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(See Tables E51 -9 through 11 in Exhibit 51). This equation assumed that the existing pool is homogeneous and
<br />that there will be instantaneous mixing of the two waters. In actuality, neither condition is met in the short-term,
<br />but for the long -term, estimated average discharge quality, it is appropriate. The Fish Creek Borehole is
<br />• pumping from the bottom of the pool where the water has been standing the longest. Therefore, it will have the
<br />worst water quality. The mine inflow will only partially mix with the large pool of water, however, as the pool
<br />is reduced in size, mixing will occur more quickly. The results of this deviation from the equation's assumptions
<br />are that the early time estimations are low and the late time estimations are high. Because the inflow rate in the
<br />first 1.4 years is much less than the outflow rate, and the pool is quite large, the under - estimation of the
<br />conductivity will be small.
<br />The average water quality discharged from the portal (Site 109), and other situations, was estimated using a
<br />simple flow - weighted mass balance equation. The equation is of the form:
<br />Caverage = (( * Q0 + (C2 * Q2) + •( * Qn)) / ( + Q2 + - - Qn)
<br />Where: C, = concentration from source I
<br />Q, = flow from source I
<br />C, = concentration from source n
<br />Q„ = flow from source n
<br />Based upon the above inputs, in Case 1 (Exhibit 51, Table E51 -6) the flow rate from Site 109 will increase from
<br />342 (0.76 cfs) to 612 gpm (1.36 cfs) at life -of -mine. The conductivity will decrease from 3,800 µmhos /cm to
<br />3,100 µmhos /cm. The discharge from Site 115 will average 300 gpm for the first 1.4 years and then 55 gpm for
<br />the remainder of the life of mine. In Case 2 the flow rate from Site 109 will peak at approximately 400 gpm
<br />(0.89 cfs) at the end of the first 1.4 years and at the end of the life -of -mine. The conductivities in the Case 2
<br />discharges from the portal will be the same as Case 1. In Case 3, water is diverted from the EMD, North Mains
<br />and 6 -Right area into the sump at the Fish Creek Borehole. This increases the required average discharge rate,
<br />• but lowers the conductivity of the discharge due to dilution from the diverted water.
<br />Water quality characteristics and parameters in the stream reaches downstream of the Sites 115, 109, and 900
<br />may be impacted by discharges from the mine. Potential impacts are summarized in Exhibit 51, by Tables E51-
<br />12 to E51 -21 based on the three different discharge scenarios (Cases 1 to 3), as previously discussed. The cases
<br />represent different possible ways of splitting the discharge of the inflow between the two discharge points. In
<br />Case 1, most of the discharge of the inflows is from Site 109, and in Cases 2 and 3 the discharges are more
<br />evenly divided between Sites 109 and 115.
<br />Estimates of potential impacts have been compared against applicable standards. A material damage level for
<br />flood irrigation of designated AVF areas on Fish Creek below Site 115 has been set at a conductivity of 1,500
<br />µmhos /cm, and conductivity was modeled for this reach. It was also modeled for other reaches to estimate
<br />overall suitability of mine discharge waters for irrigation use. In addition, SAR levels were modeled (Exhibit
<br />51, Tables E51 -19 to E51 -21). Since the SAR values for Site 109 discharges, as shown on the tables, are less
<br />than the "low level" threshold of 10, modeling was not completed for reaches that would be impacted only by
<br />this site. At the time of the original analysis, Trout Creek above it's confluence with Fish Creek was required to
<br />meet drinking water related stream standard for sulfate between June and February, and Trout Creek below the
<br />confluence was required to meet this standard year- round, therefore, modeling for sulfate was performed. It
<br />should be noted that the sulfate standard was not applicable to any other downstream reaches. Subsequently, the
<br />sole downstream residential water supply use was eliminated, so the sulfate standard is no longer applicable.
<br />Observed mine water discharges during 1984 exhibited average TDS concentrations of 2,060 mg/L The ionic
<br />composition of the discharges was dominated by calcium, magnesium, sulfate, sodium and bicarbonate. Levels
<br />of calcium, magnesium, sulfate, and iron are higher than anticipated from the leach experiments. Consequently,
<br />• sodium adsorption ratios in the mine discharge have been lower than anticipated from the leach experiments (see
<br />previous discussion of sodium absorption rations in Section 2.04.6, Geologic Description). SAR's of mine
<br />discharges have averaged about 5.3 as compared to values of 21.5, 9.5, and 8.7 for roof, floor and coal leach test
<br />results, respectively. While Site 109 has not discharged since 1996, the SAR levels for new discharges from
<br />RN08 -05 2.05 -152 03/12/10
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