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i KLEINFEI_DER 3 BACKGROUND The Disco Remediation Area is the site of a former gasoline service station located on the southern portion of the Del Monte site. The Disco Remediation Area was operated as a service station until the property was purchased by Del Monte in 1976. Del Monte never operated the service station. Three 10,000 gallon underground storage tanks (USTs) were identified on the Disco site. The USTs were removed in 1985. During the removal of the USTs impacts to soil beneath the tanks was noted. The soil was excavated and aerated on the site and backfilled into the excavation. In 1991, a soil and groundwater investigation began. That investigation included a soil gas survey, i seven soil borings, and installation of eight monitoring wells. The results showed concentrations of Total Petroleum Hydrocarbon as gasoline (TPH-g) in the soil at depths ranging from 55 feet below the ground surface(bgs) to 75 feet bgs, and also in the groundwater. In February 1995, a soil vapor extraction and air sparging system (SVE/AS) was installed and operated (CH2M Hill, 1995) at the site. An estimated 8,787 pounds of TPH-g was removed. while the system was in operation up to November 1995. The SVE/AS was shut down due to rising groundwater levels above the SVE systems screened level, caused primarily by the J shutdown of not only three Del Monte production wells, but also reportedly due to the shut down of numerous city municipal wells in the.area. The main contaminants are TPH-g, benzene, toluene, ethylbenzene, xylene, and 1,2-DCA. The site is currently being monitored on a quarterly basis. Additionally, the soil vapor extraction system was replaced in 2003 by Kleinfelder and air sparge/ozone injection systems have been installed to further remediate the plume. In general, the source area (actual Disco site) began active remediation in May 2003 using the thermal oxidizer. In rune, that portion of the remediation system began operating 24/7. In July, the vapor extraction unit was converted from Thermal Oxidizer to Catalytic Oxidizer, and was operating continually. Regarding the downgradient edge of the plume, the ozone injection system began consistent and continuous operation in the beginning of September 2003 except during times of system maintenance and enhancements. 12280.M0NIST05R6131JZ:1v Page 6 of 13 0 2005,Kleinfelder,Inc. May 20,2005