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1 COLORADO DEPARTMENT OF F~TH Water Quality Control Division Summary of Rationale Page 2 PERMIT NO.: CO-0035653 • Mining starts at the lower elevations and works uphill. A portion of the lower pit is left to collect runoff from a 100 year-6 hour storm so that no discharge con- dition exists. The discharge points will be collected at the outfall structures of the 5 detention ponds. Present- ly, there are no plans for constructing any other sedimen- tation ponds. EFFLUENT LIMITATION AND RATIONALE: Parameter pH (s. u.) Oil and Grease (mg/1) Total Iron (mg/1) Total Suspended Solids (nig/1) Salinity Limitation Rationale 6.5-9.0 Water Quality Stream Standards 10 State Effluent Standards 3.5,7.0 Best Engineering Judgement Proposed BAT 35, 70 Best Engineering Judgement Proposed BAT N/A Monitoring Only The permit shall expire March 31, 1986. DISCUSSION: A. Storm Exemption and Containment Requirements Page 3 of the permit detail the storm exemption and containment requirements, - based on the Federal Register of December 28, 1979. B. Salinity The permittee discharges to the Colorado River Basin and therefore is subject to the "Regulations for Implementation of the Colorado River Salinity Stand- _ ards Through the NPDES Permit Program." The regulations state that "the ob- jective for discharges shall be a no-salt return policy whenever practicable." However, the regulations do provide alternatives to this. Ttie no-salt require- ment may be waived in those cases where the salt load reaching the mainstem of ~ the Colorado River is less than one ton per day or 350 tons per year, whichever is less. It has been determined by the Division that the facility is essentially a "no- discharge" facility and, therefore, falls under this waiver. Monitoring, however, will be required on a quarterly basis.