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1 Minrec, Inc. - North Thompson Creek Mine Stormwater Management Plan t Page 2 b. No spills or leaks of toxic or hazardous pollutants have ' occurred at the facility. c. Mine drainage water could potentially become mixed with stormwater. The mine water drainage, prior to passive ' treatment in three ponds, contains about 100 ppm iron. c. Stormwater generated by this mining operation will not ' potentially contain any pollutants except sediment and mine drainage water. d. No existing discharge sampling exists for atormwater discharges. 4. Stormwater Quality Controls - Best Manaaement Practices Mine drainage water is the only pollutant that stormwater must be diverted away from to prevent stormwater contamination. ' The method used to prevent stormwater contamination is to contain the mine drainage. Mine drainage flows through three ponds prior to being t discharged into North Thompson Creek (Long Pond, T-1 6 T-2). The ponds provide adequate aeration and detention time to allow the iron to settle out of the mine drainage. As long as t the ponds function as designed, there is no chance that stormwater will be contaminated by the mine drainage. If any of the pond embankments overflow due to an upset condition, ' the potentially high iron content mine water would flow to sediment pond P-9. It is in sediment pond P-9 that the mine drainage and stormwater could become mixed. ' Pond P-9 is designed to contain the run-off from a 10-year 24- hour storm event. Pond P-9 would theoretically discharge stormwater from a larger event. If an upset condition ' occurred in the mine water treatment system concurrently with a 10-year 24-hour storm event, which is considered unlikely, then stormwater discharge would be contaminated. 1 1 1 1 Stormwater from the mine sites is contained in one of three sediment ponds (P-3, P-9 and the Refuse Pond). A series of collection ditches and berms directs the run-off to the ponds. The run-off from the No. 3 Mine and the Tank Area is contained in pond P-3. The run-off from the No. 1 Mine site is contained in both Sediment Pond P-9 and the Refuse Pond. Run- off from the Refuse Area is contained by the Refuse Pond. Vegetation is the primary sediment control feature for stormwater runoff. Vegetation slows the velocity of sediment laden water which allows time for the deposition of sediment.