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16 1. INTRODUCTION Exxon Retail Site (RS) 7-0137 is located at 1605 South El Dorado Street, Stockton, California, on the northwest corner of Second and South El Dorado streets The site is an active service station that has three double-walled fiberglass gasoline underground storage tanks (USTs) The ' site currently contains seven groundwater monitoring wells (MW 1—MW7) and two vapor extraction wells (VEW 1 and VEW2) The seven groundwater monitoring wells (Figure 1) are ' sampled quarterly Groundwater sampling at Exxon RS 7-0137 has been conducted regularly since 1992 A soil vapor extraction system operated at the site from November 1995 to February 1996 which extracted soil vapor through five wells (VW1, VW2, MW2, MW3, and MW5) and abated the petroleum hydrocarbons with a catalytic oxidizer unit The catalytic oxidizer unit was removed in March 1996, following a decline in the concentrations of extracted hydrocarbon vapors "' On 24 April 1996, the seven groundwater monitoring wells were purged and sampled Samples were analyzed for petroleum hydrocarbons 2. SUMMARY OF RESULTS The depth to water in each well was measured prior to purging and sampling Liquid-phase hydrocarbons (LPH) were not detected in any of the wells Groundwater elevations derived from the depth-to-groundwater measurements at the site ranged from 22 04 to 22 60 feet below mean sea level Groundwater elevations have increased approximately 3 64 feet since the previous gauging on 26 January 1996 Because groundwater elevations are inconsistent, a groundwater adient was not dete ined Gauging data and calculated groundwater elevations from 24 April 1996 are presented in boldface type in Table 1, along with previous gauging data, and shown in iFigure 1 Field documents are included as Appendix A After the depths to water were measured, each well was purged with a 2-inch PVC pipe attached to a vacuum pump until at least three casing volumes of groundwater were removed from it Samples were collected with factory-cleaned polyethylene disposable bailers that were triple-rinsed with detonized water prior to sampling The samples were poured into 40-mI glass ' VOA vials, which were then preserved in an ice-filled cooler A field-prepared sampling equipment rinse blank and a laboratory-prepared trip blank were stored and transported in the cooler with the groundwater samples The samples were handled and transported under chain of custody ' The groundwater samples were delivered to Sequoia Analytical and analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g) by Cal EPA-modified EPA Method 8015 and for benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA Method 8020 Table 1 lists the analytical results for this quarter(in boldface type) and for all previous quarterly samplings TPH-g was detected in the samples collected from MW3 and MW5, at concentrations of 240 and 120,ugIL Benzene, ethylbenzene, and xylenes were detected in the sample collected from MW3, at concentrations of 6 7 µgIL, 5 6µglL and 16 jzgIL, respectively The results are shown in WP61 70137Q496 TX 6 1