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<br /> 1• INTRODUCTION
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<br />' Former Exxon Retail Site (RS) 7-3942 is a vacant lot located at 4444 North Pershing Avenue in
<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 /> I (TPH-g), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and methyl t-butyl ether
<br /> (MTBE) in groundwater samples collected from MW8 and MW9, which are located adjacent to the
<br /> Shell site and the 7-11 site, upgradient and crossgradient of former Exxon RS 7-3942
<br /> A risk assessment work plan for the site was submitted to San Joaquin County Public Health
<br /> Services in October 2000 The proposed work was performed in December 2000
<br /> I2. GROUNDWATER MONITORING
<br /> On 13 December 2000, groundwater monitoring wells MW1-MW8, MW10, MW13, WB-MW1,
<br /> and UVB-MW2, groundwater recovery wells RW 1,RW2, and RW4, soil vapor extraction wells V1-
<br /> V4, and infection well IW1 were gauged for depth to water and for the presence of liquid-phase
<br /> hydrocarbons (LPH) Groundwater samples were collected from wells MWl-MW8, MW10, MW13,
<br /> UVB-MW1, UVB-MW2, RW1, RW2, RW4, V1-V3, and IW1 Figure 1 shows the locations of
<br /> former site facilities and the locations of all ExxonMobil wells on and off the site The locations of
<br /> Ioffsite monitoring wells MWS, MW9, MWl 1, and MW13 are shown in Figure 2
<br /> On 13 December, 20 wells were monitored for the presence of LPH using an optical interface probe
<br /> LPH was detected in well V4 at a thickness of less than 0 01 feet The depth to groundwater was
<br /> gauged, and groundwater elevations were calculated The approximate groundwater flow direction
<br /> on 13 December was to the northeast, with a gradient of approximately 0 003 to 0 005, which is
<br /> consistent with previous groundwater monitoring data for the site Groundwater elevations on 13
<br /> December are presented in boldface type in Table 1, along with previous data, and are shown in
<br /> Figure 1 Copies of the field documents are included as Appendix A
<br /> After the depths to water were measured, the wells were purged Approximately 3 well casing
<br /> volumes of purge water were removed from each well Wells that purged dry were allowed to
<br /> I recover at least 80% prior to sampling After purging, groundwater samples were collected with
<br /> factory-cleaned disposable bailers Groundwater samples were collected in 40-m1 VOA vials The
<br /> vials were labeled and stored in an ice-filled cooler and transported under chain of custody The
<br /> groundwater samples were submitted to SPL Inc , in Houston, Texas, where they were analyzed for
<br /> TPH-g by California EPA-modified EPA Method 8015 and for BTEX and MTBE by EPA Method
<br /> 8021B In addition, the samples from wells MW4 and MW8 were analyzed for MTBE by EPA
<br /> I Method 8260B for confirmation The analytical results for the samples are presented in boldface
<br /> type in Table 1, along with previous data The laboratory analytical report and chain-of-custody
<br /> documentation are included in Appendix B Groundwater sample analytical results are shown in
<br /> Figure 1
<br /> F SPrDJCCIS173942\MASTFR1WP\Q]2001tx doe 1
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