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1. INTRODUCTION ' Former Exxon Retail Site (RS) 7-3942 is a vacant lot 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 A Shell service station and a 7-11 food and gasoline service store are located on the southwest and northwest corners, respectively, of the intersection of North Pershing Avenue and Rosemarie Lane Previous laboratory analyses have consistently identified TPH-g and BTEX in ' groundwater samples collected from MW8 and MW9, which are located adjacent to the Shell site and the 7-11 site, upgradient and crossgradient of former Exxon RS 7-3942 ' On 3 February 1997, groundwater was purged and sampled from eight monitoring wells (MW 1, MW3, MW4, MWS, MW7—MW 10), three recovery wells (RW 1, RW2 and RW4), one soil vapor extraction well (V3), piezometer P2, and injection well IW 1 Monitoring well MW6 and vapor ' extraction well V 1 were not sampled on 3 February, as there was not enough water to make well purging possible 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 the locations of all offsite wells 2. SUMMARY OF RESULTS On 3 February 1997 20 wells were monitored for the presence of liquid-phase hydrocarbons, using an optical interface probe A sheen was observed in wells V2 and V4 The depths to water ranged from 16 78 (MW8) to 22 20 (MW 13) feet below ground surface Groundwater elevations ' ranged from -12 71 (MW 13) to -9 00 (MW8) feet relative to mean sea level The approximate groundwater flow direction on 3 February was to the northeast, with a gradient of approximately 0 007 (Figure 3), which is consistent with previous groundwater monitoring data for the site ' Groundwater elevations increased approximately 4 5 feet since the previous quarter Groundwater elevations on 3 February are presented in boldface type in Table 1, along with previous data, and are shown in Figure 3 Field documents are included as Appendix A ' After the depths to water were measured, the 14 wells (MW1, MW3, MW4, MW5, MW7—MW 10, RW 1, RW2 and RW4, V3, P2, and IW 1) were purged by vacuum truck and sampled At least 3 well casing volumes of purge water were removed from each well After purging, groundwater samples were collected with factory-cleaned disposable polyethylene bailers Groundwater samples were collected in 40-m1 VOA vials The vials were labeled and ' stored in an ice-filled cooler and transported under chain of custody The groundwater samples, a field-prepared rinse blank, and a laboratory-prepared trip blank were submitted to Sequoia Analytical, where they were analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g) by California DHS-modified EPA Method 8015 and for benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA Method 8020 The samples were also analyzed for methyl t-butyl ether (MTBE) by EPA Method 8020 ' WP61 73932Q297 TX 3 1