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
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