These dissolution features undoubtedly account
for, at least in part, the wide variation in depth to the top of the unit. The Ocala Limestone
appears to dip to the southeast in the study area, deepening under southern Gilchrist County.
Puri et al. (1967) attributed this southward dip to the presence of a graben in northern Levy
County. No direct evidence for such a graben was observed in the present study. Without a
more extensive drilling program, it would be difficult to ascertain if the southeastward dip is
real or due simply to drilling in paleosinks. The Ocala Limestone is unconformably overlain by
Pliocene to Holocene undifferentiated siliciclastic sediments.

Pliocene to Holocene Series
Undifferentiated sands and clays

The surficial sediments in the Waccasassa Flats are composed of a variably thick sequence
of white to gray to brown, fine to medium grained quartz sands, clayey sands, typically
containing 2 to 40 percent clay, and sandy clays, containing up to 15 percent quartz sand.
Portions of these sediments may represent reworked Miocene material from the Brooksville
Ridge immediately to the east. Figure 19 is an isopach map of the undifferentiated sands and
clays in Gilchrist County, combining data obtained in the present study with older data on file at
the Florida Geological Survey. They generally thicken under the Waccasassa Flats in
southeastern Gilchrist County, corresponding to the structural low in that area. The thinnest










Report of Investigation No. 99
REAPPRAISAL OF THE GEOLOGY AND HYDROGEOLOGY
OF GILCHRIST COUNTY, FLORIDA, WITH
EMPHASIS ON THE WACCASASSA FLATS

ERRATA

This figure replaces Figure 18 on page 33.


CONTOUR LINE (RELATIVE TO NGVD) -20'

CONTOUR INTERVAL = 10 FT


WELL NUMBER, DATA POINT
AND WELL LOCATION


15890
20


MILES
0 1 2 3 4 5
0 2 4 6
KILOMETERS


Figure 18. Top of the Floridan Aquifer System in Gilchrist County, Florida.









FLORIDA GEOLOGICAL SURVEY


CONTOUR LINE MILES

CONTOUR INTERVAL = 10 FT 4
0 24 6
WELL NUMBER, DATA POINT 1890 KILOETERS
AND WELL LOCATION
FMmS1,S7


Figre 19. Isopach of UndSffetentated Sands and Clays Unit. Gichdst County. Florida.








REPORT OF INVESTIGATION NO. 99


areas occur over the flank of the Ocala Platform in the southwestern part of the county, and
along the Santa Fe River in northeastern part of the county. Some of the anomalously thick or
thin "islands" on the map may be wells drilled in local karst features such as sinks or pinnacles.
The undifferentiated sediments typically contain organic material, but no fossils were
observed in the study cores. Presumably, these sediments have been in situ since the time of
formation of the Flats, and represent the paleoenvironment in which the area developed.
Unfortunately, without dateable or diagnostic fossil material, the age and origin of the surficial
sediments remain a subject of debate. Puri et al. (1967) called portions of these sediments
"Alachua formation", an informal term for generally sandy, phosphatic clays thought to be
reworked Hawthorn Group sediments (Scott, 1988). Although Alachua formation lithologies
occur to the east in Alachua County, and may be present in the Waccasassa Flats as fill
material in paleokarst features, none was observed in the 16 study cores.

SOILS

Soils in the Waccasassa Flats (Figure 20), belong mostly in Hydrologic Groups D and
Group C (USDA, 1992). Group D soils are clayey, characterized by very slow infiltration
rates, have a high water table or are shallow to an impervious layer. Hydrologic Group C
soils are characterized by slow infiltration rates, have sediment layers that impede the
downward movement of water or moderately fine to fine textures. Group A soils are a
minor constituent of the soil profile in the Flats. Group A soils are deep, well drained to
excessively drained sands that have high infiltration rates even when wet (USDA,1992).
In the Flats the soils and underlying unconsolidated sediments support a surficial water
table aquifer. These surficial sediments also serve as a semiconfining unit for the
underlying FAS. Outside the Flats, Hydrologic Group A is the dominant soil type in the
county.

HYDROGEOLOGY

There are two aquifer systems in Gilchrist County: the ubiquitous Floridan aquifer
system (FAS) and a limited surficial aquifer system (SAS). These aquifer systems are
defined by geology, ground-water levels and ground-water chemistry. The principal
ground-water resource in the County is the Floridan aquifer system, a notably thick
sequence of prolific water-bearing Eocene age carbonate rocks. The FAS is unconfined
and the sole source of groundwater everywhere in the County except in the Waccasassa
Flats. In the Flats, the FAS, while still the principal ground-water resource, is semiconfined
below a surficial water table aquifer. Where both aquifers occur the potentiometric
surface of the FAS is generally lower in elevation than the overlying SAS. Water quality of
the FAS is alkaline with a high specific conductance and high dissolved solids content.
Unconsolidated sands and clays provide the framework for the surficial aquifer system.
The SAS is limited both in extent and availability of ground-water supplies. The water
quality of the SAS is generally acidic with low specific conductance and low dissolved
solids content.








FLORIDA GEOLOGICAL SURVEY


Explanation
MILES
ii: Hydrologic Group A, 1 2 3 4 5
SHigh Filtration Rates.
0 2 4 6
W Hydrologic Group B, KILOMETERS
Moderate Filtration Rates.
FGS082097
Hydrologic Group C,
Slow Filtration Rates.
W Hydrologic Group D,
Very Slow Filtration Rates.


Figure 20. Soils Map of Gilchrist County, Florida (modified from U.S.D.A., 1992).








REPORT OF INVESTIGATION NO. 99


SURFICIAL AQUIFER SYSTEM

Extent

In the Waccasassa Flats unconsolidated sands and clays provide the geologic
framework for a surficial water table aquifer. These sediments also semiconfine the
underlying Floridan aquifer system (FAS). In addition to geology the surficial aquifer
system is defined by ground-water levels, which fluctuate under atmospheric conditions,
and ground-water quality. The thickness of the unconsolidated sediments based on well
logs and core samples ranges from 30 ft to 103 ft. The appreciable range in thickness of
the undifferentiated sediments underscores the vagaries of weathering. Infilling of
solutional features in the carbonate rock probably accounts for some of the thicker
sequences of unconsolidated sediments sampled (e.g., W- 16621 near site no. 24 and
W-16680 at site no. 34; Appendix I).

Hydraulic Conductivity

Permeability testing on select intervals in the unconsolidated sediments demonstrated
a wide range of hydraulic conductivity (Table 3). Surficial sediments range from medium
sands to clay (and include admixtures) which promote anisotropic vertical permeability. In
general, hydraulic conductivity appears to decrease (from 1.74 ft/day to very low or no
permeability) with depth in the surficial system. Core data show that clay(s) occur at
variable depths as stringers, in thin beds and as a matrix component in coarser sediments.
A vertically extensive or horizontally persistent confining unit does not appear to be
present in the Waccasassa Flats. The relatively lower hydraulic conductivity of the
variable surficial sediments serves to semi-confine the underlying FAS.

