Trapper Mining, Inc. WWTF Water Quality Assessment CO-0032115
<br />Table A-3
<br />Low Flows for Johnson Gulch, No Name Gulch, Far East Buzzard 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 />_~
<br />Lo/w/ ((F~+l+ow Annua! San Feb i)lar k Apr May :lun Ju! rlug ; Sep ,;°Uct. ,Nov ~ k~eC
<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 />G7uonic
<br />N. Technical Analysis
<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, Faz East Buzzard 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 parameters 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 ]ow 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 monthly low flows calcu]ated 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 />WQCD to calculate the maximum allowable concentration ofpollutants 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 standard. The mass-balance equation is expressed as:
<br />Mz _ M3Q3-M~Qi
<br />Qz -
<br />Where,
<br />Qi =Upstream low flow (lE3 or 30E3)
<br />Q1=Average daily effluent flow (design capacity)
<br />Q3 = Downsveam flow (QI + QZ)
<br />M~ = In-stream background pollutant concentrations at the existing quality
<br />1LI1=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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