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<br /> 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 underground
<br /> 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 and
<br /> northwest corners,respectively, of the intersection of North Pershing Avenue and Rosemarie Lane
<br /> Previous laboratory analyses have consistently detected Total Petroleum Hydrocarbons as gasoline
<br />' (TPH-g), and benzene, toluene, ethylbenzene, and total xylenes (BTEX) in groundwater samples
<br /> collected from MW8 and MW9, which are located adjacent to the Shell site and the 7-11 site,
<br />' upgradient and crossgradient of former Exxon RS 7-3942
<br /> On 6 December 1999,groundwater monitoring wells MWl-MW11, MW13, UVB-MW1, and UVB-
<br /> MW2, groundwater recovery wells RW 1 and RW2, soil vapor extraction well V4, and infection well
<br /> IW 1 were monitored for the presence of liquid-phase hydrocarbons (LPH) Groundwater samples
<br /> were collected from wells MW2, MW4-MW7, UVB-MW1, UVB-MW2, RW1, RW2, and IW1
<br /> Figure 1 shows the locations of former site facilities and the locations of all Exxon wells on and off
<br /> the site, except MW11 The location of MW11 is shown in Figure 2
<br /> lie The following is the proposed annual groundwater monitoring schedule for the site Wells MW1-
<br /> MW10, MW12, MW13, IW1, WB-MWl, UVB-MW2, RWl, RW2, and RW4 will be gauged
<br /> quarterly Well MW11 will be gauged once per year during the fourth quarter Wells MW4-MW7,
<br /> IIW1,RW1, RW2, RW4,UVB-MWI,UVB-MW2, and V4 will be sampled quarterly Wells MW8-
<br /> MW 13 will be sampled once per year during the fourth quarter The analyses will remain the same
<br /> I (BTEX, TPH-g, methyl t-butyl ether [MTBE])
<br /> 2 SUMMARY OF RESULTS
<br /> IOn 6 December 1999, 18 wells were monitored for the presence of LPH, using an optical interface
<br /> probe The depth to groundwater was gauged, and groundwater elevations were calculated The
<br /> I approximate groundwater flow direction on 6 December was to the northeast, with a gradient of
<br /> approximately 0 003 to 0 007 (Figure 3),which is consistent with previous groundwater monitoring
<br /> data for the site Groundwater elevations on 6 December are presented in boldface type in Table 1,
<br /> Ialong with previous data, and are shown in Figure 3 Field documents are included as Appendix A
<br /> After the depths to water were measured,wells MW2, MW4-MW7, RW1, RW2, IW1, UVB-MW1,
<br /> and UVB-MW2 were purged Approximately 3 well casing volumes of purge water were removed
<br /> from each well After purging,groundwater samples were collected with factory-cleaned disposable
<br /> I polyethylene bailers Groundwater samples were collected in 40-m1 VOA vials The vials were
<br /> labeled and stored in an ice-filled cooler and transported under chain of custody The groundwater
<br /> samples and a laboratory-prepared trip blank were submitted to SPL Inc , in Houston, Texas, where
<br /> I they were analyzed for TPH-g by California EPA-modified EPA Method 8015 and for BTEX and
<br /> MTBE by EPA Method 8021 The analytical results for the samples are presented in boldface type
<br /> in Table 1, along with previous data The laboratory analytical report and chain-of-custody
<br /> F TTGJCcis\73942\MASTPR\WP\Q]299\tx doc 1
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