Graduation Year

1985

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Department

Geology

Degree Granting Department

Geology

Major Professor

Mark T. Stewart

Abstract

An integrated geologic, hydrologic, and geophysical investigation was conducted to determine the effect of a storm-water retention pond on the Floridan aquifer. Surface DC resistivity surveys were used to delineate the hydrostratigraphy. There are four distinct geoelectric layers: (1) Layer 1, high resistivity, 3 meters thick, fine to very fine unsaturated sand; (2) Layer 2, moderate resistivity, 1 to 2.5 meters thick, saturated sands and silts; (3) Layer 3, lower resistivity, 4 to 10 meters thick, silt and clay; (4) Layer 4, moderate resistivity, argillaceous limestone. Two fracture zones are defined by resistivity lows and marked by deep, V-shaped depressions in the limestone which formed through solution.

Vertical hydraulic conductivities were combined with head differences between the water table and the Floridan aquifers to determine recharge per unit area to the Floridan at each well. The recharge per unit area at each well was weighted according to the percentage of the total area represented by the well to obtain average recharge per unit area.

A year-long hydrologic budget for the retention pond shows the change in storage to be zero. Surface runoff and precipitation provide 1460 m3 per day to the pond; evaporation accounts for 282 m3/day. The remainder (1178 m3/day) recharges the surficial aquifer. A represen- tative volume with an area twice that of the pond was chosen to eval- uate the effect of the retention pond on ground water quality. Multi- plying the average recharge rate by this area gives 212 m3/day. Under-

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