Ground-water Levels

The surficial water table, under atmospheric pressure, fluctuates in response to
rainfall, runoff, evapotranspiration and leakage to the underlying FAS. The water table
ranges from at or near land surface to 15 feet below land surface. Because of a high
water table, extensive wetlands and poorly developed drainage patterns,
evapotranspiration is high on the Flats. Ground-water levels were monitored in 10
surficial water table wells between July 1991 and June 1993 (Appendix III and SRWMD
1993 a). Fluctuations in the surficial aquifer system for the period ranged from three to
seven feet. The greatest fluctuation recorded was near Sevenmile Lake (Figure 10) on the
northwest margin of the Waccasassa Flats. The highest water table levels were recorded
in an area of topographic highs at site 32 (Figure 21). Figures 22-25 show the water table
and the potentiometric surface in close proximity. The greatest difference recorded
between the water table and the potentiometric surface of the FAS was 3.49 ft (site nos.
8 and 9, Figure 24). In some wells the potentiometric surface may be slightly higher than
the water table. The consistent relatively small differences in elevation between the
surficial water table aquifer and the potentiometric surface of the FAS coupled with the
reversal of the hydraulic gradient in some wells underscores the potential for hydraulic
communication between aquifers. Water quality data (Appendix IV and SRWMD,1993b)
also suggests that mixing of the aquifer systems may occur at some sites.










FLORIDA GEOLOGICAL SURVEY


t SUWANNEE COUNTY
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MILES
0 1 2 3 4 5

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FGS082197


Figure 21. Surficial Aquifer System Ground-water Levels Network, Gilchrist County, Florida.









REPORT OF INVESTIGATION NO. 99


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REPORT OF INVESTIGATION NO. 99


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REPORT OF INVESTIGATION NO. 99


Ground-water Quality

In 1983 the Florida Legislature passed the Water Quality Assurance Act (403.063 FS)
which in part mandated that the FDER (now FDEP), in cooperation with other agencies,
establish a ground-water quality monitor network designed to detect or predict
contamination of the ground-water resources of the state. The Background Monitor
Network (BN) in Gilchrist County, Florida, is part of the DEP/SRWMD Ground-water Quality
Monitor Program (GWQMP). A BN well is designed to monitor an area of the aquifer which
is representative of the general ground-water quality of the region (Maddox et al., 1993).
The objectives of the Background Network are to:

1. Define areas of the state where background ground-water quality conditions
currently exist.
2. Define current background ground-water quality of Florida's major aquifers.
3. Determine how background ground-water quality varies over time.
4. Determine the natural, cyclic fluctuations in background ground-water quality.

Ground-water quality was sampled at 29 sites (Figure 26), including 10 surficial
aquifer system wells, in Gilchrist County as part of the Background GWQMP. The results
are only representative of the aquifer at the time and place of sampling; the data cannot be
used to forecast trends or interpret seasonal variability. Three episodes of ground-water
quality sampling (December 1991, February 1992, and June 1992), combined to complete
the initial round of background sampling in Gilchrist County. The parameters sampled
(Table 7) included temperature, pH, specific conductance, turbidity, major ions, trace
metals and organic. Descriptive statistics, including maximum value, minimum value,
median, and standard deviation are grouped by aquifer in Appendix IV A. There are no
statistics shown for organic, pesticides and the metals barium, cadmium, chromium and
mercury because constituent values were below detection limits (BDL).
Surficial aquifer system water quality is highly variable but, in general may be
characterized as low in pH and specific conductance but, with notable chloride values.
Both variability and similarity between aquifers may be shown by comparing maximum,
minimum and median values of select parameters (Figure 27). A Piper trilinear diagram and
associated Stiff diagrams (Figure 28) show basic water types and variability of the surficial
aquifer system. The Piper trilinear diagram employs two triangular fields and a related
diamond field (Davis & DeWiest, 1966). The two triangular fields illustrate the various
percentages of anions and cations. A combined position of all major ions is represented in
the diamond field. Percentages of anions and cations are based on total equivalents per
million of major ions. Trilinear diagrams show differences or similarities of waters and can
also show the effects of mixing between waters. The Stiff graphical method uses four
parallel horizontal axes and one vertical axis to make comparisons of waters (Walton,
1970). With concentrations expressed in equivalents per million, four cations are plotted
along each axis to the left of the zero point and four anions to the right. A closed pattern
results when connecting points representing anions and cations are joined. The patterned
shape is representative or characteristic of a specific water. Predominant water types are
illustrated in Figure 29. These types run the gamut from Al (calcium bicarbonate) to E5
(sodium chloride). The variability of the data is a reflection of the influence of rainfall,
time in residence, mixing with FAS waters and land use. Low total dissolved solids which
are common in the surficial aquifer system are indicated by narrow Stiff diagrams
(Upchurch, 1990). Diagrams for sites 5 and 7 (Figure 28) indicate higher









FLORIDA GEOLOGICAL SURVEY


SUWANNEE COUNTY


COLUMBIA COUNTY


LAFAYETTE


9
* WELL LOCATION AND NUMBER


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS


FGS082697


Figure 26. Ground-water Quality Network, Gilchrist County. Florida.










REPORT OF INVESTIGATION NO. 99


Table 7. Background Ground-water Quality Parameters


Field
Parameters

Conductance

pH

Temperature


Water Levels


Major Ions,


Bicarbonate

Carbonate

Chloride


Fluoride

Nitrate

Phosphate

Sulfate


Metals


Arsenic

Barium

Cadmium


Calcium

Chromium

Copper

Iron

Lead

Magnesium

Manganese

Mercury

Nickel

Potassium

Selenium

Strontium

Silver

Sodium

Zinc


Organics & Ot
Pesticides

Total Organic Carbon Hai

Volatile Organic Carbon Alk

Aldicarb & related Sili
compounds
Tur
Purgeable Halocarbons

Purgeable Aromatics

Pesticides

PCBs, Chlorinated Pesticides

Organophosphate Pesticides

Mixed Purgeables

Base/Neutral/Acid Extract

Carbamate Pesticides

Herbicides

Fumigant Pesticides


hers


rdness

alinity

ca

bidity


The parameter units are: Temperature (degrees celsius), conductance (micromho), trace metals and organic (micrograms per
liter), turbidity (ntu), all others (milligrams per liter).









FLORIDA GEOLOGICAL SURVEY


Specific. .
Conductance
micromhos/cm 0 50 100 150 200 250 300 350 400 450 500 550 600

pH -- -

pH unlts 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10

Alkalinity -- -

mg/I 0 25 50 75 100 125 150 175 200 225 250 275 300

Ca -

mg/I 0 10 20 30 40 50 60 70 80 90 100 110 120


Mg ,

mg/I 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
L.
a

E
o mg/I 0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
1D-
II

No t-ttl i

mg/I 1 1.7 2.4 3.1 3.8 4.5 5.2 5.9 6.6 7.3 8.0 8.7 9.4


P04CI



PO, +- -
mg/I 0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4


Si _
S

mg/I 0 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0 13.5 15.0 16.5 18.0


MIN MEDIAN MAX
I CONFINED FLORIDAN AQUIFER SYSTEM
(9 samples)
- UNCONFINED FLORIDAN AQUIFER SYSTEM
(10 samples)
SURFICIAL AQUIFER SYSTEM (10 samples)

F0S012717

Figure 27. Range and Median of Select Water Quality Parameters.












REPORT OF INVESTIGATION NO. 99


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REPORT OF INVESTIGATION NO. 99


total dissolved solids which may be due to mixing with FAS waters. At sites 5 and 7 the
values for specific conductance (142 and 98 umhos/cm) and alkalinity (74 and 27 mg/I)
were significantly higher than median values (51.5 umhos and 7.5 mg/I). At sites 5 and 9
(Figure 26) hardness (79 and 57 mg/I) and calcium (30 and 21 mg/I) were higher than the
respective medians (11.95 and 3.05 mg/I). Ground-water levels in the SAS and FAS at
these sites (Figures 22-25 and SRWMD, 1993a) appear conducive to mixing.
Overall, the variability shown in the surficial aquifer system ground-water chemistry is
probably due to natural conditions. The exception is site 41 (Figure 26) which is nested in
an area used to temporarily hold and feed cattle. At this site values for turbidity (50 NTU),
specific conductance (96 umhos/cm), sodium (7.5 mg/I) and chlorides (20 mg/I) suggest
an anthropogenic influence.

