April 5, 2015

New Stormwater LID Rules Take Effect in Western Washington’s Major Urban Areas in 2015

By Sarah Washburn

Washington State recently introduced new stormwater management rules that incorporate Low Impact Development (LID) techniques.  Under the new rules, Washington counties and cities will have a legal obligation to prevent pollution from stormwater that washes over roofs, driveways, and developed areas.  The new rules will require many future developments to incorporate certain LID techniques.  These techniques are intended to mimic natural rainwater absorption processes and include rain gardens, bioretention facilities, and permeable pavement materials.


Washington State Municipal Water Permits govern how cities and counties manage stormwater runoff.  Three separate permits governing different parts of the state were updated in August 2013, and LID requirements were added.  The Phase I permit applies to Seattle, Tacoma, and the four most populous counties in Western Washington.  The new permits require Phase I cities and counties to enact codes incorporating LID measures by June 30, 2015.  The remaining areas of Washington are governed by either Phase II (Western Washington), which covers 80 cities and the urban portions of four counties, and Phase II (Eastern Washington), which covers 18 cities and the urban portions of six counties.  Phase II jurisdictions have later enactment requirements – December 31, 2015 for Phase II (Western Washington), and December 31, 2017 for Phase II (Eastern Washington).  

In Western Washington, most new developments that create at least 2,000 square feet of hard surface area or that disturb more than 7,000 square feet of land will have some LID requirements.  Projects in Western Washington will have two options for complying with LID requirements – choose from a list of LID Best Management Practices or meet the State’s Low Impact Development Performance Standard.