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f ' <br /> I <br /> j <br /> i TABLE 6 <br /> Assimilative Capacity Calculation <br /> Del Monte Disco Property <br /> Change in BTEX Mass Ratio Assimilative Capacity %Role <br /> p Y <br /> Indicator Concentration <br /> Dissolved Oxygen 4.1 mg/L 0.32 1.3 mg/L 17.1% <br /> Titrate 6.7 mg/L 0.21 1.4 mg/L 18,4%, <br /> Ferrous Iron 0.8 mg/L 0.05 0.04 mg/L 0.5% <br /> ( Sulfate 22 mg/L 0.22 4.8 mg/L 63.3% <br /> Dissolved Methane 0.4 mg/L 1.28 0.5 mg/L 0.7% <br /> l Total Assimilative Capacity 7.7 mg/L 100% <br /> j <br /> Groundwater flow rate (Q)through the zone of significant contamination is calculated by <br /> the equation: <br /> Q=WTi/ne <br /> where: <br /> W= 150 to 300(ft)plume width <br /> T= 20 to 25 (ft'/day) transmissivity <br /> i= 0.06 to 0.27% (hydraulic gradient) <br /> n,= 20 to 30% (soil porosity) <br /> The range of groundwater flow rates through the zone of contamination ranges from 2,000 <br /> to 37,000 fO/yr. Based on an assumed average BTEX concentration of 0.5 mg/L, the flow <br /> rate of BTEX may range from less than 0.1 to 2 pounds per year. Based on the removal of 7.7 <br /> mg of BTEX per liter of background water,the potential BTEX removal by ITB may be from <br /> 1 to 18 pounds per year. This range of BTEX mass removal is considered conservative <br /> because it does not take into account the process of natural reaeration associated with <br /> r oxygen diffusion into groundwater and local groundwater recharge from rainfall. <br /> However,these calculations indicate that ITB is a viable option to stabilize or reduce the size <br /> i of the plume. If ITB is selected as the final remedy for the Disco property,it is <br /> recommended that groundwater monitoring be conducted for an extended period of time to <br /> confirm plume stability and/or reduction. <br /> } <br /> f SF01WROJECTSTELMONTEWLANT_3314RPT2 971QTR_REP.DOC 16 <br />