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' Site Background Information: Ripon Farm Service • - Page'6 of 7 . VW-9B, VW-10 and VW-II were completed as vapor extraction wells, drilled to a total depth of approximately 18 feet bsg and completed with a 5-f6ot screen interval. Sol] samples were collected from air-sparge pilot borings IAS1 to IAS4 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 ata maximum concentration of 20 micrograms per kilogram (pg/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 IAS system was installed ' at the site in August 2001. The IAS system delivered 6 cfm at a pressure of 10 pounds per square inch,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 was 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 scfm 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 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 declined to the point where utilizing the unit was no longer cost effective in terms of the remediation goals.The catalytic SVE 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.