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i 1. INTRODUCTION ' Exxon Retail Site (RS) 7-0137 is located at 1605 South El Dorado Street, Stockton, California, on the southwest corner of Second and South El Dorado streets The site is an active service station with a single underground storage tank (UST) with a 20,000-gallon capacity Three ' double-walled fiberglass gasoline USTs were removed from the site in June 1992 The site currently contains seven groundwater monitoring wells (MWl—MW7) and two vapor extraction wells (VEW1 and VEW2) The seven groundwater monitoring wells (Figure 1) are sampled quarterly During the current sampling event, one of the vapor extraction wells (VEW2) contained groundwater and was sampled This was the first time groundwater was observed in a vapor extraction well Groundwater sampling at Exxon RS 7-0137 has been conducted regularly since 1991 A soil vapor extraction (SVE) system operated at the site from November 1995 to March 1996 and resumed operation in February 1997 The SVE system is designed to extract soil vapor from five wells (VEWI, VEW2, MW2, MW3, and MW5) Until March 1996 soil vapors were abated with a catalytic oxidizer unit A carbon adsorption abatement system was installed in February 1997 On 15 July 1998, the seven groundwater monitoring wells and one of the vapor extraction wells (VEW2) were purged and sampled Samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g), for benzene, toluene, ethylbenzene, and total xylenes (BTEX), and for methyl t-butyl ether (MTBE) 2. SUMMARY OF RESULTS I The depth to water in each well, including the vapor extraction wells, was measured prior to purging and sampling Liquid-phase hydrocarbons (LPH) were not detected in any of the wells Vapor extraction well VEWI was dry The monitoring wells at the site were constructed at a time when the water table was more than 15 feet lower than it is currently Monitoring wells MWI, MW2, MW3, and MW6 are screened from 35 to 55 feet below the surface, and MW4, MW5, and MW7 are screened from 40 to 60 feet below the surface Table 1 presents monitoring well construction details Histoncal and current depths to water are presented in Table 2 None of the monitoring wells is currently screened across the water table Groundwater beneath the site flows to the southeast at an approximate gradient of 0 002 Gauging data and calculated groundwater elevations from 15 July 1998 are presented in boldface type in Table 2, along with previous gauging data Field documents are included as Appendix A After the depths to water were measured, the wells were purged with a PVC pipe attached to a vacuum truck In each well, field parameters of pH, temperature, and electrical conductance of the purged water were recorded with every well casing volume purged When the field I parameters were stable (less than 10 percent change from the previous reading for temperature and electrical conductance, and 0 25 pH units or less change from the previous reading for pH) and a minimum of 3 casing volumes of groundwater were removed, purging was stopped and samples were collected using factory-cleaned disposable polyethylene bailers The samples were poured into 40 ml glass VOA vials, which were then placed in an ice-filled cooler A 70137 Q798 Tx WPB l