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PE, . EPORT (June 20, 2003) LOCKEFORD ELEMENTARY SCHOOL EXPANSION For this PEA, soil gas and soil matrix sampling was conducted at 24 on-site locations (Figure 3). Groundwater samples were collected from two locations where shallow groundwater was encountered. The shallow groundwater does not appear to be laterally continuous across the Site .and may be due to a water service pipeline that leaked for several months in 2002. The soil gas samples were analyzed for VOCs and methane by an on-site, mobile laboratory (Table 1). Soil matrix and groundwater samples were analyzed for Title 22 metals, SVOCs, OCPs, PCBs, TPHs, and VOCs (Tables 2 and 3). As shown on Figure 4 and Table 4, relatively low concentrations of benzene, toluene, ethylbenzene, xylenes, and MTBE were detected in soil gas samples from locations in and near the building, near the former UST location, and near the stormwater drop inlet for the southern parcel (SG-21). Relatively low concentrations of fluoranthene, phenanthrene, and phenol were detected in soil matrix samples (Table 7). Phenol was by far the most prevalently detected compound — being detected in over half of the soil matrix samples, including samples from the northern, western, and southern parcels and many samples below the uppermost foot of soil. TPH, Diesel Range (C13-C23) and TPH, Oil Range (C14-C40) were also widely detected in soil matrix samples at moderate concentrations, but only in two samples below the uppermost foot of soil — near the former UST location and near the southern parcel's stormwater drop inlet (Figure 5 and Table 7). TPH, Gasoline Range (C8-C 12) was only detected in one soil matrix sample near the former UST location at a relatively low concentration (Figure 5 and Table 7). A total of 21 chemicals were identified as COPCs in soil and soil gas at the site (Table 11). Six of the COPCs are considered carcinogens by USEPA or Cal/EPA. Exposure to the carcinogenic COPCs in air and soil results in an estimated cumulative excess cancer risk of 5.9 x 10-6, or approximately 5.9 in a million. The cancer risks are based on the maximum detected concentrations, and represent the incremental cancer risk for a hypothetical resident. The COPCs "driving" the predicted risk are benzene, at a risk of 3.2 x 10-6 based on exposure in indoor air, and chromium, at a risk of 2.6 x 10-6 based on exposure in air. However, benzene was detected at only two of the 24 sampling locations, and the estimate of the benzene concentration in indoor air was based on relatively conservative model parameters. Furthermore, the chromium risk estimate is based on the very conservative assumption that all of the chromium is present as hexavalent chromium. No record of hexavalent chromium usage at the Site has been identified. If the assumption of a 1:6 ratio of hexavalent chromium to trivalent chromium were used, as in USEPA Region 9's calculation of generic preliminary remediation goals (PRGs), the estimated risk due to chromium exposure would be well below the PEA screening level of 1 x 10-6. The total estimated incremental cancer risk from exposure to COPCs in soil, the only other exposure pathway for carcinogenic COPCs, is 5 x 10-10 an almost imperceptible risk compared to the air exposure pathway. For non-carcinogenic effects, the Hazard Index (HI) value for multipathway exposures to all COPCs — assuming dose additivity— is 5.9, principally based on exposure to TPHd and TPHo in soil. Dose additivity assumes that all COPCs induce the same health effect by the same mechanism(s) of action. Only two sampling locations had TPH concentrations in soil high enough to produce a Hazard Quotient (HQ) value greater than one. In addition, the HQ values were calculated based on the conservative assumption that the detected TPHd and TPHo 13-2 URS CORPORATION PAPEA Locke ford\Report\Lockeford Report Rev.doc