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i <br /> r-. <br /> Stantec <br /> December 8,2010 <br /> Page 8 of 9 <br /> potential risk via inhalation, a Tier 2 assessment using the J&E soil gas model as provided by <br /> DTSC will be used to more accurately assess the site-specific risks. <br /> WASTE HANDLING AND STORAGE <br /> During drilling operations, all auger tools, sampling tools, and down-hole equipment will be <br /> cleaned prior to use. All rinsate water and soil cuttings will be temporarily stored in Department- <br /> of-Transportation portat on (DOT) 55-gallon drums at the site pending laboratory analysis for proper <br /> disposal. <br /> SUMMARY AND CONCLUSIONS <br /> On September 18, 2000, IT Corporation supervised the installation of soil-gas probes SG-1 <br /> through SG-11 and sampled the probes. <br /> TPHg and benzene concentrations were detected in soil-vapor samples collected from SG-9, <br /> and MtBE concentrations were detected in soil-vapor samples collected from SG-8 through SG- <br /> 11. Toluene, ethylbenzene, and xylenes, concentrations were below method reporting limits in <br /> all soil vapor samples collected. <br /> i <br /> The HHRA indicated that the individual and cumulative cancer risks for the detected and non- <br /> detected COPCs were greater than 1.0E-06 and the HQs and HI for non-carcinogens were <br /> greater than the Cal-EPA target risk level of 1.0, except for toluene, ethylbenzene, and total <br /> xylenes. <br /> Given that ten years has passed since the data .described above was collected, Stantec <br /> proposes to perform an additional soil gas assessment at the site in order to accurately assess <br /> the current human health risk. <br /> REPORTING <br /> Stantec will prepare an assessment report summarizing the fieldwork completed and data <br /> collected including: <br /> • Soil gas probe construction details <br /> • Details of field procedures, soil gas sampling methods and operations <br /> • Updated maps including soil gas sampling locations . <br /> • Tabulated summary of soil gas analytical results <br /> • Human health risk assessment and vapor intrusion modeling results <br /> • Conclusions <br /> The results of the assessment work will be uploaded to the State of California GeoTracker <br /> database in electronic deliverable format (EDF), as per California code A62886. <br /> I <br /> 19976 Vapor Risk Assessment Report.doc <br />