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Trapper 1Vlining, Inc. WWTF Water Quality Assessment CO-0032115
<br />Mz = Mi
<br />Because the low flow (Ql) for Johnson Gulch, No Name Gulch, Faz East Buzzazd Gulch, Coyote
<br />Gulch, Ute Gulch, Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer Gulch, Grouse
<br />Gulch, Sage Gulch, Oak Gulch, Horse Gulch, West Horse Gulch, West Flume Gulch, Middle Flume
<br />Gulch, East. Middle Flume Gulch, East Flume Gulch, and Deal Gulch is zero, the assimilative
<br />capacity of these waters for the pollutants of concern is equal to the in-stream water quality
<br />standazds.
<br />The upstream background pollutant concentrations used in the mass-balance equation will varybased
<br />on the regulatory definition of existing ambient water quality. For most pollutants, existing quality is
<br />determined to be the 85a' percentile. For metals in the total recoverable form, existing quality is
<br />determined to be the SOa' percentile. For pathogens such as fecal coliform, existing quality is
<br />determined to be the geometric mean.
<br />For non-conservative pazameters and ammonia, the mass-balance equation is not as applicable and
<br />thus other approaches are considered where appropriate. Note that conservative pollutants aze
<br />pollutants that aze modeled as if mass is conserved and there is no degradation, whereas non-
<br />conservativepollutants degrade and sometimes are created within a receiving stream depending on
<br />stream conditions. Amore detailed discussion of the technical analysis for these parameters is
<br />provided in the pages that follow.
<br />Pollutants Evaluated
<br />The following pazameters were identified by the WQCD as pollutants to be evaluated for this
<br />facility:
<br />• Metals.
<br />During assessment of the facility, nearby facilities, and receiving stream water quality, no additional
<br />parameters were identified as pollutants of concern.
<br />Trapper Mining, Inc. WWTF: The Trapper Mining, Ina WWTF is located inportions of sections
<br />5 and 6, TSN, R90W; portions of sections 1-5, TSN, R91 W; portions of sections 30-32, T6N, R90W;
<br />portions of sections 21, 25-29, 32-36, T6N, R91 W; approximately 6 1/2 miles south of Craig, CO,
<br />off CO Hwy 13 in Moffat County. The current design capacity of the facility varies. Wastewater
<br />treatment is accomplished using several sedimentation ponds.
<br />Nearby Sources
<br />An assessment of nearby facilities based on EPA's Permit Compliance System (PCS) database found
<br />15 dischargers in the Moffat County azea, including the subject facility. All of the other facilities
<br />except one were discharging to another watershed. Several facilities conducted construction-related
<br />operations (e.g., sand and gravel) and thus had no pollutants of concern in common with Trapper
<br />Mining, Inc. W WTF. Other facilities were located more than twenty miles from the Trapper Mining,
<br />Inc. WWTF and thus were not considered. The nearest dischargers were:
<br />• Tri State Generation and Transmission-Craie Station (COG-600494), which dischazges to
<br />Johnson Gulch. This permit covers miscellaneous sources of wastewater and shares no
<br />pollutants in common with the Trapper Mining, Inc. WWTF.
<br />Appendix A Page 6 of 8 Draft
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