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US Department of the Interior
US Geological Survey
WRI 90-4108

Hydrogeology of the Surficial Aquifer System, Dade County, Florida

Water-Resources Investigations Report 90-4108

By Johnnie E. Fish and Mark Stewart

Prepared in cooperation with the South Florida Water Management District

Abstract

>Abstract
Introduction
Study Area
Aq. Framework and Definitions
Estimates of Transmissivity and Hydraulic Conductivity
Hydrogeology
Ground-Water Flow System
Summary and Conclusions
References Cited
Plates
PDF Version
An investigation of the surficial aquifer system in Dade County, begun in 1983, is part of a regional study of the aquifer system in southeastern Florida. Test drilling for lithologic samples, flow measurements during drilling, aquifer testing, and analyses of earlier data permitted delineation of the hydraulic conductivity distribution (on hydrogeologic sections), the aquifers in the system, the generalized transmissivity distribution, and interpretation of the ground-water flow system.

The surficial aquifer system, in which an unconfined ground-water flow system exists, is composed of the sediments from land surface downward to the top of a regionally extensive zone of sediments of low permeability called the intermediate confining unit. The aquifer system units, which vary in composition from clay-size sediments to cavernous limestone, are hydro stratigraphically divided into the Biscayne aquifer at the top; an intervening semiconfining unit that consists principally of clayey sand; a predominantly gray limestone aquifer in the Tamiami Formation in western and west-central Dade County; and sand or clayey sand near the base of the surficial aquifer system. The base of the surficial aquifer system ranges from a depth of about 175 to 210 feet below land surface in westernmost Dade County to greater than 270 feet in northeastern Dade County. Test drilling and aquifer-test data indicate a complex hydraulic conductivity distribution. Hydraulic conductivities of the very highly permeable zone of the Biscayne aquifer commonly exceed 10,000 feet per day; in the gray limestone aquifer, they range from 210 to 780 feet per day.

Transmissivities of the surficial aquifer system vary locally but have a recognizable areal trend. Estimated values generally are about 300,000 feet squared per day or greater in nearly all of central and eastern Dade County. Transmissivity is lower to the west, decreasing to less than 75,000 feet squared per day in western Dade County. High transmissivity usually is associated with thick sections of the Fort Thompson Formation within the Biscayne aquifer. The gray limestone aquifer of the Tamiami Formation has transmissivities that range from 5,800 to 39,000 feet squared per day in western Dade County. The transition from high transmissivity to relatively low transmissivity is often only a few miles wide and coincides with the decrease in thickness of the very highly permeable Fort Thompson Formation, which marks the western boundary of the Biscayne aquifer.

More effective drainage as a result of extensive canal systems and large-scale pumping from municipal well fields has greatly altered the predevelopment flow system in eastern Dade County by: (1) eliminating or greatly reducing a seasonal and coastal ground-water ridge; (2) reducing deep circulation; (3) reducing or eliminating seasonal westward movement of ground water; (4) causing accelerated stormwater runoff and short ground-water flow paths; and (5) generally lowering the water table and inducing saltwater intrusion. Under predevelopment conditions in western Dade County, water entered the gray limestone aquifer by lateral movement from Broward and Collier Counties, and by downward seepage from The Everglades and the Biscayne aquifer, and moved southward and southeastward into Dade County to coastal discharge areas. Circulation in the Biscayne aquifer inland also was primarily to the south and southeast. In eastern Dade County, the seasonal ground-water ridge that formed under predevelopment conditions supported both easterly and westerly ground-water flow away from the ridge axis. This seasonal flow created a zone of lower dissolved solids.

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Conversion Factors, Vertical Datum, and Abbreviated Water-Quality Units

Multiply By To obtain
inch 25.4 millimeter
foot 0.3048 meter
foot per day 0.3048 meter per day
foot per mile 0.1894 meter per kilometer
foot squared per day 0.0929 meter squared per day
mile 1.609 kilometer
square mile 2.590 square kilometer
gallon per minute 0.00006309 cubic meter per second
gallon per minute per foot 0.2070 liter per second per meter
million gallons per day 0.04381 cubic meters per second


Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 -- a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Abbreviated water-quality units used in report:

µs/cm microsiemens per centimeter
mg/L milligrams per liter


For additional information write to:

District Chief
U.S. Geological Survey
Suite 3015
227 N. Bronough Street
Tallahassee, Florida 32301

Copies of this report can be purchased from:

U.S. Geological Survey
Branch of Information Services
Box 25286
Federal Center
Denver, CO 80225


The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.


Related links:

Hydrogeology, Aquifer Characteristics, and Ground-Water Flow of the Surficial Aquifer System, Broward County, Florida (Water Resources Investigations Report 87-4034)



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