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1.
<br /> . 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 /> I 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 /> I 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 Perslung Avenue and Rosemarie Lane
<br /> Previous laboratory analyses have consistently detected Total Petroleum Hydrocarbons as gasoline
<br /> (TPH-g), and benzene, toluene, ethylbcnzene, 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 5 May 1999, 15 groundwater monitoring wells (MW 1 through MW 13, UVB-MW 1, UVB-
<br /> MW2), two groundwater recovery wells (RW 1, RW2), four soil vapor extraction wells(V 1-V4),two
<br /> piezometers (P1, P2), and one infection well (IW1)were monitored for the presence of liquid-phase
<br /> hydrocarbons (LPH) Groundwater samples were collected from wells MWl, MW3-MW13, UVB-
<br /> MW1, UVB-MW2, RW1, RW2, V2, V3, P2, and IW1 Figure 1 shows the locations of former site
<br /> facilities and the locations of all Exxon wells on and off the site, except MW11 The location of
<br /> MW 11 is shown in Figure 2
<br /> 2. SUMMARY OF RESULTS
<br /> On 5 May 1999, 24 wells were monitored for the presence of LPH, using an optical interface probe
<br /> The depth to groundwater was gauged, and groundwater elevations were calculated The
<br /> approximate groundwater flow direction on 5 May was to the northeast, with a gradient of
<br /> approximately 0 003 to 0 005 (Figure 3),which is consistent with previous groundwater monitoring
<br /> Idata for the site Groundwater elevations on 5 May are presented in boldface type in Table 1, along
<br /> with previous data, and are shown in Figure 3 Field documents are included as Appendix A
<br /> IAfter the depths to water were measured, wells MW1, MW3-MW5, MW7-MW13, IWl, RW1,
<br /> RW2, V2, V3, P2, UVB-MW I, and UVB-MW2 were purged using a vacuum truck and dedicated
<br /> PVC pipe Well MW6 was hand-bailed Approximately 3 well casing volumes of purge water were
<br /> removed from each well except wells MW3, MW5, and MW6, which purged dry These wells were
<br /> allowed to recharge to at least 80 percent prior to sampling After purging, groundwater samples
<br /> were 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 blank
<br /> I were submitted to Sequoia Analytical, where they were analyzed for TPH-g by California EPA-
<br /> modified EPA Method 8015 and for BTEX and methyl t-butyl ether(MTBE)by EPA Method 8020
<br /> The analytical results for the samples are presented in boldface type in Table 1, along with previous
<br /> I data The laboratory analytical report and chain-of-custody documentation are included in
<br /> Appendix B Groundwater sample analytical results are shown in Figure 1
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