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�. <br /> ET �TLERRYAIN: <br /> October 26, 1999 <br /> -Mr. Bob Boust <br /> Unocal Corporation DBG/AMG = <br /> 2121 North California Boulevard, Suite 250 <br /> Walnut Creek,-CA 94596 . <br /> •'Subieet: Third Quarter 1999 Monitoring and Sampling Report forthe Former Unocal Station#0123, <br /> 1034 Central-Avenue;Tracy, CA. <br /> .-Mr. Boust: <br /> At your request,Gettler-Ryan Inc.prepared these coriclusio and recommendations for the subject site.after - <br /> review of the referenced monitoring data. The former statioceased operation'in.1962. Ali`subsurface and <br /> aboveground facilities have been removed except for one ST at the.northern property boundary that was <br /> abandoned in place. The site is currently an asphalt paved parking lot. <br /> Groundwater monitoring and sampling-has occurred quarterly since June 1995. Data from the third.quarter <br /> 1999 appears consistent,with historical data. The d.issolve� hydrocarbon plume appears to be stalile, and <br /> given the .northerly groundwater, flow direction, 'the.plume appears .adequately defined: •Significant <br /> concentrations of dissolved hydrocarbons are detected only inwell MW-4, situated-in the vicinity of the'. <br /> former UST-that was abandoned in place. Since Unocal ha' not operated a service station at this site since <br /> 1962,the low concentrations of MtBE detected during previous sampling events is from another source. The-F . <br /> data collected to date.iindicate that this site is a`low risk"s te.and should be closed. <br /> It is our understanding that prior-,to considering the site for closure,the San Joaquin County Public Health' <br /> Services-Environmental Health Division (SJCPHS-EHD) equested.that additional groundwater data be <br /> collected northwest of the site,downgradient of well U-1 and U-4. A Work_Plan for this scope of work has <br /> been submitted (GR Rcport:No.•240073.03; Work Plan �or Additional Subsurface Assessment, dated <br /> October 5, 1999)..SJCPHS-EHD approval'of the Work har-was received on October 22, 1999: Following <br /> completion of the proposed scope of work the site should Ue evaluated for closure as a"low risk"site.' <br /> If you.have questions, please,call us in Sacra nto: 916. 31.1300.01 . <br /> -.Sincerely, <br /> - <br /> y <br /> Stephen.J. Ca4r <br /> No.5571 ;? <br /> Senior Geologist; N>, <br /> .. R G: 5,577 9rFpfi . <br /> C.. <br /> Attachment: GR's-.Groundwater Monitoring and Sam ling Report,,Third Quarter 1999 Event of <br /> September 9;.1999. <br /> 6"747 Sierra Court; Suite J Dublin , C =1ifo-rnid 94568- {'925 } , 551.7555 <br />