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Salim - 2.05.6 <br />evolve toward a sodium sulfate roarer type with increases in TDS and certain mineral constituents, <br />including iron and manganese. In onier to effectively prevent or mitigate these impacts, underground <br />mtmng operations will be limited to development and disturbance of the minimum area necessary to <br />provide for effective coal extraction. OMI will ako keep all development (except ramping and <br />overcasts) in the mineable coal searrss to the extent operationally practical. <br />While there will undoubtedly be some impacts on ground water quality, these impacts will generally <br />be confined to the mine and immediately adjacent areas by the relatively low permeability of the <br />geologic units and the limited hydrologic connection with other more permeable units. With gradual <br />collapse and caving of the mine workings during longwall mirrirtg and following conventional mitllng, <br />the void space available for ground water storage will be significantly reduced, expediting restoration <br />of equilibrium with the natural water table with a resulting reduction in the amount of time that rune <br />materiak will be exposed to oxidv_irtg conditions. <br />NLnor changes in ground water quality will not affect any ground water users since all existing ground <br />water use in the immediate area is limited to alluvial/colluvial deposits which are stratigraphically well <br />above the interval to be mined and any potential postntinirtg mine water discharge will be prevented <br />by closing and sealing mine openings. It should be noted that anticipated mining-related changes in <br />ground water quality should not significantly affect ground water quality, which is already a limiting <br />factor relative to potential beneficial use. This contention is supponed by historic monitoring data <br />for stored mine water, mine water discharge from historic mine workings, and area drainages, altich <br />receive some mine water drainage from old mine workings and show no significant adverse long-term <br />effects. <br />Surface placement of coal and mine development waste has the potential to affect ground water <br />quantity and quality as a result of increased nmoff from the associated disturbance areas and <br />• infiltration and leaching of the stockpiled materials. Analyses of both actual existing and potential <br />Future coal and mine development waste rnateriak are described in Section 2.04.6, Geology <br />Description. Based on analyses of coal, roof, and floor samples, pH values tend to be slightly to <br />moderately alkaline, overall sulfur content is low, and buffering capacity is relatively high due to the <br />presence of significant quantities of calcium Consequently, acid-producing potential is low. <br />Similarly, chemical analyses indicate low concentrations of most potentially toxic componenu and <br />low alkalinity potential <br />Available analysis results for existing surficial mine waste and coal refuse piles, which have been in <br />place a number of years and have had ample oppomuriry to weather and oxidize, offers an expanded <br />and probably more accurate petspettive of potential water quality impacts than chemical analysis <br />results For fresh coal, roof, and floor samples. The weathered mine waste and coal reface sarrrples <br />show no significant acid, alkaline, or toxicity potentiak. Leaching of mine waste and coal refuse <br />materials has the potential to cause a shift in the ground cater chemical type towards a sodium sulfate <br />water type and may also cause minor increases in concentrations of 'iron, manganese, and TDS• <br />These potential impacts are expected to be min~mi~Pd byspecific operational measures utilized dW~ng <br />construction and reclamation of permanent mine development waste piles, and coal piles. 'rltese <br />measures include: <br />• Controlled placement and compaction <br />• Effettive routing of surface drainage azound stockpile areas <br />• Establishment of an underdrain system (mine development waste piles only <br />• Regrading of completed development waste pile areas to provide effective surface <br />drainage including postmining stable diversion chamek <br />• Topsoil replacement (development waste piles only <br />PR04 2.05-86 Revised August 2000 <br />