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Pege 2 <br />COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division <br />Rationale -Page 22 Permlt No. CO-0045675 <br />seep/suAace water collection system, is included in Appendix A for informational purposes. At somfa <br />point, the downgredien! containment wells may also be included in the sources. The two present sources <br />(from the backfill wells and the curtain wells) are summarized in Appendix A and renect the potential <br />water quality pdor to treatment. The Division has compared the quality o(these two sources with the <br />calculated antidegredation-based allowable permit concentration levels. <br />Vl.t3.4. Discussion of Effluent limitations (Cont.) <br />d) Determination of Parameters Limded for This Permit (Cont.) <br />Metals and Inorganics LimBations: (cont.) <br />When the two untreated wastewater source(s) contain concentrations that approach and/or uxceed the:>e <br />calculated antidegredation-based levels, the Division has determined that a reasonable potential exists for <br />these parameters to possibly tie present, and the Division has established these parameters as permit <br />limitations. Where the wastewater source concenrations are substantially below the calculated <br />antidegradation-based levels, then no limitations have been established. Also, for certain parameters N~hich <br />are not expected to be found in the contdbutng wastewater sources and which have been detected below <br />minimal levels o/detection and/or at levels much below the antidegredation-based standard, the Division is <br />requidng a six-times analysis (or these pa2meters. <br />cyanide: Since both Weak Acid Dissociable (WAD) Cyanide and Total Cyanide have not been generelly <br />detected in the contributing wastewater sources or in instream data (at levels <0.0f0 mg/I, which is the <br />accepted minimum level of detection for cyanide established by the CDPHE laboratory), the Division has <br />determined that there is no reasonable potential to establish limitations !or WAD Cyanide. However, semi- <br />annual moniodng will be required for a two year period to verify that no cyanide is being discharged, since <br />the San Luis facility has previously included a milling operation utilizing a sodium cyanide CarboMn-Ce;~ch <br />circuit. This monitoring data should also be correlated to the routine instream monitodng for cyanide that <br />BMRI is required to perform under the terms of their CDMG permR. The additional insVeam/alluvial <br />monitodng for cyanide shall be submitted to the Division to confirm that cyanide is not being detected. <br />Mercury: Comparably to the previous discussion (or cyanide, no mercury has been generally detected in the <br />contributing wastewater sources, the treated discharge, or instream monitodng samples. Thus, the Division <br />has determined that there is no reasonable potential to establish limits for this parameter, but at this time, a <br />six-times analysis will6e required to substantiate that mercury is still not found at detectable levels and does <br />not occur. Based upon recent information indicated by BMRI, the Division may further determine that the <br />six-ti'me analyses will not be necessary for mercury for the 001 discharges. This determination will be <br />dependent upon substantiation of data that BMRI can submit as part of their public notice comments. <br />Radioactive Parameters: The Division is including limitations for two radioactive constituents, which area <br />Total Radium 226+228 and Total Natural Uranium. The limitations (or these two radioactive parameter,; is <br />equal to the basic radioactive standards established in the Classircations and Numeric Standards for the <br />Rio Grande Basin. These two radioactive constituents are commonly associated with Gross Alpha radiation <br />determinations. <br />e) Whole Efluent Toxicity /WETI Testing <br />For this facility, chronic WET testing is required /or all three outtalls 001a, OO1b, and OO1c. (See Parts I.A <br />and I.8 o(the permit.) <br />1) Purpose o(WET Testing: The Water Quality Control Division has established the use of WET testing <br />as a method for identifying and controlling toxic discharges from wastewater treatment (acilrlies. WET <br />testing is being utilized as a means to ensure that there are no discharges of pollutants 'in amounts, <br />concentrations or combinations which are harmlul fo the beneficial uses or toxic to humans, animals, <br />plants, or aquatic life' as required by Section 31.11 (1) of the Basic Standards and Methodoloaies~ <br />SuAace Wafers. <br />2) Instream Waste Concentration fIWCI: Where monitoring or limitations for WET are deemed <br />appropriate by the Division, chronic instream dilution as represented by the chronic IWC is critical in <br />determining whether acute or chronic conditions shall apply. For those discharges where the chronic <br />IWC is greater than (>) 9.1 %, chronic conditions apply, where the IWC is less than or equal to (y 9.1 <br />acute conditions apply. The chronic IWC is determined using the /ollowing equation: <br />IWC =(Facility Flow (FF)/(Stream Chronic Low Flow (annual) + FF)] X 100Y <br />