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• Given the relatively grid conditions at the Southfield site, measures to <br />ensure effective surface drainage, compaction of refuse materials, and <br />ongoing reclamation, it is anticipated that infiltration to the coal <br />refuse pile will be minimized, limiting the potential for significant <br />leaching. In addition, rock underdrains will tend to collect the majority <br />of any leachate which does percolate through the pile. These underdrains <br />discharge to existing permanent diversion channels which carry any <br />resulting flows to Sedimentation Pond No. 4. <br />The coal refuse pile has been in existence since mining operations were <br />initiated in 1978. To date, water quality monitoring of discharge from <br />Sedimentation Pond No. 4 indicates no significant changes in water <br />chemistry, TDS levels or concentrations of specific mineral constituents. <br />This may be due in part to relatively slow infiltration through the pile <br />which limits resulting leachate volumes, and dilution from surface runoff. <br />However, even with these considerations, observations to date provide a <br />good representation of the long-term potential for water quality impacts <br />• from the coal refuse pile. <br />If groundwater quality impacts do occur in the coal refuse pile area, they <br />are expected to be limited due to the relatively small areal extent of the <br />refuse pile and the factors previously noted. Colluvial/alluvial terrace <br />deposits which underlie the coal refuse pile are not an aquifer because <br />they are isolated and drained by intersecting ephemeral drainages. In <br />addition, stratigraphic units which underlie the terrace deposits consist <br />of relatively impermeable siltstones and shales which limit vertical <br />permeability. Any leachate from the coal refuse pile which is not <br />captured by the underdrain system will infiltrate to the terrace deposits, <br />mix with groundwater resulting from natural surface infiltration, and <br />discharge to the surface water system. Under these conditions, it is <br />anticipated that the minimal volume of resulting leachate will be <br />significantly diluted by both groundwater and subsequent surface water <br />mixing and will not significantly affect surface water quality. <br />With reference to the preceding discussion on potential impacts of surface <br />coal refuse placement on groundwater quality; similar considerations apply <br />to coal stockpiling in mine and loadout areas. Stockpile areas have been <br />2.05.6-24 <br />