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11 March 2002 • AGE NC Project No 95-0143 Page 2 of 5 and an in-situ air spargmg (LAS) unit were subsequently Installed north of the car wash canopy Details of the SVE/IAS system Installation were reported In Quarterly Report-May 1999,dated 30 July 1999 and Quarterly Report - August 1999, dated 05 October 1999, both prepared by AGE Operation of the SVE/IAS system was initiated in November 1999 and continued until November 2000 The SVE system was shut down due to a significant decrease in hydrocarbon concentrations in soil gas drawn from the vadose zone The decrease in hydrocarbon concentrations coincided with an Increase in ground water elevation that may have"drowned"the portion of vadose zone in which the extraction wells were screened Approximately 830 gallons of petroleum hydrocarbons had been extracted during operation of the SVE system On 15 and 16 March 2001, five soil borings (MW-22, MW-23, MW-24, EW-3 and EW-4) were advanced at the site Borings MW-22,MW-23 and MW-24 were completed as 2-inch ground water monitoring wells,borings EW-3 and EW-4 were completed as 4-inch ground water extraction wells Extraction wells EW-3 and EW-4 were installed to address hydrocarbon-impacted ground water at the former UST No 7 location and to induce draw-down in local ground water Draw-down of local ground water would increase vadose zone thickness and enhance SVE performance at the former UST pit Iocation Procedures and results of the well Installation were summarized In AGE's • Quarterly Report-First Quarter 2001, dated 30 May 2001 ' 3.0. PROCEDURES Field activities were performed in accordance with guidelines Issued by the Central Valley Regional ' Water Quality Control Board (CVRWQCB) and by the San Joaquin County Environmental Health Department (EHD) for investigations of underground storage tank (UST) sites and sampling of ground water monitoring wells,respectively Field procedures for the performance of ground water monitoring and sampling are described below 3 1 WELL MONITORING AND EVACUATION On 13 February 2002, a Sollnst water level meter was used to measure the depth to ground water in I twelve monitoring wells at the site and in fourteen monitoring wells at the neighboring Madison site relative to the tops of the well casings The ground water elevations(Table 1)and hydraulic gradient (Figure 3) were determined from these data After measurement of depths to water,casing water in each monitoring well was evacuated(purged) using a two-stage submersible purge pump or a new disposable plastic bailer The pump was decontaminated prior to purging each well using an Alconox solution and clean tap water • Temperature, pH and conductivity of the purged water were measured at regular intervals dunng ' purging using an Oakton water analyzer Approximately 5 to 14 gallons of water were removed from Advanced GeoEnviron mental,Inc I