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• makes use of some of this water in the conduct of various mining activities, especially dust <br />suppression. <br />Colorado Department of Public Health and Environment, Water Quality Control Division <br />has issued Pollutant Discharge Elimination System Permits (NPDES) for various discharge <br />points, including Fish and Foidel Creeks. Current levels of Total Dissolved Solids in these <br />creeks are monitored upstream of the mine activities and discharge is regulated. Discharged <br />water is also treated with sodium hydroxide (NaOH) to maintain the pH of the water <br />between 8.8 and 9 to precipitate iron and lower the TDS. When the creeks are surging with <br />spring runoff water more of the mine inflow water is released to the streams and the dilution <br />effect reduces the concentration of TDS, iron and sodium to acceptable levels to meet <br />classified uses downstream. Conversely, when low or no water flows occur, the amount of <br />water discharged is reduced accordingly. <br />Environmental Consequences: Subsidence of the ground surface likely will cause localized <br />gradient changes on soil surfaces and within stream channels. Additional sediments could <br />be generated in the short term from overland flow across soil surfaces and scouring of the <br />Fish Creek stream channel. However, localized deposition is expected to occur within the <br />stream channel, except during high runoff events. Higher levels of TDS and Total <br />Suspended Solids could result from sediment transport. No sediment dams are present <br />downstream of the area to be subsided. <br />• Mitigative Measures: Same as for Surface Hydrology <br />Name of specialist and date: Ole Olsen .5/17/06 <br />WETLANDS/RIPARIAN ZONES <br />Affected Environment: Ongoing subsidence evaluations conducted by Twentymile Coal <br />Company involving Alluvial Valley Floors associated with Fish, Foidel and Middle Creeks, <br />as well as perennial stream flow and other shallow bedrock aquifers suggests that ground <br />water levels may be minimally altered. On the larger perennial streams the effects of <br />subsidence cause a pooling of water in the zone of subsidence and more streamside riparian <br />habitat is created. One assumption stated in a recent subsidence evaluation conducted by <br />SubTerra, Inc (PR6 AVF Subsidence Evaluation) is that "Fish Creek elevation will rise, <br />relative to the surrounding ground, a distance equal to predicted ground subsidence at that <br />point." <br />Environmental Consequences: In the short term following the initial subsidence it is <br />expected that pooling of water will occur in the areas of substantial subsidence. More <br />riparian habitat would be expected. These pools are expected to decrease in area as the <br />stream channel undergoes localized scouring and deposition. If the ground water table <br />maintains its pre-subsidence elevation after subsidence more riparian vegetation and habitat <br />. could result.