Hydraulic Properties of the Karstic Upper Floridan Aquifer Near Albany, Georgia

Abstract

A multi-well aquifer test was conducted to determine the hydraulic characteristics of and vertical connection within the Upper Floridan aquifer in the Albany, Ga., area as part of a hydrogeologic investigation being conducted by the U.S. Geological Survey, in cooperation with the Albany Water, Gas, and Light Commission. The test site consisted of a production well and five clusters of observation wells (one deep, intermediate, and shallow well in each cluster). Flow-meter tests conducted in the production well between the depth interval of 110 to 140 feet (ft) below land surface show that the interval between 118 and 124 ft contributes the largest portion of the total yield to the well A 49-hour aquifer test was conducted in February 1995, at a constant rate of 3,300 gallons per minute (gal/min). The maximum drawdown measured in any observation well was about 2.4 ft at a distance of 330 ft from the pumped well Measurable drawdown was not observed at distances greater than about one mile from the pumped well The hydraulic characteristics of the Upper Floridan aquifer were evaluated using the Hantush-Jacob curve-matching and Jacob straight-line methods. Using the Haiatush-Jacob method, values for transmissivity (T) ranged from about 108,000 to 460,000 feet squared per day (ft²/d ), values for storage coefficient (S) ranged from 1.4 x 10⁻⁴ to 6.3 x 10 ⁻⁴, and values for vertical hydraulic bconductivity of the overlying confining unit (K') ranged from 4.9 to 11.4 feet per day (ft/d). Geometric averages for these values of T, S, and K' were calculated to be 211,000 ft²/d, 2.7x 10 ⁻⁴, and 73 ft/d, respectively. If dual porosity (fracture flow plus matrix flow) is assumed instead of leakage, and the Jacob straight-line method is used with late time-drawdown data the calculated T of the fractures ranged from about 222,000 to 462,000 ft²/d and S of the fractures plus the matrix ranged from 2x10⁻⁵ to 3x10⁻².