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I. INTRODUCTION
<br />' Former Exxon Retail Site (RS) 7-3942 is a vacant site located at 4444 North Pershing Avenue,
<br /> Stockton, California, on the southeast corner of the intersection of North Pershing Avenue and
<br /> Rosemarie Lane Three grades of gasoline and used oil were stored in four underground storage
<br />' 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 identified TPH-g and BTEX in
<br />' groundwater samples collected from MW8 and MW9, which are located adjacent to the Shell site
<br /> and the 7-11 site, upgradient and crossgradient of former Exxon RS 7-3942
<br />' On 13 February 1996, groundwater was purged and sampled from nine monitoring wells
<br /> (MW I—MW4, MW8—MW 10, MW 12, and MW 13), four recovery wells (RW 1, RW2, RW3, and
<br /> RW4), two piezometers (P1 and P2), one soil vapor extraction well (V3), and one injection well
<br />' (IW I) Monitoring wells MW5, MW6, and MW7 and vapor extraction well VI were not
<br /> sampled on 13 February, as there was not enough water to make well purging possible
<br /> Figure I shows the locations of all wells on and off the site, except MW 11, and the locations of
<br />' former site facilities Figure 2 shows the vicinity of former Exxon RS 7-3942 and the locations
<br /> of all offsite wells
<br /> 2. SUMMARY OF RESULTS
<br />' On 13 February, wells were monitored for the presence of liquid-phase hydrocarbons, using an
<br /> optical interface probe A sheen was seen on the water in wells V2 and V4 The depths to water
<br /> ranged from 22 15 feet to 27 85 feet below ground surface Groundwater elevations ranged from
<br />' -14 37 ft msl (below mean sea level) in MW8 to -18 36 ft msl (MW 13) The approximate
<br /> groundwater flow direction on 13 February was to the northeast, with a gradient of approximately
<br />' 0 007 (Figure 3), which is consistent with previous groundwater monitoring data for the site
<br /> Groundwater elevations have increased approximately 2 5 feet since the previous quarter
<br /> Groundwater elevations on 13 February are presented in boldface type in Table 1, along with
<br />' previous data, and are shown in Figure 3 Field documents are included as Appendix A
<br /> After the depths to water were measured, the wells (MW 1—MW4, MW8—MW I0, MW 12,
<br />' MW 13, RW 1—RW4, P1, P2, IW 1, and V3) were purged by vacuum truck and sampled V2 and
<br /> V4 were not sampled, because of the sheen At least three well casing volumes of purge water
<br /> were removed from each well After purging, groundwater samples were collected with factory-
<br /> cleaned disposable polyethylene bailers Groundwater samples were collected in 40-m1 VOA
<br /> vials The vials were labeled and stored in an ice-filled cooler and transported under chain of
<br /> custody The groundwater samples, a field-prepared rinse blank, and a laboratory-prepared trip
<br />' blank were submitted to Sequoia Analytical, where they were analyzed for Total Petroleum
<br /> Hydrocarbons as gasoline (TPH-g) by California DHS-modified EPA Method 8015 and for
<br /> benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA Method 8020 The samples from
<br /> RW3 and V3 were also analyzed for methyl t-butyl ether(MTBE) by EPA Method 8020
<br />' WP61 73942Q296 4 1
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