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' 1 INTRODUCTION
<br /> Former Exxon Retail Site (RS) 7-3942 is a vacant lot located 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 18 November 1998, groundwater was purged and sampled from 12 groundwater monitoring
<br /> wells (MW1, MW3—MWI1, UVB-MW1, and UVB-MW2), three groundwater recovery
<br />' wells (RW1, RW2, and RW4), two soil vapor extraction wells (V2, V3), one piezometer (P2),
<br /> and one injection well (IW1) Vapor extraction well V1 was not sampled on 18 November,
<br /> because it did not contain a measurable quantity of water Vapor extraction well V4 was not
<br />' sampled on 18 November, because of the presence of liquid-phase hydrocarbons (LPH)
<br /> Figure 1 shows the locations of former site facilities and the locations of all Exxon wells on and
<br /> off the site, except MW 11 The location of MW 11 is shown in Figure 2
<br /> 2. SUMMARY OF RESULTS
<br /> On 18 November 1998,
<br /> 25 wells were monitored for the presence of LPH, using an optical
<br /> interface probe LPH was observed in well V4 with an apparent thickness of 0 09 feet The
<br /> approximate groundwater flow direction on 18 November was to the north-northeast, with a
<br /> gradient of approximately 0 003 to 0 005 (Figure 3), which is consistent with previous
<br />' groundwater monitoring data for the site Groundwater elevations on 18 November are presented
<br /> in boldface type in Table 1, along with previous data, and are shown in Figure 3 Field
<br /> documents are included as Appendix A
<br /> After the depths to water were measured, wells MW1, MW3 MW11, RW1, RW2, RW4, V2,
<br /> V3, P2, IW1, UVB-MW 1,and WB-MW2 were purged using a vacuum truck and dedicated
<br />' PVC pipe. At Ieast 3 well casing volumes of purge water were removed from each well with the
<br /> exception of three wells Wells MW3, MW5, and MW6 dewatered after approximately 1-2
<br /> casing volumes were removed Each of these three wells was allowed to recover to at least 80
<br />' percent of its original level prior to sampling After purging, groundwater samples were
<br /> collected with factory-cleaned disposable polyethylene bailers Groundwater samples were
<br />' collected in 40-m1 VOA vials The vials were labeled and stored in an ice-filled cooler and
<br /> transported under chain of custody The groundwater samples and a laboratory-prepared trip
<br /> blank were submitted to Sequoia Analytical, where they were analyzed for TPH-g by California
<br /> EPA-modified EPA Method 8015 and for BTEX and methyl t-butyl ether(MTBE) by EPA
<br /> 73942 Q1198 TX WPD 1
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