EXH0708026404

5808 Lake Washington Blvd. N.E. Suite 200 Kirkland. WA 98033-7350 425-822-8880 * Fax: 425-889-8808 MEMORANDUM To: Paul Fendt July 1, 1998 From: Ken Ludwa_c" 55-2912-01 Re:ResultsofReasonablePotentialAnalysis Thismemo istodescribetheresultsoftheReasonablePotentialAnalysis(R.PA)thatwas performedyesterdayfortheSTIA ThirdRunway area.The analysiswas doneina working meetingattendedbyLisaZinncr(Ecology),LoriTerry(Preston,Gates,andEllis),Tom Hubbard (POS),JohnRogers(CH2M Hill),BillTaylor(TaylorandAssoc.),JimGood,andmyself. LisaZinnerstatedatthebeginningofthemeetingthattheanalysiswas intendedtobeinformal. Some ofthedatausedwas basedon bestavailableinformationand professionaljudgment reachedbyconsensus. Theattachedspreadsheetdocumentstheprocess,whichwasperformedinsteps: I. DatafromouffaU005 (SDS-3)wasusedtorepresentthepredictedrunofffromthe ThirdRunway (withtwo 1996deicingsamplingeventsremovedfromthedataset). The geometric95thpercentileoftheSDS-3 datawas calculatedaspertheRPA methods.Thiswas doneby calculatingthenaturallogofeachparameter'sreported value,takingthe95thpercentileofthetransformedvalues,thentakingtheantilogof that value. 2. The criteria for Miller Creek and Des Moines Creek were determined, based on backgroundconditionandhardnessinformation.The fecalcoliformcriterionisthe limit set for all class AA waters. The turbidity criterion is based on observations made in Miller Creek during winter 1997-98 storms, for NEPL treatment plant and Lake Reba discharge monitoring (to be verified upon review of the dam). The metals criteria were based on a hardness of 23 ppm in Miller Creek, and 35.6 ppm in Des Moines Creek, as discussed in the STIA 1998 NPDES Permit Fact Sheet/Response to Comments (for comparison, metals criteria were also calculated for hardness values of 20 and 70 ppm). 3. Expected pollutant removal effieiencies for various BMPs were agreed upon. The - high andlowendsofthetreatmentrange,anda recommendedvalue,orbestguess, weredeterminedbasedontheresultsofa literaturereviewthatIhadperformedfor AR 026404 PnnteclonRecycledPaper To: Paul Fendt From: Ken Ludwa Date: July 1, 1998 Page 2 this analysis (summary attached). The literaturereview was not comprehensive, and consisted of a number of other compilations and project-specific studies. The values chosen for the RPA were weighted heavily on studies done after 1990. 4. The resulting predicted effluent pollutant concentrations (high, low, and best guess) were calculated based on the…

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Call to order – Roll Call – Quorum Established – Land Acknowledgement We would like to acknowledge that our Agency operates in four present-day counties, which are the traditional lands of the Coast Salish people, past and present. This acknowledgement does not take the place of authentic relationships with indigenous communities in our jurisdiction and [...]