_GENERAL DOCUMENTS - C1981017 (262)

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-41- There is a minor potential for the Coal Basin Mine loadout and the Nor-CT 7 Thompson Creek Mine loadout to cumulatively impact the quality and quantity of ground water in the Roaring Fork alluvium, since both CU" loadouts are located on this alluvial body. However, both of these loadouts have limited surface disturbance, small amounts of disturbed d tydrainage to handle, and much of the disturbed drainage water is going into total containment lined ponds. Therefore, that minor amount of polluted drainaye which may escape from the drainage control system will n y minima impact the quality of the vast an, of Roaring Fork a uvial water. The greatest cumulative ground water impact will oe the indirect depletion of surface water flow through the yround water system to the mine workings. Since the impacts are to surface water, they are quantitatively discussed below in the Surface Water section of this Cumulative Impacts Study. The mechanism of stream depletion has been discussed in the general description of ground water. Cumulative Impacts - Surface Water One of the potential cumulative im a y l " m' en ohs. The sediment control systems in use at all mines and the strict effluent \_ \ limitations imposed on all discharges will keep sediment loads near It also should be noted that all three mines considered in this assessment are underground mines with minimal surface disturbance. Total surface disturbance is only 0.06% of the 1451 square mile RoaringFork River Basin. Because of "these facts,ese sediment loads are not expected to be significant. V� The cumulative effect of impounding water in sediment ponds at' all three mines will also be insignificant. Because of the small relative surface disturbance at each mine, pond storage volumes are likewise small . . Sedimentation ponds at all mines are dewatered within 72 hours to minimize any water loss to the hydrologic system. The total worse case depletion to the Roaring Fork River by mine inflowsLo is small . If all mine inflows were consumed and not discharged 'back to U the receiving stream, a total of 456 acre-feet/year would be depleted from the Roaring Fork. This is only 0.067 of the total flow. Even during the low flow of 179 cfs for the period of record on Roaring Fork, the total depletion .Mould be U.40/o. This amount is insignificant to the surface water system. (Refer to Table 4. ) The impact of all mine discharges on the salt load to the Roaring For< River can be c1lwilated assuming -a worse case mine discharge and average salt content. T - - '^ ' �'' t lne 1/-�iD`� C. 11l�G�le charues � _ his s is �.0�� n mean annual salt load normally carried :y the Roaring For< Ive This should not t ..BSc any easura e cnanc n water quality of the Roaring Fork �Olt fie- si, (P011A �` ( ° U S '