Ground-water Drinking Water Standards

The State of Florida has established Maximum Contaminant Levels (MCL) and
recommended guidance concentrations for certain water quality parameters in
groundwater. These water quality parameters are governed under Primary and Secondary
Drinking Water Standards (FDEP, 1993). Primary standards are designed to protect the
health of the consumer. Secondary standards govern the aesthetics: odor, taste and color.
During testing of background ground-water quality in Gilchrist County some primary and
secondary standards were exceeded. However, while time and lab constraints prohibited
resampling for confirmation at sites where samples exceeded water quality standards it is
nevertheless considered that in general, background ground-water quality in the County is
good.

Exceedance of Primary Drinking Water Standards

The primary ground-water drinking water standard for turbidity is one National
Turbidity Unit (NTU). The standard for turbidity was exceeded in eight of 10 Surficial
aquifer system samples (Appendix IV B and SRWMD, 1993b). Turbidity may be caused by
suspended clay, silt, and organic matter including bacteria. Turbidity typically results from
poor well development, problems with the pressure tank, or from microorganisms in the
water. Turbidity may also result when using the bailer method to sample. Turbidity per se
is probably not a health problem. But, health can be an issue because turbidity may mask
bacterial contamination.

Exceedance of Secondary Drinking Water Standards

In the surficial aquifer system, MCL for secondary drinking water standards were
exceeded for pH and iron. Secondary ground-water drinking water standards for pH range
from 6.5 to 8.5. All Surficial aquifer system samples had pH values below the minimum
6.5. The variable pH reflects the potential for acid-base reactions in water (Upchurch,
1990); in siliciclastic surficial aquifers, the range of pH may be 3 to 5 due to the natural
presence of carbonic and organic acids (Maddox et al., 1993).
Iron is a natural constituent of groundwater. The secondary drinking water standard
for iron is 0.3 mg/l. Six of the 10 surficial samples (Appendix IV B and SRWMD, 1993b)
had exceedances for iron. Iron in groundwater can impart objectionable color and taste
and stain porcelain fixtures. Iron in groundwater can also be a source of turbidity.









FLORIDA GEOLOGICAL SURVEY


Development

Surficial aquifer system water use is naturally restricted to the Waccasassa Flats. The
surficial system can support domestic and associated miscellaneous uses which withdraw
water from small diameter (2 to 4 inch) shallow wells with low yields. Surficial aquifer
system water use is estimated to be insignificant based on the limited supplies available,
locally sparse population and the ready availability of the FAS.

FLORIDAN AQUIFER SYSTEM

Extent

Floridan aquifer was the name given by Parker et al. (1955) to a thick sequence of
water-bearing, Eocene to Oligocene age carbonate rocks that underlie Florida and adjacent
portions of the southeastern coastal plain. This name has since been modified to Floridan
aquifer system (FAS) (Southeastern Geological Society, 1986). East and west of the
Waccasassa Flats in Gilchrist County the FAS is under water table conditions. In the
Waccasassa Flats the aquifer is semi-confined under pressure by an overlying surficial
aquifer system. The estimated thickness of the potable water zone in the FAS in Gilchrist
County ranges from 550 feet to over 750 feet (Klein, 1971; Miller, 1986).

Properties

Karstic conditions prevail for the FAS both east and west of the Flats and along its
margins. Within the Flats cavities were encountered during drilling for well construction
(Appendix I) but low rock permeabilities were also reported with depth. For Gilchrist
County, there are no available aquifer coefficient data for transmissivity and storativity.
The closest data, which may be considered comparable to conditions in the unconfined
FAS of Gilchrist County, are from western Alachua County (Rand Edelstein, 1993, personal
communication). The aquifer performance test results were considered best estimates as
transmissivity ranged from 69,000 to 177,000 gpd/ft and storativity ranged from 0.0006
to 0.0013. The reported ranges were attributed to the heterogeneous and anisotropic
karstic nature of the aquifer, to the short duration of the test, partial penetration of the
wells and proximity of the discharge point to the pumping well.

Ground-water Levels

The potentiometric surface of the FAS in Gilchrist County for June, 1993 is illustrated
in Figure 30. A potentiometric surface is an imaginary surface representing the static head
of groundwater and defined by the level to which water will rise in a tightly cased well
(United States Geological Survey, 1989). Ground-water levels are dynamic, they fluctuate
in response to changes in recharge and discharge conditions. In Gilchrist County the largest
ground-water fluctuations in the FAS (Figure 31 and Appendix III) occur along the outer
margin of the Waccasassa Flats, near rivers and where an unconfined FAS is overlain by
an appreciable thickness of unconsolidated sediments.
Gilchrist County ground-water level data are a mix of short term (less than five years
of record) and long term (greater than 10 years of record) data (Appendix III). The range
of fluctuation in FAS wells with greater than 15 years of record is from 7 to 24 feet
(SRWMD, 1993a). The greatest fluctuation in the County was recorded in the USGS










REPORT OF INVESTIGATION NO. 99


SUWANNEE COUNTY

-N- E C




LAFAYETTE COUNTY A) |


COLUMBIA COUNTY


LEVY COUNTY '


EXPLANATION


* Observation Well


Waccasassa Flats


-10- Potentiometric Contour shows
altitude at which water level would
have stood in tightly cased wells.
Potentiometric contours are
generalized and may not match
individual water level
measurements. Contour
interval 10 feet. Datum
is NGVD.


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS
FGS083097


Figure 30. Potentiometric Surface of the Floridan Aquifer System in Gilchrist County,
Florida, June, 1993.


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FLORIDA GEOLOGICAL SURVEY


LEVY COUNTY


EXPLANATION

9 Observation Well


Waccasassa Flats


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS


-2- Fluctuation Contour Lines -
show generalized ground-water level
fluctuations based on period
of record measurements. Individual
measurements may vary from
generalized contours. Contour
Interval 2 feet.


FGS083197


Figure 31. Generalized Total Fluctuation of the Floridan Aquifer System in Gilchrist County,
Florida, July 1991 to June 1993.









