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COLORADO DEPARTMENT OF PUBLIC HEALTHAND ENPIRONMENT, Water Quality Cantro(Division
<br />Rationale -Page 3, Permit No. CO-0044377
<br />ce Standards: The standards that apply to this type of facility are found under 40 CFR
<br />:e~at~g~ The limitations shat apply are:
<br />-- Federal Standards (40 CFR 434.55 -Post-mining Areas)
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<br />x.~ pt ~ as v ~ oiicentration-" . ,,,..~.~:~i5^ ai:.i~ a~:'~ohcantY,atwn;;~=-~,;~.,
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<br />`1 Hese~ nrameters apPty anty to unaergrouna mine drainage discharges from sources subjec( to New J'ource Performance J'tanaaras
<br />++This nrameter Bubb ec! to Burden of Proof Requirements, see nest section
<br />ion Burden o Proo Re uirements.~ In conformance with 40 CFR 434.63, the permittee has the burden of
<br />estin~ om sett ea-b1e solids limitations for discharges of surface runoJj- water. Relief shall be
<br />'n necessary and shall not be granted when thepermitiee has control over the discharge. The permittee
<br />to meet the primary limitations whenever possible. Relief is not available for mine drainage.
<br />For rainfall, to waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after
<br />measurable precipitation has stopped.
<br />For snowmelt, to waive settleable solids limitations, it is necessary to prove that discharge occurred within 48 hours after
<br />pond inflow has stopped.
<br />Documentation that the treatment facilities were properly operated and maintained prior to and during the storm event
<br />must be submitted with any rez~uest for relief. The Division shall determine the adequacy of proo . As part of this
<br />deter minator., the Division, steal. evaluate whether the permittee could have controlled the discharge zn such a manner that
<br />primary limitations could have been met, whether proper sediment storage levels were maintatned and the ponds had
<br />suffcient water and sediment capacity for the storm event plus other relevant factors. All manual pond dewatering must
<br />meet TSS and total iron limitattons unless previous approval has been granted for ponds that have no other method of
<br />dewatering.
<br />PostPost-Minin Areas: In conformance with 40 CFR 434.50, commencing at the time active mining has ceased and all surface
<br />areas served 6y a sedimentation pond have been returned to the required contour and reveggetation has commenced,
<br />applicable discharges may be eligible or limitations other than those specified in Part LA.1. In most cases, these post-
<br />minzng hmztations shall remain m effect until bond release. This facility has achieved this stage, thus, post-mining
<br />limitations apply.
<br />d. Pollutants Limited by Water OualiN Standards: The water quality assessment in Appendix A contains the evaluation of
<br />po u[an~by water qua ity stan ar s. The mass balance equation shown in Seaton IY o~Appendix A was used for
<br />all pollutants to calculate the maximum allowable ef/luent concentration, M2, that could be discharged without causing the
<br />water quality standard to be violated. A detailed discussion of the calculations for the maximum allowable effluent
<br />pollutant concentrations for metals and cyanide is provided in Section IV of the water quality assessment contained in
<br />Appendix A.
<br />The maximum allowable effluent pollutant concentrations determined as part ojthese calculations represent the calculated
<br />e uent limits that would e protective of water quality. These are also known as the water quality-based effluent limits
<br />(~QBELs).
<br />The Permits Unit evaluated the calculated WQBELs and has made a determination as to whether there is a reasonable
<br />potential for the facility discharge to cause or contribute to an exceedance of a stream standard. If there is a reasonable
<br />potential for the discharge to contribute to an exceedance, effluent limits are included in the permit.
<br />For metals, the approach to reasonable potential evaluations is utilized as discussed in the paragraphs that follow.
<br />i. Metals (Outfall DDI): Utilizing the assimilative cappacities contained in Appendix A, an analysis must be pert
<br />etermin~to include the calculated W BELs in the permit. The ~ttidelines for performeng a re.
<br />potential analysis are outlined in the Division's ~cument, Determination, oft+. ~ Requirement to Include Wate:
<br />po±en±ial depending on the amount
<br />The first step, determining the pollutants of concern, the permit writer, with the cooperation of the permittee, must use
<br />best professional judgment to determine the pollutants of concern ("POC's'). POC's are pollutants that mi~ht be
<br />expec~e3d in the effluent. POC's may 6e: pollutants that have been detected in the effluent (through compp lance
<br />monitoring, priority pollutant monitoring, optional monitoring, or other monitoring) in the last 5 ears; ~pol[utants
<br />with known sources; pollutants that are known to commonly occur in similar effluents; pollutants that are present in
<br />the influent or at other sampling points in the treatment or collection systems; pollutants that are present in the
<br />bioso ids or other treatment residuals; otherpo/!utants which, in thepermit water's best professional Judgment, may
<br />6e found in the effluent.
<br />Upstream and downstream data was reviewed which represents instream quality be ore and after the facility's
<br />discharge(s). This data was compared with additional ambient data provided zn t e water quality assessment
<br />(Appendix A, Table A-6), and compared with the WooBEIs to determine what the POC's were. Additionally, with the
<br />development ofELGs for the Western Alkaline CoarMining Subcategory, there was a consideration of what potential
<br />pollutants were pollutants of concern. Whereby, it was determined that total iron was the only pollutant ofconcern.
<br />e. Amide radation: Since the North Fork of the Gunnison River /Stream segment COGUNFOl) is Undesi~rtaced, an
<br />anti egd radation review is applicable pursuant to Section 31.8 of The Basic Standards and Methodoloeies for Surface
<br />Water However, the ratio of the flow of the North Fork of the un~River tote ountain oa and earl
<br />tiVW7`Fs combined design flows (see Appendixr A) is more than 150.'1 at !ow flows. Section 31.8 (3)(c) specifies that the
<br />discharge of pollutants should oat be considered to result in significant de radation of the reviewable waters of the flow
<br />rate is greater than 100:1 dilution at low flow. Thus, condition 31.8(3)(c) of the regulations is met and no further
<br />antidegradation evaluation is necessaryfor discharges to the North Fork of the Gunnison :vet.
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