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I. k" KLEINFELDER The general direction of groundwater flow in the area of the site based on the most recent data g � , issued by the San Joaquin County Flood Control and Water Conservation District, (Spring 1999), and past reported data from groundwater monitoring events, is to the southeast. The elevation of first groundwater is approximately -20 feet below mean sea level. According to the same report, F the depth to groundwater in the vicinity of the project site is approximately 45 feet below grade. The Disco Remediation Area is the location of a former gasoline 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, 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 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. 1..2 REPORT OBJECTIVE This workplan outlines a pilot test program to evaluate the feasibility of a remediation approach proposed for the Disco Site. The proposed approach addresses two unique areas of concern at the site, the source area that contains high concentrations of petroleum hydrocarbons including 1,2-Dichloroethane (DCA) and a large, dilute plume of DCA that extends approximately 500 feet offsite. The remedy being evaluated involves soil vapor extraction and air sparging in the source area and an ozone sparge curtain at the leading edge of the DCA plume. 12280 12002R476 Page 2 of 26 Copyright 2002 Kleinfelder,Inc. May 17,2002