2007-06-29_PERMIT FILE - C1981022A (2)

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Seuive - 2.05.6 quality in the smaller ephemeral and intermittent drainages is directly related to seasonal flow regime, • with significant flows «cumng only during spring snowmelt nutoff and during and following major thunderstorm evenu. When flow does «cur rn these drainages, it u typically of shoe duration, with high flow vel«iries with resultant high TSS and elevated total iron and manganese levels. Surface water quality for the perennial drainages is less sensitive to seasonal variation due to dilution effects, but still reflecu some seasonal variation in TSS, TDS, and specific chemical constituents as a result of tributary drainage inputs, particuLulyduring the spring. The regional ground water basin, which includes the mine permit and adjacent areas, generally corresponds to surface watershed area for the North Fork of the Gunnison River. Due primarily to the rugged terrain, with deeply incised drainages and some faulting, ground water is generally not available near the ground surface except as isolated «curmnces of perched ground water and in the alluvium associated with the North Fork The North Fork alluvium is considered an important aquifer in the area with direct recharge from and discharge to the river depending on river levels. Perched ground water «currences are limited in both voltune and flow since they are dependent on surface recharge and direct infiltration and maydr}~up during anyprolonged periods of drought. Ground water flows are commonly ass«iated with some of the coal searrts and ass«iated clastic interburden sequences due to the increased secondary permeability of these uniu resulting from natural fracture and cleat patterns. The Rollins Sandstone, which is the lowermost unit of the Mesa Verde Formation and is considered a regional marker bed, contains very limited amounu of ground water but is not considered an aquifer and is not utilized as a ground water source due to iu depth, low permeability, low porosity, and high TDS values. The existing and proposed mine disturbance areas are on the north side of the North Fork of the Gunnison River. In this area, the rock strata dip away from the river to the northeast at • approximately 3.5 degrees. Since all of the mineable coal uniu outcrop or sub-crop on the canyon walls of the North Fork Valley, their outcrops are generally above the present level of the river and related alluvial/colluvial deposits in the mine permit and adjacent areas. Both low permeabihty and the steep valley sideslopes limit direct recharge to most of the mineable coal uniu. The B and D coal seams are exceptions. The B-Seam sub-crops in or under the North Fork in the vicinity of the Town of Somerset. Extensive historical mining in the B coal seam (Somerset and Sanborn Creek Mures) generated very limited ground water inflows to the mine, so it appears that even though this seam sub-crops in or under the North Fork River, it is relatively tight and receives and transmiu very little ground water. The D-Seam outcrops higher in the stratigraphic sequence and appears to have significantly higher secondary permeability resulting in recharge From both the overlying unconsolidated surficial materials and flowing surface drainages where the coal seam outcrop is exposed in the drainage valleys. Existing underground mining disturbance consisu of the Somerset and Sanbom Creek NLnes in the B and C coal seams, and the Hawk's Nest Mtne in the D and E coal seams. The abandoned Somerset Mrne workings extend from the cast side o[ Ells Creek to Hubbard Creek The active Sanbom Creek Mute workings extend from east of Sanbom Creek eastward to Hawk's Nest Creek The proposed Ellt Creek Mute will mine the D coal seam from the west side of Elk Creek to the east side of Hubbard Creek Historical, existing, and proposed mining operations either have or have the potential to directly affect those stratigraphic units above the B coal seam in areas where mining extraction or mining-related subsidence «cur. No known aquifers exist below the mineable coal sequence although the Rollins Sandstone, situated approximately 20 to 120 feet below the lowermost B coal seam, u considered a regional marker bed. Ground water quality for the mine and adjacent areas is highly variable and a dependent on the • recharge source, flow path, strata with which the water comes in contact, and discharge mechanism Generally, water quality for alluvia]/colluvial ground water is very similar to the quality of the ass«iated surface water source due to close surface and ground water interaction and limited residence time. Similarly, water quality for most perched ground water sources a similar to surface PR04 2.05-75 Revised August 2000