Planning commission approves stormwater swales to filter runoff before it reaches Medical Lake

The Medical Lake Planning Commission voted to approve a city proposal to install stormwater treatment swales at multiple discharge locations around Medical Lake, a project staff said is designed to remove about 90% of roadway pollutants before they enter the lake.

Planner Alisa recommended approval with conditions, saying the swales are treated as utilities under the shoreline master program and that final engineering, construction controls and operations-and-maintenance plans would be required. "Stormwater swales are considered a utility in the shoreline master program," Alisa told the commission during the Aug. 27 hearing.

The applicant — represented by city public-works staff and the city engineer — described the designs as grassed bioinfiltration swales with a treatment soil layer and underdrain that will drain within 72 hours. "The whole goal is to remove 90% of the constituents that come off of the roadway and end up in your lake," said Scott Duncan, the city’s public works director.

Several residents raised concerns about shoreline erosion, seasonal lake-level fluctuations and the potential for swales to sit near wetland buffers. One longtime resident described worsening algae and shoreline erosion: "I used to be able to dive off my dock and swim out. Now if I were to do that, I'd come up looking like the creature from the Black Lagoon," the resident said.

Staff acknowledged those concerns and said wetlands specialists will review any sites that appear to be in buffers; Department of Ecology must also approve the project before construction. The commission moved to approve "option 1" — staff’s recommended approval with the conditions listed in the staff report — and carried the motion by voice vote.

Next steps include final engineering review by the city, coordination with Ecology and any additional critical-area reviews if work encroaches on wetland buffers.