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1 I INTRODUCTION Former Exxon Retail Site (RS) 7-0137 is an active service station located at 1605 South El Dorado ' Street in Stockton, Cahforrua There is one 20,000-gallon double-walled fiberglass underground storage tank at the site divided into compartments that contain 60 and 40 percent of the total volume capacity A soil vapor extraction system was operated at the site from approximately November 1995 until April 1998 ' 2 GROUNDWATER MONITORING On 30 July 2000, wells MW1-MW7, VEW1, and VEW2 (Figure 1)were gauged for depth to water and for liquid-phase hydrocarbons (LPH) with an optical interface probe Groundwater samples were collected from wells MW1-MW7 and VEW2, and the samples were analyzed for Total Petroleum Hydrocarbons as gasoline(TPH-g), for benzene, toluene, ethylbenzene, and total xylenes 1 (BTEX), and for methyl t-butyl ether(MTBE) Well VEW1 was not sampled because it was dry The depth-to-water measurements and calculated groundwater elevations are presented in Table 1, ' along with historical data, and current groundwater elevations are shown in Figure 1 The groundwater flow direction on 30 July was to the southeast,with a gradient of approximately 0 001 LPH was not observed in any of the wells After the depths to water were measured, the wells were purged Field parameters of pH, temperature, and electrical conductance of the purged water were measured for approximately every well casing volume 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 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 analyzed for TPH-g by Cal EPA- modified EPA Method 8015 and for BTEX and MTBE by EPA Method 8021B The samples were ' also analyzed for MTBE by EPA Method 8260B The results are presented in boldface type, along with previous analytical data, in Table 1, and are shown in Figure 1 The laboratory analytical report and chain-of-custody documentation are included in Appendix B 3. REMEDIATION SYSTEM ' A soil vapor extraction(SVE)system was installed at the site by Fugro West,Inc (Fugro) and operated for approximately 5 months from November 1995 to March 1996 A new SVE system was installed by EA Engineering, Science, and Technology and was started in February 1997 The SVE system was ' shut down in April 1998 after soil vapor sample results indicated that the SVE system had effectively removed the volatile petroleum hydrocarbons from the vadose zone F 1p.jf ets170177%f la Le,5Wp1Q7COVTc dx 1