PERMFILE126208

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/24/2004
• Section_Exhibit Name: Exhibit 07 NPDES Permit
• Media Type: D
• Archive: No

Mountain Coal and Beaz Coal Water Quality Assessment CO-0038776 and CO-0044377
The Mountain Coal WWTFs, via Outfalls 011, 012, 013 and 017, discharge to WBID stream
segment COGUNF06, which means the Gunnison River Basin, North Fork of the Gunnison River
Sub-basin, Stream Segment 06. This segment is composed of "All tributaries to the North Fork of
the Gunnison River including lakes, reservoirs, and wetlands which are not on national forest ]ands,
except for the specific listings in Segments 4, 5 and 7." Stream segment COGUNF06 is classified
for Warm Water Aquatic Life Class 2, Class lb Potential Primary Contact Recreation, Agriculture,
and Water Supply.
Numeric standards are developed on abasin-specific basis and aze adopted for particulaz stream
segments by the Water Quality Control Commission. To simplify the listing ofthesegment-specific
standards, many of the aquatic life standards are contained in a table at the beginning ofeach chapter
of the regulations. The standards in Table A-2 have been assigned to stream segment COGUNF02
and the standazds in Table A-3 have been assigned to stream segment COGUNF06 in accordance
with the Classifications and Numeric Standards for Gunnison and Lower Dolores River Basins.
It should be noted that for stream segment COGUNF06, standazds for sulfate and dissolved iron and
a chronic standard for dissolved manganese of 50 ug/1 are assigned only in the instance that the
receiving waters aze in actual use as a water supply. Based on available data, Sylvester Gulch, West
Sylvester Gulch, the Dry Fork of Minnesota Creek, and Lone Pine Gulch aze not used as a water
supply and thus the standazds for these pollutants are not applicable. Note that a chronic dissolved
manganese aquatic life based standard'applies regardless.
Also for stream segment COGLTNF06, a temporary standard has been established fox chronic
dissolved selenium based on existing quality. A value of 10.6 ug/1 was determined as the applicable
existing quality based on the Rationale for Classifications, Standards and Designations ofSegments
of the Gunnison and Lower Dolores River Basins.
Standards for metals are generzlly shown in the regulations as Table Value Standards (TVS), and
these often must be derived from equations that depend on the receiving stream hardness or species
of fish present. The Classification and Numeric Standards documents for each basin include a
specification for appropriate hardness values to be used. Specifically, the regulations state that:
The hazdness values used in calculating the appropriate metal standard should be based
on the lower 95% confidence limit of the mean hardness value at the periodic low flow
criteria as determined from a regression analysis of site-specific data. Where
insufficient site-specific data exists to define the mean hardness value at the periodic
low flow criteria, representative regional data shall be used to perform the regression
analysis. Where a regression analysis is not appropriate, asite-specific method should
be used.
Appendix A Page 4 of 20 Last Revised 3/9/2004