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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Harmon Shields, Executive Director




DIVISION OF RESOURCE MANAGEMENT
Charles M. Sanders, Director




BUREAU OF GEOLOGY
Charles W. Hendry, Jr., Chief




REPORT OF INVESTIGATIONS NO. 83




GROUND-WATER RESOURCES OF
DESOTO AND HARDEE COUNTIES, FLORIDA




By
William E. Wilson




Prepared by
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
and
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES

Tallahassee Florida
1977






/- -F
i


?K2~ ~)5


DEPARTMENT
OF
NATURAL RESOURCES




REUBIN O'D. ASKEW
Governor


BRUCE A. SMATHERS
Secretary of State





BILL GUNTER
Treasurer




RALPH D. TURLINGTON
Commissioner of Education


ROBERT L. SHEVIN
Attorney General





GERALD A. LEWIS
Comptroller




DOYLE CONNER
Commissioner of Agriculture


HARMON W. SHIELDS
Executive Director







LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
May 25, 1977

3
Governor Reubin O'D. Askew, Chairman
Florida Department of Natural Resources
Tallahassee, FL 32304

Dear Governor Askew:
The Bureau of Geology, Division of Resource Management, Department of
Natural Resources, is publishing as its Report of Investigation No. 83, the
"Ground-Water Resources of DeSoto and Hardee Counties, Florida."

Recognizing the potential for serious water resources problems, the South-
west Florida Water Management District and the Bureau of Geology request-
Sed the U.S. Geological Survey to evaluate the water resources of DeSoto and
Hardee counties.

In the investigation the significance of ground-water resources both as the
primary source of supply and as the resource most needing evaluation was
recognized. As a consequence, strong emphasis was placed on assessing the
ground-water resources in the counties.

This investigation will provide a basis for sound development and manage-
ment of the areas ground-water resources.

Sincerely,
C.W. Hendry, Jr., Chief




















































Completed manuscript received
1976
Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology
Tallahassee
1977




iv






CONTENTS


Page
A abstract ............ ........ ............................ ................... 1
Introduction ........................................... ....................... 2
Purpose and scope of investigation ....................................... 4
Previous studies and sources of data...................................... 4
Acknowledgments...................................................... 5
Well location and numbering systems ....................................... 6
Description of the area ................. ....................................... 8
Geographic setting .................................................. 8
Climate ............................................................... 10
Geologic framework.................................................... .. 11
SGround water ............................................................... 16
Surficial aquifer ........................................................ 21
Geology ..................................................... 22
Water-bearing properties........................................... 26
Development ..................................................... 28
Floridan Aquifer system ................................................. 28
Upper unit ........................................................ 29
Geology .................................................... 29
Transmissivity .............................................. 30
Development ................................................ 31
Lower unit ....................................................... 34
Geology .......................... ... ................... 34
Development ................................................ 36
Confining beds .................................................... 37
Upper unit confining bed .................................... 37
Sand and clay unit of Tampa Limestone ...................... 39
Water-bearing properties............... ............................ 40
Potentiometric surface ............................................. 42
Seasonal fluctuations ........................................... 43
Areas of flow ................................................ 47
Long-term trends ............................................ 47
Head relationships ..................... ....................... .... 50
Ground-water development, northeastern DeSoto County ..................... 52
Description and irrigation.......................................... 53
W ell field ....... ............................................ 53
Pumpage ................................................... 53
Hydraulic properties of the aquifer system ........................... 55
Aquifer model ............................................... 55
Aquifer tests ................................................ 56
Projected drawdowns.......... .... ... ......................... ..... 56
Reliability of results .......................................... 60
W ater quality ......................................... ...................... 60
Vertical and areal distribution ............................................ 62
Dissolved solids ............................................. 78

V






Temperature ...................................................... 78
Hardness ....................................... ............ 79
Sulfate ....................................... .................. 80
Chloride ......................................................... 81
Fluoride .............. ...... ... ... ......................... .. 883
Use of the resource ..................................................... ... 84
Water use-1970......................................................... 84
Irrigation ......................................................... 85
Other ............................................................ 88
Hydrologic effects of development ......................................... 88
Management considerations .............................................. 92
Additional investigations.................................................. 93
Summary .................................................................... 94
References .................................................................. 99
Appendix .......................................................... 104










































vi






ILLUSTRATIONS

Plate
1 Map of well locations
Figure Page
1. Map showing location of DeSoto and Hardee counties ................ ........ 3
2. Diagram illustrating the latitude-longitude well-numbering system ............. 7
3. Map of physiographic subdivisions ........................................ 9
4. Graphs of annual rainfall at Arcadia and Wauchula ......................... 11
5. Graphs of average, maximum, and minimum monthly rain-fall at Arcadia and
W auchula .............................................................. 12
6. Graph of average monthly and average annual air temperature at Arcadia ...... 13
7. Stratigraphic section and gamma-ray log, well 1601-3646 ..................... 16
8. Geologic section A-A' .............................. ...................... 17
9. Geologic section B-B' .................................................. .18
10. Geologic section C-C' .... ......... .................................... 19
11. Map showing distribution of sand and clay unit of Tampa.Limestone and lines
of geologic sections................ ................................... 20
12. Geological sections of surficial deposits. DeSoto and Hardee counties ........... 23
13. Map showing altitude of the top of the upper unit. Floridan Aquifer, and lines
of geologic sections of surficial deposits .................................. 24
14. Diagram of average yield and construction characteristics of wells tapping the
upper unit of the Floridan Aquifer ....................................... 33
15. Map showing altitude of the top of the Suwannee Limestone.................. 35
16. Map showing altitude of the top of the dolomite unit of the Avon Park
Limestone ........................................................... 36
17. Map of the potentiometric surface, Floridan Aquifer, peninsular Florida,
1961 ........................................ ........................... 43
18. Map of the potentiometric surface and areas of artesian flow. Floridan Aquifer.
DeSoto and Hardee counties. September 1971......................... ...... 44
19. Observation-well hydrographs. Hardee and Polk counties ..................... 45
20. Observation-well hydrographs. DeSoto County ............................ 46
21. Map of the potentiometric surface and areas of artesian flow, Floridan Aquifer,
DeSoto and Hardee counties, May 197.1 ......................... ...... 48
22. Map of rise of potentiometric surface, Floridan Aquifer. DeSoto and Hardee
counties, May to September 1971 ........................................ 49
23. Graphs of variations in water-quality parameters with depth ................... 52
24. Map of Joshua Grove and well field, northeastern DeSoto County............. 54
25. Graph of average daily irrigation pumpage, Joshua Grove .................... 55
26. Graph of test data, well 1715-3746.2, and type curve ......................... 57
27. Graph of projected drawdowns at 5 miles and 10 miles from center of Joshua
G rove ................................................................. 58
28. Graph of projected long-term changes in potentiometric surface due to
hypothetical pattern of Joshua Grove pumpage ........................... 59
29. Graph of Joshua Grove pumping rate and water-level changes in observation
wells .................................................................. 61
30. Graphs of variations in water quality parameters with depth ................. 65
31-42 Maps showing distributions of water-quality parameters, upper and lower units of
the Floridan Aquifer-







31. Dissolved solids, upper unit............................................... 65
32. Dissolved solids, lower unit............................................. 66
33. Water temperature, upper unit .......................................... 67
34. Water temperature, lower unit .......................................... 68
35. Hardness, upper unit ................................................... 69
36. Hardness, lower unit................................................... 70
37. Sulfate, upper unit ...................................................... 71
38. Sulfate. lower unit..................................................... 72
39. Chloride. upper unit ................................................... 73
40. Chloride. lower unit ............................................... .... 74
41. Fluoride. upper unit .................................................... 75
42. Fluoride. lower unit ...................................... ... ... .. 76







TABLES


Table Page
1. Age, thickness, and lithology of stratigraphic units..................... 14 & 15
2. Hydrogeologic framework and ground-water development .................... 22
3. Correlation of units of surficial deposits ................................. 25
4. Grain-size characteristics and hydraulic conductivity of upper sand and
phosphorite units ................................................... 27
5. Specific capacities of City of Arcadia wells tapping the upper unit of the
Floridan Aquifer ....................................................... 32
6. Characteristics of wells tapping only the lower unit of the Floridan Aquifer ..... 38
7. Median values and ranges of water-quality characteristics, Floridan Aquifer..... 63
8. Ground-water withdrawals, 1970 ......................................... 86
9. Water pumped for irrigation at selected sites, 1970 ......................... 87
10. Public-supply wells ..................................................... 89































































































































































d







GROUND-WATER RESOURCES OF DESOTO
AND HARDEE COUNTIES, FLORIDA


By
William E. Wilson

ABSTRACT


Ground water in DeSoto and Hardee counties, Florida, is obtained from
the surficial aquifer and the Floridan Aquifer. The surficial aquifer consists
principally of fine sand; average transmissivity is estimated at 1,300 feet
squared per day. Wells yield a few tens of gallons per minute or more for
domestic, lawn-irrigation, or stock-watering supplies.
In the two-county area, the Floridan Aquifer has been divided into an
upper part, or unit, and a lower unit, both chiefly limestone and dolomite.
The upper unit, which includes the Hawthorn Formation and the limestone
unit of the Tampa Limestone, averages about 160-200 feet in thickness. Near
Arcadia, transmissivity is estimated to be more than 4,000 feet squared per
day. Wells yield from a few tens of gallons per minute to more than 100
gallons per minute and are used mostly for domestic supplies. The lower
DeSoto and Hardee counties, large tracts of land had been leased and held in
Limestone, averages more than 900 feet in thickness. Few wells are open only
to the lower unit. Most that are yield more than 1,000 gallons per minute.
A confining bed of clay and marl separates the surficial aquifer and the
upper unit of the Floridan Aquifer. In much of the area, the sand and clay unit
of the Tampa Limestone is a confining bed between the upper and lower units
of the Floridan Aquifer.
Aquifer-test results suggest a transmissivity of the combined upper and
lower units of the Floridan Aquifer of 270,000 feet squared per day in the
northeastern part of DeSoto County. The potentiometric surface of the
Floridan Aquifer slopes toward the west and southwest. The southern tip of a
large regional depression in the surface extends from Polk County into
northern Hardee County. During dry (pumping) seasons, a pronounced
trough develops in the surface in southwestern Hardee County. In 1971,
seasonal fluctuation of the surface was less than 10 feet in most of DeSoto
County, but more than 30 feet in parts of Hardee County. During rainy (non-
pumping) seasons, wells flow in parts of both counties. During dry seasons,
areas where wells flow are nearly absent in Hardee County.
From 1949 to 1973, net declines in the potentiometric surface ranged
from a few feet or less in much of DeSoto County to about 20 feet in
northeastern Hardee County; most of the change occurred during 1962-73.
In and near the Peace River valley and in the southern part of DeSoto






BUREAU OF GEOLOGY


County, hydraulic head increases with depth in the Floridan Aquifer.
Elsewhere, head generally decreases with depth.
In northeastern DeSoto County, a citrus grove with a well-field capacity
of about 86 million gallons per day has been established. An analysis using a
hypothetical annual pumping schedule (155 days of fall and winter pumping
at 50 Mgal/d, 90 days of spring pumping at 100 Mgal/d, and 120 days of
summer shutdown) indicates that drawdowns 5 miles from the grove center
would be about 5 feet at the end of each spring pumping period. Water levels
would recover nearly fully during summer non-pumping periods.
In the Floridan Aquifer, ground water with the lowest mineral
concentration is in the upper unit and in northern Hardee County; for most
dissolved constituents, highest concentrations occur in the lower unit and in
southwestern DeSoto County. Ground water in the lower unit is commonly
warmer and more mineralized along the Peace River valley than elsewhere.
In parts of both counties, concentrations of dissolved solids, sulfate,
chloride, and fluoride in the Floridan Aquifer exceed limits recommended for
drinking water by the U. S. Public Health Service (1962). An average of about
94 million gallons per day was withdrawn in the two counties in 1970; about
96 percent was for irrigation purposes.
A long-term decline of the potentiometric surface of the Floridan
Aquifer in both counties has resulted in a diminution of the area of artesian
flow. but probably has not significantly affected the flow of the Peace River.
Upward flow within well bores probably contributes to the generally poor
quality of water in southwestern DeSoto County. Ground-water inflow or
outflow has not been significantly affected by development within the
counties. Upward intrusion of salt water is hindered by beds of low
permeability which lie beneath the Floridan Aquifer.
Management techniques that appear hydrologically suitable in the
counties involve: (1) developing specific aquifer units and areas for
particular uses; (2) enhancing aquifer recharge by use of wells that connect
the surficial aquifer with the Floridan Aquifer; (3) controlling flowing wells;
and (4) metering large ground-water withdrawals.


INTRODUCTION
The water resources of DeSoto and Hardee counties-two rural,
sparsely populated, inland counties in southwest Florida (fig. 1)-remained
relatively undeveloped as of 1970. During the decade of the 1960's, when
Florida's population increased by 38 percent, the rate of growth in these two
counties was less than half the statewide average, and the population density
of about 21 people per square mile was about one-fifth the statewide average.
Most water withdrawn was ground water for irrigation of citrus, vine crops,
and pastureland; little surface water was used, and only small amounts of






REPORT ON INVESTIGATION NO. 83 3

870 86 85
8 8I I 840 83 82 810 800
L310





-2930
SOUTHWEST
FLORIDA :
WATER /
MANAGEMENT ..
DISTRICT 280

--"'- PLP J0 C \
>- \ -< .r O b -270
5 WAUCHULA
SHARDEE -. J-260
C LT COUNTY 0C1
COUNTY I o o
lds wr cr fr f
I I / 250
r---.. \0 KL/ E TRE--
/ DE SOTO / ,









Figure 1. Location of DeSoto and Hardee counties.
I ARCADIA ,




O 10 KILOMETRES j-

Figure 1. Location of DeSoto and Hardee counties.

ground water were withdrawn for municipal and industrial uses. Water-
resources development consisted mostly of drilling irrigation wellasas new
lands were cleared for farms or pasture and as irrigation systems were
installed in groves. Thus, the counties by the late 1960's had few significant
water problems, and they had none of the problems that were accompanying
the rapid urbanization of other parts of the state.
Changes that could have substantial effects on the counties' water
resources were anticipated or underway in the late 1960's. Developers in the
populus coastal counties to the west and south, among the fastest growing
areas in the state, were looking inland for high-quality water to supply their






BUREAU OF GEOLOGY


burgeoning populations. In Polk county, which adjoins Hardee County on
the north, large withdrawals for industrial, irrigation, and municipal uses had
resulted in lowered artesian water levels in wells in Hardee County. Within
DeSoto and Hardee counties, large tracts of land had been leased and held in
reserve for possible future phosphate mining. Also, a citrus development
covering about 37 mi2and requiring large volumes of water for irrigation was
underway in DeSoto County.


PURPOSE AND SCOPE

Recognizing the potential for serious water-resources problems, the
Southwest Florida Water Management District and Bureau of Geology,
Florida Department of Natural Resources, requested the U. S. Geological
Survey to evaluate the water resources of DeSoto and Hardee counties. Such
an investigation would provide a basis for sound development and
management of the area's water resources. This report presents the results of
about 2! years of field study. The principal objectives were to: (1) obtain an
understanding of the structure, stratigraphy, and functioning of the
hydrogeologic system; (2) determine areal and temporal variations in the
quantity and quality of the water resources; and (3) inventory water uses.
Some preliminary data on stream flow characteristics and quality of surface
water were collected. However, early in the investigation the significance of
ground-water resources both as the primary source of supply and as the
resource most needing evaluation was recognized. As a consequence, full
emphasis was placed on assessing the ground-water resources in the counties,
and this report deals primarily with that aspect. In addition major
consideration was given to the principal aquifer in the area, the Floridan
Aquifer.
For the convenience of readers who may prefer to use metric units rather
than English units, conversion factors for the terms used in this report are
listed in an unnumbered table at the end of the report.

PREVIOUS STUDIES AND SOURCES OF PUBLISHED DATA
DeSoto and Hardee counties have been included in numerous statewide
regional hydrologic and geologic investigations, but the area has not
previously been the principal subject for a comprehensive ground-water
resources report. Most geologic investigations have been stratigraphic studies
related to phosphate exploration. Some recent publications with pertinent
references to DeSoto and Hardee counties are summarized briefly below.
Results of a preliminary investigation of the geology and ground-water
resources of the two counties (Woodard, 1964) provided background
information on the geologic formations and their water-bearing charac-






REPORT ON INVESTIGATION NO. 83


teristics; the configuration and fluctuation of the artesian potentiometric
surface; ground-water quality, with particular emphasis on fluoride con-
centration; and well locations and construction characteristics.
Other interpretative reports have dealt with certain hydrologic aspects of
areas that include DeSoto and Hardee counties. Kaufman and Dion (1967)
mapped the distribution of various ground-water quality parameters in the
southern Peace River basin. The maps show that concentrations of most
chemical constituents are generally higher in the deeper parts of the aquifer, in
the southern parts of the area, and near the Peace River valley. Fluoride
concentrations in streams and ground water in the Peace and Alafia River
basins were investigated by Toler (1967), who reported that concentrations in
ground water generally increased southward in DeSoto and Hardee counties
and were higher in the shallow formations than in the deep formations.
Stewart and others (1971) mapped the potentiometric surface of the
Floridan Aquifer for May 1969 in the Southwest Florida Water Management
District, which includes DeSoto and Hardee counties. The maps show that in
most of the two counties, the decline in the potentiometric surface during
1949-69 was less than 20 ft. Declines during 1964-69 ranged from 0 to 5 ft. in
southern DeSoto County to 15 to 20 ft. in northern Hardee County.
Basic data on surface water and ground water in the two counties are
contained in numerous reports. Streamflow records for the Peace River and
its tributaries and chemical analyses of water samples are published annually
in the U.S. Geological Survey series, "Water resources data for Florida." In
addition, flow-duration, low-flow, and high-flow characteristics for gaged
streams in the counties have been tabulated in a report by Heath and
Wimberly (1971). Records of water levels of observation wells are published
biannually in the Florida Bureau of Geology Information Circular series,
"Water levels in artesian and non-artesian aquifers of Florida." Well records
for DeSoto and Hardee counties are included in reports by Woodard (1964)
and Kaufman and Dion(1968). Hendry and Lavender(1959) summarized the
water-quality, construction, and yield characteristics of 548 flowing wells in
the two counties. A summary of the trends and fluctuations of ground-water
levels in five observation wells during 1967-68 is contained in a report by
Healy (1971). Healy (1972) has also summarized facilities and chemical
analyses for public water supplies at Arcadia and Wauchula.

