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-41- l <br /> There is a minor potential for the Coal Basin Mine loadout and the North <br /> Thompson Creek Mine loadout to cumulatively impact the quality and 't) <br /> quantity of ground water in the Roaring Fork alluvium, since both <br /> loadouts are located on this alluvial body. However, both of these <br /> loadouts have limited surface disturbance, small amounts of disturbed d <br /> drainage to handle, and much of the disturbed drainage water is going <br /> into total containment lined ponds. Therefore, that minor amount of ' <br /> polluted drainage which may escape from the drainage control system will <br /> n y minima impact the quality of the vast amounts of Roaring Fork <br /> a uvial water. <br /> The greatest cumulative ground water impact will be the indirect <br /> depletion of surface water flow through the yround water system to the <br /> mine workings. Since the impacts are to surface water, they are <br /> quantitatively discussed below in the Surface Water section of this <br /> Cumulative Impacts Study. The mechanism of stream depletion has been <br /> discussed in the general description of ground water. <br /> Cumulative Impacts - Surface Water L0 <br /> One of the potential cumulative im ly <br /> m en ons. The <br /> sediment control systems in use at all mines and the strict effluent <br /> limitations imposed on all discharges will keep sediment loads near ? <br /> It also should be noted that all three mines considered <br /> in this assessment are underground mines with minimal surface <br /> disturbance. Total surface disturbance is oply 0.06% of the 1451 square <br /> mile Roaring Fork River Basin. Because of these facts, cumulative V/ <br /> sediment loads are not expected to be significant. Vti <br /> The cumulative effect of impounding water in sediment ponds at all three <br /> mines will also be insignificant. Because of the small relative surface <br /> disturbance at each mine, pond storage volumes are likewise small . l � ` <br /> Sedimentation ponds at all mines are dewatered within 72 hours to r �•o <br /> minimize any water loss to the hydrologic system. Q <br /> The total worse case depletion to the Roaring Fork River by mine inflows <br /> is small . If all mine inflows were consumea and not discharged back to <br /> the receiving stream, a total of 456 acre-feet/year would be depleted <br /> from the Roaring Fork. This is only 0.06% of the total flow. Even <br /> during the low flow of 179 cfs for the period of record on Roaring Fork, <br /> the total depletion would be U.4q. This amount is insignificant to the <br /> surface water system. (Refer to Table 4. ) <br /> The impact of all mine discharges on the salt load to the Roaring Fork <br /> River can be ca elated assuming •a worse case mine discharge and average •�G 1 <br /> salt content. T - � c ine <br /> ;' har es `" ,� i s �. o mean annual (,(� <br /> salt load normally carried 5y the RoaringFor< ive This should not 4 <br /> . aise any measura e cnan5 In t eater qua ,ty or the Roaring Fork w <br /> R 1`Je J J <br /> �°'` ��� <br /> G <br /> � tt <br />