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35th Avenue SE Reconstruction
Overview
35th Avenue SE is a three-lane minor arterial in Mill Creek that carries approximately 15,000 vehicles per day. The road was widened by Snohomish County in 2003 by using lightweight fill on top of a large peat deposit. The road has been continually settling.

The City monitors over 100 points along the roadway on a six-month basis. The rate of settlement has slowed, but portions of the road have settled over two inches in the past three years and two feet over the past 10 years.

One of the biggest areas of settlement is over the Penny Creek crossing between 144th Street SE and 141st Street SE, which also has the deepest deposit of peat material as a base. The water level in the surrounding wetlands has also increased due to several factors such as upstream development and downstream beaver activity. The rising water combined with a sinking roadway has resulted in several road closures over the past few years due to flooding.

Reconstruction Project
The City is undertaking a reconstruction project to fix the road between 141st Street SE and 144th Street SE to eliminate flooding and associated road closures.

Work includes driving approximately 500 pin-piles through the peat into good bearing soil, constructing a concrete slab on top of the pilings, and then reconstructing and elevating the roadway on top of lightweight concrete fill. The project will raise the road elevation up to four feet above the existing roadway elevation.

The project also includes installing a 24-inch pipe above the existing Penny Creek culverts to increase water conveyance capacity under the road during large rainfall events.

In addition, the work includes treating stormwater from the roadway, which currently flows directly into the adjacent wetland without any treatment. Water quality and the method of distribution into the surrounding wetlands will be improved. Fish and wildlife will indirectly benefit from the improved water quality resulting from stormwater runoff treatment.

The width and alignment of the roadway will not change.

Timing
Reconstruction is projected to begin in early spring 2018 in order to coordinate with the planned Snohomish County project to widen Seattle Hill Road between 35th Avenue SE and 132nd Street SE. Each project is the detour route for the other, so both should not be under construction at the same time. The construction of the County project will occur first, likely starting in early 2017, and should take most of the year to complete.

The 35th Avenue project could be advertised for bids in late 2017 or early 2018 with construction starting that spring, depending on the county’s Seattle Hill Road project. Construction will take approximately eight months to complete.

Construction may occur between 7 a.m. and 9 p.m. Monday through Friday, or between 8 a.m. and 9 p.m. on weekends. Equipment is anticipated to run during normal working hours of 7 a.m. to 5 p.m. Monday through Friday for the majority of the project.

The pile-driving activity will be conducted over a duration of 70 working days.

Detours
The 35th Avenue SE corridor is a minor arterial in Mill Creek. A detour plan, including routes and signs, has been prepared and will be provided to the community with ample notice. Traffic that normally utilizes 35th Avenue SE as a thoroughfare will be detoured to Seattle Hill Road (local access will still be available via 3th Avenue SE).

Cost
The total cost is estimated at approximately $5.5 million.

The State Department of Transportation office has included a $4 million funding package for this project by the City of Mill Creek. This funding will become available in 2017.

The remaining funding will be provided through the City’s Real Estate Excise Tax fund.

Environmental Impacts
The project will require work over Penny Creek, where it crosses beneath the 35th Avenue SE roadway via two 54-inch culverts, and in the adjacent wetlands on the west side of the roadway and the east side of 35th Ave SE.

Raising the height of the roadway will require alteration of the existing stormwater discharge points into the adjacent wetland. The replacement storm drain lines will be placed a short distance into the wetland. A minimal amount wetland vegetation will be damaged or removed during excavation of the trenches to place the storm drain lines.

After the trenches have been backfilled and native soil placed where feasible, exposed soils and disturbed areas will be treated with native seed mix and willow stakes.

Groundwater encountered during construction will be discharged to an upland area or pumped into an above-ground tank and treated to meet state water quality standards.

There will be no discharge of waste materials to surface waters.

Update September 2015

An MDNS was issued for the 35th Avenue SE reconstruction on September 23, 2015:


35th Avenue Reconstruction Project Map
A map of the project area.