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2 04.6 Geology Description <br />2 04 6(1) General Requirements <br />The following geologic description of the Carbon Junction Mine has been summarized <br />from existing public reports and a contract report by a consulting geologist (see <br />references under Section 2.03.3(4)). This existing information has been organized, field <br />checked and combined with additional field data to provide a geologic baseline for the <br />mine. <br />A discussion about the general occurrence of ground and surface water has been set forth <br />in Section 2.04.5. There appear to be no significant groundwater resources which are <br />regional in nature. Surface and groundwater encountered within the permit area is related <br />in quantity and quality to seasonal recharge from snowmelt and high intensity and/or <br />duration precipitation events. The permit area is at or near the recharge area for the upper <br />alluvium and terrace gravels. <br />The geologic setting inherently dictates the types of mining that can be considered as <br />potentially viable. Because the coal lies in relatively thick seams that are "stacked" in a <br />steeply dipping configuration, an open pit mining method is the most economically <br />feasible. At a future time, auger mining may prove to be a viable mining method in this <br />locale. Auger mining is not proposed to be employed in this mining and reclamation <br />permit. <br />Regional hydrologic im acts to the surface and groundwater regime are not anticipated <br />g p <br />from the mining and reclamation operations. The surface and groundwater resources of <br />the permit and adjacent area are limited (based on topography and position of strata, as <br />well as size and location of the potentially impacted drainage basin). <br />2.04.6(2) Surface Mining <br />Discussion of the general stratigraphy is limited to those formations outcropping above <br />the Mesaverde Group of Upper Cretaceous Rocks (See Figure 4 -1 in Exhibit G) and is <br />illustrated on the Geologic Map (Map 4 -2). <br />Lewis Shale (Kl Upper Cretaceous) The Lewis Shale is a dark gray to black <br />homogeneous clay shale with scattered concretions of shaley limestone and a few thin <br />bentonite seams in the upper portion. The formation averages 1,800 feet in thickness. <br />Pictured Cliffs Sandstone (Kp_c Upper Cretaceous) The Pictured Cliffs Sandstone <br />consists of two members in the Carbon Junction area. The lower member overlying the <br />Lewis Shale consists of a sequence of interbedded clay shale and thin sandstone <br />averaging 80 feet in thickness. This lower member is informally noted on the geologic <br />cross sections as "Transition Zone" due to its lithologic transition from Lewis Shale to the <br />more massive sandstones of the upper Pictured Cliffs Sandstone. <br />Abridged Permit Document 4-8 Feb 2008 <br />