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<br />...~ (~ "'::'.,1 <br /> <br />00J700 <br /> <br />A new section is proposed dealing with water quality standards based on secondary <br />drinking water standards for the protection of the water supply classification. In summary, it <br />proposed to delete the water supply-based water quality standards for manganese, iron, and <br />sulfate from the basin-specific tables in the future. Where an existing water supply use is <br />present, a new narrative standard would apply either the table values, which are based on the <br />secondary drinking water standards, or existing quality as of January 1, 2000, whichever is less <br />restrictive. <br /> <br />The Division proposal includes changes to the antidegradation regulation, principally to <br />the "significance determination." More specifically, the test that is based on 10 percent of the <br />existing .load is proposed to be changes to apply to biocumulative toxic pollutants. The <br />remaining three significance tests would apply in the case of new or increased discharges of any <br />pollutants other than biocumulative toxins. In order to ensure that successive new discharges do <br />not result in an effect that is cumulatively significant without an antidegradation review, the <br />concentration-based "15 percent of the available increment" test is proposed to be modified to <br />provide that where the cumulative impact of discharges would increase the low-flow pollutant by <br />more than 15 percent, any new or increased loading would not be considered insignificant. <br /> <br />There is a proposal to modify the existing temporary modification section to allow the <br />adoption of temporary modifications where there is uncertainty as to what the standards should <br />be. This proposal would conform the regulation to existing practice by the Water Quality <br />Control Commission. <br /> <br />Finally, the Division proposal includes the possibility of a new site-specific narrative <br />standard where water quality is degraded as the result of historic mining activities and <br />improvement is likely within 20 years. <br /> <br />. In conclusion, the changes that will be considered by the Colorado Water Quality Control <br />Commission in July are broad and significant. They will in all likelihood affect most dischargers <br />in Colorado. This includes not only dischargers with their own wastewater treatment plants, but <br />in some cases will also include indirect dischargers (i.e., dischargers to publicly owned treatment <br />works) because more restrictive water quality based effluent limitations that may apply to the <br />publicly owned treatment works will in all likelihood translate to more restrictive pretreatment <br />requirements for discharges to the publicly owned treatment works. <br /> <br />This proposal will be publis~ed in the Colorado Register on April 10. Party status <br />requests are due not later than May 2 and the hearing will be held July 10 and 11, 2000. For <br />further information, including a copy of the proposal, please contact Sarah Johnson at the Water <br />Quality Control Division at 303-692-3609 or the Commission website at <br />htto://www.cdphe.state.co.us.lwq/wocchom.aso. If you have questions, contact Sarah Johnson at the <br />preceding number or contact Jerry Raisch at 303-443-6151. <br /> <br />3 <br />