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-39- <br />This resuits in a 2.6 mg/1 increase over baseline conditions, which is <br />insignificant. In addition, it is probably an over estimation, since <br />seepage in the piles is the result of snowmelt and would probably occur <br />when stream flows are much higher than average. <br />Natural faults and fractures, as well as fractures caused by subsidence, could <br />reduce streamflow by directly diverting surface flow and alluvial ground water <br />into the bedrock ground water system. This effect is undesirable both because <br />of the hydrologic effects and the mine operation problems it could induce. <br />Experience with underground mines throughout the state, as well as in the <br />North Fork area, indicates that mine inflows are not normally significant when <br />ephemeral streams are undermined. Most of the streams to be undermined in the <br />region are ephemeral and would not be expected to be significantly affected by <br />mining. Flow in these ephemeral streams are concentrated in periods of <br />snowmelt and high intensity precipitation events. The stream gradients are <br />steep and their channels contain little alluvium. For all of the above <br />reasons, very little surface water is retained long enough in the stream <br />valleys to infiltrate into the ground water systems. Therefore, the amount of <br />water observed reaching the mine workings is small. <br />Perennial and intermittent streams, however, may experience significant <br />depletions of flow if mine workings are extended adjacent to and/or below the <br />level of the stream valley (e. g., the bedrock alluvial contact). The lower <br />stream gradient and the thicker alluvial deposits in perennial stream valleys <br />favor flow retention and recharge to the ground water systems. Due to the <br />increased flow retention and ground water recharge in perennial stream <br />valleys, there is a greater potential for stream depletions by mining adjacent <br />to or under these stream valleys. The mine could generate depletions by <br />increasing mine inflows in the area. These mine inflows could be induced <br />either through the mine workings encountering existing faults or fractures or <br />strata recharged by the stream, or through the mine producing subsidence <br />fractures which extend to the stream valley bottom or to rock strata recharged <br />by the stream. <br />Two mining operations, Mt. Gunnison and Somerset, will undermine perennial <br />drainages, and one mining operation, Blue Ribbon will be mining adjacent to a <br />perennial drainage tributary to the North Fork of the Gunnison. <br />Both the Blue Ribbon and the Somerset mines have surface facilities and <br />underground mine workings located in the Hubbard Creek Drainage. The combined <br />mining operations of the Blue Ribbon and Somerset mines may impact the quality <br />of surface water flowing in Hubbard Creek. The quantity of flow may be <br />depleted through the dewatering of faults, fractures and rock strata which are <br />in direct or in indirect communication with the alluvium or stream bottom of <br />Hubbard Creek. <br />The Somerset Mine has recently mined beneath Hubbard Creek. Inspection of the <br />underground workings by CMLRD hydrologists showed this portion of the mine to <br />be making significantiamounts of water. At the present time it is <br />inconclusive whether or not surface flows are being depleted. However, there <br />is a greater concentration of inflows and increased discharges associated with <br />