SE 172nd Street Water Quality Retrofit Project

Contact Information
Kevin Evans, P.E.
Surface Water Engineer
Renton, WA 98057

Formerly known as the SE 172nd St & 125th Ave SE Green Stormwater Infrastructure Design project.

The SE 172nd Street Water Quality Retrofit project will improve the water quality of stormwater runoff from over two acres of residential roadway near the intersection of SE 172nd St & 125th Ave SE. The project will also provide improvements to the stormwater conveyance system and pedestrian safety.

Partial funding of this project is being provided by the Washington State Department of Ecology’s (Ecology) Stormwater Grant Program in the amount of $3,225,000. Additional funds required for project design and construction will be provided by the Surface Water Utility’s capital improvement program.

Contract Award Information

The Surface Water Utility solicited proposals from consultants in accordance with City policy 252-02. Five proposals were received and evaluated, and two consultant firms were selected for interviews. Osborn Consulting, Inc. ranked the highest and was selected to perform the work.

Council awarded the professional services contract to Osborn Consulting, Inc., in the amount of $257,889, at its regularly scheduled meeting on April 15, 2019. This contract has since been amended in the amount of $360,165.

Project work under the contract agreement and amendment includes survey, geotechnical, and civil engineering design services.

Project Description

This project will improve the water quality of stormwater runoff from roadways before it enters downstream natural systems. Roadway runoff is currently discharged untreated to a wetland south of 127th Avenue SE and SE 172nd Street. This stormwater continues south until eventually discharging into Big Soos Creek, a stream with known water quality issues related to pH, dissolved oxygen, and ammonia levels. Using Ecology-approved biofiltration systems, this project will provide enhanced basic water quality treatment to stormwater runoff from approximately 14 acres of area containing approximately 2 acres of untreated roadway.

This project will construct new stormwater conveyance pipe and catch basins to increase conveyance capacity of the stormwater system and reduce the likelihood of flooding. In order to help mitigate risk to homeowners and prevent future intrusive maintenance work, upstream stormwater runoff will be rerouted away from existing stormwater pipe systems running through homeowner properties and into the new stormwater system. 

New pervious concrete sidewalks will be constructed on one side of each street within the project area. In tandem with new curbs, gutters, and landscape strips, the pervious concrete sidewalks will improve pedestrian safety by providing a pedestrian path separated from traffic by a landscape strip. Additionally, the porous nature of the pervious concrete sidewalks increase pedestrian safety and provide runoff mitigation for the new sidewalk surfaces.

Project Updates

Completed project milestones are as follows:
April 2019: Awarded professional services contract to Osborn Consulting, Inc.
July 2019: 30% Design Complete
September 2020: 60% Design Complete
August 2021: 90% Design Complete
March 2024: 95% Design Complete

Construction expected to begin in the fall of 2024.

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