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COLORADO DEPARTh1ENT OF HEALTH, Water Quality Control Division Rationale -Page 18, Permit No. CO-0043648 For cyanide, the standard for the receiving stream is bused upon 'free" cyanide concentrations. However, there is no analytical procedure for measuring the concentration of free cyanide in a complex e,Qluent. Therefore, ASTM (Anun•ican Society for Testing and Materials) analytical procedure D2036-81, Method C, will be used to measure weak acid dirsociable cyanide in the effluent. This analytical procedure will detect free cyanide plus those forms of complex cyanide that are mast readily converted to free cyanide. The calculated effluent limitation (stream standard) of 0.005 mg/! is less than the detection limit of 0.030 mg/1 for this method. Therefore, a limit for weak acid dissociable cyanide will be specked, and will be set equal to the duect{on limit. Provided weak acid dlssociable cyanide concentrations are less than the method detection limit of 0.030 mg/1, it will be assumed that the 0.005 mg/l fret cyanide standard is being adequately protected. For metals with dissolved standards, corresponding ejjluent limits are based upon the potentially dsso[ved method of analysis, except for hezavalent chromium, which must 6e analyzed for using the dissolved method. In order to determine which metals require e, jfluent limiu, the receiving stream data presented in section III. A. was compared to the corresponding calculated limits (which are equal to stream standards). For metals with treasured concentrations exceeding or within a reasonable range of the calculated limits, the limits were included in the permit. As noted in the preceding section of this rationale, the water quality based metals limits were, in all cases, more stringent than the federal effluent guidelines, and therefore will be the ones included in the permit. e. Limitations Other Than Those Based Uonn Water pualirv Standards Federal Guidelines. and State EAluent ReAUlations: For discharge points OOIA, OOIB, 004A, OOSA 006A and 007A, no limits were specified for flow or hnr-lness, but these parameters mast be monitored in order to provide information that might be used in the determination of whether or not a discharge hat occurred, and ro more precisely evaluate what the impact of any discharge might be to the receiving stream. The limit.: and monitoring conditions specfied jot discharge points 002A and 003A are intended to provrde assurance that the various leach pad liner systems are functioning properly. The seepage related parameters and action codes listed in Table V!-2 are based upon project design documents that were submitted as part of the application jot the Colorado Division of Minerals and Geology mining permit. 4. Discussion of Effluent Limitations -Application to Specific Discharge Points n. All Potential Pollutant Sources - "No Di::charpe" Limitation Except as provided Uv the Annual Precipitation or Stormwater exemptions discussed below, this permit is bnscd upon the premise that there will be no discharge of pollutants from any potential point source, including those points specflcally identfled below. b. Point 007A - Discharfes From the Valley Leach Facilirv That Ounlify For Annual Precipitation or Srorrn Eretnntions. and Points OOIA. 001 B - Arenua Gulch at Station AGI. S Any discharges from the valley leach facility that would qualify for the uemptiorts described in sections Vl.A.1. and 2. (point 007AJ would likely be surface discharges. Due to the fact that any suck discharges could entrain significan[ qunn[ities of suspended solids, the 7SS limit from federal guidclirses will be applied.