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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 useof the <br /> water. <br /> Lower Middle Creek <br /> By virtue of being downstream to one of the mine discharge points Site 109, and because of the relatively small <br /> flows of Foidel 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 <br /> be maintained below Case 1 flow rates when the "Mine Discharge Calculator" indicates that the sulfate standard <br /> will be exceeded on Trout Creek (see Lower Trout Creek and Lower Trout Creek — Below Fish Creek <br /> discussion below). As indicated on Exhibit 49, Table E49 -23, this will most likely occur during irrigation <br /> season. Therefore, the maximum impacts to this reach of Middle Creek will be similar to that predicted in past <br /> modeling. In addition, since this reach is not classified as drinking water and there is no flood irrigation of <br /> AVF's for this reach, the 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 to the water <br /> quality in Fish Creek downstream of Site 115. The modeling indicates that during low flow periods, a conductivity <br /> of 1500 µmhos /cm could be exceeded (Exhibit 51, Table E51 -14). The highest modeled SAR value was 6.2, <br /> indicating that it is highly unlikely that a SAR of 10 will be exceeded (see Exhibit 51, Tables 19 to 21). Based on <br /> the potential to have a high conductivity, TCC will commit to maintaining the discharge rate from Site 115 at a <br /> level to prevent material damage. In addition to any other required monitoring, TCC will monitor the flow rate and <br /> conductivity at Site 16 to be replaced by Site 16A, (Fish Creek upstream of Site 115) and Site 115 weekly when <br /> Site 115 is discharging. The discharge from Site 115 will be adjusted using the Excel© based "Fish Creek <br /> Borehole Discharge Calculator" shown in Exhibit 51, Table E51 -25, or based on compliance considerations under <br /> TCC's CDPS discharge permits. The flow rate is calculated based upon the mass balance equation shown on this <br /> table. A summary of possible results from this calculation is shown in Exhibit 51, Table E51 -22. Site 115 could <br /> potentially be able to be discharged at 55 gpm (the rate required to maintain the pool elevation in the sump) at most <br /> instream flows. Actual discharge rates will be set based upon measured in- stream flow and water quality <br /> measurements (see Exhibit 14). Site 115 could possibly be able to discharge at least 600 gpm during mean flow <br /> periods. This may allow the sump to be drawn down to compensate for periods when Site 115 is pumped at less <br /> than 55 gpm. <br /> During the winter months, it is often not possible to get a reliable flow rate reading from Site 16. To estimate <br /> the flow rate at Site 16 at those times a linear regression has been developed between Site 16 and the Yampa <br /> River below Steamboat Springs (09239500). This station was chosen because a reasonably good correlation <br /> was achieved and the flow rate at this station is accessible in real time on the USGS's Internet site. In order to <br /> account for estimation errors, a relationship with an intercept two standard errors lower than the calculated one <br /> was used. The equation is shown in Exhibit 50, Table E50 -1 and Exhibit 51, Table E51 -25 and the regression <br /> analysis and plot are shown in Exhibit 50 (Figure E50 -1). <br /> The discharge rate from Site 115 will also have to be adjusted based upon potential impacts to Trout Creek. <br /> This will be discussed in the Lower Trout Creek sections. <br /> Lower Trout Creek <br /> The mine is not expected to impact the water quality or flow rates in Trout Creek above Middle Creek. There <br /> are no discharges from the Foidel Creek mine to this reach and this reach is not within the angle of draw of the <br /> underground workings. <br /> PRO9 -08 2.05 -154 04/27/09 <br />