Salmon-killing chemicals can be treated with bioretention, but King County says no

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Image of a bioretention facility in the town of Mill Creek. (photo by author)

Bioretention was approved for use as a stormwater treatment facility by the Washington State Department of Ecology over six years ago. But King County is lagging behind in adoption.

Bioretention is a versatile stormwater management facility and the only known water quality treatment method to combat 6PPD, a pollutant that research has linked to coho salmon deaths. 6PPD is an additive to extend the life of car tires. The toxic pollutant was discovered in stormwater runoff entering our streams.

Other water quality features such as sand filters, grass-lined bio-troughs, and retention ponds have not demonstrated an ability to address 6PPD.

Bioretention consists of an imported soil mix, plants and mulch installed to create a shallow depression for rainwater to collect. Its purpose is to capture and filter stormwater runoff, resulting in a reduction in pollutants escaping the system.

King County Executive Dow Constantine generally takes a pro-environmental stance, trying to be a frontrunner in climate action and defender of iconic species like coho and orca whales. However, he has left the district behind on the issue of bioretention.

As a civil engineer, I have specified bioretention for use in numerous jurisdictions in the Puget Sound region because it is a green, environmentally friendly method of treating stormwater runoff that is better suited to protecting salmon runs than traditional stormwater treatment systems. I’ve used it in Snohomish County, the town of Mill Creek, and in Bellevue.

In a design I created in unincorporated King County, I proposed vehicular access to a new home via a circular driveway and bioretention system within. I was pleased to provide a design that harmonizes the functional use of bioretention to capture and treat stormwater runoff from the proposed driveway while providing an aesthetically pleasing landscape feature for the homeowner.

An aerial view of the bioretention design submitted to King County for author’s approval review.

King County decides to publish its own King County Stormwater Management Manual (KCSWMM). Additionally, King County cities may adopt the KCSWMM or use the Washington State Department of Ecology Stormwater Management Manual for Western Washington. The City of Sammamish has adopted the KCSWMM and the City of Bellevue uses the State Manual.

The KCSWMM is a draft document to ensure that stormwater runoff from new hardscape surfaces is mitigated through the installation of approved stormwater management devices. The handbook provides the details and standards of applicability for stormwater designs.

Although I have submitted several designs for stormwater systems in King County, the design I submitted in early 2019 was the first time I have proposed a water quality control bioretention system in unincorporated King County.

Rainwater wet basins and a combined retention system allow sediment to settle on the pond floor. (Image credit: Environmental Protection Agency)
A sand filter bioretention system. (Source: Chesapeake Stormwater Network)

I was surprised when my design was rejected and returned with a comment that bioretention is not permitted for use as a water quality treatment facility in unincorporated King County. Of the 25+ municipalities in which I provide design services to clients, King County is the only jurisdiction I am aware of that does not allow treating water quality through the use of bioretention.

So I asked King County officials what authority they have to ban the use. I met with Department of Permitting and Environmental and Review (DPER) staff in 2019 and was unable to get a satisfactory answer. It is a system that has been tested by the Washington State Department of Ecology and meets the requirements of the Federal Clean Water Act.

Several DPER employees were surprised to see the vocabulary in the King County mManual and said they would question the Water and Land Resource Division, WRLD employees.

Later in 2019 I spoke to John Taylor of the King County Department of Local Services and he announced that in 2014 the Water and Land Resource Division (WLRD) staff met and checked among themselves and determined that King County did not have bioretention permit would be used within their jurisdiction, which is unincorporated King County.

In May 2022, after the shutdown was disrupted by Covid-19, he tried to get moving again and corresponded with Curt Crawford, Section Manager of Rainwater Service at WLRD, and Josh Baldi, Section Manager of WRLD. I pointed out the new 6PPD research and requirement that all jurisdictions be required to use DOE approved water quality equipment.

The following excerpt is from the 2019 DOE Stormwater Management Manual and provides an explanation of Washington State law requiring all jurisdictions to use DOE-approved water quality equipment.

In August, I met again with WRLD, including Curt Crawford, and despite the relevant and persuasive information discussed, the staff maintained their position that they have no intention of reconsidering the use of bioretention facilities for use in King County as a water quality treatment facility . I have pointed out that the district is required by law to accept “all known available reasonable technology” and that bioretention is uniquely suited to treat 6PPD tire pollution and thereby protect salmon runs, but was unsuccessful.

King County’s position to ban the use of bioretention is illogical, ignores current rule of law, and could have devastating long-term effects on salmon stocks.

Although King County positions itself as an environmental leader, employees appear to make their own policy decisions that are inconsistent with those leadership goals.

King County was contacted for comment but did not respond prior to the publication of this article.

The August 17, 2022 Zoom meeting information can be confirmed by:

  • Lisa Harbert, PE, (Professional Engineer) Harbert Engineering
  • Haim Strasbourger, PE City of Sammamish, Development Test Engineer

For those interested in attending, the ASCE (American Society of Civil Engineers), Seattle Section Committee has an upcoming meeting on September 21st.



Donna Breske (guest post)


Donna Breske is a licensed professional engineer in Washington state. She owns Donna Breske & Associates and her associates provide land use consulting and civil engineering design services for numerous infill projects in multiple jurisdictions in the Puget Sound area. She holds a Bachelor of Science in Civil Engineering from the University of Washington and an MBA from Seattle University. She is married to her husband Fred, with whom they share two adult children. Raised in Seattle, she is passionate about removing absurd regulatory roadblocks and ensuring consistent and predictable results.

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