February 10, 2025

National Finalist: Gold Award
Energy

Photo from ACEC Washington [enlarge]

The 16.8-megawatt battery system ensures continuous pump operation during power outages.

Brown and Caldwell

West Point Power Quality Improvements

King County

The King County Wastewater Treatment Division serves nearly 2 million people across 424 square miles near Puget Sound, ensuring effective wastewater treatment while protecting water quality. Operating three regional wastewater treatment plants, including the West Point Treatment Plant (WPTP) in Seattle, the division plays a critical role in maintaining public health.

The plant, the largest in the region, processes an average of 95 million gallons of wastewater per day and uses high-purity oxygen secondary treatment before discharging into the Puget Sound.

In 2021, King County Executive Dow Constantine signed an emergency declaration to enhance the plant’s resilience to power disruptions caused by severe weather. Voltage sags, or temporary power losses, cause large pump motors to shut down. The time required to safely restart the pumps can lead to wastewater discharges into the Puget Sound during periods of heavy flow. With the increasing frequency of such disruptions due to climate change, improving the resiliency of West Point’s electrical power supply has become essential to prevent wastewater releases and protect water quality.

To address the wastewater releases, King County partnered with Brown and Caldwell, Hoffman Construction Company and other partners to design and install a 16.8-megawatt battery system, integrating 48,000 battery cells into the facility’s electrical system. This system ensures continuous pump operation during power outages. The project, the largest application of uninterruptible power supply at a wastewater treatment plant in the U.S., was completed in just 3.5 years, a significant achievement compared to the typical seven-to-10-year timeline for such large-scale public agency projects.

In November 2024, the WPTP successfully passed its first major test, maintaining steady power through seven voltage sags during a severe weather event. The on-site battery system will continue to safeguard water quality by preventing wastewater discharge into Puget Sound for years to come.

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