UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY


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FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY


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RECHARGE AREAS OF THE FLORIDAN AQUIFER
IN SEMINOLE COUNTY AND VICINITY, FLORIDA

by
C. H. Tibbals


Prepared by
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
FLORIDA DEPARTMENT OF NATURAL RESOURCES
and
SEMINOLE COUNTY COMMISSIONERS
TALLAHASSEE, FLORIDA


INTRODUCTION

The Floridan aquifer is the most important source of water supply in
Seminole County. Virtually all public and domestic water supplies and
most of the water used for irrigation are from wells that tap the
Floridan. Hence, delineating the areas that recharge the aquifer is
important. The purpose of this report is to show those areas where the
Floridan aquifer is subject to recharge or discharge. Lichtler (1972) also
made a somewhat general description of recharge areas in Seminole
County. But this map report presents a more detailed representation of
the recharge areas on the basis of further study and field work
accomplished from July 1971 to May 1973.
This report was prepared in cooperation with the Seminole County
Board of Commissioners as part of a comprehensive study of the water
resources of Seminole County that began in July 1971. The
investigation was made under the general supervision of C. S. Conover,
Florida District Chief, and the immediate supervision of J. 0. Kimrey,
Subdistrict Chief, both of the U. S. Geological Survey.

GEOHYDROLOGY

In Seminole County, the Floridan aquifer is composed of limestone
alternating with layers of dolomite and dolomitic limestone. Depth to
the top of the aquifer ranges from about 75 feet in the northwest,
northeast (except the Geneva area) and southeast parts of the county to
as much as 200 feet in the southwest parts and 130 feet in the Geneva
area. The thickness of fresh water (chloride content less than 250
milligrams per liter) in the aquifer ranges from zero to as much as 2,000
feet (Shampine, 1965).
The Floridan aquifer is overlain by confining beds that are generally
composed of clay and clayey sand. Their thickness and permeability
vary throughout the county and exert a partial control on the amount
of water that can recharge the Floridan aquifer. Because the Floridan
aquifer is confined, the water level in a tightly cased well in the aquifer
will stand above the level at which the aquifer was first penetrated. This
water level is called the potentiometric surface. Where the
potentiometric surface is above land surface, a well that is drilled into
the aquifer will flow at the surface. The main areas of artesian flow in
Seminole County are along the Wekiva, Econlockhatchee, Little
Econlockhatchee, and St. Johns Rivers, much of the Sanford and
Oviedo areas, and in the area around Lake Jessup. These areas are
shown in yellow on figure 1.
The water table, or nonartesian, aquifer is composed primarily of
fine to very fine sand and is the uppermost ground-water reservoir in
Seminole County. The aquifer is recharged from local rainfall and, in
areas where the potentiometric surface of the Floridan aquifer is above
the water table, by upward leakage from the Floridan aquifer. Water
leaves the nonartesian aquifer by downward leakage to the Floridan
aquifer, pumpage, seepage to lakes, ditches, and streams, and, where the
water table is near land surface, by evapotranspiration. In Seminole
County, the water table occurs at depths ranging from land surface to
30 feet below land surface. In general, the depth to the water table is
greatest in the southwest and northwest sections of the county, the
Oviedo area, the Chulouta area, and in the Geneva area. Throughout the
rest of the county, the water table occurs at or near the land surface
during much of the year. In some areas, the water table has been
artificially lowered by ditching and draining.

RECHARGE

The Flondan aquifer is recharged by downward leakage of water
from the water table aquifer. Discharge from the Floridan aquifer
ocours as pumpage, as springflow, and by upward leakage in areas where
the potentiometric surface of the Floridan is above the water table.
Recharge to the Flondan aquifer is that component of the rainfall
which percolates to the water table and continues to move downward
through the confining beds and into the aquifer. That part of the
rainfall not considered as recharge either evaporates from the land or
water surfaces; is transpired by plants; or runs off or seeps toward lakes
and streams and ultimately discharges into the ocean.
Some of the water that runs off or seeps into lakes or streams may
ultimately contribute to recharge through the lake or stream bottom,
thence to the Floridan aquifer. However, the amount of water that can
recharge the Floridan aquifer through a lake or stream bottom depends
upon the effectiveness of the hydraulic connection between the water
body and the aquifer.
Recharge to the Floridan aquifer can occur wherever the water table
(or a lake surface) is above the potentiometric surface of the Floridan.
However, the rate of recharge is governed by: 1) the thickness and
permeabdity of the intervening confining beds and 2) the degree of
hydraulic potential, or head difference, between the water-table aquifer
and the Floridan aquifer.
Information concerning the position and configuration of the
potenrtiometric surface of the Floridan is obtained periodically and the
thickness of the confining beds was determined by Barraclough (1962).
However, data concerning water-table altitudes and permeabiity of the
confining beds are sparse and have little transfer value from one
location to another. Therefore, it is necessary to resort to indirect
methods of evaluating those factors and their effect on the recharge
potential of an area.

