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I } RPR 22 2003 02 36 FR WRIGHT WRTER <br />Memorandum to Mr. Henry Barbe <br />Apri121, 2003 <br />Page 2 <br />3034801020 TO 19709295595 <br />P.03i05 <br />The model predicted a relatively constant percent effluent for an LC50 for the first scenario <br />(48-50 percent ef#luent) at an alkalinity of 2,643 mgJL. It should be noted that this <br />concentration of alkalinity is well above the concentration predicted to result in a WET test <br />failure in scenario 1, above. <br />The results of the other two scenarios are plotted on the attached Figure 2. This figure <br />shows that the breakpoint for alkalinity that would result in a test failure (i.e., LC50 with <br /><100 percent effluent) is around 1,200 mg/L. <br />3) Review of PreVIOUS Data: WET test results for OutfalLs "MB-1" and "MB-2R", which <br />were used prior to Outfall 017, were reviewed to assess alkalinity concentrations, which <br />caused mortality in Daphnia These earlier data were reviewed even though flee water <br />chemistry may vary from that for Outfal! 017. <br />WET tests for 1996 for these previous outfalls show that the highest concentration of <br />alkalinity which produced no mortality in Daphnia was 1,276 mg/L (July 1, 1996 test for <br />Ouffall MB-2R). <br />RECOMMENDATION <br />The above three evaluations indicate a breakpoint of aoound 1,200 mg/L for mortality to Daphnia <br />from alkalinity. In order to provide a buffer to minimize the confounding influence from alkalinity, <br />it is recommended that the maximum alkalinity of water be 1,000 aig/L in futtffe WET testing. <br />C:1PF~831-0321580mdsMcc.wctdkdoc <br />