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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 Lan(Figure 1) Used oil and three grades of gasoline 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 detected Total Petroleum Hydrocarbons as gasoline (TPH-g), and benzene, toluene, ethylbenzene, and total xylenes (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 30 March 1999, eight groundwater morutoring wells(MW8 through MW13,UVB-MW1,UVB- MW2),two groundwater recovery wells (RW 1, RW2), two soil vapor extraction wells (V2,V3), and I one piezometer (P2) were monitored for the presence of liquid-phase hydrocarbons (LPH) Groundwater samples were collected from wells UVB-MW1, UVB-MW2, RW1,RW2,V2,V3,and P2 Figure 1 shows the locations of former site facilities and the locations of all Exxon wells on and off the site, except MW l l The location of MWl l is shown in Figure 2 2. SUMMARY OF RESULTS On 30 March 1999, 13 wells were monitored for the presence of LPH, using an optical interface probe The depth to groundwater was gauged, and groundwater elevations were calculated The Iapproximate groundwater flow direction on 30 March was to the north-northeast, with a gradient of approximately 0 003 to 0 004(Figure 3),which is consistent with previous groundwater monitoring data for the site Groundwater elevations on 30 March 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, wells RW 1, RW2, V2, V3, P2, UVB-MW 1, and UVB- MW2 were purged using a vacuum truck and dedicated PVC pipe Approximately 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 Iin 40-m1 VOA vials The vials were labeled and stored in an ice-filled cooler and transported under chain of custody The groundwater samples and a laboratory-prepared trip blank were submitted to Sequoia Analytical, where they were analyzed for TPH-g by California EPA-modified EPA Method 8015 and for BTEX and methyl t-butyl ether(MTBE)by EPA Method 8020 The analytical results for the samples are presented in boldface type in Table 1, along with previous data The laboratory I analytical report and chain-of-custody documentation are included in Appendix B Groundwater sample analytical results are shown in Figure 1 3. GROUNDWATER TREATMENT SYSTEM A vacuum vaporizer well system, known as UVB (Unterdruck Verdampfer Brannen), has been operating at the site since 6 February 1997 A description of the UVB system is included in an installation report issued in June 1997 On 15 October 1998 the UVB system was shut down for system maintenance and conversion of the vapor abatement system from a thermal/catalytic oxidizer F�PmjoM%'73942WASTER%WPV93991Gc do 1