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(2) Hardness values to be used in equations are in mg/I as calcium carbonate and shall be no <br /> greater than 400mg/L. The hardness values used in calculating the appropriate metal <br /> standard should be based on the lower 95 per cent confidence limit of the mean hardness <br /> value at the periodic low flow criteria as determined from a regression analysis of <br /> site-specific data. Where insufficient site-specific data exists to define the mean hardness <br /> value at the periodic low flow criteria, representative regional data shall be used to <br /> perform the regression analysis. Where a regression analysis is not appropriate, a <br /> site-specific method should be used. In calculating a hardness value, regression analyses <br /> should not be extrapolated past the point that data exist. <br /> (3) Both acute and chronic numbers adopted as stream standards are levels not to be <br /> exceeded more than once every three years on the average. <br /> (4 old) FT= 100.03(20-TcnP). <br /> Where TCAP is <_ T<_ 30 <br /> FT= 100.03(20-T); <br /> Where 0 is <_T<_ TCAP <br /> TCAP=20' C cold water aquatic life species present <br /> TCAP=25' C cold water aquatic life species absent <br /> FPH = 1; Where 8 <_pH <_ 9 <br /> FPH= 1 + 101H); <br /> 1.25 Where 6.5 <_ pH <_ 8 <br /> FPH means the acute pH adjustment factor, defined by the above formulas. <br /> FT Means the acute temperature adjustment factor, defined by the above formulas. <br /> T means temperature measured in degrees celsius. <br /> TCAP means temperature CAP; the maximum temperature which affects the toxicity of <br /> ammonia to salmonid and non-salmonid fish groups. <br /> NOTE:If the calculated acute value is less than the chronic value,then the chronic value <br /> shall be used as the acute standard. <br /> (4) For acute conditions the default assumption is that salmonids could be present in cold <br /> water segments and should be protected, and that salmonids do not need to be protected <br /> in warm water segments. For chronic conditions,the default assumptions are that early <br /> life stages could be present all year in cold water segments and should be protected. In <br /> warm water segments the default assumption is that early life stages are present and <br /> should be protected only from April 1 through August 31. These assumptions can be <br /> modified by the commission on a site-specific basis where appropriate evidence is <br /> submitted. <br /> (5) Unless the stability of the chromium valence state in receiving waters can be clearly <br /> demonstrated, the standard for chromium should be in terms of chromium VI. In no case <br /> can the sum of the instream levels of Hexavalent and Trivalent Chromium exceed the <br /> water supply standard of 50ug/I total chromium in those waters classified for domestic <br /> water use. <br /> (6) Selenium is a bioaccumulative metal and subject to a range of toxicity values depending <br /> upon numerous site-specific variables. <br /> (INSERT TABLES135.7-35.10 Reserved <br /> 35.11 STATEMENT OF BASIS AND PURPOSE <br /> I. Introduction <br /> 6 <br />