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kq KLEINFELDER 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 Del Monte purchased the property 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 impact 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, 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 to 75 feet below the ground surface (bgs), and also in the groundwater. In February 1995, a soil vapor extraction and air sparging system (SVE/AS) was installed and operated at the site (CH2M Hill, 1995). An estimated 8,787 pounds of TPH-g were removed while the system was in operation up to November 1995. The SVEIAS was shut down due to rising groundwater levels above the SVE systems screened level. The rising water levels were caused primarily by the shutdown of not only three Del Monte production wells, but also reportedly by the shutdown 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. In 2003 Kleinfelder replaced the soil vapor extraction system and air sparge/ozone injection systems were 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 June, that portion of the remediation system began operating full time. 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.M0NIST05R14241CD:Iv Page 6 of 14 ©2005, Kleinfelder, Inc. November 15,2005