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1 <br />' Soil excavation activities at Former Tank Site #1 were initiated on <br /> i15 October 1993 The excavation extended to a depth of approximately <br /> 9 feet with areal dimensions of 25 feet in length and 20 feet in width <br />' (including side slope dimensions) For excavation near the building, <br /> shoring equipment was used to support the building structure Ground <br />' water seepage was encountered at excavation depths below 7 feet Soil <br /> excavation proceeded until mobile laboratory analytical results indicated <br /> that the cleanup goal (100 mg/kg for TPH) was attained at the excavation <br />' sidewalls and bottom or until building structures prevented further <br /> excavation <br />' Prior to backfilling, the saturated bottom of the excavation was stabilized <br /> by placing a 4-foot-thick rock base, consisting of 1- to 2-inch-diameter <br /> rock, over a geotextile fabric liner The remainder of the excavation was <br />' then backfilled with clean fill dirt and compacted using construction <br /> equipment The backfill area was subsequently paved with asphalt cover <br /> Additional Characterization <br />' After the remedial alternative selected for soil (excavation and on-site <br /> aeration) was completed, PHS/EHD expressed concern that the <br />'• hydrocarbon-containing soil at each site may not have been adequately <br /> remediated Specifically, PHS/EHD was concerned that residual <br /> concentrations of hydrocarbon-containing soil could remain in areas <br />' underlying the former excavations and the existing buildings at both <br /> former tank sites In September 1994, Catellus conducted additional soil <br /> sampling within the former excavation footprint and underneath the <br /> existing building The purpose of these activities was to verify that <br /> residual hydrocarbon concentrations, if present in site soils, would not <br /> pose a significant risk to human health and the environment The results <br />' of these additonal characterization actvities were presented in a report <br /> entitled Environmental Conditions Report - 1325 and 1515 West Weber Avenue <br /> - Stockton, California (ERM, July 1995, hereinafter, "Environmental <br /> Conditions Report") <br />' The data collected during this investigation verified the accuracy of the <br /> 1993 excavation confirmation sampling and supported the 1993 <br /> confirmation sampling results that indicated that soils exceeding the TPH <br />' cleanup goal had been excavated Furthermore, the data indicated that <br /> significant volumes of TPH-impacted soils did not appear to be present <br /> beneath the building at Former Tank Site #1 Figure 3-1, which is <br />' reproduced from the July 1995 report, illustrates the TPH concentrations <br /> • detected in soils in the former Tank Site #1 area <br /> 3-3 <br />