Presentation Abstract

To help protect regional water quality, in 2012 King County initiated a study to review the impacts of combined sewer overflows (CSOs) and other sources of pollution to inform the region of the benefits of CSO control. King County’s Water Quality Assessment and Monitoring Study (Study) explored water quality in Lake Union/Ship Canal, Elliott Bay, and the Duwamish Estuary, where the County is planning projects to reduce the frequency of CSOs to an average of one untreated overflow per site per year over a 20-year moving average. Reducing CSO frequency to this degree is known as CSO “control” and is required by the terms of King County’s CSO consent decree and by Washington State requirements. Uncontrolled CSOs contribute about 85 percent of the annual fecal bacteria load to the waterbodies. Control of CSOs by 2030 is projected to reduce the total load by about 80 percent. The largest annual loads of copper are from leaching from antifouling vessel paint and stormwater discharges. Washington State laws to reduce copper in these products is projected to reduce copper loading by about 50 percent by 2030. The largest annual loads of polycyclic aromatic hydrocarbons (PAHs) are from leaching from creosote-treated pilings. Piling removal is projected to reduce PAH loads by 30 percent by 2030. Direct stormwater discharges and upstream sources are the predominant loading pathways for other contaminants studied. Annual load reductions of less than 10 percent were projected by 2030 for the other contaminants. The Study demonstrates that CSO control will substantial improve bacteria levels in the waterbodies, but that additional water quality improvement projects are needed to meet surface water quality standards for other contaminants.

Session Title

Monitoring Stormwater Impacts on Contaminants in Receiving Waters

Keywords

CSOs, Duwamish, Elliott Bay, Lake Union, pathways, water quality

Conference Track

SSE3: Fate, Transport, and Toxicity of Chemicals

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE3-642

Start Date

6-4-2018 1:30 PM

End Date

6-4-2018 1:45 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 6th, 1:30 PM Apr 6th, 1:45 PM

Past, present, and future water quality in Lake Union/Ship Canal, Elliott Bay, and the Duwamish Estuary and the benefits of combined sewer overflow control and other projects

To help protect regional water quality, in 2012 King County initiated a study to review the impacts of combined sewer overflows (CSOs) and other sources of pollution to inform the region of the benefits of CSO control. King County’s Water Quality Assessment and Monitoring Study (Study) explored water quality in Lake Union/Ship Canal, Elliott Bay, and the Duwamish Estuary, where the County is planning projects to reduce the frequency of CSOs to an average of one untreated overflow per site per year over a 20-year moving average. Reducing CSO frequency to this degree is known as CSO “control” and is required by the terms of King County’s CSO consent decree and by Washington State requirements. Uncontrolled CSOs contribute about 85 percent of the annual fecal bacteria load to the waterbodies. Control of CSOs by 2030 is projected to reduce the total load by about 80 percent. The largest annual loads of copper are from leaching from antifouling vessel paint and stormwater discharges. Washington State laws to reduce copper in these products is projected to reduce copper loading by about 50 percent by 2030. The largest annual loads of polycyclic aromatic hydrocarbons (PAHs) are from leaching from creosote-treated pilings. Piling removal is projected to reduce PAH loads by 30 percent by 2030. Direct stormwater discharges and upstream sources are the predominant loading pathways for other contaminants studied. Annual load reductions of less than 10 percent were projected by 2030 for the other contaminants. The Study demonstrates that CSO control will substantial improve bacteria levels in the waterbodies, but that additional water quality improvement projects are needed to meet surface water quality standards for other contaminants.