SITE INFORMATION AND CORRESPONDENCE_FILE 1

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�r NNW Chevmn Chevron U.S.A. Inc. 2410 Camino Ramon, San Ramon, California•Phone(415)842-9500 Mail Address:P.O.Box 5004,San Ramon,CA 94583-0804 Marketing Department March 1, 1991 Mr. Steve Schneider San Joaquin County Environmental Health r� P.O. Box 2009 _ Stockton, CA 95201 MAR 8 4'^ R Re: Chevron S.S. #9-6171 .' ,-NMEN 6633 Pacific Avenue, Stockton, CA r-LLRWT/SE" Dear Mr. Schneider. Enclosed is a quarterly monitoring report dated December 20, 1990 which describes groundwater sampling by Chevron's consultant, Sierra Environmental (SE), on November 29, 1990 at the site referenced above. As requested in your letter to Mr. Clint Rogers of Chevron dated January 3, 1991, a report has also been enclosed which documents sampling of MW 1 on June 4, 1988 by Chevron's consultant, Groundwater Technology (GTI). Subsequent attempts to sample MW-1 on 12/5/89, 3/13/90, 9/5/90, and 11/29/90 were unsuccessful as the well was dry. This information is included in Table 2 of Sierra Environmental's December 20, 1991 report. As requested by San Joaquin County, a groundwater sample from MW-4 was analyzed for fecal coliform. Fecal coliform was not detected above the detection limit of 2 MPN/100 ml. Analysis of a sample from MW-4 by EPA Method 8015 was reported by Superior Analytical Laboratory(SAL)as a non-gasoline pattern(possible solvent peak)at 150 parts per billion (ppb). A sample from this well the previous quarter had been reported by SAL as having a non-gasoline pattern present below the practical quantitation limit(PQL)of 50 ppb from EPA Method 8015. A copy of the chromatograph was sent to the Chevron Research and Technology Center(CRTC) in Richmond, California. CRTC chemist Elizabeth Harvey evaluated the chromatograph and interpreted the compounds observed to be solvents. A copy of Ms. Harvey's interpretation is enclosed. Ms. Harvey also commented on the reported 0.5 ppb toluene in the bailer blank. She suggested this was due to SAL rounding the calculation result off to one significant figure. As speculated in Ms. Harvey's letter, the two solvents which were detected in the sample from MW-4 were probably the same two solvents detected in water samples from MW-5, namely TCE and 1,2-DCA. This would concur with Chevron's understanding that the groundwater investigation of two nearby dry cleaners has detected TCE,although Chevron's information on the nearby dry cleaners' investigation is very limited. In an effort to share data, Chevron's consultant, SE, has tried unsuccessfully to this point to contact the consulting firm working on the nearby dry cleaners' investigation. Chevron plans to continue monitoring the wells at this site on a quarterly basis. If you have any questions or comments, please contact Clint Rogers at(415) 842-8658.