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-lz- <br />Alluvial deposits ineetiny the criteria of Ku le 2.Uo.ti(3)(c) for alluvial <br />valley flours exist downstream of the town of Somerset in the North Fork <br />drainage. Hlluvial deposits in Sections 13 and 14, T13S, kg1W, were <br />found to be agriculturally significant AVF's duriny the review of the <br />Anaconda Minerals Co. Mt. bunnison No. 1 permit application (see: page 5 <br />of the June 23, lydl findings ducuinent for the Mt. Gunnison rvo. 1 Mine). <br />Further, sonic of the arainaye from the permit area is contributed to the <br />North Fork above the Fire Mountain Ganal which provides water to users <br />far outside of the permit area. <br />The Somerset I.1ine hds surface facilities in and mine workings beneath <br />several tributaries of the North Fork. The mine therefore has the <br />potential to affect the quality and quantity of water available to the <br />Nortn Fork AVF. The Division's review of the probable magnitude of these <br />effects is discussed below. <br />quality affects: <br />Potential quality effects wnich have been examined are the salt loading <br />effect of mine water discnarge and sediment generation from disturbed <br />areas associated with the mine. <br />The Somerset Mine produces a modest amount of water which is pumped to <br />the surface in bear Creek(averaye U.24 cfs). It is stored in a large <br />cylindrical steel tank for in-mine use. Overflow water from this tank is <br />discharged into bear Creek, an undeveloped ephemeral drainage. The <br />effluent from this tank would present a salinity hazard if used directly <br />for irrigation or domestic use (Total Dissolved Solids 1,9UU-4,000 mg/1) <br />out when the discharge is diluted oy flows in the north Fork (average <br />flow = 432 cfs) an increase of only 2.L my/1 TuS would be observed. <br />Under the extreme condtion of mine water discharge duriny times of low <br />flow in the North Fork (lowest monthly mean = 45.2 cfs) an increase of <br />approximately 21 mg/1 in TuS would oe observed (see Section VIII for <br />calculations). The resulting concentration of 237 ing/1 TO5 presents no <br />limitations on downstream use. inspections conducted at tha site to date <br />nave not identified any visual effects to the riparian plant communities <br />or aquatic life in the ,nixing zone of the discharge. <br />Surface disturbed areas associated with the mine are protected by <br />sediment control systems including sediment ponds and vegetative and <br />gravel filters. These systems have perfornred very well with no <br />discnaryes from the mine exceeding the effluent limitations of the <br />national Pollution Discharge Elimination System (4VPUES). <br />