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M. Scott Mansholt -2 - 20 September 2006 <br /> Chevron <br /> Vernalis Property <br /> Groundwater samples from two upgradient borings (SB-30 and 36) were ND for TPN <br /> compounds; and the downgradient borings (SB-22, 23 and 25) respectively, reported 780, 560 <br /> and 660 pg/l TPH as diesel DTaPddtoiue� <br /> AnwerrtinB-25sample. Benzene at 0,5 pgne at2.0 pg/l was reported in SB-22; the remaining <br /> TIPH compounds were ND. <br /> Several monitoring wells (not including the onsite monitoring wells) and water supp th the y wells <br /> were identified within the well search area. The monitoring wells are associated wi <br /> Services business, north of the site. The water supply wells are situated up <br /> Western Farm nitary seats generally extending below depths where TPN <br /> id <br /> and/or crossgradient and have sa <br /> compounds have been entified at the subject properties. <br /> Based on our review, we have the following comments: <br /> Affected groundwater at the Bellini site has not been delineated downgradient (east) of <br /> borings SB-23, 24, 25 and MW-7. Additional borings and groundwater sampling and <br /> analysis are needed-, <br /> • The extent of TPH impacted groundwater has not been delineated downgradist) <br /> of the Arcos property, east of Highway 33; additional borings and groundwater sampent (ealing <br /> and analysis are needed; and, <br /> Access at certain areas east of the site has been difficult to obtain; as an alternative, <br /> and as discussed recently with SAIC staff, Chevron plans to proceed and install the <br /> proposed borings within the Highway 33 right-of-way. <br /> Regional Water Board staff concurs with the plan to complete additionaContilngency borings and/or <br /> soil borings <br /> downgradient of the Arcus and Bellini sites as discussed above. <br /> additional downgradient monitoring wells may be required. The revised gnstaled andwater <br /> monitoring should not proceed until the new monitoringlls have nd <br /> developed. at Board staff at least 48 hours in advance of conducting the additional <br /> Please advise Region <br /> drilling, sampling, and field activities. <br /> If you have any questions or comments, please contact Dean Hubbard at (559) 445-5179. <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> PG No. 6357 <br /> cc: Michael Sonke, Stanisiaus County Department of Environmental Resources,o <br /> desto <br /> Michael Infurna, San Joaquin County Environmental Health Department, Stu n <br /> Luis Mercado, SAIC, Sacramento <br />