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TANK CLOSURE REPORT—BEACON #610 -3- 3300 Waterloo Road, Stockton, CA AMV Project No 19042 01 4.0 OVEREXCAVATION AND ADDITIONAL SOIL SAMPLING Based on field observations made on October 14, 1993, a decision to overexcavate soil beneath the former USTs was made. The site was visited again on October 18, 1993, to perform the overexcavation Soil samples were collected in various locations as agreed upon by Mr. Earnest and Ms. Mary Maeys of San Joaquin County (Figures 4 and 5). The overexcavation was performed by Walton Engineering. Soil samples were collected from locations selected to assess the vertical and horizontal extent of hydrocarbon constituents in the soil underlying the site Samples collected from the southwest end of the tank basin were collected from depths of 16 to 33 feet below grade (Figure 5). The soil samples were submitted to a California -certified laboratory for analysis of BTEX, TPHg, and TPHd Analytical results from the October 18, 1993, sampling event are compiled in Table 3. Copies of certified analytical reports are presented in Appendix B Soil samples TB3-C, TB4-D, TBS -E, TB6-F, TB7-G, and TB8-H did not contain detectable concentrations of TPHg and contained less than 10 mg/kg TPHd Other soil samples contained between 19 and 2,400 mg/kg TPHg. Diesel was present at concentrations up to 7,400 mg/kg at depths ranging to 33 feet below grade 5.0 STOCKPILED SOIL Soil that was removed during excavation of the tanks and product lines was stockpiled on site Approximately 900 cubic yards of soil was generated on October 13, 14, and 18, 1993 Three hundred cubic yards of soil were excavated before the underground storage tank removal (overburden), and approximately 600 cubic yards were removed during the overexcavation of the tank pit and the former pump islands Four soil samples for every 50 cubic yards of stockpiled soil were collected (unless otherwise required for disposal) for analysis of BTEX, TPHg, and TPHd The two composite soil samples containing the highest concentrations of petroleum hydrocarbons as gasoline were submitted for analysis of total and organic lead Analysis of samples collected from stockpiled soil on October 13, 1993, indicated the presence of TPHg at concentrations ranging from less than 10 to 4 5 milligrams per kilogram (mg/kg) and TPHd at concentrations ranging from 28 to 940 mg/kg Analytical results are compiled in Table 4. Soil samples collected from stockpiled soil on October 14, 1993 (Table 4), contained TPHg concentrations ranging from 110 to 200 mg/kg Soil samples collected from stockpiled soil on October 18, 1993 (Table 4) contained TPHg concentrations ranging from 100 to 430 mg/kg Soil samples SP4 and SP5 were analyzed for total lead and organic lead Soil samples SP8 and SP9 were analyzed for total lead and EDB RPT016 ECD