Laserfiche WebLink
Stantec U <br /> December 8, 2010 <br /> Page 6 of 9 <br /> Although the property is currently used for commercial purposes, the soil gas concentrations <br /> were compared to screening levels for residential land use to provide a conservative estimate of <br /> risk and allow for unrestricted use of the site in the future. Screening levels based on residential <br /> land use are also protective of sensitive receptors (i.e, children and elderly people). <br /> Chemicals of Potential Concern <br /> The COPCs consisted of BTEX, MTBE, and TPHg.— The maximum concentrations detected <br /> were used as the representative site concentrations to evaluate the potential risks via the vapor <br /> intrusion.pathway. For chemicals that weren't detected, the analytical reporting limits were used <br /> as the EPCs:. )The COPCs and their respresentative concentrations are presented in Table 4 <br /> along with the screening levels. <br /> Screening Level HHRH Results <br /> The screening level human health risk assessment (HHRA) indicated that the individual and <br /> cumulative cancer risks for the detected and non detected chemicals were greater than the Cal- <br /> EPA and CRWQCB limit for residential property of 1.0E-06. The HQs and HI for non- <br /> carcinogens were also greater than the Cal-EPA target risk level of 1.0 for all COPCs, except for <br /> toluene, ethylbenzene, and total xylenes, which were below the laboratory reporting limit for all <br /> samples. The screening level HHRA results are presented in Table 4. <br /> PROPOSED ADDITIONAL SOIL GAS ASSESSMENT <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. Stantec proposes to install five soil gas probes for the collection <br /> of soil and soil gas samples at a depth of 5 feet bgs. Field observations and soil gas sample <br /> analytical data will be used to evaluate the potential risk to human health from vapor intrusion. <br /> Details related to the proposed scope of work are presented below. <br /> HEALTH AND SAFETY <br /> As required by the Occupational Health and Safety Administration (OSHA) Standard <br /> "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and <br /> by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste <br /> Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), Stantec will <br /> prepare a site-specific health and safety plan prior to the commencement of field work. The <br /> site-specific health and safety plan will be reviewed by the field staff and contractors before , <br /> beginning field operations at the site. <br /> PERMITTING AND UTILITY CLEARANCE <br /> Stantec will obtain soil boring permits from SJCEHD and the City of Manteca prior to initiating <br /> work. Prior to conducting subsurface work at the site, Underground Service Alert (USA) will be <br /> contacted to delineate subsurface piping near the site with surface markings. In addition, a <br /> private utility locator service will be contracted to clear the area surrounding the proposed soil <br /> boring locations. <br /> 19976 Vapor Risk Assessment Report.doc <br />