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• <br />ATTACHMENT P <br />RISK-BASED EXPOSURE PATHWAY EXCLUSION ANALYSIS <br />INTRODUCTION <br />The following text, tables, and figures describes a nsk-based exposure pathway exclusion <br />analysis (PEA) conducted for the subject site The Conceptual Site Model (CSM) developed <br />for the site (Figure 15) shows that both on- and off-site pathways may lead to significant <br />chemical exposures for on- and off-site receptors Because of the absence to date of detectable <br />concentrations of site -related chemicals in Well 12, the only source of off-site groundwater <br />exposure, the current analysis was performed to evaluate the onsite pathways, namely <br />• volatilization of VOCs from soil to indoor air, and <br />• volatilization of VOCs from groundwater to indoor air <br />Due to the depth of site contaminants, and the lack of beneficial use of onsite groundwater, the <br />. pathways listed above are the only complete and potentially significant pathways for onsite <br />exposures In particular, by using a conservative, tiered approach, similar to the approach <br />recommended by the American Society of Testing and Materials in their Risk -Based <br />Corrective Action (RSCA) protocol for petroleum-denved contaminants (ASTM, 1995), <br />SECOR evaluated the potential for onsite soil and groundwater volatilization pathways to lead <br />to risks considered unacceptable by the RWQCB This ASTM RBCA protocol has been <br />adopted throughout California, as well as most of the rest of the U S <br />DATA EVALUATION <br />SECOR first reviewed the soil and groundwater data available for the site, data were reviewed <br />for their potential use in risk assessment Once appropriate onsite soil and groundwater <br />datasets were identified, SECOR performed a statistical analysis of the datasets in order to <br />generate representative onsite concentrations for each detected chemical for use in the PEA. <br />Groundwater Data <br />SECOR identified and compiled all groundwater data for the site that had the following <br />characteristics <br />• The data were from onsite wells, <br />• The data were collected after July 3, 2400, and <br />