2010-06-04_PERMIT FILE - C1982056A (10)

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from any current mining activity. In addition, a basinwide survey of water quality conditions for the Yampa River Basin revealed ambient conditions exceeding stream standards (Wentz and Steele, 1980). . In the case of several trace metals (cadmium, lead, and perhaps mercury), the noted average or extreme concentrations may involve minimum analytical detection limits which are greater than the standard limits. At any rate, a critical assessment of currently applicable standards, and the extent to which they should be shifted downward to reflect more realistically ambient conditions, should be conducted before conducting a post mining mine impact analysis. No recent (since 1997) exceedances of discharge limits of pH were recorded at the mine. In addition no exceedances of the manganese or iron in- stream standards attributable to the mining operations have been observed (Annual Hydrologic Reports). (Note: The previous calculations and analysis were based on the premise that EC and sulfate standards were applicable for Lower Trout Creek, based on the stream designation for water supply. Subsequent review by the WQCD determined that these standards are not applicable if there is no active water supply useage. So the following information is no longer valid. In addition, the applicable standards have, in many cases been converted to calculated Table Value Standards (TVS), which take into account acute and chronic toxicity relative to specific aquatic indicator species) Exhibit 51, Tables E51 -12 to E51 -14 present predicted in- stream TDS, conductivity and sulfate values for Cases 1, 2 and 3 for normal and dry years. The tables indicate that the mine should be able to meet the conductivity limit of 1,500 µmhos /cm under most conditions, but will not be able to discharge at maximum rates during low flow conditions due to the inability to meet the sulfate standard (250 mg/L). Exhibit 51 Tables E51 -15 presents the maximum discharge rates from Sites 109 and 115 that will not cause an exceedance of the sulfate standard during a normal year. It indicates that in the future, Site 115 should be able to be discharged at higher rates than at present. Table Exhibit 51, Tables E51 -16 and E51 -17 present the in- stream flow rates required to not exceed the sulfate standard using dry year water quality data and maximum discharge rates from Sites 109 and 115. These tables also indicate that • Site 115 may be able to discharge at higher rates in the future. Exhibit 51, Table E51 -18 shows the minimum in- stream flow rate required in order to meet the sulfate standard using low flow water quality data and the minimum discharge rates from Sites 109 and 115 required to dewater all inflow. This table indicates that the mine can discharge at these rates under most conditions. Discharge of Ephemeral Runoff From Disturbed Areas Runoff from surface areas disturbed during construction of roads and facilities or by activities during operation and reclamation would be expected to be higher in suspended solids. The potential problem of increased levels of suspended solids in the surface runoff will effectively be mitigated during operations by construction and operation of sedimentation control structures. The sedimentation control structures will be operated to effect compliance with the effluent limitations of the NPDES permit. Under the stringent limitations of the NPDES permit, the suspended solid concentrations of the discharge will be lower than the streams during the spring run- off period. Successful completion of reclamation activities as described under Rule 2.05.4 will provide effective surface erosion control and will result in runoff characteristics similar to the premining conditions. RN08 -05 2.05 -158 03/12/10