EFFECT OF SCALING ON HYDRAULIC CONDUCTIVITY IN A KARST AQUIFER

Karst aquifers are known for variability within their properties. The intent of this study is to determine and quantify the effect, if any, of scaling on hydraulic conductivity in a karst aquifer. Testing will be done on three formations in the Biscayne Aquifer of South Florida, a highly transmissive, unconfined, karst aquifer. The Biscayne Aquifer is the sole source aquifer for the Miami area and is the dominant aquifer underlying the Everglades. Understanding it’s properties is imperative to maintaining the water supply for Miami and to the Everglades Restoration effort. Models generated for these efforts will benefit from accurate hydraulic conductivity values.

Scales to be used are 20 cm and 30 cm cubes, slug tests, and possibly a tracer injection test. Slug tests have been conducted in nine 2-inch wells in the Miami Oolite Formation of the Biscayne Aquifer at the Homestead General Airport (HGA). During the tests head level measurements were taken every .02 seconds. This brief time interval insured collecting the maximum and minimum values of the rapidly oscillating head levels. Data points were normalized, plotted, and matched to curves, using the Butler spreadsheets for high hydraulic conductivity aquifers to determine hydraulic conductivity (Butler and Garnett 2000). Hydraulic conductivity values for wells tested at the HGA ranged from 341 ft/d to 661 ft/d with a mean of 541.8 ± 83 ft/d. These values fall within the range of hydraulic conductivity values of 100 ft/d to >1000 ft/d for Miami Oolite with apparent solution holes reported by Fish and Stewart (1991).

Hydraulic conductivity testing of the 20 cm and 30 cm cubes in a permeameter is in progress. Results will be compared for differences amongst different sized cubes, amongst cube and slug test results, and amongst formations. These results will provide water managers with an understanding of the variations of hydraulic conductivity within the Biscayne Aquifer. The results of this study will also provide an assessment of the effect of scaling on hydraulic conductivity of a karst aquifer.