REPORT OF INVESTIGATION NO. 99


continuous ground-water levels recorder well at site 36 (Figure 32). For the period July
1991 through June 1993, ground-water levels at site 36 fluctuated 19.5 feet. For the
period of record April 1982 through May 1993 (SRWMD, 1993a), the total range of
fluctuation was approximately 24 feet. Site 36 is located near the eastern edge of the
Waccasassa Flats, and proximate to Franklin Sink, a karst feature. Franklin Sink appears
to be a vertical conduit for local runoff from the Waccasassa Flats to enter and recharge
the FAS .
Figure 33 shows daily FAS ground-water levels (at site 36) compared to rainfall as
recorded for the period July, 1991 to June, 1993 at Trenton, Florida. Prominent spikes in
the ground-water level hydrograph are in response to major rainfall events. The rapid
response between rainfall and rise in ground-water levels is because local runoff from the
Waccasassa Flats enters Franklin Sink to directly recharge the FAS (as opposed to the
slower more circuitous route presented by a complete soil profile over unconsolidated
surficial sediments).
In the short term between July 1991 and June 1993 FAS ground-water levels in the
county fluctuated from two (2) to 20 feet. The smallest fluctuations (two to five feet)
generally occur in the interior portion of Waccasassa Flats where the potentiometric
surface of the semi-confined FAS is near land surface (Figure 31). The largest ground-
water fluctuation in the Waccasassa Flats was seven feet, recorded at site 8 (Figure 32)
near Sevenmile Lake. Ground-water level fluctuations generally increase radially outward
from the center of the Flats (Figure 31). The highest ground-water level fluctuation,
however, (20 feet) is on the eastern margin of the Waccasassa Flats at site 36 where the
semiconfining unit has been breached.
A comparison of ground-water levels at four of the nine sites in the Waccasassa Flats
where both the surficial and FAS are monitored is shown in figures 22-25. Data (SRWMD,
1993a) show that at most sites there is one foot or less difference between the water
table and the potentiometric surface of the FAS. At times, in some wells, the
potentiometric surface of the FAS exceeds the elevation of the water table (Figures 22,
23, and 25). When the potentiometric surface is higher than the water table the FAS may
locally recharge the surficial system. The maximum difference recorded between the two
aquifers was 3.5 feet in the monitor wells (sites 8 and 9) near Sevenmile Lake (Figure 24).
Ground-water level fluctuations in the FAS for the period July, 1991 to June, 1993 at the
cluster well sites ranged from 2.4 feet to 6.8 feet (Appendix III and SRWMD, 1993a).
The mirror fluctuation patterns between aquifers and minimal head difference indicates
a high degree of hydraulic communication between the water table and the FAS. The
proximity of the water table and the potentiometric surface to land surface in the
Waccasassa Flats, coupled with poorly drained soils and numerous wetlands, however,
suggest a low recharge potential for the FAS.
Figure 25 compares ground-water levels (for the period July, 1991 to June, 1993) in
a water table and FAS wells (sites 31 and 32) to rainfall as recorded at Bell, Florida. In
general, perturbations in response to natural conditions in the two aquifers are mirror
images. The lag in ground-water response as recorded in June, 1992 and again in June,
1993 may be attributed to the increase in evapotranspiration rates associated with rising
temperatures.










FLORIDA GEOLOGICAL SURVEY


t SUWANNEE COUNTY
-N-




LAFAYETTE COUNTY


9
* WELL LOCATION AND NUMBER


COLUMBIA COUNTY


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS


FGS083297


Figure 32. Floridan Aquifer System Ground-water Levels Network, Gilchrist County,
Florida.










REPORT OF INVESTIGATION NO. 99


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FLORIDA GEOLOGICAL SURVEY


Recharge

A potentiometric high is centered on the Waccasassa Flats in Gilchrist County (Figure
30). Concentric potentiometric high contour lines indicate ground-water mounding and
recharge. A potentiometric high, however, does not necessarily indicate the significance
or rate of recharge. A low recharge rate can maintain a potentiometric high where lateral
migration of water along a flow path toward a discharge area is impeded by poor aquifer
permeability. Potentiometric highs can also occur where the aquifer is confined but the
overburden is thin and leaky or breached by sinkholes. Often, there are wetlands and
surface water features associated with potentiometric highs which indicate rejected
recharge. Lichtler (1972) stated that there are four conditions conducive to maximum
recharge:

1. the surface materials must be sufficiently permeable to absorb the heaviest rainfall
without surface runoff
2. the permeable surface material must be thick enough to store the water from a
prolonged rain without the water table rising to the root zone
3. the vertical hydraulic gradient between the water table and the confined
potentiometric surface and the vertical hydraulic conductivity of any confining beds
between the water table and the FAS must be sufficient to move all available water
to the aquifer, and
4. the transmissivity of the FAS and the confined potentiometric gradient must be
sufficient to move the water from the area.

The four conditions conducive for high recharge are not met in the Waccasassa Flats
of Gilchrist County. The ground-water mounding in the Waccasassa Flats area of Gilchrist
County results from a high water table in the semi-confining Surficial aquifer system and
low aquifer permeabilities in the FAS as estimated from field observations and lithologic
logs. Recharge potential (Figure 34) increases along the edge of the Waccasassa Flats
where the semi-confining overburden is thin or breached while, in the remainder of the
County, recharge potential is high (Col and Horvath, 1994).

Discharge

FAS ground-water discharges to springs and seeps in the Suwannee and Santa Fe
River corridors as well as in Cow Creek. There are 14 known springs or spring groups
cropping out along the northern and western boundaries of Gilchrist County (Figure 10).
These springs, which augment surface water flow, are ground-water discharge points
located in the floodplains of the Santa Fe and Suwannee Rivers (Rosenau et al., 1977).
Groundwater from the FAS also augments low flows in lower Cow Creek, a tributary to
the Santa Fe River. The springs in Gilchrist County (Table 8) include two first magnitude
systems with an average discharge of greater than 100 cubic feet per second (cfs) or 64.6
million gallons per day (mgd); six second magnitude systems with an average discharge of
10 to 100 cfs and eight third magnitude systems with an average discharge less than 10
cfs. A spring's location however, is not necessarily indicative of ground-water origin and
area of contribution. For example, the first magnitude Siphon Creek Rise, which crops out
in the Santa Fe River approximately one mile upstream of State Road 47, is the resurgence
of a portion of the Santa Fe River which goes underground approximately one mile
upstream from the Santa Fe Rise in Columbia and Alachua counties (Wilson and Skiles,









REPORT OF INVESTIGATION NO. 99


SUWANNEE COUNTY




LAFAYETTE COUNTY


LEVY COUNTY


EXPLANATION

W High recharge potential

Moderate recharge potential

W Low recharge potential

Discharge Area
FGS083497


MILES
0 1 2 3 4 5
0 2 4 6
KILOMETERS


t~~y


U.S. HIGHWAY

STATE/COUNTY ROAD


Figure 34. Recharge Potential of the Floridan Aquifer System in Gilchrist County, Florida.












FLORIDA GEOLOGICAL SURVEY









































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REPORT OF INVESTIGATION NO. 99


1988). The Devils Eye Group (Santa Fe River corridor) with spring vents in both Gilchrist
and Columbia Counties drains a ground-water basin in Columbia County (Wilson and Skiles,
1989).
Ground-water Quality

Lithology, residence time and land use can impart particular physical and chemical
"flavors" to an aquifer's water quality. FAS water quality can be characterized as alkaline
with relatively high values for pH, specific conductance, calcium and magnesium. Basic
water types and variability of the FAS are shown in the Piper trilinear diagrams and
associated Stiff diagrams (Figures 35 and 36). Upchurch (1990) classified groundwater in
the FAS in Gilchrist County as a calcium bicarbonate water type which reflects dissolution
of the aquifer's limestone framework. Sites 13, 24 and 28 (Figures 35 and 36) show
relative variability in the Stiff diagrams. These sites have relatively low values as
compared to their respective medians (Appendix IV-A), for specific conductance (150-179
umhos/cm), hardness (57-86 mg/I), calcium (22-33 mg/l) and alkalinity (66-87mg/I). The
relatively low values may reflect mixing of SAS and FAS waters or recharge and a short
residence time in the unconfined FAS.

Exceedance of Primary Drinking Water Standards

Primary ground-water drinking water standards in the FAS were only exceeded for
turbidity. Exceedances were reported in 15 of 19 FAS samples (Appendix IV B).

