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Wallingford CSO #147. How might we mitigate excessive number of overflows/year into Lk Union while embracing further high-density development?. CSO # 147 @ bottom of Stone Way Out of Compliance!. CSO#147 overflows more than any other, per 2010 Long term Plan ( Appendix C--Table C2 .).

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wallingford cso 147

Wallingford CSO #147

How might we mitigate excessive number of overflows/year into Lk Union while embracing further high-density development?

cso 147 @ bottom of stone way out of compliance
CSO # 147 @ bottom of Stone WayOut of Compliance!

CSO#147 overflows more than any other, per 2010 Long term Plan (Appendix C--Table C2.)

npdes permits
NPDES permits
  • The NPDES Permits allow wet weather discharges of untreated sewage & stormwater from CSO outfalls (like CSO#147) listed in the PERMIT to various receiving waters,e.g., Lake Union!
  • Current NPDES permit allows for 1 overflow per year from CSO’s. (#147 averages 45 overflows/year.)
rcw 90 48 480 reduction of sewer overflows
RCW 90.48.480Reduction of Sewer Overflows
  • The department of ecology shall work with local governments to develop reasonable plans and compliance schedules for the greatest reasonable reduction of combined sewer overflows. The plan shall address various options, including construction of storage tanks for sewage and separation of sewage and stormwater transport systems. The compliance schedule shall be designed to achieve the greatest reasonable reduction of combined sewer overflows at the earliest possible date. The plans & compliance schedules shall be completed by January 1, 1988. A compliance schedule will be a condition of any waste discharge permit issued or renewed after January 1, 1988.
what we know
2007 - 2011 CSO #147 was significantly above the once/yr regulation overflow.

Averaging 45.6 overflows per year!

Averaging 542 hrs of overflow per yr! ~12 hrs per event

Averaging 18,419,784 gallons/yr of EFFLUENT into Lake Union.

Excessive overflows from #147 Stone Way N. -- likely to be adversely impacted by future high-density additions, if not addressed. Currently low priority!!?

What we know!
what we don t know
What we don’t know…
  • Given that Stone Way has been historically a commercial strip & as such has a lot of paved area & has a distinct grade from 45th to Lk Union, can green measures be effective in such an environment… (Most GSI swales, rain gardens, etc. tend to be on more level ground or in small gulleys in more leveled areas.) Will the Stone drainage need a more mechanical fix?
long term control plan
Long Term Control Plan
  • #147 is "low priority" for City of Seattle CSO Capitol improvement Plan. May not be fixed for 10 or more years!
  • Can Green Stormwater Infrastructure (GSI) control CSO#147 (with all the pavement in area) & how & when will this be implemented.
  • http://www.seattle.gov/util/groups/public/@spu/@drainsew/documents/webcontent/01_026050.pdf
overall ammonia cyanide fecal coliform etc
Overall Ammonia, Cyanide, Fecal coliform, etc.

Combined drainage days for all of Seattle represent approximately 30% of the year

current questions
Current Questions
  • Can we get an expert from Seattle Public Utilities to come & clarify where lower Wallingford Main & Sanitary lines drain & if they contribute to CSO#147?
  • How do they see further/future high-density impacting CSO#147?
  • Can City move forward sooner with #147, if high-density is a value?
  • Should further permits for h-d construction in subbasin 147A be approved prior to updating?
  • Combined Sewer Overflow Reduction Program -- 2011 Annual Report: Sewage Overflow Prevention / Seattle Public Utilities. p. 5, 66: http://www.seattle.gov/util/groups/public/@spu/@usm/documents/webcontent/01_016565.pdf
  • Seattle Side Sewer Cards & Maps: http://web1.seattle.gov/dpd/sidesewercardsv2/
  • Protecting Seattle’s Waterways: Community Guide to the Plan; Issue 2, Spring 2013 / Seattle Public Utilities.(long term plans for CSO#147!) http://www.seattle.gov/util/groups/public/@spu/@drainsew/documents/webcontent/01_026050.pdf
  • Sub-basin 147A Monitoring Site Location Map
  • CSO Overview & Issues of NWRO (PowerPt), 2010: http://www.ecy.wa.gov/programs/wq/permits/csodocs/csoover.pdf
  • Focus on Sewage & Stormwater: Protecting our Waters from CSO (Feb. 2011): https://fortress.wa.gov/ecy/publications/publications/0010080.pdf
  • Major Lakes Monitoring -- Lake Union:http://green.kingcounty.gov/lakes/lakeunion.aspx
  • GSI = Green Stormwater Infrastructure, e.g. roadside rain gardens, permeable pavements, downspout disconnects?
  • Stormwater storage tanks: Fremont-Wallingford, 3 million gallons storage currently needed (SPU’s Protecting Seattle’s Waterways: Community Plan, 2013. p. 8)
  • RainWise = Managing stormwater @ home: http://www.seattle.gov/util/MyServices/DrainageSewer/Projects/GreenStormwaterInfrastructure/RainWise/index.htm