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1• INTRODUCTION <br /> Exxon Retail Site (RS) 7-0137 is located at 1605 South El Dorado Street, Stockton, California, <br /> on the southwest corner of Second and South El Dorado streets The site is an active service <br /> station that has three double-walled fiberglass gasoline underground storage tanks (USTs) The <br /> tsite currently contains seven groundwater monitoring wells (MW I—MW7) and two vapor <br /> extraction wells (VEW1 and VEW2) The seven groundwater monitonng wells (Figure 1) are <br />' sampled quarterly <br /> Groundwater sampling at Exxon RS 7-0137 has been conducted regularly since 1992 A soil <br /> vapor extraction system operated at the site from November 1995 to March 1996, which <br /> extracted soil vapor through five wells (VEW 1, VEW2, MW2, MW3, and MW5) and abated the <br /> petroleum hydrocarbons with a catalytic oxidizer unit The catalytic oxidizer unit was removed <br /> in March 1996, following a decline in the concentrations of extracted hydrocarbon vapors <br /> On 1 April 1997, the seven groundwater monitoring wells were purged and sampled Samples <br />' were analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g) and for benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX) <br /> 2. SUMMARY OF RESULTS <br /> The depth to water in each well was measured prior to purging and sampling Liquid-phase <br /> hydrocarbons (LPH) were not detected in any of the wells Groundwater elevations at the site <br /> ranged from 18 78 to 17 33 feet below mean sea level Groundwater elevations have increased <br /> an average of 2 8 feet since the previous gauging on 21 January 1997 The monitoring wells at <br /> the site were constructed at a time when the water table was more than 10 feet Iower than it is <br /> currently Monitoring wells MW1,MW2,MW3, and MW6 are screened from 35 to 55 feet <br /> below the surface, and MW4, MW5, and MW7 are screened from 40 to 60 feet below the <br /> surface Table 1 presents monitoring well construction details Historical and current depths to <br /> water are presented in Table 2 The depth to the water on 1 April 1997 ranged from 29 11 to <br /> 30 90 feet below the top of the well casing, therefore, none of the wells are currently screenciLL <br /> across the water table In order to estimate the groundwater gradient and flow direction, a water <br />' table contour map was prepared (Figure 1) using the following wells screened near the water <br /> table MW I, MW2, MW3, and MW6 The flow direction based on data from these wells was <br /> toward the southeast at an a[)vroximatezradientof00lto002 Gauging data and calculated <br /> groundwater elevations from 1 April 1997 are presented in boldface type in Table 2, along with <br /> previous gauging data Field documents are included as Appendix A <br /> After the depths to water were measured, each groundwater monitoring well was purged with a <br /> 2-inch PVC pipe attached to a vacuum pump until at least 3 casing volumes of groundwater were <br /> removed Samples were collected using factory-cleaned disposable polyethylene bailers The <br /> samples were poured into 40 ml glass VOA vials, which were then preserved in an ice-filled <br /> cooler A field-prepared sampling equipment rinse blank and a laboratory-prepared tnp blank <br /> were stored and transported in the cooler with the groundwater samples The samples were <br /> handled and transported under chain of custody <br /> WP61 70137 Q497 TX 2 I <br />