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'wee w WELLS FARGO BANK PROPERTY REVISED 49 SOUTH WILSON WAY PRIVILEGED&CONFIDENTIAL STOCKTON, CALIFORNIA `r MAY 3, 1999 Page 4 existing groundwater monitoring wells. The following is a summary of the findings from the investigation and monitoring event: 0 The groundwater flow direction was measured to be to the northeast with a hydraulic gradient of 0.0055; • TPH-g concentrations between 1.3 and 590 milligrams per kilogram (mg/kg) were reported in the soil samples collected from Boring B5 at depths between 35 and f 61 feet bgs. The deepest sample, B5-78, collected at 78 feet bgs, was reported to contain 2.8 mg/kg of TPH-g; • Only sample B5-50, collected at 50 feet bgs, was reported to contain benzene, at 0.006 mg/kg. • TPH-g and BTEX were not reported in groundwater samples collected from monitoring wells MW-1 or MW-3; • TPH-g was reported in the groundwater samples collected from Boring B5, MW-2 �• and MW-4 at concentrations of up to 13 ppm; • Benzene was reported in the groundwater samples collected from Boring B5 and MW-4, at concentrations of 2 ppb and 8 ppb, respectively; • MTBE and other fuel oxygenates were not reported in the soil or groundwater samples collected; and • A review of a historical photograph of the site, historical Sanborn Fire Insurance Maps, and the current concentrations of TPH-g and benzene indicate that the most probable locations of the former underground storage tanks (USTs) were east of the former pump island, near the corner of East Market Street and South Wilson Way, which is beneath the current bank building. Based on the above-mentioned observations, analytical results, and telephone conversations with the SJCEHD, Building Analytics has concluded that the TPH plume beneath the site has been sufficiently delineated, has not significantly impacted the site, and does not pose a significant threat to human health. ti Location of Former USTs Subsequent to the Phase I ESA, Building Analytics further reviewed historical fire insurance maps as well as historical photographs, to assess the location of the former USTs. A review of a historic photograph circa 1950, supplied by the Bank of Stockton Archives, and a 1950 Sanborn Fire Insurance Map, revealed that the southeast corner of the subject property was occupied by a Golden Eagle gasoline service station. The gasoline service station consisted of a small building and one pump island. The pump island was located to the east of the small building and consisted of two pump dispensers. Based on the general layout of the former gasoline service station, the location of the pump dispensers and the current concentrations of TPH-g and benzene in the soil, it is Building Analytics' opinion that the USTs for the former gasoline service station were located near to the southeast corner of the property. More specifically, the USTs would have been located east of the former pump island close to the corner of East Market Street