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Californi egional Water Quality Cool Board <br /> Central Valley Region s- <br /> Karl E. Longley,ScD, P.E.,Chair <br /> Linda S.Adams Arnold <br /> Secreraryfor Sacramento Cordova, <br /> Schwarzenegger <br /> F,'m rro,vnenm/ 11020 Sun Center Drive#200.Rancho Cordova,California 95670-6114 Gowrnor <br /> Protection Phone(916)464-3291 •FAX(916)464.4645 <br /> bttp://"v.waterboards,ca.gov/centrolvalley <br /> 24 March 2008 D (� Q <br /> Mr. Ed Ralston MAR 2 5 2008 <br /> ConocoPhillips <br /> 76 Broadway y <br /> Sacramento, CA 95818 <br /> CLOSURE REPORT, FORMER UNION OIL BULK PLANT NO. 788, 8203 EAST 11TH <br /> STREET, TRACY, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Regional Water <br /> Board) staff reviewed the 13 December 2007 Closure Report (Report) prepared by SECOR <br /> International, Inc. (SECOR) on behalf of ConocoPhillips for the former Union Oil Bulk Plant at <br /> 8203 East 111" Street in Tracy(Site). <br /> Since 1989, Union Oil (now ConocoPhillips) has installed 13soilborings, sampled 13 test pits, <br /> collected 55 soil samples, and installed 10 monitoring wells. In 1993, Site operations ceased, <br /> and ConocoPhillips removed all the tanks and associated piping and structures. Petroleum <br /> hydrocarbons in Site wells have been below water quality objectives since November 2004, <br /> with the exception of total petroleum hydrocarbons as diesel (TPHd). Since that time, TPHd <br /> was detected three times, but the laboratory flagged each of these sample results because the <br /> laboratory control sample surrogate recoveries were not within the established laboratory <br /> control limits. <br /> ConocoPhillips samples two domestic wells (one onsite and one offsite). No petroleum <br /> hydrocarbons have been detected in the onsite well. TPHd was detected in the offsite <br /> domestic well, but the laboratory flagged these detections because the laboratory control <br /> sample surrogate recoveries were not within the established laboratory control limits and the <br /> method blanks contained TPHd. ConocoPhillips resampled the domestic well using a different <br /> laboratory, and no petroleum hydrocarbons were detected. <br /> Our comments are presented below: <br /> 1. ConocoPhillips collected soil samples during well installation and test pit investigation <br /> activities from 1990 to 9994. Soil samples collected from five to six feet below ground <br /> surface (bgs) in borings U-1, U-2, U-5, U-C, and T-11 contained the highest <br /> concentrations of TPHd and TPH as gasoline (TPHg). ConocoPhillips concludes that <br /> any remaining mass of petroleum hydrocarbon in soil would have leached into the <br /> groundwater and be observed in Site monitoring wells. Regional Water Board staff do <br /> not agree. The highest concentrations in soil above the water table exceed the gross <br /> contamination and direct exposure environmental screening levels for TPHg, TPHd, <br /> benzene, ethylbenzene, and xylenes. Therefore, ConocoPhillips needs to drill five soil <br /> borings near U-1, U-2, U-5, U-C, and T-11 and collect two soil samples in each boring. <br /> CaliforniaEnvironmentalProtection Agency <br /> 0 Recy,*,l Paper <br />