EXH0271019507

- """_:_ overflows occur when the 50-year KCRTS period of record is simulated for the conditions described in Table 4-2. If any future additionaldiversion to the IWS is proposed, then the performanceof the IWS system will be evaluated prior to the diversion to verify that SMP performancestandardsarcmet. Table 4-2. I_S configuration (land use, stortge, treatnnut rate, discharge rate, number of overflows) Parameter Value [.and Use Till Grass 16.53acres Outwash Ca'ass g.16acres A_rt Fill 0.01aCztt Wetland 0.01 acres ImperviousArea 419.00 acres TOTAL 434.71 aa'u* Storage Volume Lagoon I 1.6mg Lagoon 2 3.3 rag Lagoon 3 72.0 mt TOTAL 76.9 mg Outfall Discharge Capacity 7.1 mild Treatment Rate 4.0 mgd Number of Overflows in 5U-yearSimulation 0 Treatment Rate at Which One Overflow Occurs 3.1 mlgd Treatment Rate at Which Two Overflows Occur 2.4 mlgd • Althoughall majorplannedadditionsto the IWSaremcluded,thisareaconservativelytncludesapprommately16acresof imperious areato accountforfutureumplmnedadditionstotheIWS. . " To demonstrateIWS performanceat reducedtreatmentrates, an analysis was also performed to determinethetreaUnentratesat which one and two overflowswould occurover the 50-yearKCRTS periodof record,withall other futureconditions(Table4-2) held constant(see AppendixZ). This analysis determinedthatone overflow would occur at a treatmentrateof approximately3.l mgd, and two overflowswouldoccurat a treatmentrate of approximately2.4 mgd. If the safe storage capacity of IWS storage is exceeded during extreme precipitationevents untreatedwaterwould ha,,eto be releasedto Des MoinesCreek. Thishasoccurredonly once under Comprehensive5tormwater Management Plan July 2001 5TIA Master Plan Update Improvements 4-8 5$6-29i 2-001(28) AR 019507 the current configuration of the IWS, during an extreme rain-on-snow event in December 1996- January 1997. The release lasted only a few hours. No petroleum hydrocarbons…

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PSCAA Advisory Council Meeting Agenda
Add to CalendarMWednesday Mar 11, 9:00am - 11:35am
1904 3rd Avenue, Suite 105, Seattle, WA 98101
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 [...]