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PARSONS <br /> Parsons Engineering Science,Inc.•A Unit of Parsons Infrastructure&Technology Group Ina <br /> 2101 Webster Street,Suite 700•Oakland,California 94612•(510)891-9085•Fax:(510)835-4355• sorh :c „-' JI <br /> JL <br /> January 12, 2001 <br /> Ref: 729801 JAN 16 2001 <br /> ENVIRONMENT HEALTH <br /> California Regional Water Quality Control Board PERMIT/SERVICES <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, California 95827-3098 <br /> Attention: Mr. Philip S. Isorena <br /> Subject: Soil Closure Work Plan <br /> for Former Hazardous Materials/Waste Storage Area <br /> Applied Aerospace Structures Corporation (AASC) Facility <br /> Stockton, California <br /> Reference: Amendment to Remedial Action Work Plan <br /> Letter from Fred Kintzer, Parsons Engineering Science, Inc. <br /> to Philip Isorena, California RWQCB, Central Valley Region <br /> Dated: 19 November 1998 <br /> Dear Mr. Isorena: <br /> This letter presents a plan for closure of the Source Area vadose zone soils at the AASC <br /> site and is submitted by Parsons Engineering Science, Inc. (Parsons) on behalf of BP <br /> Amoco Corporation. In the above-referenced letter, Parsons proposed to discontinue soil <br /> vapor extraction (SVE) treatment of the vadose zone soils in the Former Hazardous <br /> Materials/Waste Storage Area when SVE operation achieves low contaminant <br /> concentrations that no longer have the potential to impact groundwater. The following <br /> steps are proposed to demonstrate no impact to groundwater: <br /> 1. Show that low VOC concentrations were achieved in vapor extraction wells (VEWs) <br /> and at the peripheral vapor monitoring points (VMPs). <br /> 2. Show that asymptotic contaminant mass removal rates have been achieved by SVE. <br /> 3. Confirm that the reduction in VOC concentration has been achieved throughout the <br /> Source Area by profiling soil vapor at new sampling locations. <br /> 4. Model vertical leaching of residual contamination in order to show that future impacts <br /> to groundwater quality would be negligible. <br /> 5. Prepare a memorandum report summarizing the above findings and recommendations <br /> for soil closure. <br /> Low Concentrations Achieved at the End of Phase III SVE <br /> This section presents and evaluates summary data from the recent Phase III of SVE <br /> operation in support of the proposed soil closure approach. Additional information <br />