Drawdown and recovery data from two aquifer tests conducted in central Nassau County were used to calculate aquifer characteristics by six methods to aid in predicting the response of the aquifer sysstem to stress. The first test, on May 12, 1978, entailed pumping the Magothy aquifer for 12 hours; the second, on July 30-31, 1985, entailed pumping the upper glacial aquifer for 24 hours. Drawdown and recovery data from both tests were analyzed by three analytical solutions and two curve-matching procedures, and the resulting hydraulic values were used as initial values in a finite-element radial-flow numerical model to simulate the observed drawdowns and recoveries. Storativity values obtained by all methods were consistent with published estimates, but hydraulic-conductivity values were higher than published estimates. The simple analytical solutions and curve-matching procedures gave reasonable values of most terms quickly, but the estimates made with the finite-element model have the greatest confidence level. This is because the model can represent the aquifer geometry and field conditions of the aquifer tests more accurately than the analytical procedures. These estimates for the Magothy aquifer were: horizontal hydraulic conductivity, 100 feet per day; ratio of horizontal to vertical hydraulic conductivity, 5; and specific storage, 1.0 x 10~4. Estimates for the upper glacial aquifer were: horizontal hydraulic conductivity, 380 feet per day; ratio of horizontal to vertical hydraulic conductivity, 2.5; and specific yield, 0.15.
Stiff diagrams showing concentrations of selected ions: A. In composite sample of native ground water from 12 wells tapping the upper glacial aquifer. B. In reclaimed water from the storage tank. C. In well N10069, a shallow well affected by reclaimed water .
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