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COLORADO DEPARTMENT OF PUb...C HEALTH AND ENV/RONMENT, Water Qu,.,try Control Division <br />Rationale -Page 3, Permit No. CO-0036684 <br />B. Wastewater Treatment Description <br />Twentymile Coal Company has installed an aerator in the sedimentation pond ro mitigate tosicin~ believed ro be caused <br />by metals. The effectiveness of the aeration is being evaluated. No other changes have occured in the trearrrrent svstettr. <br />The permittee employs a Class D certified wastewater operator to conform with Article 9, Title 25, Reeulations (or the <br />Certification of Water Treatment Plant and Wastewater Treatment Plant Ooerators. <br />V. PERFORMANCE H/STORY <br />A. Monitoring Data <br />Discharge Monitorine Reoorts: Table V-1 summarizes the effluent data reported on the month!}' Discharge <br />Monitoring Reports (DMR) for the Twentymife Coal Company facility from April 1 through December 31, 1995 <br />(three calendar quarters). The permittee reported "No Discharge" for the first calendar quarter of 1995. <br />Table V-1 -- Self-Afonitoring Results for Outfall 001 <br />Reported Previous A'o. of <br />Concentrations Permit Limitation <br />Parameter Avg/Min/Mss limitation Excursions <br />Flow, MGD <br />30-day avg <br />daily mar <br /> <br />TSS, mg/P <br />30-dav avg <br />daily inax <br />Total Recoverable Iron, mg/P <br />30-day avg <br />daily max <br />Oil & Grease, mg/P <br />pH, s. u. <br />Conductivity, umho/cm <br />30-dm' avg <br />daily inax <br />0.0301/0.0204/0.0488 None <br />0.0597/0.0245/0.1089 None <br />11/4/18 35 <br />15/10/18 70 <br />0.04/0.01/0.05 1.9 <br />0.06/0.01/0.1 None <br />None Visible/Norse Visible 10 <br />-/7.1/8.4 6.5-9.0 <br />3267/2672/3626 None <br />3697/2880/4430 Notre <br />0 <br />Whale Effluent Toxicity, Acute <br />Ceriodaphnia 1 Pass, 3 Fail /WC=50% 3 <br />Fathead Minnow !Pass, 3 Fail IWC=50% 3 <br />State Samofine: There are no stare sampling results available for this facility. <br />B. Compliance With Ternts and Conditions of Previous Permit <br />EfRrtent Limitations: The data shown in the preceding table indicate that Twenrymile Coal has maintained <br />compliance with the previous permit with the exception of acute Whole Effluent Toxicity. The facility has had <br />severs! WET failures over the past few years. Often, toxicity spontaneously disappeared during accelerated testing. <br />It appears that the permittee has never determined with certainty the cause(s) of toxicity, although metals and TDS <br />are suspected. <br />2. Other Permit Rearrirements: The permittee has been in compliance with all other terms and conditions of the <br />permit. <br />