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
• Table A-5b
Low Flows for the Left Fork of A ache Can on Creek at the New Elk Mine Outfal1009
Low Flow , Md :Jun Jul Aug ' 'Sep' Oct ' _Nov Dec
Y
Annual Jan Feb Mar Apr.
IS .. 0 0 0 0 0 0 ., 0 0 0 0 0 0 0
Acute
30E3 0 0 0 0 0 0 0 0 0 0 0 0 0
Chronic
IV, Technical Analysis
In-stream background data and low flows evaluated in Sections atoire River and the Left Fork of
determine the assimilative capacity of the Middle Fork of he Purg
Apache Canyon Creek near the New Elk Mine for pollutants atechnical analysisoof 1 _
stream assimilation
ammonia, it is the Division's approach to conduct
capacity using the lowest of the monthly low flows (referred to as theof annual low flow)
to calcur cried
in the low flow analysis. For ammonia, it is the standard procedure the Division
assimilative capacities for each month using the mo lwhen establishing ass milative capacities.
analysis, as the regulations allow the use of seasonal flows
The Division's standard analysis consists of steady-state, mass-balance calculations for most
pollutants and modeling for pollutants such as ammonia. The mass-balance equ tthion e is used by the
Division to calculate the maximum allowable concentration pollutants and
The mquay,
asstbalancecritical
accounts for the upstream concentration of a pollutant standard. the existing
equationois
(minimal dilution), effluent flow and the water quality
expressed as:
M3Q3 - M1Q1
Mz = Qz
Where,
Q, = Upstream low flow (IE3 or 30E3)
Q2 = Average daily effluent flow (design capacity)
Q3 = Downstream flow (Q1 + Qz)
Mf = In-stream background pollutant concentrations at the existing quality
M =Calculated maximum instream e effluent concentration (water quality standards)
M3 3 -Maximum allowable P1 utnt
For the Middle Fork of the Purgatoire River, the upstream background pollutant concentrations used
in the mass-balance equation will vary based on the regulatory definition of existing ambient water
quality. For most pollutants, existing quality is determined to be the 85`h percentile. For metals in
the total recoverable form, existing quality is determined to be the 50th percentile.
•
Pa e 11 of 29 Last Revised August 26, 2008
Appendix A cWQA Version s-acFASL» g