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i <br /> R10/71 51-1C <br /> minimize downward leaching hydrocarbons <br /> Passive remediation, sometimes referred to as a "no-action" alternative, is applicable to <br /> sites where environmental conditions and regulatory polices are such that no other <br /> remedial action is required Although environmental and waste characteristic are at times <br /> amenable to passive remediation, this alternative is rarely implemented because of local <br /> regulatory policies and site conditions <br /> The decision to utilize passive remediation involves numerous site-specific as well as <br /> regulatory considerations The factors favoring the possible suitability of this approach <br /> are <br /> o The regulatory policies allow considerations of passive remediation This <br /> may not be the case at Shop 10 <br /> o The site is far from downstream receptors Neighbors should be distant <br /> and on municipal water supplies The groundwater underneath the subject <br /> facility is a source of potable water <br /> o The depth to groundwater is large <br /> o A favorable soil profile is present A permeable surface soil layer enhances <br /> biodegradation and low permeability soils between the surface sods and <br /> water table and inhibits downward migration of infiltrating water Hydraulic <br /> conductivity ranges from greater than 1002 cm/sec for highly permeable sod <br /> to less than 10-6 cm/sec for low permeability soils The hydraulic <br /> conductivity for the soil at the site has not been determined However, it <br /> appears, that the sal (clays and silts) above the groundwater may inhibit <br /> downward migration of contaminants On the other hand, the same low <br /> permeability sods will inhibit biodegradation of soil contaminants <br /> o The land is microbially fertile with population of approximately 10 million <br /> microbes/gm or more This has not been determined for Shop 10 <br /> o Rainfall is moderate to light with only a small probability of surface ponding <br /> o The contaminant is highly biodegradable and soil concentrations are initially <br /> low enough for biodegradation to proceed This would require pilot testing <br /> to determine <br /> 26 <br />