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• Table 4 combines predicted concentrations at the Foidel Creek-Middle Creek confluence with measured water <br />quality concentrations from Station 301 ott Trout Creek to estimate concentrations at the Middle Creek-Trout <br />Creek confluence. When compared with water quality analyses from Station 301, this analysis shows that Ca <br />and Mg concentrations are approximately equal and well within the range of seasonal variability. Na <br />concentrations are slightly elevated at the Middle Creek-Trout Creek confluence compared with Station 301 <br />(33.34 mg/I versos 11.61 mg/I); however, the SAR is now down to 0.76, a very low value. TDS is predicted to <br />be 558.97 ntg/I versus 387.56 mg/I at Station 301 and sulfate is predicted to be 268.07 mg/I versus 138.26 mg!I <br />at Station 301. <br />Table 5 coittbiites predicted concentrations at the Middle Creek-Trout Creek confluence with measured water <br />quality concentrations from Station 1003 on lower Fish Creek to estimate concentrations at the Fish Creek- <br />Trout Creek confluence. Wlten compared with water quality analyses from Station 1003, this analysis shoes <br />that Ca and Mg concentrations are approximately equal and within the range of seasonal variability. Na <br />concentrations are predicted to be lower at the Fislt Creek-Trout Creek confluence than at Station 1003 (34.71 <br />mg/I versus 55.84 mg/I) and sulfate concentrations are predicted to be lower (270.91 versus 314.86). <br />The estimated concentrations of water quality parameters shown in Table 5 include the estimated [nine discharge <br />Flow, Foidel Creek flow, Middle Creek flow, Fislt Creek flow, and Trout Creek flow. These estimates may be <br />compared to measured concentrations at Station 69 on Trout Creek, which is a short distance upstream from the <br />Fislt Creek-Trout Creek confluence. Ca attd Mg concentrations are 77.51 mg/I versus 70.74 mg/I and 41.36 mg/I <br />versus 36.5 ittg/I, respectively. Na is 34.71 mg/I versus 21.71 mg/I and the SAR is 0.79 versus 0.~2 at Station <br />69. TDS and sulfate are 564.16 mg/I versus 477.4 mg/I and 270.91 mg/I versus 22159 mg/I, respectively. <br />• Comparison of Water Quality Estimates with Water Quality Standards <br />The SAR is used [o predict the degree [o wlticlt sodium ions in irrigation water will replace calcium and <br />magnesium ions in cation exchange reactions in soil. High values of SAR indicate a potential for sodium to <br />replace absorbed calcium and magnesium in the clay structure thereby damaging the soil by reducins <br />permeability. Water with SAR values of less than 10 is classified as low-sodium water and can be used on <br />almost all soils with little potential of developing harmful levels of exchangeable sodium. As is shown on Table <br />I, all of the SAR values at fire listed monitoring stations are very low. The estimated [nine discharge Itas a high <br />SAR (31.08) due to relatively high amounts of sodium compared with calcium and magnesium in the ground <br />water around the proposed mining operations. Note, however, that by the time mine discharge water reaches the <br />Foidel Creek-Middle Creek confluence the SAR is reduced to 1.87, well within the range of low sodium water. <br />By the time waters reach the Fish Creek-Trout Creek confluence (Table 5), the predicted SAR (0.79) is not <br />significantly different than historically measured SARs at Station 69 (0.52). <br />The U.S. EPA (1977) Secondary Drinking Water Standards for sulfate and TDS are 250 mg/I and 500 tng/I. <br />respectively. The estimated concentrations at the Fish Creek-Trout Creek confluence are 270.91 mg/I for sulfate <br />and 564.16 ing/I for "fDS, thus only slightly exceeding the Secondary Standards. <br />umma • <br />The Flow rate used for mine discharge in these calculations (0.9 cfs) is the average maximum rate using [he <br />maximum hydraulic conductivity for the time molten panels 2 Rigltt - 9 Right are being mined. This snakes the <br />estimate inherently conservative in nature. <br />. The overall pattern of this analysis is one of successive reduction in concentrations of sodium, sulfate, and TDS <br />from original high levels in mine water discharge to levels that are indistinguishable from levels measured over <br />the last ten years in the lower reaches of Trout Creek. <br />PR 93-03 EX. 7h-3 3/12/96 <br />