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1 INTRODUCTION <br /> Former Exxon Retail Site (RS) 7-3942 is a vacant lot Iocated at 4444 North Pershing Avenue, <br /> Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and <br /> Rosemarie Lane (Figure 1) Used oil and three grades of gasoline were stored in four <br /> underground storage tanks, which were removed in July 1986 <br /> A Shell service station and a 7-11 food and gasoline service store are located on the southwest <br /> and northwest corners, respectively, of the intersection of North Pershing Avenue and Rosemarie <br /> Lane Previous laboratory analyses have consistently detected Total Petroleum Hydrocarbons as <br />' gasoline (TPH-g) and benzene, toluene, ethylbenzene, and total xylenes (BTEX) in groundwater <br /> samples collected from MW8 and MW9, which are located adjacent to the Shell site and the 7-11 <br /> site, upgradient and crossgradient of former Exxon RS 7-3942 <br /> On 3 March 1998, groundwater was purged and sampled from 14 groundwater monitoring wells <br /> (MW2—MW13, UVB-MWI, UVB-MW2), three groundwater recovery wells (RW1, RW2, and <br /> RW4),two soil vapor extraction wells (V2, V3), two piezometers (PI, P2), and one infection <br /> well (I W I) Vapor extraction well VI was not sampled on 3 March, because it did not contain a <br /> measurable quantity of water Vapor extraction well V4 was not sampled on 3 March, because <br /> of the presence of liquid-phase hydrocarbons (LPH) Figure 1 shows the locations of former site <br /> facilities and the locations of all Exxon wells on and off the site, except MW I 1 The location of <br /> MWi 1 is shown in Figure 2 <br /> 2. SUMMARY OF RESULTS <br /> On 3 March 1998, 25 wells were monitored for the presence of LPH, using an optical interface <br /> probe LPH was observed in well V4 with an apparent thickness of 0 01 feet The depths to <br /> water ranged from 13 02 (MW8)to 20 11 (MW11) feet below ground surface Groundwater <br /> elevations ranged from-10 01 (MW13)to -6 57 (MW8) feet relative to mean sea level The <br /> approximate groundwater flow direction on 3 March was to the north, with a gradient of <br /> approximately 0 007 to 0 02 (Figure 3), which is consistent with previous groundwater <br /> monitoring data for the site Groundwater elevations on 3 March are presented in boldface type <br /> in Table 1, along with previous data, and are shown in Figure 3 Field documents are included as <br /> Appendix A <br /> After the depths to water were measured, wells MW2—MWI3, RW 1, RW2, RW4, V2, V3, P1, <br /> P2, IWI, UVB-MW1, and UVB-MW2 were purged by vacuum truck and sampled At least <br /> 3 well casing volumes of purge water were removed from each well with the exception of three <br /> wells Wells MW3, MW5, and MW6 dewatered after approximately 1 casing volume was <br /> removed Each of these three wells was allowed to recover to at least 80 percent of its original <br /> level prior to sampling After purging, groundwater samples were collected with factory-cleaned <br /> disposable polyethylene bailers Groundwater samples were collected in 40-m1 VOA vials The <br /> vials were labeled and stored in an ice-filled cooler and transported under chain of custody The <br /> groundwater samples, a field-prepared rinse blank, and a laboratory-prepared trip blank were <br />' WPGI 73942 Q398 TX 2 1 <br />