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 3-3 3.2 Uncertainty Assessment As discussed in Section 2.0, May and September 2010 data were not determined to be of sufficient quality for risk assessment. However, as a conservative worst-case evaluation, soil vapor data from all three sampling events at the site (May, September, and October 2010)were used to evaluate the worst-case potential risk associated with the vapor intrusion inhalation pathway as part of an uncertainty assessment This evaluation is discussed further in this section and refers to associated tables. 3.2.1 Step 1: Screening Level /COPC Selection The only detections of compounds in soil vapor in any of the sampling events were in sample SV-1 (and its duplicate sample)and sample SV-3 Table 3 (attached)shows that benzene, toluene, xylenes, and TPHg are the only compounds detected in soil vapor. TPHg is the only compound detected at concentrations above the published commercialtindustrial CHHSL and/or ESL. TPHg and benzene are detected atconcentrations above the residential CHHSL and/or ESL, therefore, TPHg and benzene were selected as COPCs in soil vapor for further evaluation. There are no published CHHSLs for the carbon fractions analyzed by APH methods or the TICS (consisting mostly of C8 compounds); therefore,the carbon fractions and TICS were also selected as COPCs for further evaluation, as described in Section 3.2.2. Due to the elevated TPHg concentrations, dilution of the sample was required. As a result of the dilution, the detection limits for naphthalene at location SV-1 were elevated to concentrations above the CHHSL for a residential and commercial/industrial exposure scenario. Therefore, since the naphthalene concentration at SV-1 could, theoretically, be as high as the detection limit, the detection limit for naphthalene was evaluated in the May 2010 preliminary evaluation as a worst-;ase scenario. In the May 2010 preliminary risk evaluation,the maximum detection limit for naphthalene of 290 pg/m3 was evaluated and was found to present a potential risk and hazard quotient(HQ)below target levels (7.3x10-7 and 0.0056, respectively). In the October 2010 sampling event, the maximum detection limit for naphthalene is 310 pg/m3. Therefore, the potential risk and HQ for naphthalene, based on the detection limit of 310 pg/m3,would be approximately a factor of 1.07 times(310 pg/m3/210 pg/m3)higher than those estimated based on a detection limit of 290 Ng/m3, resulting in a potential risk/HQ of 7.8x107 and 0.0059, respectively. Therefore, since the detection limit for naphthalene,which is likely higher than the naphthalene concentration detected in soil vapor at the site, does not pose a potential risk/HQ above target levels (and would also not cause the cumulative risk or hazard index to be above target levels), it was not further evaluated in this revised risk evaluation of the October 2010 soil vapor data. The indoor air modeling and estimation of potential risk for the selected COPCs is discussed in the following section. 3.2.2 Step 2: Indoor Air Modeling and Estimation of Potential Risk 3.22.1 Methods In the second step of the evaluation,the vapor intrusion model developed by Johnson and Ettinger, and spreadsheets provided by CaIEPA DTSC/HERD (JE Model)(DTSC, 2004),were used to estimate the potential ELCR and non-cancer HQ associated with COPC concentrations in soil vapor for an on-site commercial/industrial worker and a hypothetical future on-site resident.Available site- December 15,2010 60146576-M10