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Wes( Elk Mine <br />• percent of the average annual stream flow on the North Fork. Since less than 70 percent of this use <br />is deemed to be consumptive use, the loss is actually less than 0.03 percent of the average stream <br />flow. As discussed in this plan, actual production is much less than was anticipated when the mine <br />opened in 1982. Thus water use is significantly less than discussed above. <br />Water quality changes resulting from discharge of waste water will not constitute material damage <br />because no measurable change in water quality is expected to occur. Of the 200,000 gallons/day <br />maximum projected use, 38,000 gallons/day (28.5 acre-feet/yeaz) would be required for potable <br />water use. Consumptive use of potable water would be minimal. Assuming no consumptive use, <br />one would expect a discharge of less than 0.06 cfs during plant operation. This use and return flow <br />is insignificant compared to the flows in the North Fork of the Gunnison. Even during the lowest <br />flow on record (17 cfs) for the 1934 through 1979 period of record on the North Fork at Somerset, <br />the potable water use would be less than 0.4 percent of the flow. The return water will be treated to <br />meet NPDES effluent limits and should pose no problem for downstream irrigation use of AVF's. <br />See the Section on Agricultural Monitoring Plan for further discussion. <br />The sewage collected from the site will be domestic in nature and will consist of soluble B.O.D., <br />volatile suspended solids, and inert solids which will be treated using biological organisms to <br />aerobically stabilize the waste. Since biological treatment will be used, with no chemical treatment <br />required, there should be no secondary by-products which would not be similar to those existing in <br />the North Fork of the Gunnison. <br />• The effluent from the treatment unit has the following chazacteristics: <br />Soluble B.O.D. 16 mg/L <br />Suspended Solids B.O.D. 14 m <br /> 30 mg/L <br />Suspended Solids 30 mg/L <br />Ammonia (NHS) 1.0 mg/L <br />Nitrate (NO,) 29 mg/L <br />Combined Chlorine Residual 0.1 mg/L <br />Fecal Coliforms 10,000/100m1 <br />Ammonia varies from 2 to 100 times the concentrations measured in the North Fork. The <br />suspended solids value varies from 0.2 to 15 times the suspended solids concentrations reported in <br />the M & R Plan. The nitrate values are ten times the values reported for baseline conditions <br />measured in the North Fork, while B.O.D. values vary from 2 to 60 times the values encountered in <br />baseline monitoring. Considering the degree of dilution is considerably greater than two hundred- <br />fold even during extreme low flow conditions, it is unlikely that a water quality change would be <br />detected in the North Fork as a result of the discharge. Furthermore, the water quality parameters <br />that might be marginally increased by the effluent would not pose a problem for imgation use. <br />On an annual basis the water use is insignificant relative to the flow in the North Fork. To further <br />evaluate the risk of material damage to quantity and quality of water supplying downstream AVF's, <br />• the daily water use scenario was considered. The 200,000 gallons/day maximum projected water <br />use represents less than two percent (2 percent) of the lowest flow on record (17 cfs). As previously <br />2.06-9 <br />