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Groundwater was encountered in Geoprobe soil borings from approximately 27 to 32 feet bgs. ` Groundwater was encountered in wells MWA through MW-3 at a depth of approximately 30 feet �.. bgs. s 5.9 Zone of influence calculated and assumptions used for subsurface remediation system and the zone of capture attained for the soil and groundwater remediation system. Remedial systems have not been employed at this site. LW 5.10 Reports/Information: Unauthorized release form, QMRs, PAR, FRP, other, well and boring logs. An unauthorized release report was issued to the PHSSJC-EHD on March 16, 1999. A copy of the � unauthorized release report is presented in Appendix B. Copies of well and boring logs are presented in Appendix C. 5.11 Best Available Technology (BAT) used or an explanation for not using BAT. Based on the low concentrations of diesel fuel detected in the groundwater, the limited area of L, impact, and the slow rate of migration of the impacted groundwater, no remedial efforts were attempted on the groundwater. Impacted soil in the immediate vicinity of the UST was excavated and removed to a depth of 16 feet bgs following removal of the UST. The excavation was not +.. made deeper to the presence of a Iarge concrete slab that had been poured in place prior to installation of the UST. Approximately 371 tons of diesel fuel-impacted soil were transported to the BFI Livermore, California landfill for disposal on March 23, 1999. 5.12 Reasons why "background"was/is unattainable using BAT. Background concentrations of diesel fuel in the soil and groundwater were established at non- detectable levels. 5.13 Mass balance calculation of substance treated versus that remaining. Approximately 255 cubic yards (382 tons) of diesel fuel impacted soil are estimated to remain in 4 place beneath the former UST location. Diesel fuel concentrations at the top of the plume were detected at a maximum concentration of 4,900 mg/kg, and near the base of the plume at 490 mg/kg. LW It is reasonable to assume that diesel fuel concentrations in the soil attenuate laterally and vertically from the UST source. Therefore, ATC estimates that diesel fuel is present within the plume at an average concentration of 2,000 mg/kg. Based on these figures, approximately 1528 pounds (183 �. gallons) of diesel fuel remain in the soil on site. Floating product was not encountered in the groundwater. The highest concentration of diesel fuel found in the groundwater was 150 ug/L. Therefore, the volume of diesel fuel present in the groundwater is negligible. ATC Associates Inc. 8 Project No,53.75129.0001