|The I-405 Bellevue to Lynnwood project reuses soil moved|
from other parts of the project area to build retaining walls,
shown above, and sections of new roadway.
As part of the I-405 NE 6th Street to I-5 Widening and Express Toll Lanes Project, our crews and contractor, Flatiron Constructors, are using a number of sustainable practices to build a better project for our environment and taxpayers. In this case, going green also helps us save a little green. And who doesn’t like that?
So what are we doing to reduce our carbon footprint?
|To reduce impacts on nearby aquatic resources, project crews|
have built three mitigation sites. Improvements completed this
October in Kirkland, shown above, include new trees,
plantings, rocks and drainage pipes.
Major construction projects typically truck in thousands of cubic yards of soil, crushed rock and other organic materials from off-site locations. Using a little creativity, we were able to design the I-405 project and schedule the construction in a way that recycles tested and approved soil and earthen fill material directly from the project site. We then use the recycled soil and fill material in other places on the job. For example, we’re building two retaining walls and a noise berm in Kirkland by reusing earthen material dug up from the footprint of a new northbound I-405 on-ramp in Bothell and other locations throughout the project area.
By reusing soil on site instead of disposing it off-site and buying new material, our crews:
- Cut back on heavy trucking at longer distances.
- Save fuel and decrease carbon emissions.
- Prevent damage to our roads.
- Reduce the cost and space used at off-site disposal locations.
Recycling demolished concrete structures
We’re removing many concrete structures, such as roadway barriers, so that they can be updated to current standards. For this project, crews haul all of this rubble to local recycling facilities that process and repurpose the steel and concrete for other local projects.
Recycling old asphalt pavement
We’re also removing existing asphalt pavement that is past its service life. Crews are grinding and breaking the removed asphalt to build temporary access roads and embankments, as well as reprocessing it back into new asphalt for this and other local projects.
Installing bioswales: smarter drainage ditches
Urban stormwater – the rain and snow melt that runs off surfaces like rooftops, sidewalks, paved streets, highways and parking lots – is one of the biggest environmental threats to the Puget Sound region. Left untreated, stormwater runoff can carry pollutants like oil, fertilizers and pesticides into our waterways, harming creeks, streams and rivers that provide important habitat for fish and wildlife.
Cleaning pollutants from this water and reducing the rate of runoff is a critical component to the Bellevue to Lynnwood project in order to help protect the many nearby wetlands.
To clean pollutants and control the rate of runoff, this project will construct:
- Eight new or enlarged standard treatment and detention ponds.
- 3,550 linear feet (more than half a mile) of biofiltration swales, also known as bioswales, which help capture and treat stormwater by filtering the water through vegetated channels comprised of organic materials like grass and shrubs.
- 11,200 linear feet, or more than two miles, of new media filter drains, which we construct along the highway shoulder area. The media filter drains consist of a no-vegetation zone, a grass strip and a mix of native vegetation. These pollutant filters are great for where there is limited space.