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• in the unaccounted flow. This conclusion is impart based on the decrease <br />in TDS between TR-C and TR-D (1970 mg/1 to 1940 mg/1). Therefore, it is <br />believed that the TDS concentration in surface water flow from CDPS 009 was <br />significantly higher than its average concentration. <br />Applying the same methods and assumptions employed for the annual <br />predictions to the irrigation season (July, August and September), TDS <br />concentrations in Trout Creek may be expected to reach an upper limit of <br />approximately 1,050 mg/1 at some time during the irrigation months of the <br />mining and postmining era at the Edna Mine (1,050 mg/1 = average (381 mg/1) <br />+ 3s (s = 223 mg/1)). As before, all TDS concentrations observed during <br />the irrigation season, except one, are below the predicted upper limit. <br />The exception value was 1,076 mg/1 observed on July 25, 1999. This value <br />_~`~ <br />is very close to the predicted upper limit and may be considered the result <br />of laboratory analytical limitations or part of the normal population which <br />lies outside the limits set by statistical analysis. <br />The statistical mass balance equation analysis is useful for <br />predicting impacts to Trout Creek from mining activities. As discussed <br />previously, all TDS observations, except one in each case, fell below the <br />predicted upper limit. The highest levels of TDS can be expected to occur <br />in spring when the snowmelt at the mine has occurred and moisture passes <br />• through the spoil of the mined areas and enters Trout Creek, but prior to <br />peak runoff from the upper Trout Creek watershed. The highest TDS levels <br />during the irrigation months are probably most related to the driest <br />periods when the amount of irrigation water drawn from Trout Creek upstream <br />of TR-A causes Trout Creek to be at the lowest point of baseflow. <br />Concentrations of TDS are not anticipated to exceed the estimated <br />upper limits predicted in the future for several reasons: 1) peak flow from <br />discharge point 007 should decrease over time as the vegetation on West <br />Ridge becomes established; 2) the exposed spoil on the Moffat area will be <br />eliminated, and; 3) the completion of reclamation activities in the Moffat <br />final pit area will increase the area's water carrying capacity. As a <br />result, the flow from TDS enriched ground water sources on the east side of <br />Trout Creek is predicted to decrease over time. <br />• <br />Renewal 3 2.SA-9 June 13,1997 <br />