ACKNOWLEDGMENTS

The author gratefully acknowledges the valuable assistance provided by
many organizations and individuals in conducting this investigation. Per-
sonnel of the Florida Bureau of Geology provided access to well records
and cuttings and conducted geophysical logging of many wells in the counties.
Personnel of the Southwest Florida Water Management District participated







BUREAU OF GEOLOGY


in aquifer tests and well inventories. Many drillers personally provided well
data; the author wishes to thank in particular the owners and drillers of Gator
Well Drilling, Inc., and Palmer and Pritchard Well Drilling for their generous
assistance.
The author is grateful to the many ranchers, grove operators, and other
land owners who permitted access to their land and allowed the sampling of
water and measuring of water levels in their wells. The cooperation and
assistance of personnel of American Agronomics Corporation and American
International Food Corporation were invaluable in the data-collection
program at Tropical River Groves. Personnel of the Turner Realty Company
permitted frequent examination of their catalog of aerial photographs.
William J. Lang, U. S. Geological Survey, Sarasota, assisted in sup-
plying stratigraphic interpretations, on the basis of his examination and
description of well cuttings and geophysical well logs.
This investigation was conducted under the general supervision of C.S.
Conover, District Chief, and under the direct supervision ofJ. S. Rosenshein,
Subdistrict Chief, Water Resources Division, U.S. Geological Survey.


WELL LOCATION AND NUMBERING SYSTEMS

All inventoried wells referred to in this report have been located in the
field; their positions are plotted on plate I included in the pocket at the back
of this report. The principal well-numbering system used in this report is that
of the U. S. Geological Survey. The system is based on the position of wells
within a one-second grid of parallels of latitude and meridians of longitude.
The Geological Survey number used to catalog wells is a 16-character
number that defines the latitude and longitude of the south-east corner of a 1-
second quadrangle in which the well is located. The first 6 characters of the
well number include the digits of the degrees, minutes, and seconds of
latitude, in that order. The 6 digits defining the latitude are followed by the
letter N which indicates north latitude for wells in the northern hemisphere.
The 7 digits following the letter N give the degrees, minutes, and seconds of
longitude. The last digit, set off by a period from the rest of the number, is
assigned sequentially to identify wells inventoried within the 1-second
quadrangle.
An example of the well number is illustrated in figure 2. The designation
270744N0815030.1 indicates the first well inventoried in the 1-second
quadrangle bounded on the south by latitude 27007'44" and on the east by
longitude 081 050'30".
An 8-digit reference number is used to facilitate identification of wells in
the text, tables, and illustrations of this report. The reference number consists
of the minutes and seconds of latitude and longitude, followed by a sequential
number only if that number is greater than one. The degrees of latitude and







REPORT ON INVESTIGATION NO. 83


840 830 820 81 800
I I I310




/
S 2300



0-290

:. : : 270


'I-


Figure 2. Latitude-longitude well-numbering system.




longitude and the letter N can be omitted from the full number because all
wells in DeSoto and Hardee counties are in 270 N latitude and 081 or 0820
longitude, and each reference number refers to a unique well location in the
counties.
As an example of the reference number, the well number 270744N0815030.1,
used in the example and illustrated in figure 2, is shortened to 0744-5030. This
well can be found on plate 1 by first locating the 5-minute rectangle that con-
tains latitude 7 minutes and longitude 50 minutes. The imaginary block con-
taining the precise minutes of latitude and longitude can then be determined
from the 1-minute tick marks on the grid lines. The well site is identified within
this block by the dot and the number 44-30, which denotes the seconds of
latitude and longitude.






BUREAU OF GEOLOGY


DESCRIPTION OF THE AREA
GEOGRAPHIC SETTING

DeSoto and Hardee counties are contiguous and occupy 721 mi2 and 650
mi2, respectively, in southwestern Florida (fig. 1). The shape and character of
landforms determine to a great extent land use, which in turn affects the
demands and uses for water resources. Both counties lie entirely in the mid-
peninsular physiographic zone of White (1970); included are three
subdivisions, the Polk Upland, DeSoto Plain, and Gulf Coastal Lowlands
(fig. 3). These sub-divisions correspond approximately to several marine
plains or terraces formed by invasions of the sea during the Pleistocene
Epoch. The Polk Upland is a broad, slightly dissected upland in northern
Hardee County, usually at altitudes above 100 ft. The gently sloping, nearly
undissected DeSoto Plain lies between about 30 ft and 100 ft altitude, and the
Coastal Lowlands proper consists of the poorly drained, low-lying land at
altitudes below 30 to 40 ft, in central and south-western DeSoto County.
Each surface is bounded inland by a low scarp or break in slope that
represents the position of a former marine shoreline. The 100-ft and 30-ft
topographic contour lines correspond approximately to the Wicomico and
Pamlico shorelines, respectively (fig. 3) (Cooke, 1945; MacNeil, 1950). Other
shorelines in Florida were recognized by Cooke (1945) at 70 ft (Penholoway
shoreline) and 42 ft (Talbot shoreline), and these were regarded by Cooke
(1945) to represent pauses in the retreat of the sea from the 100-ft level.
The older marine surfaces have been dissected, but large segments of the
younger ones remain nearly uneroded (Parker and others, 1955, pl. 12). The
land is characteristically poorly drained; numerous marshes, many in shallow
saucer-like sink-hole depressions, dot the landscape. The counties are,
however, nearly bisected by one of the principal rivers of southwestern
Florida, the southward-flowing Peace River (fig. 1). They lie almost entirely
within the Peace River drainage basin. Several square miles of southwestern
Hardee County are in the headwaters of the Myakka River basin. At times of
high flow, water from the large marsh and grassland areas in eastern and
southeastern DeSoto County probably drains eastward into central Florida
watersheds.
Much of the land area in the counties remains undeveloped. Hardwood
forests predominate in the bottomlands of the Peace River and its tributaries.
Away from the river, most of the undeveloped land is pine flatwoods, saw
palmetto, and, in eastern DeSoto County, prairie grassland.
In 1969, about 16 percent of the total land area in the counties was
cropland, much of it requiring irrigation. Hardee County (22.6 percent of
county land area in cropland) was more intensely cultivated than DeSoto
County (10.6 percent). More than half of the total cropland was citrus groves,
and most of the remainder was pastureland. In 1969, citrus acreage in Hardee
County (50,716 acres) was nearly twice that of DeSoto County (25,478 acres),







REPORT ON INVESTIGATION NO. 83


GULF 31
| \ 3 LUOWLANDA 4 6 KILOMETRESI
S.DE SOT. COUNTY
CHARLOTTE COUNTY
S 82000' 55' 50' 45' 4' 8135'
Figure 3. Physiographic subdivisions.

but by 1972 the citrus acreage in DeSoto County had nearly doubled with the
addition of 25,000 acres from a single grove (Wilson, 1972) in the northeastern
part of the county.
The principal vegetable crops grown in the counties are watermelons,
cucumbers, and tomatoes. Cucumbers and tomatoes are commonly harvested
twice a year, but because of nematode problems they generally cannot be
grown on the same land in successive years. Thus annually 6,000-8,000 acres
of new land are cleared, drained, and irrigated; commonly the abandoned
land is converted to irrigated pastureland.






BUREAU OF GEOLOGY


The rural aspect of the counties is reflected in the sparseness of the
population and absence of major urban centers. In 1970, about a third of the
counties population of 27,949 resided in the two county seats, Arcadia (pop.
5,658) in DeSoto County and Wauchula (pop. 3,007) in Hardee County.
Bowling Green (pop..1,357) and Zolfo Springs (pop. 1,117), both in Hardee
County, are the only other sizeable communities (U.S. Dept. Commerce,
1970).


CLIMATE
Climate is a major factor in determining the seasonal availability and use
of water. The climate of south central peninsular Florida is classed as
subtropical humid and is characterized by long, warm, relatively wet
summers, and mild, relatively dry winters.
Rainfall, the ultimate source of all fresh water, has been measured at
Arcadia since 1907 and at Wauchula since 1933. Rainfall patterns at the two
stations are similar (fig. 4 and 5), averaging about 55 in. In the wettest years
of record, rainfall exceeded 80 in., and in the driest years, rainfall was less than
40 in. Figure 4 indicates no apparent long-term trend in precipitation; rather,
a series of wet years, such as in the late 1950's, is generally offset by a
succeeding series of dry years, such as in the 1960's. On the other hand, two
consecutive years often have a difference in rainfall of more than 25 in.
As shown by the monthly normal values in figure 5, precipitation is
unevenly distributed throughout the year. At both Arcadia and Wauchula,
about 60 percent of the annual total falls during four summer months, June
through September. Most of the summer rainfall is derived from local
showers or thunderstorms, but it may be substantially augmented by tropical
storms that periodically affect the peninsula. The rainy season generally
begins and ends abruptly: average June precipitation is more than double
that of May, and average October rainfall is about half that of September (fig.
5).
The seasonal pattern of rainfall is also reflected in the monthly extremes
(fig. 5). During the periods of record, at least I in. and a maximum of more
than 15 in. have been recorded during each of the four rainy months. On the
other hand, the minimum recorded for each of the eight remaining months is
less than 0.20 in., and at Arcadia no rain has been observed in five of those
months during the period of record.
The mildness of the climate is indicated by mean monthly temperatures
at Arcadia (fig. 6), which range from 62.90 F (17.20 C) in January to 82.00 F
(28.90 C) in August. Temperature during the four warmest months, June
through September, averages 81.00 F (27.20 C). Corresponding average
temperatures at Wauchula are a few tenths of a Fahrenheit degree lower.
Although temperature exceeds 900 F (320 C) on about a third of the days in an








REPORT ON INVESTIGATION NO. 83


ANNUAL CUMULATIVE -
DEPARTURE FROM
NORMAL






I I I I I I I I l I I II I I I tI I t ti i ti I

5-YEAR MOVING
AVERAGE




1941-70 NORMAL\
IIIIIIIII11111 IIIIIII I1llill


- ARCADIA

ARCADIA


n 0 o- 0 i n
ao, o, _, _, _
WAUCH ULA


Figure 4. Annual rainfall at Arcadia and Wauchula.


average year, only in an occasional year does it exceed 1000 F (380 C).
Freezing temperatures occur 5 to 7 days each year on the average, and
although temperatures dip into the low or mid-twenties in most years, no
value below 200 F (-70 C) has been recorded at Arcadia or Wauchula.



GEOLOGIC FRAMEWORK

DeSoto and Hardee counties are underlain by a thick sequence of
sedimentary rocks whose lithology and structure control the occurrence and
movement of ground water. The principal elements of this geologic
framework are described below; more detailed discussions of the geology and
aquifer and confining-bed characteristics are contained in the Ground Water
section of this report. The stratigraphic nomenclature used in this report was
determined from several sources and may not necessarily follow the usage of
the U. S. Geological Survey.
Table I shows the age, thickness, and lithology of the stratigraphic units
penetrated by wells in the area. These units include, in order of penetration
when drilling, the following: surficial deposits, Hawthorn Formation,


- A --1000



0

ANNUAL CUMULATIVE
DEPARTURE FROM NORMAL --500
I I I I I I I I 1I I I I I I I I l l l l l l!R


-1200

-1200


l l l t i l l I I I I I I I II II lI II I I I
5-YEAR MOVING
AVERAGE




1941 70 NORMAL
I 111111111 111111111 | 111111


1941-70 ANNUAL RAINFALL
NORMAL







............. ......


I1IIII IlII Itt I 1111111II l
-1941-70 ANNUAL RAINFALL
NORMAL



I F- II i 'lA" '


) fo 0
I, s a


-2000



-1000


J







BUREAU OF GEOLOGY


WAUCHULA
S(1933-70)

M Maximum and year

ENormal (1941-70)

]Minimum and year

1954


1946















93962


1959









::677


1953-


J F M A M J J A S 0 N D


1958


1951









I e


1952


1958


=-


Figure 5. Average, maximum, and minimum monthly rainfall at Arcadia and Wauchula.


1949















19S8


16

14

12


V)


-0 I-





J
-500

-j

-400
z



-300




-200




-100




0


1939


1947


1936


1952


'''


"" '
:[Qfib


mrtif


IOdn






REPORT ON INVESTIGATION NO. 83


90
9 AVERAGE -30
SLL 80


>WW
S ANNUAL



7 50 \-O





SJ F M A M J Ji A S 0


Figure 6. Average monthly and average annual air temperature at Arcadia.

Tampa Limestone, Suwannee Limestone, Ocala Group, and Avon Park
Limestone. The surficial deposits have been subdivided into three lithologic
units: upper sand, shell and sand, and phosphorite. In this report, the
Hawthorn Formation and the upper part of the Tampa Limestone
(designated the limestone unit of the Tampa Limestone) have not been
differentiated. The lower part of the Tampa Limestone has been designated
the sand and clay unit. In addition, a dolomite unit of the Avon Park
Limestone has been identified and mapped separately from the rest of the
formation. All these rocks are Quaternary or Tertiary in age. In much of the
area, the section is more than 1,500 ft thick; only the surficial deposits and
Hawthorn Formation are exposed in outcrops in the two counties.
Among the criteria used in this study for identifying stratigraphic units
are characteristic patterns on geophysical well logs, as described in table I and
illustrated in figure 7. Gamma-ray logs are particularly useful for correlating
certain stratigraphic boundaries. Rocks of Miocene and younger age com-
monly contain nodules of phosphorite, and the relatively high natural-gamma
radiation produced by these phosphate-rich rocks is reflected in the trace of
the gamma-ray log. In figure 7, the upper andlower boundaries of the Haw-
thorn Formation and limestone unit of the Tampa Limestone and sand and
clay unit of the Tampa Limestone, as determined from well cuttings, corre-
spond closely to changes in radiation indicated by the trace of the gamma-ray
log.
Variations in the distribution, thickness, and dip of stratigraphic units in
the counties are depicted in the geologic sections in figures 8, 9, and 10. The
sections show that the units are widespread, generally uniform in thickness,
and dip gently to the south and west. Thus, wells drilled in the northern part of
the area penetrate a given unit at higher altitudes than those in the southern
the area penetrate a given unit at higher altitudes than those in the southern







Table 1. Age, thickness, and lltholog) of tlrailgraphic unlit

Geologic age Straligraphic Thlcknem Remarks and identifying
Period Epoch unit (feel) Litbology criteria
Sand, clayey, very fine to medium-
grained, predominantly fine-grained;
white to brown; trace of phosphate in
Upper sand unit 0-70 lower part, minor thin beds of lime-
stone and bluish gray clayey sand
and clay.

Quaternary Holocene. & Sand and clayey sand, very fine to
and Pleistocene, V Shell and fine-grained, gray to green; minor to
Tertiary Pliocene. 3 sand unit 0-55 abundant shells, including large oyster
and Miocene and barnacle shells.
SClayey sand and sandy clay, fine-
grained. calcareous to noncalcareous;
abundant phosphorite nodules up to
Phosphorite unit 0-40 pebble size, white to gray in upper
part, amber or black in lower part:
includes beds of clean phosphatic
sand and sand and gravel.


Hawthorn
Formation and
limestone unit
of Tampa
Limestone.
undivided


160-370


SI I


In upper part, predominantly marl.
dolomite, and limestone; soft, chalky,
fine-grained to sandy or pebbly:
abundant brown or black phosphorite
grains or pebbles; minor thin-bedded
sand and clay.


In lower part, predominantly lime-
stone, massive or thick-bedded.
hard, dense, cherty, fossiliferous,
phosphatic, white to gray and brown;
minor thin-bedded sand and clay.
Where underlying sand and clay unit
is absent, equivalent beds are lime-
stone. predominantly sandv. fossii-


Generally the uppermost
limestone in the section,
less plastic than under-
lying sand and clay unit of
Tampa Limestone, phos-
phatic throughout. Shows
highest radioactivity of the
section on gamma-ray logs.


I ~ s~ i-I-r -- ______


Miocene


I -




o Tampa-I J amy, sanuy, U4I~, *- ,-- I


Lime-
Sstone

I-


and hard, waxy, dark green to black,
marly; minor limestone.


gamma log. Sand and clay
unit grades westward to
sandy limestone (limestone
unit ofTampa Limestone).


Oligocene Suwannee Limestone, nodular, granular, chalky, Clean, nodular, non-
Limestone some fragmental, some oolitic, usually phosphatic limestone con-
very fossiliferous, cream to white, trasts to overlying phos-
100-250 occasionally some clear quartz grains. phatic plastics. Very low
radioactivity on gamma-
ray log.


Ocala Group'


Avon Park
Limestone


260-400


200-470


Dolomite Maximum at
unit Ileast 150


Limestone, chalky, nodular, granular,
fragmental, some oolitic, generally
very fossiliferous, cream, white, some
buff; occasional dolomite in lower
part, sucrosic to dense and cherty,
yellowish brown to dark-brown
and gray.


Limestone, chalky, nodular, oolitic,
fragmental, intergranular anhydrite
and gypsum, very fossiliferous, cream,
white, and buff; commonly thin
dolomite in middle part, dense to
finely crystalline or sucrosic, yellow
to grayish brown.


Dolomite; massive, dense to finely
crystalline or sucrosic, some coarsely
crystalline, pale-yellow and brown to
dark-brown and gray, mottled.


