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November 24, 1997 Harding Lawson Associates 399601 Margaret Lagorio, Supervising REHS San Joaquin County Public Health Services Environmental Health Division Page 4 Analytical Program Up to four soil samples from each boring will be submitted to a State certified analytical laboratory for the analyses listed below. • TPH-d and TPH-motor oil using EPA Method 8015M • BTEX using EPA Method 8020 One soil sample from the vadose zone from each boring, and possessing the highest concentrations, will also be submitted for soluble analyses,using deionized water, for the above constituents that are detected. In addition, depending on the soluble results, the sample with the highest TPH concentration may be analyzed for polycyclic aromatic hydrocarbons(PAHs) using EPA Method 8310. If groundwater is encountered in the borings, groundwater samples will be collected from the boreholes for the same analyses indicated above. Task 3.0: Risk-Based Corrective Action(RBCA) Site Assessment Depending on the results of the soluble analyses, a Risk Based Corrective Action (RBCA) Site Assessment may be performed. The American Society for Testing and Materials (ASTM) has, with EPA's approval, issued guidance called the Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (ASTM, 1995), which describes a three-tiered process for evaluating leaking underground tank sites with TPH in soil and/or groundwater. This process was developed to be streamlined and cost-effective, and to standardize and speed up the evaluation and closure of fuel-impacted sites. Although the State of California has not yet issued guidelines for adapting RBCA for California fuel sites, various regional State and county agencies in California are now requiring site evaluations based on modifications of the RBCA framework. Tier 1 involves a comparison of chemical concentrations (e.g., BTEX) detected in site soil, air, or groundwater to generic Risk-Based Screening Levels (RBSLs) that are based on the human receptor pathways considered most likely to occur at the site. Tier 1 is a conservative screen; if detected concentrations do not exceed RBSLs, they are unlikely to pose a health risk to human receptors, and the site can proceed toward closure. If concentrations exceed RBSLs,Tiers 2 and 3 of the RBCA process are the next options to consider. For Tier 2, Site-Specific Target Levels (SSTLs) are developed for soil and groundwater, which are similar to RBSLs but less conservative because they are based on site-specific exposure assumptions and soil and groundwater parameters. If detected chemical concentrations exceed SSTLs, there are several options including proceeding to Tier 3, which is a comprehensive,baseline human health risk assessment. According to the ASTM (1995), most fuel sites can be evaluated by Tiers 1 and 2. At complex sites with multiple receptors and pathways, and possible ecological receptors, Tier 3 provides the most site-specific approach. Based on the analytical results,HLA has assumed that the Tier 2 assessment may be required for this site. r