2009-04-27_PERMIT FILE - C1996083A

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. 2.05.6 According to data supplied by the USGS, the annual seven day minimum flow for the North Fork of the Gunnison River is 25 cfs. This low flow value occurred February 17, 1978, is for the period of record from 1934 through 1995 and is measured upstream of the Town of Somerset, CO. inflow/discharge of 1,000 gpm from Outfall 006 is utilized. As explained in Section 2.04.7, the Bowie No. 2 Mine is experiencing an inflow of approximately 700 gpm. Recent mine water quality analysis are shown above in section 2.05.6(3)(a)(iv). For the purposes of this PHC a worst case mine Flow from outfall 006 need only travel a short distance to enter a highway culvert and join the North Fork of the Gunnison River. See Map 41, Mine Discharge Pipe Alignment. The heavily vegetated water course from Outfall 006 to the highway culvert will eliminate the possibility of sediment entering the North Fork of the Gunnison River due to erosion. Since the mine discharge will mix with the River water in a relatively short distance, there are no lands, river banks, structures, alluvial valley floors or prime farm land on either side of State Highway 133 that potentially may be adversely affected by the mine water discharge quantity or quality. The average TDS and total recoverable Manganese measurements at the upstream • North Fork of the Gunnison River monitoring station for the baseline period (2007 AHR) are 130 and 0.015 mg/I respectively. The average iron measurement at the upstream North Fork of the Gunnison River monitoring station for the baseline period (2007 AHR) is 0.09 mg/I. The following table presents the estimated affect the average mine water quality (page 2.05-70i) will have on the quality of water in the North Fork of the Gunnison River at low flow: PHC North Fork of the Gunnison River • Flow Flow TDS Manganese Iron Gpm Cfs mg/I Trec. mg/I Trec, mg/I North Fork 11,220 25 130 0.015 0.09 Mine Discharge 1,000 2.2 2,838 0.037 2.43 Combined Flow 12,220 27.2 352 0.017 0.28 Based upon the above calculations, the mine discharge into the North Fork of the Gunnison River will not have a measurable impact on total recoverable manganese or total recoverable iron in the river. TDS values in the river would increase under rare low flow conditions. The pH of the North Fork of the Gunnison River varies from 7.5 to 8.8 according to the 2007 AHR. The average pH of the mine discharge water is 8.4. Therefore, the mine discharge water should not adversely affect the pH in the North Fork of the Gunnison River. See the following table for addition PHC analysis. TR-54 2.05 - 73 12/08 ~ PpRdv~ I/~~~~~