Exceedance of Secondary Drinking Water Standards

In the FAS secondary drinking water standards were exceeded for pH, iron and
manganese (Appendix IV-B). Only one sample (site 13) exceeded secondary drinking
water standards for pH (6.5 to 8.5). The high pH (9.36) is probably due to the influence of
remnant well construction drilling fluids or grout in the well bore.
The secondary drinking water standard for iron, a natural ubiquitous constituent of
groundwater is 0.3 mg/I. Eleven of 19 FAS samples exceeded the standard for iron
(Appendix IV B). Iron in household water supplies may stain laundry and plumbing fixtures.
The secondary drinking water standard for manganese (0.05 mg/l) was exceeded at
site 34. Manganese commonly substitutes for calcium in limestone and dolomite and may
also be found in iron-rich clays deposited in solution features (Upchurch, 1990). In
groundwater, manganese may also accompany high iron concentrations (Hem, 1985).
Metals found in trace amounts (Appendix IV-B) that did not exceed any standards
include arsenic (site 31), zinc (site 8), and copper and lead (site 11). In Florida's past
arsenic was widely used as a pesticide to control cattle ticks. Today, arsenic remains in
soils and may contaminate aquifer systems (Maddox et al., 1993). Zinc is a constituent of
brass and bronze and used in galvanizing, paints and rubber (Hem, 1985). Zinc in
groundwater may be attributed to human influence. Copper may be dissolved from water
pipes and plumbing fixtures; and it has also been used in pesticides (Hem, 1985). Lead in
groundwater in Florida is associated with human activity (Maddox et al., 1993). Possible
sources of lead include gasoline, coal, oil, paint, pesticides, lead weights used in water
level measurements, bullets and solder.













FLORIDA GEOLOGICAL SURVEY


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FLORIDA GEOLOGICAL SURVEY


Development

The SRWMD issued approximately 3,351 water well construction permits between
January 1976 and June 1993 in Gilchrist County, Florida. Water well permit activity is
shown by section in Figure 37. The largest number of permits issued per section are in
Fanning Springs and near Waccasassa Lake. The majority of the permits (3,205, or 96%)
are for small (two to four inch) diameter wells which are primarily for residential use. The
143 large diameter wells in the County (5 to 21 inches) are predominantly used in
agriculture, but may also serve pther purposes. The large diameter wells can produce from
100 to 7,000 gpm.
There are an estimated 212 wells constructed in or on the margin of the Waccasassa
Flats in Gilchrist County. The majority of the wells are constructed on small lots and tracts
along or adjacent to the boundaries of the Waccasassa Flats. These include 20 small
diameter (4 inches or less) monitor wells, two public supply wells and at least 14 large
diameter (5 inches or larger) irrigation wells. The remainder are small diameter wells used
for domestic, lawn and garden irrigation purposes.
The FAS is Gilchrist County's primary potable water resource. The estimated 1993
Gilchrist County population is 10,500 (Bureau of Economic and Business Research, 1994).
The permitted public supply system for the City of Trenton serves an estimated population
of 1,176. The remainder of the County's 9,324 people are self-supplied. Non-permitted
domestic water use, approximately 174 gallons per day per capital (gpdpc), in Gilchrist
County including Bell and Fanning Springs is estimated to be 1,622,376 gallons per day
(North Central Florida Regional Planning Council, 1991). Total estimated ground-water use
in Gilchrist County including non-permitted domestic supplies is 26,493,676 gpd. Total
estimated surface water use is 165,500 gpd. Total estimated daily water use in the
county is 26,659,176 gallons.
Between October 1982 and May 1993 the District issued 205 water use permits (not
including Rural Domestic). Agriculture represents 68% (140) of the permits issued and
87% (21.748 mgd) of the permitted volume of water used in the county. Public supply is
the second largest water use group both by permits issued, 61 (30%) and volume,
3.2692 mgd (13%). All other uses combined represent only 2% of the permits issued
and less than 1% (0.0196 mgd) of the permitted daily volume used. Groundwater is the
primary water resource accounting for 99% of the permitted water use in the county.
There are only three (agriculture) permits issued for surface water use in the county.
Water use by section is shown in Figure 38. There are five sections of land in the
county where the total permitted volume exceeds 1 mgd. The largest permitted water use
in the county (2.5 mgd) is for an inoperative water bottling company near the Santa Fe
River. The other large volume permitted use is for agriculture. The larger
operations/enterprises employ center pivot and traveling guns to irrigate. Table 9 shows
permitted water use by group and average daily use in mgd.
Agriculture as a water use group is not required by the District to monitor or report
water use. Agricultural water use is an estimate supplied by the permit applicant after
considering soil conditions, crop, acreage, livestock, rainfall, well size, pump capacity and
efficiency of delivery systems. Since crops are seasonal and rotated, rainfall variable,
acreage, livestock and land use subject to change, and permits are issued for 20 years,
actual daily agricultural water use may differ from that permitted.
In the Waccasassa Flats agriculture accounts for more than 99% of the permitted
water use. There are 14 agricultural and two public supply permits for FAS water use in
the Flats. The total permitted average daily rate (ADR) water use for the 16 permits is









REPORT OF INVESTIGATION NO. 99




SUWANNEE COUNTY .


S... ................. lUCLUMBIA UU I


TE COUNTY ............ ..







"'..', ...." ............. .. .^. .. .......





















R14E R15E

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............
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T10S


EXPLANATION
Water Well Permits
Issued By Section

S0 Permits

S1 25 Permits

S26 50 Permits


51 75 Permits

76 100 Permits


MILES
0 1 2 3 4 5

0 2 4 6
KILOMETERS
FGS083797


Figure 37. Gilchrist County Water Well Permits Issued by Section, January 1976 June
1993 (SRWMD, 1993c).



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FLORIDA GEOLOGICAL SURVEY


SUWANNEE COUNTY


LAFAYETTE COUNTY
LAFAYETTE COUNTY


COLUMBIA COUNTY


R14E R15E


EXPLANATION
Permitted Water Use In
* MGD By Section

D 0 MGD

D .0001 .5 MGD
M .5 1.0 MGD


l 1.0 10.0 MGD
'D Waccasassa Flats Boundary

F Located Water Use Wells


MILES
0 1 2 3 4 5
0 2 4 6
KILOMETERS
FGS08o397


MGD is Million Gallons Per Day

Figure 38. Gilchrist County Permitted Water Use in Million Gallons per Day (MGD) by
Section, October 1, 1982 June, 1993 (SRWMD, 1993c).


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ii









REPORT OF INVESTIGATION NO. 99


Table 9: Permitted Water Use in Gilchrist County, Florida (SRWMD, 1993c).


*GW represents GROUNDWATER and SW represents
SURFACEWATER withdrawals.

* ADR represents the average daily rate of withdrawal in million
gallons per day.


TYPE OF No. OF
WATER USE GROUPS WITH- PERMITS ** ADR
DRAWAL


Public supply GW 61 3.2692
Industrial/Commercial GW 1 0.0036
Agricultural GW 137 21.5825
Agricultural SW 3 0.1655
Rural Domestic GW 7 0.0178
Power Production GW 0 0.0000
Recreational GW 1 0.0003
Other/Miscellaneous GW 2 0.0157




Total 212 25.0546









FLORIDA GEOLOGICAL SURVEY


approximately 3.76 mgd. Four agricultural permits account for 2.95 mgd while the
remaining agriculture use is approximately 0.81 mgd. The two small volume public supplies
are permitted for 0.002 mgd.

