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COLORADO DEPARTMEM OF PUBLIC HEALTH AND ENV/RONMENT, Water Quality Control Division <br />Rationa/c -Page 6, Permit No. CO-0044776 <br />Where: • <br />Qt =Upstream law flow (30E3) from Pan III.B.2 (36 cfs) <br />Q= =Average daily effluent flow (mine drainage design capacity - 0.144 MGD or 0.22 cfs) <br />Qi =Combined downstream Jlow (Q, + Q~ <br />Mr = Upstream background pollutant concentration from III.B.1 <br />Ms =Unknown; Maximum allowable effluent pollutant concentration calculated using mass batance equation <br />M~ =Maximum downstream allowable pollutaru concentration (stream standard) <br />Total Recoverable Iron <br />1.7 1.0 <br />(negative) ^ <br />• Because the result is a negative number, the Basic Standards and Methodologies for Surface Water (5 <br />CCR 1002-31) state that the [imitation shall be specified as equal to the standard. <br />As stated above, this evaluation was performed to determine the applicable limitation for mine drainage <br />discharge to the North Fork of the Gunnison River. However, the discharge goes directly to Deer Trail <br />Ditch, an irrigation conveyance that is privately owned and operated and is not state waters. The ditch <br />meets the North Fork of the Gunnison River at a point approximately one mile below the point of the <br />permiaee's discharges. Since the entire flow from the mine drainage discharge is not expected to reach the <br />river undiluted by other flows during !ow flow periods, this limitation will not be applied. The federal <br />efluent guideline-based limitation for [oral iron of 3.0 mg/P will be applied. According to reference <br />dacttments available to the Division, this limitation will protect all potential agricultural uses for which Deer <br />Trail Ditch water may be consruned. It is expected that any remaining flow that might eventually reach the <br />river would not impact the standard for the river. <br />d) Antj~,gradatian: Since the receiving water is unclassified, an antidegradarion review is not required <br />pursuant to section 31.8(1) of The Basic Standards and Methodologies for Sr4rfgce Water. <br />e) Salinity Regularions: In compliance with the Colorado River Salinirv Standards and the Colorado Dsschareg <br />Permit Svstem Regulations. the permittee shall monitor for total dissolved solids on a quarterly basis. <br />Samples shall be taken at the e~4uent discharge poin[s. Salinity requirements are intruded in Parr I.B.2. of <br />the permit. <br />f) Whole jfluent Toxicirv l1VE77 Testine: For outfall 002, acute WET testing is required. (See Part I.A. of <br />the permit.). Ibis applies only ro discharges from this outfall that include a mine drainage component. <br /> <br />1) Purpose f WET Testine: The Water Quality Control Division has established the use of WET testing at <br />a method far identifying and controlling toxic discharges from wastewater treatment facilities. WET <br />testing is being utifi~ed as a means to ensure that there are no discharges of pollutants 'in amounts, <br />concentrations or combinations which are harmful to the beneficial uses or toxic to humans, animals, <br />plants, or aquatic life' as required by Section 31.11 of the Bacir Ctandard<c and Methodologies for <br />Surface Waters. <br />