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4s, 16 July 2002 AGE-NC Project No. 95-0135 Page 2 of 7 2.2. UNDERGROUND STORAGE TANK REMOVAL On 25 and 26 May 1995, four USTs and associated piping were removed from the site by Valley Environmental Solutions(VES)of Stockton,California. One 8,000-gallon regular gasoline UST,one 7,000-gallon gasoline UST and one 5,000-gallon gasoline UST were removed from a large excavation located on north of the building; a single 500-gallon waste oil UST was removed from an excavation located on the south side of the building (Figure 2). Upon removal of the USTs, soil samples were collected from beneath each UST, piping areas and excavated soil. Total petroleum hydrocarbons quantified as gasoline (TPH-g) were detected in the soil samples at concentrations up to 9,100 part per million(ppm) in sample TK3-N, collected from the northern boundary of the property. Analytical results of the soil samples collected during May 1995 are displayed in Table 1. 2.3. PREVIOUS SITE ASSESSMENT AND SAMPLING On 23 June 1997, three soil probe borings (B1 through B3) were advanced at the site. Three additional soil borings (134 through 136) were advanced and completed as ground water monitoring wells on 08 to 11 September 1997; boring B4 (MW-1) was established at the western edge of the station parking lot, boring B5 (MW-2) was advanced at the north end of the drive way entrance to the parking lot and boring B6 (MW-3)was advanced at the east edge of the parking lot. Analytical results of soil samples collected from the soil borings indicated that: • Hydrocarbon-impacted soil was present in the vadose zone below the former UST location, within saturated zone in the locations of the newly installed well MW-1, and distributed in the capillary zone. Soil encountered at 35 feet bsg in the boring established for well MW-1 was not impacted by detectable concentrations of petroleum hydrocarbons, while soil at depths between 43 and 70 feet bsg were impacted by petroleum hydrocarbons. • The impacted soil encountered between 43 and 70 feet bsg in MW-1 appears to be part of a significant, undefined plume,possible associated with the former dispenser island more than 20 feet southeast of the well. • Impacted soil encountered in the former UST cluster may extend,at depth,to the MW-1 area, but the lower hydrocarbon concentrations in the former UST cluster suggest otherwise. No soil contamination was encountered in boring B2, which extended only to 35 feet bsg. The ground water monitoring network has been monitored nine times since September 1997. Over that time span, the highest concentrations of dissolved hydrocarbons was detected at well MW-1, at the western edge of the site. Advanced GeoEnvironmental,Inc.