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INTRODUCTION
<br /> i
<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 TPH-g and 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 26 August 1997, groundwater was purged and sampled from 11 groundwater monitoring
<br />!1 wells (MW 1, MW2, MW4, MW5, MWS-MW 10, MW 12, MW 13, UVB-MW 1, UVB-MW2),
<br /> three groundwater recovery wells (RW 1, RW2, and RW4), two soil vapor extraction wells (V2,
<br /> V3), two piezometers (P1, P2), and one infection well (IW1) Five of the wells were sampled
<br /> inadvertently due to an oversight of the reduced sampling for these wells Consequently, the
<br /> samples collected from wells MW 1, MW2, MW 12, MW 13, and P1 were put on hold and were
<br /> not analyzed, as shown on the chain-of-custody form in Appendix B Monitoring wells MW3,
<br /> MW6, and MW7 and vapor extraction well V 1 were not sampled on 26 August 1997, because
<br /> they were dry Figure 1 shows the locations of former site facilities and the locations of all Exxon
<br />! wells on and off the site, except MW 11
<br /> 2. SUMMARY OF RESULTS
<br /> On 26 August 1997, 24 wells were monitored for the presence of liquid-phase hydrocarbons,
<br /> using an optical interface probe LPH was found in well V4, at a thickness of 0 15 feet The
<br /> depths to water ranged from 18 46 (MW8) to 22 69 (MW 13) feet below ground surface
<br /> Groundwater elevations ranged from-14 61 (MW13) to -11 56 (MWS) feet relative to mean sea
<br /> level The approximate groundwater flow direction on 26 August was to the north, with a
<br /> gradient of approximately 0 003 to 0 01 (Figure 2), which is consistent with previous
<br /> groundwater monitoring data for the site Groundwater elevations on 26 August are presented in
<br />' boldface type in Table 1, along with previous data, and are shown in Figure 2 Field documents
<br /> are included as Appendix A
<br /> After the depths to water were measured, wells MW 1, MW2, MW4, MW5, MW8-MW 10,
<br /> MW12, MW13, RW1, RW2, RW4, V2, V3, P1, P2, IW1, UVB-MW1, and UVB-MW2 were
<br />' purged by vacuum truck and sampled At least 3 well casing volumes of purge water were
<br /> 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 /> tHydrocarbons as gasoline (TPH-g) by California DHS-modified EPA Method 8015 and for
<br />! WP61 73942 Q597 TX 4 1
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