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SPX CORPORATION ORDER R5-2019-0018 <br /> SPX MARLEY COOLING TECHNOLOGIES GROUNDWATER CLEANUP NPDES NO. CA0081787 <br /> and the CTR do not discuss the manner in which hardness is to be ascertained, <br /> thus regional water boards have considerable discretion in determining ambient <br /> hardness so long as the selected value is protective of water quality criteria under <br /> the given flow conditions. (Davis Order, p.10). The State Water Board explained <br /> that it is necessary that, "The [hardness] value selected should provide protection <br /> for all times of discharge under varying hardness conditions." (Yuba City Order, p. <br /> 8). The Davis Order also provides that, "Regardless of the hardness used, the <br /> resulting limits must always be protective of water quality criteria under all flow <br /> conditions." (Davis Order, p. 11) <br /> The equation describing the total recoverable regulatory criterion, as established in <br /> the CTR, is as follows: <br /> CTR Criterion = WER x (em['n(")]+b) (Equation 1) <br /> Where: <br /> H = ambient hardness (as CaCO3) 7 <br /> WEIR = water-effect ratio <br /> m, b = metal- and criterion-specific constants <br /> The direction in the CTR regarding hardness selection is that it must be based on <br /> ambient hardness and consistent with design discharge conditions for design flows <br /> and mixing zones. Consistent with design discharge conditions and design flows <br /> means that the selected "design" hardness must result in effluent limitations under <br /> design discharge conditions that do not result in more than one exceedance of the <br /> applicable criteria in a three year period.$ Where design flows for aquatic life <br /> criteria include the lowest one-day flow with an average reoccurrence frequency of <br /> once in ten years (1 Q10) and the lowest average seven consecutive day flow with <br /> an average reoccurrence frequency of once in ten years (7Q10). The 1Q10 and <br /> 7Q10 Stockton Diverting Canal flows are 34.1 cfs and 34.1 cfs, respectively. <br /> Ambient conditions <br /> The ambient receiving water hardness varied from 56 mg/L to 89 mg/L, based on 8 <br /> samples collected between March 2014 through September 2017 (see Figure F-1). <br /> For this discussion, all hardness values are expressed in mg/L as CaCO3. <br /> 8 40 C.F.R. §131.38(c)(2)(iii) Table 4, notes 1 and 2 <br /> ATTACHMENT F— FACT SHEET F-16 <br />