SURFACE WATER

Three major surface water basins (Figure 10) hydrologically divide Gilchrist County.
Approximately 171 square miles of the county is in the Suwannee River basin,
approximately 132 square miles is in the Santa Fe River basin and approximately 49 square
miles is in the Waccasassa River basin. The county is bounded on the north by the Santa
Fe River, a primary tributary of the Suwannee River which bounds the county on the west.
The Waccasassa River is an independent hydrologic unit discharging to the Gulf of Mexico.
There are numerous (named and unnamed) small lakes and wet prairies perched in
poorly drained soils within the area of the Waccasassa Flats in Gilchrist County. Most of
these lakes are perched along the edge of the Waccasassa Flats. The largest open water in
the interior portion of the Waccasassa Flats are Fourmile and Threemile lakes.
Named lakes and other surface water features with select physical characteristics are
shown in Table 10. Waters Lake is the only local surface water body with "long term"
stage monitoring. Most lakes in Gilchrist County are shallow with small drainage basins
and small surface areas. During drought periods these small lakes and ponds may go dry.

Water Quality

The Suwannee River and the Santa Fe River are classified as Outstanding Florida
Waters. The Lower Suwannee River Basin water quality has been rated good in all reaches
(Hand, et al, 1994). In the Santa Fe River water quality has been characterized as good
although a portion of the river basin near the confluence of the Suwannee River is
considered threatened due to agricultural land use.
Physical water quality parameters at select lakes in the Waccasassa Flats were
sampled twice (Table 10). Most of the lakes tested were relatively shallow, very acidic
water bodies characterized by dark color and low dissolved solids. Baggett and Sevenmile
lakes on the edge of the Flats have relatively higher pH and specific conductance which
may reflect the influence of mixing with FAS groundwater and/or evaporation.











REPORT OF INVESTIGATION NO. 99


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FLORIDA GEOLOGICAL SURVEY

REFERENCES

Applin, P., and Applin, E. R., 1944, Regional subsurface stratigraphy and structure of
Florida and southern Georgia: American Association of Petroleum Geologists
Bulletin, v. 28, n. 12, p. 1673-1753.

Balsillie, J. H., 1995, William F. Tanner on environmental plastic granulometry: Florida
Geological Survey Special Publication 40, 142 p.

Brooks, H. K., 1981, Guide to the physiographic divisions of Florida: Gainesville, Florida
Cooperative Extension Service, IFAS, University of Florida Map 8-5 M-82.

Bureau of Economic and Business Research, 1994, Florida Statistical Abstract 1994:
Gainesville, University Presses of Florida, 794 p.

Central Florida Regional Planning Council, 1991 a, Gilchrist County comprehensive plan,
168 p.

1991b, Gilchrist County data and analysis: Gilchrist County Board of County
Commissioners, 281 p.

Col, N. and Horvath, G., 1994, Recharge potential of the Floridan Aquifer in the SRWMD:
SRWMD unpublished report; 23 p.

Dall, W. H., and Harris, G. D., 1892, Correlation papers Neocene: U.S. Geological Survey
Bulletin 84, 349 p.

Davis, S. and DeWiest, R., 1966, Hydrogeology: New York, John Wiley and Sons, 463 p.

FDEP (Florida Department of Environmental Protection), 1993, Florida ground-water
guidance concentrations: Draft 1993, 14 p.

Freeze, R., and Cherry, J., 1979, Groundwater: Englewood Cliffs, Prentice Hall, Inc., 604
p.

Gilman, C. S., 1964, Rainfall in: Chow, V. T. (ed.), Handbook of applied hydrology: New
York, McGraw-Hill, Inc. p. 9-1 to 9-68.

Hand, J., Col, J. and Grimison, E., 1994 Northeast Florida District Water Quality
Assessment 1994 305(b) Technical Appendix. Florida Department of Environmental
Protection, Nov. 1994, 114 p.

Hem, J. D., 1985, Study and interpretation of the chemical characteristics of natural
water: U.S. Geological Survey Water-Supply Paper 2254.

Klein, H., 1971, Depth to the base of potable water in the Floridan Aquifer: Florida
Geological Survey Map Series 42.









REPORT OF INVESTIGATION NO. 99


Lichtler, W. F., 1972, Appraisal of water resources in the east central Florida region:
Florida Geological Survey Report of Investigation 61, 52 p.

Maddox, G. L. Lloyd, J. M., Scott, T. M., Upchurch S. B., and Copeland, R., 1993,
Florida's ground-water Quality Monitoring Program, background hydrogeochemistry:
Florida Geological Survey Special Publication 34, 364 p.

Miller, J. A., 1986, Hydrogeologic framework of the Floridan aquifer system in Florida and
in parts of Georgia, Alabama, and South Carolina: U.S. Geological Survey
Professional Paper 1403-B, 99 p.

North Central Florida Regional Planning Council, 1991, City of Trenton Comprehensive Plan
Transmittal Draft, Plan Elements, May 1991.

Parker, G. G., Ferguson, G. E., and Love, S. K., 1955, Water resources of Southeastern
Florida: U.S. Geological Survey Water Supply Paper 1255, 965 p.

Puri, H. S., Yon, J. W., Jr., and Oglesby, W. R., 1967, Geology of Dixie and Gilchrist
Counties, Florida: Florida Geological Survey Bulletin 49, 155 p.

Rupert, F. R., 1988, The geology and geomorphology of Gilchrist County, Florida: Florida
Geological Survey Open File Report 18, 10 p.

Rupert, F. R., and Campbell, K. M., 1993, Geologic map of Gilchrist County Florida: Florida
Geological Survey Open File Map Series 36.

Rosenau, J. C., Faulkner, G. L., Hendry, C. W. Jr., and Hull, R. W., 1977, Springs of
Florida: Florida Geological Survey Bulletin 31 (revised), 461 p.

Scott, T. M., 1988, The lithostratigraphy of the Hawthorn Group (Miocene) of Florida:
Florida Geological Survey Bulletin 59, 148 p.

Scott, T. M., Lloyd, J. M., and Maddox, G. L., (eds.), 1991, Florida's Ground-water
Quality Monitoring Program, hydrogeological framework: Florida Geological Survey
Special Publication 32, 97 p.

Simpson, J.C., 1956, A provisional gazetteer of Florida place names of indian derivation,
either obsolescent or retained together with others of recent application: Florida
Geological Survey Special Publication 1, 158 p.

Southeastern Geological Society Ad Hoc Committee, 1986, Hydrogeological units of
Florida: Florida Geological Survey Special Publication 28, 8 p.

SRWMD (Suwannee River Water Management District), 1993a, unpublished ground-water
levels data base.

1993b, unpublished ground-water quality data base.

1993c, unpublished permit data base.









FLORIDA GEOLOGICAL SURVEY


1993d, unpublished precipitation data base.

Tanner, W. F., 1991 a, Suite statistics: the hydrodynamic evolution of the sediment pool:
in, Syvitski, J. P. M., (ed.), Principles, methods, and application of particle size
analysis, Cambridge University Press, p. 225-236.

1991b, Application of suite statistics to stratigraphy and sea-level changes:
in Syvitski, J. P. M., (ed.), Principles, methods, and application of particle size
analysis, Cambridge University Press, p. 283-292.

U.S.D.A. (U.S. Department of Agriculture Soil Conservation Service), 1992, Soil survey for
Gilchrist County, p. 172.

United States Geological Survey, 1989, Federal glossary of selected terms: subsurface-
water flow and solute transport: Ground Water Subcommittee of the Federal
Interagency Advisory Committee on Water Data.

