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West Elk Mine percent of the average annual stream flow on the North Fork. Since less than 70 percent of this use is deemed to be consumptive use, the loss is actually less than 0.03 percent of the average stream flow. As discussed in this plan, actual production is much less than was anticipated when the mine opened in 1982. Thus water use is significantly less than discussed above. Water quality changes resulting from dischazge of waste water will not constitute material damage because no measurable change in water quality is expected to occur. Of the 200,000 gallons/day maximum projected use, 38,000 gallons/day (28.5 acre-feetlyeaz) would be required for potable water use. Consumptive use of potable water would be minimal. Assuming no consumptive use, one would expect a dischazge of less than 0.06 cfs during plant operation. This use and return flow is insignificant compazed to the flows in the North Fork of the Gunnison. Even during the lowest flow on record (17 cfs) for the 1934 through 1979 period of record on the North Fork at Somerset, the potable water use would be less than 0.4 percent of the flow. The return water will be treated to meet NPDES effluent limits and should pose no problem for downstream irrigation use of AVF's. See the Section on Agricultural Monitoring Plan for further discussion. The impacts of the dischazge of water to the North Fork from West Elk Mine is discussed in detail in the Probable Hydrogogic Consequences - 2.05.6(3)(b)(iii & viii), section "Surface Water Quality Effects". Both the short term and long term "worst case" scenarios aze addressed. It is important to note that predicting the future "worst case" scenario is extremely difficult to predict with 100% accuracy. However, these scenarios have been presented in the aforementioned section using current mine discharge histories and anticipated conditions to be encountered in future mining. The fmdings of anticipated affects of mine water dischazge to the quality suitablity of waters used to irrigate to the downstream AVFs aze summarized in the following text. The quality of mine water dischazges from the B Seam in the cunent permit area and in the South of Divide permit revision azea, and from the B and E Seams in the Apache Rocks permit azea, aze expected to be good enough to meet NPDES dischazge standards. TDS levels in the North Fork are elevated under natural conditions. Under the worst case scenazio, the downstream mixed TDS concentration would be approximately 670 mg/L. This concentration would occur only during the short duration over which the dischazges occur (i.e., less than two days to empty both ponds at their maximum dischazge rates), or while the North Fork flows are at the 7-day, 10- yeaz (7Q10) low flow conditions. This is important since TDS is a pazameter that is of concern only when the concentration is elevated for significant periods of time (i.e., months to yeazs). Additionally, the primary concern with elevated TDS is for agricultural uses. The 7Q101ow flow is most likely to occur during the winter months, when irrigation is not occun•ing. There would be no material damage to irrigated agricultural operations as a result of the short-term increases in salinity to 670 mg/L. The increased TDS levels would occur for a duration of less than one week. Since adverse salinity impact to crops result from an accumulation of salts in the soil, a minor, short-term increase would have no effect on the crops. Dr. Robert Weiner of W WE has evaluated the concentrations of the individual constituents which collectively constitute TDS in mine dischazges. Dr. Weiner has determined that the mine pond dischazge water is predominantly sodium carbonate/sodium bicazbonate in nature. Aside from high concentrations of sodium, none of the other parameters, including the heavy metals, are found in significant concentrations. As for sodium, there are no applicable numeric standards 2.06-9