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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 19 August 1998, groundwater was purged and sampled from 14 groundwater monitoring
<br /> wells (MW2—MW13, UVB-MW 1, UVB-MW2), three groundwater recovery wells (RW I, RW2,
<br /> and RW4), two soil vapor extraction wells (V2, V3),two piezometers (P1, P2), and one injection
<br /> well (IW 1) Vapor extraction well VI was not sampled on 19 August, because it did not contain
<br /> a measurable quantity of water Vapor extraction well V4 was not sampled on 19 August,
<br />' because of the presence of liquid-phase hydrocarbons (LPH) Figure 1 shows the locations of
<br /> former site facilities and the locations of all Exxon wells on and off the site, except MW 11 The
<br /> . location of MW11 is shown in Figure 2
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<br /> 2. SUMMARY OF RESULTS
<br />' On 19 August 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 13 feet The approximate
<br /> groundwater flow direction on 19 August was to the north-northeast, with a gradient of
<br /> approximately 0 003 to 0 007 (Figure 3), which is consistent with previous groundwater
<br />' monitoring data for the site Groundwater elevations on 19 August are presented in boldface
<br /> type in Table 1, along with previous data, and are shown in Figure 3 Field documents are
<br /> included as Appendix A
<br /> 1 After the depths to water were measured, wells MW2—MW 13, RW 1, RW2, RW4, V2, V3, P1,
<br /> P2, IW1,UVB-MW1, and UVB-MW2 were purged using a vacuum truck and dedicated PVC
<br /> pipe At least 3 well casing volumes of purge water were removed from each well with the
<br /> exception of three wells Wells MW3, MWS, and MW6 dewatered after approximately 1 casing
<br /> volume was removed Each of these three wells was allowed to recover to at least 80 percent of
<br /> its original level prior to sampling After purging, groundwater samples were collected with
<br /> factory-cleaned disposable polyethylene bailers Groundwater samples were collected in 40-m1
<br />' VOA vials The vials were labeled and stored in an ice-filled cooler and transported under chain
<br /> of custody The groundwater samples, a field-prepared rinse blank, and a laboratory-prepared
<br /> . trip blank were submitted to Sequoia Analytical, where they were analyzed for TPH-g by
<br /> California EPA-modified EPA Method 8015 and for BTEX by EPA Method 8020 The samples
<br /> 73942 Q898 TX WPD 1
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