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San Joaquin County DIRECTOR <br /> .C,.OG Environmental Health Department Donna Heran, REHS <br /> ASSISTANT DIRECTOR <br /> Z 600 East Main Street Laurie Cotulla, REHS <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> ' — — Carl Borgman,REHS <br /> Mike Huggins, REHS. RDI <br /> Website: www.sjgov.org/ehd Margaret Lagorio, REHS <br /> Phone: (209) 468-3420 Robert McClellon, REHS <br /> Fax: (209) 464-0138 Jeff Carruesco, REHS, RDI <br /> DEC 2 4 2007 Kasey Foley. RENS <br /> STEPHANIE FURGAL <br /> CHEVRON ENV MGMT COMPANY CHRISTINE CORONEO <br /> 6001 BOLLINGER CANYON RD SUTTER OFFICE CENTER <br /> ROOM K2240 2001 UNION STREET #300 <br /> SAN RAMON CA 94583 SAN FRANCISCO CA 94123 <br /> RE: Former Chevron Station 9-8227 SITE CODE: 9327 <br /> Sutter Office Center <br /> 242 Sutter Street <br /> Stockton CA 95202 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed <br /> Supplemental Assessment Work Plan (Work Plan) dated November 26, 2007, <br /> submitted on your behalf by Arcadis BBL (Arcadis) and has the following <br /> comments. <br /> In this Work Plan, Arcadis proposes to continue the investigation of the vertical <br /> and lateral extent of the contamination to both soil and water with the installation of <br /> one soil boring for collection of soil and grab groundwater samples, and by <br /> incorporating the sampling results from the wells of a neighboring site in your site <br /> conceptual model. <br /> The proposed boring will be completed by rota-sonic drilling method, which utilizes <br /> a dual casing technique to advance the boring to depth. Proposed total depth of <br /> this boring is 150 feet below surface grade (bsg); groundwater samples will be <br /> collected at 125 feet bsg and 150 feet bsg during the drilling of the borehole. <br /> Arcadis states "groundwater samples collected during an upcoming monitoring <br /> event from downgradient monitoring wells U-7, U-8 and U-10 (associated with <br /> former Unocal service station #0187) will be analyzed for total petroleum <br /> hydrocarbons as diesel (TPH-DRO)". Arcadis did not provide construction details <br /> of these wells, or a map showing all their locations. This information is required to <br /> properly integrate the data into your site conceptual model. <br /> SJC/EHD approves the installation of the proposed boring and collection of soil <br /> and groundwater samples for investigation of the vertical extent of the <br /> contamination. However, deep screened monitoring wells may still be necessary. <br />