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_2g_ The mine has the potential to increase total dissolved solids content of the North Thompson Creek. To evaluate this impact, the Division considered the additional total salt load on Thompson Creek. The mine discharges an average salt load of 193 metric tonslyear (see Table 4). This compares to an average normal salt load of 5284 metric tonslyear in the total Thompson Creek drainage. The additional contribution by the mine on Thompson Creek is 3.7%, the contribution to North Thompson Creek alone is 8.3%. Both of these values are low and will not result in salinity increases above any standards. The salt load on Thompson Creek during a mean monthly low flow might be more critical. This can be calculated assuming an average monthly low flow of 4.4 cfs (10 years of record}, an average normal salt load of 160 mgfl, and a mine discharge of 0.3 cfs. Using these values, the mine will Increase salt loads by 16.1 metric tons/month over an estimated low flow value of 51.6 metric tons/month. This is a 31% increase during this low flow period. Although this increase appears significant, a 3l% increase in baseline total dissolved solids will still mean the water quality will be classified as good for irrigation and aquatic life. No receiving stream standards, water quality criteria, or irrigation standards should be exceeded. Also, past monitoring has not identified any unsuitable levels of dissolved solids in Thompson Creek. The magnitude of tfiis salt increase will decrease at the confluence of Thompson Creek and the Crystal River. The low flow of record on the crystal river near Redstone is 22 cfs (28 years of data) which would result in a dilution ratio of 22cfs/4.7cfs or about 5:1 ratio. The sediment ponds and refuse area at the mine may add an additional salt load to the Thompson Creek drainage. However, the impacts are expected to be small due to their limited discharge, and the fact that the discharge would be during a rain event, when dilution factors are highest. The mine may affect the surface water regime in still another way. Mining may cause the depletion of springs and seeps above the undermined areas. A spring and seep survey conducted by the mine has only identified two springs within the five-year mine plan area. Both springs (designated on the mine subsidence map) flow less than one gallon per minute, except during the spring, when site SP-2 flows 20-40 gallons per minute. Both springs flow from the Upper Sandstone and are not adjudicated. Based on the low flow and poor quality, it does not appear that the springs were, or are, a significant component of the surface water regime. Any depletions will therefore not be a significant impact to the Hydrologic Balance. The mine loadout facility should not significantly impact the Roaring Fork River. The loadout disturbs less than 20 acres. Sediment control structures are in use and all conveyor wash water systems recycle with no discharge. No quantifiable impacts were predicted at the loadout. To assure that adverse impacts are identified early, the Division has proposed that all mines in the area adequately monitor the potential tmpdcts of their mining operation. The operator has committed to an acceptable monitoring plan and has committed to submitting a yearly hydrologic report which presents and interprets the past year's eionitoring results and project future impacts.