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 ambient water quality background concentrations used in the mass-balance equation account for
pollutants of concern contributed by upstream sources, and thus it was not necessary to model
upstream dischargers together with the Mountain Coal and Beaz Coal W WTFs when determining the
available assirilative capacities in the North Fork of the Gunnison River. Due to the distance
traveled, the significant dilution of the North Fork of the Gunnison River, and the changes in the
chazacteristics ofthe receiving stream, modeling downstream facilities in conjunctionwith Mountain
Coal and Beaz Coal WWTFs was not necessary.
Due to the low flow of zero, consideration of other sources when allocating assimilative capacities to
discharges to Sylvester Gulch, West Sylvester Gulch, the Dry Fork of Minnesota Creek and Lone
Pine Gulch was not necessarybecause the full assirilative capacities of these receiving streams aze
equal to the stream standards.
Based on available information, there is no indication that non-point sources were a significant
source of pollutants of concern. Thus, non-point sources were not considered in this assessment.
Chlorine: The mass-balance equation was used to determine the assimilative capacity for chlorine
for Outfa11004, which receives effluent from the domestic W WTF (Internal Outfa11007). There aze
no point sources dischazging total residual chlorine within one mile of the Mountain Coal W WTF
Outfa11004. Because chlorine is rapidly oxidized, in-stream levels of residual chlorine aze detected
only for a short distance below.a source. Ambient chlorine was therefore assumed to be zero.
Using theinass-balance equation provided in the beginning of Section N, the acute and chronic low ~ .
flows set out in Section III, the chlorine background concentration of zero as discussed above, and
the in-stream standards for chlorine shown in Section II, assimilative capacities for chlorine were
calculated. The effluent flow, Q1, reflects the design flow from Outfa11004 and Internal Outfa11007
in the respective calculations. The data used and the resulting calculations ofthe allowable dischazge
concentration, MZ, aze set forth below.
7VnrtA Fnr4 nftho ('rrmnicnn Rivor
V
Parameter Q~ (cfs) QZ (cfs) Qe (cfs) M~ (mg/I) Ms (mg/!) Mz (mg/1)
Acute Chlorine 32 0.28 32.28 0 0.019 2.2
Chronic Chlorine 43 0.28 43.28 0 0.011 1.7
Outf_all 007
Parameter Q ~ (cfs) Q Z (cfs) Q 3 (cfs) Mt (mg/1) M j (mg/1) Mz (mg/1)
Acute Chlorine 32 0.016 32.016 0 0.019 38
Chronic Chlorine 43 0.016 43.016 0 0.011 30
Fecal Coliform: There aze no point sources discharging fecal coliform within one mile of the
Mountain Coal WWTF Outfa11004. Thus, fecal coliform assimilative capacities for Outfall 004
were evaluated sepazately.
Appendix A Page 14 of 20 Last Revised 3/912004