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Trapper Mining, htc. WWTF Water Quality Assessment CO-0032115
<br />Table A-3
<br />Low Flows for Johnson Gulch, No Name Gulch, Far East Buaard Gulch, Coyote
<br />Gulch, Ute Gulch, Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer
<br />Gulch, Grouse Gulch, Sage Gulch, Oak Gulch, Horse Gulch, West Horse Gulch, West
<br />Flume Gulch, Middle Flume Gulch, East Middle Flume Gulch, East Flume Gulch, Deal
<br />Gulch at the Tra er Minin , Inc. WWTF
<br />Low Flow Annuol Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
<br />(cfs)
<br />lE3 0 0 0 0 0 0 0 0 0 0 0 0 0
<br />Acute
<br />30E3 0 0 0 0 0 0 0 0 0 0 0 0 0
<br />Chronic
<br />N. Technical Analyses
<br />In-stream background data and low flows evaluated in Sections II and III aze ultimately used to
<br />determine the assimilative capacity of Johnson Gulch, No Name Gulch, Far East Buzzazd Gulch,
<br />Coyote Gulch, Ute Gulch, Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer Gulch,
<br />Grouse Gulch, Sage Gulch, Oak Gulch, Horse Gulch, West Horse Gulch, West Flume Gulch, Middle
<br />Flume Gulch, East Middle Flume Gulch, East Flume Gulch, and Deal Gulch neaz the Trapper
<br />Mining, Inc. WWTF for pollutants of concern. For all pazameters except ammonia, it is the
<br />WQCD's approach to conduct a technical analysis of stream assimilation capacity using the lowest
<br />of the monthly low flows (referred to as the annual low flow) as calculated in the low flow analysis.
<br />For ammonia, it is the standard procedure ofthe WQCD to determine assimilative capacities for each
<br />month using the montltly low flows calculated in the low flow analysis, as the regulations allow the
<br />use of seasonal flows when establishing assimilative capacities.
<br />The WQCD's standard analysis consists of steady-state, mass-balance calculations for most
<br />pollutants and modeling for pollutants such as ammonia. The mass-balance equation is used by the
<br />W QCD to calculate the maximum allowable concentration of pollutants in the effluent, and accounts
<br />for the upstream concentration of a pollutant at the existing quality, critical low flow (minimal
<br />dilution), effluent flow and the water quality standazd. The mass-balance equation is expressed as:
<br />Mz = MsQs -M~Q~
<br />Qz
<br />Where,
<br />Q~ =Upstream low flow (IE3 or 30E3)
<br />Q2 =Average daily effluent flow (design capacity)
<br />Q3 =Downstream flow (QI + Qz)
<br />M~ = In-stream background pollutant concentrations at the existing quality
<br />Mz =Calculated maximum allowable effluent pollutant concentration
<br />M3 =Maximum allowable in-stream pollutant concentration (water quality standards)
<br />When Q~ equals zero, Qz equals Q3, and the following results:
<br />Appendix A Page 5 of 8 Draft
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