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. 4 <br /> Scott Mansholt • - 2 - • 12 June 2007 <br /> Chevron-Lyoth Offsite <br /> Water Quality Control Board (RWQCB) Environmental Screening Levels (ESLs, RWQCB, <br /> 2005). The ESLs and PRGs are used to assist defining the extent of any affected soil and <br /> groundwater and also to streamline the human health risk assessment process. The Central <br /> Valley Water Quality Objectives (WQOs) are referenced for determining if affected <br /> groundwater may require additional characterization. The PRGs, ESLs, and WQOs are used <br /> as screening levels to assist defining the extent of affected soil and groundwater, and not to <br /> assess health or ecological risk or to establish cleanup levels. <br /> TPH as diesel (TPHd) was 120 pg/I in B-4 and below the WQOs and ESLs for the other two <br /> boring samples. Benzene, toluene, ethylbenzene, and xylenes (BTEX) results did not exceed <br /> their respective laboratory reporting limits. With the exception of naphthalene at slightly above <br /> the method detection limit (MDL), the polynuclear aromatic hydrocarbons (PAHs) were non <br /> detect and/or below their respective MDLs and environmental screening levels. <br /> Fuel fingerprint analysis was conducted for the three groundwater samples. According to the <br /> chromatogram review, two samples did not contain petroleum hydrocarbon constituents. <br /> Sample B-4 contained 20 pg/I TPH as gasoline (TPHg), minor BTEX constituents, and other <br /> compounds typical of gasoline. <br /> Based on our review, we have the following comments: <br /> • The fuel fingerprint analysis reported low TPHg concentrations (20 Ng/1) in groundwater <br /> sample B-4; San Joaquin Valley crude oil was not reported in the groundwater samples <br /> submitted for fuel fingerprint determination; <br /> • No crude oil-affected soil was observed during the investigation; and, <br /> • Affected groundwater has been adequately defined north of the site by 2007 borings <br /> B-4, B-5, and B-6. <br /> Regional Water Board staff concurs that the affected groundwater at Lyoth Offsite has been <br /> adequately delineated and additional characterization is not needed. <br /> If you have any questions or comments, please contact Dean Hubbard at (559) 445-5179. <br /> Oz (� pwu�:)_ <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> P.G. No. 6357 <br /> cc: Michael J. Infurna, San Joaquin County EHD, Stockton <br /> Michael Jenkins, SAIC, Sacramento <br /> CDKR\commonChev0VP0.yoth Offsite,7MayW Soil/GWrevulJune 07 <br />