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1 <br /> concentrations Well MW7 had high initial dissolved levels (7,100 ug/l benzene) which <br /> have decreased with time to lower levels (generally <10 ug/I benzene) Further details on <br /> the results of the first phase of investigation are presented in Thrifty's report dated June <br /> 13, 1994 Results of quarterly groundwater sampling are provided in the Quarterly Status <br /> Reports that are submitted to PHS/EHD <br /> Shortly after this field investigation was conducted, the site was scheduled for <br /> reconstruction The reconstruction effort includes removal of the tanks, replacement with <br /> new fiberglass tanks and construction of a new market in the southwest corner of the site <br /> Because many of the existing wells are located in these areas and could have been <br /> destroyed during construction, PHS/EHD requested that six wells be properly abandoned <br /> prior to construction At the writing of this report, the well abandonment has been <br /> completed and the tanks have been removed and replaced <br /> GEOLOGY <br /> The site is located in the San Joaquin Valley of the Central Valley geomorphic province Holocene age <br /> flood-basin deposits extend from the ground surface to a maximum depth of about 100 feet below the <br /> site Oligocene to Holocene age alluvial deposits lie below the younger flood-basin deposits to a <br /> maximum depth of about 3,500 feet below grade Continental and marine rocks of pre-Tertiary to <br /> Oligocene age underlie the alluvial deposits, and are composed of shale, sandstone and conglomerate <br /> Crystalline bedrock underlies the sedimentary formations <br /> Based on boring logs recorded during drilling activities, the hthologic section beneath the site generally <br /> consists of interbedded silty clay, silt and silty sand to about 45 feet below grade These fine grained <br /> units are underlain by sand and silty sand to at least 75 feet below grade, the deepest interval explored <br /> by drilling Descriptions of these sediments are presented in the drilling logs, attached as Appendix A <br /> Figure 3 is a geologic cross-section showing the generalized lithologic relationships <br /> Page 3 <br />