UPDATED: We’re working to improve power supply quality at West Point Treatment Plant to continue our clean-water mission

Power disruptions during heavy rainfall

  • collage of all the images in this slideshow
  • CoGen system
  • CoGen power controls
  • A battery system drawing by Hitachi
  • Southern California Edison's battery system
  • Aerial view of West Point Treatment Plant

As a clean water agency, our mission is to protect public health and the environment. We work 24/7 to serve over 1.8 million residents and clean about 190 million gallons of water per day. Even in massive rainstorms that generate more volume than the system can handle, we feel bypass of our treatment plants is unacceptable.

West Point Treatment Plant on average experiences a disruption in power every two months.  Most of the time, we are able to store incoming wastewater-stormwater flows and get all the systems running smoothly again. However, when power disruptions happen during heavy rain, we don’t always have enough room to store flows and can be forced to use the bypass to protect the plant and workers from flooding. As climate disruptions become more frequent, West Point is expected to experience more days of maximum flows. 

Most power disruptions are in the form of voltage sags. From a residential perspective, a voltage sag is similar to the lights in the house flickering, while a power outage would be equivalent to losing all power in the house. The difference is, it takes a lot more energy to safely clean wastewater than keep the lights and appliances on in a house, and the existing West Point peak demand of 10 Megawatts is equal to the power needs of 11,000 homes.

Power disruptions, including voltage sags, cause our equipment to turn off and requires West Point operators to manage and restart the equipment. When shutdowns happen and there isn’t enough capacity in the system to store incoming stormwater and wastewater flows, the plant performs as it was designed, and directs flows through the emergency bypass directly into Puget Sound to protect the plant and employees.

UPDATE: Fast-tracking power improvements

On Feb. 25, 2021, King County Executive Dow Constantine transmitted legislation to the King County Council and signed an emergency declaration that would authorize up to $65 million to provide West Point with more reliable power in response to increasing power disruptions. The package would look at either modifying on-site power generation at West Point, or using a large battery system to help buffer the power supply – allowing plant equipment to continue operating during power disruptions. This work is expected to be completed within 24 months because of the declaration of emergency.

Also included in the funding package is $3 million to analyze schedules and cost estimates of bringing dedicated high-voltage power lines to West Point (see more below).

Working with Seattle City Light

West Point Treatment Plant relies on power supplied by Seattle City Light. The other two King County wastewater treatments at South Plant in Renton and Brightwater, north of Woodinville, are serviced directly by high-voltage power; neither has bypassed stormwater and wastewater as a result of power problems.

In 2019, King County and City Light partnered to perform a study to:

  • Characterize the nature of voltage sags at West Point.
  • Understand the critical systems at West Point impacted by voltage sags.
  • Recommend measures for City Light and King County to consider that reduce bypass events caused by voltage sags.

The study was completed in May 2020. As a result, we have adjusted the tolerance level of the large pumps that rely on electricity, so that they can withstand or “ride out” a three-second sag. We cannot adjust them any further for fear of power disruptions ruining the equipment that treats the wastewater.

Our capital budget and planning experts are evaluating the technology available to further reduce the influence of power disruptions, including upgrading older systems to increase power reliability, and evaluating future planned improvement for power.

In addition, King County and City Light will be evaluating the potential to build a new transmission level power line to West Point.

Continuous improvement at West Point

We’ve made significant improvements over the past four years at West Point to make it more resilient to storms and power fluctuations.

  • Improved safety protocols include:
    • Enhanced staff training;
    • Installed new electrical and control systems;
    • Added redundancy at pump stations; and
    • Made the equipment less sensitive to power fluctuations.

We take our responsibility to treat wastewater, protect public health and the environment seriously, and ensuring we have reliable power is essential for fulfilling our mission.

FOR MORE INFORMATION, CONTACT:
Marie Fiore, 206-263-0284 or mfiore@kingcounty.gov