|
1
<br /> INTRODU
<br /> • CTION
<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), 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 />' On 29 February 2000, groundwater monitoring wells MW2-MW 11, MW13,UVB-MW 1, and UVB-
<br /> MW2, groundwater recovery wells RW 1 and RW2, soil vapor extraction well V4, and infection well
<br />' IW1 were monitored for the presence of liquid-phase hydrocarbons (LPH) Groundwater samples
<br /> were collected from wells MW2, MW4-MWI 1,MW13,UVB-MWI, UVB-MW2, RW1, RW2, and
<br /> IW1 Figure 1 shows the locations of former site facilities and the locations of all Exxon wells on
<br />' and off the site The locations of offsite monitoring wells MW8, MW9, MW11, and MW13 are
<br /> shown in Figure 2
<br /> lie2. SUMMARY OF RESULTS
<br /> On 29 February 2000, 17 wells were monitored for the presence of LPH, using an optical interface
<br />' probe LPH was detected in well V4 at a thickness of 0 06 feet The depth to groundwater was
<br /> gauged, and groundwater elevations were calculated The approximate groundwater flow direction
<br /> on 29 February was to the northeast, with a gradient of approximately 0 003 to 0 007 (Figure 3),
<br />' which is consistent with previous groundwater monitoring data for the site Groundwater elevations
<br /> on 29 February are presented in boldface type in Table 1, along with previous data, and are shown
<br /> in Figure 3 Field documents are included as Appendix A
<br />' After the depths to water were measured, wells MW2, MW4-MW 11, MW 13, RW 1, RW2, IW 1,
<br /> UVB-MWI, and WB-MW2 were purged Approximately 3 well casing volumes of purge water
<br /> Iwere removed from each well After purging, groundwater samples were collected with factory-
<br /> cleaned disposable bailers Groundwater samples were collected in 40-m1 VOA vials The vials
<br /> were labeled and stored in an ice-filled cooler and transported under chain of custody The
<br /> groundwater samples and a laboratory-prepared trip blank were submitted to SPL Inc , in Houston,
<br /> Texas, where they were analyzed for TPH-g by California EPA-modified EPA Method 8015 and for
<br /> BTEX and MTBE by EPA Method 8021 The analytical results for the samples are presented in
<br /> boldface type in Table 1, along with previous data The laboratory analytical report and chain-of-
<br /> custody documentation are included in Appendix B Groundwater sample analytical results are
<br /> Ishown in Figure 1
<br /> •', 3. GROUNDWATER TREATMENT SYSTEM
<br /> A vacuum vaporizer well system, known as UVB (Unterdruck Verdampfer Brunnen), has been
<br /> operating at the site since 6 February 1997 A description of the UVB system is included in an
<br /> IF\PrgectS1739421MASTERIWP\Q2COVtx doc 1
<br />
|