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1. INTRODUCTION Former Exxon Retail Site (RS) 7-3942 is a vacant site located at 4444 North 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 Groundwater monitoring wells MW 1–MW7 were installed on site and MW8–MW 10 were ' installed off site between January 1987 and April 1988 RW 1–RW3 were installed on site in May 1990 From January through April 1991, EA installed IW1, Pl, P2, RW4, V1–V4, ' MW 11, MW 12, and two vapor monitoring cluster wells on and off the site Two air sparging wells (SWI, SW2) and one off-site monitoring well (MW13) were installed in May 1993 ' Soils beneath the site consist of clayey and salty alluvial sediments to a depth of 10-15 ft below ground surface Between 10-15 ft and 35-40 ft the soils consist of coarser seditnents—clayey sands, sands, and gravels--that are intersected by discontinuous clayey lenses ranging from a few ft to 25 ft in thickness The coarser sediments are underlain by clays and salts to an unknown depth A Shell service station and a 7-11 food and gasoline service store are located at the southwest and northwest comers, respectively, of the intersection of North Pershing Avenue and Rosemarie Lane Previous sampling has consistently found TPH-g and BTEX in MW8, which is located adjacent to the Shell site, upgradient to former Exxon RS 7-3942 On 10 May 1994, groundwater from six monitoring wells (MW1, MW8, MW9, MW10, ' MW 12, and MW13), four groundwater recovery wells (RW 1–RW4), two piezometers (P1 and P2), and two soil vapor extraction wells (V1 and V2) were purged and sampled Figure 1 shows the locations of all wells on and off the site except MW 11 and the locations ' of former site facilities Figure 2 shows the vicinity of former Exxon RS 7-3942 and locations of all wells off the site ' 2. SUMMARY OF RESULTS ' On 10 May, wells were monitored for the presence of liquid-phase hydrocarbons and water levels in all wells on and off the site (with the exception of wells MW7, MW 11, and SW 1) were measured with an optical interface probe Measurements and groundwater elevations for ' 10 May are presented in boldface type in Table 1 with previous data The inferred direction of groundwater gradient is to the north-northeast, at a magnitude of 0 009 (Figure 3), which is ' consistent with previous data Groundwater elevations have increased an average of 0 34 ft since the previous quarter Field documents are included as Appendix A ' After the depths to water were measured, selected wells (MW 1, MW8–MW 10, MW 12, MW13, RW1–RW4, P1–P2, IW1, V1--V2) were purged by vacuum truck and sampled At least three well casing volumes of purge water were removed from each well before purging was terminated After purging, groundwater samples were collected with disposable ' 73942Q594 2 1