U.S. DEPARTMENT OF THEINTERIOR
U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

OPEN-FILE REPORT 96-595

Mattie, J A and others, 1996. Potentiometricsurfaces of the
intennediate aquifer system, west-central Flonda, May 1996

WATER LEVEL, IN FEET ABOVE OR BELOW NATIONAL GEODETIC VERTICAL DATUM OF 1929

STUDY
AREA

INTRODUCTION

The intermediate aquifer system underlies a 5,000-square-mile area within the
Southwest Florida Management District including De Soto, Sarasota, Hardee,
Manatee, and parts of Charlotte, Hillsborough, Highlands, and Polk Counties. It is
overlain by the surficial aquifer system and is underlain by the Floridan aquifer
system. The intermediate aquifer system consists of layers of sand, shell, clay.
calcareous clays, limestone, and dolomite of the Tamiami Formation and Hawthorn
Group of Pleistocene to Oligocene age (Wingard and others, 1995). The intermediate
aquifer system contains one or more water-bearing units separated by discontinuous
confining units. This aquifer system is the principle source of potable water in the
southwestern part of the study area and is widely used as a source of water where
wells are open to the intermediate aquifer system or to both the intermediate and
Floridan aquifer systems. Yields of individual wells open to the intermediate aquifer
system vary from a few gallons to several hundred gallons per minute. The volume
of water withdrawn from thé intermediate aquifer system is considerably less than
that withdrawn from the Floridan aquifer system in the study area (Duerr and others,
1988).

In areas where multiple water-bearing units exist in the system, wells open to
individual units were selected for water-level measurements whenever possible. The
water levels along the northern boundary of the intermediate aquifer system generally
are similar to water levels in the underlying Floridan aquifer system because the
confining unit that separates the two aquifers is either absent or discontinuous in that
area, permitting direct hydraulic connection between the two aquifer systems. In the
southwestern and lower coastal region of the study area, the intermediate aquifer
system is composed of the Tamiami-upper Hawthorn aquifer and the underlying
lower Hawthorn-upper Tampa aquifer and is separated by intervening confining units
(Wolansky, 1983). Lateral boundaries for the Tamiami-upper Hawthorn aquifer are
undetermined because of limited hydrogeologic data. The potentiometric surface of
the Tamiami-upper Hawthorn aquifer is shown separately from the potentiometric
surface of the intermediate aquifer system

The purpose of this report is to show the potentiometric surfaces of the
intermediate aquifer system in May 1996. The potentiometric surface is an imaginary
surface represented by the level to which water will rise in tightly cased wells that lap
a confined aquifer system. The surface is mapped by measuring the altitude of water
levels in a network of wells and is represented on maps by contours that connect
points of equal altitude. This map represents water-level conditions near the end of
the dry season when ground-water withdrawals for agricultural use typically are high.
The cumulative rainfall for the study area was 12.35 inches above average for the
period from June 1995 through May 1996 (Southwest Florida Water Management
District, 1996).

This report, prepared by the U.S. Geological Survey in cooperation with the
Southwest Water Management District, is one of a series of intermediate aquifer
system potentiometric-surface map reports made for the study area since September
1985. Water-level data are collected in May and September to show the annual low
and high water-level conditions, respectively. Most of the water-level data for this
map were collected by the U.S. Geological Survey during the period of May 20-24,
1996.

SUMMARY OF GROUND-WATER CONDITIONS,

The composite potentiometric surface of all water-bearing units within the
intermediate aquifer system is show in figure 1. The potentiometric surface of the
Tamiami-upper Hawthorn aquifer is shown in figure 2 and is based on water levels
‘open only to this aquifer. The long-term hydrographs for selected wells, shown in
figure 3, indicate that the annual and seasonal fluctuations of the water levels
generally are large (greater than 15 feet) in the central interior region where water
demand for irrigation is high during fall and spring (hydrographs 1, 2, and 3)
Seasonal fluctuations are smaller in the southern area (hydrographs 4 and 5) where
water use is predominantly for public supply. Hydrographs in figure 4 show the
maximum daily water-level altitudes in selected wells from May 1995 through May
1996.

Most water levels measured in May 1996 for the composite intermediate aquifer
potentiometric surface generally were lower than those measured in September 1995
(Metz, and others, 1996). In 132 wells with paired measurements, the May 1996
levels ranged from 30 feet below to 5 feet above the September 1995 levels and
averaged 7 feet below the September 1995 levels. In 32 wells with paired
measurements in the Tamiami-upper Hawthorn aquifer, the May 1996 levels ranged
from } foot above to 16 feet below the September 1995 levels and averaged 4 feet
below the September 1995 levels.

May 1996 water-levels for the intermediate aquifer system composite
potentiometric surface generally were slightly higher than those reported for May
1995 (Metz and Stelman, 1995). In 132 wells with paired measurements, the May
1996 levels ranged from 5 feet below to 12 feet above the May 1995 levels and
averaged approximately | foot above the May 1995 levels. In 33 wells with paired
measurements in the Tamiami-upper Hawthorn aquifer, the May 1996 levels ranged
from 5 feet below to 9 feet above the May 1995 levels and averaged approximately
1 foot above the May 1995 levels. Pumping from the wellfield that supplies Fort
Myers has resulted in a cone of depression in the potentiometric surface of the
Tamiami-upper Hawthorn aquifer in northern Lee County (figure 2). Natural
discharge from Warm Mineral Springs affects both the composite potentiometric
surface and that of the Tamiami-upper Hawthorn aquifer.

