NE 40th Street Stormwater Treatment Retrofit

Graphic of NE 40th SW Treatment location - aerial photo

Project Overview

This project constructed a water quality treatment facility adjacent to the Overlake Technology Light Rail Station. The facility serves one of Redmond’s highest traffic volume (and highest pollutant load) areas by intercepting flow from SR 520 and NE 40th Street and discharging cleaned water to the existing drainage path, which eventually flows to Villa Marina Creek and Lake Sammamish. 

Untreated water is pumped from the existing storm trunkline in NE 40th Street to the surface, then drained through a Filterra Bioscape to remove oils and grease, sediment, dissolved metals and phosphorous prior to discharging into the existing drainage path. The Filterra Bioscape includes native plantings landscaped to enhance the aesthetic value of the light rail station. Discharging cleaned water into Villa Marina Creek will help protect Chinook, Kokanee, Coho and Sockeye salmon that inhabit these waters.

Grant Funding

Design and construction of the NE 40th Street Stormwater Treatment Retrofit project was primarily funded through the generous support of grants, with remaining funding ($100,000) from the Stormwater CIP. Grant funding is as follows: 

  • Microsoft Corporation – Community Facilities District – $2,077,565
  • Washington Department of Ecology – Water Quality Combined Assistance 2021 Grant – $3,592,500 
  • King County WaterWorks 2019 Grant – $150,000