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1 GeoAudit 2/26/93 Page 2 of 4 the VES design were presented in the referenced work plan. The volume of gasoline in the soil was "liberally" estimated in the ' work plan to be 18,500 pounds (3000 gallons) . A vapor extraction well was installed at the location of the former UST and a VES consisting of a 100 cubic feet per minute (CFM) ' blower, internal combustion engine and peripheral equipment was installed. Operation of the system began on August 15, 1991 . ' VES OPERATION The VES has been in operation for approximately 81 percent of the ' time since start-up except for a period between February 14 , 1992 and March 27, 1992 when the system was down for repairs. Total hours of operation were 8,864 on December 28, 1992 . The VES is operated under permit requirements of The San Joaquin Air Pollution ' Control District order number 91-61 . The VES has extracted vapors at a rate of approximately 60 CFM during the project. VES intake, pre-catalyzer and outlet hydrocarbon vapor concentrations are measured on a weekly basis except when the system is down. Organic vapors are measured using a photoionizati.on detector (PID) calibrated to isobutylene. ' The VES stream has extracted vapor from Well MW-2 for the entire project except when switched to Well MW-1 for approximately four ' days in December 1992 . Very low hydrocarbon concentrations were measured in the inlet soil vapor stream from Well MW-1, therefore, the system was switched back to Well MW-2 . STATUS OF THE REMEDIATION PROGRAM ' Hydrocarbon concentrations in recovered soil vapors have been reduced from a high approaching 2,500 ppm in mid 1991 to approximately 500 ppm at the end of 1992 . A plot of the inlet hydrocarbon vapor concentrations versus time is presented in Figure ' 3 . A comparison of Inlet and outlet concentrations indicate that a hydrocarbon destruction efficiency of greater than 90 percent has been achieved throughout the remediation project. ' The relationship between the actual concentrations of hydrocarbons in the inlet stream and the monitoring values as isobutylene using the PID have been reported in the past to be approximately 10: 1 . This relationship effects the timing of future activities. Therefore, actions are planned to more accurately determine this relationship. These actions are discussed in the following ' section.