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• \+,,1 ATC Associates Inc. <br /> 1117 Lone Palm Avenue,Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> fax:209-579-2225 <br /> ASSOCIATES INC. <br /> Confirmation samples collected from each of the soil gas sampling points will be transferred under <br /> chain-of-custody procedures to a State-certified laboratory for chemical analysis. The samples will <br /> be analyzed for TPHg by EPA Method TO-3 and for BTEX, MTBE, TBA, DIPE, TAME, ETBE, <br /> 1,2-DCA, and EDB using EPA Method TO-15. Selected soil gas samples will be analyzed for <br /> methane by EPA Method8015 and for oxygen and carbon_dioxide by ASTM Method 1945-96a <br /> using a GC and/or a TCD. ATC ill request detection limits for the analytes of interest that are less <br /> than pr equal to the residential sce ario screening•levels provided in Table E of the ESLs for Indoor <br /> Air and Soil Gas (Vapor Intrusio Concerns) as published by the RWQCB San Francisco Bay <br /> Region in November 2007. <br /> Geotechnical Analyses <br /> At least one soil sample will be collected for geotechnical analyses from the base of the soil gas <br /> sampling points. The sample will be collected in a brass or acetate sleeve, using the best suited <br /> method to capture an undisturbed sample. The sample will be analyzed for porosity, density, and <br /> moisture content using API Method RP40; particle size distribution by ASTM Method D4464M; and <br /> total organic carbon using the Walkley-Black method. The data obtained from these analyses will be <br /> useful for vapor intrusion modeling applications. <br /> Indoor Air Risk Assessment <br /> A tiered evaluation will be conducted using the laboratory analytical data. The soil gas data will be <br /> compared to the values listed in Table E of the Tier 1 ESLs as published by the RWQCB San <br /> Francisco Bay Region in November 2007 and the CHHSLs published by the CAL EPA in January <br /> 2005. If any of the analytes of interest exceed the ESLs and/or CHHSLs, these analytes will be <br /> evaluated utilizing the Tier 2 Modeling program. ATC will use the appropriate Johnson and Ettinger <br /> Vapor Intrusion Model based on subsurface soil encountered and property usage to estimate the <br /> cumulative risk of exposure to all applicable analytes of interest using site specific data. Analytes of <br /> interest detected above laboratory method detection limits from vapor sampling will be input into the <br /> model to evaluate the Hazard Quotient for carcinogens and non-carcinogens. Analytes of interest not <br /> detected will be input into the model using the lowest applicable laboratory method detection limit. <br /> For the purpose of this indoor air risk assessment, ATC will assume the building is slab on grade. <br /> ATC will compare Hazard Quotient Ratios to conservative and action levels established by the <br /> RWQCB and evaluate if additional sampling, modeling, and/or mitigation efforts are necessary. <br /> Report Preparation <br /> Upon completion of the soil vapor study activities, a summary report will be prepared and will <br /> include a description of field activities, laboratory analytical data in tabular form, boring logs, site <br /> plans, laboratory report sheets, a comparison of soil vapor analytical data to the RWQCB San <br /> Francisco Bay Region ESLs, CHHSLs, and any additional modeling, if necessary. <br /> S:\Environmental\25847\38\Workplans\2010 May SGS.doc 6 <br />