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Pittsburg and Midway Coal Company Edna Mine Water Quality Assessment CO-0032638 <br />Where, <br />Mpe.mlrred =Current permit limit or implicit permit limit (mg/1) <br />Qpermtrred =Design flow or the maximum of the 30-day average flows reported during <br />the life of the previous permit (mgd), which is coincidentally also equal to <br />the Qz, the design flow reflecting recent post reclamation flows <br />MZ =Maximum allowable discharge concentration (mg/1) <br />Qz =Average daily effluent flow (design capacity in mgd) <br />For purposes of selecting the current permit limit, M~„„;,rep, where more than one limit has been <br />established (e.g., a 30-day average limit and a daily maximum limit), the most stringent was used. <br />Similarly, when selecting the MZ, where both chronic and acute allowable discharge concentrations <br />have been calculated, the most stringent was used. In the interests of limiting tables to only those <br />explicitly necessary, detailed calculations of the current permitted load, proposed WQBELs load and <br />NIL are not provided. However, the values for each factor in the equations noted above can be easily <br />found in this assessment and therefore calculations can be easily verified. <br />As noted in Tables A-13 and A-14, ADBACs and NILs are not applicable when the new WQBEL <br />load is less than the current permitted load, or when the new WQBELs are less than the ADBACs. <br />For the pollutants for which ADBACs and NILs apply, as highlighted by bold and italicized font, if <br />the facility chooses the NIL as the proposed permit limit, ADBACs will not be applied. Note that the <br />most likely selection between ADBACs and NILs is highlighted in underlined, bold, italics font. <br />Additionally, the facility may complete an alternatives analysis, which would also result in ADBACs <br />not being applied. These options are further discussed in the rationale. <br />VI. References <br />Colorado Total Maximum Daily Load and Wasteload Allocation Guidance, CDPHE, WQCD, <br />November 1991. <br />Classifications and Numeric Standards for Upper Colorado River Basin and North Platte River <br />(Planning Region 12), Regulation No. 33, CDPHE, WQCC, effective January 2Q 2004. <br />The Basic Standards and Methodologies for Surface Water, Regulation 31, CDPHE, WQCC, <br />Effective March 22, 2005. <br />Antidegradation Significance Determination for New or Increased Water Quality Impacts, <br />Procedural Guidance, CDPHE, WQCD, December 2001. <br />Memorandum Re: First Update to Guidance Version 1.0, CDPHE, WQCD, April 23, 2002. <br />Appendix A twQn sP v~s~o~ a-a Fne~> Page 19 of 19 Last Revised September 2, 2005 <br />