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California 4-gional Water Quality Coi_ A Board <br /> Central Valley Region <br /> J <br /> Karl E. Longley,ScD,P.E., Chair <br /> Linda S.Adams Arnold <br /> Secretaryfor Sacramento Main Office ^ i Arnold <br /> 11020 Sun Center Drive#200,Rancho Co iFOta'y ��lrt <br /> Envrro coon l �m, t� Governor <br /> Protection Phone(916)464-3291 •FA l� '�6�" - <br /> http://www.waterboards.ca.gov/centralvalley <br /> O C i - t 2007 <br /> ENVIRON A[-N, T HEA0H <br /> 25 September 2007 PEWi1T"SERVICES <br /> Mr. Jeff Whitworth <br /> Shell Oil Products US <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> REVIEW OF SOIL VAPOR SAMPLING WORK PLAN, MOUNTAIN HOUSE <br /> NEIGHBORHOOD B, FORMER SHELL CENTRAL VALLEY CRUDE OIL PIPELINES, <br /> TRACY, SAN JOAQUIN COUNTY <br /> Staff of the Regional Water Quality Control Board, Central Valley Region (Regional Water <br /> Board) has reviewed the 15 August 2007 Soil-Vapor Sampling and Analysis Work Plan, <br /> Mountain House Neighborhood B (Soil Vapor Work Plan) submitted by Science Applications <br /> International Corporation (SAIC) on behalf of Shell Oil Products US (Shell). The Soil Vapor <br /> Work Plan proposes the collection and analysis of soil vapor samples in remedial soil <br /> excavation areas at the former location of Shell crude oil pipelines within the planned <br /> Mountain House Neighborhood B residential development in Tracy. Data collected during the <br /> investigation will be used to evaluate the risk to indoor air from organic vapor intrusion <br /> following property development. <br /> Shell proposes to collect soil vapor samples along the trace of the former crude oil pipeline to <br /> evaluate the risk of vapor migration to indoor air following site development. Previous <br /> investigations have identified the presence of Total Petroleum Hydrocarbons as diesel and <br /> motor oil (TPHd and TPHmo) and benzene, toluene, ethylbenzene, and xylenes (BTEX) in soil <br /> and groundwater at the site. Soil vapor sampling is proposed at 12 locations in six remedial <br /> soil excavation areas, designated as Areas B2, B3, B6, B8, B9, and B12. Sampling is <br /> proposed at two locations in each area, one boring within the excavation and a second boring <br /> in the inferred downgradient direction Northeast of the excavation. Direct push equipment will <br /> be used to advance temporary vapor probes to the desired depth. Vapor samples will be <br /> collected within the backfilled excavations from approximately 1 foot below the base of the <br /> excavation between 11 and 31 feet below ground surface (bgs). In addition, vertical profile <br /> vapor samples will be collected at 5 feet, 10 feet, and 15 feet bgs at one location northeast of <br /> each excavation area. If sample collection within an excavation area is not possible due to <br /> penetration refusal or high moisture content, the sample location will be abandoned. Shell <br /> plans to collect a total of 24 vapor samples. <br /> Soil vapor sampling methodology will follow guidance provided in the 2003 Advisory—Active <br /> Soil Gas Investigations published by the Los Angeles Regional Water Quality Control Board <br /> and the 2005 Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to <br /> California Environmental Protection Agency <br /> �Ci'Recycled Paper <br />