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<br />Two of these areas, Minnesota Creek and Dry Fork ~4innesota Creek, <br />although geographically adjacent to the permit area, are not <br />hydrologically adjacent to the activities approved in the permit. Both <br />a surface water divide and a ground water divide separate these areas <br />from mining activities. However, since part of the Minnesota Creek <br />drainage lies within the 40-year Life-of-Mine lease boundary and may be <br />affected by future anticipated mining it will be considered in this <br />determination (See Exhibits 2.8.1.C and 3.4.4.6.1). Determination of <br />alluvial valley floors at or near the Mt. Gunnison No. 1 Mine will be <br />divided into two sections: the first section, "North Fork and Sylvester <br />Gulch", will discuss potential AVF's affected by the proposed 5-year <br />permit term renewal area; the second section, "Minnesota Creek <br />Drainage", will discuss potential AVF's affected by all future and <br />anticipated mining within the life of mine lease boundary. <br />North Fork and Sylvester Gulch <br />One area specifically identified in the permit application which may <br />meet the geomorphic criteria of alluvial valley floors is located along <br />Sylvester Gulch. The proposed area of disturbance for the permanent <br />lower waste pile would occur in a portion of this area. Specifically, <br />the pile is being constructed west of the mouth of Sylvester Gulch. As <br />identified in the Mt. Gunnison application, this area is approximately <br />20 acres in size. Examination of the Division's aerial photography <br />suggests that the area of possible fill may be considerably smaller. <br />The applicant notes (2-34a) that the "alluvial origin of the valley <br />deposits at this location is doubtful". The non-alluvial origin of this <br />fill is confirmed by geologic mapping by the Colorado Geological Survey <br />(lunge, 1978, see attached map) which identifies the fill material as <br />colluvial-wedge deposits formed by gravity-dominated processes (Qcw). <br />On the basis of this information, this area is found not to meet the <br />geomorphic criteria for an alluvial valley floor. <br />Another of the locations for possible alluvial deposits within the mine <br />permit area is within the west branch of Sylvester Gulch. However, the <br />alluvial origin of the valley deposits at this location is doubtful. <br />The soils are deep clay Arquistolls susceptible to mass movement and are <br />typically found on side hill locations. The lack of base level control <br />that would favor clay deposits in this reach of Sylvester Gulch suggests <br />that the valley deposits are of glacial or perhaps colluvial (mass <br />movement) origin. <br />The flood irrigation potential of the site is also questionable. Stream <br />flow records near the mouth of Sylvester Gulch indicate that flow during <br />the critical months of July and August are not common. Agricultural <br />development would be limited to grasses and pasture because of the <br />elevation and short growing season. Based on the soils review and <br />hydrologic characteristics of this site the Division does not find the <br />west branch area of Sylvester Gulch to be an alluvial valley floor. <br />19 <br />