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<br />Structural basins strongly influence the direction of ground water flow in <br />contiguous regional aquifers and thus, those areas which are considered <br />hydrologically adjacent. For purposes of a CHIS, this means that the impacts <br />to ground water in adjacent structural basins are considered separate except <br />to the extent that those basins interact through some component of the surface <br />water system. The ground water impacts of mining within a distinct structural <br />basin are analyzed and the sum of those impacts are considered as they affect <br />both the ground water and surface water systems. Since the Trapper Mine has a <br />proposed life-of-mine area within the Big Bottom structural basin (see Figure <br />3), the ground water portions of this CHIS are limited to analyzing the <br />cumulative impacts of anticipated mining within this basin. The cumulative <br />hydrologic impact of mining in other structural basins along the Yampa River <br />have been considered as they interact with the surface water systems in <br />previous cumulative hydrologic impacts studies and are therefore considered as <br />a component of the surface water portions of this CHIS. Coal mining <br />operations in the surface water study area are summarized in Table 1. <br />Anticipated mining in the ground water general area include both surface and <br />underground mines (See Figure 2). They are as follows. <br />Trapper Mining, Inc. - Trapper Mine - CMLRD Permit No. C-81-010 <br />Empire Energy Corporation - Eagle No. 5 and 6 Mines, CMLRD Permit <br />No. C-81-044 <br />C. Description of the Existing Environment <br />1. Regional Geology <br />The Trapper Mine lies within the Sand Wash structural basin of northwest <br />Colorado. The Sand Wash basin is a product of the Laramide Orogeny, a period <br />of regional geologic structural development that began in late Cretaceous time <br />and continued into the Tertiary Eocene. The Sand Wash basin is bounded by <br />uplifts of similar age including the Uinta Mountains on the west and the Axial <br />Basin anticline, the structural extension of the Uinta uplift, on the south. <br />The South Park Range borders the Sand Wash basin on the east while the <br />subsurface Cherokee Ridge lies to the north. (See Figure 3). <br />The influence of several folds of lesser magnitude within the Sand Wash basin <br />is seen in the permit area of the Trapper Mine (See Figure 2). All of these <br />folds have general NW-SE axial trend. The Trapper Mine lies within the <br />southwestern flank of one of these folds, the Btg Bottom syncline. Structural <br />dips in the mine area range from F to 12 degrees north and northeast towa-d <br />the axis of the syncline. <br />Faults with several miles of surface expression 1te to the north and west of <br />the Big Bottom syncline (See Figure 2). In the area of the Trapper Mine, <br />relatively minor normal faults with less than 50 feet of displacement have <br />been encountered. Some but not all of these also have surface traces. Most <br />of these faults conform to regional structural grain and trend roughly NW-SE. <br />_2 P_ <br />