ARCHIVED REPORTS XR0008614 - Laserfiche WebLink

Home Browse Search

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 that has three double-walled fiberglass gasoline underground storage tanks (USTs) The site currently contains seven groundwater monitoring wells (MW I—MW7) and two vapor extraction wells (VEWI 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 e vapor extraction system operated at the site from November 1995 to March 1996, which extracted soil vapor through five wells (VEW 1, 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 /On21 January 1997, the seven groundwater monitoring wells were purged and sampled Samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g) and for benzene, toluene, ethylbenzene, and total xylenes (BTEX) 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 at the site ranged from 23 56 to 20 49 feet below mean sea level Groundwater elevations have increased an average of 2 4 feet since the previous gauging on 16 October 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 MW1, 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, and Appendix A presents well construction detail reports Table 2 shows that the depth to the water table on 21 January 1997 ' ranged from 32 10 to 34 36 feet Therefore, none of the wells were screened across the water table on that date In order to estimate the groundwater gradient and flow direction, we Eave ' prepared a water table contour map (Figure 1) using the following wells screened near the water table MW 1, MW2, and MW3 The flow direction based on data from these wells was toward the southeast at an approximate gradient of 0 004 Gauging data and calculated groundwater elevations from 21 January 1997 are presented in boldface type in Table 2, along with previous gauging data Field documents are included as Appendix B 1 After the depths to water were measured, each groundwater monitoring 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 ml 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 70137 Q197 TX 2 l