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the potential for increased erosion. TSS concentrations of streams should not increase because flows from disturbed and reclaimed areas will be treated in sedimentation ponds to meet NPDES effluent limits. The effects • of leaching in exposed spoil and waste rock piles, detention of water in sedimentation ponds, and pumping water out of pits and underground mine workings have the potential to increase TDS concentrations and change ionic composition of surface waters. The planned underground mining activities have the potential of creating changes in the existing surface water quantity in terms of runoff Flows and Flow rates including changes in peak flows and low Flow conditions. Likewise, the planned underground mining activities have the potential of producing changes in the existing surface water quality in terms of conductivity, total dissolved solids (TDS), total suspended solids (TSS), ionic composition, sodium absorption ratio (SAR), pH, and trace metals with iron and manganese, the primary indicators. Water quality impacts will be addressed for all seasonal conditions including both high and low Flow conditions. The underground mining activities that have the potential of impacting surface water Flows and water quality are described below along with an assessment of the nature and magnitude of potential impact. The primary surface water impact will result from the discharge to Foidel Creek and Fish Creek of mine inflows that are collected in sumps and pumped to sedimentation ponds and settling ponds for treatment prior to release. Impacts of Mine Water Discharee The relatively continuous discharge of anticipated mine water to Foidel Creek constitutes a significant proportion of total stream flow during low Flow periods. This will result in perennial Flow in Foidel Creek while the mine is discharging to Foidel Creek. When the Fish Creek dewatering site is operating it can represent a significant portion of [he Fish Creek Flow. Runoff Flows in Foidel Creek should increase during the period when the mine is .discharging. Projected mine inflows through the life of the mine have been re-estimated based on current data and are discussed in the GROUND WATER PHC section, Ground Water Infow to the Mine. The maximum discharge to Foidel Creek is expected to be a maximum of approximately 400 gpm on an annual basis by the end of the mine life and at the end of lowering of the water level in the Fish Creek Borehole sump. Daily discharge from the Fish Creek borehole and Site 115 will range up to ]200 gpm, however, average annual discharges will range from 55 to 300 gpm. Mine Discharges The 1998 inflows and the estimated future mine inflows are shown in Exhibit 49, Table E49-4. Projected mine discharges are shown on Exhibit 49, Tables E49-6 through E49-8. The mining rate used in these projections was 8,000,00() tons per year. An increased mining rate will not effect the maximum flow rates but only move them forward in time. The mine groundwater inflow numbers are discussed above in the Ground Water Inflow to the Mine section. Much of the mine inflows will be discharged and removed through the Fish Creek borehole. During periods when these pumps are not operating the sump below the borehole fills with mine inflow water. The present (1998/1999) pool volume is estimated to be 546,000,000 gallons (Ground Water Inflow to the Mine, Mine Water Balance). When both pumps at the borehole are running it is capable of discharging at approximately 850 gpm, although this rate may be increased to 1200 gpm if warranted, however, the average annual future pumping rate is estimated to be 300 gpm. At this rate, it is estimated that it will take 1.4 years to drop the pool elevation to the required operational level of 5800 feet. At that time, the pumping rate will be maintained at a rate sufficient to maintain the water level by removing inflows from the WMD. This rate is estimated to be 55 gpm if no water is transferred from other parts of the mine. ~As of June 1999, the mine had completed a system to recycle some of the water that is produced underground. The average amount the system can recycle is over i75 gpm. The average annual recycling rate has been conservatively estimated to be 100 gpm. This will allow for the addition of some makeup water if needed to dilute PR 99-OS 2.05- 151 '~'~'~'~ ~ ~ ~ ~ `~~ N 2 8 2000 03/28/00