Laserfiche WebLink
The DEPOSITS model (Ward et. al 1979) was used to determine the capacity and effectiveness of Sedimentation <br />Pond D to handle inflows from all tributary sources, during a 10 -year, 24-hour precipitation event. The output from <br />the DEPOSITS model is given in Exhibit 28, Deposits Model Output. Several assumptions were made in <br />calibrating the DEPOSITS model. First, it was assumed that two perennial sources of water will be tributary to <br />Pond D: drainage from the upgradient spoils through the overflow channel, and discharge from the underground <br />mine through Ditch D-2. The inflow to the pond from these sources was assumed to fill the impoundment to the <br />sediment storage level; thus dead storage was set equal to the permanent pool volume. Second, it was assumed that <br />the runoff from the design event will enter the pond from all tributary areas simultaneously, without regard to lag <br />time due to diversion. These assumptions make the flood routing and sedimentation analyses more conservative. <br />The inflow hydrograph calculated by the DEPOSITS model is derived by applying the 10 -year, 24-hour SCS Type <br />11 storm and the SCS unit hydrograph to derive the runoff response. The outflow hydrograph is derived by <br />calculating the cumulative volume in the pond and applying stage -storage relationships to determine head on the <br />decant orifice, which is used in the orifice equation to derive the discharge. The outflow sediment -graph is derived <br />by applying the variable rates of inflow and outflow to determine detention time, and applying representative <br />particle -size distributions to Stokes' Law in an iterative analysis. <br />Leachate studies conducted at Energy Mine No. 1 with mixed overburden spoil, and at the Foidel Creek Mine with <br />underground waste rock, yielded similar results. Monitoring of actual leachate water at Energy Mine No. 1 yielded <br />results which are comparable to the column leach tests. Ground water chemistry at the mine site will change from a <br />predominantly sodium -sulfate type to a calcium -sulfate type. Total dissolved solids concentration in leachate <br />waters will be approximately 2,800 mg/l. This concentration is less than the maximum allowed for agricultural <br />uses. Solute transport will carry leachate into the adjacent overburden aquifer. Dilution of leachate through <br />intermixing with ground water in the adjacent overburden aquifer will occur, and concentrations of leachate outside <br />the permit and adjacent areas will be below the level of detection. Therefore, the production of leachate will not <br />affect the postmining land use, and ground water quality will not be degraded by the proposed disposal operations. <br />The output from the DEPOSITS model shows that the average eluent concentration from Pond D of Total Suspended <br />Solids (TSS) is 20.7 mg/l. This is in compliance with the average monthly effluent limitation for TSS set in the NPDES <br />permit. Based on this analysis and monitoring records for pH, total iron, total manganese, oil and grease, and other <br />parameters, the effluent limitation set for discharge point 005 (Site 84 in NPDES Permit CO -0027154 are expected to <br />be met. Therefore, coal waste disposal operations in the Area 1 Pit will not compromise the existing sediment control <br />plan and will not degrade surface water quality. <br />As noted in the geology section, under the discussion of the geology of the Eastern Mining District, the overburden <br />strata is the same as that overlying the initial mining area. Roof and floor analysis was completed on those materials <br />obtained from exploration holes 93001, 93003, 93004, and 93005. The results of the analysis do not indicated any <br />problems with these materials. The data is presented in Exhibits JOA through 10E. As stated in the preceeding <br />sections, no leaching problems, which would affect the postmining land use, are anticipated from mining in the Eastern <br />Mining District. As is the case with the current mining area, increases in TDS are associated with the spoil water that is <br />used for underground dust suppression. The present demonstration, however, does not indicate that the elevated TDS <br />concentrations are impacting existing land uses. <br />EMD (Panels 2-Ri2ht through 6 -Right, PR 97-04) <br />The geology discussion provided for PR 93-03 applies to the areas covered by this permit revision. As stated in PR <br />93-03, and as it carries forward into this permit revision, no leaching problems are anticipated from mining in the <br />EMD. Also, it is planned to return all of the mine water to the underground workings so that no discharge is <br />anticipated into Foidel Creek. Therefore, the mining operation should not impact the postmining land use. <br />TR05-49 2.05-95 Revised - May 2005 <br />