On February 9, 2017, the West Point Treatment Plant fails catastrophically. Located in Seattle's Magnolia neighborhood and operated by King County's Wastewater Treatment Division, West Point is the largest wastewater-treatment plant in the Pacific Northwest, handling sewage produced by some 700,000 people along with stormwater. At 2:12 a.m. on a night of heavy rain, a power outage shuts down pumps that push effluent (treated water) into Puget Sound. As crewmembers struggle to restart the effluent pumps, influent (wastewater) continues to surge into the plant. Effluent, though, is blocked. Within 51 minutes 2,315 alarms go off. Float-switch alarms in primary-treatment tanks, designed to prevent flooding, fail and at 2:25 a.m. the primary-treatment tanks overflow, flooding tunnels and equipment galleries. To stop the flood, crewmembers manually shut down influent pumps. The influent control structure fills and float switches there automatically open an emergency-bypass gate, permitting 180 million gallons of wastewater, including 30 million gallons of raw sewage, to flow into Puget Sound. The plant is severely damaged, but no lives are lost. Tremendous work to review systems and repair the plant will get it functioning back up to environmental standards by May 12, 2017.
A Night of Heavy Rain
King County's West Point Treatment Plant is located on a point of land that extends into Puget Sound from Seattle's Discovery Park. It covers 32 acres and has a mile of gallery tunnels that contain electrical equipment and control panels. It has two miles worth of pipe insulation. A staff of about 160 people in the county's Wastewater Treatment Division operates the plant.
On the night of February 8-9, 2017, it was raining hard and the plant was working at peak hydraulic capacity, taking in wastewater (consisting of sewage, gray water, and stormwater) at the rate of 440 million gallons per day (mgd) versus the more ordinary 300 mgd, or a monthly average of 215 mgd. There were nine people on the night crew, including supervisor Charles Wenig (b. 1962) and one apprentice. The other seven workers on the night crew were licensed, trained professionals. According to a subsequent independent assessment commissioned by the King County Council and conducted by the consulting firm AECOM, "plant operators had very little time to respond" when the failure occurred. ("Final Report," iv). In fact the entire episode took place within less than an hour. It caused massive damage to the plant and was very much a life-threatening event. That no lives were lost was likely due to the fact that the event happened on the night shift and no workers were in the tunnels.
How West Point Works
To understand the event it helps to understand how the plant works. Wastewater arrives at the plant through two underground sewer pipes. It collects in a large tank, the influent control structure, from where it is pumped into the plant. Connected to the influent tank is an emergency-bypass outflow. Only in a life-threatening or facility-threatening emergency, all wastewater coming into the influent tank can be (and must be) drained directly into Puget Sound, bypassing the plant altogether.
From the influent control structure, water proceeds through the treatment plant as follows:
- Influent pumps: First, influent pumps pump wastewater into the plant from the influent tank.
- Preliminary Treatment: Next, bar screens screen out trash, such as the quite unflushable "flushable" wipes, leaves, feminine products, condoms, paper towels, rags, etc. Next, grit and gravel are removed in a tank that blows air into the mixture to separate it. Trash, grit, and gravel are trucked to landfill.
- Primary Sedimentation Treatment: The huge primary sedimentation (or primary treatment) tanks still (slow down) the mixture. Organic solids (human waste and food) sink to the bottom; grease and hair float to the top, where scrapers scrape them off. Solids from the bottom and top are removed, which takes care of about 50 percent of the solid waste.
- Treatment of Solids in Digesters: Organic solids from the primary treatment tanks are sent to digesters where bacteria break down the organic matter. After 30 days in the digesters, water is removed from the solids in a centrifuge (a high-powered spinning machine). The remaining solid material, now called biosolids, is trucked to Eastern Washington and sold for use as an alternative to chemical fertilizers. The West Point plant produces about 120 tons of biosolids per day. Gas (methane) emitted by the solids in the digesters is used to heat the plant and its tanks; the excess is scrubbed of impurities and sold to Seattle City Light for use as natural gas.
