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• Pumping approximately,500;gallons of groundwater from.the-excavation-into a Baker <br /> ttank.prior to testing anddischarge-to the,sani ary sewer;_. <br /> • Collecting a soil and.groundwater sample from the base of the shored excavation for <br /> laboratory analyses; <br /> • Placing approximately 800 lbs of oxygen.release compound(ORC) into the base of the <br /> shored excavation prior to backfilling; <br /> • Backfilling and compacting clean imported.soil in the excavation; and <br /> • Disposing of contaminated.soil at Altamont Landfill in Stockton,California. <br /> 4.1' - . Rationale for Remediation <br /> Site soil and.groundwater data showed that significant concentrations of petroleum hydrocarbons <br /> were present at sampling location CPT-EXC-BT-19; and likely extended deeper. As described <br /> in Section 3.0,rising groundwater at the Site has resulted in.a smear zone of soil with TPH-g <br /> concentrations generally to at least 10 feet below the-water table. <br /> ,Excavation of contaminated soil;,pumping contaminated groundwater from the excavation,and 7 <br /> ,adding ORC to the excavation to help create aerobic conditions that Will enhance_in=situ , <br /> bioremediation was selected-as the mitigation,inethod-because. - <br /> • In-situ remedial cleanup of contaminated soil is difficult at sites with significant <br /> concentrations of hydrocarbons in fine grained sediments below the water table, and <br /> • The planned development at the site could limit.access,for managing potential long-term <br /> in-situ cleanup. . <br /> • Spreading ORC at the base of the excavation is an effective way to deliver time released <br /> oxygen to the subsurface. <br /> i <br />.I <br /> 25971024.DGD 5 7 June 2005 <br /> i <br />