REFERENCES

Duerr, A.D., Hunn, J.D., Lewelling, B.R., and Trommer, J.T., 1988, Geohydrology
and 1985 water withdrawals of the aquifer systems in southwest Florida, with
emphasis on the intermediate aquifer system: U.S. Geological Survey Water-
Resources Investigations Report 87-4259, 115 p.

Metz, P.A. and Stelman, K.A., 1995, Potentiometric surface of the intermediate
aquifer system, west-central Florida, May 1995: U.S. Geological Survey Open-
File Report 95-707, 1 sheet.

Metz, P.A., Swenson, E.S., and Stelman, K.A., 1996, Potentiometric surface of the
intermediate aquifer system, west-central Florida, September 1995: U.S
Geological Survey Open-File Report 96-136, | sheet.

Southwest Florida Water Management District, 1996, Summary of hydrologic
conditions, May 1996, 56 p.

Wingard, G.L., Weedman, S.D., Scott, T.M., Edwards, L-E., and Green, R.C., 1995.
Preliminary analysis of integrated stratigraphic data from the South Venice
corehole, Sarasota County. Florida: U.S. Geological Survey Open-File Report
95-3, 129 p.

Wolansky, R.M., 1983, Hydrogeology of the Sarasota-Port Charlotte area, Florida:
USS. Geological Survey Water-Resources Investigations Report 82-4089, 48 p

275314081514202') (2) 2753408151420) (2)
ROMP 59 Hawthorn Well near Bartow ROMP 50 Hawthorn Well near Bartovs
$20 ot 120 r
110F *
100
90
80
70
COMTTRSOND TEMA
1995 1996
273851082031502 273851082031 502
ROMP 40 Hawthorn Well near Duette ROMP 40 Hawthorn Well near Duette
160 ty 160, T
150 | 150}. 4
140- 4 140}. 4
130F, 5 130F
120 [a toot 5
DEPTH 180 Ft
110F 1 MOF CASING 76 FEE 7
100 bight ttt 100! naa
BE2SSE R93 859 2588 MT foes ST Fides:
271757081493003 271757081493003
ROMP 26 Hawthorn Well near Gardner ROMP 26 Hawthorn Well near Gardner
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30} 4 30+ 4
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DEPTH 205 Hi |
oF 1 OF CASING 87 FEE
Pe rarer a ree ere Pe 10

() station number based on latitude and longitude

oP 59 (Regional Observation and Monitor Well
Program) is a Southwest Florida Water Management
District monitor well and identification number.

Figi

¢ site.

ure 3. Maximum daily water
levels in selected wells open to
the intermediate aquifer system.

MITASONOTEMK
1995 1996

D Station number based on latitude and longitude

of the site.

2) ROMP 59 (Regional Observation and Monitor Well
Program) is a Southwest Florida Water Management
District monitor well and identification number.

Figure 4, Maximum daily water
levels in selected wells from

May 1995 to May 1996.

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Figure 1. Composite potentiometric surface of the intermediate aquifer system.

EXPLANATION

MUNICIPAL WELL FIELD PRODUCING 50,000 GALLONS PER DAY OR MORE

POTENTIOMETRIC CONTOUR -- Shows altitude at which water would have
stood in tightly cased wells. Contour interval 5 and 10 feet. Datum is National

Geodetic Vertical Datum (NGVD) of 1929. Hachures indicate depressions
Dashed where approximately located.

BOUNDARY OF SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT.

OBSERVATION WELLS -- Large number identifies hydrograph. Small number

is altitude of water level in feet above or below NGVD of 1929
SPRING

NOTE: The potentiometric contours are generalized to portray synoptically the

head in adynamic hydrologic system. taking due account of the variations in
hydrogeologic conditions. such as differing depths of wells, non-simultaneous
measurements of water levels, variable s of pumping. and changing
climatic influence. The potentiometric contours may not conform exactly

with individual measurements of water level

APPROXIMATE NORTHERN BOUNDARY OF THE INTERMEDIATE AQUIFER

APPROXIMATE BOUNDARY OF THE TAMIAMI- UPPER HAWTHORN AQUIFER

82°45" 30° 15” 2°00" , f °15”
27°30’ -—yF- aT | , - 8 = - 4 30 81°15
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Figure 2. Potentiometric surface of the Tamiami-upper Hawthorn aquifer.

Base from Southwest Florida Water Management District digital data, 1992.
Universal Transverse Mercator projection, Zone 17

Scale 1:500,000

AQUIFER SYSTEM, WEST- CENTRAL FLORIDA, MAY 1996

POTENTIOMETRIC SURFACES OF THE INTERMEDIATE

By J.A. Mattie, P. A. Metz, and A.E. Torres

1996

Geological Surv
Branch of Information
Box 28286

of this map can be purchased from:

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Denver, Colorado 80225-0286