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the potential for increased erosion. TSS concentrations of streams should not increase because flows from <br />distwbed and reclaimed aeeas will be treated in sedimentation ponds to meet NPDES effluent limits. The effects of <br />leaching in exposed spoil and waste rock plies, detention of water in sedimentation ponds, and pumping water out <br />("^ of pits and underground mine workings have the potential to increase TDS concentrations and change ionic <br />composition of surface waters. <br />The planned underground mining activities have the potential of creating changes in the existing surface water <br />quantity in terms of runoff flows and flow rates including changes in peak flows and low flow conditions. <br />Likewise, the planned undergound mining activities have the potential of producing changes in the existing surface <br />water quality in terms of conductivity, total dissolved solids (T'DS), total suspended solids (TSS), ionic <br />composition, sodium adsorption ratio (S.4R), pH, and trace metals with iron and manganese, the primary indicators. <br />Water quality impacts will be addressed for all seasonal conditions including both high and low flow conditions. <br />The underground mining and related activities that have the potential of impacting surface water flows and water <br />quality are described below along with an assessment of the natwe and magnitude of potential impact. The primary <br />surface water impact will result from the dischazge to Foidel Creek and Fish Creek of mine inflows that aze <br />collected in sumps and pumped to sedimentation ponds and settling ponds for treatment prior to release. <br />Impacts of Direct Disturbance of Surface Flow Channels <br />Direct distwbance of surface flow channels may occw either when temporary construction activities require a <br />stream crossing for installation of pipelines or other utilities, or for long-term road or raih•oad crossings. In both <br />cases, normal streamflows will not be interrupted and any stream channel distwbance will be mitigated through <br />reconstruction of the natwal stream channel and floodplain configuration. <br />Normally, any distwbance in stream channel aeeas will occw during low-flow periods to minimize disruption of <br />flow. If flow characteristics of the affected channel are ephemeral or internuttent, it may be possible to complete <br />work in the stream channel when there is little or no flow. If any significant flow is occurring during the <br />construction period, flows will be temporarily diverted around the distwbance azea during construction using a <br />pump(s) and pipeline. Normal flow will be restored, once construction is completed and the affected channel aeeas <br />restored. <br />For temporary construction distwbance, the effective distwbance azea will be minimized to the extent reasonably <br />feasible, and the affected stream channel, banks, and any affected floodplain aeeas will be restored to their original <br />configuration through backfilling, compaction, grading, and placement of armoring (as appropriate). Distwbance <br />areas will be reseeded with TCC's standazd riparian seed mix. <br />For long-term road or railroad crossings, culverts or other appropriate designed flow structures will be installed to <br />safely pass the design flows in compliance with applicable provisions of Rule 4.03, and inlets will be armored to <br />protect against erosion. If the road/railroad is approved as a permanent postmining featwe, the associated drainage <br />structwes will remain in place. If the road/railroad crossing is to be removed as a part of mine reclamation, the <br />affected stream channel, banks, and floodplain aeeas will be restored at that time, as previously described. <br />Impacts of Mine Water Discharee <br />The relatively continuous discharge of anticipated mine water to Foidel Creek constitutes a significant proportion of <br />total streamflow during low flow periods. This will result in perennial flow in Foidel Creek, while the mine is <br />discharging to Foidel Creek. When the Fish Creek dewatering site is operating it can represent a significant portion <br />of the Fish Creek flow. Runoff flows in Foidel Creek should increase during the period when the mine is <br />discharging. Projected mine inflows through the life of the mine have been re-estimated based on current data and <br />are discussed in the Ground Water PHC section, Ground Water Inflow to the Mine. The maximum dischazge to <br />Foidel Creek is expected to be a maximum of approximately 400 gpm on an annual basis by the end of the mine life <br />and at the end of lowering of the water level in the Fish Creek Borehole sump. Daily discharge from the Fish Creek <br />borehole and Site 115 will range up to 1200 gpm, however, average annual dischazges will range from 55 to 300 <br />gpm. <br />TR07-60 2.05-I51 05/01/07 <br />