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V saturation using API RP40; total organic carbon and fraction organic carbon using Walkley- `r Black; hydraulic conductivity and intrinsic permeability using ASTM D5084; Atterberg Limits (LL, PL, and PI) using ASTM D4318; USCS/Plasticity identification using ASTM D4318; USCS classification using ASTM D2487; and USDA soil texture scheme classification. 9.5 Soil Disposal The soil cuttings generated from the soil and vapor probe borings will be placed in a secured 55-gallon drum and placed on-site pending waste characterization. The soil will be disposed at a California approved disposal facility upon approval. 10.0 VAPOR INTRUSION MODELING 10.1 Risk based Corrective Action Methodology The Risk Based Corrective Action (RBCA) process was first established by the ASTM to provide a consistent decision-making process for the assessment and response to a petroleum release, based on the protection of human health and the environment. It is an integration of site assessment, remedial action selection, and site monitoring with standard exposure and risk assessment practices (ASTM, 1997). The RBCA process can be expanded to include other types of contaminated sites. It is typically implemented in a tiered approach, involving increasingly sophisticated levels of data collection and analysis. Upon .r completion of each tier, the results are evaluated and, if warranted, conservative default assumptions of the earlier tier are replaced with site-specific data and the analysis proceeds to the next tier. Typically, for screening purposes, Tier 1 risk-based screening levels (RBSLs) are derived, using simplified ASTM fate and transport models and USEPA or Cal-EPA standard default exposure parameters, to address relevant direct and indirect exposure pathways for the appropriate property use categories. Tier 1 RBSL "look-up" tables are used to determine whether site conditions satisfy the criteria for a quick regulatory closure or warrant a more site-specific evaluation. If site concentrations exceed Tier 1 RBSLs, then Tier 2 site-specific target levels (SSTLs) at the point of compliance are derived using site-specific information in the fate and transport models. These site-specific parameters may include soil bulk density, total soil porosity, volumetric air/water content, depth to subsurface soil source, depth to groundwater, and area fraction of cracks in foundation walls, etc. When Tier 2 SSTLs are exceeded, a Tier 3 RBCA assessment can be performed to provide a more complex assessment, which may include additional site assessment, probabilistic evaluations, and sophisticated chemical fate and transport models (ASTM, 1997). V The RBCA analysis for this Site follows the San Francisco RWQCB Guidance Document (RWQCB, 2003). In the interim final version, the RWQCB changed the terminology of Tier 1 RBSLs to Tier 1 ESLs to indicate that ESLs are not strictly "risk-based" in a strict toxicological definition of this term. ESLs are meant to protect both human health and the environment and also protect against adverse nuisance conditions, (e.g. odor and taste). For those ESLs that are risk-based, ESLs based on carcinogenic effects reflect a target ECR value of 1 E-06; and ESLs based on non-carcinogenic effects reflect a target hazard quotient (HQ) of 0.2 to address potential cumulative health concerns for chemicals (up to five hazardous chemicals)with similar toxicological modes of action. V Workplan to Conduct Subsurface Soil Vapor Intrusion Study ��/> , ATC Project 54.26874.0001V s V Page 8 4