2009-03-06_PERMIT FILE - C1981012A ‎(6)‎

• Permit No: C1981012A
• IBM Index Class Name: Permit File
• Doc Date: 3/6/2009
• Section_Exhibit Name: Exhibit 22 NPDES Permit
• Media Type: D
• Archive: Yes

CO-0000906
New Elk Mine Water Quality Assessment
is accomplished by revising the
Solving for the maximum allowable in-stream sodium concentration
•
previously set forth SAR equation, to solve for sodium, specifically:
Purgaroire + Mg Purgaroire
2
Na + Pwguroire - SA Purgamire x
= 4.5 x 1.7 -+0. 6 7 = 4.9 meq/1
Na+ Purgntour 2
This converts to a maximum allowable in-stream sodi um concentration in the Purgatoire River of
113 mg/1(4.9 meq/1 x 23 mg/meq).
The mass balance equation found at the beginning of Section N can then be used to determine the icy, sodium effluent limit. Note that in accordance with
and therefore the maximum al allowable in1 st eam
SAR standard is imposed as a chronic standard
sodium concentration is determined as a chronic value. Therefore, the chronic low flows in the
Middle Fork of the Purgatoire River were used together with the 85`" percentile of the in-stream
sodium concentration when executing the calculations. The data used and the resulting calculations
of the allowable discharge concentrations, MZ, are set forth in the following table.
• Tier 1 - 2500 m 3.6 m d, 5.6 cM3 Mz ' NNtes";
Parameter QI (cfs) Qfs) EQ s'. (cfs) 181
Na, mg/1 4.3 5.9.9 24 1 l3
Tier 2 - 900 m 1.3 m d, 2.0 cfs
Ma M2
Parameter Q, (efsl Qz (c Qj (0) Mr
Na, mg/I 4.3 2.0 6.3 24 113 304
Tier 3 - 200 m 0.Fgna
Parameter Na, mg/1 4.75 24 113 963
VI. Antidegradation Review
As set out in The Basic Standards and Methodologies for Surface Water, Section 31.8(2)(b), an
antidegradation analysis is required except in cases where the receiving water is designated as "Use
Protected." Note that "Use Protected" waters are waters "that the Commission has determined do
not warrant the special protection provided by the outstanding waters designation or the
antidegradation review process" as set out in Section 31.8(2)(b). The antidegradation section of the
regulation became effective in December 2000, and therefore antidegradation considerations are
• applicable to this WQA analysis.
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Appendix A (WQA version 5-4(FASL)) Page 22 of 29 Last Revised August 2, 2008