Seattle Hill Road Improvement Project

LOCATION:  Mill Creek, WA TIMEFRAME: April 2017-Summer 2018 SCOPE OF WORK: Supply & Install 7 Brentwood Stormtank Systems with non-woven geotextile PROJECT PARTNERS: Owner: Snohomish County Public Works Contractor: Taylor’s Excavators Supplier: Layfield USA Ltd Engineer: City of Mill Creek

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Background Information and ChallengeSeattle-Hill-1.JPG

The Seattle Hill Road Improvement Project is a $13.2m project for road improvements in Mill Creek, WA. The project calls for 1.6 miles of roadway to be widened from 2 lanes to 3 for a center turn lane, resurfacing, regrading for fewer hills and sharp turns, dedicated sidewalks and bike lanes, planter strips, tree box filters, grass-lined retention areas, and porous concrete sidewalks. The project is a collaboration between Snohomish County Public Works and City of Mill Creek. Construction began on April 20, 2017 and is anticipated to complete Summer 2018.

The extant road had 15,000 passenger vehicles and 67 buses per day using a 2-lane road through a medium density residential district with ongoing development. The extant road had no dedicated turn lane causing traffic congestion at peak travel times, no dedicated sidewalks or bike lanes, a road surface full of potholes and alligatoring, frequent flooding due to an insufficient stormwater system, and frequent collisions due to reduced sight distance from local topography.

Brentwood and Layfield USA worked with Snohomish County Public Works to approve use of the StormTank system rather than a traditional stormwater detention system. This is a new system for Snohomish County.


Layfield USA provided and installed 7 roadside StormTank systems over the course of the 1.6 mile road improvement project which will provide retention of approximately 35,000cf of stormwater which can be pre-treated then metered into the local stormwater system.


Layfield USA supplied  approx..5,000 Storm Tank units. Taylor Excavators provided site preparation, which included excavation, liner installation, and subgrade crushed rock and will provide cover and attachment. The Brentwood systems will alleviate historic roadway flooding and soil saturation and allow pre-treatment prior to introduction in the general stormwater system.

The StormTank systems also provide a location for the introduction of porous sidewalks, bike lanes, and planter strips, replacing the current storm drain and dry well system which gave a very narrow road shoulder. The customer is pleased with the installation to date and Snohomish County intends to allow specification of  the Brentwood StormTank for future stormwater detention and retention applications. 3 of the 7 planned systems have been installed at this time, with the remaining 4 systems to be installed as road improvements progresses.