Upchurch, S. B., 1990, Quality of ground water in the Suwannee River Water Management
District: Results of the first sampling of the background water-quality network,
University of South Florida, Tampa, 175 p.

Vernon, R. 0., 1951, Geology of Citrus and Levy Counties, Florida: Florida Geological
Survey Bulletin 33, 256 p.

Walton, W. C., 1970, Groundwater resource evaluation: New York McGraw-Hill Book Co.,
664 p.

White, W. A., 1970, Geomorphology of the Florida peninsula: Florida Geological Survey
Bulletin 51, 164 p.

Wilson, W. L., and Skiles, W. C., 1988, Aquifer characterization by quantitative dye
tracing at Ginnie Spring, Northern Florida: Proceedings of the Second Conference on
Environmental Problems in Karst Terranes and Their Solutions: Nashville,
Tennessee, November 16-18, 1988, 20 p.

1989, Partial reclassification of first-magnitude springs in Florida:
Proceedings of the Third Multidisciplinary Conference on Sinkholes and the
Environmental Impacts of Karst, St. Petersburg, FL, October 4-7, 1989. 7 p.

Winsberg, M. D., 1990, Florida weather: University of Central Florida Press, Orlando.
171 p.

Yon, J. W., Jr., and H. S. Puri, 1962, Geology of Waccasassa Flats, Gilchrist County,
Florida: American Association of Petroleum Geologists Bulletin, v. 46, n. 5, p.
674-684.










REPORT OF INVESTIGATION NO. 99


Appendix I. Geologic Summary of Wells Drilled During Study
This table represents only those wells drilled for the present study. The depth below land surface
of the top of each lithologic unit is Indicated. Multiple wells were drilled at most sites. At some
multiple-well sites, two or more wells were included under one FGS well accession number.


Geologic Formation Tops
Site FGS Well Total Elev. (depth below land surface in ft.)
No. N. .. D h N D Pleistocene- Upper Eocene Middle Eocene
No. No. I.D. Depth NGVD Holocene Ocal Avon Park
(ft.) (ft.) Undifferentiated Limestone Formation
s and ndclay
3 W-16549 -71525001 65 44 0 15.5 NR
4 W-16599 -71526001 228 73 0 36 144
5 W-16598 -71526002 78 66 0 41.8 NR
6 W-16547 -71528001 270 75 0 92 144.8
8,9 W-16537 -71529003 167 68 0 90 150
12 W-16550 -71630004 125 48 0 21.8 NR
16 W-16595 -81513001 97 62 0 17.8 NR
W_-16594 -81513000 167 62 0 16.5 132
17 W-16604 -81515002 155 75 0 48 131
19 W-16619 -81517003 151 86 0 68.2 131
22 W-16613 -81535001 150 85 0 47.5 NR
24 W-16624 -81536002 150 83 0 32.2 140
W-16621 -81536000 247 79 0 NR NR
W-16622 -81536000 34 79 0 33.5 NR
W-16623 -81536000 48 79 0 25 NR
25 W-16593 -81605003 281 67 0 44 123.2
28,29 W-16636 -81632001 168 82 0 10.7 114.5
31 W-16635 -91504001 151 89 0 27 131
32 W-16634 -91504001 35 85 0 28.5 NR
34 W-16680 -91534001 200 69 0 103.3 183
35 W-16681 -91534002 60 77 0 NR NR
37 W-16646 -91628005 177 88 0 55.4 144.8
W_-16645 -91628001 78 90 0 52.7 NR
40 W-16662 -101634001 78 82 0 57.4 NR
41 W-16663 -101634002 172 70 0 50 118
W-16684 -101634000 100 66 0 NR NR
*Site number refers to Figure 2 in text.
NR = not reached
Well I.D. = Township, Range, Section and sequence number.









FLORIDA GEOLOGICAL SURVEY



Appendix II. Monitor Well Data


Site FGS No. Well I.D. Aquifer Elev. (ft.) Casing Total Diameter
No. NGVD Deth Depth (ft) (in)
1 D-3 -71401005 F 33.45 10 40 3
2 -71515001 F 85.35 76 83 4
3 W-16549 -71525001 F 43.69 20 50 4
4 W-16599 -71526001 F 72.72 42.5 62.5 4
5 -71526002 S 72.60 3 23 4
6 W-16547 -71528001 F 75.35 110 130 4
7 -71528002 S 75.35 5.5 55.5 4
8 W-16537 -71529003 F 68.19 10 120 4
9 -71529004 S 69.01 6 36 4
10 -71532001 F 70.93 81 98 4
11 -71630002 F 42.64 10 30 3
12 W-16550 -71630004 F 47.70 27 47 4
13 -81412001 F 83.68 140 160 3
14 -81416001 F 37.54 42 90 4
15 -81425001 F 67.83 NR 82 2
16 -81513001 F 67.56 17 49 4
17 W-16604 -81515002 F 74.61 97.5 127.5 4
18 -81515003 S 74.53 5 25 4
19 -81517003 S 85.98 1 11 4
20 -81518005 F 69.30 151 155 4
21 -81535001 S 84.86 8 28 4
22 W-16613 -81535001 S 84.96 103 113 4
23 -81536001 S 82.36 8 28 4
24 W-16624 -81536002 F 83.3 36 56 4
26 -81618001 F 63.68 57 61 2
27 D-28 -81624004 F 86.48 63 85 4
28 -81631001 F 69.03 25 55 3
30 -91420001 F 34.26 55 65 4
31 W-16635 -91504001 F 88.53 41 51 4
32 -91504002 S 88.12 7.5 17.5 4
33 -91530005 F 51.80 25 55 3
34 W-16680 -91534001 F 69.29 108 128 4
35 -91534002 S 67.35 20 40 4
36 -91607001 F 87.31 55 103 6
37 W-16646 -91628005 F 87.72 58 78 4
38 W-318 -101516001 F 55.74 61 100 12
39 D-50 -101601002 F 88.14 30 60 3
40 -101634001 F 69.56 68 88 4
41 W-16662 -101634002 S 69.92 26 46 4


*Site number refers to Figure 2 in text. W# = FGS well accession
Well I.D. = Township, Range, Section and sequence number.
Aquifers: F= Floridan aquifer system, S = surficial aquifer system.
If a site is not listed, a monitor well was not constructed.


number. NR = not recorded.