Lepidocyclina sp. and/or
Camerina fossils abundant.
Lepidocyclina usually ap-
pears 20-40 feet above
Camerina. Zone of low
radio-activity occasionally
marks the top on gamma-
ray logs.


Distinctive fossil Dictyo-
conus cookei.


Lithology contrasts to over-
lying limestones; dolomite
has high resistivity and self
potential on electric log,
and'commonly high gamma
radiation on gamma-ray
log.


'Designated Ocala Limestone by the U. S. Geological Survey.


Tertiary


Eocene


0.
2w











00



-0


--







BUREAU OF GEOLOGY


Figure 7. Stratigraphic section and gamma-ray log, well 1601-3646.

part. Locations of the geologic sections are shown on the map in figure 11, on
which is also shown the distribution of the sand and clay unit of the Tampa
Limestone.

GROUND WATER
The source of ground water in DeSoto and Hardee counties is
infiltrating rainwater within and to the north and east of the counties. Ground
water moves downgradient from areas of recharge and leaves the counties
through discharge to streams, by evapotranspiration, as underflow, and
through wells. All the stratigraphic units of the counties yield some water to









REPORT ON INVESTIGATION NO. 83


Fr
I1

s
!


0 5 MILES
I-----i~---'
0 5 KILOMETRES
VERTICAL SCALE
GREATLY EXAGGERATED


EXPLANATION
t0


I


Well used for control,
and well number


Figure 8. Geologic section A-A'.




wells, but water-bearing characteristics differ considerably among the units.
Therefore, they have been categorized hydrologically as aquifers or confining
beds. Some of the terms used to describe them and their water-bearing
characteristics are defined in the following paragraphs. Definitions are based
on those of Lohman and others (1972) and Lohman (1972); dimensions given
are those used in this report.
Aquifer: A formation, group of formations, or part of a formation that
contains sufficient permeable material to yield sufficient quantities of water
to wells and springs.
Confining bed: A body of "impermeable" material stratigraphically
adjacent to one or more aquifers.
Hydraulic Conductivity, K: The rate (ft3/d) at which water of the
prevailing kinematic viscosity is transmitted through a unit area (ft2) of


A
FEET
200-

SEA _
EVEL

200-


600




1000-

1200 -


1400-


A'

METRES


SEA
LEVEL



-100



-200



-300



400












3~


B
p
FEET

400*

SEA
LEVL'

H
200


400


600-


800-


1000-


1200-


1400


100


0 5 MILES
I-----,~---
0 5 KILOMETRES
VERTICAL SCALE
GREATLY EXAGGERATED


EXPLANATION




------

Well used or control,
ed well number

Figure 9. Geologic section B-B'.


a U


z


B!
; B'

* METRES


S

LEVEL



-K00



-200




300




400








REPORT ON INVESTIGATION NO. 83


ZI


W4.


EXPLANATION
t0

I-


0 5 MILES
I ----I--
0 5 KILOMETRES
VERTICAL SCALE
GREATLY EXAGGERATED


Well used for control,
and well number
Figure 10. Geologic section C-C'.


aquifer at right angles to the direction of flow, under unit hydraulic gradient
(ft/ft): expressed as ft/d.
Transmissivity, T: The rate (ft3/d) at which water of the prevailing
kinematic viscosity is transmitted through a unit width (ft) of the aquifer
under unit hydraulic gradient (ft/ft); expressed as ft2/d.
Storage Coefficient, S: The volume (ft3) of water an aquifer releases
from or takes into storage per unit surface area (ft2) of the aquifer per "nit
change in head (ft); dimensionless.


C I

FEET
200-


SEA
LEVEL

200


400-


600-


800


1000-


1200 -


1400 -


C'

0
4 METRES



SEA
LEVEL




100




200




300




-400







BUREAU OF GEOLOGY


EXPLANATION
2129-
3910
A ------A'
Line of geologic wetlon
wltl well location and
number. See figure s 4,9 10i
Aiso of sand and eloy
unit of Tampa LieletMe
0 1 4 MILES
0 1 4 6 KILOMIMTSth i


Failure II. D)htrlbutlon of tand end clay unit of 'Tmpn LinmMtone mnd Iliea of geololgi
%ectionw.


.cakance Coefficient: The ratio of vertical hydraulic conductivity, K'.
and thickness. h'. of a confining bed; expressed as (ft/d)/ft.
The terms "hydraulic conductivity" and "transmissivity" have replaced
"coefficient of permeability" and "coefficient of transmissibility," respective-
ly. in U. S. Gelogical Survey terminology. Values of hydraulic conductivity
and t ransmissivity mayeach be multiplied by 7.48 gal / ft' to obtain values ofthe







REPORT ON INVESTIGATION NO. 83


correspondingg former terms, expressed in the inconsistent units of gallons-
lays-feet.
Because confining beds have relatively low hydraulic conductivity
compared to aquifers, they restrict the flow of water between aquifers and
Aield only small amounts of water to wells. The effectiveness of confinement
varies, however, depending on confining-bed thickness and head differences
between aquifers as well as vertical hydraulic conductivity. Under suitable
conditions, considerable amounts of water can leak through and be derived
from confining beds.
The rocks in DeSoto and Hardee counties are of two principal
types: (1) unconsolidated sand and clay, and (2) limestone and dolomite
(table 1). Sand and clay are the principal materials in the upper part of the
section, in Miocene and younger rocks. Water in these plastic deposits occurs
in primary openings, the spaces between the grains comprising the deposits.
Limestone is a sedimentary rock consisting chiefly of calcium carbonate,
chiefly in the form of the mineral calcite, and dolomite is a sedimentary rock
consisting chiefly of the mineral dolomite. The two rock types make up part of
the rocks of Miocene age and are the only rock types in the lower part. or
Eocene- and Oligocene-age part, of the stratigraphic section. Water in these
carbonate rocks occurs and moves principally in secondary openings,
including joints, openings along bedding planes, and pores that commonly
have been enlarged from solution by ground water,
In the counties, two aquifers have been identified, the surficial aquifer
and the Floridan Aquifer, which are separated from each other by a confining
bed. In the two-county area, the Floridan Aquifer is divided into an upper part.
or unit, and a lower part, or unit. For convenience, in this report, the
expression "unit" rather than "part" was preferred in discussing these two
segments of the Floridan Aquifer. The expression "unit" is used here in a
hydrogeologic sense, and should not be confused with the lithologic"unit" as
here applied to divisions of the surficial deposits, or with the stratigraphic
"unit" as applied in this report to the named formations.
Some features of these two hydrogeologic units, as related to the
development of ground water, are summarized in table 2. The descriptions
and values shown are generalized and intended primarily to provide an
impression of broad characteristics and relative values. Details of geology.
water-bearing characteristics, and development of each unit are discussed in
the next section of this report.

SURFICIAL AQUIFER
The surficial aquifer consists of the three units of the surficial
deposits: upper sand, shell and sand, and phosphorite. Except for minor
thin-bedded limestone, these deposits are unconsolidated, and the principal








BUREAU OF GEOLOGY


constituent is fine-grained quartz sand. Wells drilled into the underlying
limestone of the Floridan Aquifer are cased off opposite the surficial aquifei,
but many wells in the area are screened or drilled open hole or open end in th:
surficial aquifer.


GEOLOGY

The stratigraphy of Miocene and younger deposits in DeSoto and
Hardee counties has been interpreted variously by previous investigators
(Bergendahl, 1956; Carr and Alverson, 1959; Ketner and McGreevy, 1959;
Cathcart and McGreevy, 1959; and Cathcart, 1966). These investigators were
concerned primarily with the extent, origin, and composition of economic
phosphate deposits. From a hydrologic standpoint, a classification based on
lithology rather than age or origin suffices for this report (table 1). The
distribution of the three units of the surficial aquifer-upper sand, shell and
sand, and phosphorite-is illustrated in the geologic sections of figure 12. The
lines of sections are shown on figure 13. The sections are modified from
published sections and logs of Bergendahl (1956), Ketner and McGreevy



Table 2. Hydrogeologic framework and ground-water development

Hydrgeollglc Equlvalent Predominant Approximate Yields of Well Common uses
unit stratllraphie lithology average wells (gal/min) construction
unit thickness (ft)

Surficial aquifer Surficial Sand 40 A few to Open end, open Domestic, stock
deposits several tens hole, well point, watering, lawn
screen, slotted irrigation
casing. Cased
off in deeper
wells
Upper unit Clay. marl 30 Cased oil
confining
hbcd

Vpper Hawthorn Limestone, marl. 200 Several Open hole Domestic, stock
unit of Formation and dolomite hundred watering, citrus
Floridan limestone unit irrigation, puhlie
] Aquifer of Tampa time- supply
Stonc, undivided
S Con- Sand 7?
fining and clay Sandy Clay. Open
bed unit of lime- marl, 130 141) hole or Cased
< rTampa tone sand caused off
Lime- off
stone
I owner unit Suwanne Generally Citrus, vegetable
of Florndan Limcstone more than and pasture
Aquifer Ocala Group Ltimestone oo00 00H as much Open hole irrigation: public
Avon Park as 2.500 supply
I imestone
Avon Park
Limestone Dolomite
(dolomite unit)









REPORT ON INVESTIGATION NO. 83 23


(1959), and Cathcart and McGreevy (1959). Sections published in these
earlier reports are based on cuttings from augered test holes; test-hole

numbers used on the geologic sections of this report correspond to the
previously published test-hole numbers. Land-surface altitudes assigned to

some test-hole sites were revised to conform to altitudes indicated on modern
topographic maps. Table 3 shows the correlations used to construct the
geologic sections of figure 12.
The surficial aquifer underlies the entire area, except in a few places
where limestone of the Floridan Aquifer crops out or is within a few feet of the

land surface, as along some reaches of the Peace River. Analysis of depths of


IUT METRES
140
140 -

j _.



20
SEA, "l 6i. SE







u*W c LEVE


MCTIES


100
_30
to


40
10 1

KA J!. tL
Ito

10 40


EXPLANATION
Section bams bg" W4
I ut Mr w 0fWon 11959),
wod Coatheori and Mc 0evj
(1959). TIesthoI" mimbi
ctalp0. A W those pWevioust
published,


o MILES
0 7 KILOMETRES
WVrtikl e erewHmon X422









H--
2 --to
S-10

SEA
LEVEL

K)


Figure 12. Geologic sections ofsurficial deposits. DeSoto and Hardee counties.


SEA
LEVtL
10
nT

100



to


-H

-2 K
B ? "






S'<'' :>







BUREAU OF GEOLOGY


I




ei
di
4
r
I:


0 1 2 3 4MILES
0 2 4 6 KILOMETRES


82000'


-50-
Structure contour
Shows altitude of lop of the
upper unit, Floridan Aquifer.
Contour interval 50 feet.
Datum is mean sea level


55' 50'

EXPLANATION


45' 40' 81035'


E*------ *-E'
Line of geologic section
with test hole location.


Figure 13. Altitude of the top of the upper unit, Floridan Aquifer, and lines of geologic sections
of surficial deposits.






REPORT ON INVESTIGATION NO. 83


Table 3. Correlations of units of surficial deposits

Cathcart and
Bergendahl Ketner and McGreevy McGreevy
This report (1956) (1959) (1959)
Upper Pleistocene sand Surficial sand Terrace sand
sand Upper micaceous sand Bone Valley Formation,
Lower micaceous sand upper unit
Hawthorn Formation,
S sand unit
a Shell Sand of late Unnamed sand
"5 and Miocene age and limestone
'5 sand Caloosahatchee Marl
J Phos- Undifferentiated Hawthorn Formation, Bone Valley Formation,
phorite phosphatic sand phosphorite unit lower unit
and clay Hawthorn Formation,
Sandy clay unit


wells tapping the surficial aquifer, as reported on 134 drillers' completion
reports submitted to Southwest Florida Water Management District during
1970-72, suggests that the aquifer thickens toward the south. The average
depth of 81 wells in Hardee County was 40 ft and of 53 wells in DeSoto
County, 65 ft. Average static water level, reported for 103 of the wells, was
about 7 ft. below land surface in both counties. The 41 test holes on the
geologic sections of figure 12 penetrated, on the average, about 45 ft of
surficial deposits. Most of the test holes in Hardee County penetrated the full
thickness of surficial deposits, whereas most of those in DeSoto County did
not. Few test holes were drilled in the eastern half of DeSoto County; thus, the
lithology and thickness of surficial deposits in DeSoto County are not as well
known as they are in Hardee County.
The upper sand unit, principally a fine-grained sand, averages about 25 ft
thick and blankets most of the two counties. The shell and sand unit averages
more than 28 ft thick. It occurs throughout DeSoto County and extends into
southern Hardee County. The unit also includes the unnamed sand and
limestone unit of Cathcart and McGreevy (1959) in eastern Hardee County
(table 3; figure 12, section F-F). In most of DeSoto County, the shell and
sand unit correlates with the sand of late Miocene age of Bergendahl (1956)
(table 3) and includes the Caloosahatchee Marl in southern and southeastern
DeSoto County. This marl is predominantly a "fine-grained gray sand,
slightly clayey to clayey in places, with large marine shells" (Bergendahl, 1956,
p. 84). In some parts of DeSoto County, as along Prairie Creek, the shell and
sand unit is composed mostly of shells.
The phosphorite unit averages more than 14 ft thick and underlies most
of Hardee County and northern DeSoto County (fig. 12, sections E-E' and F-
F'); it corresponds in extent generally to the area mapped as Bone Valley






BUREAU OF GEOLOGY


Formation by Puri and Vernon (1964). To the south, drillers' logs indicate
localized deposits of phosphatic sand and gravel underlying the shell and sand
unit near Arcadia. The deposits are commonly described by such terms as
"black sand and gravel" and "phosphate gravel," suggesting a coarse textured
and permeable material. The age, origin, and extent of the unit in this area are
unknown, but the deposits are assigned to the phosphorite unit of the surficial
aquifer on the basis of lithology.


WATER-BEARING PROPERTIES
The water-bearing properties of the surficial aquifer are largely
dependent upon grain-size distribution of the sediments. Analyses of 46
samples of the surficial aquifer in the two counties, summarized in table 4,
suggest only slight differences in average grain-size distribution between the
upper sand and phosphorite units of the aquifer. Variability within each unit
is greater than differences in average characteristics between them. The
samples generally had a median grain size in the fine-sand range, containing
only small amounts of coarse sand to gravel and of silt and clay (table 4).
Samples from the upper sand unit were consistently better sorted (had a lower
uniformity coefficient) because of lower proportions of both coarse and fine
fractions compared to samples from the phosphorite unit. Bergendahl (1956,
p. 92) reported that the surficial sand was also consistently finer grained than
the underlying units.
No analyses of samples of the shell and sand unit are shown in table 4; 13
samples of this unit in DeSoto County, reported by Bergendahl (1956, p. 3),
had an average median grain size of 0.22 mm (fine sand). However, these
samples were treated with acid before analysis, and the results are not directly
comparable to those in table 4 because the results represent only the sand
portion of the samples and not all types of material present. The 13 samples
did not include coarse shell beds, which are not as amenable to grain-size
analysis as the sandy deposits.
None of the phosphorite samples listed in table 4 were from the Arcadia
area; based on yields of wells and lithologic descriptions, phosphorite
deposits in this area are probably coarser grained than the deposits from most
of the remainder of the two-county area.
Average hydraulic conductivity of the surficial aquifer is estimated
to be a few tens of feet per day, based on the generally fine-grained texture of
the deposits. Average hydraulic conductivities listed in table 4 are 34 ft/ d for
the upper sand and 20 ft/d for phosphorite. The values were derived by use of
a method that relates permeability to sorting and median grain size (Masch
and Denny, 1966). Coarser grained and better sorted beds, such as coarse
sand, gravel, and clean shell, have hydraulic conductivities greater than the
listed average; finer grained and more poorly sorted beds, such as clay and














Table 4. Grain-size characteristics and hydraulic conductivity of the upper sand and phosphorite units

Proportion of -
No. Median Uniformity Average
Unit sam- grain size Coarse sand Silt and clay coefficient hydraulic
pies (mm) to gravel (percent) conductivity
(percent) (ft/day)
Average Raange Avege I Range Average Range Average Range
Upper sand 16 0.20 0.12-0.34 10 1-38 3 0-15 2.3 1.6-4.2 34

Phosphorite 30 .22 .12- .42 16 1-40 8 0-36 3.4 1.5-10 20






BUREAU OF GEOLOGY


sandy clay, have lower hydraulic conductivities. Hutchinson and Wilson
(1974) reported a value of 120 ft/d for a coarse-grained sand bed in
northeastern DeSoto County, based on laboratory measurements made on
undisturbed samples.
Average transmissivity of the surficial aquifer is probably about 1,100
ft2/ d. This value was determined from average hydraulic conductivity values
of the aquifer units and saturated thicknesses determined from logs of test
holes shown in figure 12. Average hydraulic conductivities shown in table 4
were used for the upper sand and phosphorite units; 20 ft/d was estimated for
the shell and sand unit. Average water-table depth was estimated at 7 ft.
Transmissivity values undoubtedly have a wide range in the counties because
of large differences in thickness and lithology of the aquifer.

DEVELOPMENT
Many hundreds of wells in DeSoto and Hardee counties tap the surficial
aquifer. Most of these are 2 in. in diameter, and the water from them is used
for domestic, lawn-irrigation, or stock-watering purposes. In a sample of 134
drillers' completion reports of wells drilled in 1971-72 fiscal years, well depths
averaged 65 ft in DeSoto County (81 wells) and 40 ft in Hardee County (53
wells). The greater depths in DeSoto County reflect the greater aquifer
thickness in that county. Most were finished as open hole; many of these
probably penetrate limestone stringers or cemented sands which allow the
holes to stay open. About 5 percent of the 134 wells have some form of screen
or slotted casing. Most wells reportedly pump a few tens of gallons per minute
and some more than 100 gal/ min. One 8-in. well, 54 ft deep, reportedly pump-
ed 600 gal/min from shell beds in southeastern DeSoto County.

