2011-05-18_PERMIT FILE - C1981012 (2)

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Probable Hydrologic Consequences New Elk Mine 6 Coal- bearing strata of the Raton Formation are underlain by Late Cretaceous sedimentary rocks of the Vermejo Formation, Trinidad Sandstone, and Pierre Shale, in descending order. The Vermejo Formation ranges in thickness from 150 feet in the southern part of the basin to 410 feet in the northern part of the basin. It consists of interbedded gray to black carbonaceous mudstone and shale that may be coaly or silty, weakly arkosic sandstone, carbonaceous siltstone, and numerous coal beds. Coal beds in the Vermejo Formation are also a target of CBM production in the permit and surrounding area. The Poison Canyon Formation overlies the Raton Formation and caps hills and upland areas in the vicinity of the mine. It is composed of medium to coarse - grained or conglomeratic arkosic sandstone beds that are intercalated and interbedded with greenish gray to maroon mudstone and siltstone. The contact between the Poison Canyon Formation and the Raton Formation is gradational. Locally, the Poison Canyon formation may be several hundred feet thick. Quaternary sediments including alluvium, outwash, and landslide material are present in the bottom of the valley along the Purgatoire River and tributary drainages. Alluvium consists of clay and silt to cobble size clasts. Drilling records for water wells indicate that it may reach a thickness of 70 feet in some areas adjacent to the Purgatoire River. Alluvium may not be present in some areas of the smaller drainages or may be only a few feet thick. A description of the quaternary geology and geomorphology of the permit area was prepared by Waste Water and Land (WWL, 1980) and is included in Exhibit 8 of the permit application. 3.2 Hydrogeology Groundwater flow in the Raton Basin is largely dependent on geologic structure and topography. Regional flow is generally to the east and is deflected toward stream valleys. The water table north of the permit area slopes southeast away from the Spanish Peaks (Figure 3). Locally, igneous intrusions (dikes) may form barriers to ground -water flow (Geldon, 1989). Flow paths within the Raton - Vermejo- Trinidad aquifer and overlying aquifers are complex because of the effects of geology and topography. The United States Geological Survey (USGS) recognizes two bedrock aquifers above the Pierre Shale in the Raton Basin; the Cuchara- Poison Canyon Aquifer and the Raton - Vermejo- Trinidad Aquifer. The aquifers are defined on the basis of stratigraphy, but because they consist of thick sequences of discontinuous sandstone, shale, and coal with hydraulic and storage properties that vary spatially, the aquifers are highly heterogeneous and anisotropic. Watts (2006a) noted that the spatial distribution of hydrologic properties within the Cuchara- Poison Canyon and Raton- Vermejo- Trinidad aquifers could only be defined in a probabilistic manner and found that subdivision of the aquifers allows for definition of less heterogeneous hydrostratigraphic units. The probable hydrologic consequences analysis for the New Elk Mine follows Watt's recommendations and defines the hydrostratigraphic units in the mine areas to include the Trinidad, Vermejo, Raton, and Poison Canyon Aquifers. Alluvium along the Purgatoire River and its tributaries is also water- bearing and is an important source of groundwater for domestic and agricultural supplies. The Raton Formation, Vermejo Formation and alluvium are the aquifers of principal concern for the New Elk Mine. The Trinidad Sandstone occurs several hundred feet below the mining horizon and is separated from the Raton Formation by the Vermejo Formation. The Poison Canyon Formation crops out on hill tops in the permit area (Figure 2). 4164A.110421 Whetstone Associates