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Clearwater

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Fort Ogden

Frostproof

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SCALE 1:500,000MILES

KILOMETERS

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STUDY AREA

MAP AREA

ALABAMA GEORGIA

FLORIDA

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

Scientific Investigations Map 3183

A.G. Ortiz , 2011, Potentiometric surface of the upper

Floridan aquifer, west-central Florida, May 2011

POTENTIOMETRIC SURFACE OF THE UPPER FLORIDAN AQUIFER,

WEST-CENTRAL FLORIDA, MAY 2011

By A.G. Ortiz

Base from Southwest Florida Water Management District digital data, 1992,

State Plane Florida East projection, NAD83Copies of this map can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, Colorodo 80225-0286

Figure 1. Change in potentiometric surface of the Upper Floridan aquifer from May 2010 to

May 2011 in west-central Florida. Positive values indicate an increase in water-level altitudes.

Negative values indicate a decrease in water-level altitudes.

EXPLANATION

MUNICIPAL WELL FIELD

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

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

BOUNDARY OF SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

OBSERVATION WELL -- Number is altitude of water level in feet above or below NGVD of 1929.

SPRING

" CITY OR TOWN

OBSERVATION WELL -- Number is altitude of water level in feet above or below NGVD of 1929.

Bold number indicates water levels corrected for salinity.

VERNA

A

20

16

20

EXPLANATION

Change in the potentiometric

surface, in feet

(Positive values indicate an

increase in water-level altitudes)

-5 to -9.99

>0 to 4.99

0 to -4.99

<= -10.00

HYDROLOGIC CONDITIONS IN WEST-CENTRAL FLORIDA

The Floridan aquifer system consists of the Upper and Lower Floridan aquifers separated by the

middle confining unit. The middle confining unit and the Lower Floridan aquifer in west-central

Florida generally contain highly mineralized water. The water-bearing units containing fresh

water are herein referred to as the Upper Floridan aquifer. The Upper Floridan aquifer is the

principal source of water in the Southwest Florida Water Management District and is used for

major public supply, domestic use, irrigation, and brackish water desalination in coastal

communities (Southwest Florida Water Management District, 2000).

This map report shows the potentiometric surface of the Upper Floridan aquifer measured in

May 2011. The potentiometric surface is an imaginary surface connecting points of equal

altitude to which water will rise in tightly-cased wells that tap a confined aquifer system

(Lohman, 1979). This map represents water-level conditions near the end of the dry season,

when groundwater levels usually are at an annual low and withdrawals for agricultural use

typically are high. The cumulative average rainfall of 45.74 inches for west-central Florida (from

June 2010 through May 2011) was 6.85 inches below the historical cumulative average of 52.59

inches (Southwest Florida Water Management District, 2011). Historical cumulative averages

are calculated from regional rainfall summary reports (1915 to most recent complete calendar

year) and are updated monthly by the Southwest Florida Water Management District.

This report, prepared by the U.S. Geological Survey in cooperation with the Southwest Florida

Water Management District, is part of a semi-annual series of Upper Floridan aquifer

potentiometric-surface map reports for west-central Florida. Potentiometric-surface maps have

been prepared for January 1964, May 1969, May 1971, May 1973, May 1974, and for each May

and September from 1975 through 2010. Water-level data are collected in May and September

each year to show the approximate 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 May 23-27, 2011. Supplemental water-level data were collected by other agencies

and companies. Most water-level measurements were made during a 5-day period; therefore,

measurements do not represent a "snapshot" of conditions at a specific time, nor do they

necessarily coincide with the seasonal low water-level condition.

WATER-LEVEL CHANGES

Water levels in about 95 percent of the wells measured in May 2011 were lower than the May

2010 water levels (Ortiz, 2010). Data from 399 wells indicate the May 2011 water levels ranged

from about 12 feet below to about 2.5 feet above the May 2010 water levels (fig. 1). The largest

water level increase occurred in northeast Pinellas County. The largest water level declines

occurred in east-central Hillsborough County and south-central Polk County (fig. 1).

Water levels in about 99 percent of the wells measured in May 2011 were lower than the

September 2010 water levels (Ortiz, 2011). Data from 400 wells indicate the May 2011 water

levels ranged from about 25 feet below to about 0.5 feet above the September 2010 water levels.

The largest water level decline was in west-central Pasco County and the largest rise in water

levels was in east-central Manatee County.

ACKNOWLEDGMENTS

The author thanks Tampa Bay Water and CF Industries for their assistance with the collection

of data used to prepare this report.

SELECTED REFERENCES

Lohman, S. W., 1979, Ground-water hydraulics: U. S. Geological Survey Professional Paper 708,

72 p.

Ortiz, A.G., 2010, Potentiometric surface of the Upper Floridan aquifer, west-central Florida, May

2010: U.S. Geological Survey Scientific Investigations Map 3139, 1 sheet.

Ortiz, A.G., 2011, Potentiometric surface of the Upper Floridan aquifer, west-central Florida,

September 2010: U.S. Geological Survey Scientific Investigations Map 3148, 1 sheet.

Southwest Florida Water Management District, 2000, Aquifer characteristics within the

Southwest Florida Water Management District: Brooksville, FL, 123 p.

Southwest Florida Water Management District, 2011, Hydrologic conditions for the month of

May 2011: Brooksville, FL, 84 p.