FLORIDAN AQUIFER SYSTEM
The Floridan Aquifer is the most productive and widely used aquifer in
DeSoto and Hardee counties. The aquifer, which underlies all of Florida and
parts of other southeastern states, was originally defined by Parker (Parker
and others, 1955, p. 189) to include all or parts of the Lake City Limestone,
Avon Park Limestone, Ocala Group, Suwannee Limestone, Tampa Lime-
stone, and "permeable parts of the Hawthorn Formation that are in hydro-
logic contact with the rest of the aquifer."
In this report, the top of the aquifer is considered to be the top of the
uppermost limestone of the Hawthorn Formation. Few, if any, wells in the
two counties penetrate the Lake City Limestone, and thus the depth to the
base of the aquifer has not been determined.
In most of Florida, the thick sequence of limestones and dolomites
constituting the Floridan Aquifer has been treated as a single hydrologic unit
(Parker and others, 1955). Locally, however, at least two and sometimes more







REPORT ON INVESTIGATION NO. 83


distinct and widespread water-bearing zones are known to exist within this
sequence, each with unique hydraulic head, water-quality, and yield
characteristics. In DeSoto and Hardee counties, the Floridan Aquifer can
conveniently be divided into an upper unit and a lower unit separated by a
confining bed, and this terminology is followed in this report. As used in this
report, the expression "Floridan Aquifer System" refers to the upper and
lower units, the intervening confining bed and the upper unit confining bed.
Further study may show that further subdivision is warranted and feasible in
the two counties. In some areas, these zones have received separate
designations. For example, individual zones have been given aquifer names in
Lee County (Sproul and others, 1972) although some are a part of the Florida
Aquifer, and Sutcliffe (1973) assigned numbers to four such zones in
Charlotte County.
In DeSoto and Hardee counties, the Floridan Aquifer can conveniently
be subdivided into an upper unit and a lower unit separated by a confining
bed, and this terminology is followed in this report. As used in this report, the
"Floridan Aquifer system" refers to the upper and lower units, the intervening
confining bed, and the upper unit confining bed. Further study may show that
further subdivision is warranted and feasible in the two counties.

UPPER UNIT
The upper unit of the Floridan Aquifer consists of permeable limestone
and dolomite beds of the Hawthorn Formation and Tampa Limestone
(limestone unit), which in this report are undifferentiated. The upper unit
underlies all of DeSoto and Hardee counties and in much of the area is
hydraulically separated from the surficial aquifer by clay and marl, and from
the lower unit of the Floridan Aquifer by the sand and clay unit of the Tampa
Limestone. The sand and clay unit grades westward into a sandy limestone,
and in the western third of DeSoto County and south-western part of Hardee
County this limestone is included in the upper unit as part of the
undifferentiated Hawthorn Formation and Tampa Limestone (limestone
unit) (table 1).
The upper unit is equivalent to the secondary artesian aquifer as used by
Stewart (1966) for Polk County; to zones 2 and 3 as used by Sutcliffe (1973)
'or Charlotte County; and to the upper and lower Hawthorn aquifers as used
)y Sproul and others (1972) for part of Lee County.
The upper unit of the Floridan Aquifer is widely used as a source of
water, although yields of individual wells (table 2) and total withdrawals from
his aquifer are generally less than those associated with the lower unit of the
Floridan Aquifer.
GEOLOGY
The upper unit consists principally of sandy phosphatic limestone,
dolomite, and sandy, chalky-to-granular phosphatic marl. Marl and dolomite







BUREAU OF GEOLOGY


predominate in the upper part of the upper unit, and limestone, including
hard, dense cherty limestone, in the lower part (table 1). As used in this report,
the top of the aquifer is the top of the uppermost limestone, dolomite, or semi-
consolidated marl that is persistent with depth. Generally, this contact corre-
sponds to the top of the Hawthorn Formation, but in places soft marl of the
upper part of the Hawthorn has low permeabiltiy and is included in the over-
lying confining beds (table 2). In addition, the upper unit includes some lime-
stones assigned to an age younger than Hawthorn by some workers (Bergen-
dahl, 1956; Cathcart and McGreevy, 1959). Limestones of the Tamiami
Formation probably extend northward from Charlotte County into DeSoto
County, based on the geologic sections of Sutcliffe (1973), but this formation
was not identified during this investigation.
Altitude of the top of the upper unit, and thus of the Floridan Aquifer,
ranges from more than 50 ft above sea level to more than 50 ft below sea level,
as shown in the contour map of figure 13. The map indicates that this surface
in most of Hardee County lies above sea level and that in most of DeSoto
County, it is below sea level. The lowest altitudes are in the eastern parts of
both counties, where limestone is mostly more than 50 ft below sea level.
Only the broad features of the surface are shown in figure 13, which was
prepared from geologists' and drillers' logs of wells and test holes, and from
known outcrops along the Peace River. Because of weathering, the contact
between surficial deposits and the Hawthorn Formation in many areas is
gradational and therefore difficult to pick on the basis of well cuttings and
descriptive logs. In addition the surface is an erosional one and highly
irregular. Nonetheless, figure 13 can be used in combination with land-
surface altitudes to obtain an approximate thickness of surficial deposits and
an approximate depth setting for casings of wells that are finished as open
hole in the upper unit of the Floridan Aquifer.
As indicated by the geologic sections of figures 8 and 10, the upper unit
comprises formations that thicken toward the south. At the 10 well sites in
Hardee County shown on figure 11, the upper unit ranges in thickness from
104 to 280 ft and averages about 160 ft. In DeSoto County, the thickness at 13
well sites ranges from 135 to 319 ft and averages about 200 ft.


TRANSMISSIVITY
Transmissivity probably ranges widely in the two counties, as suggested
by the differences in the lithology of the upper unit (table 1), and by the wide
range in yields of wells. The specific capacity of a well, its yield per foot of
drawdown, can be used as an index to aquifer transmissivity. Average specific
capacity for 5 public-supply wells for the city of Arcadia is 11.4 (gal/ min)/ ft
(table 5). Using this specific capacity and an assumed storage coefficient of
0.0001, average transmissivity of the upper unit in the vicinity of the Arcadia







REPORT ON INVESTIGATION NO. 83


wells is approximately 4,000 ft2/d, as determined from a graph presented by
Meyer (1963). The graph is based on the assumptions that specific capacity
was determined at the end of 1 day's pumping, that the wells fully penetrate
the aquifer, and that the wells tap the aquifer with 100 percent efficiency.
These conditions are either not fully met or are unknown for the Arcadia
wells. However, the transmissivity of 4,000 ft2/d is probably a minimum
average value for the area because, owing to well inefficiences, measured
specific-capacity values are lower than they would be if the wells tapped the
aquifer with 100 percent efficiency.
Driller's records of 383 wells in the counties tapping the upper unit of the
Floridan Aquifer were examined for well-construction and yield character-
istics. Yields reported 250 of the wells ranged as follows, grouped according
to well diameter.

Well
diameter Range in yield (gal/min)
(in.) DeSoto Hardee
2 1-150 7-60
4 10-300 6-1,800
6 5-1.800 56-200

Although the table does not incorporate drawdown or duration of pumping,
and thus does not fully reflect the yield capabilities of the upper unit, the wide
range in yield suggests that transmissivity varies greatly throughout the two
counties.
The lower part of the upper unit of the Floridan Aquifer is generally
more permeable than the upper part. Black, Crow, and Eidsness (1965)
reports that a 4-in. test well (1310-5227), 313 ft deep with 84 ft of casing,
drilled on the west side of Arcadia, had a specific capacity of 6.2 (gal/ min)/ ft.
After the well was reamed to 10 in. and plugged from the bottom to 250 ft, the
specific capacity was 1.5 (gal/min)/ft. The marked reduction in specific
capacity after plugging, despite the hole enlargement, indicates the lower part
of the aquifer at this site is substantially more transmissive than the upper
part. That this condition may be widespread is suggested by lithologic
differences within the Hawthorn Formation and Tampa Limestone
(limestone unit); the soft clayey limestone, dolomite, and marl that
predominate in the upper part (table 1) are probably less permeable than the
hard limestone containing solution openings that predominates in the lower
part.

DEVELOPMENT

Many hundreds of wells tap the upper unit in DeSoto and Hardee
counties. In a sample of 525 drillers' completion reports submitted from the
















Table 5. Specific capacities of City of Arcadia wells tapping the upper unit of the Floridan Aquifer"

Well number Total Casing Specific
depth depthb Yield Drawdown capacity
City USGS (ft) (ft) ( m) ) gal/mn) (f) [(gal/in)/ft]
1 1303-5037 320 141 508 56 9.1
2 1257-5042 318 130 497 90 c5.5
3 1256-5028 320 160 704 36 19.6
4 1244-5042 353 112 508 72 c7.0
5 1244-5031 253 130 508 32 15.9


aData from Black, Crow, & Eidsness, Inc. (1965)
bAll casings are 10 inches in diameter
c After acidizing


Mean = 11.4







REPORT ON INVESTIGATION NO. 83 33

wo counties during 1970-72, and to which aquifer designations could be
assigned, about 60 percent were for wells tapping this unit. More than 90
percent of these were for domestic supplies; others were principally for stock
watering and irrigation. Wells tapping this unit also provide a public supply
for the city of Arcadia.
Wells open to the upper unit are finished almost exclusively as open hole
in rock. Average casing depths and total depths of 383 wells in the two
counties (fig. 14) show that for a given well diameter, casing and total depths
are generally greater in DeSoto County than in Hardee County. This
difference reflects the deeper position of the unit top and the unit's greater
thickness in DeSoto County. As shown in figure 14, large-diameter wells
generally are drilled deeper, have more open-hole section and larger yields
than small-diameter wells. Water-supply requirements commonly dictate
well size and yield. For example, shallow 2-in. wells usually provide supplies
sufficient for domestic use, a few tens of gallons per minute or less. Suitable
irrigation supplies, however, requiring 100 gal/ min or more, can be obtained
more consistently from larger diameter wells with tens or hundreds of feet of
open-hole section.

DE SOTO COUNTY HARDEE COUNTY
Well diameter
(inches) 2 4 6 or 2 4 6or
more more
Yield -12 50 300 19 20 140
FEET (got/min) V V METRES
0 0
(. Casing
depth
d (7t) 48
60 65 65
r) Open 82
hole (ft) -63 86
O100 -
j depth (ft) (163) 130


Q-7
Number of wells 193 -50

M 200 -


Q 279
300 (52) 298 -
2(0(
I-I
100



400 399 -
(65)


Figure 14. Average yield and construction characteristics of wells tapping the upper unit of
the Floridan Aquifer.






BUREAU OF GEOLOGY


LOWER UNIT

The lower unit of the Floridan Aquifer consists of the limestone andc
dolomite beds of the Suwannee Limestone, Ocala Group, and Avon Park
Limestone (table 2). This unit is approximately equivalent to zones 4 and 5
in Charlotte County (Sutcliffe, 1973) and includes the Suwannee aquifer ir_
part of Lee County (Sproul and others, 1972). The unit yields abundant
supplies to wells and is widely used as a source of water for irrigation.

GEOLOGY
The limestone and dolomite of the lower unit are, on the average, more
than 800 ft thick in DeSoto and Hardee counties. The altitude of the top of the
Suwannee Limestone, and thus of the top of the lower unit, is shown on the
contour map of figure 15. Altitudes range from about 150 ft below sea level in
the north to about 750 ft below in the south. The contact between the Tampa
Limestone and Suwannee Limestone can often readily be identified on
gamma logs by the marked decrease in gamma radiation in the Suwannee
Limestone; an example of the radiation decrease is illustrated by the log in
figure 7. The top of the Suwannee commonly is the horizon at which liner
casings are set and below which wells are finished open hole in rock. The
Suwannee is about 245 ft thick, on the average, and is a pure, cream to white,
nodular, fossiliferous limestone that contrasts strikingly in most parts of the
counties with the overlying phosphatic plastic deposits that confine the lower
unit of the Floridan Aquifer.
The Ocala Group, underlying the Suwannee Limestone throughout the
area, is a chalky, very fossiliferous, cream limestone, with some dolomite in
the lower part. The average thickness of the Ocala Group is about 285 ft, on
the basis of litholigic information for the 23 wells plotted on figure 11.
The underlying Avon Park Limestone is similar in lithology to the Ocala
Group, except that the Avon Park Limestone commonly contains intergran-
ular gypsum and anhydrite. In addition, a massive dolomite commonly
occurs in the lower part of the Avon Park Limestone (tables 1 and 2). This
dolomite, commonly recognized and logged "hard brown lime" by drillers,
often signals the occurrence of a highly permeable water-bearing zone, prob-
ably a zone of solution in the dolomite, within the next tens of feet of drilling.
As shown on the contour map of figure 16, the top of the dolomite unit of the
Avon Park Limestone slopes southward from about 900 ft below sea level in
northeastern Hardee County to more than 1,400 ft below sea level in southern
DeSoto County.
Maximum thickness of the dolomite unit is unknown because most wells
that penetrate the unit terminate in it. In a sample of 45 wells in which the unit
was recognized, median thickness of penetration was 51 ft and the maximum
was 241 ft. Ten of the wells penetrated the unit to a depth of 100 feet or more.







REPORT ON INVESTIGATION NO. 83


EXPLANATION
--350--
Structure contour
Shows altitude of top of
Suwannee Limestone. Con-
tour interval 50 feet.
Datum is mean sea level


0 1 2 3 4MILES
0 2 4 6 KILOMETRES


Figure 15. Altitude of the top of the Suwannee Limestone.







REPORT ON INVESTIGATION NO. 83


Beds of brown dolomite also occur in the lower part of the Ocala Group
and middle part of the Avon Park Limestone. Although similar in appearance
to the lower dolomite they are thinner and interbedded with limestone, less
extensive really, less massive, and less productive.


DEVELOPMENT
Many hundreds-perhaps thousands-of wells in the two counties tap
the lower unit of the Floridan Aquifer. In most areas, the unit yields supplies


DE SOTO_ COUNTY
CHARLOTTE COUNTY
82o000 55' 50' 45' 40' 81035'
Figure 16. Altitude of the top of the dolomite unit of the Avon Park Limestone.






REPORT ON INVESTIGATION NO. 83


suitablee in quantity and quality for irrigation purposes; in Hardee County,
public supplies for Zolfo Springs, Wauchula, and Bowling Green are
obtained principally from the lower unit. Most wells that tap this unit are
drilled into the Avon Park limestone. In a sample of 216 inventoried wells that
tap the lower unit, in which the deepest formation penetrated could be
determined, 66 percent reached the Avon Park Limestone, 22 percent
terminated in the Ocala Group, and 12 percent reached only the Suwannee
limestone.
Although many wells in the counties tap the lower unit, relatively few of
these tap only this unit; most are open to both the upper and lower units.
Characteristics of 19 wells that tap only the lower unit are shown in table 6.
Most of these 19 wells are drilled into the Avon Park Limestone, are more
than 1,000 ft deep, and yield more than 1,000 gal/min; all are used for
irrigation or public-supply.
Specific capacities of three of the wells average 46.9 (gal/ min) / ft, about 4
times the average specific capacity of Arcadia's public-supply wells, which tap
only the upper unit (table 5).


CONFINING BEDS

In DeSoto and Hardee counties, extensive confining beds separate the
surficial and Floridan Aquifers and separate the upper and lower units of the
Floridan Aquifer. In addition, beds of dense, impermeable limestone and
dolomite locally confine ground water in discrete water-bearing zones in the
section. These confining beds have low hydraulic conductivity and conse-
quently retard inter-aquifer or inter-zone ground-water flow and yield little
water to wells. However, these confining beds do transmit, or leak, water
from one aquifer to another, and the system is referred to as a leaky-aquifer
system.


UPPER UNIT CONFINING BED

Ground water in the upper unit of the Floridan Aquifer is confined by
overlying clay, marl and soft clayey dolostone and limestone (tables 1 and 2).
Sn many parts of the counties, the sand deposits of the surficial aquifer grade
downward to finer grained deposits, generally clay, clayey sand, and inter-
)edded sand and clay. The calcareous clayey deposits-marl and soft, clayey
imestone and dolostone-are at least in part weathered residiuum of the
7-awthorn Formation.
The thickness of this confining bed varies widely in the counties,
probably from a few feet to several tens of feet. Areal variations in thickness,
exture, and hydrologic properties of the confining unit are unknown.










