Toxic Chemicals in Puget Sound: The Impact of Mixing Zones on Permitted Discharges

Despite improvements in sewage and industrial waste treatment since the 1970s, harmful levels of toxic chemicals have continued to be legally discharged into Puget Sound.

People For Puget Sound conducted a study (Toxic Chemicals in Puget Sound:  The Impact of Mixing Zones on Permitted Discharges, June 2008) of the Sewage Treatment Plants and the major industrial facilities that send treated wastewater to our rivers, creeks and Sound.  Under Washington State regulations, facilities may discharge wastewaters with levels of pollutants above water quality standards in an area around their outfall pipe called “mixing zones.”

The study for the first time maps and analyzes the locations and configurations of mixing zones in the Puget Sound basin. The study supports the Puget Sound Partnership¹s efforts to assess toxics loading to Puget Sound and reduce those loadings to achieve the Governor¹s initiative to restore the Sound to health by 2020.

There are 103 municipal sewage treatment plants, 10 combined sewage overflow systems (CSOs) and 15 major industrial facilities in the Puget Sound basin, as of March 2007.  Total design flow from sewage treatment plants is over 260 billion gallons per year and from major industrial facilities is almost 43 billion gallons per year. 

We found that:

• The Federal Clean Water Act does not include explicit authority for allowing mixing zones, although USEPA has allowed States to permit them.
• Washington regulations are indefinite in not specifying exactly how aquatic life health in mixing zones should be measured, especially cumulative impacts.
• Washington regulators lack sufficient resources to assess aquatic health impacts and to address pollution prevention and source control strategies to reduce toxic chemical discharges.
• Mixing zones are used extensively in discharge permitting rather than being used as a last resort.
• To reduce toxic loadings from direct discharges, mixing zones should be phased out or significantly reduced.

The report was completed with the assistance of University of Washington Geographic Information System students.

Downloads:

		June 02, 2008 Press Release Download PDF (68kb)
		Impact of Mixing Zones Text and Tables Download PDF(1.2mb)
		Figures 1-4 Download PDF(696kb)
		Figures 5-7 Download PDF(540kb)
		Figures 8-13 Download PDF(860kb)
		Appendix 1-2 Download PDF(224kb)
		Appendix 3 Download PDF(448kb)
		Appendix 4 Download PDF(3.8mb)
		Fact Sheet Download (PDF 304kb)

For more information contact: Heather Trim | Urban Bays and Toxics Program Manager | 206.3382.7007 x215