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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale - Page 5. Permit No. CO-0042161 DISCUSSION: (Cont.) D. Salinity (Total Dissolved Solids) (Cont.) River Basin be evaluated for impact on the system. The Division has determined that monitoring for total dissolved solids (TDS) shall be the method used to measure salinity. Therefore, in compliance with this, the permittee shall sample for TDS in the wastewater effluent on a monthly basis until six samples have been analyzed. Thereafter, monitoring shall continue on a quarterly basis. The Division will review the first six months of data and determine if a waiver of numeric limitations can be granted based on the salt-load to the river being less than one ton/day (or 350 tons/year). If a waiver is not granted, the permittee has an additional six months to submit a report in accordance with the Salinity Regulations, addressing the economic feasability of salt-removal. E. Dissolved Aluminum Monitoring for this parameter is required due to the possible use of an aluminum sulfate coagulant during treatment. However, monitoring will not be required if the coagulant is not being used. • F. Iron The permit includes a limit for Total Recoverable Iron (based on antidegradation - see Discussion, paragraph G), as opposed to Total Iron (based on NSPS). This is because the antidegradation-based limit is stricter than the NSPS (even though the analysis required is different). G. Antidegradation As per the Basic Standards regulation (3.1.8), all new or increased water quality impacts regulated under 402 permits must go through an antidegradation review. This is a new facility, and the receiving waters are classified as Aquatic Life, Class 1 (Cold). Therefore, an antidegradation review was conducted. The review showed that the project was not expected to result in significant degradation, since the new load to the stream for iron (the parameter of concern in this case) will be less than 10% of the existing load. This means that the permittee is not required to go through the steps required to prove that the expected degradation is necessary to accommodate important economic or social development in the area, and that feasible alternatives do not exist. In order for the discharge to not result in significant degradation, the iron limit will be 0.066 mg/1 (this is the maximum level allowed before • loading would be greater than 10% of the existing load). The monitoring data submitted by the permittee (see Appendix B) indicates that this limit can be met, although additional treatment may be needed at a future date.