Table 6, Characteristics of wells tapping only the lower unit of the Florldan Aquifer

Well Deepest Total Casing Pumping Water
number formation depth Diameter Depth rate useb
penetrated' (ft) (in) (ft) (gpm)
0333-4731 AP 1,211 12,10 685 1,100 Irr
04424943 AP 1,189 12 640 Irr
1314-4459 APd 1,412 16 630 4,200 Irr
1402-4910 APd 1,535 12 630 2,000 Irr
1438-5138 APd 1,410 8 900 500 Irr
1717-5226 Oc 893 12 511 Irr
Q 1723-5156 AP 1,275 12 500 Irr
1724-5227 Oc 1,009 12,10 462 1,400 Irr
2554-5336 AP 1,080 12 385 Irr
2944-4740 AP 1,002 16,10 350 700 PS
3 3112-5956 APd 1,360 10 900 2,000 Irr
S3249-4805 APd 1,103 16,14 404 d ,512 PS
S3252-4807 AP 970 10 323 550 SPS
S3254-4806 APd 1,152 14 420 e2,000 PS
S3605-0248 AP 900 12 400 Irr
3634-4024 APd 1,082 12 278 Irr
3821-4937 AP 1,027 12 395 1,800 PS
3823-4924 S 380 4 300 200 PS
3823-4925 Oc 690 6 300 480 PS
aAP, Avon Park Limestone; APd, Avon Park Limestone (dolomite unit); Oc, Ocala Group; S, Suwannee Limestone
blrr, irrigation; PS, public supply; SPS, standby public supply
cSpecific capacity, 46.7 gpm/ft
d Specific capacity, 68.7 gpm/ft
e Specific capacity, 25.3 gpm/ft







REPORT ON INVESTIGATION NO. 83


SAND AND CLAY UNIT OF TAMPA LIMESTONE

In much of DeSoto and Hardee counties, the upper and lower units of the
Floridan Aquifer are separated by a confining bed designated the sand and
clay unit of the Tampa Limestone (table 2; figs. 8-11). The lithology of the
sand and clay unit is not uniform and consists mostly of mixtures of sand,
clay, and marl; limestones and dolomites do occur but are subordinate. In the
17 wells that penetrate this unit on the geologic sections shown on figures 8-
10, the sand and clay unit ranges in thickness from 38 ft to 210 ft, and averages
144 ft.
The mixed lithology of the sand and clay unit of the Tampa Limestone is
illustrated by the following partial log of well 2741-4144, summarized from
preliminary core descriptions by the Florida Bureau of Geology (J. W. Yon,
written commun., 1974):

Depth Thickness Description
(ft below (ft)
land surface)

236 2 DOLOMITE, dark yellowish brown,
sandy, phosphatic, with lenses of CLAY,
olive gray, slightly sandy, waxy
238 10 CLAY, olive gray, and interbedded
DOLOMITE, slightly sandy,
phosphatic, dense
248 7 CLAY, olive black, waxy, hard
255 13 SAND, very fine to medium, phos-
phatic, clayey
268 14 DOLOMITE, olive gray, sandy, phos-
phatic, with pockets of SAND and
lenses of CLAY, olive gray, waxy,
sandy
282 1 SAND, light gray, very fine to
medium, phosphatic, calcareous
at 283 SUWANNEE LIMESTONE

As can be seen from the log, the sand and clay unit includes beds of
dense, waxy, shaley clay. These commonly occur in the lower part of the unit
and in places directly overlie the Suwannee Limstone. The clay beds, often
identified by local drillers as blue or green clay or shale, were recognized in
Polk County by Stewart (1966, p. 45). He designated this deposit the Tampa
Formation, which he described as "generally comprised of a bluish to
greenish gray, calcareous, locally phosphoritic, sandy, shaley clay that
contains lenses, fragments, and occasional thin beds of white to gray sandy
limestone." Drillers' logs of wells in eastern Hardee County indicate that in
that area the clay beds within the sand and clay unit range in thickness from
about 10 ft to about 80 ft and probably average 30 to 40 ft.






BUREAU OF GEOLOGY


In much of northeastern DeSoto County the clay section in the sand and
clay unit is 50 to 100 ft thick. At well 1601-3646, for example, where the sane
and clay unit is 170 ft thick (fig. 10), examination of cuttings shows 100 ft o'
greenish-gray to black, sandy to shaley, calcareous clay from 380 to 480 ft; the
clay overlies 10 ft of marl which rests on the Suwannee Limestone.
The sand and clay unit is low yielding and, when penetrated by wells.
tends to slough. Consequently, in areas where this unit occurs (fig. 11), large-
diameter wells are commonly open to the upper and lower units of the
Floridan Aquifer but cased off opposite the sand and clay unit.
The effectiveness of the sand and clay unit of the Tampa Limestone as a
confining bed is variable. The variability in lithology of this unit and of
thickness of clay beds contained in it result in wide variations in the amount of
leakance occurring through the unit. Because of the common practice of
constructing wells open to both units of the Floridan Aquifer, no leakance
values for the confining bed between them are available from the results of
aquifer tests.
The sand and clay unit in DeSoto and Hardee counties shows an
irregular but noticeable westward increase in the proportion of limestone. In
the western third of DeSoto County and in southwestern Hardee County, the
equivalent rocks are predominantly sandy limestone (table 2; figs. 9 and 10).
This sandy limestone is included as part of the upper unit of the Floridan
Aquifer, because most wells drilled into the sandy limestone are not cased off
opposite it and many obtain water from it. Nonetheless, differences in head
between limestones above and below the sandy limestone and the occurrence
of some clay beds in it suggest that in some areas the sandy limestone, too, has
relatively low hydraulic conductivity and acts as a leaky confining bed.


WATER-BEARING PROPERTIES
The Floridan Aquifer yeilds abundant supplies of water to thousands of
wells in Florida. Yet, perhaps in part because of nearly unfailingyields to wells,
quantitative information on its transmissive and storage properties is
scattered and incomplete. For example, published reports of aquifer
transmissivity in central Florida, based on aquifer tests, indicate a wide range
of values, from a few tens of thousands to more than a million gallons per day
per foot (Stringfield, 1966). This range serves to emphasize the heterogeneity
of the aquifer. Most published results are based on analytical techniques that
preceded the general application of leaky-aquifer analysis, and thus these
published values may not be suitable for predicting aquifer response to
proposed or hypothetical ground-water withdrawals.
Carefully controlled aquifer tests probably provide the most reliable
means of determining aquifer coefficients. The results of several tests made or
observed during the course of this investigation provide some indication of






REPORT ON INVESTIGATION NO. 83


:he probable range of aquifer characteristics in DeSoto and Hardee counties.
Extensive tests made in northeastern DeSoto County suggest the
,ransmissivity of the combined upper and lower units of the Floridan Aquifer
;n that area is about 270,000 ft2/ d and the aquifer storage coefficient is 3 x 10-5
Wilson, 1972). The relatively high transmissivity, combined with a leaky-
aquifer system, means that large withdrawals would result in relatively slight
drawdowns in the area. Details of these tests and an analysis of projected
drawdowns are described in the section of this report entitled, "Ground-water
development, northeastern DeSoto County."
In August 1973, a test was made on the Floridan Aquifer in southwestern
DeSoto County near the Peace River, about 2.3 mi north of the DeSoto-
Charlotte County lines. Well 0414-5847 was pumped at a constant rate of
1,750 gal/min for 1,650 min, and water-level changes were observed in two
zones separated from each other by a cement plug in well 0413-5858, 1,000 ft
away. The pumped well is cased to 105 ft and is finished open hole in the
Hawthorn Formation, Tampa Limestone, Suwannee Limestone, and Ocala
Group. The observation well is cased to 124 ft and is also open to these
stratigraphic units. In addition, the observation well has a cement plug from
1,072 to 1,190 ft, and is open from 1,190 to 1,304 ft, in the Avon Park
Limestone. A 1-in. pipe extended from the land surface through the plug,
providing access for head measurements in the zone below 1,190 ft.
Analysis of test data, utilizing the inflection-point method of Hantush
(1964, p. 417-418), indicated the following aquifer and confining-bed
coefficients:

Aquifer transmissivity, 10,900 ft2/d;
Aquifer storage coefficient, 2.0 x 10-4;
Confining-bed leakance coefficient, 3.14 x 10-4 (ft/d)/ft.

The transmissivity and storage coefficient are for the combined upper
and lower units of the Floridan Aquifer, exclusive of the Avon Park
Limestone. The confining-bed leakance coefficient is the net value for the
upper unit confining bed and beds of low hydraulic conductivity underlying
and within the pumped section.
Transmissivity at the Peace River site is substantially less than that
determined from tests in northeastern DeSoto County. The difference may
represent an actual change in aquifer characteristics, but probably is because
the wells in northeastern DeSoto County are open to a highly transmissive
zone in the Avon Park Limestone, whereas the well tested near the Peace
River is completed in the overlying Ocala Group. At well 0413-5858, the head
in the isolated zone of the Avon Park Limestone did not noticeably respond
to pumping of well 0414-5847, indicating little or no hydraulic interconnec-
tion between that zone and the pumped section at that site.






BUREAU OF GEOLOGY


POTENTIOMETRIC SURFACE
The potentiometric surface, as used in this report, represents the height
to which water levels would rise in tightly cased wells tapping an artesian
aquifer. Figure 17 shows the regional configuration of the potentiometric
surface of the Floridan Aquifer in peninsular Florida. Although the map
represents conditions in 1961, the major features of the potentiometric
surface have changed little since 1961 or even since it was mapped by
Stringfield in 1936 (Stringfield, 1966, p. 119). Figure 17 shows that the area
included in DeSoto and Hardee counties is on the southwestern flank of a
large potentiometric high whose crest is about 30 miles to the north. The
regional flow of ground water in the Floridan Aquifer in the area of investiga-
tion is toward the southwest, from areas of high altitude of the pontentio-
metric surface toward areas of low altitude.
Figure 18 is a map of the potentiometric surface in DeSoto and Hardee
counties, based on water-level measurements in 97 wells in September 1971.
In constructing the map, only water levels from wells drilled into the Avon
Park Limestone were used as control. Most of the control wells are open to
both the upper and lower units of the Floridan Aquifer, and the surface
represents an integrated pressure surface of the two units. In parts of the
counties, little head difference exists between them, and the map closely
reflects conditions in the Floridan Aquifer. Elsewhere, especially in southern
DeSoto County and along the Peace River valley, a gradient exists between
the two units, and the mapped surface may differ from the potentiometric
surface of either unit alone by several feet or more. Changes in hydraulic head
with depth are discussed in detail in the section entitled, "Head relationships."
The potentiometric surface in figure 18 represents conditions near the
end of the summer rainy season and at a time when the aquifer was practically
unstressed by irrigation pumping. The surface has a relatively steep slope of
about 1.6 ft/ mi in eastern Hardee County, but flattens markedly to the south
and west and is slightly undulate in DeSoto County. The mapped
irregularities in the surface in Desoto County may be due partly to
deficiencies in accuracy of land-surface altitude control and may not truly
reflect details of natural conditions in the aquifer. The pronounced change in
steepness of the slope is well defined, however, and could be attributed
to: (1) an increase in aquifer transmissivity in western Hardee County and in
DeSoto County; (2) a change from an area of predominantly lateral or
downward ground-water flow in eastern Hardee County to one of upward
ground-water discharge elsewhere in the area; or (3) a combination of these
factors.
The southern end of a large regional depression in the potentiometric
surface extends into northern Hardee County, as indicated by the hachured
contour line at Bowling Green (fig. 18). This depression, centered in
southwestern Polk County, was identified by Kaufman (1967) and first






REPORT ON INVESTIGATION NO. 83


840


830 82


81


800


Figure 17. Potentiometric surface, Floridan Aquifer, peninsular Florida, 1961.


mapped as a closed depression in May 1969 by Stewart and others (1971).

SEASONAL FLUCTUATIONS
The altitude of the potentiometric surface changes almost constantly in
response to changes in recharge and discharge. Seasonal and year-to-year
fluctuations during 1962-72 are represented by the hydrographs of seven
observation wells in the two counties and one in Polk County (figs. 19 and 20).
The graphs show that during the course of a year, the potentiometric surface
may undergo several cycles of decline and rise. Generally, however, the


290


250






44 BUREAU OF GEOLOGY


Figure IL Potentiometric surface and areas of artesian flow, Floridan Aquifer, DeSoto and
Hardee counties, September 1971.






REPORT ON INVESTIGATION NO. 83


surface is highest in autumn and lowest in late spring. Spring is characterized
)y several months of dry weather and large ground-water withdrawals for
irrigation. The steep downward trend of the potentiometric surface during
his period is reversed, often abruptly, by the onset of summer rains in May or
.june and the consequent cessation of irrigation pumping. Very soon after the
onset of summer rains, water levels rise rapidly, often several feet or more in
one or two weeks.
The potentiometric surface of figure 21 is based on water-level
measurements made in late May 1971, during the days immediately following
the first heavy summer rainfall. The map thus closely reflects the
configuration and altitude of the surface at the end of a long season of dry
weather and irrigation pumpage. The major feature of the potentiometric
surface is the pronounced trough that lies across southern Hardee County
with its axis sloping toward Manatee County. A similar trough was mapped
by Kaufman and Dion (1967), is implied in a water-level change map of
Woodard (1964, p. 41), and was duplicted by the author from water-level
measurements of May 1972. The trough is not present in the map of Septem-

IrM WMCTC FMT MC~


Figure 19. Observation-well hydrographs, Hardee and Polk counties.








BUREAU OF GEOLOGY


METRES


FEET


16 -- 1 \ I \ \ \ -




1246-4322
24 UPPER AND LOWER UNITS,
FLORIDAN AQUIFER
28- 1 I I I I I I I I I


Figure 20. Observation-well hydrographs, DeSoto County.






REPORT ON INVESTIGATION NO. 83


.er 1971 (fig. 18), and thus probably develops only when the aquifer system
s stressed by heavy pumping. The broad depression could develop either be-
.ause of a concentration of pumpage in southwestern Hardee County, or
because a given amount of pumpage produces a greater depression in the
potentiometric surface owing to a change in aquifer-system characteristics in
that area. No field of evidence was obtained during this investigation that
would indicate that either of these conditions exists, and the cause of the trough
remains unknown.
Another significant feature of the May map is the southern tip of the
closed depression near Bowling Green. Its presence in both the May and
September maps suggests that by 1971 this depression had become an
established year-round feature. Still another feature, an elongate depression
mapped in May 1965 along the Peace River valley in DeSoto County
(Kaufman and Dion, 1967), was not identified in May 1971.
The approximate magnitude of seasonal fluctuations of the potentio-
metric surface is reflected in the May-September change map of figure 22. The
map shows that the altitude change was less than 10 ft in most of DeSoto
County and more than 30 ft in parts of Hardee County.


AREAS OF FLOW

Where the potentiometric surface of an aquifer lies above the land surface,
wells tapping that aquifer will flow. Areas of flow for wells tapping the Floridan
Aquifer in DeSoto and Hardee counties are shown on the potentiometric
maps of figures 18 and 2 1. The extent of the flow area varies with fluctuations of
the potentiometric surface. In September 1971, when the potentiometric
surface was seasonally high, the flow area covered about 318 mi2 in the two
counties; in May of the same year, when the potentiometric surface was
seasonally low, the flow area was much less extensive, covering about 176 mi2,
almost entirely in DeSoto County. In Hardee County, areas of flow in
September occurred in about 100 mi2 of low-lying lands paralleling the valleys
of the Peace River and Charlie Creek, but in May flow areas were nearly ab-
sent.
In DeSoto County, the flow area covered 218 mi2 in September, and
included most of the southwestern quarter of the county as well as upstream
along the lowlands of the Peace River, Horse Creek, Prairie Creek, and Joshua
Creek.


LONG-TERM TRENDS

The hydrographs of observation wells in Desoto, Hardee, and Polk
counties (figs. 19 and 20) indicate a general downward trend of the seasonal
peaks during 1962-73. The net decline of these peaks ranged from 14.8 ft in well







BUREAU OF GEOLOGY


0






0 1 2 3 4 MILES
0 2 4 6 KILOMETRES'
7 I


50' 45' 40' 8165'
EXPLANATION


Anm of ertelen flow

Obervatlo well;
water level meued
May 1971


-50--

Potentiometric contour
Shows altitude of potentlo-
metric surface. Contour In-
terval 5 feet. Datum Is mean
sea level


Figure 21. Potentiometric surface and areas of artesian flow, Floridan Aquifer, DeSoto and
Hardee counties, May 1971.






REPORT ON INVESTIGATION NO. 83


Figure 22. Rise in the potentiometric surface, Floridan Aquifer, DeSoto and Hardee counties,
to September 1971.

3849-5111 to 1.6 ft in well 1246-4322. Water levels in most of these observation
wells are affected to some degree by pumping of nearby irrigation wells, which
accounts for the more erratic year-to-year variations in altitudes of the troughs
in the spring seasons.
Long-term water-level trends in these counties are difficult to determine
because of the paucity of periodic and continuous water-level measurements
before 1962. Some general conclusions can be made from comparisons of








BUREAU OF GEOLOGY


regional potentiometric maps that include DeSoto and Hardee counties anc
represent conditions in 1934 (Stringfield, 1936), 1949 (Peek, 1958) and 196i
(Healy, 1962, and fig. 17 of this report). These comparisons indicate little or nc
differences in the altitudes of the potentiometric surfaces in 1934 and 1949, and
that in 1961 the surface was about 10 ft lower in northeastern Hardee Count3
than it was in 1949, but little changed elsewhere in the counties. These
potentiometric maps are based on water levels measured at various times;
during a particular year, and the maps therefore represent average or
composite conditions for that year. Because seasonal and even year-to-year
fluctuations of the potentiometric surfaces can be substantial, especially in
Hardee County, differences or similarities in the potentiometric surfaces
shown on these maps do not necessarily reflect long-term trends.
Water-level declines associated with the large depression in the
potentiometric surface centered in Polk County have reportedly spread into
northern Hardee County (Kaufman, 1967; Stewart and others, 1971). Stewart
and others (1971) mapped declines of 10 to 20 ft in northern Hardee County
between January 1964 and May 1969, and 20 to 40 ft between September 1949
and May 1969. Because January and September water levels in any year are
generally substantially higher than those in May, the mapped declines are
probably larger than the actual water-level differences between comparable
seasons ofthose years. Kaufman (1967) mapped declines of 10 to 30 ft in Hardee
County between 1934 and late May 1965, but points out(p. 23) that"beyond the
20-foot line, it is difficult to distinguish between seasonal and long-term
effects."
In summary, the potentiometric surface in DeSoto and Hardee counties
probably showed little or no net decline from 1934 to 1949, but from 1949 to
1973 declines ranged from about 20 ft in northeastern Hardee County to a few
feet or less in much of DeSoto County, and most of this change occurred dur-
ing 1962-73.


