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rP <br /> 3.4 Human Health Risk Assessment <br /> 3.4.1 Risk Assessment Meth6d6logy <br /> IF.3 . <br /> Incorporating the soil vapor sample analytical results, WRM completed a human health risk. <br /> assessment (HHRA) using the RISC4— Risk Integrated Software for Clean-ups (RISCO) <br /> software program developed.by BP Oil International. The HHRA considered potential risks to an <br /> adult worker and a child resident at reasonable maximum exposure (RME) levels associated <br /> r with the following exposure pathways: <br /> • Inhalation of indoor air; <br /> • Dermal contact with soil; <br /> • Ingestion of soil; <br /> • Dermal contact with groundwater; and <br /> • Ingestion of groundwater; <br /> The constituents of concern (COC) considered in the HHRA included:`TPH-as-diesel, TPH-as- <br /> gasoline, BTEX and MTBE. Lead was also considered as a COC in the soil exposure pathways <br /> section of the HHRA. In the HHRA;WRM evaluated a target cumulative carcinogenic risk level <br /> of one in one million and target cumulative hazard quotient of one. <br /> RISC4 applies the widely accepted.Johnson and Ettinger model to predict levels of CDCs in <br /> indoor air based upon COC concentrations detected in soil vapor. For the groundwater <br /> exposure pathways, RISC4 applies a dissolved-phase fate and transport model to simulate COC <br /> migration from groundwater beneath the site to an off-site domestic well. For this application, <br /> RISC4 default carcinogenic risk slope factors were adjusted as needed to comply with the <br /> t California Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria <br /> Database. Specifically, slope levels for benzene, ethylbenzene, and MTBE were adjusted. <br /> 3.4.2 RISC4 Input Parameters <br /> To assess potential risks associated with indoor air inhalation, WRM included the analytical <br /> results from soil vapor samples collected on April 30, 2008 (Table 4). Asa conservative <br /> measure, since COC concentrations in all five soil vapor samples were below laboratory. <br /> reporting limits, the laboratory reporking limit was used as the representative concentration for. <br /> each COC. For the model, WRM a <br /> ssumed a instance of one meter from:the soil vapor source to <br /> the on-site building, and based upon soil boring logs, selected silty clay as the representative <br /> vadose zone soil type and silty sand'as the representative saturated zone soil type. <br /> 11 <br /> _T <br />