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The levels of iron that will discharge into North Thompson Creek after this treatment system are so low that no affect will be noted on aquatic life or the stream itself. The total dissolved salt content of the water is of greater concern. The mixing of a 40 gallon per minute mine discharge at 2,800 mg/1 TDS into the average monthly low flow of 4.4 cfs and an average normal salt load of 160 mg/1 increases the base total dissolved solids to 213 mg/1. This still does not exceed any receiving stream standards, water quality criteria, or irrigation standards. Another mitigating factor is that the high flow in the discharge tends to coincide with high fl ow or snowmelt runoff in the stream itself. Historically, by the time the stream has reached low flow, mine discharges have nearly ceased to exist. The original Findings Document discussed possible depletions to the North and Middle Thompson Creeks due to water consumption by the mining operation. In the original Findings all inflows were assumed to came from stream flow. Based on this assumption the amount of water predicted to be depleted from the North and Middle Thompson Creeks by the No. 1 and No. 3 Mines was projected to be .3 cfs. Assuming that all mine inflows were consumed a total depletion for the water year to the North Thompson Creek was a reduction of less than 1% of flow. However, .3 cfs during low flow could be critical to North Thompson Creek. For this reason further study was required by the operator to determine the worst-case impacts that could occur in depletions to both steams. The methods of determination included the placement of flumes with continuous monitors on both up and downstream sections of the North and Middle Thompson Creeks. These flumes were installed to measure low flow periods on the stream and to determine if depletion of the stream was occurring between these reaches due to inflow into the voids of the underground mine. The mine never progressed to the extent that the crucial area of undermining occurred, and for the year of record with continuous monitoring, no depletion was noted from upstream to downstream. However, the potential for stream flow depletion still existed when the mines were shut down, allowed to infill, and pumping of inflow water ceased to North Thompson Creek. The operator therefore did a further study to evaluate the total impact to the creek at this point. The No. 1 Mine filling rate was projected in a study finished in 1986. In order to mitigate the infill assuming that all flows came from North Thompson Creek, the No. 3 Mine was allowed to discharge. A permanent discharge point has been established on the North Thompson Creek from the No. 3 Mine. Filling rates based on void space for the No. 1 Mine show that the rate of inflow to the mine is decreasing due to decrease in head from the stream system. The filling rate is now projected at 63.1 gpm for the No. 1 Mine and 9.5 gpm for the No. 3 Mine during October of 1987. -6-