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CVATC A S S O C I A T E S I N C BACKGROUND The site is located on the south side of Highway 88 (Waterloo Road) and on the east side of Fairchild Lane, Stockton, California, as shown on Figure 1. The site is presently occupied by Three Palms Grocery (a convenience store), a beauty salon, and an adjacent residence. A domestic well, which provides water to the site, is located north of the residence (Figure 2). Prior to July 1984, one 550-gallon waste oil underground storage tank (UST), identified as Tank #4, was emptied of product, filled with sand, and capped with concrete. In November 1986, one 1,000-gallon regular gasoline UST, identified as Tank #3, was removed and disposed of. A soil sample collected during the removal of Tank #3 contained elevated concentrations of petroleum hydrocarbons. In May 1989, one 1,000-gallon unleaded gasoline UST, identified as Tank #1 was filled with five cubic yards of concrete. Currently, two other USTs remain in place and are in operation at the site. These USTs are located approximately 40 feet east of the tanks which were closed in place. On June 18, 1998, an ATC geologist supervised the advancement of two soil borings (SB 1 and S132) to 86.5 feet below ground surface (bgs) to assess current subsurface conditions at the site. Petroleum hydrocarbon constituents were detected in soil samples collected from borings SB 1 and S132. The highest reported constituent concentrations were observed in soil samples collected at 25.5 feet bgs in each of the borings. The highest concentrations of petroleum constituents at this depth were observed in SBI and include TPHg (9,500 mg/kg), toluene (65 mg/kg), ethyl benzene (82 mg/kg), and xylenes (470 mg/kg). The petroleum hydrocarbons appear to attenuate rapidly with depth as indicated greatest by soil samples from SB 1 at 45.5 feet bgs and S132 at 55.5 feet bgs which contained only trace or nondetectable concentrations of petroleum hydrocarbons. Total lead was detected at 5.5 mg/kg in the soil sample collected from SBI at 25.5 feet bgs. Neither benzene, fuel oxygenate additives, nor VOCs were detected above laboratory method detection limits in any of the soil samples analyzed. Petroleum hydrocarbon constituents, including TPHg and BTEX, were detected in initial groundwater grab samples collected from borings SBI and S132. Only benzene, which was reported at concentrations of 7.6 parts per billion (ppb) and 12 ppb, exceeded California's Maximum Contaminant Level (MCL) for drinking water. On June 15 and 16, 1999, a total of three soil borings (MW 1 through MW3) were advanced at the site in the vicinity of the "closed" or former USTs to evaluate determine the lateral extent of petroleum affected soil and groundwater. Following soil sample collection the borings were completed as groundwater monitoring wells. The initial sampling of the on-site wells indicated only low levels of petroleum hydrocarbons were present in MW-1. On October 26, 2001, ATC submitted a request for closure. The San Joaquin County EHD requested that an additional monitoring event be performed. w:\14885\workplan%\wkpin2005.doc 2