METHODS OF LOCATING AND EVALUATING
RECHARGE AREAS

The indirect methods used in defining and evaluating the recharge
areas shown on figure 1 consist of analyzing rainfall-runoff relationships
in stream basins; evaluating the configuration of the potentiometric
surface of the Flondan aquifer; observing the significance of the degree
of mineralization of water in the Floridan aquifer; and evaluating the
topography and landforms with respect to altitude of the
potentiometric surface of the Floridan aquifer. In addition, analysis of
soils maps helps determine the location of recharge areas. Such maps
are prepared and made available by the U.S. Soil Conservation Service
(U.S. Department of Agriculture, 1966).
Rainfall-runoff relationships provide only a rough estimate of the
quantity of water that is available for recharge. The most important
variable is the amount of evapotranspiration that occurs in each
surface-water drainage basin. Even within the same basin, the
relationship of rainfall to runoff may vary considerably. In general, a
basin that has a small amount of runoff per unit area has more water
available for recharge.
A map of the potentiometric surface of the Floridan aquifer (figure
1) is useful m detecting and delineating areas where recharge or
discharge occurs. "Bulges" on the potentiometric surface (as in the
Geneva area) generally coincide with areas of recharge; "holes"
(Sanlando Springs area) or "troughs" (west end of Lake Jessup)
generally coincide with areas of discharge. This map must be used with
caumotion in selecting areas of recharge because area changes in aquifer
transmissivity (the ability of the aquifer to transmit water) and the
effects of pumping can also exert control on the configuration of the
potentiometric surface.
The degree of mineralization of water in the Floridan aquifer
generally reflects the solubility of the rock materials and, also, the
length of time the water has been in contact with the matenals. The
dissolved solids content of water from the upper 200 feet of the
Floridan aquifer can be generalized really as shown on figure 2. The
dissolved-sohds content is a measure of the degree of mineralization. In
Seminole County, some of the minerahzation is due to sea water that
entered the aquifer during interglacial periods of the Pleistocene epoch
or from sea water that was trapped in the rocks when they were
deposited (Barraclough, 1962). Water in the Floridan aquifer moves
from places of recharge to places of discharge. The less mineralized
water that enters the aquifer as recharge reacts with the rock materials
as it moves through the aquifer and also dilutes and flushes out the
more highly mineralized sea water. In Seminole County, areas where
the Flondan aquifer contains water with a relatively small amount of
dissolved solids are areas where recharge is either occurring or occurring
nearby.
The evaluation of topography and landforms with respect to the
altitude of the potentiometric surface can be used to help determine
the relative effectiveness of recharge areas.
In areas where the potentiometric surface of the Flondan is many
tens of feet below land surface, the water table may be near land
surface or it may be many feet below and only slightly above the
potentiometric surface of the Floridan. Where the potentiometric
surface of the Floridan is at considerable depth below land surface and
where the head difference between the water table and the
potentiometric surface is small and where the surface drainage is not
well developed (such as the area along Interstate 4 between State Roads
434 and S-46A), the confining beds are only slightly effective and
recharge is occurring. A well-developed surface drainage system on
relatively high land (such as along Gee Creek, Howell Creek, and the
Econlockhatchee and Little Econlockhatchee Rivers), may indicate
that, even though the potentiometric surface of the Floridan is several
tens of feet below land surface and the water table is several feet below
land surface (therefore, little water is lost to evapotranspiration), some
of the potential Floridan recharge water may ultimately seep laterally
via the water-table aquifer and discharge into streams. Where the
altitude of land surface is relatively high and the potentiometric surface
is far below land surface, the water table may be near land surface
(because of relatively effective confining beds) and the aea may have
little surface drainage. An example would be the area about 1.5 miles
west of Longwood. Here, the head difference between the water table
and the potentiometric surface is sufficient to drive the recharge water
across the confining beds and into the aquifer while the remainder is
lost to evapotranspiration.


