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Proposal No. P1-410-0587 August 27,2010 Page 2 by which chemicals in soil and groundwater can migrate into indoor air. Chemical vapors moving up through soil and into a building are a potential source of indoor air contamination and may pose a risk to human health. Consequently,SALEM recommends conducting a soil vapor gas survey within the proposed subject building footprint for the purpose of assessing potential indoor vapor concentrations associated with the proposed Fresh & Easy Neighborhood Market building. Additionally, SALEM recommends placement of a vapor barrier beneath the proposed subject building's concrete slab-on-grade foundation to prevent the potential migration of chemical vapors into the subject building interior. Based upon the historical use of petroleum hydrocarbons and chlorinated solvents at the subject site vicinity, and the presence of these compounds in soil and groundwater in the area adjacent north of the proposed Fresh & Easy Neighborhood Market tenant space, it was SALEM's opinion that a potential vapor intrusion condition may exist within the proposed tenant space as a result of past releases of these constituents from former fuel storage and dispensing and/or dry cleaning operations into on-site soil and groundwater. Because of the above potential for vapor intrusion, SALEM recommended conducting a Limited Soils Assessment of the subject property's shallow soils to determine the presence or absence of VOCs (including chlorinated solvents) related to the historical use of the subject property vicinity for fuel storage and dispensing and/or dry cleaning operations, and for the purpose of determining if historical or current property uses may have impacted the subject property. This proposal has been prepared to address SALEM's recommendation for additional subsurface investigation. 2.0 SAMPLING RATIONALE In 2002, the Environmental Protection Agency (EPA) released "OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance)".This draft guidance recommends a tiered approach to evaluation of the vapor intrusion pathway. This guidance includes record sheets containing a series of questions that guide users through a stepwise evaluation of the subsurface vapor intrusion pathway. The EPA recommends an assessment of the vapor intrusion pathway include multiple lines of evidence if available. The first tier of the USEPA's tiered approach to evaluation of the vapor intrusion pathway includes an evaluation of COCs for volatility and potential for toxicity. The second tier includes a comparison of analytical data collected in groundwater or soil gas to conservative groundwater screening levels. These target groundwater concentrations will be back calculated from risk-based target indoor air concentrations and an indoor air to groundwater attenuation factor of 0.001 (USEPA, 2002). In the event that concentrations in groundwater exceed these screening levels, soil gas samples may also be collected. The analytical data from these soil gas samples are then compared to conservative soil gas screening levels. In the event that site conditions or data limitations preclude the use of these screening levels, or if a refined vapor pathway assessment is warranted, a site-specific vapor pathway assessment (Tier 3) may be conducted using the Johnson&Ettinger model,additional site-specific data collection,or a combination of both(USEPA,2002). A previous Phase II Environmental Site Assessment (by others) just north of the subject site property noted the presence of naphthalene on soil at a depth of 5 feet bgs and PCE in groundwater at a depth of approximately 40 feet bgs. Please refer to Figure 1 (attached) for sample locations. Based on the presence of known or suspected soil vapor sources on the subject site, collection of soil gas samples is recommended to refine the vapor intrusion pathway assessment.