SITE INFORMATION AND CORRESPONDENCE FILE 1

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CLEARWA" TE G R O U P, 1 N C. £nvi rnn mentnl Services 0.04 feet in MW-3 to 0.24 feet in MW-2. Drawdown in the majority of the observation wells had stabilized after approximately 10 hours of pumping. Water table elevations at the end of the test.are presented on—Figure-9 Pumping and observation well drawdown data are presented in Appendix D. The specific capacity of a well is defined as drawdown per flowrate. This can be approximated by dividing the pumping rate by the total drawdown in the pumping well, assuming that well loss created by turbulent flow through the well screen is negligible (Freeze and Cherry, 1979). Using the drawdown and flowrate mentioned above, the specific capacity of RW-1 is calculated as 1.24 feet/gpm. This is useful in predicting drawdown in the recovery well at various pumping rates. The Cooper-Jacob (1946) analytical method was used to determine hydraulic { properties underlying the site. The Cooper-Jacob method uses observation well drawdown data versus time to calculate transmissivity (T) (see Freeze and Cheery, 1979 for a summary of the 'method). Transmissivities were calculated using drawdown data from observation wells MW=2, MW-4, MW-5, MW-6, and MW-7. The mean transmissivity calculated from the five observation wells is 17,083 g al/day/ft with a standard deviation of 2,905 gal/day/ft. A summary of calculated aquifer parameters is presented on Table 3. Pumping well and observation well drawdown curves and tranty Appendix calculations are included in pp endix D. Hydraulic conductivity (K) can be calculated by dividing transmissivity by aquifer thickness for unconfined aquifers. Although exact thickness of the shallow water bearing zone is unknown, a thickness of 15 feet is a conservative estimate assuming the shallow water bearing zone is slightly,thicker than the approximately 10 feet of saturated' columns in the monitoring wells. Assuming this aquifer thickness, the 4 mean hydraulic conductivity for the site is 1,139 gal/day/ft2 (equivalent to 6.3 darcies for soil air permeability). This value correlates well with known hydraulic I4 conductivities for .sandy silts. and silty sands, the predominant sediment type E underlying the site (Freeze and Cherry, 1979). Groundwater extraction has. typically been .used to control plume migration and recover SPH. The potentiat for this can be assessed by calculating the zone of capture for the pumping well. Keely and Tsang (1983) developed an equation to quickly calculate the zone of capture from a well for given values of flowrate, transmissivity, and hydraulic gradient. Using the mean transmissivity presented above; a hydraulic gradient of 0.0015, and the flowrate of 5 gprn (nearly the ' maximum flow possible from RW-1 before dewatering), the downgradient stagnation point from RW-1 is approximately 50 feet, and the cross gradient capture point is approximately 150 feet (Figure 9). Pumping solely from RW-1 .at its i4 maximum capacity (5 gprn) will not entirely capture the dissolved plume and, most l� importantly, the SPH in MW-1. I D-107,PAR/RAP 10 June 11,1996