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I ' 1• INTRODUCTION • ' Former Exxon Retail Site (RS) 7-3942 is a vacant lot located at 4444 North Pershing Avenue in Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and ' Rosemarie Lane (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), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and methyl t-butyl ether (MTBE) 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 ' A nsk assessment work plan for the site was submitted to San Joaquin County Public Health Services in October 2000 The proposed work was performed in December 2000 The Request for ' No Further Remedial Action report was submitted to the California Regional Water Quality Control Board in October 2001 ' 2. GROUNDWATER MONITORING ' On 20 September 2001, groundwater monitoring wells MWI-MW 13, UVB-MW1, and UVB-MW2, groundwater recovery wells RW 1, RW2, and RW4, soil vapor extraction wells V1-V4, and infection well IW1 were gauged Groundwater samples were collected from wells MW4, MW5, MW11, ' WB-MWI, UVB-MW2, RW2, RW4, V1-V3, and IW1 Figure 1 shows the locations of former site facilities and the locations of all ExxonMobil wells on and off the site The locations of offsite monitoring wells MW8, MW9, MW11, and MW13 are shown in Figure 2 Well MWll was ' resampled on 8 November 2001 because the analytical results from the 20 September sampling event were inconsistent with historical data ' On 20 September 2001, wells were monitored for the presence of liquid-phase hydrocarbons (LPH) using an optical interface probe A thickness of 0 01 feet of LPH was measured in wells V4 and RW 1 LPH was not observed in any other well The depth to groundwater was gauged, and ' groundwater elevations were calculated The approximate groundwater flow direction on 20 September was to the northeast, with a gradient of approximately 0 004, which is consistent with previous groundwater monitoring data for the site Current groundwater elevations are presented ' in boldface type in Table 1, along with previous data, and are shown in Figure 1 Copies of the field documents are included as Appendix A ' After the depths to water were measured, the wells were purged Approximately 3 well casing volumes of purge water were removed from each well Wells that dewatered during purging were allowed to recover prior to sampling After purging, groundwater samples were collected with ' factory-cleaned disposable bailers Groundwater samples were collected in 40-m1 glass VOA vials The vials were labeled and stored in an ice-filled cooler and transported under chain of custody The ' groundwater samples were submitted to SPL, Inc , in Houston, Texas, where they were analyzed for TPH-g by California EPA-modified EPA Method 8015, and for BTEX and MTBE by EPA Method 8021B Samples in which MTBE was detected were also analyzed for MTBE by EPA Method ' G 1Pr0l«[s%73912%I�STMW PIQa01 tie day 1