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FEB 26 1997 I. INTRODUCTION ENVIRONNIENTAI.MFALZH PERW/SERVICES 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 that has three double-walled fiberglass gasoline underground storage tanks (USTs) The site currently contains seven groundwater monitonng 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 (VEW1, VEW2, 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 16 July 1996, the seven groundwater monitoring wells were purged and sampled Samples t were analyzed for petroleum hydrocarbons Presentation of these results was inadvertently overlooked October 1996 monitoring results have already been submitted 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 43 to -21 92 feet relative to mean sea level Groundwater elevations have increased approximately 0 15 feet since the previous gauging on 24 April 1996 The monitoring wells at the site were constructed at a time when the water table was more than 10 feet lower than it is currently Monitoring wells MW I, ' 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 shows that the depth to the ' water table on 16 July 1996 ranged from 32 76 to 35 35 Therefore, the only well that appears to have been screened across the water table on that date was MW4 In order to estimate the groundwater gradient and flow direction, we have prepared a water table contour map (Figure 1) ' using the wells screened closest to the water table MW I, MW2, MW3, and MW6 The flow direction based on data from these wells was towards the southeast at an approximate gradient of 0 002 Gauging data and calculated groundwater elevations from 16 July 1996 are presented in boldface type in Table 1, along with previous gauging data 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 3 casing volumes of groundwater were removed from it Samples were collected with factory-cleaned disposable polyethylene bailers The samples were poured into 40-m1 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 WP61 70137Q796 TX 2 1