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COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENV/RONMENT, Water Quality Control Division
<br />Rariowle -Page 11, Permit No. CO-000022/
<br />• Alternate Limitation Burden of Proof Reauiremems: !n conformance with 40 CFR 434.63, the permittee has the
<br />burden of proof when requesting relief from total suspended solids (TSS), total iron and/or settleable solids
<br />limitations, as appropriate. The imetu of this regulation is to afford relief only when needed due to a volume of
<br />water generated by a specific storm event, it is not imended to be automatically applied to all discharges caused
<br />by precipitation, nor to be used to discJtarge volumes in excess ojthar generated by the storm evem. On this
<br />basis, relief shall be granted only when necessary and shall not be granted when the permittee has control over
<br />the discharge, enabling them to meet the primary limitations. The permittee should endeavor to meet the
<br />primary limitations whenever possible. All manual dewatering ojponds that are equipped with aruomaric
<br />dewatering .systems mutt meet TSS and total iron limitations. If a pond has only manual dewatering capability,
<br />relief is available only to the euem required to regain necessary stability and capadty. The Division shall have
<br />final authority in determining whether relief is granted. As parr of this determination, the Division steal! evaluate
<br />whether the permittee cmtld have comrolled the discharge in such a manner that primary limitations could have
<br />been met.
<br />1) For rainfall, to waive TSS and total iror. limitations, it is necessary to demonstrate that discharge occurred
<br />x~ithin 48 hours after measurable precipitation has stopped. To waive settleable solids limitations, it is
<br />necessary ro prove that discharge occurred within 48 hours after precipitation greater than the ]0-year,
<br />24-hour event has stopped.
<br />2) For snox~melt, ro waive TSS and rota! iron limitations, it is necessary to demonstrate that discharge occurred
<br />within 48 hours after pond infIox has stopped. To waive settleable solids limitations, it is necessary to
<br />proti•e that discharge occurred within 48 hours after pond inflow volume greater than the 10-year, 24-hour
<br />everu has stopped.
<br />c) Sa[inirv Regulations: In compliance with section 6.9.2 (12) of the Colorado Discharge Permit System
<br />Regulations, the perrnittee shall monitor for total dissolved solids on a quarterly basis. Samples shall be taken ar
<br />• the effluent discharge point(s). Sa[iniq requirements are included in Pan /.B.l.e. of the permit.
<br />d) Whole Effluent Toxicity (l4'ET) Testing: Acute WET testing is required for outfalls 002, 003, 005, 006, 010 and
<br />011; and chronic WET testing is required for outfal/s 004 and 008. See following discussion for WET testing for
<br />a1f ojthese outfalls. (Also see Pans I.A.4. and /.A.S. ojrhe permit.)
<br />1) Purpose of R'E7'Testing: The Water Quality Control Division has established the rue of WEI'testing as a
<br />method for identrfi~ing and controlling toxic discharges from wastewater treatment facilities. WET testing is
<br />being utilised as a means to ensure that there are no discharges of pollutants "in amounts, concemrations or
<br />combinations which are harmful to the beneficial uses or toxic to humans, animals, plants, or aquatic life"
<br />as required b~~ Section 3.1.11 (I) of the Basic Standards and Methodologies for Surface Waters.
<br />2) /nsrream Waste Corscentration (IwCI: Where monitoring or limitations for WET are deemed appropriate b~'
<br />the Division, chronic insrream dilution as represented by the chronic IA'C is critical in determining whether
<br />acute or chronic conditions shall apply. For those discharges x~here the chronic /WC is greater than (>)
<br />9.1 rr, chronic conditrons app!), where the IWC rs less than or equal ro (<_) 9.1 acute conditions apply.
<br />The chronic IN'C is determined using the following equalion:
<br />IWC = (Facilin Flow (FF)/(Stream Chronic Lax Flow (annual) + FF)J X 100 ro
<br />Floxs and 1~~'C calculations for ourfalls 002, 003, 005, 006, 010 and 011 are irrelevant because, in
<br />~ addition to the IWC value Jor determining whether chronic or acute WET resting requirements are
<br />applicable, the classification of the receiving stream must be considered. According to the Colorado Water
<br />Oualiro Control Division Biomonitoring Guidance Document. dared !u!y 1, ]993, where the receiving warm
<br />is classified aquatic life, class 2 x~irhour all of the appropriate aquatic life numeric standards, acute WET
<br />• testing is required, regardless of dilution. Since the receiving wafers for outfalls 002, 003, 005, 006, 010
<br />and 011 are classified as Class 2 Aquatic Life use, but without all of the appropriate aquatic life numeric
<br />standards, the Division has determined that acute WET testing is applicable for these outfalls (also see
<br />jollox~ing paragraph). Since segment 12 is classified this way, outfalls 002, 003. 005, 006, 010 and 011
<br />are subject ro acute WET testing requirements.
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