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Hydrogeology and results of tracer tests at the old Tampa well field in Hillsborough County, with implications for wellhead-protection strategies in west-central Florida

Water-Resources Investigations Report 93-4171

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Abstract

Wellhead-protection strategies were evaluated for the Upper Floridan aquifer of west-central Florida using the old Tampa well field in northeastern Hillsborough County, Florida, as a test site. The upper 400 feet of the Upper Floridan aquifer responded to pumping as an equivalent, porous medium for a range of discharge rates from 450 to 1,000 gallons per minute. Transmissivity and storage coefficient values determined for the Upper Floridan aquifer were 23,000 feet squared per day and 0.0001, respectively. Rock cores from the Upper Floridan aquifer have effective porosity values from 21 to 46 percent. Tracer tests were conducted using a fluorescent dye. A bimodal distribution of tracer arrival times indicates ground-water flow through a dual porosity system. Analysis of tracer test results an effective porosity of 25 percent and a longitudinal dispersivity of 1.3 feet for the aquifer matrix. A numerical aquifer-simulation equivalent porous media model of the Upper Floridan aquifer was calibrated using results of aquifer tests. A particle-tracking program was used to simulate the matrix flow groundwater travel time measured with the fluorescent dye tracer test. An evaluation of wellhead-protection strategies was conducted using the particle-tracking program to simulate areas of contribution from the aquifer matrix. The results of this study demonstrate the heterogeneity of the Upper Floridan aquifer. Because of this heterogeneity, the use of uniform porosity models to delineate time-related areas of wellhead protection in the karst Upper Floridan aquifer is inappropriate; however, ground-water movement in the aquifer matrix can be simulated with uniform porosity models.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Hydrogeology and results of tracer tests at the old Tampa well field in Hillsborough County, with implications for wellhead-protection strategies in west-central Florida
Series title:
Water-Resources Investigations Report
Series number:
93-4171
Edition:
-
Year Published:
1995
Language:
ENGLISH
Publisher:
U.S. Dept. of the Interior, U.S. Geological Survey ; Earth Science Information Center, Open-File Reports Section [distributor],
Description:
vi, 63 p. :ill., maps ;28 cm.