ARCHIVED REPORTS_SOIL AND GROUNDWATER INVESTIGATION REPORT 2008

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Soil and Groundwater Investigation Report Vernalis Offsite June 2008 • Benzo(b)fluoranthene: SB-28 (0.039 µg/L), SB-31 (0.031 gg/L), and SB-33 (0.038 ug/L). The estimated extent of crude-oil affected groundwater,based on evaluation of the groundwater data from this and previous site investigations, is presented on Figure 3. 5.2.1 Suitability of the Groundwater for Drinking TDS concentrations in groundwater samples collected from SB-27 and SB-32 were 888 mg/L and 1,390 mg/L respectively. The criteria of the Water Quality Control Plan for the Sacramento River Basin and the San Joaquin River Basin,for which an aquifer is considered a potential source of drinking water, are as follows: ' • TDS in groundwater less than or equal to 3,000 milligrams per liter(mg/L); and • Groundwater yield greater than 200 gallons per day. TDS results indicate that the groundwater is a potential drinking water source; however,both reported concentrations of TDS are above the secondary maximum contaminant level(MCL) of 500 mg/L. Secondary MCLs are used for risk assessment purposes and will be addressed in a future human health ' risk assessment(HHRH). 6. CONCLUSIONS AND RECOMMENDATIONS SAIC reviewed the findings of this and previous site investigations, and concludes and recommends the following: • The area of affected soil has been delineated: o The lateral extent of COCs in soil is defined by borings SB-26 through SB-33 as all soil analytical results were below respective PRGs and ESLs. o The vertical extent of affected soil was defined to a maximum depth of 80 feet bgs in a previous investigation The vertical extent of affected groundwater was defined to a maximum depth of 80 feet bgs in a 1 previous investigation. • Concentrations of TPHd in down-gradient boring SB-26(160 gg/L) slightly exceeded the ESL and WQO of 100 gg/L. However,the immobile nature of the weathered residual crude oil,age of the release,continued degradation of petroleum hydrocarbons mass by natural attenuation, and groundwater analytical results collected from SB-27, SB-28, and S13-29, suggest that TPHd concentrations in groundwater will drop below the ESL/WQO a short distance away from these borings. No additional delineation is recommended. • Concentrations of TPHd(240 gg/L) also exceeded the ESL/WQO in near boring S13-33,which is located nearly down gradient from the former TAOC Ohm Pump Station and is scheduled for a tpreliminary investigation in 2008. Borings SB-31 and SB-32, also installed along the Highway 33 ROW, are closer to the source areas (former pump house and former boiler house) and did not exceed ESL/WQO for TPHd. SAIC recommends that any additional investigation in the vicinity ' of SB-33 be conducted in conjunction with the TAOC Ohm Pump Station investigation. The concentrations in boring SB-33 are just slightly above the respective WQOs/ESLs, and thus likely define the down-gradient extent of affected groundwater. Additionally, access to the property beyond SB-33 has not been and is not likely to be obtained. • Concentrations of the PAHs benzo(b)fluoranthene(SB-28, SB-31, and SB-33) and benzo(a)anthracene(SB-33) were reported as exceeding ESL/WQO in one or more borings. 1 These detections just slightly exceeded the 0.029 gg/L ESL(the more conservative of the two ' 7 mac*on mmgjm%ff` From Science to Solutions