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' Beacon Station No 3641 September 9,2002 Stockton California Work flan on Figure 1 The site is located in a commercial) zoned area and the parcel is known to the g Y San Joaquin County assessor as APN 094-03-12 Site facilities include a service station/convenience store, two canopy-covered dispenser islands situated in the central portion of the property, and three double-walled underground storage tanks (USTs) located in the western portion of the property The locations of these facilities and other pertinent site features are shown on Figure 2 In June 1996, four steel, single-walled, 10,000-gallon unleaded gasoline USTs (T-1 through T-4) were excavated and removed from a common basin at the site Associated dispenser and product lines were also removed with the UST systems The UST cavity was over- excavated to 19 feet bsg beneath former USTs T-1 and the west half of T-2 Additional over-excavation could not be conducted because of the proximity of the sidewalk and street Soil analytical results indicated total petroleum hydrocarbons as gasoline (TPHg) concentrations to 6,800 milligrams per kilogram (parts per million or ppm) and benzene concentrations to 80 ppm at depths of 14 to 19 feet beneath former USTs T-1 and T-2 Historical soil analytical data are summarized in Table 1 Two 10,000-gallon and one 12,000-gallon, double-walled, fiberglass-clad, steel USTs were installed in the former UST basin in June 1996 During installation of the new USTs, ten 18-inch diameter conductor casings were installed in the former UST cavity to facilitate future assessment and/or confirmation drilling through the backfilled UST cavity In July 1996, Horizon drilled soil borings B-1 and B-2 through two of the UST cavity conductor casings Groundwater was encountered in the borings at depths of approximately 64 feet bsg Soil boring B-1 was completed as dual soil vapor extraction well VW-3NW-4 Soil boring B-2 was completed as groundwater monitoring well MW-1 and dual vapor extraction well VW-I/V W-2 In September 1997, Horizon drilled eight soil borings Seven borings were completed as groundwater monitoring wells MW-2 through MW-5, dual vapor extraction well VW-5/6, 641„x9-o2 Project No 164E 15 2 HORIZON ENVIRONMENTAL INC.