2013-01-29_PERMIT FILE - C1981022A (3)

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Spurr ~ 2.05.6 • Reclamation of the completed mine development waste piles • It is anticipated that infiltration to the mine development waste piles and subsequent leaching will be minimal green the relatively and conditions and enguteering controk that will be implemented. These controk include diversion of upgradient surface drainage azound the piles, grading of pile surfaces to promote effective drainage ofE the piles, compaction of development waste materiak, and ongoing reclamation. In addition, rock underdrains will tend to collect the majority of any leachate that does percolate through the piles. Any leachate collected in the underdrains k routed in diversion channek to existing sedimentation ponds where it is retained and sampled prior co release to natural drainages. Under the ®PS permit for the existing ponds, any discharge of leachate from the mine development waste piles and stormwater is subject to the same discharge effluent standard as normal stormwater discharges from the pond. If ground water quality impacts do occur in mine development waste pile areas, they are expected to be limited due to the relatively small areal extent of the development waste piles and the factors previously noted. Although it is not likely to occur, any leachate from the piles which is not captured by the underdrain system will infiltrate to the colluvia]/alluvial deposits, mix with groundwater resulting from natural surface infiltration, and discharge to the surface water system Under these conditions, i[ is anticipated that the minimal volume of resulting leachate will be significantly diluted by both ground water and subsequent surface water mixing and will not significantly affect surface water quality. Stratigraphic units that underlie the alluvia]/colluvial deposits consist of relatively impemteable siltstones and shales that limit vertical permeability and effectively m~~+m+~P the potential for ground water itttpatts to any deeper aquifers. With reference to the preceding dkctusion on potential impacts of surface placement of mine development waste on ground water quantity and quality, similar considerations apply to coal • stockpiling. Stockpile areas will be constructed to provide effective drainage of both runoff from stockpile surfaces and infiltration through the stockpiles. Runoff from stockpile areas will be collected and routed to nearbysedimentation ponds. OMI will utilize sedimentation ponds and associated drainage stmctures to intercept and route runoff from dkturbed areas, retain runoff for sediment control, and to control discharges to stream drainages. Operation of the sedimentation ponds has the potential to affect both ground water quantity and quality by altering the timing and volume of discharge flows, providing additional recharge to alluviaVcolluvial ground water systems, causing changes in water chemistry, increasing TDS levek, decreasing TSS levek and increasing the concentrations of specific mineral components. Disturbed area runoff flowing into sedimentation ponds will be retained to allow suspended sediment to settle out prior to dscharge to natural drainages. During the time that water k retained in the sedimentauon structures, some evaporation will occur, resulting in reduction of overall water volume and inherently increasing concentrations of TDS and individual chemical constituents. Since most of the sedimentation ponds are located in lowland areas, any infiltration losses through the bottom of the ponds will have similar effects on surface discharge volumes and chemical characteristics. Any changes in surface water quality or chemistry have the potential to effect groundwater resources since surface flows are a component of down-gradient groundwater recharge. EFFetts of evaporation will be mirtim~~rr~ by limiting detention time in the sedimentation stmcnues to that interval required for effettive reduction of suspended solids. Because runoff typically occurs only in response to snowmelt and major storm events, evaporation will be further limited by cold temperatures during spring when the majority of snowmelt occtus. Pond designs, as outlined in Exhibit 2.05-E3, Drainage and Sediment Control Plan, provide for both nturirttal detention times and • effective pond routing so anydelayin discharge to the receiving drainages will be limited. With pond routing, discharge will occur continuously once the water reaches the dscharge elevation so effecu on downstream flows will likewise be minimal. Infiltration will similarly be limited by minutaal detention PR04 2.05-87 Revised August 2000