REPORT OF INVESTIGATION NO. 99


Appendix III: Ground-Water Levels


Short Term Sites ( < 5 years of record )
Aquifer
Site No. Well ID System Maximum Minimum Mean Median Range
1 -71401005 F 26.55 5.96 11.94 11.13 20.59
3 -71525001 F 40.80 35.34 37.92 37.70 5.46
4 -71526001 F 69.74 67.00 68.51 68.60 2.74
5 -71526002 S 70.27 66.90 68.32 68.44 3.37
6 -71528001 F 71.10 67.47 69.26 69.25 3.63
7 -71528002 S 71.93 67.72 69.70 69.57 4.21
8 -71529003 F 63.23 52.05 57.26 58.06 11.18
9 -71529004 S 64.95 53.18 59.55 60.30 11.77
11 -71630002 F 27.50 17.23 22.29 23.31 10.27
12 -71630004 F 43.63 37.87 41.67 42.17 5.76
16 -81513001 F 64.60 61.14 63.09 63.17 3.46
17 -81515002 F 71.11 66.69 68.84 69.04 4.42
18 -81515003 S 71.40 67.58 69.39 69.29 3.82
19 -81517003 S 79.86 75.50 77.26 77.11 4.36
20 -81518005 F 32.04 25.11 28.71 28.60 6.93
21 -81535001 S 81.78 77.82 79.73 79.69 3.96
22 -81535002 F 81.59 77.67 79.51 79.62 3.92
23 -81536001 S 74.13 71.39 72.85 72.86 2.74
24 -81536002 F 74.08 71.40 72.82 72.84 2.68
27 -81624004 F 33.38 26.59 30.78 30.83 6.79
28 -81631001 F 57.93 45.58 52.99 53.33 12.35
31 -91504001 F 84.67 81.50 83.09 83.28 3.17
32 -91504002 S 84.63 81.63 83.14 83.19 3.00
33 -91530005 F 16.77 7.11 11.77 11.95 9.66
34 -91534001 F 65.87 62.59 64.49 64.66 3.28
35 -91534002 S 66.44 63.25 65.02 65.07 3.19
37 -91628005 F 77.68 73.29 75.81 75.64 4.39
39 -101601002 F 44.29 39.74 42.17 42.15 4.55
40 -101634001 F 64.41 60.41 62.43 62.72 4.00
41 -101634002 S 65.60 61.30 63.28 63.15 4.30
Long Term Sites ( >10 years of record )
2 -71515001 F 76.05 67.44 71.31 71.80 8.61
10 -71532001 F 40.00 25.43 32.06 32.03 14.57
14 -81416001 F 23.11 7.00 13.52 12.82 16.11
15 -81425001 F 30.38 13.48 19.67 19.80 16.90
26 -81618001 F 45.58 33.85 38.72 39.00 11.73
30 -91420001 F 19.69 3.78 8.51 7.68 15.91
36 -91607001 F 69.61 45.52 56.99 56.35 24.09
38 -101516001 F 24.63 7.28 15.17 15.28 17.35


Site number refers to Figure 2 in text.
F = Floridan aquifer system.
S = Surficial aquifer system









FLORIDA GEOLOGICAL SURVEY


Appendix IV: Gilchrist County Background Ground-Water Quality.
Part A: Descriptive Statistics
Water Temperature C Calcium (mg/I)
Aquifer FL FC FU Surf. Aquifer FL FC FU Surf.
Maximum 23.5 22.5 23.5 23.9 Maximum 100 86 100 30
Minimum 21.2 21.2 21.9 21.9 Minimum 22 22 30 0.9
Median 22 21.6 22.4 22.5 Median 73 73 72.5 3.05
Standard Standard
Deviation 0.63 0.42 0.51 0.63 Deviation 22.36 20.14 24.18 9.42
Turbidity (NTU) Magnesium (mg/l)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 48 48 23 50 Maximum 5 5 4.3 2
Minimum 0.77 0.77 1.4 0.84 Minimum 0.4 0.4 0.7 0.3
Median 3.2 2.2 5.3 3.9 Median 1.6 1.9 1.3 0.7
Standard Standard
Deviation 10.96 14.53 6.19 14.06 Deviation 1.28 1.37 1.15 0.52
Specific Conductance (um/cm) _Sodium (mg/I_
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 512 467 512 142 Maximum 8.4 8.4 5.9 7.5
Minimum 150 150 177 26 Minimum 1.7 1.9 1.7 1.5
Median 388 376 389.5 51.5 Median 3.1 5.1 2.75 2.6
Standard Standard
Deviation 106.25 95.04 115.39 39.88 Deviation 1.93 2.08 1.10 2.00
pH (S.U.) _Potassium (mg/I)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 9.36 8.51 9.36 6.17 Maximum 1.5 1.5 1.4 1.4
Minimum 6.82 6.98 6.82 4.95 Minimum 0.4 0.4 0.4 0.3
Median 7.12 7.21 7.11 5.27 Median 0.5 0.6 0.45 0.6
Standard Standard
Deviation 0.59 0.45 0.70 0.45 Deviation 0.37 0.38 0.32 0.30
Nitrate (mg/l) _Chloride (mg/1)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 3.3 0.48 3.3 0.29 Maximum 8.2 8.2 8.2 20
Minimum 0.02 0.02 0.02 0.02 Minimum 2.2 2.2 3 1
Median 0.02 0.02 0.06 0.02 Median 4.8 4.7 5.3 3.5
Standard Standard
Deviation 0.78 0.14 1.01 0.11 Deviation 1.56 1.54 1.52 5.17
Ortho-Phosphate (mg/I) _Sulfate (mg/l)_
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 1.7 1.7 0.45 1 Maximum 15 2.9 15 8.5
Minimum 0.03 0.03 0.05 0.02 Minimum 0.2 0.2 0.2 0.2
Median 0.10 0.10 0.09 0.08 Median 1.9 1.3 2.7 2.2
Standard Standard
Deviation 0.38 0.51 0.13 0.28 Deviation 3.89 0.88 4.88 2.71
Total Hardness (mg/l) Fluoride (mg/l)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 270 240 270 79 Maximum 0.3 0.2 0.3 0.1
Minimum 57 57 85.39 4 Minimum 0.1 0.1 0.1 0.1
Median 190 190 189.6 11.953 Median 0.1 0.1 0.1 0.1
Standard Standard
Deviation 59.67 54.49 63.97 23.87 Deviation 0.07 0.03 0.08 0.00









REPORT OF INVESTIGATION NO. 99


Appendix IV: Gilchrist County Background Ground-Water Quality.
Part A: Descriptive Statistics
Silica (mg/l) Arsenic (ug/l)
Aquifer FL FC FU Surf. Aquifer FL FC FU Surf
Maximum 15 15 8.1 6.7 Maximum 14 14 1 1
Minimum 4.5 5.2 4.5 1.9 Minimum 1 1 1 1
Median 7 7.2 6.9 4.4 Median 1 I 1 1
Standard Standard
Deviation 2.14 2.82 1.04 1.33 Deviation 2.89 4.03 0.00 0.00
Copper (ug/l) Iron (ug/I)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf
Maximum 14 4 14 5 Maximum 4200 4200 1000 7000
Minimum 1 1 1 1 Minimum 60 80 60 60
Median 2 2 2 2 Median 430 390 645 420
Standard Standard
Deviation 2.92 0.99 3.75 1.17 Deviation 941.19 1286.11 320.45 2023.78
Lead (ug/l) Manganese (ug/I)__
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 6 2 6 1 Maximum 110 110 30 20
Minimum 1 1 1 1 Minimum 5 10 5 10
Median 1 1 1 1 Median 20 20 10 10
Standard Standard
Deviation 1.14 0.31 1.47 0.00 Deviation 22.94 29.44 7.23 4.90
Strontium (ug/l) Zinc (ug/l)
Aquifer FL FC FU Surf Aquifer FL FC FU Surf.
Maximum 160 130 160 50 Maximum 100 100 16 60
Minimum 60 60 60 20 Minimum 10 10 10 10
Median 100 90 100 30 Median 10 10 10 25
Standard Standard
Deviation 25.93 23.93 26.17 10.77 Deviation 21.42 29.10 1.80 16.61
Alkalinity (mg/l)
Aquifer FL FC FU Surf
Maximum 265 242 265 74
Minimum 66 66 81 1.3
Median 185 192 180.5 7.5
Standard
Deviation 57.67 52.25 62.00 23.54

Aquifers: FL equals all Floridan aquifer system samples. FC equals Floridan aquifer system confined.
FU equals Floridan aquifer system unconfined. Surf. equals Surficial aquifer system samples.











FLORIDA GEOLOGICAL SURVEY


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