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Cleanup in Vulnerable Communities'Initiative Final Project Reference:Bobson Cleaners Discovery and Enforcement Discovery Project Number:60688620-5.1 Investigation Work Plan 7. Screening Risk Evaluations One specific objective of the DI is to estimate the potential threat to public health and/or the environment posed by the Site and compare estimated risk/hazards among sites being evaluated. The human health screening evaluation will be performed in accordance with the protocols detailed in the Programmatic QAPP Section 7.1 "Human Health Screening Evaluation". In addition, project-specific guidance on the performance of the screening evaluation will be requested from the DTSC PM and DTSC staff toxicologist. 7.1 Human Health Screening Risk Evaluation The first step of the human health risk evaluation will be to construct a conceptual site model (CSM)pertinent to potential vapor intrusion inhalation exposure for the property.A preliminary CSM for the human health vapor intrusion screening evaluation is presented in Figure 5.The CSM will identify the potential receptor groups, exposure media and exposure pathways associated with the site. Chemicals of potential concern (COPCs)will then be identified.All organic chemicals detected in at least one sample will be included as COPCs.The maximum detected concentration of each COPC will be used as the exposure point concentration in the risk assessment. Land use will be considered residential in nature, unless otherwise specified. Default exposure values provided by the DTSC per Human Health Risk Assessment Note 1 that represent the Reasonable Maximum Exposure and applied in developing the HHRA Note 3 screening levels will be utilized in calculating risk and hazard.The exposure pathway that likely will drive the D&E Discovery Investigation is inhalation of chemical vapors emanating into indoor air from subsurface sources (vapor intrusion). If VOCs are detected onsite in the subsurface and/or onsite or offsite in indoor air, an assessment of potential infiltration to indoor air will be conducted as per the Programmatic QAPP.A multiple lines of evidence approach as described in the VIG may be adopted to refine the risk evaluation. Cumulative cancer risk and non-cancer hazard estimates may be used to determine whether additional investigations or remediation is needed at the site. Prepared for: Department of Toxic Substances Control AECOM 30