Title: U. S. Geological Survey, Water Resources Investigation
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Permanent Link: http://ufdc.ufl.edu/UF00052830/00001
 Material Information
Title: U. S. Geological Survey, Water Resources Investigation
Alternate Title: Mills, L. R. and Ryder, P. D. Saltwater Intrusion in the Floridan Aquifer, Coastal Citrus and Hernando Counties, Florida, 1975., U. S. Geological Survey, Water Resources Investigation No. 77-100. 1977. Text and map. 30 x 26.5 in.
Physical Description: Book
Language: English
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
General Note: Box 5, Folder 19 ( SF SALT WATER INTRUSION-FLORIDA, PINELLAS AND INTERBAY PENINSULA ), Item 1
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
 Record Information
Bibliographic ID: UF00052830
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Full Text




DEPARTMENT OF THE INTERIOR
UNITED STATES GEOLOGICAL SURVEY







SALTWATER INTRUSION

IN THE FLORIDAN AQUIFER,

COASTAL CITRUS AND HERNANDO COUNTIES,

FLORIDA, 1975

By
L. R. Mills and P. D. Ryder

Prepared by
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

TALLAHASSEE, FLORIDA
1977



INTRODUCTION
The coastal parts of Citrus and Hernando Counties--
particularly Citrus County-are undergoing extensive ur-
ban development along U.S. Highway 19 (fig. 1). The
Floridan aquifer, a thick sequence of limestone and dolo-
mite, is the principal source of water supply for the coastal
parts of these two counties. The construction of canals that
penetrate the Floridan aquifer, deficient rainfall during
1964-75, and pumping of ground water, have caused salt-
water to intrude the aquifer. The purpose of this report is
to show the inland extent of that intrusion as of 1975. The
report is based on field data collected in 1964, 1973, and
1975. Field data were collected and the report was pre-
pared in cooperation with the Southwest Florida Water
Management District. Tables 1 and 2 constitute a sum-
mary of data collected.
GEOHYDROLOGY
The Floridan aquifer consists of a thick sequence of
limestone and dolomite of Eocene age that dips about 1
ft/mi southwestward in the study area. Along the coast and
along the lower reaches of the Crystal, Homosassa, and
Chassahowitzka Rivers the Floridan aquifer is unconfined.
In the remainder of the coastal zone the aquifer is confined
by overlying unconsolidated deposits. The top of the Flori-
dan aquifer is near or below mean sea level in this coastal
area. For a more detailed discussion of the geology of the
area see Vernon (1951). In general, the Floridan aquifer is
recharged by rainfall which is stored in surficial sands and
lakes and which then infiltrates to the underlying Floridan
aquifer. The major recharge areas are in the interior of the
Florida Peninsula and the general pattern of ground-water
S...... ..... flow is from anterior toward the coastline. -
The potentiometric contours on the map indicate the
direction in which water moves in the Floridan aquifer in
this area; water moves from areas of high potential to
areas of low potential and the general direction of flow is
perpendicular to the contour lines. The pronounced inland
curvature of the potentiometric contours on the upper half
of the map are the result of large amounts of ground water
discharging from the Floridan aquifer to springs in the
Homosassa and Crystal Rivers. In addition, the Floridan
aquifer not only discharges water to other large springs in
the coastal zone, but also by upward leakage through the
sea floor. This discharge from the Floridan varies in quan-
tity with the season and with the locations of the areas of
leakage along the coast.
SALTWATER INTRUSION
In November 1964, water samples were collected from
141 wells in the coastal parts of Citrus and Hernando
Counties and were analyzed for chloride concentration. In
December 1975, 42 of the 141 wells were resampled. Dur-
ing the 11-year period, the concentration of chloride in-
creased in water from 22 wells, decreased in water from 7,
Iranw] tit nt ihanorro in 1 Tn 1 fi ant ncrnin in 1071 water





















1964-75, and pumping of ground water, have caused salt-
water to intrude the aquifer. The purpose of this report is
to show the inland extent of that intrusion as of 1975. The
report is based on field data collected in 1964, 1973, and
1975. Field data were collected and the report was pre-
pared in cooperation with the Southwest Florida Water
Management District. Tables 1 and 2 constitute a sum-
mary of data collected.

