PERMFILE119809

• Permit No: C1981022A
• IBM Index Class Name: Permit File
• Doc Date: 3/21/2006
• Doc Name: NPDES Permit ‎(CO-000132)‎
• Section_Exhibit Name: Exhibit 2.03-E4 Part 3c
• Media Type: D
• Archive: Yes

Oxbow Mining WWTF Water Quality Assessment CO-0000132
The full assimilative capacity of the stream for total residual chlorine was determined to equal the in-
stream water quality standazds of 19 ug/1(acute) and 11 ug/1(chronic).
Metals: Metals may occur naturally in rock around coal seams. Earth disturbances, such as mining
operations, expose rock to air and water creating a potential for these elements to be present in
elevated concentrations. Thus, arsenic, cadmium, copper, chromium, iron, lead, manganese,
mercury, nickel, selenium, silver and zinc, which have been identified as pollutants potentially
present in mine water discharges, aze evaluated in this assessment. According to the Agency for
Toxic Substances and Disease Registry, chromium in the trivalent form occurs naturally in the
environment whereas hexavalent chromium is produced by industrial processes. Industrial processes
at this facility would not generate hexavalent chromium and therefore the evaluation for chromium is
limited to the trivalent form.
Because the low flow for the receiving stream is considered zero, the assimilative capacities are
equal to in-stream water quality standards. The data used and the resulting calculations of the
allowable discharge concentrations, M2, applicable to outfall 015 aze set forth in Table A-5 for
chronic and acute assimilative capacities for stream segment COGUNF06.
Table A-5
Chronic and Acute Assimilative Ca acities for Metals Outfall 015)
Parameter ChroncAssimilgtive Capac:ty
, Acute''AssimilaY:ve Capacity
:..
As, Trec (ug/1) NA 50
Cd; Dis (ug/1) 6.2 19
Cr+3, Trec (ug/1) NA 50
Cu, Dis (ug/1) 29 50
Fe, Dis (ug/1) 300 NA
Fe, Trec (ug/1) 1,000 NA
Mn, Dis (ug/I) 50 4738
Hg, Tot (ug/1) 0.01 NA
Ni, Dis (ug/1) 168 1513
Se, Dis (ug/1) 10.6 18
Ag, Dis (ug/1) 3.5 22
Zn, Dis (ug/1) 382 379
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 in December 2000, and therefore antidegradation considerations aze
applicable to this WQA development.
Appendix A Page 9 of 10 Draft