2009-08-10_PERMIT FILE - C1982056A (5)

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The 6RT water and the Fish Creek Dewatering Well discharge water are strongly sodium sulfate waters. The Pond A water is calcium-magnesium sulfate water, with a conductivity averaging 2900 umhos/cm. Use of the Pond .A water helps balance the salt loading levels and sulfate of the ground water inflows to the mine, and reduces SAR. The potential impact of past mine discharge to Foidel Creek is addressed in WATBALP, a water quantity anal quality model of the Trout Creek drainage (Exhibit 32, Quantity and Quality Modeling Analyses of Surface-Water Resources of the Trout Creek Basin). The modeling analysis was based on mine discharge projections in Table D of Exhibit 33, Mine Water Control Plan. The comparison on Figure 4-g, Ground Water Quality Data, of this sample with average mine discharge characteristics in 1984, shows that the sample is more representative of spoil discharges than actual mine discharges and thus constitutes a worse case estimate of mine discharge quality. The assumed water quality characteristics of mine discharge were based upon a single sample that was assumed to bye representative of mine outflows (Exhibit 33, Mine Water Control Plan). Mine inflow projections have changed since the original modeling. The streamflow numbers and baseline water quality numbers from the model combined with new (April 1999) projected mine inflow and discharge projections (Exhibit 49, Table E49-12 to E49-14) were used to project future impacts on the local drainages. Similar calculations were performed to predict the sodium adsorption ratio conditions that might occur in Fish Creek and Trout Creek because of discharge of mine inflows to Fish and Foidel Creeks. This was performed primarily to evaluate possible effects on the use of Fish and Trout Creek waters for irrigation purposes. Average values for the respective components were used. Calculations were performed for Fish Creek below the proposed Fish Creek dewatering discharge point and far Trout Creek at two points (equivalents of Sites 69 and 1005) below the confluences with Middle Creek and Fish Creeks. The results of these analyses are shown in Exhibit 49, E49-19 to E49-21, Table 63. The results indicate that SAR conditions may reach up to 6.2 in Fish Creek and up to 3.0 in Trout Creek. Since water with a SAR of below 10 is considered low hazard, the discharges should have no significant impact on agricultural us of the water. Lower Middle Creek By virtue of being downstream to one of the mine discharge points Site 109, and because of the relatively small flows of Foidel Creek and Middle Creek, impacts of mine flows will be pronounced in this reach. In the original modeling, the increase in specific conductance and dissolved solids at Middle Creek increased by approximately 20 percent, and sulfate concentration increased by over 50 percent. This was based upon a flow of 1 cfs and a conductivity of 3250 umhos/cm (yielding a conductivity load (flow times conductivity) of 3250 cfs-umhos/cm). The maximum load from Case 1 is 4228 cfs-umhos/cm while the maximum loads for Cases 2 and 3 are less tha~i 3250 cfs- umhos/cm. Due to the potential for excessive sulfate loading in Trout Creek, Site 109 discharges will be maintained below Case 1 flow rates when the "Mine Discharge Calculator" indicates that the sulfate standard will be exceeded on Trout Creek (see Lower Trout Creek and Lower Trout Creek -Below Fish Creek discussion below). As indicated on Exhibit 49, Table E49-23, this will most likely occur during irrigation season. Therefore, the maximum impacts to this reach of Middle Creek will be similar to that predicted in past modeling. In addition, since this reach is not classified as drinking water and there is no flood irrigation of AVF's for this reach, the respective sulfate standard and conductivity limit do not apply. Lower Fish Creek Based upon the TR-32 update to the original modeling, there is a potential for significant impacts to the water quality in Fish Creek downstream of Site 115. The modeling indicates that during low flow periods, a conductivity of 1500 µmhos/cm could be exceeded (Exhibit 49, Table E49-14). The highest modeled SAR value was 6.2, indicating that it is highly unlikely that a SAR of 10 will be exceeded (see Exhibit 49, Tables 19 to 21). MR08-230 2.05-154 11/20/08