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COLORADO DEPARTMENT OF PUBL/C HEALTH AND ENVIRONMENT, Water Quality Control Division Amendment No. / -Rationale. Page S, Permit No. CO-0032638 Nickel (PD), ug/P 1062.6/109.78 71690/1210 Silver (PO), ug/P 2.79/0.10 31/1./ Zinc (PD), ug/P 136.57//23.7 /500/1360 Sulfate, mg/P N/A/250 N/A/2750 !PD): Potentially Dissolved Frarrion (IR): Total Rcrovrra6/e Frarrion /ton: The federal effluent guideline limitations for total iron (3.5/7.0) are more restrictive than the water quality based limitation for total recoverable iron (11.0 mg/P). Thus, iron limitations in this permit are based on the federal effluent guidelines. However, the federal (imitation may drop out during qualifying storm events (see Alternate Limitation Burden of Proof Reartirements above). This would leave the discharge without any limitation for iron during these periods (the alternate limitation regulation does not apply to other metals that are limited in this permit). However, this exemption would only be allowable during periods when stream flow is higher than low flow conditions and only when ezceedence is caused by precipitation (exceedences resulting from the spoils spring discharge would not be eligible), so it is probable that the receiving water would be protected during these periods. The permittee is already required to monitor total iron during a!! periods of discharge and also required 1o monitor upstream flow in Trout Creek. Thus, the data will be available if the Division chooses at some time in the future to evaluate whether the instream standards are being met during these periods. B. Monitoring Requirements 1. Effluent Monirorirt¢: Effluent monitoring will be required as shown in Table V-4. Tab/e V-0 -Monitoring Requirements for Oulfall 007 Parameter Monitoring Sample Type Freouencv Effluent Flow, MGD Weekly /nstantaneous or Continuous Uppstream Trout Creek Flow, Weekly /nstantaneous MCD or Continuous TSS, mg/P Monthly Grab Oil and Grease, mg/P Weekly Visual pH, s. u. Weekly /n-Situ Settleable Solids, mP/P Monthly Grab TDS, mg/P Quarterly Grab Sulfate, mg/P Monthly Grab WET, Acute Quarterly Grab Iron (Total), mg/P Weekly Grab Manganese (7R), mg/P Weekly Grab Manganese (PO), mg/P Weekly Grab Mercury (Total), mR/P Weekly Grab (PD): Potentially Dissolved Fraction (TR): Total Recoverable Frarrion V1. PERMIT CHANGES As a result of this permit amendment, pages iii - zii, xxiii (Figure 2) and xziv (Figure 3) of the permit are amended. Jon C. Kubic November 28, 1995