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biological community as defined by Rule 4.05.18(3). A map of the Sylvester <br />Gulch Facilities Area, which delineates the area within 100 feet of Sylvester <br />Gulch, is incorporated into Exhibit 69 of the permit document. The Division <br />approved this stream buffer zone variance in accordance with Rule 4.05.18(1) <br />based on a finding that the original stream channel will not be disturbed, water <br />quality and quantity will not be adversely affected, and appropriate riparian <br />vegetation will be reestablished. These conditions will be met by the effective <br />use of slope stabilization methods including Best Management Practices, <br />appropriate use of sediment control structures during construction, <br />revegetation, and mechanically stabilized earth (MSE) walls. <br />3. In Permit Revision 11, Mountain Coal Company proposed a buffer beneath <br />the riparian area of Raven Creek as stipulated in lease No. COC-67011, of <br />660 feet (1/8 mile) on either side of the creek. This is shown on Map 52. <br />Since there is no mining proposed to the North of Raven Creek, the affected <br />area occurs only to the south of that stream and does not surround it. <br />K. Probable Hydrologic Consequences <br />Under Rule 2.07.6(2)(c), the Division is required to make an assessment of the <br />probable cumulative impacts of all anticipated coal mining in the general area on <br />the hydrologic balance and to make a finding (as discussed in Section A of this <br />document) that the operations proposed in the permit application have been <br />designed to prevent material damage to the hydrologic balance outside of the <br />proposed permit area. This section of the findings document is divided into the <br />following subsections: Description of the Hydrologic Environment, Probable <br />Hydrologic Consequences of the West Elk Mine, and Summary and Findings. A <br />separate Cumulative Hydrologic Impact Study (CHIS) is available for review at the <br />Division of Reclamation, Mining and Safety. The Cumulative Hydrologic Impact <br />Study (CHIS) filed at the DMG office assesses the projected cumulative hydrologic <br />impacts of all anticipated mining operations in the general area of the West Elk <br />Mine on the North Fork of the Gunnison River Valley. <br />Description of the Hydrologic Environment <br />a. Regional Geology <br />For information regarding regional geology, see Section A, Description <br />of the Environment, Geology in this Findings Document. <br />b. Groundwater <br />Seven categories of potential aquifers occur in the Somerset Coal Field. <br />These are: 1) the alluvial and terrace deposits associated with the North <br />Fork of the Gunnison River; 2) the localized, shallow alluvium along <br />creeks tributary to the North Fork; 3) the discontinuous, lenticular and <br />laminar sandstones of the Mesaverde Formation; 4) the Rollins <br />27 <br />