Where the potentiometric surface is near or, perhaps, above land
surface, the water table is usually near land surface. These areas are
generally not effective recharge areas because 1) there is little
downward head difference between the water table and the
potentiometric surface (the potentiometric surface of the Floridan
aquifer, in some areas, may actually be above the water table and (or)
land surface and upward leakage is occurring, thereby precluding
recharge); 2) evapotranspiration rates are generally high because the
water table is at or near land sufrace; and 3) surface drainage is usually
developed to such an extent that it removes any water that is not lost
to evapotranspiration.
Areas that are pocked with sinkholes and lakes of probable sinkhole
origin are generally effective recharge areas even though the lakes and
sinks themselves may, or may not, contribute the majority of the
recharge water. The fact that there was previous sinkhole formation is
evidence that large quantities of water were (and probably still are)
being recharged throughout the entire area. The sinkholes were formed
because slightly acid water (formed from the contact of rainfall with
carbon dioxide in the atmosphere and soil) percolated downward and
slowly dissolved the limestone. When caverns in the limestone become
so large that their roofs are unable to sustain the weight of the
overburden, the roofs collapse and the overlying sands flow into the
caverns. The depressions formed on the land surface are merely the
surface expressions of subsurface subsidence.
The recharge areas of varying effectiveness that are shown in figure 1
were delineated on the basis of all the previously-discussed methods
except the analysis of a soils map. The soils map was not referred to
until the recharge map was almost completed; so the soils map was a
final check. The results obtained from analysis of the soils map was in
very close agreement with the results obtained by the other
independent methods of analysis. However, as a tool to delineate
recharge areas, soils maps cannot be used exclusively. For example, a
well-drained soil may be the result of ultimate lateral drainage to lakes
and streams as well as vertical drainage (recharge) to the Floridan
aquifer. Also, the fact that a soil is not well-drained does not preclude
the possibility that recharge is taking place.

DESCRIPTIONS OF RECHARGE AREAS

The most effective recharge areas to the Floridan aquifer in Seminole
County and vicinity are shown in red on figure 1. These areas are
generally described as follows: 1) the natural surface drainage system is
poorly developed and the amount of runoff with respect to rainfall is
relatively low; 2) the potentiometric surface of the Floridan aquifer
-may show "bulges" as in the Geneva area; 3) the mineralization of
water in the Floridan aquifer (fig. 3) is less than that in the poor and
very poor recharge areas; 4) the land surface is many feet above the
potentiometric surface of the Floridan and is characterized by many
closed depressions, lakes, and ponds that are indicative of past sinkhole
activity; 5) the soils are generally well drained. The data available
indicate that recharge rates in the most effective recharge areas
probably range from 10 inches to as much as 21 inches of rainfall per
year.
The moderately-effective recharge areas are shown in blue on figure 1
and are described as follows: 1) the surface drainage system tends to be
more developed than in the most effective recharge areas and the
amount of runoff with respect to rainfall is relatively higher. In these
areas, the surface drainage system may be entirely natural or it may
have been enhanced by man's activities. In either case, more runoff is
likely to occur than in the most effective recharge areas; 2) the
potentiometric surface of the Floridan may show evidence of "bulging"
although it is generally less pronounced than in the most effective
recharge areas; 3) the mineralization of water in the Floridan aquifer
(fig. 3) is about the same as that in the most effective recharge areas but
less mineralized than that in the poor and very poor recharge areas; 4)
the distance between land surface and the potentiometric surface is
generally not as great as in the most effective recharge areas and there is
less evidence of past sinkhole activity (that is, closed depressions, lakes,
and ponds); 5) the soils are generally well drained. The recharge rates in
the moderately- effective recharge areas probably range from 3 to 10
inches of rainfall per year.
The poor recharge areas are shown in green on figure 1. These areas
are described as follows: 1) the surface drainage system may or may rot
be well developed. Where the surface drainage system is well developed,
the percentage of rainfall that runs off is relatively high. Where the
surface drainage system is poorly developed, much of the rainfall that
doesn't ultimately run off to streams stands in marsh or wet areas and is
lost to evapotranspiration, therefore; 2) the land may be characterized
by swamps and other areas where water stands on or near the surface
throughout most of the year; 3) the potentiometnc surface of the
Floridan generally tends to be featureless with no well-defined
naturally-occurring "bulges" or "troughs" that can be attributed to
natural recharge or discharge; 4) the degree of mineralization of the
water in the Floridan aquifer (fig. 3) generally is higher than in the
better recharge areas; 5) the soils generally tend to be poorly drained.
The recharge rates in poor recharge areas probably range from 0 to 3
inches of rainfall per year.
Very poor recharge areas are shown in yellow on figure 1. These
areas are described as follows: 1) the potentiometric surface of the
Floridan aquifer is above land surface (and, hence, the water table) so
these are areas of artesian flow and upward leakage, or rejected
recharge; 2) the surface drainage system may or may not be well
developed although much of the very poor recharge areas shown in
yellow is of agricultural importance and, except for the area south of
State Road 46 along the Wekiva River, Little Wekiva River, and Rock
Springs Run, much ditching and dreaming has been done to facilitate
farming activity. Where not ditched and drained, many of these areas
are swampy and water stands on the surface most of the year. All of the
rainfall that does not run off is lost to evapotranspiration; 3) the
mineralization of water in the Floridan aquifer (fig. 3) is generally
greater than in the most effective and moderately effective recharge
areas; 4) the soils are generally poorly drained. The recharge rate in
those areas classified as very poor recharge areas could actually be
considered as zero or some negative amount because discharge, rather
than recharge, is hkely to be occurring most of the year.

