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In the case of several trace metals (cadmium, lead, and perhaps mercury), the noted average or extreme <br />concentrations may involve minimum analytical detection limits which are greater than the standard limits. At any <br />• rate, a critical assessment of currently applicable standards, and the extent to which they should be shifted <br />downward to reflect more realistically ambient conditions, should be conducted before conducting a post mining <br />mine impact analysis. <br />No recent (since 1997) exceedances of discharge limits of pH were recorded at the mine. In addition no <br />exceedances of the manganese or iron in-stream standards attributable to the mining operations have been <br />observed (Annual Hydrologic Reports). <br />Exhibit 49, Tables E49-12 to E49-14 present predicted in-stream TDS, conductivity and sulfate values for Cases 1, <br />2 and 3 for normal and dry years. The tables indicate that the mine should be able to meet the conductivity limit of <br />1500 pmhos/cm under most conditions but will not be able to discharge at maximum rates during low flow <br />conditions due to the inability to meet the sulfate standard (250 mg/L). Exhibit 49, Tables E49-15 presents the <br />maximum discharge rates from Sitcs 109 and 115 that will not cause an exceedance of the sulfate standard during a <br />normal year. ]t indicates that in the future, Site ] ] 5 should be able to be discharged at higher rates than at present. <br />Table Exhibit 49, Tables E49-16 and E49-17 present the in-stream flow rates required to not exceed the sulfate <br />standard using dry year water quality data and maximum discharge rates from Sites 109 and 1 I5. These tables <br />also indicate that Site 115 may be able to discharge at higher rates in the future. Exhibit 49, Tables E49-18 shows <br />the minimum in-stream flow rate required in order to meet the sulfate standard using low flow water quality data <br />and the minimum discharge rates from Sites ]09 and ] IS required to dewater al] inflow. This table indicates that <br />the mine can discharge at these rates under most conditions. <br />Discharee of Eahemeral Runoff From Disturbed Areas <br />• Runoff from surface areas disturbed during construction of roads and facilities or by activities during operation <br />and reclamation would be expected to be higher in suspended solids. <br />The potential problem of increased levels of suspended solids in the surface runoff will effectively be mitigated <br />during operations by construction and operation of sedimentation control structures. The sedimentation control <br />structures will be operated to effect compliance with the effluent limitations of the NPDES permit. Under the <br />stringent limitations of the NPDES permit, the suspended solid concentrations of the discharge will be lower than <br />the streams during the spring run-off period. Successful completion of reclamation activities as described under <br />Rule 2.05.4 will provide effective surface erosion control and will result in runoff characteristics similar to the <br />premining conditions. <br />Streamflow -Ground Water Relationshias <br />Underground mining operations may also affect Streamflow conditions by affecting ground water discharge or by <br />induced recharge. The two streams that could be affected are Foidel Creek and Fish Creek. Although <br />underground mining activities are below or downgradient from Foidel Creek, it is conceivable that underground <br />mining and reclamation activities could influence ground water discharge from surface mine spoils upgradient <br />(south) of Foidel Creek. Underground mining by increasing the effective permeability and storativity of the <br />Wadge overburden unit could increase the rate of recharge and thereby reduce ground water discharge to Foidel <br />Creek from upgradient mine spoils. This does not appear to have occurred to date. Springs from backfill spoils <br />have appeared since the onset of underground mining. The clay barrier constructed to cut off spoil water inflows <br />in the vicinity of the portal may have reduced the effective permeability of the Wadge overburden unit to levels <br />rrurgrmdrl~ sn 'ruwet 1;rdr~ Ete~simis~g. Sn55, svrrre sgruh •awdrrt 5•rts 4ry• ;i>~3~5 ~~ie 4rastiret ~~ is~dit,d~g5 ire .5re <br />.discussion on this issue in the ground water baseline section. <br />APPROFlED Fee o s 2000 <br />TR 99-32 2.05-159 1/3/00 <br />