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<br />decant orifice, which is used in the orifice equation to derive the discharge. The outflow sedimentgraph 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 />Conclusions <br />Leachate studies conducted at Energy Mine No. l 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 acalcium-sulfate type. Total dissolved solids concentration in leachate <br />waters will be approximately 2,800 mg/I. 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 post-mining 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 effluent concentration from Pond D of Total Suspended <br />Solids (TSS) is 20.7 mg/I. This is incompliance with the average morthly 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 />pazameters, the effluent limitation set for discharge point 005 (Site 84 in NPDES PermitCO-0027154 are expected to <br />be met. Therefore, the waste rock disposal operation will not compromise the existing sediment control plan and will <br />not degrade surface water quality. <br />Concerning the Fish Creek Tipple, no excess spoil or underground development waste will be generated in connection <br />with the operation. Thus, the requirements of this section and Rule 4.09 are not applicable. <br />EASTERN MINING DISTRICT <br />As noted in the geology section, the geology of the Eastern Mining District the overburden stata is the same as that <br />overlying the present mining area. Roof and floor analysis was completed on those materials obtained from <br />exploration holes 93001, 93003, 93004, and 93005. The results of the analysis does not indicated any problems with <br />these. materials. The data is presented in Exhibits l0A through ] OE. As stated in the above sections, no leaching <br />problems, which would affect the postmining land use, are anticipated from mining in the Eastem Mining District. <br />As is the case with the current mining area, increases in TDS are associated with the spoil water that is used for <br />underground dust suppression. However, the present demonstration does not indicate that the elevated TDS <br />concentrations are impacting existing lard uses. <br />EMD (Panels 2 right 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 ae anticipated from mining in the EMD <br />Also, it is planned to return all of the mine water to the underground workings so that no discharge is anticipated into <br />Foidel Creek. Therefore, the mining operation should not impact the postmining land use. <br />NMD (Panels 12 Right through 16 Right)(PR 99-05) <br />The geology description provided in PR-03 can be applied to the description for the NMD. One item to note is that <br />TCC discontinued pumping from the Fish Creek Borehole for a period of approximately 18 months. When pumping <br />commenced the total recoverable iron and total dissolved solids concentrations increased to approximately 17 mg/I <br />and 7200 mg/I respectively. TCC is applying caustic soda to reduce the total recoverable iron concentration as is per <br />• its CDPHE discharge permit. TCC believes the elevated concentrations are the results of the water stagnating in the <br />underground sump. Once this pool of water is discharged, TCC believes the concentration will return to levels <br />PR 99-OS 2.05-97 ~~~~~'~':~ ,JUG 2 8 2000 11/17/99 <br />