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any salt build-up. However, it does not take into account that additional water can be used to replace surface uses <br />of water such as in the truck wash, road watering and the preparation plant further decreasing the water discharged <br />• from Site 109. Three cases are presented. In Case 1 (Exhibit 49, Table E49-6) all the water is pumped from Site <br />109 except the WMD inflow to the Fish Creek Borehole sump. in Case 2 (Exhibit 49, Table E49-7), after the <br />water level in the sump is lowered, 245 gpm of water is transferred into the sump from the eastern and northern <br />pans of the mine. In Case 3 (Exhibit 49, Table E49-8), water is continuously diverted into the sump and the <br />discharge rate from Site 115 increased to compensate for the diversion. <br />The average water quality discharged from the Site 115 was estimated by incrementally averaging the average <br />conductivity in the water in storage with the estimated conductivity of the WMD ground water inflow (See Tables <br />E49-9 through 1 I in Exhibit 49). This equation assumes that the present pool is homogeneous and that there will <br />be instantaneous mixing of the two waters. In actuality, neither condition is met in the short term, but for the long <br />term estimated of average discharge quality, it is appropriate. The Fish Creek Borehole is pumping from the <br />bottom of the pool where the water has been standing the longest. Therefore, it will have the worst water quality. <br />The mine inflow will only partially mix with the large pool of water, however, as the pool reduces in size mixing <br />will occur more quickly. The results of this deviation from the equation's assumptions are that the early time <br />estimations are low and the late time estimations are high. Because the inflow rate in the first 1.4 years is much <br />less than the outFlow rate and the pool is quite large the under-estimation of the conductivity will be small. <br />The average water quality discharged from the portal (Site 109), and other situations, was estimated using a simple <br />Flow weighted mass balance equation. The equation is of the form: <br />Coverage = ((CI * QJ + (Cz * Qz) + ....(C~ * Q~)) / (Qi + Qz + ....Q~) <br />Where: C, =concentration from source I <br />• Q, =flow from source 1 <br />C„ =concentration from source n <br />Q„ =flow from source n <br />Based upon the above inputs in Case 1 (Exhibit 49, Table E49-6) the Flow rate from the 109 will increase from 342 <br />(0.76 cfs) to 612 gpm (1.36 cfs) at life of mine. The conductivity will decrease from 3800 µmhos/cm to 3100 <br />µmhos/cm. The discharge from 115 will average 300 gpm for the first 1.4 years and then 55 gpm for the remainder <br />of the life of mine. In Case 2 the flow rate from 109 will peak at approximately 400 gpm (0.89 cfs) at the end of <br />the first 1.4 yeazs and at the end of the life of mine. The conductivities in the Case 2 discharges from the portal <br />will be the same as Case 1. Tn Case 3, water is diverted from the EMD, North Mains and 6-Right area into the <br />sump at the Fish Creek Borehole. This increases the required average discharge rate but lowers the conductivity of <br />the dischazge due to dilution from the diverted water. <br />Water quality change in the stream reaches downstream of the Site 115 and the Site 109 will be impacted by the <br />discharges from the mine. The potential impacts have been estimated in Exhibit 49, Table E49-12 to E49-21 based <br />upon three different discharge scenarios (Cases 1 to 3) discussed immediately above. The cases represent different <br />possible ways of splitting the. discharge of the inflow between the two discharge points. >n Case 1 most of the <br />discharge of the inFlows is from Site 109 and in Cases 2 and 3 the discharges are more evenly divided between <br />Sites 109 and 1 I5. <br />The impacts have been compared against applicable standards that may be impacted by the discharges. There are <br />AVF's on Fish Creek below Site 115. A material damage level for flood irrigation of these AVF's has been set at <br />a conductivity of 1500 umhos/cm. The conductivity was modeled for this reach. It was also modeled for other <br />reaches to estimate overall suitability for irrigation use. In addition, SAR levels were modeled (Exhibit 49, Tables <br />`E49-19 to E49-21). Since the SAR values for Site 109 discharges, as shown on the tables, are less than ]0, (the <br />level at which SAR hazard is no longer low) no modeling or reaches only impacted by this site were done. Trout <br />Creek above Fish <br />~,L~ L ;r ~. !:Slu~ JUiJ 2 8 200fl <br />PR 99-OS 2.05-152 03/28/00 <br />