U.S. GEOLOGICAL SURVEY

U.S. DEPARTMENT OF THE INTERIOR

Prepared in cooperation with

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

OPEN FILE REPORT 97-178

Metz, P.A. and others, 1997, Potentiometric surfaces of the Intermediate
Aquifer System, west-central Florida, September 1996

INTRODUCTION

The intermediaie aquifer system underlies a 5,000-square-mile area within the
Southwest Florida Water 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of water withdrawn from the intermediate aquifer system is considerably less than
that withdrawn from the Floridan aquifer system in the study area (Duerr and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 September 1996 (fig. 1 and 2). The potentiometric
surface is an imaginary surface represented by the level to which water will rise in
tightly cased wells that tap 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 wet season when ground-water withdrawals for
agricultural use typically are low. The cumulative rainfall for the study area was
2.62 inches below average for the period from October 1995 through September 1996
(Southwest Florida Water Management District, 1996).

This report, prepared by the U.S. Geological Survey in cooperation with the
Southwest Florida Water Management District, is one of a series of semi-annual
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 September 9-13, 1996.

SUMMARY OF GROUND-WATER CONDITIONS

The composite potentiometric surface of all water-bearing units within the
intermediate aquifer system is shown 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 September 1995 through
September 1996.

Most water levels measured in September 1996 for the composite intermediate
aquifer potentiometric surface generally were lower than those measured in
September 1995 (Metz and others, 1996). In 129 wells with paired measurements, the
September 1996 levels ranged from 22 feet below to 5 feet above the September 1995
levels and averaged 4 feet below the September 1995 levels. In 27 wells with paired
measurements in the Tamiami-upper Hawthorn aquifer the September 1996 levels
ranged from 0.5 feet below to 6 feet below the September 1995 levels and averaged
3 feet below the September 1995 level.

September 1996 water-levels for the intermediate aquifer system composite
potentiometric surface generally were higher than those reported for May 1996
(Mattie and others, 1996). In 128 wells with paired measurements, the September
1996 levels ranged from 3 feet below to 17 feet above the May 1996 levels and
averaged approximately 3 feet above the May 1996 levels. In 29 wells with paired
measurements in the Tamiami-upper Hawthorn aquifer, the September 1996 levels
ranged from 19 feet below to 10 feet above the May 1996 levels and averaged
approximately 2 feet above the May 1996 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 (fig. 2). Natural
discharge from Warm Mineral Springs affects both the composite potentiometric
surface and that of the Tamiami-upper Hawthorn aquifer (fig. | and 2).

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.

Mattie, J.A., Metz, P.A. and Torres, A.E., 1996, Potentiometric surface of the
intermediate aquifer system, west-central Florida, May 1996: U.S. Geological
Survey Open-FileReport 96-595, | 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, September 1996, 58 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:
U.S. Geological Survey Water-Resources Investigations Report 82-4089, 48 p.

275314081514202" -
ROMP 59 Hawthorn Well near Bartow’

a
110 4

#85938

Za3es

1978 |-

1980

1984

1982 |"

2 273851082031502
ROMP 40 Hawthorn Well near Duette

San i i i

150) 7
140/- be
130} A
-_ oo VyeTM
110}- 5
qooLt1 tits iriiiiii
Row 2 Havthor

jorn Well near Gardner
60
50)
40
30

Glide

i od
5238988338
A SE
jeep 14 near Englewood

60 poppy
50
4ol- 4
30
20 PRAT Ninny anal}
10
old
8558 8 8 8

270959082203002

ROMP 19 WUAM Well near Sarasota
(7 et a
ell 4
a 4

Ss aaNet aS
i =
oO 4
AOL Li ti tiiiii

eeeee

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

1996

Station number based on latitude and longitude
of the site.

® ROMP 59 (Regional Observation and Monitor Well

Program) is a Southwest Florida Water Management
District monitor well and identification number.

aquifer system.

Figure 3. Annual and seasonal fluctuations
in selected wells open to the intermediate

275314081514202
ROMP 59 Hawthorn Well near Bartow

$20 rt

110}- =

100}- |
oa

90 4

80}- al
DEPTH 142 FEET

70 CASING 122 FEET a

60

ee a a een
SONDJFMAMJJAS
1995 1996

2 273851082031502
ROMP 40 Hawthorn Well near Duette

1600

DEPTH 180 FEET
| CASING 76 FEET

etl iil sei
SON DJJ FMAMJJAS
1995 1996

100

3 271757081493003
ROMP 26 Hawthorn Well near Gardner

SST

8

30+ 4

20+ 4
DEPTH 180 FEET
10° CASING 140 FEET

a a oY
SON DJJ FMAMJJAS
1995 1996

4 270137082235301
Manasota Deep 14 near Englewood

i ]
a |
go} |
et | a
10 | DEPTH 305 FEET 4
Se eeieeim
O'SON DIS FMAMJJAS
1995, 1996
270959082203002
ROMP 19 WUAM Well near Sarasota
407 q

| DEPTH 205 FEET
CASING 87 FEET

AGL

°

SON DIU FMAMJJAS
1995 1996

Figure 4. Maximum daily water
levels in selected wells from
September 1995 to September 1996.

FP NGVD of 1929.
Q, SPRING
. CITY OR TOWN

measurements of water level.

EXPLANATION

VERNA MUNICIPAL WELL FIELD PRODUCING 500,000 GALLONS PER DAY OR MORE

—20-—— POTENTIOMETRIC CONTOUR - - Shows altitude at which water would have stood in tightly cased wells. Contour intervals are 5 and 10
feet. National Geodetic Vertical Datum of 1929. Hachures indicate depressions. Dashed where approximately located.

————_—s: BOUNDARY OF SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
@—e—e-— APPROXIMATE NORTHERN BOUNDARY OF THE INTERMEDIATE AQUIFER SYSTEM
@ ¢ ¢ APPROXIMATE BOUNDARY OF THE TAMIAMI-UPPER HAWTHORN AQUIFER

eo e OBSERVATION WELLS - - Large number identifies hydrograph (figs. 1,2). Small number is altitude of water level in feet above or below

NOTE: The potentiometric contours are generalized to synoptically portray the head in a dynamic hydrologic system, taking due account
of the variations in hydrogeologic conditions, such as differing depths of wells, nonsimultaneous measurements of water levels, variable
effects of pumping, and changing climatic influence. The potentiometric contours may not conform exactly with the individual

Hamilton

.
Winter Haven

East Lake
Tohopekaliga

= 2
Saint Cloud ©

Alligator
Lake

(BU! Clearwater

CITY OF SARASOT)
BDOWNIOWN WELLFIR

SCALE 1:500,000
1 INCH EQUALS APPROXIMATELY 8 MILES

5 oO 5 10 15 20 MILES
Carer )

10 15 20 KILOMETERS

82°30" 82°00"

27°30"

27°00°

a Palmdale

GLADES

SCALE 1:500,000
1 INCH EQUALS APPROXIMATELY 8 MILES

5 oO 10 15 20 MILES
= 1

10 15 20 KILOMETERS

A EN BRT y

82°30" 82°00°
Figure 2. Potentiometric surface of the Tamiami-upper Hawthorn aquifer.

81°30’

81°00’

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

POTENTIOMETRIC SURFACES OF THE INTERMEDIATE AQUIFER

SYSTEM, WEST-CENTRAL FLORIDA, SEPTEMBER 1996

By P.A. Metz, J.A. Mattie, and M. A. Corral
1997

ies of this map can be purchased from:
U.S. Geological ie

Branch of Information Services

Box 25286

Denver, Colorado 80225-0286