- Secondary Treatment: What remains in the primary sedimentation tanks after about 50 percent of the solid waste has been extracted goes into secondary treatment tanks. Secondary treatment is biological. Helpful bacteria consume most of the rest of the solids. Warm air is constantly added so this is a warm, oxygen-rich environment. The capacity of the secondary treatment tanks is 300 mgd.
- Clarifying: After about four hours in the secondary treatment tanks the mixture is sent to a clarifying tank, in which bacteria sink to the bottom and are returned to the secondary treatment tanks to continue their job of breaking down the organic matter.
- Chlorination: Next, a bleach, sodium hypochlorite, is added to kill most remaining pathogens.
- Dechlorination: To protect marine life, the bleach is neutralized with sodium bisulphite.
- Effluent Pumps: At low tide the treated water flows by gravity out a pipe to Puget Sound. At high tide four pumps pump the water out to the sound. The event on February 9 occurred during high tide.
- Tertiary Treatment: Some of the water is sent to a sand filter and is further purified of pathogens. The resulting recycled water is used in the plant and for irrigation (of golf courses, for example).
Crucial to this flow of material are pumps that push or lift material from one tank to another, gates and valves that allow material to enter or block it from entering, and bypass pipes. For example, when the hydraulic volume of the plant exceeds 300 mgd, the wastewater in the primary tanks must bypass the secondary tanks, which are then at capacity. Or, in the event of extreme danger to life or to the facility itself, raw sewage can be pumped out of the influent tank and directly into Puget Sound through the emergency bypass outflow. This pollutes Puget Sound but there are situations in which that is unavoidable.
Float switches are important. They float in the tanks rather like the float in the back of a home toilet. In an emergency, when the wastewater in a tank gets too high, the float switches can close gates or turn off pumps. In the February 9 emergency some of the float switches worked, but the ones in the primary sedimentation tanks did not. If they had worked they would have shut off the influent pumps that pump raw sewage into the plant. This would have caused sewage to rise in the influent tank. The float switch in the influent tank would have opened the emergency bypass gate. Raw sewage would have flowed into Puget Sound, which in an emergency it must do, but the plant would have been saved.
At 2:12 a.m. on February 9, 2017, a power interruption to Electrical Switchgear A shut down one of the three pumps then pumping effluent (treated wastewater) into Puget Sound. The pumps (a fourth pump was on standby) were needed because the gravity system works only at low tide and the tide was high. The cause of the power failure has not been determined, but it was this outage that caused the cascade of events that culminated in disaster.
Electrical Switchgear A powered only two of the four effluent pumps (including the one then on standby), but it was also the only power source for the control valves of all four effluent pumps. Lacking power, all four control valves shut. Treated wastewater couldn't get out. It started to back up. The two still-operating pumps, pushing effluent into shut valves, began vibrating violently and two minutes later shut down. Effluent continued backing up. Electricians on call were called but they failed to answer their phones.
The plant supervisor instructed workers to restart the effluent pumps. They attempted to do so but were unsuccessful. The supervisor then slowed down the influent pumps bringing wastewater into the plant, and began procedures for storing excess wastewater in a conveyance system provided for this purpose.
Tank levels in the plant continue to rise, backing up in sequence from the effluent pump station tanks (tanks holding treated water ready to be released into Puget Sound) to secondary-treatment tanks and primary-treatment tanks. Rising water in the effluent pump station tanks tripped the high-level float switch, and this in turn automatically shut the gates in the primary tanks that let partially treated wastewater into the secondary tanks. This mechanism is in place because the biologically based secondary-treatment tanks are highly sensitive to overloading. It can take months to get the secondary tanks to run properly again after being disrupted.
