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,(LVvAT.1 A S S O C I A T E S I N C . L r INTRODUCTION LOn behalf of Diesel Performance, ATC Associates Inc:'(ATC) has developed a site conceptual model (SCM) and corrective action plan (CAP) for Diesel Performance located at ,2804 Freemont Street in Stockton, California(Figure 1). This SCM/CAP was prepared in response to a request from Ms. Lori Duncan of the San Joaquin County Environmental Health Department (SJCEHD). The corrective actions proposed in this SCM/CAP were prepared to address petroleum impacted soil and groundwater in the vicinity of the former underground storage tank(UST)location. L BACKGROUND INFORMATION LIn February 1987, SEMCO removed and disposed of':one 3,000-gallon; unleaded gasoline UST, associated piping, and fuel dispenses from the location shown on;Figure 2. A soil sample collected from 13 feet below ground surface (bgs) contained elevated concentrations of petroleum hydrocarbon contaminants. The 1 L excavation was subsequently backfilled and resurfaced. On July 23, 1997, an ATC geologist supervised the advancement of five soil borings ranging in depth from 6 to L 46 feet bgs. The soil borings were advanced using a truck mounted Geoprobe®narrow diameter rig employing direct push technology. ' Petroleum hydrocarbons were detected in soil samples submitted for laboratory analyses. Site activities are summarized in ATC's Summary Report for Subsurface Investigation, dated October 20, 1997. On September 25, 1998, ATC personnel supervised the{advancement of soil boring MW 1 at the site to a depth Lof approximately 65 feet'.bgs to evaluate groundwater for-the presence of petroleum hydrocarbons. The soil boring was completed as'a groundwater monitoring well and on September 28, 1998 the well was developed and sampled. Analytical data indicated that soil and groundwater samples contained detectable concentrations Lof petroleum hydrocarbons. Field activities and analytical results are detailed in ATC's Summary Report of Additional Subsurface Investigation, dated January 8, 1999. 3� In December 1999, ATC,,personnel supervised the advancement of soil borings MW2,'MW3, and MW4 at the site to depths of approximately 65 feet bgs to evaluate groundwater for the presence of petroleum hydrocarbons and to determine the gradient direction and magnitude. The borings were completed as monitoring wells. ` Analytical data indicatedhat soil samples collected from boring MW2 contained detectable concentrations of petroleum hydrocarbons.:Petroleum hydrocarbons were also detected in a groundwater sample collected from well MW2. A groundwater sample collected from MW3,contained very low concentrations of only a few of the requested analytes. Petroleum hydrocarbons were not detected in the groundwater sample collected from MW4. L .Field activities and analytical results are detailed its ATC's Summary Report of Additional Subsurface Investigation, dated February 24, 2000. In December 2001, soil-boring VEW1 was advanced to approximately 35 feet bgs, and borings 'VEW2 and VEW3 were advanced to. approximately 45 feet bgs.` Borings MW5; MW6, and MW7 were advanced to approximately 65 feet bgs. Soil borings VEW 1, VEW2, and VEW3 were completed as 2-inch diameter vapor extraction wells and soil borings MWS, MW6, and MW7 were completed as 2-inch diameter groundwater monitoring wells. Boring CPTl was advanced to appz'oximately 100 feet bgs utilizing a truck-mounted cone penetration test (CPT) rig. A soil vapor extraction pilot test was conducted which yielded a radius of influence Diesel Performance �} January 5,2004 ATC Project Number 5462577 5 k:p, .70-60, Page 1