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-59- <br />Possible Effects of Mining Upon Surface Water Quality and Quantity <br />Review of the permit applications for the mining operations considered in this <br />assessment and Division experience with other mining operations throughout the <br />State has identified several possible mining effects to surface water quality <br />and quantity (Table IO). Surface water quality might be effected by the discharge <br />of mine water from underground workings or by seepage from waste rock or coal <br />refuse piles to the stream - alluvial aquifer system.. The underground mining <br />operations, by altering ground water flow reversing hydraulic gradients, and <br />through subsidence effects, may deplete springs and seeps or storm flow. In <br />addition, the withdrawl of water for mine usage may deplete surface flows. <br />Each of these possible effects is discussed below. <br />Two other possible surface water effects, increased infiltration in the areas <br />overlying underground workings and increased erosion from disturbed areas, were <br />briefly considered but then deleted from further analysis. Although subsidence <br />might logically increase infiltration rates in an undermined watershed (and <br />therefore decrease runoff), the Division is unaware of any literature documenting <br />that this effect actually occurs. <br />Surface flow from disturbed areas would carry higher sediment concentrations <br />than natural runoff. However, Rule 4.05 of the Regulations requires that aI1 disturbed <br />flow pass through a properly designed sediment control pond. Effluent from the <br />pond is required to meet NPDES limitations. During operation, monitoring and <br />inspection by the Division ensures that the sediment control system is maintained <br />to function as designed. At the close of operations, surface disturbances would <br />be reclaimed and the sedirrent control system would be removed. As a result, the <br />increased sediment Ioad carried by disturbed flows would not be expected to reach <br />receiving streams. <br />1. Discharge of Mine Water from Underground Workings <br />Underground mines in the North Fork area are generally dry. The only operation <br />to discharge mine water from the underground workings on a continuing basis is <br />the Somerset mine. Somerset discharges this water to Bear Creek at a site <br />approximately 3/4 mile upstream from its confluence with the North Fork of the <br />Gunnison river. The current permit application anticipates a discharge rate of <br />Z15 gpm. Review of NPDES monitoring reports on file with the Division indicate <br />that the discharge has averaged 107 gpm over the past three years. The data <br />indicate that the discharge rate has increased over the past two years. It is <br />unknown whether or not this trend will continue. NPDES records indicate an <br />average total dissolved solids concentration of approximately 3,500 mg/1. <br />Since Bear Creek is an ephemeral stream it is appropriate to consider the effects <br />of this discharge on the North Fork of the Gunnison. The mass balance - mixing <br />model (Report by Water, Waste, and Land, Ltd. I980): <br />