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<br />Surface water in the general area is dominated by the North Fork of the <br />Gunnison River. Flow records exist fora U. S.G.S. Gaging Station near <br />Somerset. Data from this station (Table 4) show inflows to the area and <br />releases from Paonia Reservoir. Outfl ow from the basin is not as easily <br />determined. For example, the nearest station to Paonia is located on <br />the Gunnison River near Lazear, Colorado, 11 miles southwest of Paonia. <br />Such a station is too far from the study area to be acceptable for this <br />analysis since many inflows and outflows occur between Paonia and <br />Lazear. However, a review of past U.S. Geological Survey (U.S.G.S.) <br />records indicates that for the years 1922 through 1932, a gaging station <br />existed on the North Fork of the Gunnison River near Paonia. Also, for <br />the years 1932 through 1950, a gaging station existed in Somerset. <br />These two stations are important since Paonia Reservoir was not yet <br />constructed and, thus, did not affect inflows to the basin. <br />Use of these stations allows determination of approximate inflows to the <br />North Fork of the Gunnison River contributed by the study watershed <br />boundary located on Figure 2. The average monthly flows are illustrated <br />on Table 4, along with the inflows to the North Fork of the Gunnison <br />River from Minnesota Creek. These figures were used to determine the <br />amount of outflow via the North Fork of the Gunnison River from the <br />basin. Obviously, such predictions are not absolutely accurate. For <br />example, less than 3 years of data existed for Minnesota Creek and 1 <br />year (1977) experienced drought conditions. However, for purposes of <br />this assessment, such figures provide a rough approximation of flows <br />through the general area. <br />B. PROBABLE HYDROLOGIC CONSEQUENCES <br />Effects of Mining on Ground Water <br />Ground Water <br />Since the Mt. Gunnison No. 1 Mine began operations, it has <br />experienced some mine inflows. There are three basic types of mine <br />inflows that are seen at the mine. The first type of inflow is due <br />to primary permeability which is ground water flow through the <br />competent portions of F-Seam and lower Barren Member. The second <br />type of inflow occurs in the coal seam and overlying Barren Member <br />in areas of shallow overburden; this is secondary permeability and <br />is the result of ground water flow through the fractured and <br />weathered portions of these strata. The fractured rock acts as a <br />conduit to the surface colluvial aquifers. The third type of <br />inflow is also due to secondary permeability and it is the result <br />of ground water flow along fault zones. These fault zones may be <br />in contact with surface aquifers or with other water bearing zones <br />in the overburden. The streams in the North Fork area are <br />generally fault controlled and may be a source of recharge for <br />fault related inflows. <br />42 <br />