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Mr. Maurice Benson <br /> May 29, 2009 <br /> Page 2 <br /> o MW537 Cluster—West of P-5A Source Area <br /> • Evaluate TCE concentrations in transition between B, C and <br /> C/D-zones in flow-path area between extraction wells (EW) <br /> EWCC1 and EWCC3; <br /> ■ Monitor plume stability including water level and gradient data in <br /> areas between EWCC1 and EWCC3; <br /> • Improve groundwater model fate and transport predictions with <br /> monitoring well's hydraulic and chemical data. <br /> o MW538 Cluster— Southwest of EWC4 in Woodbridge Estates <br /> • Guard well for TCE, tetrachloroethene and carbon tetrachloride <br /> commingled plume migration from DDJC-Sharpe westward in B, C <br /> and C/D-zones; <br /> • Provide water level and chemical data to assist in groundwater <br /> model fate and transport predictions; <br /> • Provide better understanding of hydraulic gradients between <br /> operating extraction wells EWC4 and EWA5. <br /> DTSC has reviewed the work plan and has the following comments: <br /> Comment <br /> 1. Page 4, Table 2-1, Soil Sampling Matrix: DTSC notes that no VOC analyses <br /> are proposed for soil samples at MW537CD below the depth of 60 feet below <br /> ground surface (bgs). DTSC recommends that one additional VOC analysis <br /> is performed on the "fines" sample location at 125' bgs to be consistent with <br /> the EWCC3 screen depth interval (128'-138' bgs), VOC mass and likely <br /> contaminant flow paths. <br /> Conclusion <br /> DTSC concurs with the proposed fieldwork efforts of installing three offsite groundwater <br /> monitoring wells to better define the offsite contaminant plumes, provide guard well <br /> notification and analyze chemical and groundwater level data to assist groundwater <br /> model fate and transport predictions. DTSC recommends adding one additional VOC <br /> soil analyses for the "fines" sample at the MW537CD boring to provide a more <br /> representative soil sample reflecting the most likely contaminant pathway for VOC mass <br /> traveling to EWCC3 for extraction/remediation. <br />