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1. INTRODUCTION Former Exxon Retail Site (RS) 7-3942 is a vacant site located at 4444 Pershing Avenue, Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and Rosemarie Lane Three grades of gasoline and used oil were stored in four underground storage tanks, which were removed in July 1986 On 23 February 1993, the 4 groundwater monitoring wells (MW8 and MW10-MW12), four groundwater recovery wells (RW1--RW4), two vapor extraction wells (V1 and V4), and two piezometers (P1 and P2) were sampled The samples were analyzed for petroleum hydrocarbons Figure I a shows the locations of all wells on and off the site (except MW 11), and the locations of former site facilities Figure lb shows the vicinity of RS 7-3942 and locations of all wells off the site Passive liquid-phase hydrocarbon (LPH) skimmers were installed in wells RW3 and VI on 11 December 1992 On 27 December 1992, the skimmers were checked for LPH No LPH was measured in either of the skimmers or in any of the monitoring wells on or off the site 2. SUMMARY OF CURRENT STATUS Groundwater monitoring wells MW 1-MW7 were installed on the site and MW8-MW 10 were installed off the site between January 1987 and April 1988 RW1-RW3 were installed on the site in May 1990 From January through April 1991, EA installed IW1, P1, P2, RW4, V1-V4, MW 11, MW 12, and two vapor monitoring cluster wells on and off the site Water is presently found at 30 feet below ground surface at the site (In 1987, groundwater was found at 18 feet below ground surface ) The inferred direction of the groundwater gradient is east to northeast at a magnitude of 0 01 Soils beneath the site consist of clayey and silty alluvial sediments to a depth of 10 to 15 feet below ground surface Between 10 to 15 feet and 35 to 40 feet the soils consist of coarser sediments—clayey sands, sands, and gravels hat are intersected by discontinuous clayey lenses ranging from a few feet to 25 feet in ttuckness. The coarser sediments are underlain by clays and silts to an unknown depth The groundwater table has dropped approximately 12 feet since 1987 Petroleum hydrocarbons have been detected in all wells sampled except MW 11 and MW 12, which are the wells farthest downgradient of the site Petroleum hydrocarbons are concentrated in the northeast quadrant of the site, in the area around and downgradient of the Itank field, and off the site to the northeast of the former tank field LPH has been measured in wells MW3, MW6, RW3, V1, V2, and V4 A proposed combined soil vapor extraction (SVE) system and groundwater extraction and treatment (GET) system will remediate the soil and groundwater by catalytic oxidation of petroleum hydrocarbons in the extracted soil vapors and carbon adsorption of petroleum hydrocarbons in the extracted groundwater Air sparging will assist in the in situ removal of hydrocarbons from the groundwater Treated groundwater may be re-infected along the northwest border of the site in order to prevent hydrocarbons from being drawn across Pershing Avenue (see results from MW8) 73942(1)/Q293/TX 3 I I