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i <br /> d ' <br /> 715 Hunter, Stockton <br /> April 24, 2006 <br /> Page 2 <br /> EHD concurs with report's conclusion that the increasing concentrations of <br /> dissolved contaminants may indicate that the contaminant mass in the vadose <br /> zone is likely continuing to leach into groundwater. The DPE soil sample <br /> results indicate a significant mass likely remains in the vadose zone and the <br /> capillary fringe. Based on the influent vapor sample results from the DPE <br /> pilot test and the inferred contaminant mass still in the vadose and capillary <br /> fringe zones at this site, the sorbed contaminant appears to be susceptible to <br /> soil vapor extraction. EHD recommends interim remediation be implemented <br /> immediately to mitigate further degradation of groundwater, and more <br /> importantly, to address contaminants while still in the vadose zone, when <br /> remediation is usually most effective, both in cost and total mass removal. <br /> Further delay may allow contaminants the time to dissolve into groundwater, <br /> and thereby increasing the overall cost and difficulty of cleanup . EHD directs <br /> that the DPE report be submitted to this office by May 15, 2006; for <br /> expedience, please include an interim remediation workplan. <br /> If you have any questions, please contact Jeffrey Wong at (209) 468-0335 . <br /> Donna Heran, REHS, Director <br /> Environmental Health Department <br /> Aeffteyong , Senior REHS <br /> ongNuel C. Henderson, Jr., PG <br /> LOP/Site Mitigation Unit N LOP/Site Mitigation Unit IV <br /> c: RWQCB, Central Valley Region — James L. L. Barton, PG <br /> c: Advanced GeoEnvironmental, Inc. (AGE) — Tim Cuellar <br />'i <br /> a <br /> i <br /> I <br />