Laserfiche WebLink
T}ie 6 Right water and the Fish Creek Borehole discharge water are strongly sodium sulfate waters. The Pond A <br />water is calcium-magnesium sulfate water with a conductivity averaging 2900 umhos/cm. The use of the Pond A <br />.water helps maintain the sah loading levels and sulfate of the ground u-ater inflows to the mine but does help <br />reduce the SAR. <br />The potential impact of past mine discharge to Fotdel Creek is addressed in WATBALP, a water quantity and <br />quality model of the Trout Creek drainage (Exhibit 32, Quantity and Qualiry• Modeling Analyses of Surface-Water <br />Resources of the Trout Creek Basin). The modeling analysts was based on mine discharge projections in Table D <br />of Exhibit 33, Mine Water Control Plan. The comparison on Figure 4-g, Ground Water Quality Data, of this <br />sample with average mine discharge characteristics in 1984, shows that the sample is more representative of spoil <br />discharges than actual mine discharges and thus constitutes a worse case estimate of mine discharge quality. The <br />assumed water quality characteristics of mine discharge were based upon a single sample that was assumed to be <br />representative of mine outflows (Exhibit 33, Mine Water Control Plan). Mine inflow projections have changed <br />since the original modeling. The streamflow numbers and baseline water qualiy numbers from the model <br />combined with new (April 1999) protected mine inflow and discharge projecttons (Exhibit 49, Table E49-12 to <br />E49-14) were used to project future impacts on the local drainages. <br />Similar calculations were performed to predict the sodium adsorption ratio conditions [hat might occur in Fish <br />Creek and Trout Creek because of discharge of mine inflows to Fish and Fotdel Creeks. This vas performed <br />primarily to evaluate possible effects on the use of Fish and Trout Creek waters for irrigation purposes. Average <br />values for the respective components were used. <br />Calculations were performed for Fish Creek beloa•the proposed Fish Creek dewatering discharge point and for <br />Trout Creek at two points (equivalents of Sites 69 and 1005) below the confluences with Middle Creek and Fish <br />Creeks. The results of these analyses are shoti3m in Exhibit 49, E49-] 9 to E49-2 ], Table 63. The results indicate <br />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 <br />.below 10 is considered low hazard, the discharges should have no significant impact on agricultural us of the <br />water. <br />Lower 119iddle Creek <br />By virtue of being downstream to one of the mine discharge points Site ]09, and because of the relatively small <br />flows of Fotdel Creek and Middle Creek, impacts of mine flows will be pronounced in this reach. In the original <br />modeling, the increase in specific conductance and dissolved solids at Middle Creek increased by approximately <br />20 percent, and sulfate concentration increased by over 50 percent. This was based upon a flow of 1 cfs and a <br />conductivity of 3250 umhos/cm (yielding a conductivity load (flow times conductivity) of 3250 cfs-umhos/cm). <br />The maximum load from Case 1 is 4228 cfs-umhos/cm while the maximum loads for Cases 2 and 3 are less than <br />3250 cfs- umhos/cm. Due to the potential for excessive sulfate loading in Trout Creek, Site 109 discharges will be <br />maintained below Case 1 flow rates when [he "Mine Discharge Calculator" indicates that the sulfate standard will <br />be exceeded on Trout Creek (see Lower Trout Creek and Lower Trout Creek -Below Fish Creek discussion <br />below). As indicated on Exhibit 49, Table E49-23, this will most likely occur during irrigation season. Therefore, <br />the maximum impacts to this reach of Middle Creek will be similar to that predicted in past modeling. In addition, <br />since this reach is not classified as drinking water and there is no flood irrigation of AVF's for this reach, the <br />respective sulfate standard and conductivity limit do not apply. <br />Lower Fish Creek <br />Based upon the TR-32 update to the original modeling, there is a potential for significant impacts [o the wale[ <br />quality in Fish Creek downstream of Site 115. The modeling indicates that during low flow periods, the <br />conductivity limit of I500 µmhos/cm could be exceeded (Exhibit 44, Table E44-I4). The highest modeled SAfZ <br />~alue was 6.2, indicating that it is highly unlikely that a SAR of 10 will be exceeded (see Exhibit 49, Tables 19 to <br />TR 99-32 2.05-154 APPR®d~fl ~ l.e~ 0 ii 2000 1/3/00 <br />