2018-03-01_HYDROLOGY - C1981010 ‎(2)‎

• Permit No: C1981010
• IBM Index Class Name: Hydrology
• Doc Date: 3/1/2018
• Doc Name: CDPS/NPDES Permit
• From: Department of Public Health & Environment
• To: DRMS
• Permit Index Doc Type: NPDES
• Email Name: RAR
• Media Type: D
• Archive: No

COLORADO
Department of Public Water Quality Assessment
Health b Environment
The following parameters were identified by the Division as pollutants to be evaluated for this facility:
• Metals
• Sulfate
• SAR and EC
• TDS
• Benzene, Toluene, Ethylbenzene (outfall 002 only)
• PAHs (outfall 002 only)
Metals 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 at elevated concentrations.
Thus, metals have been identified as pollutants potentially present in mine water discharges and are
evaluated in this assessment. Sulfate results from oxidation of metal sulfide minerals and can be present
in mine drainage.
Chromium consists primarily of trivalent and hexavalent forms. Hexavalent forms are produced by
industrial sources, which are not expected to be present at this facility. Therefore, the following analyses
will include trivalent chromium only.
VI. Determination of Water Quality Based Effluent Limitations (WQBELs)
Technical Information
Note that the WQBELs developed in the following paragraphs, are calculations of what an effluent limitation
may be in a permit. The WQBELs for any given parameter will be compared to other potential limitations
(federal effluent limitations guidelines, state effluent limitations, or other applicable [imitation) and
typically the more stringent limit is incorporated into a permit. If the WQBEL is the more stringent limitation,
incorporation into a permit is dependent upon a reasonable potential analysis.
In -stream background data and low flows evaluated in Sections II and III are used to determine the
assimilative capacity of No -Name Gulch, East Pyeatt Gulch, Middle Flume Gulch, East Middle Flume Gulch,
East Flume Gulch, Oak Gulch, Deacon Gulch and the Yampa River near the Trapper Mine for pollutants of
concern, and to calculate the WQBELs. For all parameters except ammonia, it is the Division's approach to
calculate the WQBELs using the lowest of the monthly low flows (referred to as the annual low flow) as
determined in the low flow analysis.
The Division's standard analysis consists of steady-state, mass -balance calculations for most pollutants and
modeling for pollutants such as ammonia. The mass -balance equation is used by the Division to calculate
the WQBELs, and accounts for the upstream concentration of a pollutant at the existing quality, critical low
flow (minimal dilution), effluent flow and the water quality standard. The mass -balance equation is
expressed as:
M2 _ M3Q3—MIQI
Q2
Where,
Q, = Upstream low flow (1 E3 or 30E3)
02 = Average daily effluent flow (design capacity for domestic wastewater treatment facilities)
Q,3 = Downstream flow (Q, + Q2)
M, = In -stream background pollutant concentrations at the existing quality
M2 = Calculated WQBEL
M3 = Water Quality Standard, or other maximum allowable pollutant concentration
When Q, equals zero, Qz equals Q3i and the following results: M2 = M3
Pae 20 of 40 . .
4300 Cherry Creek Drive S., Denver, CO 80246-1530 303-692-2000 www.colorado.gov/cdphe/wqcd
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