2009-05-12_GENERAL DOCUMENTS - C1981025

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Baseline flows of North Thompson Creek, as recorded by the United States Geological Service at a gage station just above the mine permit area, ranged from a high May 1964 flow of 322 cubic feet per second (cfs) to a low September 1964 flow of 0.3 cfs. Discharges from Outfall 001 have ranged from 160 gallons per minute (gpm) to 15.3 gpm (0.36 - 0.034 cfs) during 1996 through 2002. September Outfall 001 flows have ranged from 61.1 gpm in 1997 to 21.8 gpm in 2002 (0.049 cfs). The September 2002 Outfall 001 discharge of 0.049 cfs would be 14 percent of downstream North Thompson flow at the 0.3 cfs baseline. Flows from springs, seeps, and from Mine No. 2, are low (one gallon per minute or less each), but indicate that certain constituents are introduced into North Thompson Creek from other than Outfall 001 discharges. In general, the increases between upstream and downstream North Thompson Creek receiving stream standards parameters are greatest during low flows. The effects of Outfall 001, and discharges from other sources, on North Thompson Creek are expected to be greatest during low-flow conditions of North Thompson Creek, and September data, when available, is evaluated as such in this renewal findings. In this review, Table Value Standards of Numeric Standards were calculated based on a water hardness of 174.69, as determined from a calcium concentration of 46.6 mg/1 and a magnesium concentration of 14.14 mg/1. These values were from a downstream North Thompson Creek sample of September 8, 2002. Numeric Standards Physical and Biological Dissolved Oxygen (D.O.) There has been no monitoring for dissolved oxygen, thus impacts of the mine water discharges regarding dissolved oxygen are not known. However, impacts on downstream dissolved oxygen may be insignificant, and concentrations may meet the Numeric Standard of 6.0 mg/l. Flows in North Thompson Creek are turbulent, mine water discharge inflows are aerated at the beginning of the treatment system, and Outfall 001 discharges are aerated by the drop outlet and runout from outfall to the stream. pH Monitoring results suggest that there is no effect on the pH of North Thompson Creek from Outfall 001 discharges, and that downstream pH values are within the Numeric Standard. The Numeric Standard for pH is 6.5 - 9.0. Fecal Coli (F. Coli) There has been no monitoring for fecal coliforms (F. Coli), thus effects of the mine water discharges on fecal coliforms in North Thompson Creek are not known. Sewage treatment facilities at the site have been removed and disturbances reclaimed. It is unlikely that any current mine-related activities have a potential for introduction of fecal North Thompson Creek C-1981-025 Permit Renewal 05 12 May 2009 23