HEAD RELATIONSHIPS
Where aquifers are separated by confining beds, hydraulic heads may
differ among the zones. These conditions set up the potential for vertical
ground-water flow, from zones of higher head, through leaky confining beds,
to zones of lower head. Where confining beds are regional, such as the
confining beds overlying the upper unit of the Floridan Aquifer and separating
the upper and lower units, systematic and consistent head differences are
observed. On the other hand, substantial but generally less predictable head
differences also occur where discrete water-bearing zones in the limestone and
dolostone section are locally separated by dense, impermeable rock. Even
within a single hydrologic unit, differences in head occur if the area is one of
ground-water recharge (downward flow) or discharge (upward flow). In








REPORT ON INVESTIGATION NO. 83


Aardee and DeSoto counties, water levels may differ either in nearby wells
)pen to different parts of the section, or in single wells as they are drilled deeper.
A downward gradient exists between the surficial aquifer and the Flori-
Jan Aquifer in some areas mapped as non-flowing on the potentiometric
:naps of figures 18 and 21. In most of these areas, the potentiometric surface
;s below the water table, and the surficial aquifer is therefore potentially a
,ource of recharge to the Floridan Aquifer.
In several parts of the counties a downward gradient has been observed
between the upper unit and the lower unit of the Floridan Aquifer. Figure 23
shows variations in water levels in three wells as measured during the course of
drilling. Each water level represents the integrated head of allzones open to the
well at the time of measurement. The level in well 3530-0053 in northwestern
Hardee County, declined substantially at a depth of about 300 ft, and the water
level continued to decline during the remainder of drilling (fig. 23). Other wells
in which water levels declined as drilling progressed have been reported in
eastern Manatee County (Woodard, 1964). In northeastern DeSoto County,
where more than 30 irrigation wells have been drilled for a single citrus project,
a driller reported that generally water levels in wells declined 1 to 3 ft or showed
no noticeable change with depth; however, at one well, 1747-3352, he reported
the water level dropped 31 ft when he drilled into a cavity in the dolostone unit
of the Avon Park Limestone (V. W. Athey, oral communication, 1972).
In and near the Peace River valley and in most of southern DeSoto
County, head in the lower unit of the Floridan Aquifer is generally higher
than that in the upper unit. The increase in head with depth is illustrated by
the graphs for wells 0414-5847 and 1405-4532 (fig. 23).
Woodard (1964, p. 28-29) reported that the water level in well 3249-4805
in Wauchula was 2 to 8 ft below land surface when it was open to the upper
unit. When completed at a depth of 1,103 ft, and with the upper unit cased off,
water level was 5.9 ft above land surface. Similarly the water level in well
0333-4731, open only to the lower unit (table 6), was 10.3 ft above land surface
in September 1971. Well 0333-4734 is about 350 ft away, at the same land-
surface elevation, but open only to the upper unit; its water level was 0.52 ft
above land surface in September 1971.
Substantial differences in head have been observed within the upper unit
in the Peace River valley. At Arcadia, well 1310-5227 is constructed open hole
from 84 to 250 ft; nearby well 1308-5226 is open hole from 263 to 372 ft. The
head in the shallower well is generally about 10 ft below that in the deeper
well, based on bimonthly measurements since 1970.
The condition of increasing head with depth in the Peace River valley is
probably related to the river and the low topographic position of the valley
floor. The river acts as a ground-water sink, receiving ground-water discharge
from the surficial aquifer. In the low-lying valley floor, as in all other areas of
artesian flow.shown on figures 18 and 21, the potentiometric surface is









52 BUREAU OF GEOLOGY

FEET WELL DEPTH, METRES BELOW LAND SURFACE METRES
S 0 50 100 150 200 250 300 350
40 t l I I-n- \ --- I I -- L --- -

0 -10
S Well 0414-5847
j -5
23 20

S-5
-J
I,-
S0 0
o

SWell 1405-4532







> ell 3530 -0053

2 0 200 400 600 800 1000 1200
.I-







WELL DEPTH, FEET BELOW LAND SURFACE

Figure 23. Water-level changes with well depths.

generally above the water table. As a result, in these areas ground water
moves upward from the upper unit of the Floridan Aquifer into the surficial
aquifer. The upward flow tends to depress the potentiometric surface of the
upper unit, thus establishing an upward gradient between the upper and lower
units of the aquifer. Along reaches of the river where the Hawthorn
Formation crops out, as in parts of Hardee and northern DeSoto counties,
ground water may discharge directly from the upper unit to the river, thus
further depressing the potentiometric surface of the upper unit. The resulting
condition is one of increasing head with depth and upward flow of ground
water. Although the contour lines on the potentiometric maps of figures 18
and 21 show no influence of this ground-water sink, probably more detailed
mapping, with greater control in the valley itself, or mapping of the upper unit
alone, would reflect local influences of the river and valley on flow patterns.


GROUND-WATER DEVELOPMENT, NORTHEASTERN DESOTO
COUNTY

The most extensive and systematic development of water resources in the
two counties is in the northeastern DeSoto County. In 1969, the first irrigation







REPORT ON INVESTIGATION NO. 83


wells were drilled for Joshua Grove, a division of Tropical River Groves. By
the end of 1972, this citrus grove covered about 37.5 mi2 (fig. 24), and the 37
irrigation wells at the grove had a total pumping capacity of about 86 Mgal/d.
The grove's development provided an opportunity to evaluate regional
aquifer characteristics and thereby assess the probable effects of expected
large-scale ground-water withdrawals over a wide area.
Since the establishment of Joshua Grove, the wells have been logged,
pumpage monitored, and two aquifer tests conducted. The results of
investigations at the grove were reported by this author in a previous paper
(Wilson, 1972); the following discussion includes pertinent and updated
hydrologic aspects from that paper.


DESCRIPTION AND IRRIGATION

WELL FIELD
By the end of 1972, 37 irrigation wells had been drilled on 1-mile centers
(fig. 24). The wells are about 1,340 ft deep on the average; most have 150 to
200 ft of 12-in. upper casing, followed by an interval of about 100 ft of open
hole in the upper unit of the Floridan Aquifer. About 200 to 300 ft of 10-in.
lower casing, seated in the Suwannee Limestone, seals off the sand and clay
unit of the Tampa Limestone. Below a depth of 450 to 500 ft, the wells are
open hole in the lower unit of the Floridan Aquifer. Drilling was generally
continued until the highly permeable zone in the dolomite unit of the Avon
Park Limestone was penetrated, usually at depths greater than 1,100 ft. The
wells thus tap both units of the Floridan Aquifer and are open to 900 to 1,100
ft of rock.
Pumping rates of 29 of the wells range from 1,158 to 1,921 gal/min and
average 1,618 gal/min, based on 1974 yield tests. Field specific capacities
computed for 15 wells range from 13 to 121 (gal / min) / ft and average 62
(gal/min)/ft.


PUMPAGE

During this investigation, irrigation was accomplished by pumping from
the wells directly into ditches. Control structures on these ditches are used to
maintain the shallow water table at a desired level under new plantings and to
minimize runoff from the grove during irrigation periods. The ditches also
lower the initially high water table and carry away excess runoff during non-
irrigation periods.
Pumpage has been monitored approximately monthly since the first
wells were pumped in the fall of 1969. Each well was rated to determine a
relation between discharge and electric-power consumption, and pumpage








BUREAU OF GEOLOGY


Figure 24. Joshua Grove and well field, northeastern DeSoto County.


was computed from kilowatt-hours consumed. Pumpage at the grove was
greatest during winters and springs and least during summers (fig. 25). The
highest average daily pumpage for one time interval on figure 25 was 38.5
Mgal, in the spring of 1971. On May 1,9, 1971, 21 wells pumped 53.5 Mgal, the
highest single daily pumpage of record. Average daily pumpage in 1971 (12.6
Mgal) was more than twice that in 1970 (5.5 Mgal), reflecting major
expansion of the grove during 1971. Despite further expansion in 1972,
average daily pumpage that year was identical to that in 1971, reflecting
improved water-management procedures and a higher rainfall during the
irrigation season in 1972 compared to 1971.


27* 20'













27 15'


1040'


8 t35'








REPORT ON INVESTIGATION NO. 83


HYDRAULIC PROPERTIES OF THE AQUIFER SYSTEM
AQUIFER MODEL

The hydrogeologic conditions at Joshua Grove can be represented by
Hantush's mathematical model for leaky artesian systems (Hantush, 1964, p.
325-326). The general system is composed of a semipermeable bed confining a
main artesian aquifer that rests on an impermeable bed. In a special case
applicable to the grove, the semipermeable layer is overlain by a saturated
sand bed in which the head distribution remains constant. The discharge to
wells is supplied from local storage in the artesian aquifer and from leakage
through and storage in the confining bed.
Modeling the field conditions at the grove is complicated by the presence
of two units of the artesian Floridan Aquifer separated by a confining bed. In
the model these units were treated as a single main artesian aquifer, because
data are insufficient to allow them to be modelled separately. The rocks
beneath the Floridan Aquifer act as the underlying impermeable bed, and the
clay and marl beds overlying limestone of the Hawthorn Formation act as the


40



-1.4
30 a
z
< .-1.2 I







||. I 0 2
Z -0.8 g a
5 i

2 ':':-0.6 2


Figure 25. Average daily irrigation pumpage, Joshua Grove.







BUREAU OF GEOLOGY


overlying semipermeable confining beds. Results of aquifer tests, described
below, indicate that some water is derived from storage in the confining beds.
As required by the model, the water table in the surficial aquifer is controlled
at a relatively constant level at the grove.


AQUIFER TESTS
Analyses of data from aquifer tests made at the well field indicate the
aquifer system has a high transmissivity. In one test, a well was pumped at a
constant rate of 2,075 gal/min for 4.1 days. Net water-level decline was 0.6 ft
in an observation well I mile away. In an effort to increase the drawdown due to
pumping, a second test was made in which seven wells were pumped at an
initial combined rate of 12,530 gal/min, and water-level changes were
observed in four observation wells. During the first day of the test, pumping
of the seven wells stopped because of a series of electric-power failures caused
by lightning. The pumps were turned on again, but the test was terminated
after about 30 hours because of additional lightning strikes.
A reasonably good fit can be made between the observed data at the
second test and a modified leaky-aquifer type curve plotted from the tables of
Hantush (1960. 1964) (fig. 26). In the analysis, the distance from each
observation well to an effective center of pumpage T, was computed as
follows: the products of the logarithm of the distance to each pumping well
and the logarithm of the discharge rate of each well were summed and divided
by the logarithm of total discharge; r equals the antilogarithm of that
quotient. A revised value was computed at each time of change in discharge
rate, and drawdown, s, was divided by discharge, Q, to account for the
variable pumping rates. Average values of aquifer and confining-bed
characteristics determined from the tests are as follows (Wilson, 1972):

Aquifer transmissivity, 270,000 ft2/d;
Aquifer storage coefficient, 3 x 10-5; and
Confining-bed leakance coefficient, 1.5 x 10-4 (ft/d)/ft.


PROJECTED DRAWDOWNS
The values of aquifer and confining-bed characteristics determined from
the tests were used to project drawdowns in the vicinity of the well field for
various pumping rates and durations (fig. 27). The storage coefficient of the
confining bed was assumed to be 0.05. In the analysis, the pumpage was
considered to be from a single well at the center of the well field as it existed in
1972. During actual irrigation operations, the drawdown distribution near
the well field would differ slightly from that shown whenever the center of
pumpage differed from the well-field center.









FE
z 0
a.
10-5
















z
0



















o
: I0
" 10-
Irh




1%.




| 0


10-10


10E
TIME /


10-8
DISTANCE 2 P, 2,


10-7
DAYS / FEET 2


Figure 26. Test data, well 1715-3746.2, and type curve.


0

MATCH POINT ----
0 o-. -
= 5 TYPE CURVE

u=I
s/Q =7.3 x0-5
t/f2=.1 ZI00-12

1971 aquifer test, 0=12,530 gpm
& 1971 aquifer test, Q variable
a 1970-71 Well-field pumping rote,
S0Q variable


O




m
;01


0




0n
z
>
-4.


rz!

00
0o


I I _


10-6








BUREAU OF GEOLOGY


The equations of Hantush (1960, 1964) for computing drawdowns are
applicable only within certain time ranges that depend on confining-bed
characteristics. Drawdown solutions were obtainable for times less than 33
days and more than 670 days. Following the procedures suggested by
Hantush (1960, 1964), drawdowns for intermediate times were obtained by
drawing a smooth curve between the two plotted segments (fig. 27).
The graph shows, for example, that if wells were pumped at 100 Mgal/d
for 100 days, drawdown in the aquifer 5 mi from the 1972 grove center would
be less than 5 ft, and at 10 mi drawdown would be about 2 ft. If wells were
pumped at 200 Mgal/d for 10 days, drawdown at 5 mi would be about 4 ft.
Figure 27 also indicates that after pumping at any constant rate up to 200
Mgal/d for about 2 years (670 days), no further drawdown of the
potentiometric surface would occur as long as that rate were maintained.
Under these conditions, water derived from storage in and leakage through
the confining beds would be sufficient to supply the amount pumped.
Irrigation at the citrus grove is seasonal, not continuous, and therefore
figure 27 cannot be used to predict drawdowns resulting from long-term
grove operations. In order to assess the magnitude of drawdowns that might

FEET METRES
0O L 0



2












AT 10 MILES INA "'tit D


s
^0-






SI- I ----I I^ ,




AT2 5 20 50 100 200 500 1000
TIME SINCE PUMPING STARTED, DAYS
Figure 27. Projected drawdowns at 5 miles and 10 miles from center of Joshua Grove.








REPORT ON INVESTIGATION NO. 83


be expected over a period of several dry years, a hypothetical annual pumping
schedule was assumed and drawdown at 5 mi computed (fig. 28). The
schedule consisted of 155 days of fall and winter pumping at 50 Mgal/d, 90
days of spring pumping at 100 Mgal/d and 120 days of summer shutdown.
The durations of pumping correspond approximately to those of 1970-71; the
pumping rates are reasonable for a mature grove during a dry year. Average
daily pumpage for the year with this pattern would be about 46 Mgal/d.
Figure 28 shows that pumping according to the hypothetical schedule
would result in a lowering of the potentiometric surface to approximately the
same level at the end of each spring pumping period. At the end of the first
year's recovery period, the potentiometric surface would show a small net


FEET

01


2 I
w


I--

0o
a.
z"
laJ

4



2 5


Cn 6
0 100


Szzg 50

> :
a--2 0


METRES


;., a ..X.,
''' W .......::
X....~~E
X:;I
C .n


LCie.
W '''

C n :


LS
-4 -


W Z


0 5 C


TIME, YEARS

Figure 28. Projected long-term changes in potentiometric surface due to hypothetical pattern
of Joshua Grove pumpage.


m


I r I..... -.I








BUREAU OF GEOLOGY


decline, but in succeeding years additional net declines would be negligible.
The initial net decline represents water removed from aquifer storage; in
succeeding pumping cycles, water would be obtained from leakage, These
water-level fluctuations, resulting solely from irrigation operations at
Joshua Grove, would be superimposed upon seasonal fluctuations resulting
from variations both in natural recharge and discharge and in withdrawals
from other wells in the area.

RELIABILITY OF RESULTS
The aquifer model is a simplified representation of a complex and really
extensive multi-aquifer system. A meaningful test of the applicability of the
model in the area of the grove would require extensive pumpage and water-
level history before and after the installation of the well field at the grove.
Such data are not available, but some indication of the degree of reliability
can be obtained by analyzing nearly a year's record of well-field pumpage and
the corresponding water-level fluctuations at two observation wells (fig. 29),
One well (1743-3746.2), called the Joshua observation well, is at the margin of
the grove and the other (0412-4749), called Foster Farms observation well, is
about 17 mi southwest of the grove.
In the analysis, the actual grove pumpage for 335 days was treated as a
long-term aquifer test with variable discharge. Drawdown at the Joshua
observation well caused by this pumpage was estimated by subtracting the
measured water-level changes at the Foster Farms observation well from
those at the Joshua well. Fluctuations in the Foster Farms observation well
were considered to represent the regional seasonal changes unaffected by
pumpage at Joshua Grove. As in the short-term aquifer tests, revised values of
r and s/Q were computed each time average aggregate well discharge
changed. The data points, shown as squares in figure 26, plot in a scatter
about the type curve, but fall within the log cycles that would be expected
from an extension of the short-term aquifer-test data.
Considering the many variables involved in comparing and analyzing
water-level fluctuations in observation wells, these results suggest that the
model is a reasonable representation of the aquifer system at Joshua Grove. If
actual grove irrigation approximates the durations and rates assumed in the
analysis, drawdowns near the grove would probably be small, on the order of
feet rather than tens of feet. During nonirrigating seasons, the potentiometric
surface would probably recover nearly fully from the effects of pumping.
Thus. long-term net declines due to grove pumping would probably be small.

WATER QUALITY
The chemical characteristics of ground water may influence the uses to
which the water is put. The U. S. Public Health Service (1962), for example,








REPORT ON INVESTIGATION NO. 83


FEET METRES
0 o 0
1N FOSTER FARMS
l\ OSEiVATION /
S 2 WELL

4

w \\ /
-I 6 2

-.. JOSHUA N
< OROVE
SOSS0ERHVATION -. \
WELL
10 -3
W -) I-~-

2 0 -15 W (n
$19 0WZ 0
770 1.71
0 1 . i .. .. ...... 1 u A s i
0 10i 200 300
TIME, DAYS

Figure 29. Joshua Grove pumping rate and water-level changes in observation wells.


has set minimum standards for the quality of drinking water used by
interstate carriers and others subject to Federal quarantine regulations. Many
states, including Florida, have adopted many of these standards for
regulating public water supplies, In addition, criteria have been developed for
evaluating water quality for irrigation and industrial purposes (Natl. Acad.
Sci. and Natl. Acad, Eng., 1973). Thus knowledge of the quality as well as
quantity of water may assist in the development of the resource.
Many factors affect the chemical characteristics of ground water,
including the initial chemical character of the water when it recharges the
aquifers, the types of rocks it is in contact with, and the length of time the
water has been in circulation. Wells in Hardee and DeSoto counties are
commonly constructed with tens to many hundreds of feet of open-hole
section. Water pumped from these wells may come from more than one
aquifer or water-bearing zone, and the water from each may have distinctive
water-quality characteristics. Thus the quality of water pumped from a well
depends upon which zones are tapped and the proportion of water derived







BUREAU OF GEOLOGY


from each zone; in some areas, quality of water from nearby wells differs
markedly, depending on well depth and amount of casing.
Despite these complexities, broad water-quality characteristics of the
upper and lower units of the Floridan Aquifer have been delineated and
mapped from analyses of water samples from 233 wells in the two counties.
The results, described and portrayed on the following pages, are to some
extent an expansion and revision of water-quality mapping by Kaufman and
Dion (1967). The results presented herein are based on additional sampling
and a more detailed subdivision of aquifer units.