GEOHYDROLOGY
The Floridan aquifer consists of a thick sequence of
limestone and dolomite of Eocene age that dips about 1
ft/mi southwestward in the study area. Along the coast and
along the lower reaches of the Crystal, Homosassa, and
Chassahowitzka Rivers the Floridan aquifer is unconfined.
In the remainder of the coastal zone the aquifer is confined
by overlying unconsolidated deposits. The top of the Flori-
dan aquifer is near or below mean sea level in this coastal
area. For a more detailed discussion of the geology of the
area see Vernon (1951). In general, the Floridan aquifer is
recharged by rainfall which is stored in surficial sands and
lakes and which then infiltrates to the underlying Floridan
aquifer. The major recharge areas are in the interior of the
SFlorida Penisulanad the general patten of gfe d-water
flow is from tite oward e io-iWine. .
The potentiometric contours on the map indicate the
direction in which water moves in the Floridan aquifer in
this area; water moves from areas of high potential to
areas of low potential and the general direction of flow is
perpendicular to the contour lines. The pronounced inland
curvature of the potentiometric contours on the upper half
of the map are the result of large amounts of ground water
discharging from the Floridan aquifer to springs in the
Homosassa and Crystal Rivers. In addition, the Floridan
aquifer not only discharges water to other large springs in
the coastal zone, but also by upward leakage through the
sea floor. This discharge from the Floridan varies in quan-
tity with the season and with the locations of the areas of
leakage along the coast.

SALTWATER INTRUSION
In November 1964, water samples were collected from
141 wells in the coastal parts of Citrus and Hernando
Counties and were analyzed for chloride concentration. In
December 1975, 42 of the 141 wells were resampled. Dur-
ing the 11-year period, the concentration of chloride in-
creased in water from 22 wells, decreased in water from 7,
and did not change in 13. In 1964, and again in 1973, water
samples were collected from 32 surface-water sites for
chloride analysis. Over the 9-year period, chloride concen-
tration increased in 21 samples, decreased in 6, and re-
mained the same in 5. The 1973 sampling included three
sites not sampled in 1964. The three sites were resampled
in 1975 with no resulting change in chloride concentration.
To determine the inland extent of saltwater intrusion
"shown on figure 1, analyses were made for the 42 wells
mentioned above, and an additional 26 random samples
from wells (68 in all). The boundary between freshwater
and saltwater was arbitrarily drawn on the basis of a
Chloride concentration of 250 mg/L in ground water at a
depth of 100 ft below sea level. For the area of the Cross-
Florida Barge Canal and the lower Withlacoochee River,
data available from previous studies (Bush, 1973, and
Faulkner, 1973) were plotted on figure 1. However, all the
wells except wells 71 and 78 were less than 100 ft deep and
yielded water with low chloride concentrations. Therefore,
the 250 mg/L isochlor was estimated and appears as a
Dashed line. (See also figure 2 which shows a geohydrologic
section across the saltwater-freshwater interface.) Figure 1
shows that saltwater intrusion extends farther inland in
Citrus County than in Hernando County. This intrusion is
related to a direct recharge of saltwater to the Floridan
aquifer along canals and rivers during periods of reduced
freshwater runoff and of large ground-water withdrawals
for the heavily urbanized coastal area of Citrus County.

SELECTED REFERENCES
Bush, P. W.
1973 Saltwater movement in the lower Withlacoochee
River-Cross-Florida Barge Canal complex: U.S.
Geol. Survey Water-Resources Inv. 5-72, 32 p.
Cherry, R. N., Stewart, J. W., and Mann, J. A.
1970 General hydrology of the middle Gulf area, Flor-
ida: Florida Dept. Nat. Resources, Bur. Geology,
Rept. Inv. 56, 96 p.
Faulkner, G. L.
1973 Ground-water conditions in the lower Withlacoo-
chee River-Cross-Florida Barge Canal complex
area: U.S. Geol. Survey Water-Resources Inv.
4-72, 31 p.
Reichenbaugh, R. C.
1972 Seawater intrusion in the upper part of the Flori-
dan aquifer in coastal Pasco County. Florida





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