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CO-0000906 <br />New Elk Mine Water Quality Assessment <br />The EC, that is used in the development of permit limits is determined <br />ormation the Farm Service <br />• of the ECH,'s for the crops grown in the area. According tom provided by <br />Agency, irrigated water from the Purgatoire River in this area is primarily <br />and band for alf <br />rop al In ums, the <br />rotations every few years also result in corn (mainly silage), wheat ey c. used to <br />most sensitive crop was determined to be corn (silage). Thus, the EC, for corn (silage) was <br />determine the EC limit in a permit. <br />For the Purgatoire River, the EC limit is calculated using the mass balance equation found at the policy beginning of Section IV in accordance with the Division's Narrative Standards w flow Rather than <br />model in all the dischargers that contribute to the Purgatoire <br />calculation is the low flows determined for the Middle Fork of the <br />Mine as there are no upstream dischargers <br />dilution flows are exclusively available to the New Elk <br />along the Middle Fork of the Purgatoire River. <br />The data used and the resulting calculations of the EC limit, MZ, are set forth in the table below. <br />Note that in accordance with the Division's Narrative Standards policy, the EC limit will be imposed <br />as a chronic (30-day average) limit and therefore chronic low flows were used together with 85`x' <br />percentile EC concentrations when calculating the limit. <br />Tier 1 - 2500 m 3.6 m d, 5.6 cfs M3 M2 1Votes. <br />Parameter Q) (cfs) Q2 (efS) . Q3 (efS) Ml 1.2 12 <br />4.3 5.6 9.9 0.36 <br />• =d <br />Tier 2 - 900 m 1.3 m d, 2.0 cfs M3 M? Notes <br />Parameter Qr (efS) Q2 (C.M Q3 (ifs) M2 1 2 32 <br />EC, dS/m 4.3 2.0 6.3 0.36 <br />Tier 3 - 200 m 0.29 m d, 0.45 cfs M, M3 M2. <br />eter Q1 (efS) Q2 (efS) Q3 (ifs) 9.227 <br />45 4.75 0.36 1.2 <br />4.3 0. <br />?MC,7/rn <br />Sodium and SAR- SAR means Sodium Adsorption Ratio, which is a representation of the relative <br />proportion of sodium cations to calcium and magnesium cations (also known as the "sodium <br />hazard"). <br />The SAR standard is established using Figure A-2, which is of 1.2, which reproduced oesponds to the EC,, for the mo t <br />Standards policy. Specifically, the EC, standard <br />sensitive crop of corn (silage), was used to establish a SAR standard of 4.5. <br />SAR is the ratio of sodium to a combination of calcium and magnesium, and therefore is a parameter <br />that has no units. The equation for SAR follows: <br />• <br />Appendix A (WQA version 5-4(FABI.)) Page 19 of 29 Last Revised August 26, 2008