- Prevent constant flooding in areas with lots of pavement: The ponds are built to accommodate daily water runoff from the road and major 100 year storm events.
- Improve water quality: The ponds filter out oil and hazardous metals from surface water from the road, protecting ground water and sensitive waterways near the project.
- Prevent erosion: The ponds meter the release of water. This ensures that the increase in highway runoff from the new pavement will not damage the banks of sensitive waterways such as the Hylebos Creek.
Pond near Weyerhaeuser Way in the city of Federal Way along I-5.
A total of
six ponds will be constructed between 320th and the city of Milton along Interstate 5 as a part of the Pierce County Line to Tukwila stage 4 project. The six ponds can treat water runoff from approximately 2.23 million square feet of roadway surface. The average cost per square foot to construct was only 67 cents.