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1 <br /> 1 <br /> Division (PHS/EHD) in October 1990 . In February 1993 , Mr. Harlan <br /> Knoll of PHS/EHD required a groundwater investigation. GeoAudit was <br />' retained by Mr. Conway to perform this investigation. <br /> On April 9, 1993 , three groundwater monitoring wells and one soil <br />' boring were installed. Soni samples were collected at 5-foot depth <br /> intervals, and selected samples were analyzed for total petroleum <br /> hydrocarbons (TPH as gasoline) , purgeable aromatics (BTE&X) and <br /> total lead. A soil sample was also collected from the previously <br />' excavated soil, which had been stockpiled on-site. <br /> The results of the investigation were reported in the Preliminary <br />' Investigation and Evaluation Report (PIER) submitted by GeoAudit in <br /> May 1993 . All soil samples were reported as non-detect for total <br /> petroleum hydrocarbons, but BTE&X compounds were detected in one <br />' sample from the soil boring. <br /> The monitoring wells were surveyed on April 14 , 1993 and the depth <br /> to groundwater was measured in each well. Water samples were <br />' collected and analyzed for TPH as gasoline and BTE&X. <br /> Toluene was detected at a concentration of 0. 39 µg/L (ppb) in the <br /> most down-gradient well (MW-3) . No contaminants were detected in <br /> the samples from MW-1 or MW-2 . GeoAudit recommended that the wells <br /> be monitored within 90 days, and that the remaining soil <br /> contamination be removed by further excavation. An interim work <br /> plan for these tasks was submitted in May 1993 . <br /> 3. 0 PROCEDURES <br /> 3. 1 Overexcavation <br /> In order to remove the residual contamination, a backhoe was used <br /> to overexcavate the tank cavity on May 26, 1993 . The backhoe and <br /> operator were supplied by Helmick and Lerner of Sacramento, <br /> California. A photoionization detector (PID) was used to monitor <br /> contamination levels during excavation and direct the backhoe. The <br /> excavation was approximately 15 by 15 feet and deepened to <br /> approximately 16 ft, the maximum depth reachable by backhoe from <br /> the surface. <br /> Excavation continued on May 27 . A stepdown was made to allow the <br /> backhoe to reach to greater depths. The excavation was extended to <br /> approximately 17 by 20 feet and deepened to approximately 20 feet. <br /> I Approximately 250 cubic yards of soil were removed from the <br /> excavation. A PID was used to screen the soil and segregate <br /> contaminated soil from uncontaminated soil. Contaminated soil was <br /> stockpiled adjacent to the tank cavity and covered with plastic. <br /> The uncontaminated soil was returned to the excavation on July 10, <br /> 1993 . <br /> 2 <br />