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Trapper Mining, Inc. WWTF Water Quality Assessment CO-0032115
<br />• City of Craig WWTF (CO-0040037), which dischazges to the Yampa River. This facility.
<br />shazes no pollutants in common with the Trapper Mining, Inc. W WTF.
<br />Due to the low flow of zero, consideration of other sources when allocating assimilative capacities to
<br />discharges to Johnson Gulch, No Name Gulch, Faz East Buzzazd Gulch, Coyote Gulch, Ute Gulch,
<br />Middle Pyeatt Gulch, East Pyeatt Gulch, West Pyeatt Gulch, Deer Gulch, Grouse Gulch, Sage Gulch,
<br />Oak Gulch, Horse Gulch, West Horse Gulch, West Flume Gulch, Middle Flume Gulch, East Middle
<br />Flume Gulch, East Flume Gulch, and Deal Gulch was not necessary because the full assimilative
<br />capacities of these receiving streams are equal to the stream standards.
<br />Based on available information, there is no indication that non-point sources were a significant
<br />source of pollutants of concern. Thus, non-point sources were not considered in this assessment.
<br />Metals: Metals may occur naturally in rock azound coal seams. Earth disturbances, such as mining
<br />operations, expose rock to air and water creating a potential for these elements to be present in
<br />elevated concentrations. Thus, arsenic, cadmium, copper, chromium, lead, selenium, and zinc,
<br />which have been identified as pollutants poten6allypresent in mine water dischazges, aze evaluated
<br />in this assessment. According to the Agency for Toxic Substances and Disease Registry, chromium
<br />in the trivalent form occurs naturally in the envirpnment whereas hexavalent chromium is produced
<br />by industrial processes. Industrial processes at this facility would not generate hexavalent chromium
<br />and therefore the evaluation for chromium is limited to the trivalent form.
<br />Because the ]ow flow for.the,receiving streams is considered zero, the assimilative capacities are
<br />equal to in-stream water quality standards. The data used and the resulting calculations of the
<br />allowable dischazge concentrations, Mz, aze set forth in Table A-4 for chronic assimilative capacities
<br />(no acute assimilative capacities apply).
<br />Table A-4
<br />Chronic Assimilative Capacities for Metals-
<br />COLCLY03b
<br />Segment
<br />Parairiefer
<br />.. ,mot ..., ... Chrontc'Asstmalafve Capacity
<br />~ ~.~:~, .: ~ _.~ . _. s .M ,
<br />As, Trec (ug/1) 100
<br />Cd, Trec (u 1) 50
<br />Cr+3, Tot (ug/1) 1,000
<br />Cry, Tot (ug/I) 1,000
<br />Cu, Trec (ug/1) 500
<br />Pb, Trec (ug/1) 100
<br />Se, Trec (ug/1) 50
<br />Zn, Trec (ug/1) 15,000
<br />V. Antidegradation Review
<br />As set out in The Basic Standards and Methodologies of Surface Water, Section 31.8(2)(b), an
<br />antidegradation analysis is required except in cases where the receiving water is designated as "Use
<br />Appendix A Page 7 of 8 Draft
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