2009-08-10_PERMIT FILE - C1982056A (5)

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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 anv 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 minim; 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 So the following information is no longer valid) Exhibit 49, Tables E49-12 to E49-14 present predicted in-stream TDS, conductivity and sulfate values for Cases 1, 2 and 3 for normal and dry years.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 1500 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 49, Tables E49-15 presents the maximum discharge rates from Sites 109 and 115 that will not cause ari exceedance of the sulfate standard during a normal year. It indicates that in the future, Site 115 should be able to bc; discharged at higher rates than at present. Table Exhibit 49, Tables E49-16 and E49-17 present the in-stream flow rates required to not exceed the sulfate standard using dry year water quality data and maximum discharge rate:; from Sites 109 and 115. These tables also indicate that Site 115 may be able to discharge at higher rates in thc; future. Exhibit 49, Tables E49-18 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 anti 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 premising conditions. Streamflow -Ground Water Relationships Underground mining operations may also affect streamflow conditions by affecting ground water discharge or by induced recharge. The two streams that could be affected are Foidel Creek and Fish Creek. Although underground mining activities are below or downgradient from Foidel Creek, it is conceivable that underground mining and reclamation activities could influence ground water discharge from surface mine spoils upgradient (south) of Foidel Creek. Underground mining by increasing the effective permeability and storativity of the Wadge overburden unit could increase the rate of recharge and thereby reduce ground water discharge to Foidel Creek from upgradient mine spoils. This does not appear to have occurred to date. Springs from backfill spoils have appeared since the onset of underground mining. The clay barrier constructed to cut off spoil water inflows in the vicinity of the portal may have reduced the effective permeability of the Wadge overburden unit to levels comparable or lower than . premising. Still, some spoil water has by passed the barrier as indicated in the discussion on this issue in the ground water baseline section. MR08-230 2.05-159 09/05/08