West Point Treatment Plant suffered severe equipment failure and flooding early in the morning of Feb. 9, 2017, while operating at maximum capacity during a storm. The flooding severely damaged mechanical and electrical systems needed to provide secondary treatment of the wastewater and provide heat to the solids reduction biology, which essentially crippled the plant’s solids handling capabilities. For three months, the plant was unable to treat to secondary levels required under its state and federal permits.

In response to the incident, WTD completed a number of upgrades and improvements at West Point following the recommendations of its initial root cause analysis and an independent review commissioned by the King County Council. All repairs critical to plant operations were completed in April 2017. The plant resumed full compliance with environmental permits in May, and all long-term repairs and upgrades were completed as-scheduled by the end of 2017. Improvements also include strengthened safety training and clearer emergency protocols to protect workers and equipment.

Reports and resources

• King County Council's Independent Review reports:
  • Final Report - Implementation Plan for AECOM Recommendations Q3 2019 , November 2019
  • Final Report - West Point Treatment Plant Independent Evaluation of Mitigation Strategies , March 1, 2019
  • Final Report - West Point Treatment Plant Independent Assessment , July 18, 2017
  • Presentation to the King County Council on the Independent Assessment of the West Point Treatment Plant , July 18, 2017
• Frequently Asked Questions – West Point Treatment Plant Restoration , revised May 19, 2017
• Presentation: Restoring the West Point Treatment Plant , March 18, 2017
• West Point Flooding Preliminary Findings Report, March 10, 2017 - 55MB
• Letter to Council , March 7, 2017
• Executive Summary – West Point Flood Investigation Findings Report , March 7, 2017
• System flow map
• Float switches

Marine monitoring

King County has completed analysis of water quality monitoring data that were collected during the restoration of the West Point treatment facilities damaged by the flooding of the plant that occurred on February 9, 2017. The West Point Flooding Event Water Quality Monitoring Report (27MB) was peer-reviewed by three external scientists and presents the data and findings regarding the effects of the flooding event on effluent and marine water quality.

• West Point Flooding Event Water Quality Monitoring Report , February 2018
• June 23, 2017 update
• June 9, 2017 update
• May 26, 2017 update
• May 12, 2017 update
• April 28, 2017 update
• April 14, 2017 update
• March 31, 2017 update
• March 17, 2017 update
• Summary: Marine and Environmental Monitoring Results as of June 23, 2017

Environmental monitoring

King County monitors the West Point wastewater coming into the plant (influent) and the discharge to Puget Sound (effluent) for multiple parameters that can affect water quality: flow, total suspended solids, biochemical oxygen demand, pH, fecal coliform bacteria, residual chlorine, and nutrients. These parameters are routinely sampled either daily, weekly, or monthly, as required in the NPDES permit for West Point that is overseen by the Department of Ecology. This data is used with the marine water quality monitoring data, and compared to permit limits.

West Point Treatment Plant Restoration Routine Effluent Water Quality Monitoring Data

• June 23, 2017 update
• June 9, 2017
• May 26, 2017
• May 12, 2017
• April 28, 2017
• April 14, 2017
• April 7, 2017
• Chronic whole effluent toxicity report  (April 27, 2017, summary pages)
• Acute whole effluent toxicity report  (March 31, 2017)

West Point Treatment Plant Restoration Effluent Priority Pollutant Monitoring Data

• June 23, 2017 update
• June 9, 2017
• May 12, 2017
• April 28, 2017
• April 7, 2017

West Point Treatment Plant Restoration Near-Field Effluent Mixing Water Quality Analysis

• June 12, 2017 update
• May 12, 2017
• April 28, 2017
• April 7, 2017

Discharge Dispersion in Puget Sound

Map of Typical Winter/Spring Dispersion of the West Point Treatment Plant Effluent , April 2017

Historical technical reports on effluent plume studies of West Point:

• Bendiner , 1976
• Evans-Hamilton , 1975

West Point sediment and tissue reports

Following collection of initial water quality monitoring data after the West Point Treatment Plant flooding event on February 9, 2017, and during the period of reduced treatment, a water quality monitoring summary report was prepared in February 2018 that evaluated effluent and Puget Sound water quality monitoring data collected in 2017. Additionally, the County collected chemical contaminant data for bottom sediments and marine organism tissues from different areas of Puget Sound in 2017, 2018, and 2019, and prepared six individual technical reports that evaluated any changes due to the flooding event:

• West Point Flooding Event Intertidal Sediment and Clam Tissue Report , February 2019
• Subtidal Sediment Report , November 2019
• West Point Flooding Event Dungeness Crab Tissue Report , February 2020
• Zooplankton Tissue Report , August 2020
• English Sole Tissue Monitoring Final Report , March 2022
• Synthesis Report on Impacts to Puget Sound from West Point Flooding Event , June 2022