HYDRO28372

• Permit No: C1980007
• IBM Index Class Name: Hydrology
• Doc Date: 4/19/2004
• Doc Name: Exhibit 7 NPDES Permit
• From: Colorado Health Department of Public Health & Environment
• To: Mountain Coal Company
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

Mountain Coal and Beaz Coal Water Quality Assessment CO-0038776 and CO-0044377
Table A-5
TVS-Based Metals Water Quality Standards for Sylvester Gulch, West Sylvester Gulch,
the Dry Fork of Minnesota Creek, and Lone Pine Gulch
Based on the Table Value Standazds Contained in the Colorado Department of Public Health
and Environment Water Quality Control Commission Re lation 35
Calculated Using the Following Value for Hazdness as CaCO3: 400 mg/1
In-.Strekm'jYa[er -
Parameter .Quality"Standard; _
: Formula Used„ ,
AGUte -19 Ug/1 [1.13667-0.041841n(bardness)][e (1.128(]n(haidness)}3.6867)]
Cadmium, Dissolved

Chronic
6.2 ug/1 (o.78sz(ln(baraness>}z.ns>]
p.1o167-o.oalsamlbarane~s)1[e
Hexavalent Chromium, Acute 16 ug/1 Numeric standards provided, formula not applicable
Dissolved ChIOn1C 11 Ug/1 Numeric standards provided, foratula not applicable
Acute 50 ug/1 a (o.9azz(m(bardn~5)}7.7aos)
Copper, Dissolved Chronic 29 u ] e (o.ssas(ln(naranes:>}t.7aza)
ACnte 4738 ug/1 a (0.3331(In(hardness)j+6.4676)
Manganese
Chronic
2618 u I (0.3331(In(bardness))+5.8743)
e
Acute , 1
513 ug/1 a (o.sa6(In(bardness)}Fz2s3>
d
i .
ssolve
Nickel, D Chronic 168 ug/1 a (o.8a6(ln(baraness>}w.ossa) .
Selenium, Dissolved ACllte 18 llg/1 Numeric standards provided, fomula not applicable

d Acute 22 ug/1 ~ C (1.72(In(hardness»-6s2)
Silver, Dissolve Chronic 3.5 ug/I a (1.72(ln(hardnws))-9.06)
Acute 379 ug/1 a (o.sa73(In(hataness>}ro.8618)
Zinc, Dissolved
ChI0111C
382 ug/1
e(0.8473(In(hazdness))+0.8699)
Ambient Water Quality
The WQCD evaluates ambient water quality based on a variety of statistical methods as prescribed in
Section 31.8(2)(a)(i) and 31.8(2)(b)(i)(B) of the Colorado Department of Public Health and
Environment Water Quality Control Commission Regulation No. 31. Ambient water quality is
evaluated in this WQA for use in determining assimilative capacities and in completing
antidegradation reviews for pollutants of concern.
North Fork of the Gunnison River: To conduct an assessment of the ambient water quality of the
North Fork of the Gunnison River upstream of the Mountain Coal and Bear Coal W WTFs, data were
gathered from USGS water quality station 09132500 (North Fork of the Gunnison River near
Somerset, CO) and from the permittee's Upper North Fork station, both located at the same point
approximately 1 mile upstream from the neazest discharge. Data for the USGS station were available
for a period of record from October 1996 through August 2001, except for total ammonia and total
chromium data, for which recent data were not available. Thus, historical data for a period ofrecord
from October 1977 through August 1982 were used. Data from the perrnittee's Upper North Fork
r~~
Appendix A Page 8 of 20 Last Revised 3/9/2004