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' In February 1993, IT installed six off-site soil borings to examine the extent of petroleum <br /> hydrocarbon migration from the site. Analysis of soil samples from these boreholes revealed <br /> no detectable petroleum hydrocarbons. Analysis of groundwater samples, collected from the <br /> boreholes, revealed no detectable diesel concentrations. No detectable volatile hydrocarbons <br /> were encountered in the groundwater samples collected from borings SB-1 through SB-4 and <br /> SB-6 upon analysis. The water sample collected from SB-5 revealed 0.8 ppb toluene only, <br /> upon analysis. <br />' In March 1993, IT submitted an "Offsite Investigation Report' to San Joaquin County Public <br /> Health Services (SJCPHS), Environmental Health Division, requesting site closure. At this <br /> time, quarterly monitoring activities were halted, pending data evaluation by the regulatory <br /> agency. In a letter dated June 1, 1993, SJCPHS representatives requested further investigation <br /> of soil quality beneath the site building. <br /> Quarterly monitoring activities were resumed in July 1993. Upon analysis, no detectable <br /> concentrations of petroleum hydrocarbons have been encountered in the samples collected <br /> during the July 1993, October 1993, and January 1994 sampling events. <br /> In November 1993, three 25,000 gallon diesel USTs were removed from beneath the Lindsay <br /> Street sidewalk (adjacent to the Pacific Bell facilities north wall) by representatives of <br /> Aronson Engineering Incorporated. Soil samples were collected from the excavation by <br /> representatives of Riedel Environmental Services Incorporated, which revealed detectable <br /> concentrations of diesel fuel (near the west end of the middle tank) upon analysis. No <br /> detectable BTEX constituents were encountered in any of the samples. <br /> Over excavation efforts were conducted on November 11, 1993 which extended the <br /> excavation to 17.5 feet below grade. A series of confirmatory soil samples were collected <br /> from the excavation. Upon analysis, detectable diesel concentrations (up to-8300 ppm) were <br />' encountered between 20 and 27.5 feet below grade near the west end of the middle tank. No <br /> detectable BTEX concentrations were encountered. <br /> 1 <br /> MZ05-10-94/UST/94-"2.nbr 1-3 <br />