VERTICAL AND AREAL DISTRIBUTION
Table 7 and figures 30-42 portray the vertical and areal distribution of
some water-quality parameters that are significant in determining the quality
characteristics and usefulness of ground water in the counties.
Table 7 shows median values and ranges of mineral concentration,
hardness, and temperature of water in various artesian aquifer units in the
two counties. A comparison of median values in the table shows that ground
water is generally less mineralized, less hard, and cooler in Hardee County
and in the upper unit of the Floridan Aquifer, compared to ground water in
DeSoto County and in the lower unit. Exceptions are bicarbonate, chloride,
and fluoride, whose concentrations either show no apparent trend with
aquifer unit or are lower in the lower unit of the Floridan Aquifer than in the
upper unit.
Figure 30 shows quality and depth data from several wells in the
counties. Samples for wells A, C, and D were taken at the well discharge
points at various times during drilling and thus are composite samples
representing the open-hole section at the time of sampling. Samples from well
B were taken after it was first drilled to 750 ft and again after it was deepened
to 1,356 ft. Those from well E are bailer samples taken from near-bottom
depths during drilling and thus approximate point samples from the section.
The data in figure 30 show the general increase with depth in dissolved-
solids concentration, hardness, and sulfate concentration, and the general
uniformity with depth in chloride and fluoride concentrations. Large changes
in values can be found in relatively short depth intervals, as shown, for
example, by the changes in hardness and sulfate concentration of water from
well C. The data from well E suggest that values can increase and decrease
alternately in successive depth intervals.
The maps of figures 31-42 show quality characteristics for the upper and
lower units of the Floridan Aquifer. Also shown are inventoried wells used for
control within the two counties. Omitted are wells in adjoining counties and
wells in DeSoto County where water samples were collected and analyzed by
personnel of General Development Utilities; but quality data from both sets
of wells were used as guides in mapping.

















Table 7. Median value aud rueng or water-qualitr ehalcterlnOti Floriden Aquifer
(All values in mg/ I except as noted)

Flordn Hadee DSotao Harda DSoto Hardo DeSoto
trer ,No.lI Md.', Rnp No. Md. luege INo. Md. I Ranpg No.. I Md. Range No. Md. Ranl, No. I Md. I Range
Dissolved solids Hardness (as CaCOJ) Teperature n
Upper 12 236 174300 56 490 155 -1280 7 160 130 -200 46 340 190 530 10 23.5 23.0- 24.5 56 25.5 21.5- 28.0
Upper and lower 3 305 114-712 65 670 435 .1490 20 260 73 -530 31 410 270 -1300 38 25.5 23.5- 30.0 65 2.5 25.5- 32.5
Lower 6 479 242623 7 670 490 .910 9 280 180 -380 7 470 310 830 8 27.0 25.5- 29.5 4 29.0 2.3- 31.5

Calcium (Ca) Magnesium (Mg) Total Sodium (Na) Bicarbonate (HCOJ
Upper 7 47 44. 58 33 93 05 170 7 9.3 6.5- 13 26 44 20 -200 7 160 100 -200 34 220 150 -390
Upper and lower 85 24-170 30 130 87 180 14 8.4 3. 16 25 40 12 140 20 160 85 -220 32 17 130 .260
Lower 7 68 58- 31 5 160 100 280 6 II 8.1- 14 0 -- 7 1 1 50 IS 200 6 160 140 -190

Sulfate (SO') Fluoride(F) Chloride(CI)
Upper 7 3.6 0.100 42 70 0.8- 340 8 1.1 0.5. ,.7 35 1.7 0.4- 2.9 13 12 6.0. 36 54 69 2.8400
Upper and ttwr 108 0.420 45 20 I -1200 28 1.0 .4- 2.6 35 1.3 .7- 2. 5 16 4,5- 81 61 45 13 .370
.,uwer 7 200 47-300 6 340 150 -650 6 .8 .I1-1.1 5 1.6 1.0- 1.8 10 13 9.0 30 7 I 20 I 1 .110
I Number of samples analyzed
2 Median value


C I








0 1 I I -
DISSOLVED SOLIDS


200





sooo
1 00-








o -o
0 3 600








100 00 00 000




^^00 Goo Soo 1000


SULFATE


I I I I I I -
200 400 600 0 200 400

CONCENTRATION, MILLIGRAMS PER LITRE


- s


-100 1



P1
o









.
.B

-300 .







.400


0 200 0 10 20 3.0








REPORT ON INVESTIGATION NO. 83


Figures 31 through 42. Distributions of water-quality parameters.


CONTROL WELL


Upper unit of the Floridan Aquifer
0 I 2 3 4 MILES
S2 6 KILOMEi TR
0 2 4 6 KILOMETRES


COUNTY

45' 40' S1035'
GENERALIZED DISTRIBUTION OF
DISSOLVED SOLIDS
Concentration in milllgram per lilre

D 0
250 or 251-500
m

501-1000 more than 1000


31. Dissolved solids, upper unit of the Floridan Aquifer.






BUREAU OF GEOLOGY


20 i : : : D 0 : jx

20' :" *0::: -:-:. ::" : :: -:: :: :- ; ==========30 ='O::::=COUN TS: ::::::=:: ::



(IC' z >: :::. .:: : :: :


.. .. :::..: ::: :::: : :::::.: === .=* \= = = = =..'.::....'...: :g








0 ::: ::':: O : : : ::: .:: ::::. M IL ::::::::::::::
rros c- `L 6 MT
tg j ,: r .... :: S0-'T.. . O : .:... 1 .



.so.-ro.. ,..: : ..: ... countt.,
SC.A.LOTT. COUNTY
SI II I
. . . . . . .


62O00o


55s 50' 45'
EXPLANATION


CONTROL WELL
0
Upper and lower units
of the Floridan Aquifer

Lower unit of the Floridan
Aqulfer


40' 8135'

GENERALIZED DISTRIBUTION OF
DISSOLVED SOLIDS
Coneentrtlein in llli|rems pr Iltr

250 or Ior 251-.00

E n
501-1000 more than 1000


32. Dissolved solids, lower unit of the Floridan Aquifer.





REPORT ON INVESTIGATION NO. 83


33. Water temperature, upper unit of the Floridan Aquifer.






BUREAU OF GEOLOGY


27S35S'


V14 o.


g4
.. :0;; 0 0 i




::: g & U,%,: O ::: !;:* 1
-0-0
00 0 b T '1
: CI : ; ^ i -









I i (g --- f r I I


'~7 : o I'' M I ii lSi~ij
- SI 0 1 2 4 4 IL911~ S

w 0 0 o
J RLOTTE. i 4 7 -

CHARLOTTE COUNTY


55' 50' 45' 40' 01035'


CONTROL WELL
0
Upper and lower units
of the Floridan Aquifer

Lower unit of the Floridan
Aquifer


GENERALIZED DISTRIBUTION OF
TEMPERATURE,
degrees Celsius

OD 0
15 rose JM


34. Water temperature, lower unit of the Floridan Aquifer.


20'




is'




100.





27005'


zoo00'


20-^


I






REPORT ON INVESTIGATION NO. 83


8o000'


CONTROL WELL


Upper unit of the Florldon Aqulfer
0 1 8 3 4MILES
*tV4 "1 KILOMETRES


GENERALIZED DISTRIBUTION OF
HARDNESS as CaCO3,
mtlligrame per 111ir

D 0

301.-00 more than 500


35. Hardness, upper unit of the Floridan Aquifer.






70 BUREAU OF GEOLOGY





POLK COUNTY



















6 0 :**:::2 000' :::::::: ',::: 2:::: ;:::::
S:: : : : .





























200 .0' 45 40' ....35

GENERALIZED DISTRIBUTION OF
CONTROL WELL HARDNESS o CoC


0 mllligroms per litre
Upper and lower units
of the Florldan Aqulfer -
180 lao?* 181-300
Lower unit of the Floridan u K,



36. Hardness, lower unit of the Floridan Aquifer.






REPORT ON INVESTIGATION NO. 83


CONTROL WELL
0
Uppe unit of the Florldan Aqulfer
O I 1 3 MILES
0 2 4 6 KILOMETRES


GENERALIZED DISTRIBUTION OF
SULFATE CONCENTRATION,
Illlgrams per litre


100 or 101-250


251-500


37. Sulfate, upper unit of the Floridan Aquifer.


_ __ __ __ __


_ __ __







BUREAU OF GEOLOGY


CONTROL WELL
o
Upper and lower units
of the Floridan Aquifer

Lower unit of the Floridan
Aquifer


GENERALIZED DISTRIBUTION OF
SULFATE CONCENTRATION,
milligrams per litre

100 loes 101-2.


251-500 more than 500


38. Sulfate, lower unit of the Floridan Aquifer.








REPORT ON INVESTIGATION NO. 83


. ........... .



.....................................



CHARLOTTE COUNTY ~ |


CONTROL WELL
0
Upper unit of- the Floridan Aquifer
0 I 2 3 MILES
0 2 4 6 KILOMETRES


GENERALIZED DISTRIBUTION OF
CHLORIDE CONCENTRATION,
milligrams per litre


50 51-100


101-250 more than 250


39. Chloride, upper unit of the Floridan Aquifer.


27o35


27o05'








74 BUREAU OF GEOLOGY




I I I I I
___""4550. T_5 _0 P.OLK OUNTY
S-MAU M UN TY

--" ------ Y







-------- -- O






_O, Z- -
.- ---- -E- -
-0- -- 1 M




_e .- 0 o_ .._o__
230
-- -- + -- -- ---- O-q




--o --O ---- -I
-" --- -O-- e- -
,-- ------; -- o-0-









--- -CHARLOTTE K -E COUNT-- --









2-00' 55' 50' 45' 40' T1035'

GENERALIZED DISTRIBUTION OF
soro-- -- -
C AcADLT COUNTY















CONTROL WELL CHLORIDE CONCENTRATION,
0 milligrams per litre
Upper and lower units
of the Florldan Alquifer F
10 of












l seI 11 IISO 00
Lower unit of the Floridan
Aquifer 3
101-20 more than 250


40. Chloride, lower unit of the Floridan Aquifer.








REPORT ON INVESTIGATION NO. 83


iii iiiiiiii iiii!



DE SOTO COUNTY
t / ,, i i ii j j : i




i-:
I -,,, .... ...... .......~jY



z ......
i r7 : '


CONTROL WELL
0
Upper unit of the Florldan Aquifer
0 I 2 3 4 MILES
0 2 4 6 KILOMEtTRM


40' a135s'
GENERALIZED DISTRIBUTION OF
FLUORIDE CONCENTRATION,
mllllgrams per ltte
0 0
0. ls 0.o9-1.4


1.5 or more


41. Fluoride, upper unit of the Floridan Aquifer.









BUREAU OF GEOLOGY


2703s'






30





23





20'





IS





10





2703'5


*200'


55' 50' 45' 40' 1035'


CONTROL WELL
0
Upper and lower units
of the Floridan Aquler

Lower unit of the Floridan
Aquiter


GENERALIZED DISTRIBUTION OF
FLUORIDE CONCENTRATION
milligram* per litre


teas 0.9-1.4


1.5-1.9 2.0 or more


42. Fluoride. lower unit of the Floridan Aquifer.


I I I ////I//////^ /' 'LI' I
vi ^ / KILOMEThIB ~


COUNTY
CHARLOTTE COUNTY
L I I I I I


r r _







REPORT ON INVESTIGATION NO. 83


The water-quality maps of the lower unit of the Floridan Aquifer are
based mostly on data from wells open to both the upper and lower units.
These maps probably closely represent the quality of water in the lower unit,
however, because the characteristics of water from wells open to both units
are determined primarily by the characteristics of water in the lower unit,
which is generally substantially higher yielding. This relationship is supported
by water-quality data from the few wells open only to the lower unit. Quality
of water from these wells was generally similar to that from nearby wells open
to both units.
In constructing the water-quality maps, emphasis was placed on data
from wells open to the full section of the aquifer unit being considered. The
data of table 7 and figure 30 indicate that quality characteristics of water from
an individual well drilled in a given area may differ from the mapped values
shown on figures 31-42, depending on the depth interval of open hole. For
example, water from wells open only to the Hawthorn Formation generally is
not as mineralized as water from wells open only to the underlying Tampa
Limestone or to both formations. Similarly, water from wells drilled only to
the Suwannee Limestone or Ocala Group generally is not as mineralized as
that from wells drilled to the Avon Park Limestone and open to the full
thickness of the Floridan Aquifer. In southwestern DeSoto County, few wells
penetrate the Avon Park Limestone, and values shown in this area for the
lower unit generally represent quality characteristics of the unit down
through the Ocala Group.
The maps indicate that ground water with the lowest mineralization is in
northwestern and northeastern Hardee County, and for most parameters
highest values are found in southwestern DeSoto County. Ground water in
the lower unit is generally warmer and more mineralized alongthe Peace River
valley than it is away from the river.
As might be expected, low mineralization and temperatures occur
upgradient in recharge areas, where flow is primarily downward, and high
mineralization and temperatures occur downgradient in discharge areas,
where flow is primarily upward. The high mineral concentration of water in
southwestern DeSoto County is probably largely the result of mixing of
circulating potable ground water with saline water.
A discussion of these water-quality conditions and the significance of
each mapped parameter and its vertical and areal distribution follows. Where
pertinent, comparisons are made with U.S. Public Health Service (1962)
standards for quality of drinking water. Many factors affect the suitability of
water for irrigation, including soil, plant, and climate variables and
interactions, and the frequency and amount of water applied (Natl. Acad. Sci.
and Natl. Acad. Eng., 1973). Thus, although the major use of water in the
counties is for irrigation, no discussion of water-quality criteria for irrigation
is included. The successful production of irrigated citrus and vegetable crops





BUREAU OF GEOLOGY


throughout the two counties demonstrates the general suitability of ground
water for supplemental irrigation.

DISSOLVED SOLIDS
Dissolved solids in water refers to all the dissolved mineral constituents
contained in it. Precipitation contains some dissolved mineral matter; in
ground water, the rest is derived from soil and rocks as the water recharges
and circulates through the aquifers.
The dissolved-solids concentrations mapped on figures 31 and 32 were
determined from water samples as the residue of evaporation at 1800C, or
from specific conductance. Specific conductance is the capacity of water to
conduct an electric current, measured in micromhos at 250 C, and is an index
to total mineral concentration. In Hardee and DeSoto counties, dissolved-
solids concentration is approximately equivalent to 0.7 times specific
conductance. This relationship, based upon a plot of 83 analyses from the two
counties, is most reliable for specific conductances less than 1,000
micromhos.
The U. S. Public Health Service (1962) has recommended a maximum
limit of 500 mg/ I dissolved solids for public drinking-water supplies, but has
permitted concentrations up to 1,000 mg/1. Under proposed revisions to
these standards, dissolved solids is no longer included (Natl. Acad. Sci. and
Natl. Acad. Eng., 1973). When chloride and sulfate concentrations are each
less than 250 mg/ 1 (the recommended limit for these constituents) dissolved
solids will usually be less than 500 mg/ 1. Dissolved-solids concentrations
greater than 1.000 mg/ are unsuitable for many industrial purposes. In the
two counties, dissolved-solids concentrations of 500 and 1,000 mg/ are
equivalent approximately to specific conductance of 715 and 1,430
micromhos, respectively.
The maps of figures 31 and 32 show that dissolved-solids concentration
generally increases toward the south and southwest and is greater in the lower
unit than in the upper unit. The concentration in the upper unit exceeds 500
mgi I in most of the southern half of DeSoto County; in the lower unit, this
value is exceeded along the Peace River valley, in the southern part of Hardee
County. and in all of DeSoto County. Values greater than 1,000 mg/ occur
in both units in parts of DeSoto County.

TEMPERATURE
Ground water is warmed as it circulates downward through aquifers,
owing to the natural increase in temperature of rocks with depth. U. S. Public
Health Service (1962) recommendations for drinking water do not include
limits for temperature; however, high temperatures may severely restrict the
usefulness of water for cooling purposes. For convenience, equivalent






REPORT ON INVESTIGATION NO. 83


temperatures in the more familiar Fahrenheit scale are listed below for some
of the Celsius values used on the maps of figures 33 and 34:


23 73.4
25 77.0
27 80.6
29 84.2
32 89.6


Figures 33 and 34 show that temperature generally increases southward
and that in a given area, water in the lower unit is several degrees warmer than
that in the upper unit. Commonly, the temperature of shallow ground water
approximates mean daily air temperature, and rock temperatures tend to
increase with depth. Mean daily air temperature in DeSoto and Hardee
counties is 22.70C; ground-water temperature throughout the area exceeds
this value in some parts by as much as 90C. The high ground-water
temperatures probably result in part from recharge of warm water during
summer months, when rainfall is greatest and air temperatures are highest,
and in part from warming of ground water as it circulates through the deeper
parts of the aquifer system.

