West Point environmental monitoring
Monitoring update: May 12, 2017
The Wastewater Treatment Division is conducting water quality and environmental monitoring to assess the effects of West Point operations to Puget Sound while there was a reduced level of treatment being provided following the Feb. 9th flooding and damage to the treatment facilities. We are coordinating closely with the State Department of Ecology. Download and view the environmental monitoring work plan .
King County Wastewater Treatment Division (WTD) takes our commitment to environmental stewardship seriously.
WTD is conducting permit-required and supplemental monitoring following the major equipment failure at the West Point Treatment Plant on Feb. 9. Flooding of the treatment plant resulted in bypasses of untreated stormwater and wastewater into Puget Sound and reduced the level of wastewater treatment while repairs were being made.
The focus and primary objectives of this work plan are:
- Provide comprehensive, representative, and accurate monitoring and analyses of West Point discharge conditions and effects to the marine environment of Puget Sound.
- Document West Point treatment performance and effluent quality improvements over time as repairs to West Point are made.
- Evaluate the potential for short-term water quality effects of wastewater discharges to Puget Sound while repairs to West Point occur.
- Evaluate West Point effluent quality for correlations with any observed significant changes in marine water quality from offshore marine monitoring program data.
- Evaluate the potential long-term water quality and sediment quality effects in Puget Sound (if any).
King County is monitoring 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.
Information can be found here regarding:
- Bi-weekly updates of laboratory data for routine West Point effluent monitoring and comparisons to our NPDES permit limits.
- Results of effluent tests that evaluate the potential for acute and chronic toxicity on marine life.
West Point Treatment Plant Restoration Routine Effluent Water Quality Monitoring Data
The monitoring update for May 12, 2017 shows the completed draft data collected in April and preliminary recent data through May 9, 2017. The data shows that with the reduced level of treatment at West Point while repairs to the secondary treatment process were underway during April, effluent was not meeting the NPDES permit limits for biochemical oxygen demand, total suspended solids, and chlorine residual. However, the secondary treatment process was restored by the end of April and fully resumed the ability to comply with these effluent limits on May 10th. With the plant now fully operational, it is anticipated that reduction of these parameters to compliant levels observed in early May will continue.
The first quarter 2017 test for acute toxicity in West Point effluent was conducted for samples collected on March 21, 2017, and second quarter test for chronic toxicity was conducted for samples collected during the period of April 4-9, 2017. Both toxicity tests were conducted while the treatment plant was at a reduced level of treatment due to the flooding incident on February 9th. The acute toxicity test is conducted to observe for potential adverse effects of exposing sensitive aquatic organisms to effluent over short test periods (2 to 4 days depending on the test organism used). The chronic toxicity test is used to observe for potential adverse effects to organisms over a longer period of 7 days.
For both the acute and chronic toxicity tests, the data show that the test results have been normal with no substantial toxicity observed in the effluent. The detailed reports for download are:
Immediately following the damage to West Point on February 9th, King County conducted its required 1st quarter monitoring for EPA priority pollutants (i.e., primarily metals and organic compounds found in trace levels) in the influent and effluent. While repairs to West Point have been underway, we collected additional samples for the priority pollutants on a generally bi-weekly frequency. We are continuing to monitor priority pollutants the plant is back to normal operations. We compare the data to water quality criteria and historical conditions to evaluate effects on Puget Sound.
Information can be found here regarding:
- Bi-weekly updates of routine and additional West Point monitoring data for the priority pollutants.
- Comparisons to water quality criteria and historical conditions to evaluate potential effects on Puget Sound.
West Point Treatment Plant Restoration Effluent Priority Pollutant Monitoring Data
The attached report provides an update with the additional monitoring data for the EPA-designated priority pollutants evaluated in samples of West Point influent and effluent collected on April 24th. King County reviews the priority pollutant concentrations in the effluent for the potential to exceed Washington’s marine water quality criteria for protection of aquatic organisms in Puget Sound.
West Point Treatment Plant Restoration Near-Field Effluent Mixing Water Quality Analysis
- The attached technical report discusses the effects of West Point effluent discharge to trace metals, ammonia, and residual chlorine concentrations in the initial zone of mixing created by the discharge outfall. These parameters, when elevated above water quality criteria, may cause harmful effects to aquatic organisms.
- The analysis compares estimated concentrations in the zone of mixing for conditions through April 4th (i.e., reflecting the reduced level of treatment that was occurring while repairs to West Point were underway) to normal West Point conditions.
- The analysis shows that under normal conditions, West Point effluent results in water quality concentrations that are well below any of the applicable water quality criteria for aquatic organisms.
- The analysis also shows that with the reduced level of treatment while repairs at West Point have been underway, the effluent also is not causing any concentrations to rise above any water quality criteria.
This information addresses questions about how effluent is discharged from the West Point deepwater outfall, and how it disperses with tidal flow in Puget Sound.
The West Point effluent is discharged approximately 3,600 feet offshore from West Point at a depth of about 240 feet below mean lower low water. The last 600 feet of the outfall pipeline contains multiple ports to increase the dispersion of effluent.
The discharge pattern and mixing (or dispersion) of the West Point effluent in the tidal flows within the central basin of Puget Sound are generally well understood through numerous studies conducted over the past 40 years.
- The effluent is buoyant and rises through the water column to the water surface during the winter and spring periods of the year.
- The diffuser creates rapid mixing of effluent with seawater such that by the time the effluent reaches the surface, the mixture is about 1 part effluent to 99 parts seawater (or 100:1 dilution).
- Within this initial zone of mixing, the mixture of effluent must not exceed Washington’s water quality criteria.
- During the winter and spring cold and wet months, typical of conditions while the West Point restoration is underway, the tidal currents result in effluent being dispersed along a dominant north-south axis near the outfall.
- During each tidal cycle, the initial buoyant and rapidly mixed plume then disperses as a generally well-defined plume and moves about 5 miles north on ebb tides, and 2.5 miles south on flood tides.
- As the plume moves with each tidal cycle, the plume with initial 100:1 diluted plume is further mixed by an additional factor of 5 to 10 fold (i.e., diluted to ratios of 500:1 to 1000:1).
- During slack tide conditions, and through the reversal of tidal flow direction, additional and greater levels of dispersion and dilution occur.
- Dye tracer study by King County and University of Washington researchers in the 1970’s found that the area of detectable dye levels, indicating effluent dispersion, was limited to the east side of the sound (grey outline shown in the map).
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:
For questions or inquiries related to the West Point restoration, please do not call the West Point Treatment Plant.
206-477-5371 (after hours, leave message)