ARCHIVED REPORTS XR0003425 - Laserfiche WebLink

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' 1 INTRODUCTION ' Former Exxon Retail Site (RS) 7-3708 is an active U S A Petroleum station located at 2705 Country Club Boulevard in Stockton, California, at the northwest corner of the intersection of Ryde Avenue and Country Club Boulevard Elevation of the ground surface at the site is approximately 1 to 2 feet above mean sea level The site slopes down toward the northeast and southwest corners from a slight topographic high across the center ' There are two underground storage tanks at the site containing diesel fuel and unleaded gasoline Groundwater monitoring has been conducted at the site since 1991 ' 2 GROUNDWATER MONITORING On 16 August 2001, wells MW 1, MW4-MW 10, VEW 1, and VEW3 were gauged Groundwater ' samples were collected from wells MW1, MW4-MWI0, and VEWI, and the 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) Well VEW3 was dry on 16 August ' The current depth-to-water measurements and calculated groundwater elevations are presented in boldface type in Table 1, along with previous data Current groundwater elevations are also shown ' in Figure I The groundwater flow direction on 16 August was to the north, with a gradient of approximately 0 0006 Liquid-phase hydrocarbons were not observed in any of the wells ' after the depths to water were measured, the wells were purged Field parameters of pfi temperature and electrical conductance of the purged water were measured for approximately every well casing volume removed during' purging Copies of the field documents are included as Appendix A When the field parameters were stable (less than a 10 percent change from the previous reading for temperature and electrical conductance and not more than 0 1 pH units) and approximately 3 casing volumes were removed from each well, purging was stopped and samples ' were collected using factory-cleaned disposable bailers Wells that dewatered were allowed to recharge prior to sampling The samples were poured into 40-m1 glass VOA vials and stored in an ' ice-filled cooler All samples were handled and transported under chain of custody The samples were submitted to SPL, Inc in Houston, Texas, and were analyzed for TPH-g by Cal ' EPA-modified EPA Method 8015, for BTEX by EPA Method 8021B, and for MTBE by EPA Method 8260B The results are presented in boldface type in Table 1, along with previous analytical data, and are shown in Figure I The laboratory analytical report and chain-of-custody ' documentation are included in Appendix B As presented in Figure 1 and Table 1, MTBE was detected in well MW7 at a concentration of 74 ' µg/L MTBE was first detected in this well in August 2000, which is more than six years after Exxon transferred the property to New West Petroleum Well MW7 is located approximately 60 feet downgradient of the neighboring 7-Eleven Facility No 14117, which has had MTBE detected at concentrations up to 9,800 µg/L PA ,rlis it (»ii I