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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page S. PERMIT NUMBER: COG-850000 Salinity Regulation 3.10.0, Regulations for Implementation of the Colorado River Salinity Standards Through the Colorado Discharge Permit Program, addresses the discharge of total dissolved solids (TDS) to the Colorado River Basin. It is a requirement of the regulation that the TDS level of each discharge in the Colorado River Basin be evaluated for impact on the system. Generally, the net impact of TDS to the basin from coal mining surface runoff treatment facilities is negligible due to the intermittent nature of the discharger. Nonetheless, the division reserves the right to refuse the certification to the general permit if it appears that the discharge will not be consistent with the regulations. Settling Agents Because of the wide variety of available chemical flocculanta, the use of such settling aids must be subject to prior approval by the permitting authority. Additionally, if over-application of a flocculant appears to be a problem, revocation of the general permit discharge certification may be warranted. Phosphorus Individual permits will be required for any facilities is the Cherry Creek Basin upstream of Cherry Creek Reservoir or in the Chatfield Basin which is defined as downstream of the IISGS gage at Waterton for the South Platte River or in the Plum Creek drainage. This determination is based on controls established (or in the process of being established) to maintain the phosphorus standard in Cherry Creek Reservoir and Chatfield Reservoir. The management plan for maintaining the phosphorus standard in Dillon Reservoir recommends total phosphorus monitoring for minor industrial discharges including coal mining facilities. Therefore phosphorus monitoring shall be required for those facilities which discharge into the Dillon Reservoir drainage. Individual certifications shall state if this requirement applies to the specific facility. If monitoring shows the facility to contribute significantly, the permittee may be required to obtain an individual permit. MONITORING FREQUENCIES: For active mining, pH, oil and grease and flow monitoring is required by the permittee on a weekly basis. TSS, total iron and settleable solids are to be monitored monthly. For post-mining, pH, oil and grease, flow and settleable solids are to be monitored monthly. The division requires less frequent monitoring for poet-mining discharges because no activity takes place on site, reclamation including revegetatian has begun and therefore effluent quality should vary little. Quarterly TDS monitoring is required for all discharges to the Colorado River Basin in compliance with the Colorado River Salinity Regulations.