Estimation of hydraulic characteristics of the upper glacial and Magothy aquifers at East Meadow, New York, by use of aquifer tests

Abstract

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.

Distribution of selected hydrogeologic characteristics of the upper glacial and Magothy aquifers, Long Island, New York

“…These were included in the analysis by identifying intervals of coarse-and fine-grained sediments from the geophysical logs (both natural gamma and electromagnetic logs); intervals of coarse-grained sediments were assumed to be medium sand, and intervals of finegrained sediments were assumed to be silt. Categorial classifications of the lithologic descriptions (table 1) were assigned estimated values of horizontal and vertical hydraulic conductivity based on published values for the Long Island aquifer system (McClymonds and Franke, 1972;Franke and Getzen, 1976;Lindner and Reilly, 1983;Prince and Schneider, 1987;Smolensky and others, 1989;Cartwright, 1996;Misut and Busciolano, 2010) and similar hydrogeologic environments on the coastal plain of Massachusetts (Guswa and Londquist, 1976;Guswa and LeBlanc, 1985;LeBlanc and others, 1986;Barlow, 1989;Barlow and Hess, 1993;Moench and others, 1996;Walter and others, 1996;Masterson and Barlow, 1997;Masterson and others, 1997).…”

Aquifer transmissivity in Nassau, Queens, and Kings Counties, New York, estimated from specific-capacity tests at production wells

“…Storage coefficients for the aquifers at the productionwell test sites were not known but were approximated based on published values from Lindner and Reilly (1982), Prince and Schneider (1989), Cartwright (1997), and Misut and Busciolano (2009). Storage values used in the present analysis were as follows: 0.15 for wells screened within 200 ft of the water table in the unconfined upper glacial and Magothy aquifers; 0.003 for wells screened 200 ft below the water table in the semiconfined upper glacial and Magothy aquifers; and 2×10 −5 for the confined Jameco, Magothy, and Lloyd aquifers.…”

“…McClymonds and Franke (1972) also published statistical summaries and contoured maps of transmissivity and hydraulic conductivity of the aquifers based on an analysis of specific capacities, screen lengths, and lithologic logs from production-well completion reports. Lindner and Reilly (1982), Aronson and others (1983), Prince and Schneider (1989), and Cartwright (1997) used numerical radial-flow models, and Misut and Busciolano (2009) used analytical models to estimate hydraulic properties at selected aquifer-test sites on Long Island. Estimates of aquifer hydraulic properties from these previous studies associated with specific well sites are available from the USGS National Water Information System database (NWIS; U.S. Geological Survey, 2020a) and can be viewed through the Aquifer Test Locator graphical user interface (U.S. Geological Survey, 2020b).…”