CONFIGURATION OF POTENTIOMETRIC SURFACE
OF FLORIDAN AQUIFER

The contours (fig. 1) depict the configuration of the potentiometric
surface, or pressure surface, of the Floridan aquifer in Seminole County
and vicinity. The movement of water in the aquifer is at right angles to
the lines of equal head (pressure) in the direction of decreasing head
and from areas of recharge to areas of discharge. Thus, figure 1 shows
that most of the ground water that flows into Seminole County from
Orange County by way of the Floridan aquifer is subsequently
discharged from the aquifer into the Wekiva River via Wekiva,
Sanlando, Palm, and Starbuck Springs. A small amount of inflow from
Orange County occurs in the extreme southeast part of Seminole
County. Thus, aside from the southwest and extreme southeast parts of
the county, Seminole County is largely self-sufficient in its
ground-water supply because, in the remainder of the county, all of the
water in the Floridan aquifer originated as rainfall on the county. Even
in the southwest section of the county, it is estimated that 44 percent
of the water being discharged from Sanlando, Palm, and Starbuck
Springs is derived from local (within the county) recharge. Further, it is
estimated that 18 percent of the water being discharged from Wekiva
Spring originated as rainfall on Seminole County.
From 1961 to 1973, Seminole County and vicinity has been, on the
whole, about 38 inches deficient in rainfall (fig. 3) with about 19 inches
of the deficiency having occurred since 1969. As a result,
potentiometric levels of the Floridan aquifer (fig. 3) have declined.
Since 1969, Seminole County has experienced unprecedented growth
resulting in increased stress on the ground-water resources. However,
even in southwest Seminole County, where most of the recent growth
has occurred, there is no evidence to show that the declining
potentiometric levels can be attributed to anything other than deficient
rainfall. This may be due in part to the fact that most of the increase in
ground-water withdrawals has occurred in an area that is predominately
drained by Sanlando, Palm, and Starbuck Springs, major discharge
points for the Floridan aquifer. It is possible that the effects of man's
increased ground-water withdrawals on potentiometric levels have been
partially offset by a reduction in springflow, or natural discharge.

SELECTED REFERENCES

Barraclough, J.T.,
1962 Ground-water resources of Seminole County, Florida:
Florida GeoL Survey Rept. Inv. 27.
Hoy, N.D. and Teel, J.R.,
1963 Hydrologic features of the Floridan aquifer in Seminole
County. Florida: Florida Geol. Survey Map Series 5.
Lichtler, W.F. and others,
1968 Water resources of Orange County, Florida: Florida Dept.
Nat. Resources, Bur. Geology Rept. Inv. 50.
Lichtler, W.F.,
1972 Appraisal of water resources in the East Central Florida
region: Florida Dept. Nat. Resources, Bur. Geology Rept.
Inv. 61.
Shampine, William J.,
1965 Chloride concentration in water from the upper part of
the Floridan aquifer in Florida: Florida Geol. Survey Map
Series 12.
U.S. Department of Agriculture,
1966 Soil survey, Seminole County, Florida: Soil Conservation
Service.


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SMOvsT EFFECTIVE RECHARGE AREA
RECHARGE RATE 10-21 IN PER YEAR -

I MODERATELY EFFECTIVE RECHARGE
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I-11-50- CONTOUR REPRESENTS ALTITUDE
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.TMiE FLORIDAN AQUIF ER. MAY 1973,
FEET ABOVE MEAN SEA LEVEL
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Figure 1. Map of Seminole County and vicinity showing recharge areas, selected drainage basins, selected hydrologic data collection stations, and potentiometric surface of the Floridan aquifer, May 1973.
Recharge areas in Orange County taken from Lichtler (1968).


800'


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LOCATION OF INVESTIGATION, (SEMINOLE
COUNTY AND SURROUNDING AREAS )


FLORIDA DEPARTMENT OF NATURAL RESOURCES
BUREAU OF GEOLOGY


This public document was promulgated at a total
cost of $420.00 or a per copy cost of $.28 for the
purpose of disseminating hydrologic data.


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Figure 2. Map of Seminole County showing dissolved solids content of water from the upper 250 feet of the Floridan
aquifer (from Hoy and Teel, 1962).


I-Irs. fi8
1975


MAP SERIES NO. 68


ORANGE 47 NEAR ORLANDO


AVERAGE 1944-72







AVERAGE 1952-72



SEMINOLE 125 NEAR LONGWOOD





AVERAGE 1952-72


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