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11C\vVr , 16 A S S O C I A T E S I N C method 8015 modified, and benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA method 8020 Groundwater well purge and sample logs are contained in Appendix A 2.2 Analytical Results The groundwater sample collected from well MW2 contained detectable concentrations of TPHg, TPHd, toluene, ethylbenzene, and xylenes The TPHg concentration was 3,400 parts per billion (ppb), the TPHd concentration was 1,200 ppb, and toluene, ethylbenzene, and xylenes concentrations ranged from 3 4 to 560 ppb The groundwater samples collected from wells MW 1, MW4, and MW5 contained TPHd at concentrations of 210 ppb, 160 ppb, and 79 ppb, respectively The groundwater samples from wells MW 1, MW4, and MW5 did not contain detectable concentrations of TPHg or BTEX The groundwater sample from well MW3 did not contain detectable concentrations of TPHg, TPHd, or BTEX Analytical results of groundwater samples are summarized in Table 2 and laboratory data sheets are contained in Appendix B 1 2.3 Groundwater Flow Direction Water level measurements were collected from wells MW1 through MW5 on December 10, 1999 Water levels ranged from 20 89 to 21 81 feet below the tops of the well casing elevations, representing an average decrease in the water table elevation of approximately 0 24 feet since rSeptember 1999 The water level data were used to develop the groundwater elevation contour map (Figure 3) Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed towards the southwest The average hydraulic gradient on December 10, 1999 was calculated to be 0 0004 ft/ft or approximately 2 ft/mile A summary of groundwater monitoring data is presented in Table 1 3.0 PUMPING TEST METHODS AND PROCEDURES A groundwater pumping test was proposed in ATC's Workplan for Pumping Test and Remedial Investigation Feasibility Study at 304 North Acacia Avenue, Ripon, California, dated September 20, 1999 The goals of the groundwater pumping test were to provide aquifer data necessary to ' characterize the feasibility of operating a groundwater treatment system at the site by providing the following parameters • Radius of influence of groundwater extraction, • Groundwater drawdown, • Hydrogeologic properties of the aquifer, • Mass extraction rate of groundwater • w I130991reportslsumweli doe 3