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CLEARWATER <br />' G R O U P <br /> Environmental Srrvfeea <br />' RSBLs for Subsurface Sod(>3m bgs) (mg/kg) Groundwater RBSL(pg/L) <br /> Groundwater is Groundwater Is Not Drinking Drinking Drinking <br />' Drinking Water Water Resource Water Water Not <br /> Resource Threatened Theatened <br /> Contaminant Residential, Residential Industrial/ <br />' Industrial/ Land Use Commercial <br /> Commercial Permitted Land Use <br /> Land Use Only <br /> Total Petroleum 1001100 4001500 400/500 1001100 5001640 <br /> Hydrocarbons <br /> (gas/diesel) <br /> Benzene 0 045 0 18 039 10 46 <br /> Toluene 26 84 84 40 130 <br />' Ethvlbenzene 25 24 24 30 290 <br /> Xylenes 10 to 10 13 13 <br /> MTBE 0 028 10 1o__ 50 1,800 <br />' Clearwater believes that the listed RBSLs provide adequate guidance in determining final soil <br /> and groundwater cleanup levels The most conservative soil RBSLs listed are 100 mg/Kg TPHg <br />' and TPHd for soil and 100 µg/L TPHg and TPHd for groundwater, assuming drinking water is <br /> threatened The results of the sensitive receptor survey performed by Clearwater at the site <br /> indicate no drinking water sources are threatened at this time <br /> It should be noted that these are clean-up goals, and that it is often extremely difficult or <br />' impossible to achieve such clean-up goals It is likely that at some point during the course of <br /> active remediation that contaminant recovery rates will become negligible, and continued <br />' remedial operation costs cannot be justified If such a scenario came to pass, it would be worth <br /> evaluating the rate at which the residual dissolved-phase plume would naturally attenuate to <br />' below the clean-up goals as a final plume management plan <br /> 1 <br /> 1 <br /> ZBt78C RAP 18 May 18,2004 <br /> 1 <br />