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COLORADO DEPARTMENT OF HEATH, Winer Qrmlip~ Division Rnliormle - Pnge 12. Pennil No. CO-0043648 n•iteria based on the delineation of the aquatic convmuni[y through the 1998 UAA. The combinatimt of the UAA and the recalculation demonstrates that the metals standards for aluminum protect the existing aquatic life that can be expected in Arequa Gulch. Subsection 61.8(2)(b)(i)(E) of the State permit regulations (5 CCR 1002-61) states in relevant part that: "Limits on whole effluent toxicity are not necessary where the Division demonstrates in the rationale of the permit, using the procedures in subsection: (b)(i)(B) of this section, that chemical-specific limits for the effluent are sufficient to attain mtd maintain applicable numeric and narrative water quality standards." The TIE found that aluminum was the pnrmne[er causing toxicity in the routine WET tests, which use species not expected to be found in Arequa Gulch. In this case, the Commission has adopted site-specific water quality standards for theparnmeter ofconcern identified in the TIE (aluminum) based on studies that indicate thatspecies in Arequa Gulch will beprotected at the level of the standard. The species used in the WET test are more sensitive than the indigenous species ar:d further WET testing using Ceriodaphnia and fathead minnows will rtot be indicative of an exceedance of the narrative standard. Therefore, CC&V will not be required to conduct WET testing in the renewal permit. 5. Storm Water Storm venter pernittirtg requirements, for discharges consisting of neon-effluent guideline storm water (storm water not covered by 40 CFR 440), have been and will continue to be implemented through the General Storm Water Permit No. COR-040000, Certificatia: No. COR-040049. 6. Best Management Practices CC&V shall take all reasonable precautions to prevent any point source discharge into surface waters of the State except as authorized through the terms and conditions that have been assigned to specific outfalls that have been identified in the applicable stor•rn venter permit. _ CC& V shell ensure that the excavation, movemer:t andplacement of any materials that might be contaminated with cyanide or other environnrentnl pollutmtts is carried out in n manner which will avoid any discharge ofpollutnrnts to surface venters of the State. 7. Economic Reasonableness Evaluation: Section 25-8-503(8) of the revised (June 1985) Colorado Water Quality Control Act required the Division to "determine whether or not ariy or all of the water quality standard based effluent limitations are reasonably related to the economic, environmental, public health and energy impacts to the public and affected persons, and are in furtherance of the policies set forth in sectior:s 25-8-192 and 25-8-104. " The Regulations for the State Discharge Permit System, 5 CCR 1002-61, further define this requirement under Section 61.11 (a) and state: "Where economic, environmental, public /wealth, mtd energy impacts to the public and affected persons have been considered in the classifications and standards setting process, permits written to meet the standards may be presumed to have taken into consideration economic factors unless: i) A newperrtit is issuedwhere the discharge was not in existence at the time of the classif:catiorr arnd standards rulernnldng, or ii) In the case ofa continuing discharge, additional information or factors have emerged that were not anh'crpated or consftlered at the time of the class cation and standards rulemaking. " The evalnnntion for this permit shows that this facility was in existence at the tinne of water quality standards rulerttaking. Additionally, based on available data, the resulting water quality standard-based effluent limitations are determined to be reasonably related to the economic, environmental, public health, and energy irnpncts to the public and affected persons. Ifthe Pernittee disagrees with this finding, pursuant to 5 CCR 1002-61.17(b)(ii) the Permittee should submit all pertinent information to the Division during the public notice period. 8. Antibackslidine The evaluation for this pernit included n review for nntibnckslidingpursuant to S CCR 1002-61.10. Section 61.10 allowsfor less stringentpermit1imitations in subsequentpernitsforArequa Gulch when apernit limitation is based on waterqualirystandards and the standards are being met (provided other criteria also are met). Aregua Gulch has been classified as "Use Protected" and