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feet (Figures 5 and b) Groundwater occurs at a depth of about 28-30 feet, an elevation of 20-22 feet below mean sea level, and flows northeast (Figure 7) at an average gradient of 0 008, about 40 feet per mile Groundwater occurs in the lenses of silty-to-coarse-grained sand extending from approximately 30 to 40 feet below ground surface, the sands are underlain by silty/clayey sediments to the explored depth of 50 feet Groundwater elevations in the investigated area have continued to drop P (more than three feet ' since December 1989) as a result of the drought of the past four years The results of well gauging are presented in Table 1 The values of transmissivity for the aquifer estimated from bailing, pumping, and injection tests conducted at the site range from 140 to 400 ft2/day The average transmissivity is about 200 fO/day (determined from pumping and injection tests) and is equivalent to a hydraulic conductiv- ity of about 10 ft/day (3 05 m/day) This is characteristic of silty sands (Freeze and Cherry 1979) tThe highest expected velocity is calculated with Darcy's equation V = KI/n where ' K= hydraulic conductivity (10 ft/day) I = average hydraulic gradient under the site (0.008) n = effective porosity of the aquifer (0 2 for silty sand) MUsing these values, the velocity (V) of groundwater flowing beneath former RS 7-3942 is esti- mated to be 0 4 ft/day, about 150 ft/year. Based on pumping test data, each of the recovery wells can be pumped continuous) at a rate of P P g rY P P Y about 3 gpm, creating about 10 feet of drawdown in each well These rates of pumping and drawdown should result in the water table dropping 5-8 feet in the area between wells with a capture zone extending about 150 feet off the site in a downgradient direction (Figure 8) Treat- ed groundwater can be reinjected upgradient into three injection wells, interrupting the effective radius of influence in this area and preventing any upgradient plume from infiltrating further toward the site The injection of 5 gpm into each of these wells (IW1, MW4, MW7) located as ' shown in Figure 4, would create an estimated 4-foot high mound in groundwater between injec- tion wells r cWw-739I�a19Vm 3