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V i 3164 Gold Camp Drive �/. Delta Suite 200 Rancho Cordova,CA 95670-6021 Environmental U.S.A. Consultants,Inc. 916/638-2085 FAX:916/638-8385 December 14, 1999 L Mr.Dann L.Rouse Exxon Company,U.S.A. 2300 Clayton Road, Suite 1250 LConcord,California 94520 Subject: Quarterly Ground Water Monitoring Report, Fourth Quarter 1999 L Exxon Service Station No. 7-0137 1605 South El Dorado Street Stockton, California Delta Project No. D099-865 LDear Mr.Rouse: L Delta Environmental Consultants,Inc. (Delta)has been authorized by Exxon Company,U.S.A. (Exxon) to prepare a report summarizing results of quarterly ground water monitoring and sampling conducted by Blaine Tech Service at the subject site which is currently operating as an Exxon Service Station. L This report presents the results of quarterly ground water monitoring and sampling conducted on I October 28, 1999. The field methods and procedures used are presented in Enclosure A. LWork Performed On October 28, 1999, depth to ground water was measured in ground water monitoring wells MW-1 L through MW-7, and vapor extraction well VEW-2. Vapor extraction well VEW-1 was dry. A map illustrating ground water elevation and flow direction is included as Figure 1. Ground water samples were collected from monitoring wells MW-1 through MW-7, and vapor extraction well VEW-2. The samples were submitted to Southern Petroleum Laboratory in Houston, Texas (a California-certified laboratory) for analysis of benzene, toluene, ethylbenzene, and total xylenes (BTEX), and methyl tertiary butyl ether (MTBE) using EPA Method 8021B, and total purgeable petroleum hydrocarbons L (TPPH) as gasoline using EPA Method 8015 Modified. A map illustrating concentrations of benzene, TPPH as gasoline, and MTBE is included as Figure 2. Cumulative ground water data are summarized in Table 1. Field sampling data sheets for the site are included as Enclosure B. A copy of the laboratory analytical report with chain-of-custody documentation for the October 28, 1999 sampling event is presented in Enclosure C. LRemediation System Status 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, and a new SVE system was installed by EA Engineering, Science & Technology (EA) and operated from February 21,1997 to April 10, 1998. Performance data collected by Fugro and EA are presented in Table 2. Table 3 L summarizes laboratory analytical results for soil vapor samples collected by EA. LProviding a Competitive Edge