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lowR <br /> ARCADIS saL Mr. Michael J . Infurna <br /> April 5, 2007 <br /> then be collected using a 6-Liter SUMMATO canister at a flow rate of 2_200 mL/min for <br /> a period of approximately 30 minutes. Soil gas samples will be either shipped or <br /> hand delivered to the appropriate laboratory and analyzed for: <br /> • benzene, ethylbenzene, toluene, total xylenes (BTEX) , naphthalene, and the <br /> tracer gas by United States Environmental Protection Agency (USEPA) <br /> Method TO-15 <br /> • oxygen, carbon dioxide, nitrogen , and methane by American Society for <br /> Testing and Materials (ASTM) Method D-1946 <br /> Soil Vapor Data Evaluation and Reporting <br /> Soil vapor data will be evaluated against the OEHHA soil-gas screening levels based <br /> on residential land use as outlined in the Human-Exposure-Based Screening <br /> Numbers Developed to Aid Estimation of Cleanup Costs for Contaminated Soil, <br /> dated November 2004 (Revised January 2005) and values calculated using the <br /> DTSC-derived screening approach as outlined in the Interim Final — Guidance for the <br /> Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air, dated <br /> December 25, 2004. Consideration will be given to the degree of biodegradation that <br /> may have taken place as a function of oxygen content in samples (pg . 14, DTSC <br /> guidance) . <br /> Exceedances of the OEHHA screening values will be reevaluated using the USEPA <br /> version of the Johnson and Ettinger-based vapor intrusion model incorporating a site- <br /> specific diffusion coefficient derived from soil porosity and moisture content. <br /> The results of the soil vapor assessment will be submitted 4o the County prior to June <br /> j 29, 2007. <br /> Soil Vapor Probe Destruction Procedure <br /> At the completion of the assessment and agreement with the County, the nine soil <br /> vapor sample probes will be destroyed in accordance with San Joaquin County <br /> Requirements and with Bulletin 74-90, California Well Standards, California <br /> Department of Water Resources, June 1991 . The vapor sampling probes will be <br /> destroyed by drilling out and removing all material within the original borehole. The <br /> boreholes will then be grouted from the total depth of the borehole to ground surface <br /> using a tremie pipe and cement-bentonite grout. <br /> i <br /> Page. <br /> �RWHEWONWMSRI ManrwRsa?„mMan•,mtmHWRI 3/4 <br /> ii <br />