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The analyses of leachate water, shown in Exhibit 27, Column Leach Study of Mine Waste Material, were compared <br />to existing pit water chemistry shown in Table 50, Energy Mine No. 1 Pit Water Quality. The average <br />concentrations of major cations and anions were converted to milli-equivalents per liter and plotted on a piper <br />• diagram, shown in Figure 10, Leachate Chemistry, Energy Mine No. 1. In addition, the average concentrations of <br />major ions in ground water adjacent to the Energy Mine No. 1 pit were plotted. The piper diagram shows similar <br />water chemistry for leachate from underground mine waste and existing undisturbed overburden aquifer, although <br />the leachate water has much higher concentrations initially. These waters show asodium-sulfate dominance. The <br />water quality of the Mine 1 Pit shows acalcium-sulfate dominance, which indicates a large proportion of surface <br />runoff. <br />As previously stated, leachate water will percolate into the adjacent overburden aquifer under the influence of <br />potentiometric head. An analysis of solute transport through the aquifer was performed, using flow equations to <br />model a plume of saline water as it would be distributed in a confined aquifer with time. The equations which <br />describe the travel of dissolved solids through an aquifer are the same as those used in tracer dye studies of porous <br />media. The equations contain. complex mathematical functions which can be solved by algebraic approximations. <br />The basic components of the equations are: 1) Aquifer characteristics; 2) The rate of ground water flow; 3) <br />Concentration of dissolved solids; 4) Values of longitudinal and transverse dispersivity; and 5) Retardation factors <br />to account for ion exchange, solute absorption, and radioactive decay. Aquifer characteristics are determined from <br />pump tests and drillhole data presented earlier. The rate of ground water flow is calculated from the average <br />permeability and potentiometric gradient within the overburden aquifer in this area. Concentration of dissolved <br />soils for these tests was measured through column leaching studies as shown in Figure 9, Predicted Leachate <br />Concentration, Energy Mine No. 1. Dispersivity is a parameter which is difficult to measure in the field and must <br />be assumed. Dispersivity is the ratio of solute dispersion to flow velocity. As the saline water leached from the <br />spoils enters the aquifer, a "plume" of solute spreads through the aquifer in the direction of ground water flow. As <br />the plume moves through the aquifer, the dissolved solids are diluted, diffused, and absorbed by physical and <br />chemical interaction with the natural ground water. The greatest effect on dispersion in aquifers associated with <br />coal strata is the heterogeneous nature of the formation. The lithology of the Williams Fork Formation is variable, <br />displaying many facies changes, pinch-outs, and thin sandstone lenses. Ground water movement in such an aquifer <br />is non-laminar, thus absorption and diffusion of highly saline water is enhanced. Longitudinal dispersivity is <br />measured in the direction of ground water flow; transverse dispersivity is measured in a lateral direction. <br />The measurements, calculations and assumptions discussed above were used in a predictive analysis to model the <br />distribution of a plume of saline water emanating from the Energy Mine No. 1 into the Twentymile Park ground <br />water basin. The OSM Plume Management Model (1981) was used to estimate concentrations of total dissolved <br />solids (TDS) in milligrams per liter above baseline concentration after 50 years of solute intrusion. The results in <br />Figure 11, Predictive Analysis -TDS Concentrations after 50 Years, show concentrations to be diluted to <br />acceptable levels of TDS concentration. <br />The disturbed area is tributary to Sedimentation Pond D, as shown on Map 24, Surface Facilities. Pond D serves as <br />the treatment facility for discharge point 005 (Site 84) under NPDES Permit CO-0027154. A system of diversion <br />ditches and transfer pipelines delivers water to Pond D from underground operations and reclaimed surface mined <br />areas. As stated previously, the Area 1 Pit receives water from surface runoff and infiltration from upgradient <br />reclaimed spoils. In addition, backfilling operations necessary for reclamation and waste rock disposal previously <br />displaced water in the pit, causing an overflow at the final highwall. The overflow has been directed into Pond D <br />through a designed channel. Sufficient freeboard has been provided to handle rates of flow higher than the design <br />flow of 0.8 cfs. The drainage from the Area 1 Pit will be treated in Pond D to -meet the effluent limitations <br />applicable under the NPDES Permit issued to CYCC, before being released to Foidel Creek. The overflow channel <br />has been constructed at the lowest topographic point on the highwall, and conforms to the requirements for <br />temporary diversions set forth in Rule 4.05.3. Designs for the overflow channel are given in Table 51, Overflow <br />Channel Specifications. <br />• <br />MR08-230 2.05-94 09/05/08 <br />