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California Ronal Water Quality Contr oard <br /> Central Valley Region <br /> Katherine Hart Chair <br /> Arnold <br /> 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Schwarzenegger <br /> Phone(916)464-3291 •FAX(916)464-4645 Governor _ <br /> btip.//www waterboards.ca.eov/centralvalley <br /> 23 July 2010LU10 <br /> JUL 2 S <br /> ENPERM� E�VICES H <br /> Mr. Ed Ralston <br /> ConocoPhillips <br /> 76 Broadway <br /> Sacramento, CA 95818 <br /> SOIL GAS RE-SAMPLING REPORT, FORMER UNION OIL BULK PLANT NO. 788, <br /> 8203 EAST 11'" STREET, TRACY, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 30 June 2010 Soil Gas Re-Sampling Report (Report) prepared by <br /> Stantec Consulting Corporation (Stantec) on behalf of ConocoPhillips for the former Union Oil <br /> 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. In the first half of 2009, ConocoPhillips properly abandoned all Site <br /> monitoring wells, excavated contaminated soil to depths of up to 10 feet below ground surface <br /> (bgs), installed five temporary soil gas vapor probes, and collected soil gas samples. <br /> On 16 June 2010, ConocoPhillips installed temporary soil gas sampling point SG-11 near <br /> previous sample SG-8. The soil gas sample from SG-8 contained petroleum hydrocarbons <br /> above the California Regional Water Quality Control Board, San Francisco Bay Region <br /> Environmental Screening Level (ESL) for commercial/industrial and residential land use. Thus, <br /> Central Valley Water Board staff requested ConocoPhillips to collect an additional sample in this <br /> location. The soil gas sample collected at SG-11 contained total petroleum hydrocarbons as <br /> gasoline (TPHg) at 100,000 micrograms per cubic meter. This concentration is above the ESL. <br /> SG-8 and SG-11 are about 20 feet east of the excavation and near an area of remaining soil <br /> concentrations. <br /> Our comments are presented below: <br /> 1. Central Valley Water Board staff concurs with ConocoPhillips' recommendation to <br /> conduct a limited excavation in the area of SG-8 and SG-11 to remove remaining soil <br /> contamination. <br /> 2. ConocoPhillips rreeds tocollectconfirmation soil samples from the floor and sidewalls of <br /> the excavation prior to backfilling and analyze them for petroleum hydrocarbons. <br /> California Environmental Protection Agency <br /> p�dRerycled Paper <br />