ARCHIVED REPORTS_REPORT ON SOIL VAPOR SAMPLING AND HUMAN HEALTH RISK ASSESSMENT DEC 2010

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AECOM Report on Soil Vapor Sampling and Human Health Risk Assessment 2-5 2.4 October 20, 2010, Event In accordance with recommendations presented in the July 15, 2010, report a "seasonal"variation sampling event of all three soil vapor wells(SV-1 through SV-3)was conducted on October 20, 2010. No significant(>0.5-inch)rainfall occurred during or immediately prior to(within 24 hours)this event. However, the ground surface in the vicinity of SV-1 was observed to be damp in areas and approximately 1-2 inches of water was observed in the well box. The dampness observed was either a result of rain that had occurred several days prior to the event, or to automatic sprinklers(reported to have been turned off:24 hours prior to event). Regardless of the source, based on the limited nature of the dampness, it is expected to have occurred greater than 24 hours before the sampling event.As previously stated in Section 2.3, soil moisture observed at the surface cannot be directly related to soil moisture at depth. [No matter what impact moisture may have on soil gas concentrations, as indicated in Section 3.0, we have demonstrated that the ELCR and HI results are below the California EPA and USEPA's target cancerrisk range (1x10 to 1x10°)and total HI of 1, for the residential scenario.] Sample SV-1 was collected over a period of 45 minutes using a 1-liter Summa canister. The type of Summa canister used for sample collection was changed from a 6-liter to a 1-liter canister due to low vapor recovery rates observed during the previous sampling events. Sample SV-1 was collected with a final container vacuum of approximately 5 inches Hg (reported upon receipt by the laboratory to be 6.8 inches Hg). Sample SV-2 was collected with a duplicate(SV-2D)sample. Both canisters were allowed to fill for a total of 75 minutes, and were collected with final canister vacuum of approximately 5 inches of mercury(ireported upon receipt by the laboratory to be 5.4 inches Hg). Sample SV-3 was collected over a period of 30 minutes and was collected with a final canister vacuum of 7 inches Hg (reported upon receipt by the laboratory to be 8.6 inch Hg). One field blank sample(FB-1)was collected by running laboratory certified zero air through a manifold with a 1-foot length of Teflon tubing connected to the sample container. Sample FB-1 was collected over a period of 30 minutes and was collected with a final canister vacuum of 6.5 inches Hg (reported upon receipt by the laboratory to be 7.2 incites Hg). 2.4.1 Analytical Results Air Toxics analyzed a trial of four soil vapor samples from the three soil vapor wells(SV-1 through SV-3 and SV-21D as a duplicate sample). The samples were analyzed for TPHg, BTEX, and naphthalene by Method TO-15; and atmospheric gas percentages (oxygen, methane, carbon dioxide, and nitrogen)and the tracer gas helium by modified ASTM Method D-1946, to assess sample train integrity during the sampling event. Method TO-15 soil vapor analytical results for SV-1 are summarized in the table below,with references to CHHSLs and ESLs for commercial/industrial locations. CHHSLs and ESLs for a residential exposure scenario are noted in brackets ([]). No compounds were detected in the samples collected from SV-2, SV-3, or the duplicate sample (SV-21D). No compounds were detected in the field blank. 6014657&M16 December 15,2010