Aquifer Characterization at the Veterans Administration Hospital, Tuscaloosa, Alabama.

摘要

The Veterans Administration (VA) is studying the feasibility of aquifer thermal storage (ATES) at their Tuscaloosa, Alabama, facility. To determine the characteristics of the aquifer underlying the facility, the Pacific Northwest Laboratory gathered information about the environment of the aquifer and conducted tests to estimate the aquifer's transmissivity, ground-water flow direction, and velocity. Seven wells were drilled at the VA site. It was found that ground-water flow direction at the site is generally toward the southwest. The magnitude of the gradient is approximately 2.5 (times) 10(sup -3) to 3 (times) 10(sup -3) ft/ft. For six of the seven wells, clay lenses or thick clay layers appear to be acting locally as confining or semi-confining layers. Three types of test were conducted at the site: a step drawdown test, a constant discharge and recover test, and a single-well tracer test. The data yielded responses suggesting leaky confined or delayed yield models for the aquifer. Drawdown and recovery versus time were matched type curves for delayed yield to obtain estimates of transmissivity and storage. This recovery method gave the best fit to the drawdown-versus-time curves. Using this method it was found that transmissivity ranged from 500 to 9000 ft(sup 2)/day and storage ranged from 1.5 (times) 10(sup -4) to 4.5 (times) 10(sup -2) for the wells tested. Using the results of the pump and tracer tests simultaneously, ground-water velocity was estimated to be approximately 0.8 ft/day, with an effective porosity of approximately 12%. 4 refs., 7 figs., 3 tabs.