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<br />more critical. This can be calculated assuming an average monthly low flow <br />of 4.4 cfs (10 years of record), an average annual salt load of 1424 mg/I for <br />Mines No. 1 and No. 3, in 1997, and a mine discharge of 0.12 cfs. Using <br />these values, the mine will increase salt loads by 14.3 tons/month over an <br />estimated low flow value of 57 tons/month. This is a 19 percent increase <br />during this low flow period. Although this increase appears significant, a <br />25 percent increase in baseline total dissolved solids will still mean the water <br />quality will be classified as good for irrigation and aquatic life. No receiving <br />stream standards, water quality criteria, or irrigation standards should be <br />exceeded. Also, past monitoring has not identified any unsuitable levels of <br />dissolved solids in Thompson Creek. The magnitude of this salt increase will <br />decrease at the confluence of Thompson Creek and the Crystal River. The <br />low flow of record on the Crystal River near Redstone is 22 cfs (28 years of <br />data), which would result in a dilution ratio of 22 cfs/4.4cfs or a 5:1 ratio. <br />The sediment ponds and refuse area at the mine may add an additional salt <br />load to the Thompson Creek drainage. However, the impacts are expected to <br />be small due to their limited discharge, and the fact that the discharge would <br />be during a rain event, when dilution factors are highest. <br />The mine may affect the surface water regime in still another way. Mining <br />may cause the depletion of springs and seeps above the undermined areas. A <br />spring and seep survey conducted by the mine has only identified two springs <br />within the five-year mine plan area. Both springs (designated on the mine <br />subsidence map) flow less than one gallon per minute, except during the <br />spring, when site SP-2 flows 200 gallons per minute. Both springs flow <br />from the Upper Sandstone and are not adjudicated. Based on the low flow <br />and poor quality, it does not appear that the springs were, or are, a significant <br />component of the surface water regime. Any depletions will therefore not be <br />a significant impact to the hydrologic balance. <br />The mine loadout facility should not significantly impact the Roaring Fork <br />River. The loadout disturbed less than 20 acres. Sediment control structures <br />have been removed following reclamation of the site and no quantifiable <br />impacts were documented at the loadout. <br />III. Sealing of Drilled Holes and Underground Openings <br />A. The applicant has proposed to manage development, exploration, drill or bore <br />holes, wells, or other exposed underground openings in a manner other than by <br />sealing and plugging. The Division proposes to approve the manner proposed <br />since it should prevent acid or toxic drainage, minimize disturbance to the <br />prevailing hydrologic balance, and ensure the safety of people, livestock, fish and <br />wildlife, and machinery in the permit and adjacent areas (4.07.1). <br />zo <br />