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California Re ional Water Quality Control Board <br /> ' <br /> `- Central Valley Region <br /> v Karl E.Longley,ScD,P.E.,Chair <br /> Arnold <br /> Linda S.Adams <br /> 11020 Sun Center Drive 9200,Rancho Cordova,California 95670-6114 Schwarzenegger <br /> Secreraryfor Phone(916)464-3291 •FAX(916)464-4645 <br /> Environmental http://www.waterboards.ca.gov/centralvalley Governor <br /> Prorection �Ir1r-��- 'l/�,,Ih���-- \�/�I�—� <br /> IJ II IAV E� V IF DD <br /> 28 August 2009 <br /> AUG 3 1 2009 <br /> Mr. Ed Ralston ENVIR014NIENT HEALTH <br /> ConocoPhillips PERMITISERVICES <br /> 76 Broadway <br /> Sacramento, CA 95818 <br /> CLOSURE ASSESSMENT ACTIVITIES REPORT, FORMER UNION OIL BULK PLANT <br /> NO, 788, 8203 EAST 11TH STREET, TRACY, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 30 July 2009 Closure Assessment Activities Report (Report) prepared <br /> by Stantec Consulting Corporation (Stantec) on behalf of ConocoPhillips for the former Union <br /> Oil Bulk Plant at 8203 East 11th Street in Tracy (Site). <br /> The Site is a former bulk fuel storage facility in the City of Tracy. In 1993, Site operations <br /> ceased, and all the tanks and associated piping and structures were removed. The Site is <br /> currently vacant and no longer in use. Since 1989, Union Oil (now ConocoPhillips) has installed <br /> 13 soil borings, sampled 13 test pits, collected 55 soil samples, and installed and sampled <br /> 10 monitoring wells. <br /> The Report summarizes ConocoPhillips' activities to address the remaining Central Valley <br /> Water Board staff concerns prior to Site closure. In March 2009, ConocoPhillips properly <br /> abandoned all Site monitoring wells prior to Site excavation. In May 2009, ConocoPhillips <br /> excavated contaminated soil to depths of up to 10 feet below ground surface (bgs). The <br /> excavation continued laterally until all visually contaminated soil was removed. ConocoPhillips <br /> collected floor and sidewall samples from the excavation. The maximum remaining soil <br /> concentrations of total petroleum hydrocarbons as gasoline (TPHg) and TPH as diesel (TPHd) <br /> were 3.8 milligrams per kilogram (mg/kg) and 79 mg/kg, respectively. <br /> In June 2009, ConocoPhillips installed five temporary soil gas vapor probes and collected soil <br /> gas samples. TPHg was detected in all five samples at a maximum concentration of <br /> 6,300,000 micrograms per cubic meter (Ng/m). Soil gas samples near the excavation area <br /> contained the maximum concentrations. TPHg was detected in the two samples collected near <br /> the warehouse at concentrations of 14,000 ug/m3 and 12,000 ug/m3, which are above the <br /> California Regional Water Quality Control Board — San Francisco Region Environmental <br /> Screening Level (ESL) for residential land use of 10,000 Ng/m3. These concentrations are <br /> below the commercial/industrial land use ESL of 29,000 Ng/m3. <br /> Central Valley Water Board staff concurs with ConocoPhillips' recommendation to resample the <br /> soil gas locations. The two soil vapor samples near the onsite warehouse were above the <br /> residential ESLs and the three soil vapor samples near the excavation were above both the <br /> California Environmental Protection Agency <br /> Cd4ecycled Paper <br />