Nancy Chambers of the Wallingford Community Council writes:
Wallingford CC has submitted a November letter to the Seattle City Council concerning excessive combined sewer outflow into Lake Union from outlet pipe #147 at bottom of Stone Way. Some highlights: Fecal coliform counts during overflow events have, at times, exceeded 1,000 times the quality standard. Ammonia & cyanide samples have also shown elevated levels. Though only one overflow event per year is officially permitted by a federal permit process, CSO #147 averages 45 outflows / year. Each stormwater event averages ~12 hours, resulting in more than 18 million gallons of sewage overflow annually.
CSO#147 is one of Seattle’s worst offenders, yet is currently listed as low priority in Seattle Utilities Long Term Control Plan. A similar outlet in Ballard is being addressed now, but #147 is not set to be fixed for 10 years or more. In that time, 2,000 or more additional residential units are anticipated to be built in CSO #147 drainage basin/Stone Way corridor before this problem is fixed.
Because of the steep gradient and amount of pavement in the #147 drainage area, it’s unclear how effective Green Stormwater Infrastructure (GSI) like swales and voluntary homeowner rain-gardens may be here. Cisterns and porous pavers may be the most helpful. Much of Wallingford may be ineligible for RainWise rebates for these solutions.
The text of the letter sent by the Wallingford Council to the Seattle City Council (click the image for the accompanying Powerpoint deck):
From: G. Lee Raaen, President, Wallingford Community Council
To: Seattle City Councilmembers
Re: Lake Union Outflow Contamination
Of significant and increasing concern in our community is the annual average overflow of 18,000,000 gallons of combined sewage(storm water, grey water and raw sewage) from the Combined Sewer Overflow (CSO) #147 Outfall into Lake Union located at the south end of Stone Way N. The overflows occur an average of about 46 times a year (the legal limit is once/year) mostly during rainfalls in the fall, winter and spring but occasionally in the summer. The source of flow into CSO #147 is from the subbasins 147A and B which drain the area located between Ashworth Ave. N. and Aurora Ave. N. and from 45th St. to Lake Union. The drainage area in the north part of the subbasins extends from Bagley Ave. N. to Fremont Ave N. Fecal coliform counts done during overflow events have, at times, exceeded >1000 times what water quality standards permit.Ammonia and cyanide samples have also shown elevated levels.
Needless to say this situation raises serious health concerns. It takes sewage contamination levels 48 hours to normalize after an overflow event due to the slow flow of lake water to the west. Taking this into account the Lake Union water extending from CSO #147 outfall pipe would be contaminated for about 100 days each year. The CSO #174 at the south end of the Fremont area also has significant sewage overflows.
As you are aware, the City of Seattle in conjunction with King County has developed the Long Term Control Plan which requires that capital improvements be made that will eliminate the overflow of storm water, grey water and raw sewage into our public waterways including Lake Union. The period from 2025 to 2030 has been set as a target date to complete all the construction projects that will resolve this problem. The Long Term Control Plan requires that this overflow problem be fixed within 12 or 17 years, but the CSO #147 problem, according to SPU sources, may not be fixed for 10 years or more.
This raises questions about the rapid development that is occurring in the subbasin areas 147A and B which includes the western part of Wallingford and the eastern part of Fremont. Building permits for large residential projects are regularly being approved for the Stone Way corridor and surrounding areas. This will significantly increase the flow of grey water and raw sewage that will overflow through the CSO #147 Outfall on rainy days. It appears that the problem of the contamination of Lake Union is going to get significantly worse before any scheduled improvements to the system.
We would appreciate your thoughts regarding the following questions:
- High density construction is of value, but should the permitting of large residential projects take into consideration the potential overflow impacts to our public waterways in the affected subbasins?
- Should further development be restricted or conditioned to avoid an increase in outflow contamination until the Control Plan can be implemented to accommodate its impacts?
- Should the storm water detention vaults in planned new buildings and other Green Stormwater Infrastructure (GSI) efforts be maximized to limit stormwater drainage into our sewers?
Thank you for your consideration of our concerns.
G. Lee Raaen, President
Wallingford Community Council