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COLORADO DEPARTMENT OF HEnLTH, Water Qualiry Control Division Rationale -Page 5, Permit No. CO-0043648 Metals Standard -For Segment 22 Metal Criteria Standard. ug/! Analvtical Method Arsenic (As) CJtronic !00 Total Recoverable Iron (Fe) Chronic 1000 Tatnl Recoverable Manganese (Mn) Chronic 1000 Dissolved Mercury (Hg) Chronic 0.0/ Total Aluminum (Al) Ague and Guonic TVS TVS Cadmium (Cd) Acute and Chronic TVS TVS Chromium, tri (Cr III) Acute and Chronic TVS TVS Chromium, hex (Cr V!) Acute and Chronic TVS TVS Copper (Cu) Acute and Chronic TVS TYS Lead (Pb) Acute and Chronic TVS TVS Nickel (Ni) Acute and Chronic TVS TVS Selenium (Se) Acute and Chronic TVS TVS Silver (Ag) Acute TVS TVS Silver (Ag) Chronic TVS-trout TVS (Chronic silver standard becomes effective March 2, 1998) Zinc (Zn) Acute and Chronic TVS TVS (NS =Table Ya[ue Standards) Temporary Modi cations for Segment 22 - Mainstem of Arequa Culch Effective Through 12/3!/97 pH = 4.3 - 9.0 s. u. Cyanide = 0.021 mg/1 (Weak Acid Dissociable) Meta[ Criteria Standard. u¢/1 Analvtical Method Aluminum (Al) Chronic 22,000 Dissolved Cadmium (Cd) Chronic l7 Dissolved Iron (Fe) Chronic 3,000 Total Recoverable Manganese (Mn) Chronic 9,000 Dissolved Zinc (Ln) Chronic 1,700 Dissolved Table Value Standards (I'VS) refers to numerical criteria initially set forth in Tables /, II and /!I of the Basic Standards and Methodologies jot Surface Water. The criteria or TVS may be adopted as standards jot a receiving stream. The standards are listed by segment in the Classhcations and Numeric Standards for the Arkansas River Basin. Where a standard for a parameter is given as TVS in the Classifications and Numeric Standards i! corresponds only to those criteria or TVS in the Basic Standards that are based upon the protection of the aquatic life use classification, as explained in section 3.2.6 of the Classifications and Numeric Standards. The aquatic life use standards consist of both an acute and chronic standard and are generally more stringent than those for the protection of either agricultural or drinking water uses. Therefore, they are usually considered protective of all three uses. /n cases where a standard is based on something other than the acute and chronic TVS criteria, a numeric value rather than the TVS designation has been specified in the Classifications and Numeric Standards. For hardness-dependent metals standards, the numerical value of the aquatic life use based standard depends upon the combined effluent/receiving stream hardness below the discharge point. The hardness values to be used are those which correspond to the lower 95th percent confidence limit of the mean hardness value at the periodic low flow criteria, as determined from a regression analysis of site-specific data. If data for such an analysis is not available, or if a regression analysis is not appropriate, other methods may 6e used.