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1 <br /> ' Site Background Information - Ripon Farm Service <br /> Page 7 of 9 <br /> Elevated concentrations of dissolved oxygen were periodically detected in monitoring wells used <br /> as 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 Spargmg 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 analysts 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 <br /> of 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 /> ' During this period, the petroleum-hydrocarbon concentrations had declined to the pomt where <br /> utilizing the unit was no longer cost effective in terms of the remediation goals The catalytic SVE <br /> 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 /> Impacted soil was present below the ground water table when remediation began,due to historically <br /> ' lower ground water elevations at the site during which time a portion of the unauthorized <br /> hydrocarbon release occurred The former UST area was impacted by diesel fuel compounds, but <br /> is also impacted by significant concentrations of gasoline fuel compounds <br /> The volume of soil addressed by the remediation system was estimated to be 645 cubic meters, <br /> based on the limited lateral extent of the vadose zone contamination and a depth to ground water of <br /> ' 20 feet bsg The generalized mass of vadose-adsorbed TPH-g was approximately 65 2 lbs, or <br /> 29 58 kg, and the generalized mass of adsorbed TPH-d was approximately 77 16 lbs, or 35 kg <br /> ' The total volume of impacted soil addressed by the remediation system was estimated to be <br /> 1,240 cubic meters, from the base of the former UST excavation to the depth of 30 feet bsg The <br /> total mass of adsorbed TPH-g was approximately 123 5 lbs, or 56 8 kg, and the mass of total <br /> ' adsorbed TPH-d was approximately 150 lbs, or 68 2 kg <br /> Hydrocarbon-impacted ground water in the former UST area has higher average TPH-g to TPH-d <br /> ' ratios(0 702- 1 852),indicating a greater contribution to ground water of TPH-g in the former UST <br /> area <br /> ' Advanced GeoEnvirown ental,Inc <br />