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California Ogional Water Quality Cool Board ,4 <br /> Central Valley Region :I) <br /> Katherine Hart, Chair <br /> 11020 Sun Center Drive,#200,Rancho Cordova,California 95670-6114 <br /> Linda S.Adams (916)464-3291 •FAX(916)4644645 ^p—,ry ��p�I�Brown Jr. <br /> Acting Secretary for . http://www.waterboards.ca.gov/centralvalley ,Ki i!�Yi# EI�/�--r�",�rnor <br /> Environmental Protection 1� V ``YJ <br /> 0 7 2011 <br /> 5 April 2011 <br /> ENVIRONMENTAL HEALTH <br /> PERMIT/SERVICES <br /> DESJC, M.BENSON <br /> Defense Distribution Depot San Joaquin <br /> P.O. Box 960001 <br /> Stockton, CA 95296 <br /> DRAFT— RESULTS OF VAPOR INTRUSION MODELING TECHNICAL MEMORANDUM <br /> BUILDING 255/UST 25, DEFENSE DISTRIBUTION DEPOT SAN JOAQUIN TRACY SITE, <br /> SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff has reviewed the 16 August 2010 Draft— Results of Vapor Intrusion Modeling <br /> Technical Memorandum Building 255/UST 25 (draft memorandum), received 17 August 2010. <br /> HDR I e 2 prepared the Draft Memorandum on behalf of Defense Logistics Agency Enterprise <br /> Support San Joaquin, California (DLA) for the Defense Distribution Depot San Joaquin facility <br /> located in Tracy, California. <br /> The draft memorandum summarizes the results of modeling to estimate the risk of vapor <br /> migration to indoor air from petroleum hydrocarbon, volatile organic compound (VOC), and <br /> semi-VOC contaminants in soil and groundwater beneath Building 255. Maximum laboratory <br /> chemical analyses results on samples collected in February and May 2010 were input into the <br /> Johnson and Ettinger model. The excess cancer risk and non-cancer impacts from exposure <br /> were estimated. <br /> The results of the DLA human health risk assessment modeling for vapor intrusion found an <br /> excess cancer risk from exposure to VOCs and diesel-range TPH in soil of 5.8x10-9 and from <br /> groundwater of 3.33x10"6, for a cumulative excess cancer risk of 3.91x10-6. The resulting <br /> hazard quotient for vapor intrusion from soil was 9.37x10-1 and from groundwater was <br /> 5.38x10-1, for a cumulative hazard quotient of 1.47. <br /> Background <br /> DLA installed Underground Storage Tank 25 (UST 25) before 1982 in the south courtyard of <br /> Building 255 at the Tracy facility. The 500-gallon UST was used to store fuel oil to heat the <br /> building. In 1988, DLA removed the UST and excavated and disposed of an unknown volume <br /> of contaminated soil. At the time it was removed, only one soil sample was collected at an <br /> unspecified depth from beneath the tank location. Laboratory chemical analysis on the sample <br /> detected diesel-range total petroleum hydrocarbon (TPH) at a concentration of <br /> 26,000 milligrams per kilogram (mg/kg). <br /> In 1993, DLA collected soil and groundwater samples from borings within the former UST <br /> excavation and performed laboratory chemical analyses. The maximum concentration of <br /> California Environmental Protection Agency <br /> �aRecycled Paper <br />