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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division Amendment No. I -Rationale. Page 2, Permit No. CO-0032638 Effluent limitations jot otfrfal(s 002, 003 and 006 will be eliminated when limitations jot outjall 007 become effective and outal[ 007 will determine the quality ajdischarge jrom these three points, which will continue to enter the ditch. Minimal loss is expected within the ditch, thus this new outjall is believed to be represemarive of the combined flows jrom outfalls 002, 003 and 006. Under its current configuration, the ditch cars be used jot irrigation flow and has a working headgate. Ir is likely !o lranspor! irrigation flow arsd flow from the three existing outfalls plus any minor amounts of direct precipitation that should jai( into the ditch. Because of the construction of the ditch, significant rursoff cannot enter it. The changes contained in this permit amendment are based on the assumption that this ditch does carry irrigation flow, bur does not commingle it with effluent during periods ojmonitoring. The permittee agrees that when the ditch is used for irrigation, appropriated streamflow shall not be combined with effluent jot the purpose ojdiluting effluent at outjall 007. To ensure a representative sample of the effluent quality is obtained jot the purpose ojdetermining compliance with the effluent limitations, the headgate of the irrigation ditch will be closed a minimum of 24 hours prior to the collection of an effluent sample. This would result in no discharge from outjall 007 other than effluent during such periods. The permittee will be required ro monitor upstream flow in Trout Creek. This will be used to verify that the dilution remains ar least 10:1 (see discussion following effluent (imitation table). Ijfuture measurements indicate that this dilution does not occur consistently, the permit may have to be reopened to revise effluent limitations appropriately. During periods of no discharge from ort(ja[l 007, ij no discharge was occurring from outjall 004 also, the permittee would not be required to monitor Trout Creek streanflow. If ei1lter outjall is discharging, stream Jlow shall 6e monitored. If irrigation Jlow is routed through this ditch and allowed to combine with effluent and/or discharge directly to Trout Creek during the 24 hour period prior to sample collection or during sample collection, the Division will reopen the permit to set effluent limitations for outfalls 002. 003 and 006. Such action would be subject to public notice provisions and the permittee would have full adjudication rights regarding such a change. V. TERMS AND COND/TIONS A. Determination of EjJluent (imitations /. E(lluent Limitations: The following linti(afions will apply to existing outjall (X14 and new outjaf[ 007 and are discussed in Sections V. A.2 and VA.3. Table V-! -- E(Ruenr limitations for Out(alls 004 and 007 Discharge limitations Maximum Concentrations Parameter 30-Day AvA. 7-Day AvR. Daily Mai. Rationale Flow, Ratio (Combined Ef(luenr 0.100•• N/A Report Design Cnpaciry !o Upstream Trout Creek) TSS, mg/P 35• N/A 70* Federal Effluent! Guidelines Oil and Grease, mg/P N/A N/A 10 State £jfiuenr Regulatiats pH, s.u. (Minimum-MazintuntJ N/A N/A 6.5-9.0 Water Quality Standards Settleable Solids, rrtP/P N/A N/A 0.5* Federal Effluent Guidelines TDS, mg/P N/A N/A Report Salinity Regu(arions Sulfate, mg/P 2750 N/A Report Water Quality Standards WET, Acute State Pennir Regulations through 06/30/98 N/A N/A Report beginning 07/0//98 N/A N/A LC ra > 100% Iron (/'oral), mg/P 3.5• N/A 7.0• Federal Effluent Guidelines Manganese (I'R), mg/P /!.0 N/A Report Wafer Quality Standards Manganese (PD), mg/P 0.55 N/A Report Water Quality Standards Mercury (Total), mR/P 0.0001 / N/A Report Water ualiry Standards • See srnron V.A.3. b/ Ahrrnarr Burden a Proo Re uiremenrs. •• 7hif it rhr diyrira/ rqurva enr o a ratio. (PD): Potentially Orrsoh•rd Fraruon (TR/: Toro! Rttoverabfe Frarrion