Massive tunnels beneath the Rainier Valley bring the promise of clean water

After more than three years of construction, King County celebrated the Oct. 26 completion of its last major clean-water project to control overflows of untreated stormwater and sewage into Lake Washington with the Rainier Beach community.

The $77 million "Henderson/Martin Luther King Combined Sewer Overflow (CSO) Project" features a giant, 15-foot-diameter pipe that will hold millions of gallons of dirty water until it can be treated. It's creation promises to significantly reduce untreated discharges of combined stormwater and sewage.

Before this project, rainy weather contributed from 30 to 60 million gallons of untreated waste and stormwater overflowing into Lake Washington every year from sewer overflows throughout the county.

"With the project complete, CSOs will be dramatically reduced, and our beaches will be cleaner and safer," said King County Executive Ron Sims. "Completing this project upholds a clean-water legacy that residents established when they founded our regional wastewater treatment utility more than 40 years ago. These new facilities will add safeguards to protect water quality as we increase our attention on restoring Puget Sound. "

Sims thanked the Rainier Beach community, including neighboring Rainier Beach High School, for its patience and help during construction activities.

Along with helping to protect the water quality of Lake Washington, the completed project will provide many needed improvements to the Rainier Beach sewer system, much of which is more than 50 years old. The project includes more than two miles of tunnels and pipelines and expands the Henderson Pump Station and flow regulator facilities. Improvements include:

* The Henderson Pump Station can now push more than 20 million gallons a day of combined stormwater and wastewater away from Lake Washington.

* The package of pipelines tunneled and trenched along South Henderson Street and South Norfolk Street run from the shore of Lake Washington, beneath Martin Luther King Jr. Way South, under Interstate 5 and below the railroad tracks south of the King County International Airport.

* The huge 15-foot-diameter Beacon Hill Tunnel running two-thirds of a mile under 42nd Avenue South allows for critical storage and treatment.

* Two flow-regulator facilities at each end of the Beacon Hill Tunnel control water entering and leaving the storage facility.

During storms, the new tunnel under Beacon Hill can hold 4 million gallons of dirty water. After the storm settles down, the system will send flows to either the West Point Treatment Plant in Seattle or the South Treatment Plant in Renton. The tunnel runs two-thirds of a mile at depths of 30 to 100 feet beneath 42nd Avenue South.

More information about the project is available on the county Web site: For photographs of project construction, click on:

King County's Wastewater Treatment Division protects public health and water quality by serving 17 cities, 17 local sewer utilities and more than 1.4 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the county agency has been preventing water pollution for 40 years.

[[In-content Ad]]