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-37- ~ ~ ~~ The Eagle No. 9 Mine discharge is of the sodium bicarbonate type and is similar to the Eagle No. 5 Mine discharge, but with a higher percentage of sodium. Dissolved solids concentrations average 749 mg/l, with a maximum value of 880 mg/1. The pH values range from 8.83 to 9.32 and average 9.08. Iron values are similar to those found at the Eagle No. 5 Mine. Concentrations ranged from less than 0.03 mq/1 to 1.53 mg/1. Manganese concentrations were all less than 0.02 mg/1. (full suite analyses and statistical summaries of the mine water discharge are provided in Tables III-lOd and a of the permit application.) The applicant has estimated the effects of this mine water discharge upon the mean monthly dissolved solids concentrations in the Williams fork and Yampa Rivers using a mass balance analysis. For the Williams Fork River, the mean dissolved solids concentrations for the Eagle No. 5 and No. 9 mine water discharge, and the spring discharge from the No. 1 strip pit, were added to the mean monthly flow and dissolved solids concentrations for the upstream gaging station in order to predict the effects of mining. The calculated effect of the mine discharges and the strip pit discharge is to increase dissolved solids concentrations during low flow months by as much as 18 percent. During periods of high flow, discharge is increased by about 2 percent. The calculated total dissolved solids concentrations range from 233 mg/1 in June during snowmelt runoff to a high of 407 mg/1 during the month of March. Similar calculations projecting the effects upon mean monthly dissolved solids concentrations in the Yampa River range from a low of 106 mg/1 in June to a pro,iected maximum of 444 mg/1 in March. The applicant has also considered the effects of these discharges upon dissolved solids concentrations during the 7-day, 10-year low flow. This is the standard used by the Colorado Department of Health for receiving streams. The results of this analysis indicate a 28X increase in concentrations in the Yampa River below the confluence with the Williams Fork River. The effects of the high sodium content of the Eagle No. 5 and No. 9 mine discharges and strip pit discharge on the Williams Fork River water quality were analyzed to determine the extent of the salinity hazard. Sodium, calcium, and magnesium mass balances were calculated for the 7-day, 10-year low flow value of the Williams Fork River using mean monthly values for each parameter. These analyses indicated an increase in sodium from 23.5 mg/1 to 92.2 mg/] and minor decreases in both calcium and magnesium. The derived values for each value were input into the sodium adsorption-ratio equation (SAR). The SAR was determined to be 2.94. Utilizing a diagram in Hem (1970), relating the SAR and specific conductance to the sodium hazard and salinity hazard, it was determined that the Williams Fork River has a low sodium hazard and a medium salinity hazard below the mine site. Based on the results of the hazard analyses, the calculated Williams fork water quality would not cause a change in the hazard rating and, therefore, its suitability for agricultural use would not change.