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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Page 7, Pennir No. CO-0043648 Table III-2, cont'd Metals Standards Summary - Arequa Gulch, Segment 22 of the Upper Arkansas Sub-basin of the Arkausas River Basin, All Concentratiorss Are uR/l Stream Standard, ug/l Metal Acute Chronic Analytical Method T~p~ry Modifications -Effective Throitglt 12/3]/97 Aluntinunt - 22, 000 Cadmium - 77 Iron - 3, 000 Manganese - 9, 000 Zinc - 1,700 Underlying Standards -Effective 1/1/98 Aluminum 750 87 Cadmium 19 3.4 Iron - 1,000 Manganese - 1,000 Zinc 379 343 Dissolved Dissolved Total Recoverable Dissolved Dissolved Dissolved Dissolved Total Recoverable Dissolved Dissolved Allowable /nstrenm Total Ammonia No significant quantities of ammonia are expected to be !n any discharge associated with the active operation of the mine. However, ammonia will likely be produced in the treatment of cyanide, and if unexpectedly high concentrations of cyanide appear in any wastestreant flowing to compliance points included in this permit, such treatment will be required. Then, both ammonia as well as cyanide concentrations will need to 6e controlled. In order to insure that the instream standard for un-ionized ammonia will be protected, effluent limitations for total ammonia must be evaluated. To do so, the Division standardly uses the Colorado Ammonia Model when sufficient stream and effluent pH and temperature data is available. This model requires 3 to 4 years worth of weekly instream pH and temperature measurements. In this case, such data is not available. /t was therefore necessary to use the results of regional analyses that have been performed for the whole State of Colorado. From these analyses, the maximum allowable instream total ammonia concentration below the discharge has been estimated to be 0.2 mg/l. Effluent limitations based upon the allowable instream total ammonia concentration listed above are discussed in section Vl.A. Another consideration is that after the active operation of the facility is completed, the leaching solution will need to be detoxified and discharged. Then, ammonia limits will be a more significant issue, and the Colorado Ammonia Model will need to be used in order to determine ammonia limits in the renewal of this permit. In order to insure that enough pH and temperature data will be collected for use in the model, a compliance schedule requiring their collection will be included in the permit.