2016-05-04_REVISION - C1982056 (12)

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benches, the combined total seam thickness ranges from 7.5 to 14 feet. Between the Wadge Coal Seam and the Wolf Creek Seams, there is interbedded sandstone and shales. Interbedded sandstones and shales and the massive Trout Creek Sandstone are below the Wolf Creek Seam. Surface Water Hydrology The mine is located in the upper reaches of the Yampa River Basin. The permit area and adjacent areas are drained by Foidel Creek, an intermittent stream, and Fish Creek and Middle Creek, both perennial streams. Fish Creek drains east into Trout Creek whereas Foidel Creek drains northeast to Middle Creek before Middle Creek joins Trout Creek. The quality of water in the Fish Creek and Foidel Creek drainages has been affected previously by surface mining upstream and downstream of the underground mine's existing surface facilities. Alluvial valley floors are identified downstream of the mining area at the confluence of Foidel and Middle Creek, and on Trout Creek from its confluence with Middle Creek downstream to the Yampa River. Permit Revision No. 3 declassified portions of Foidel and Middle creeks previously classified as AVF's. Detailed discussion concerning alluvial valley floors can be found in Section B, part XVIII of this document as well as Exhibit 7j of the permit. Ground Water Hydrology The stratigraphy and geologic structure within the Twentymile Park Synclinal Basin control the ground water flow within the permit and adjacent areas. There are three regional bedrock aquifers within the permit and adjacent areas of the Foidel Creek underground mine. These aquifers are the Trout Creek sandstone, the Twentymile sandstone, and the Wadge/Wolf Creek coal-overburden/interburden zones. All three aquifers exhibit artesian conditions in central portions of Twentymile Park Basin. Ground water in the Twentymile Park Basin is not suitable for most domestic uses. Use of groundwater in the general area is restricted to livestock watering, irrigation and limited domestic use (PAP, page 2.04-24) . The geologic structure created by folding and faulting within the Twentymile Park Synclinal Basin affects the direction of flow within the rock aquifers. In the permit and adjacent areas, the direction of ground water flow in the bedrock aquifers is down dip toward the center of the Twentymile Park Basin. Faults in the area produce localized fracture zones within the rock strata. These zones of increased permeability increase the potential for vertical and horizontal movement of ground water within the rock strata. However, experience to date in the Foidel Creek Mine shows little to no inflow along the fault zones at the level of the Wadge coal seam. Some inflows were encountered in 9 Right and 6 Right gateroads as they were developed into the Eastern Mining District. These inflows appeared to be localized, and tapered off over time. The Twentymile sandstone is separated from the underlying Wadge coal -overburden aquifer by up to 700 feet of impermeable shale within the permit and adjacent areas. The underlying 700 -foot shale and the overlying shales and siltstones of the upper Williams Fork Formation and the Lewis Shale Formations produce the confined artesian conditions within the Twentymile sandstone aquifer. To the northeast, the Twentymile sandstone recharges the alluvial aquifer and provides base flow to the tributaries of Trout Creek down gradient of the mine. Salts in the Twentymile sandstone waters are predominantly sodium bicarbonate and result in TDS levels of 150 mg/l. This aquifer is occasionally used for domestic needs. Page 13 of 52