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1 <br /> r <br /> • Site Background Information - Ripon Farm Service <br /> ' Page 6 of 8 <br /> ' completed as vapor extraction wells, drilled to a total depth of approximately 18 feet bsg and <br /> completed with 5-foot screen intervals. <br /> Soil samples were collected from air-sparge pilot borings IAS1 to IAS4 ahead of the drill bit using <br /> a core barrel. TPH-g was detected in each of the samples at concentrations as high as 990 mg/kg. <br /> TPH-d was also detected in each sample analyzed at concentrations as high as 1,000 mg/kg. BTEX <br /> r compounds were detected in each sample analyzed.Benzene was detected at concentrations as high <br /> as 0.63 mg/kg at a depth of 18 feet bsg. The only fuel additive detected was 1,2 DCA at a <br /> concentration up to 20 micrograms per kilogram (µg/kg). <br /> rA Solleco catalytic-oxidation soil vapor extraction (SVE) unit began operation at the site in <br /> December 2000. The system was monitored monthly during operation and after re-start events. <br /> ' During each monitoring event, the SVE flow rate, vacuum (potential), and concentrations of <br /> hydrocarbons in the extracted soil-vapor were measured, and a set of soil-vapor samples were <br /> collected by AGE personnel. The unit operated at an average extraction flow rate of 85 and <br /> 90 standard cubic feet per minute(cfm).A compressor-based EnviroSparge IAS system was installed <br /> at the site in August 2001. The IAS system delivered 6 cfm at a pressure of 10 pounds per square <br /> inch (psi), adequate to displace the static water within each sparge well. In addition, the dissolved <br /> oxygen in the ground water wells was measured to monitor the efficiency of the IAS system. <br /> ' Elevated concentrations of dissolved oxygen were periodically detected in monitoring wells used as <br /> observation wells within and outside the IAS network on the site. The highest dissolved oxygen <br /> value measured in well MW-1 was at 12.1%, and in well MW-2 at 20.8%. Generally, dissolved <br /> oxygen concentrations measured in the wells remained stable at, or sporadically increased above, <br /> pre-remedial levels. Sparging rates were measured at approximately 6 cfm during each monitoring <br /> event. A pressure of approximately 10 psi was maintained for the air sparging flow rate. <br /> The estimated mass of hydrocarbons removed was based on laboratory analysis of soil-vapor <br /> samples. The mass of extracted hydrocarbons was calculated for each time period using average <br /> hydrocarbon concentrations of influent soil-vapor sample data and average air flow rates.A total of <br /> 2,122.45 kg (4,229.12 lbs), or a volume of 748.5 gallons hydrocarbons as gasoline, was removed <br /> between December 2000 and December 2003. <br /> rDuring this period, the petroleum-hydrocarbon concentrations had declined to the point where <br /> utilizing the unit was no longer cost effective in terms of the remediation goals. The catalytic SVE <br /> r system was replaced on 13 December 2002 with a vacuum blower and 55-gallon moisture collection <br /> canister. Operation of a soil vapor extraction(SVE)vacuum blower ceased in January 2004 due to <br /> malfunction of the equipment. A sample of the soil vapor from the monitoring events during the last <br /> ' quarter of 2003 was absent of detectable hydrocarbons, therefore SVE was not restarted. <br /> r <br /> Advanced GcoEnvironmental,Inc. <br /> r <br />