REP20447 - Laserfiche WebLink

Home Browse Search

Susan Burgmeier - 2 - March 3, 1994 Investigation reveals that the operator did not quantify or include in the calculations NPDES outfalls 002, 003, and 004. These outfalls are mine generated, spoil springs which cumulatively have flows of a significant magnitude and this should be collectively included in any calculations in much the same way as NPDES 006. Additionally, the operator assumes that flow measurements at TR-a and TR-b are representative of actual conditions. One immediate discrepancy which requires further study is that TR-a discharge (upstream Trout) average flows upstream average of only 45 percent of flows measured downstream. The watershed between these two sites is very small relative to the upstream area and would not be much of a factor. Groundwater contribution of this magnitude would also not be significant due to the geology and geohydrology of the area. Furthermore, the most direct source of appreciable water would be leakage of the spoil water to the alluvium, yet quality data would not support a large contribution for this source. This leaves data integrity or irrigation as the remaining reason for the large difference in flow values between TR-a and TR-b. The operator should commit to quantifying all irrigation activities and use accurate and reliable techniques to measure flow and quality at TR-a and TR-b. 3. The operator then proceeds to make predictions of short-term impacts to Trout Creek TDS loading using predicted Moffat spoil spring discharge and quality data, TR-a discharge and quality data, NPDES 006 discharge and quality data, and "other" sources discharge and quality data. From these data the operator predicts a maximum annual average TDS to be 669mg/1. He goes on to add 3 standard deviations of 191mg/1 to predict a maximum TDS loading of 1242mg/1 which may occur in April of a given year. Two main problems are noted with this calculation. a. Since the relationship between TR-a flow data and TR-b flow is highly questionable and these data were used to quantify "other" source data, then the final calculation is suspect due to this potential erroneous input. b. Known spoil spring discharge which sources to Trout Creek through NPDES points 002, 003, and 004 were excluded from all calculations. Although these sources may be small they are nonetheless measurable and should be included. Summary and Conclusions The operator must collect reliable data along Trout Creek, specifically at stations TR-a and TR-b. These sites are key to any calculations and invalid or unreliable data at these sites subjects any further calculations and predictions to many questions. 2. All mine sources of discharge should be quantified and included in any further calculations. Spoil springs are of particular concern. Irrigation activities that could possibly affect flow and quality data should be quantified.