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OVER-EXCAVATION AND DOCUMENTATION SAMPLING Upon removal and sampling of the existing double contained fiberglass piping system, it was discovered that older abandoned steel piping still existed beneath the dispenser areas The old piping system was inspected and removed on February 25, 2000 Letitia Bi eggs, Senior Registeied Environmental Health Specialist, Public Health Services, San Joaquin County (PHS-SJC) noted obvious soil contamination beneath the southernmost and south central dispenses areas and directed confirmation sampling for documentation (samples SBI, SB2, SB3, SB4 SB5 and S135), see Table 1, Figure 6 Appendix B —Laboiatory Reports and Appendix C —Field Notes Western Geo-Engineers, updated the Risk Base Corrective Action Tiet 2 (RBCA Tier 2) modeling based on the above obtained soil samples, Appendix D The main concern was leachability to gioundwatei from soil contaminants (gasoline range hydrocarbons) left in place The RBCA Tiei 2 indicated that the following concentrations in soils could remain, Benzene at 0 011 mc,/Kg, Toluene at 6 6 ing/Kg, Ethyl Benzene @ 2 4 mg/Kg and MTBE at 0 22 mg/Kg Xylenes risk based target concentration is greater than constituent residual saturation value Ovei-excavationwas directed by Mr Michael Infurna of PHS-SJC, pre-approval had been obtained from the State Water Resources Control Board, see Appendix A Over-excavation occurred in three areas the southernmost dispenser area (PIT 1) at sample point PL-6 (PIT 2) and the southern middle dispenser area (PIT 3) FIELD SCREENING OF SOILS EXPOSED IN THE OVER-EXCAVATION AREAS ASSOCIATED WITH THE PRODUCT DISPENSING SYSTEM EXCAVATIONS Upon removal of the product dispensing piping the native soils were field screened using a photo- ionizing detector (PID) with a 10 2 ev bulb Once the PID showed no responses, approximately 20 grams of that soil was placed into a 40 cc VOA vial, capped and Heated on a hot plate to volatilize any petroleum hydrocarbons that still may exist in the soils A 0 5 cc sainple of the headspace of the soil san-ipte was then obtained and injected into a field gas chromatograph with a 10 2 ev PID The responding gas chromatogram was then compared to a standard chromatogram which contained 10 mg/I. degraded gasoline and 0 05 mg/L benzene Based on this field scieening a decision was made if further excavating was needed or confirmation samples were obtained This detector is sensitive to volatile organic compounds that have an electron potential of of less than 102 ev Gasoline vapors ate readily detected with this detector and it is the preferred field- screening instrument for soils at suspected gasoline-contannrnated sites PIT I Em,avating of the southernmost dispenser area commenced on March 1, 2000, based primarily on sample South Dispenser which contained 86 mg/Kg TPHg and 0 053 mg/Kg Benzene or 5 tine the amount that was predicted could be left in place and secondary on odor and visual staining An estitnatud 24 yards of gasoline contaminated soils (PIT 1) was removed and placed on plastic liner foi later removal and disposal In the process of excavating the gasoline-contaminated soils from Pit 1, the footing supporting the canopy was exposed, see Figure 7 Neil 0 Anderson (ROE 2245) R-603 over-ex 4-2000