SITE INFORMATION AND CORRESPONDENCE_FILE 2

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REGULATORY MEETING SITE: Former Exxon RAS#7-3942,4444 North Pershing Avenue, Stockton, California SUBJECT: REQUEST FOR NO FURTHER REMEDIAL ACTION DATE: APRIL 17,2002 In a letter received in December 2000, SJCPHS concurred with (1) discontinuing operation of the UVB remediation system, and (2) directed ExxonMobil to evaluate other remedial alternatives for groundwater cleanup. This evaluation of remedial alternatives was presented in the Request for No Further Action Report dated October 2001. A summary of the site history, as well as the conclusions and recommendations presented in this report are presented below. SITE LOCATION AND LAND USE Former Exxon RS 7-3942 is currently a vacant lot located on the southeast corner of the intersection of North Pershing Avenue and Rosemarie Lane (Figure 1). Used oil and three grades of gasoline were stored in four underground storage tanks, which were removed from the site in July 1986 (Figure 2). Land use in the vicinity of the site is primarily commercial and residential. A Shell service station and a 7-11 food and gasoline service store are located on the southwest and northwest comers, respectively, of the intersection of North Pershing Avenue and Rosemarie Lane. The convalescent home Chateau Hospital is located approximately 200 feet northwest of the site across Rosemarie Lane. There is an apartment complex to the east of the site and a commercial building to the south. SITE GEOLOGY AND HYDROGEOLOGY The geology and hydrogeology of the site have been evaluated using existing boring logs from previous site investigations and monitoring data. The site is generally underlain by silty-to-clayey sediment to a total depth of approximately 50 feet below ground surface (bgs), with generally discontinuous sand to silty sand lenses at approximately 10-20 feet bgs and at approximately 30-40 feet bgs. Four cross-section locations are shown on Figure 3 and cross-sections A-A', B-B', C-C' and D-D' are shown as Figures 4a, 4b,4c, and 4d, respectively. Historically, groundwater has been encountered at the site at depths ranging from approximately 13 to 41 feet bgs. Based on hydrographs presenting well construction details, groundwater elevations, and concentrations of benzene, methyl t-butyl ether (MTBE), and Total Petroleum Hydrocarbons as gasoline (TPH-g) over time, there has been an approximately 25-foot rise in groundwater elevations over time at the site from—30.55 feet above mean sea level (msl)in October 1992 to—5.24 feet msl in June 2001. These historical groundwater elevation high and low points are also presented on the geologic cross- sections (Figures 4a-4d), as are the analytical results for soil samples collected during this ongoing hydrogeologic investigation. As presented on these cross-sections, petroleum hydrocarbons occur in soil at the site between approximately 17 and 42 feet bgs. Currently, these petroleum hydrocarbons entrapped in soil at the site are submerged. The soil analytical data presented in these figures suggest that the hydrocarbon release occurred when the water level was approximately 23 feet lower than current levels. The only significant soil concentrations are found below the water table. The groundwater flow direction has generally been to the northeast with a historical average of N53E and an average gradient of 0.006. PREVIOUS ENVIRONMENTAL ACTIVITIES AT THE SITE In October 1990, EA submitted a Combined Work Plan to Remediate Soil and Groundwater (EA 1990). Under this plan, EA proposed to remediate groundwater through conventional technology available at the time: a groundwater extraction, treatment, and re-injection system. Pursuant to the 1990 plan, EA G:T.jt \73942WUBLICy,mati.&44 C.do I