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DEER <br /> RESPONSE <br /> As identified by LPL, the proposed Phase III IRA comprising groundwater extraction with B-zone <br /> wells along Pacific Avenue and A- and B-zone wells along Inglewood Avenue, will mitigate the <br /> potential for downgradient migration of hazardous substances in both A- and B-zone groundwater. <br /> Based on our experience with implementation of the Phase I and Phase H IRAs at the Site, the <br /> proposed remedial measures will also be effective in reducing concentrations of hazardous <br /> substances in groundwater. LFR does acknowledge LPL's comments; the text in Sections 1.2 and <br /> 3.3 is hereby modified from "reduce concentrations of PCE in ... groundwater" to the following: <br /> "limit the downgradient migration of Hazardous Substances in groundwater to the extent <br /> practicable, and to reduce concentrations of Hazardous Substances in A- and B-zone <br /> groundwater." <br /> A review of current analytical data indicates that implementation of the two existing IRAs has been <br /> effective in remediating both soil and groundwater beneath the Site. Concentrations of <br /> tetrachlorethylene(PCE), as well as other VOCs, detected in soil-vapor samples collected from <br /> soil-vapor extraction wells and monitoring wells located within the vicinity of the former source <br /> area have significantly decreased, as a result of implementing the soil vapor extraction and <br /> treatment system (SVETS). As such, the data suggests that any dense nonaqueous phase liquid <br /> (DNAPL) that may have been formerly present in the former source area has likely been removed <br /> or significantly reduced as a result of the operation of the SVETS. However, the presence of <br /> DNAPL, if any, in this area will be further investigated in the upcoming additional source area <br /> investigation as proposed in our letter, "Proposed Additional Historical Source Area Investigation, <br /> Lincoln Center, Stockton, California," submitted to the RWQCB on May 4, 2001. If DNAPL is <br /> observed during this investigation, additional remedial measures may be implemented to control or <br /> remove the DNAPL. <br /> Current groundwater data indicates that only elevated dissolved concentrations of PCE currently <br /> exist in groundwater at the Site. Additionally, review of groundwater data indicates that the <br /> removal of the PCE from the vadose zone in the former source area by the SVETS has resulted in <br /> significant decreases in the concentration of PCE in underlying groundwater. As expected, the <br /> highest concentrations of PCE in groundwater are no longer located in the historical source area, <br /> but are currently immediately downgradient from the former source area, in groundwater <br /> monitoring and extraction wells located at the Chevron Station on the corner of Ben Holt and <br /> Pacific. It appears that the successful removal of the high concentrations of PCE within the vadose <br /> zone by the SVETS, and the operation of the groundwater extraction and treatment system <br /> (GWETS), have reduced overall concentrations of PCE in groundwater at the Site. <br /> However, elevated concentrations of PCE in B-zone groundwater in the vicinity of Pacific Avenue <br /> and residual concentrations of PCE in A- and B-zone groundwater downgradient from Pacific <br /> Avenue still exist. Hence, the Phase III IRA, comprised of the expanding of the Phase I B-zone <br /> GWETS along Pacific Avenue and the addition of downgradient A- and B-zone groundwater <br /> MAA REVISIONS-rsp-PheseIII-IRA-06752:DEE 2 <br />