HYDRO20139

• Permit No: C1980007
• IBM Index Class Name: Hydrology
• Doc Date: 12/12/2005
• Doc Name: Discharge Permit CO-0038776
• From: Colorado Department of Public Health
• To: Mountain Coal Company, LLC
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

Mountain Coal and Bear Coal Water Oualitv Assessment CO-0038776 and CO-0044377
V. Antidegradation Review
As set out in The Basic Standards and Methodologies of 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 aze waters "that the Commission has determined do
not warrant the special protection provided by the outstanding waters designation or the
antidegradation review process"asset out in Section 31.8(2)(b). The antidegradation section of the
regulation became effective ut December 2000, and therefore antidegradation considerations aze
applicable to this WQA development.
According to the Classiftcations and Numeric Standards for Gunnison and Lower Dolores River
Basins, stream segment COGUNF02 is Undesignated. Thus, an antidegradation review may be
conducted for this segment if new or increased impacts are found to occur. However, the ratio ofthe
flow of the North Fork of the Gunnison River to the Mountain Coal and Bear Coal WWTFs
combined design flows is more than 150:1 at low flows. Section 31.8 (3)(c) specifies that the
discharge ofpollutants should not be considered to result in significant degradatiori ofthe reviewable
waters if the flow rate is greater than 100:1 dilution at low flow. Thus, condition 31.8(3)(c) of the
regulations is met and no further antidegradation evaluation is necessary for dischazges to the North
Fork of the Gunnison River.
Stream segment COGUNF06 is designated as Use Protected. Because the receiving waters ace
designated as Use Protected, no antidegradation review is necessary in accordance with the
regulations. Thus, for purposes of this WQA, antidegradation review requirements have been;met
for the discharges to Sylvester Gulch, West Sylvester Gulch, the Dry Fork of Minnesota Creek and
Lone Pine Gulch.
VI. References
Colorado Total Maximum Daily Load and Wasteload Allocation Guidance, CDPi~, WQCD,
November 1991.
Classifications and Numeric Standards for Gunnison and Lowerpolores River Basins, Regulation
No. 35, CDPHE, WQCC, Effective February 20, 2002.
The Basic Standards and Methodologies for Surface Water, Regulation 31, CDPHE, WQCC,
Effective October 30, 2001.
CDPS Summary of Rationale General Permit for Domestic Wastewater Treatment Facilities that
Discharge to Receiving Waters with a Chronic Low Flow: Design Flow Ratio of 100.•1 or Greater,
CDPS Permit COG-5840DD, Statewide, CDPHE, WQCD, September 14, 1994.
Antidegradation Significance Determination for New or Increased Water Quality Impacts,
Procedural Guidance, CDPHE, WQCD, December 2001.
Memorandum Re: First Update to Guidance Version I.0, CDPHE, WQCD, Apri123, 2002.
Appendix A Page 20 of 20 Last Revised 3/9/2004