EXH0630024560

Date: Tue, Jun 1, 1999 6:50 PM Subject: Receiving Stream Data: Upstream Compliance As Brian suggested, I looked at the receiving stream (upstream) data to determine whether the receiving stream is in compliance with standards. The best existing data that I've found for upstreamconditions is (I) the Stream Effects Study, and (2) the upstreamsamples we took for de-icing last winter. I have previously asked Scott and Tom about existing data. They've both suggested King County and the City of Des Moines Report,s, neither of which have any additional upstream data. Using methods analogous to the Reasonable PotentialAnalysis, I calculated the 90th percentile value for instream copper data and compared it to the standard for the 10th percentile hardness value. Neither stream is currently in compliance, as shown below: Stream 90th %lie Cu 10th %lieHard Standard Miller 16.4 23.0 4.3 DM 7.5 33.0 6.0 As we discussed, a WER of 2 or more for Des Moines and 4 or more for Miller (both of which seem like pretty reasonable bets) would get the receiving streams to "compliance." Also, if we do clean sampling techniques and they reflect lower instream concentrations, we may be able to throw out the previous data. CC: Brian Pippin AR 024560 EXH0630024560

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