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1 Site Background Information -Ripon Farm Service Page 6 of 8 completed as vapor extraction wells, drilled to a total depth of approximately 18 feet bsg and ' completed with 5-foot screen intervals. Soil samples were collected from air-sparge pilot borings 1AS 1 to 1AS4 ahead of the drill bit using ' a core barrel. TPH-g was detected in each of the samples at concentrations as high as 990 mg/kg. TPH-d was also detected in each sample analyzed at concentrations as high as 1,000 mg/kg. BTEX compounds were detected in each sample analyzed.Benzene was detected at concentrations as high ' as 0.63 mg/kg at a depth of 18 feet bsg. The only fuel additive detected was 1,2 DCA at a concentration up to 20 micrograms per kilogram (gg/kg). ' A Solleco catalytic-oxidation soil vapor extraction (SVE) unit began operation at the site in December 2000. The system was monitored monthly during operation and after re-start events. During each monitoring event, the SVE flow rate, vacuum (potential), and concentrations of ' hydrocarbons in the extracted soil-vapor were measured, and a set of soil-vapor samples were collected by AGE personnel. The unit operated at an average extraction flow rate of 85 and ' 90 standard cubic feet per minute(cfm).A compressor-based EnviroSparge 1AS system was installed at the site in August 2001. The 1AS system delivered 6 cfin at a pressure of 10 pounds per square inch (psi), adequate to displace the static water within each sparge well. In addition, the dissolved ' oxygen in the ground water wells was measured to monitor the efficiency of the IAS system. Elevated concentrations of dissolved oxygen were periodically detected in monitoring wells used as ' observation wells within and outside the IAS network on the site. The highest dissolved oxygen value measured in well MW-1 was at 12.1%, and in well MW-2 at 20.8%. Generally, dissolved oxygen concentrations measured in the wells remained stable at, or sporadically increased above, ' pre-remedial levels. Sparging rates were measured at approximately 6 cfm during each monitoring event. A pressure of approximately 10 psi was maintained for the air sparging flow rate. The estimated mass of hydrocarbons removed was based on laboratory analysis of soil-vapor samples. The mass of extracted hydrocarbons was calculated for each time period using average hydrocarbon concentrations of influent soil-vapor sample data and average air flow rates.A total of t 2,122.45 kg (4,229.12 lbs), or a volume of 748.5 gallons hydrocarbons as gasoline, was removed between December 2000 and December 2003. During this period, the petroleum-hydrocarbon concentrations had declined to the point where ' utilizingthe unit was no longer cost effective in terms of the remediation goals. The catalytic SVE g y� system was replaced on 13 December 2002 with a vacuum blower and 55-gallon moisture collection canister.Operation of a soil vapor extraction(SVE)vacuum blower ceased in January 2004 due to malfunction of the equipment.A sample of the soil vapor from the monitoring events during the last ' quarter of 2003 was absent of detectable hydrocarbons, therefore SVE was not restarted. ' Advanced GeoEnvironmental,Inc.