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Mr Ron Rowe Project 22611-100 001 <br /> October 7, 1996 <br /> Page 3 <br /> Task 3 - Risk-Based Corrective Action Analysis <br /> The RBCA analysis will be conducted consistent with ASTM ES-39 guidelines Additional <br /> information regarding individual components of the process is provided below <br /> Subtask 3A - Tier 1 Analysis <br /> EMCON will perform a Tier 1 RBCA analysis, which compares maximum detected <br /> chemical concentrations in soil and groundwater with conservative, health risk-based <br /> screening values These screening values will Likely be for petroleum-related compounds, <br /> including USEPA Region 9 preliirunary remediation goals (PRGs) Maximum detected <br /> chenucal concentrations in groundwater will also be compared with maximum contaminant <br /> levels (MCLS) A table summarizing the maximum detected concentrations, screening <br /> levels used, and results will be prepared, and chemicals detected at concentrations above <br /> the conservative screening levels will be identified and further evaluated in Tier 2, as <br /> discussed below <br /> Subtask 3B - Tier 2 Analysis <br /> The Tier 2 evaluation will conform with ASTM ES-38 guidance In accordance with regulatory <br /> guidance, the following activities are anticipated <br /> • Summarization and Statistical Evaluation of Chemical Data. Chemicals exceeding <br /> Tier 1 values will be further evaluated in this step to identify appropnate concentrations <br /> for use in modeling exposures <br /> • Exposure Assessment. For each exposure pathway that is considered to be complete <br /> at the site, estimates of daily doses to relevant receptors (e g , workers) will be made <br /> using agency-accepted exposure models <br /> • Toxicity Assessment. Toxicity information for each of the chemicals of potential <br /> concern will be evaluated consistent with California risk assessment guidelines <br /> • Risk Characterization Estimated exposures will be combined with toxicity <br /> values to calculate possible cancer risks and noncancer hazards associated with the <br /> evaluated chemicals If risks and/or hazards exceed regulatory-based levels for a <br /> chemical, target levels will be calculated that may be used as remediation goals <br /> SA"\PJZ\261 1\261 11000 IAN-96\pas 1 <br />