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E T TL ER YA N INC. May 3,2001 i Mr.Nick Nickerson Unocal-DBGIAMG 8788 Elk Grove Boulevard Building 3, Suite 15 Elk Grove,CA 95624 Subject: Review of Monitoring Data from Former Unocal Service Station#0123,1034 Central Avenue, Tracy,CA. Mr.Nickerson: I have reviewed the data from the first quarter 2001 and previous monitoring and sampling events for the subject site. Groundwater levels dropped an average of 0.30 feet from levels measured during the fourth quarter 2000. These levels are within the historical fluctuation range. During the first quarter 2000 groundwater flow was toward the north- northwest at a gradient of 0.003. These groundwater data are consistent with the historical record. Low concentrations of benzene and Total Petroleum Hydrocarbons as gasoline(TPHg)and as diesel(TPHd)continue to be detected in on-site monitoring well U-4,situated in the source area. However,these concentrations are very low, and continue to show a declining trend. Low concentrations of T?Hd were also detected in wells U-1,U-2 and U-6. Very low concentrations of TPHg,toluene,ethylbenzene and xylenes were detected in well U-1,and ethylbenzene was detected in well U4. MtBE was not detected in any of the monitoring wells this quarter.Hydrocarbon concentrations and distribution detected during the first quarter 2001 are consistent with historical data. Since this station ceased operation in the early 1960s,the historical presence of MtBE suggests at least some of the dissolved hydrocarbons detected in the groundwater beneath they site are due to an off-site source. The presence of chlorinated hydrocarbons in all site wells also indicates the presence beneath the subject site of hydrocarbons from an off-site source. Historical analytical data indicate the dissolved plume is defined and stable.Based on these data and conclusions,the site appears to be of low risk. GR has submitted a Request for Closure report(GR Report No.24 073.06,dated April 19,200 1)to San Joaquin County Environmental Health Division(SJCEHD)and the California Regional Water Quality Control Board(CRWQCB). GR requests that quarterly monitoring and sampling be suspended pending regulatory response to the Request for Closure. Please call us at 916.631.1300 if you have quDG 0" Sincerely, J. C i Gettler-Ra n cc i9 Stephen J.Carter W S ! �r Senior Geologist R.G. 5577 'SOF CAL�F�� Attachment: First Quarter 2001 Groundwater m oring&Sampling Report,G-R Job#280047 dated April 19,2001. cc: Mr.Mike Infuma,San Joaquin County Department of Environmental Health' Kimberly Ayers and Leesa Ward,Ayers&Ward Real Estate Investment Services, 1034 Central Avenue,Tracy, CA 95376(without attachment) 6747 Sierra Court , Suite J - Dublin , California 94568 ( 925 ) 551 -7555 240073.01