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-2B- <br />station is too far from the study area to be acceptable for this analysis <br />since many inflows and outflows occur between Paonia and Lazear. However, a <br />review of past U.S. Geological Survey (U. S. G.S.) records indicates that for <br />the years 1922 through 1932, a gaging station existed on the North Fork of the <br />Gunnison River near Paonia. Also, for the years 1932 through 1950, a gaging <br />station existed in Somerset. These two stations are important since Paonia <br />Reservoir was not yet constructed and, thus, did not affect inflows to the <br />basin. Use of these stations allows determination of approximate inflows to <br />the North Fork of the Gunnison River contributed by the study watershed <br />boundary located on Figure 1. The average monthly flows are illustrated on <br />Table 2, along with the inflows to the North Fork of the Gunnison River from <br />Minnesota Creek. These figures were used to determine the amount of outflow <br />via the North Fork of the Gunnison River from the basin. Obviously, such <br />predictions are not absolutely accurate. For example, less than 3 years of <br />data existed for Minnesota Creek and 1 year (1977) experienced drought <br />conditions. However, for purposes of this assessment, such figures provide a <br />rough approximation of flows through the general area. <br />PROBABLE HYDROLOGIC CONSEQUENCES OF THE ORCHARD VALLEY MINE <br />Effect of the Orchard Valley Mine - Ground Water <br />The Orchard Valley Mine workings have the potential to deplete the quantity of <br />ground water through mine induced ground water inflows. The mining operation <br />will induce inflows by dewatering the coal seam and the associated roof and <br />floor strata as the mine workings advance. The mining operation may induce <br />inflows from underlying or overlying units through: 1) the dewatering of <br />fractures and faults which intersect both the mine workings and the overlying <br />or underlying saturated horizons; or 2) the dewatering of overlying saturated <br />horizons through subsidence related fractures produced by the mining <br />operation. The potential for encountering mine inflows increases with depth <br />since the overlying and underlying saturated horizons will be under increasing <br />hydrostatic heads. <br />To date, however, the Orchard Valley Mine has only encountered minor inflows <br />to the underground workings. During the year 1983, approximately 300,000 <br />gallons of water flowed into the mine (page 139 of Section 2.05.6 of Volume <br />1B). An inspection conducted by the Division in March 1986 showed that <br />inflows were averaging 200 gallons per day. The source of ground water inflow <br />to the mine is from perched, discontinous, water-bearing sandstones overlying <br />the "D" seam. These sandstones are of lenticular character and the water <br />bearing strata are only present sporatically within the permit area. <br />It is anticipated that these locally perched ground water aquifers in strata <br />directly above the workings will be dewatered through subsidence cracks or <br />fractures. This predicted impact of dewatering these aquifers is considered <br />to be insignficant in terms of volumes of mine inflow or impact on the overall <br />hydrologic balance, based on the lack of appreciable amounts of ground water <br />encountered above the "D" seam during exploration drilling activities (see <br />Tables 7 an 10 in Volume 10, Map 10-1 in Volume 10A, and page 406 of Section <br />2.04.7 in volume lA). Prior to the submittal of the permit revision to <br />