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 _
the calculated BWQ
In cases where the BWQ concentration exceeds the water quality standard,
concentration must then be set equal to the water quality standard. This occurred for none of the
pollutants.
Determinations of Antide radation Based Average Concentrations
New or increased impacts on the receiving stream are expected as a result of this permit issuance
because the concentration or loading based on proposed at quality-based f Suent limits
(WQBELs) is greater than the existing permit limit or load or the Total recoverable arsenic
Dissolved cadmium
Total recoverable trivalent chromium
Dissolved copper
Dissolved lead
Dissolved manganese
Total mercury
Dissolved nickel
Dissolve selenium
Dissolved silver
Dissolved zinc
Total boron
Dissolved arsenic
. . Total recoverable aluminum.
Note that the evaluation of the existing permit limit and load and the water quality-based effluent
limit and load is further discussed at the end of this assessment.
For total recoverable iron, new or increased impacts are not expected to result from this permit
issuance because the proposed water quality-based effluent limits and loads are more stringent than
existing limits and loads, and therefore the antidegradation review process is concluded for this
pollutant.
For the bulleted pollutants, the antidegradation review procedure must continue to determine if
impacts are significant. Impacts are deemed to be significant if the calculated assimilative capacity
exceeds the calculated antidegradation-based average concentration (ADBAC). ADBACs are
calculated using the significant concentration threshold (SCT), which is the additional amount of
pollutant above BWQ concentration that would not cause significant degradation. Section 31.8
(3)(c) specifies that the discharge of pollutants should not be considered to result in significant
degradation of the reviewable waters if one of the following summarized conditions is met:
For bioaccumulative toxic pollutants such as mercury, the new or increased loading from
the source under review is less than 10 percent of the existing total load to that portion of
the segment impacted
For all other pollutants
o the flow rate is greater than 100:1 dilution at low flow; or
o the new effluent load is less than 15 percent of the remaining assimilative capacity; or
• o only a temporary change in water quality will result.
Appendix A (WQA version s-a(FASL)) Page 25 of'29 Last Revised August 26, 2008