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' Site Background Information - Ripon Farm Service . Page 7 of 9 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 cfin 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 had 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 Impacted soil was present below the ground water table when remediation began,due to historically ' lower ground water elevations at the site during which time a portion of the unauthorized hydrocarbon release occurred The former UST area was impacted by diesel fuel compounds,but is also impacted by significant concentrations of gasoline fuel compounds ' The volume of soil addressed by the remediation system was estimated to be 645 cubic meters,based on the limited lateral extent of the vadose zone contamination and a depth to ground water of ' 20 feet bsg The generalized mass of vadose-adsorbed TPH-g was approximately 65 2 lbs, or 29 58 kg, and the generalized mass of adsorbed TPH-d was approximately 77 16 lbs, or 35 kg ' The total volume of impacted soil addressed by the remediation system was estimated to be 1,240 cubic meters,from the base of the former UST excavation to the depth of 30 feet bsg The total mass of adsorbed TPH-g was approximately 123 5 lbs, or 56 8 kg, and the mass of total adsorbed ' TPH-d was approximately 150 lbs,or 68 2 kg ' Hydrocarbon-impacted ground water in the former UST area has higher average TPH-g to TPH-d ratios(0 702- 1 852),indicating a greater contribution to ground water of TPH-g in the former UST area ' Advanced GeoEnvironmentni,Inc 1