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samples Laboratory analyses detected significant concentrations of petroleum hydrocarbons in both samples (TPH as gasoline at 4,000 ppm and 10,000 ppm, benzene at 62 ppm and 41 ppm, toluene at 87 ppm and 430 ppm, ethylbenzene, at 35 ppm and 150 ppm, and xylene at 293 ppm and 850 ppm) 2.4 Site Assessment I Further assessment of contamination at this site was requested by San Joaquin County Public Health Service, Environmental Health Division (PHS/EHD) in October 1990 In February 1993, Mr Harlin Knoll of PHS/EHD required a groundwater investigation ' GeoAudit was retained by Mr Conway to perform this investigation On April 9, 1993, three groundwater monitoring wells and one soil boring were installed ' Soil samples were collected at 5-foot depth intervals, and selected samples were analyzed for total petroleum hydrocarbons (TPH as gasoline), purgeable aromatics (BTE&X) and total lead A soil sample was also collected from the previously excavated soil, which had ' been stockpiled on-site The results of the investigation were reported in the Preliminary Investigation and Evaluation Report (PIER) submitted by GeoAudit in May 1993 All soil samples were reported as non-detect for total petroleum hydrocarbons, but BTE&X compounds were detected in one sample from the soil boring The monitoringwells were surveyed on April 14, 1993 and the depth to groundwater was Y P measured in each well Water samples were collected and analyzed for TPH as gasoline and BTE&X I Toluene was detected at a concentration of 0 39 µg/L (ppb) in the most down-gradient well (MW-3) No contaminants were detected in the samples from MW-1 or MW-2 The groundwater gradient was determined to be northeast On May 26-27, 1993, the tank cavity was overexcavated to remove the residual contamination The excavation was extended to approximately 17 by 20 feet and deepened I to approximately 20 feet Approximately 250 cubic yards of soil were removed and stockpiled adjacent to the excavation Excavated soil was monitored using a PID and placed into contaminated and non-contaminated stockpiles When excavation was completed, four soil samples were collected from the sidewalls and the bottom of the excavation using the backhoe bucket and analyzed for TPH as gasohne and BTE&X TPH as gasoline was detected in the sample from the west sidewall of the excavation at a concentration of 17 ppm No other contaminants were detected in the samples collected from the excavation Non-contaminated soil from the top five feet of the excavation was placed back into the tank pit on July 10, 1993 p...wrl,R".M2 Mss s