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As discussed in more detail subsequently, any seepage resulting <br />from net infiltration on the pile is e~cpected to be very small (0 to 1 <br />inches per year). Strata with very low permeability are required to <br />cause seepage at such rates to become penrched and form a saturated zone. <br />Alternatively, seepage could persist as partially saturated flow to <br />depths below the elevation of the valley floor. If a perched water table <br />is formed, it is likely that the direction of flow will be toward the <br />valley as dictated by the topography of the contact between the refuse <br />and the foundation materials. <br />The water content of the refuse at placement will be about 15 <br />percent by weight. No significant internal drainage is anticipated. Net <br />infiltration, defined as the difference between total infiltration aryl <br />actual evapotranspiration, is expected to be zero for an average year. <br />This conclusion is based upon a monthly water balance calculation that <br />considered precipitation, evaporation from the snow pack, infiltration, <br />soil.-moisture storage, and evapotranspiration. A similar calculation for <br />an abnormally wet year resulted in an estimate of deep percolation of 0.7 <br />inches; surface runoff was taken as zero for that computation, so the 0.7 <br />inches estimate is believed to be conservatively large. • <br />A second potential source of water input to the pile is seepage <br />from surface water diversion ditches, both during construction and after <br />reclamation is complete. These ditches will contain water for a short <br />time only during runoff events. Seepage from this source is expected to <br />be negligibly small. <br />A wet year seepage of 0.7 inches translates to a volume of 3.6 <br />acre-ft for the maximum exposed area of 66 acres. Based on the leaching <br />tests of existing coal waste, the dissolved solids concentration in this <br />seepage is expected to approximate 4200 mg/1. The dissolved solids load <br />added to the Purgatoire River as the result of wet year seepage could be <br />as much as 20 tons, therefore. This is about 0.2 percent of the average <br />salt load as measured at the Madrid gaging station. An input of 20 tons <br />of additional dissolved solids will increase the average concentration <br />for an average year by 0.5 mg/1. The calculated changes in the in-stream <br />(Revised 05111/94) • <br />2.05-81 <br />