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• • RECEIVED . , F) 20 i6 Appendix A - Site Background Information ENVIRONMENTAL Page 4 of 5 HEALTH DEPARTMENT at the site by continuously extracting groundwater from well EW-1 at a rate of approximately 5 gallons per minute. The extracted groundwater was processed through a ground water treatment system consisting of 8,000-pounds of granular activated carbon (GAC). Following treatment, water was discharged directly to the City of Manteca sewer system, located approximately 25 feet south of the ground system. Interim ground water pump-and-treat operation and maintenance procedures for the site were outlined in AGE's Interim Remediation Work Plan - June 2001, dated 21 June 2001. 5.0. QUARTERLY GROUNDWATER MONITORING Between July 2000 and December 2007, thirty (30) ground water monitoring events have been conducted at the site to monitor dissolved petroleum hydrocarbon concentrations in ground water and to characterize ground water flow direction and gradient. Since initiation of ground water monitoring at the site in July 2000, the depth to ground water has generally ranged between 15 and 25 feet bsg. The ground water elevation has ranged between 7 and 17 feet above mean sea level (MSL),with a dominant flow direction towards the northwest. Laboratory analysis of first zone (shallow)ground water monitoring well samples (between 8'/2 and 35 feet bsg) generally has detected significant TPH-g and BTEX compounds in water samples collected from wells MW-2, MW-3, MW-6 and MW-7A. The most intense gasoline-impacted ground water(core)was centered in the area of wells MW-2, MW-6 and MW-7A at maximum concentrations of 190,000 pg/I TPH-g, 18,000 pg/I benzene, 44,000 pg/I toluene, 5,800 ethylbenzene and 30,000 xylene. Fuel additives detected in site monitoring wells included MTBE, TAME and 1,2-DCA. The most intense MTBE-impacted ground water has consistently been detected from wells MW-2, MW-3, MW-6 and MW-7A at concentrations as high as 2,000,000 pg/I (MW-6).The most intense TAME-impacted ground water has consistently been detected from wells MW-2, MW-3, MW-6 and MW-7A at concentrations as high as 3,700 pg/I. The most intense 1,2-DCA-impacted ground water has consistently been detected from well MW-2 at a concentration of 130 pg/I. Chlorinated solvents PCE and TCE have consistently been detected at most wells at the site at concentrations as great as 4,900 pg/I PCE from well MW-4 and as high as 470 pg/I TCE from well MW-10B. However, PCE and TCE-impact are not considered constituents of concern for the Rainwater car wash. Advanced GeoEnviron mental,Inc.