2018-01-31_PERMIT FILE - C2009087A (3)

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RULE 2 - PERMITS aquifer. and both marine shale and altered volcanic ash (Yampa Iced) separating the NN'adpe coal f -0111 the underlying front Creek aquifer. PSCM development also has the potential to affect the Seneca II spoil aquifer, located upOradient and In ]lN drologlc connection vl It{1 the units to he disturbed bN 111111ing. and Illav lead to increased spoil aquifer effects on ground�wter quality. As detailed in the Probable Hydrologic Consequences. the spoils aquifer has ten times the recharge rate and hundreds of times the hydraulic conductivity 01 the Undisturbed bedrock units. (7I-01-Indwater flo« from the spoils agLllfel- to the Millie workings «ill thcrc�linre be limited by the lo\� - permeability bedrock that separates the portal box cut fi,onl the Seneca 11 spoils. and x\ill not materially affect the spoil aquifer levels. Spoil water \viii gradually replace a portion Of the native ` (1r01- 01 in these intervenitiL, undisturbed bedrock units that \v III discharge to the mine workings. This effect is highly localized, and does not occur in any geologic units characterized as regional aquifers of significance. During the initial permit term, all mining will be conducted with continuous Villiers, and no Subsidence is aIticipated. Revisions to this PAP for subsequent pern-dt terms will address the potential effects of subsidence on groundwater resources. UndergrOUnd mining operations will expose coal. floor, and roof materials to oxidation and increased leaching as mining is completed and workino areas are abandoned. Natural caving \vill also expose substantial quantities of broken coal and roof material to oxidation and leaching as groundwater floods these areas. It is anticipated pll will increase slightly and the ground water cllellllsti'y will evolve toward a calcinni- inagneslurn sullate water type with increases in IDS and certain mineral Constituents, including Iron and inallganese. In order to effectively prevent or 11ntlgatC these irnpaCts. underground mining operations \\111 be limned to development and disturbance of the Inini111Llnl area necessary to provide for effective coal extraction. PSCM «111 also keep all development within the mineable coal seams to the extent operationally practical. While there will undoubtedly be some impacts on ground water quality, these impacts Nvill generally be confined to the mine and immediately adjacent areas by the relatively low permeability of the geologic units and the limited hydrologic connection Nvith other more permeable units. With gradual collapse and caving of the mine workings following conventional mining, the void space available for ground water storage will be significantly reduced, expediting restoration of equilibrium with the natural water table with a resulting reduction in the amount of time that mine materials will be exposed to oxidizing conditions. Minor changes in ground water quality will not affect any ground water users since existing ground water use in the immediate area is limited to the Trout Creek and Twentymile aquifers, which are isolated from the affected units by thick, relatively impermeable shale and /or ash deposits. Any potential postmining mine water discharge will be prevented by closing and sealing mine openings, and restoring the portal access pit to the approximate original contour. Anticipated mining- related changes in ground water quality should not significantly affect the beneficial use of any groundwater. Surface placement of coal has the potential to affect ground water quantity and quality as a result of increased runoff from the associated disturbance areas. and reinfiltration of this runoff into alluvial aquifers. Analyses of both actual existing and potential future coal and mine development waste Midterm Review 2.05- !flp Revision 04/2013