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
0
• utfall According to the Classifications and Numeric Standards for Arkansas s thRiver e re Basin, inOwaters are
receiving stream segment COARLA06 is Use Protected
designated as Use Protected, no antidegradation review is necessary in accordance with the
regulations.
According to the Classifications and Numeric Standards for Arkansas River Basin, Outfall 001
receiving stream segment COARLA05a is Undesignated. Thus, an antidegradation review is
required for this segment if new or increased impacts are found to occur for Outfall 001.
Note that the AD review will be completed on the 200 gpm flow rate, as this is the expected flow
rate from this facility after mine dewatering is completed. As facility data for the parameters covered
under this review does not exist, a MON outfall is being incorporated into the permit to collect data.
By the time data is collected, and potentially used to perform a Reasonable Potential analysis, the
facility should only be discharging at the 200 gpm now rate.
The Division's Antidegradation Significance Determination for New or Increased Water Quality
Impacts Procedural Guidance provides guidance on the determination of new or increased water
quality impacts and significant degradation. Consistent with current Division procedures, the
baseline water quality (BWQ) concentrations for pollutants of concern should be established so that
it can be used as part of anti degradation reviews. BWQ is defined by the Division as the condition of
the water quality as of September 30, 2000. Furthermore, the Division specifies that BWQ
concentration will include the influence of the discharger if it was in place on September 30, 2000.
Accordingly, BWQ concentrations are determined based on either downstream ambient water quality
data, or based on the following equation:
BWQ = Mef-Qejr +MU/5 QuIs
Qeff + Q„/5
Where,
BWQ = Baseline water quality
QUIS = Upstream low flow during the antidegradation period
XIS = Upstream background pollutant concentration at the existing quality during the
Qeff
Me
antidegradation period
= 2-year average flow
= 2-year average effluent pollutant concentration
Because the New Elk Mine Outfall 001 did not discharge to the Middle Fork of the Purgatoire River
for the time frame from October 1, 1995 to September 30, 2000, a value of zero was used for Qeffand
Meffwhen establishing the BWQ. When Qeffand M,•ffare equal to zero, the following results:
0 BWQ=M./,
Appendix A (wQn Version s-a(FASL)) Page 23 of 29 Last Revised August 26, 2008