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Geological Tecluucs lfu Page 3 Groundwater Monitoring Report Project No 662 2 November 30,2001 13 Laboratory Analyses tThe groundwater samples collected on October 12, 2001 were delivered to California Laboratory Services of Rancho Cordova, California (Department of Health Services ' Certification No 1233), for the following analyses • Benzene, Toluene, Ethyl Benzene, and Xylene(BTEX) by EPA method 602 ' • Total Petroleum Hydrocarbons as Gasoline (TPH-G)by EPA method 503018015(M) • MTBE, DIPE, ETBE, TAME and TBA by EPA method 8260 ' The detection limits for the above analyses are listed in Table 2 of Appendix A while the lab analytical results are presented in Appendix B 2.0 FINDINGS AND DISCUSSION tThe results of the groundwater sample analysis show the following • Well MW-1 contained gasoline oxygenates MTBE and TBA at 1800 gg/1 and 520 µg11, respectively • Well MW-3 contained gasoline oxygenates MTBE and TBA at 1500 and 940 µg11, ' respectively • MW-2, which is upgradtent of the former USTs, has not contained contaminant concentrations above the laboratory for all eight quarterly events completed thus far in ' the investigation • Neither BTEX nor TPH-G was present in any of the groundwater samples above the laboratory reporting limits ' • Oxidation.-Reduction Potential measurements (Table 3) show that the values for all three wells are positive, suggesting that there is a limited amount of biodegradation of the contaminant plume occurring This is to be expected, since the primary contaminant is ' MTBE, which is very resistant to biodegradation ' The lateral extent of the groundwater contamination plume is only defined upgradient to the northwest by MW-2 The vertical extent has not been defined ' GTI makes the following recommendations • Perform plume definition and evaluate the mass of contaminants present by installing additional monitoring wells GTI has submitted to the SJC PHSIEHD a "Soil & Groundwater Investigation Work Plan" dated October 8, 2001 The work plan was approved with conditions in the SJC PHS/EHD's October 26, 2001 correspondence The work plan will be implemented pending cost pre-approval from the USTCFP