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Wendy L. Cohen -4- 5 May 1994 <br /> The extent of chlorinated hydrocarbon contamination in ground water in the vicinity of Site 4 <br /> was not defined during the July 1993 investigation, and PRC did not recommend additional <br /> ground water investigation in this area. It appears that additional ground water investigation at <br /> Site 4, if any, will not be forthcoming in the near future. If such an investigation was to be <br /> conducted in the foreseeable future, we ought to wait until the Navy completes its investigation <br /> before requiring Shell to investigate the extent of the petroleum hydrocarbon plume <br /> west/southwest of Hooper Drive to avoid duplication of efforts. However, since we do not know <br /> when the additional investigation will be conducted, Site 4 is an unlikely source of the <br /> petroleum hydrocarbons being detected in the area south/southwest of Shell and east of Hooper <br /> Drive, and the petroleum hydrocarbon contamination being detected west/southwest of Hooper <br /> Drive is most likely a part of Shell's plume east of Hooper Drive, we should require Shell to <br /> define the extent of the latter petroleum hydrocarbon plume. Shell also should install <br /> monitoring wells on the east side of Hooper Drive where the contamination has clearly been <br /> caused by Shell. In addition, Shell should test the ground water in the new wells for chlorinated <br /> hydrocarbons and pesticides to determine if they contain the chemicals found at Site 4. The <br /> presence of these chemicals in the ground water could affect the performance of Shell's <br /> remediation system. <br /> Summary <br /> 1. The ground water extraction and treatment system needs to be restarted. <br /> 2. The vertical extent of ground water contamination, and the vertical gradient and flow direction <br /> need to be determined. <br /> 3. MWs 24-27 and DW-1 need to be surveyed. <br /> 4. Additional wells are needed in SSA 3 east of Hooper Drive. The ground water in SSA 3 need <br /> to be tested for chlorinated hydrocarbons which could affect the efficiency of the treatment <br /> system. <br /> 5. The Navy's investigation indicates that Site 4 is an unlikely source of.the petroleum hydrocarbon <br /> plume west/southwest of Hooper Drive. Shell should submit a work plan to define the extent of <br /> this plume. <br /> 6. The ground water extraction system should be expanded to capture the entire dissolved plume. <br /> PSI:sjs <br />