Computation of leakance of the middle semiconfining unit, Floridan Aquifer system, Berwick Plantation, Chatham County, Georgia
Faye, Robert E.
Gill, Harold E.
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Changes in tidal cycle amplitude observed in the Upper Floridan Aquifer during a 72-hour test of the Lower Floridan Aquifer at Berwick Plantation, Chatham County, Georgia were used in conjunction with a ground-water flow model to estimate leakance of the Middle Semiconfiining Unit, between the aquifers. Test discharge was continuous at 718 gallons per minute. Observed water levels in the Upper Floridan Aquifer were influenced by regional pumping and a test-specific drawdown was not obvious. Accordingly, maximum drawdown in the Upper Floridan Aquifer caused by test pumping was estimated by comparing tidal cycle amplitudes prior to and during the test. Maximum amplitude change was about 0.2 feet and was considered the maximum drawdown in the Upper Floridan Aquifer caused by test pumping. This drawdown and site specific hydraulic characteristics of the Upper and Lower Floridan Aquifers were applied to a ground-water flow model to simulate aquifer-test results and estimate Middle Semiconfining Unit leakance. Computed leakance was 5x10-8 per minute.