HARDNESS
Hardness is a property of water that represents its soap-consuming
capacity. Hardness results from the presence of calcium and magnesium ions,
and hardness is generally defined in terms of these constituents, expressed as
calcium carbonate (Hem, 1970, p. 224). The terms "hard" and "soft" are
imprecise, and the classification used by the U. S. Geological Survey is as
follows (Hem, 1970, p. 225):


Hardness range
(mg/1 of CaCO3) Description
0-60 Soft
61-120 Moderately hard
120-180 Hard
More than 180 Very hard

The U. S. Public Health Service (1962) has no recommended limit for
hardness in its drinking-water standards. Hardness for domestic purposes is







BUREAU OF GEOLOGY


not particularly objectionable until it reaches about 100 mg/ ; at 200-300
mg I. hardness becomes noticeable in all uses (Hem, 1970, p. 225-226). The
most commonly encountered characteristic is that the harder water is, the
more difficult it is to work up a lather from soap. In addition, hardness forms
scale in boilers, water heaters, and pipes, causing a decreased rate in heat
transfer and restricted flow of water.
Figures 35 and 36 show that most water in the Floridan Aquifer in the
two counties is very hard. In the upper unit, water in the northern half of
Hardee County is generally moderately hard to hard; in the lower unit, only in
the northeastern part of Hardee County does moderately-hard to hard water
occur. The high hardness in the two counties is the result of the predominance
of calcium- and magnesium-rich limestone and dolomite in the Floridan
Aquifer.
SULFATE
High sulfate concentrations are difficult to treat and may cause severe
scaling problems on pipes and boilers, and in drinking water may produce
undesirable laxative effects. The recommended limit for drinking water is
250 mg! I of sulfate (U. S. Public Health Service, 1962).
The sulfate plots in figure 30 suggest that sulfate concentrations general-
ly increase with depth in the two counties. Relatively high concentrations may
occur locally in the section, as indicated by the peak at 600 ft (in the Suwannee
Limestone) at well E.
As shown in figures 37 and 38, in most of Hardee and DeSoto counties,
sulfate concentrations in ground water in the upper unit of the Floridan
Aquifer are less than 100 mg/ In the southwestern quarter of DeSoto
County. sulfate concentrations exceed 100 mg/ I and in some areas exceed
250 mg I.
Water from the lower unit contains less than 100 mg/I only in the
northern half of Hardee County, excluding an area along the Peace River (fig.
38). A tone of water containing more than 250 mg/ 1 of sulfate extends across
southernmost Hardee County, the northern part of DeSoto County, and
southward along the Peace River valley. In most of the southern part of
DeSoto County. water in these aquifers contains less sulfate (101-250 mg/ ).
In Hardee and DeSoto counties, most sulfate in ground water is
probably derived from the solution of gypsum and anhydrite (calcium-sulfate
minerals) found principally in the Avon Park Limestone and deeper rocks.
Many deep irrigation wells in Hardee and northern DeSoto counties tap the
Avon Park Limestone. Few wells in southern DeSoto County penetrate the
Avon Park Limestone, and this probably explains why figure 38 shows the
relatively low concentrations of sulfate in water from the lower unit in that
area. The low concentrations also indicate that water with high
concentrations of sulfate from these deep rocks has not circulated up into the







REPORT ON INVESTIGATION NO. 83


section tapped by wells, except along the Peace River valley (fig. 38).
Variations in the distribution of sulfate-bearing minerals is likely a
controlling factor, as suggested by local occurrences of unusually high sulfate
concentrations northwest of Arcadia (fig. 38), by marked variations in sulfate
concentrations with depth (fig. 30, well E), and by the relatively low
concentration of sulfate (155 mg/1) in water from a well 1,542 feet deep (well
0345-4659) tapping the Avon Park Limestone in southern DeSoto County.

CHLORIDE
Water containing large amounts of chloride combined with sodium has a
salty taste, and, when combined with calcium, such water is corrosive. The U. S.
Public Health Service (1962) has recommended a limit of 250 mg/I chloride
for drinking water.
As shown by a comparison of figures 39 and 40, the distribution of
chloride concentration is similar in both the upper and lower units. In most of
Hardee and DeSoto counties, chloride concentration is less than 50 mg/1.
South of Arcadia, the concentration increases and in places near the
Charlotte and Sarasota county lines exceeds 250 mg/1. In the southwestern
part of DeSoto County, however, wells in the Hawthorn Formation with
total depths less than about 200 ft yield water with chloride concentrations of
about 100 mg/I or less. No well sampled in either Hardee or DeSoto counties
yields water with a chloride concentration greater than 400 mg/I (table 7).
The vertical profiles of chloride concentration shown in figure 30 indi-
cate a relatively uniform distribution below the upper 100 to 200 ft in the
section tapped by wells. Where chloride concentrations are relatively low (50
mg/1 or less), as in water from wells B and C in figure 30, concentrations may
even decrease slightly with depth.
Chloride in ground water may be derived from several sources, including
recharging rainwater containing chloride ions; intrusion of salt water into
aquifers, either from below or laterally from nearby saline surface-water
bodies; from solution of aquifer minerals containing chloride; and from
pollution sources such as sewage and industrial wastes. In addition, aquifers
may contain salty water that in part is connate water (water of deposition) or
was introduced during high stands of the sea subsequent to deposition. In
either case, such aquifers have not been completely flushed of salty water by
fresh-water circulation,
Very salty water, containing more than 1,000 mg/ 1 chloride, underlies all
of peninsular Florida at depths that generally increase inland away from
coastal areas. The depth to salty water in Hardee and DeSoto counties is
unknown, because no known water wells are deep enough to tap it. Wells in
southwestern DeSoto County more than 1,500 ft deep pump water with
chloride concentrations of only a few hundred milligrams per litre, indicating







BUREAU OF GEOLOGY


that the depth to salty water in this area, which is nearest to the coast, exceeds
these depths. Elsewhere in the counties, the depth to salty water is probably
greater than 2,000 ft.
Data from Polk County suggests that fresh water in the Floridan Aquifer
is hydrologically separated from the underlying salt water by a sequence of
relatively impermeable limestones and dolomites. Although long-term
declines in the potentiometric surface in parts of southern Polk County
amount to 40-60 ft (Stewart and others, 1971), no upward encroachment of
salt water has been reported in the area. At the site of an industrial-waste
injection well at the Kaiser Aluminum and Chemical Corporation plant,
about 17 mi north of the Polk-Hardee county line, samples taken July 25,
1974. from a shallow monitor well contained 45 mg/ chloride, and from a
deep monitor well. 1.700 mg/ chloride. The shallow monitor well is open to
the Avon Park Limestone, in the lower part of the Floridan Aquifer (depth
interval 1.254-1,264 ft); the deep one is open to the Oldsmar Limestone, in a
saline-water aquifer (depth interval 2,775-2, 788 ft) (Wilson and others, 1973).
Dolomites of the Lake City Limestone separate the two aquifers at the site.
Similar conditions probably exist in Hardee and DeSoto counties, where, as
in Polk County, the Lake City Limestone and Oldsmar Limestone underlie
the Avon Park Limestone.
Small amounts of chloride are probably derived from phosphate
minerals that occur only in the upper unit of the Floridan Aquifer and in
younger rocks. The principal phosphate mineral, fluorapatite, commonly
contains chloride instead of fluoride in the crystal structure (Toler, 1967, p.
13). This occurrence of chloride could account for some anomalously high
chloride concentrations in water in the upper unit in northeastern DeSoto
County (fig. 39). and for the decrease in chloride content with depth in some
wells (fig. 30. wells B and C).
Ground water containing 100 mg/1 or more of chloride in southern
DeSoto County may be largely a mixture of circulating low-chloride ground
water and residual salt water in aquifers and confining beds that have not
been completely flushed. This source is suggested by the similarity in area
distribution of chloride concentration for the upper and lower units (figs. 39
and 40). by the uniformity of chloride concentration in vertical profile (fig.
30), and by the occurrence of ground water with high chloride concentrations
even at considerable distances from possible saline surface-water sources.
High chloride concentrations in the upper unit in this area may also result in
part from upward flow of salty water along well bores that are open to both
the lower and upper units. In Charlotte County, for example, the
phenomenon of internal flow along hundreds of well bores has resulted in the
alteration of water quality in shallow water-bearing zones (Sutcliffe, 1973).
More detailed hydrogeochemical studies are needed in DeSoto and Hardee
counties before the origins and distribution of the chloride in these waters are
fully understood.







REPORT ON INVESTIGATION NO. 83


Some wells are close to the salty reaches of the Peace River in
southwestern DeSoto County, but high chloride concentrations have not
been a significant problem in ground water near the river. Water from well
0235-5905, 100 ft deep and about 150 ft from the river's edge, for example,
contains 110 mg/1 chloride, considerably below the recommended limit for
drinking water. This part of the county is a ground-water discharge area,
where the potentiometric surface is above land surface, and this condition
reduces the potential of contamination from the river.

FLUORIDE
Concentrations of fluoride in ground water are generally low, less than a
few milligrams per liter. But the presence of this ion is significant because
fluoride in certain concentrations is believed effective in reducing the
incidence of tooth decay in small children, and excessive amounts may cause
mottled enamel on teeth (Lohr and Love, 1954, p. 39). The U. S. Public
Health Service (1962) has recommended the following limits for drinking
water for an area such as Hardee and DeSoto counties, where maximum daily
air temperature averages 30.30 C: lower, 0.6 mg/ ; optimum 0.7 mg/ ; and
upper 0.8 mg/1. When the concentration is optimum, no ill effects will result,
and caries rates will be 60-65 percent below rates in communities with little or
no fluoride (U. S. Public Health Service, 1962, p. 41). The standards indicate
that concentrations should not average more than the upper limit, and
fluoride in concentrations greater than twice the optimum value (or greater
than 1.4 mg/ in the two counties) constitutes grounds for rejection of the
water for public supply.
As shown in figures 41 and 42, fluoride concentrations in Hardee and
DeSoto counties form a concentric pattern, with increasing concentrations
toward center. In both units, concentrations of 0.8 mg/1 or less occur only in
the periphery of the 2-county area, except along the western boundary, where
higher concentrations occur. In the upper unit, concentrations in much of the
central part of the 2-county area exceed 1.4 mg/I, with some values in this
area greater than 2.0 mg/1. In the lower unit, values exceeding 1.4 mg/ 1 are
restricted to western DeSoto County. Woodard (1964) and Toler (1967) both
reported higher concentrations of fluoride in Hardee and DeSoto Counties
compared to Polk County, and higher concentrations in the western
compared to the eastern parts of the two counties.
In vertical profile, the graphs for wells A, C, and E in figure 30 indicate
little change in fluoride concentration among the depth intervals sampled. In
well A, however, a marked decrease in concentration occurs below the upper
unit of the Floridan Aquifer. These differences are probably related to the
distribution of fluoride source minerals, as described below.
The principal source of fluoride in the counties is fluorapatite, a mineral
that is restricted to rocks of the upper unit of the Floridan Aquifer and







BUREAU OF GEOLOGY


younger deposits. Fluorapatite is also the principal source mineral of
phosphate in the land-pebble mining district of central Florida. The general
form of fluorapatite is Ca5 (P04)3F; in this form, the mineral contains about
3.8 percent fluoride. The areal distribution of phosphate minerals containing
fluoride in the Hawthorn Formation and Tampa Limestone has not been
mapped in the two counties. Geophysical logs of wells indicate that some
phosphate minerals occur in these formations throughout the two counties.
Younger deposits containing concentrated amounts of phosphorite are
probably more extensive in Hardee County and the northern third of DeSoto
County than in southern DeSoto County. This distribution is suggested by
the distribution of the phosphorite unit in the surficial aquifer (fig. 12) and by
the maps of the land-pebble phosphate district by Ketner and McGreevy
(1959).
Woodard (1964) suggested the fluoride distribution in central Florida is
related to ground-water flow, with higher concentrations occurring
downgradient, away from recharge areas. Although the concentration of
fluoride in Hardee and DeSoto counties does fit the flow pattern in a general
way. fluoride distribution is probably also related to other factors, including
the vertical and areal distribution of fluoride source minerals. The
interrelationship of factors is undoubtedly complex, and more detailed
knowledge of flow patterns and geology is needed before a full understanding
of areal variations in fluoride concentrations is gained.

USE OF THE RESOURCE
In DeSoto and Hardee counties, man has modified the natural
hydrologic system through development and use of the ground-water
resource. Sound planning and management of the resource can best be made
with an understanding of the amount of water used, the effects of
development, and the functioning of the hydrogeologic system.

WATER USE-1970
Knowledge of the amount of water used in DeSoto and Hardee counties
can be used as a basis for sound planning and management of water resources.
For example, historical information on water use would be needed as an input
to any modeling of the hydrologic system in the area. To provide this
background statewide, the U. S. Geological Survey conducted a survey of
Florida's water use in 1970, largely through personal contact with major
agricultural, industrial, and municipal water users (Healy, 1972; Pride, 1973).
The results of that survey and of additional and revised information are
summarized for DeSoto and Hardee counties in table 8. All withdrawals
listed are from ground-water sources; small amounts of ground water
withdrawn for lawn irrigation, stock watering, and supplying institutions are







REPORT ON INVESTIGATION NO. 83


not included. About 34 billion gallons was withdrawn for use in the two
counties in 1970, or an average of about 94 Mgal/d (table 8).


IRRIGATION
About 96 percent of the water use in DeSoto and Hardee counties in 1970
was for irrigation of citrus, vegetables, and pastureland. Withdrawals in the
two counties for irrigation are nearly equal; in DeSoto County most was used
for improved pasture, and in Hardee County most was used for citrus.
Withdrawls for irrigation are based on an average application rate of
12 inches in 1970 for all types of crops. This value is based in part upon
estimates by citrus experiment station personnel (Johnson, 1965; Kaufman,
1967, p. 7) of water requirements for citrus irrigation, and in part on irrigation
applications in DeSoto County monitored or reported in 1970 as part of this
investigation (table 9). This rate is an estimate because as of 1970 no records of
irrigation pumpage were required by management or regulatory agencies,
and few such records are known in the area. The pumping rates of most
irrigation wells are not known precisely, and the times and durations of
irrigation applications were estimated by individual irrigation operators.
Many citrus groves in both counties are not irrigated at all, and some are
irrigated only rarely, during extreme dry weather. Despite these variables,
monitoring of 4 different systems in DeSoto County in 1970 showed a narrow
range of application rate (10.8 to 12.4 inches) (table 9).
Monthly pumpage has been monitored at Joshua Grove in northeastern
DeSoto County since its establishment in 1969. The relation between
discharge and electric-power consumption was determined at each irrigation
well and grove pumpage was computed from kilowatt-hours consumed. In
1970, 7,160 acres were irrigated, and withdrawals averaged 5.7 Mgal/d, or
about 42 percent of total withdrawals for citrus irrigation in DeSoto County.
Application rate was 10.8 inches per year, below the estimated average for the
counties. The lower rate is attributable to the lesser water requirements of a
young grove compared to those of the mature groves that constitute most of
the area's citrus. By the end of 1972, irrigated acreage at this grove had
increased to 25,000, and pumpage during that year averaged 12.6 Mgal/d.
Irrigation pumpage is seasonal, generally heaviest during winter and
spring and practically nonexistent during summer. In 1970, for example, well
1415-4139 (table 9) pumped 4.2 weeks, or 78 percent of the year's total
pumpage time, prior to June, only 2 percent during June through September,
and 20 percent during October through December. At Joshua Grove, in
northeastern DeSoto County, 53 percent of the pumpage occurred during the
first five months of the year; most of the rest was in December, with only a few
percent during the summer. Vegetables such as tomatoes and cucumbers are
harvested twice a year and thus have two distinct irrigation periods, in early





Table 8. (round-waler withdrawal, 1970,

Type of use .___ ) eSoto County IHlard.e County ___ Total
Acreage Water withdrawn Acreage Water withdrawn Acreage Water withdrawn
Irrigated (mgd) (ac-ft) I (by) Irrisated (mid) (ae.ft) (by) j rrilated I(md) (ac.ft) (bly)
Irrigation
Citrus b16,000 13.6 15,270 4.97 c25,500 22.7 25,500 8.28 41,500 36.3 40,770 13.25
Vegetables d3,200 2.8 3,200 1.02 d4.500 4.0 4,500 1.46 7,700 6.8 7,700 2.48
Pasture 030,000 26.8 30,000 9.78 122,500 20.1 22,500 7.34 52,500 46.9 52,500 17.12

Sub-total 49.200 43.2 48,470 15.77 52,500 46.8 52,500 17.08 93.200 90.0 100.970 32.85
Industrial
(Self-supplied) .7 .26 .I .04 _.8 .30
Domestic Population Population Population
(Self-supplied) served served served
7.000 .7 .26 8,400 .8 .29 15.400 1.5 .55
Public supply
Arcadia 6,000 .5 .18
Bowling Green 1.400 .1.04
Wauchula 4,000 .6 .23
Zolfo Springs I 100 .1 .04

Sub-total 6.000 .5 .18 6,500 .8 .31 12,500 1.3 .49
Total 45.1 16.46 48.5 17.72 93.6 34.18

a Based on an average application rate of 12 inches per year, except 10.8 inches per year for citrus irrigation in northeastern
DeSoto County
b Estimated to be 40 percent of total citrus acreage exclusive of northeastern DeSoto County, where 7,160 acres of citrus were
irrigated
c Estimated to be 50 percent of total citrus acreage
d From Crop and Livestock Reporting Service, 1969-70. Irrigated acreage is 100 percent of total acreage
e Estimated from 1969 Census of Agriculture
r U. S. Department of Agriculture (T. W. Robinson, District Conservationist, U. S. Department of Agriculture, written
commun.. 1973)













Table 9. Water pumped for irrigation at selected sites, 1970


Crop Type Pumping Weeks Acres Volume pumped
Wells irri- of rate pumped, irri- (acre- (inches)
gated irrigation (gal/min) 1970 Rgated ft)
0345-4546 Melons Seepage 1,400 b6.4 285 278 11.7
and and
citrus overhead
sprinklers
1415-4139 Pasture Seepage 1,800 c5.3 320 296 11.1
1507-4242 Pasture Seepage 1,740 c6.2 320 332 12.4
NE DeSoto Co. Citrus Seepage 25,560 c7.5 7,160 6,430 10.8
(17 wells)
a Duration of pumpage converted to equivalent weeks of continuous pumpage.
b Reported by grove manager.
c Based on observed rate of consumption of kilowatt hours per unit of time.


C LI I ~C- --