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000099 Parameter Proposed Standard Existing Standard Fecal coliform N03 Phosphorus Total organic carbon 2.2 dUllOO ml 5 mg/L 0.3.mgIL 2.0 mgIL 2000 cfu/lOOml 10 mgIL none none The Water Quality Control Division proposal includes changes to the recreation classification and pathogen standards. The Division's proposal reiterates that Colorado waters shall be presumed to be Recreation Class 1 unless a use attainability analysis demonstrates that there is not a reasonable potential for primary contact uses to occur within the next 20-year period. Recreation Class 1 is broken into two subcategories: Class lA, existing primary contact, and Class 1B, potential primary contact. It is proposed that these recreation classifications contain the following pathogen standards: Parameter Class 1A Class 1B Class 2 Fecal coliform E. coli 200 dUl100ml 126 cfu/100ml 325 cfu/100ml 205 cfu/100ml 2000 cfu/lOOml 630 cfullOOml The proposal indicates the Division's preference to shift from fecal coliform to E. coli, although . a discharger may choose which parameter it prefers to be regulated by for the next few years. The Water Quality Control Division proposal includes a new section on mixing zones that may adversely affect a significant number of Colorado dis~hargers. In the past, the Division assumed that 100 percent mixing took place at the point of discharge. The Division's proposal, which was developed by a Mixing Zone work group, will in some cases make water quality- based effluent limitations more restrictive. There are two primary components of the new mixing zone provisions. First; new criteria are proposed to be used by the Division in determining a "regulatory mixing zone," which is the allowable mixing zone for an individual point source discharge. Second, the proposal includes criteria to be used by the Division in applying the mixing zone provisions to determine the allowable dilution when developing a discharge permit for aparticular point source. The Division proposal revises the hardness-based metals standards to incorporate changes made over the last few years by EP A in its metals criteria documents. Among other changes, the zinc and cadmium values become less restrictive and the lead and copper values become more restrictive. The proposal also incorporates total recoverable/dissolved conversion factors that nominally reduce all of the hardness-based values. Another proposed change to the metals standards is a proposal by Climax Molybdenum Company to change the aquatic life hardness- based equation for manganese to incorporate toxicity data that was not available when the original equation was previously adopted by the Commission. Changes are proposed to the organic pollutant tables to conform these values to changes made by EP A over the last few years. Also proposed are three sets of human health-based standards that apply. depending on whether a water supply classification, a Class 1 aquatic life, or a Class 2 with recurrent fishing, or both of these uses, is present. 2