Now wastewater levels in the primary-treatment tanks could not pass to the secondary tanks and began to rise. The high-level float switch in the primary treatment tanks failed to go off due to a bent rod in the float switch that prevented the bulb from rising on the rod. Had this float switch gone off, it would have sent a signal to the influent pumps to put them on "idle." This in turn would have caused the raw sewage in the influent control structure to rise, which would have caused the (correctly working) float switch in that influent tank to automatically open the emergency bypass gate, allowing the raw sewage to bypass the plant and flow directly into Puget Sound, rather than destroying the plant.
The supervisor observed that the gates from the primary tanks to the secondary tanks were closed and instructed that they be reopened manually. Operators were unaware that the gates had closed with an interlock system and could not be reopened manually.
At 2:25 a.m. the primary-treatment tanks began to rapidly overflow. High-level float switches in these tanks failed to activate. Flooding began less than 13 minutes after the electrical outage. Sewage lifted the covers on the primary tanks and wastewater began gushing into the pipe and equipment galleries below. Wastewater and sewage began rising in the tunnels, fast. Operators on the primary decks (who had been trying to reopen the gates between the primary and secondary tanks) saw the emergency and began running for the exits. They were running through wastewater so deep that they could not see the deck. The flood pushed aside a section of grating on the walkway and the apprentice tripped and fell. Two operators assisted her back to an Area Control Center. Instead of calling the supervisor to inform him of the flood, they gave her first aid and dry clothes and explained procedures for reporting the incident. They did not inform the supervisor because they assumed that he knew about the flood.
The supervisor did not know about the flood. He was focused (and had his remote camera set) on the operators attempting to restart the effluent pump station pumps.
Meanwhile alarms were going off -- 2,315 of them in 51 minutes. This was far more than any one person could comprehend. The alarms in the alarm system were not prioritized and the most urgent alarms flashed and then went off, rather than staying on until an operator turned them off.
When he turned his camera around and thus viewed the flood, the supervisor instructed the operators to manually shut down the influent pumps that were pumping sewage into the plant.
At 3:03 a.m. operators manually shut down the influent pumps. Flooding in the plant ended at 3:05 a.m.
Upstream of these pumps, the raw sewage began to rise in the influent control structure. The float switches in the influent control tank worked correctly. They automatically opened the emergency bypass gate, which allowed the raw sewage to bypass the plant and go into the emergency bypass outfall (into Puget Sound). One hundred and eighty million gallons of storm water, including 30 million gallons of raw sewage, went into the sound that night.
For a time the digesters, in the solids treatment process, kept working. But when power failed in this area "sludge began to produce gases and foam that forced the lids and belched liquid out of the digesters and onto the surrounding plant site" ("Final Report," 21).
Assessment: Life Safety
During the event, the danger to life was extreme. Tunnels were inundated up to the light fixtures. One operator was in a tunnel, returning to a locker room to obtain higher boots, when he saw the flood rising and decided correctly to leave immediately. The danger included engulfment, entrapment, and electrocution. In daytime, many workers and contractors work within the mile-long system of tunnels. Had the disaster happened during the day, it would have been much worse.
The two operators (along with the operator-in-training, who fell and was injured) attempting to reopen the gates leading from the primary tanks to the secondary tanks were on the primary-sedimentation basin deck. It is likely that no one had any idea how fast these basins could flood, lifting panels and grates.
Assessment: The Physical Plant
Plant equipment destroyed in the disaster included "pumps, motors, electrical panels, wiring, transformers, lighting, switches, and motor control centers" ("Final Report," 21). Effluent from the secondary treatment tanks damaged the effluent pumping system.
The flood contaminated "the entire surface area of the mile of gallery tunnels and 2 miles of pipe insulation"("Final Report," 21). It destroyed the staff's locker and shower facilities. It was major work to clean up after the digesters and to get their biological processes working properly again.
Repairing damage to the physical plant ended up costing about $26 million, with most, except for a $250,000 deductible, paid by insurance.
Assessment: Puget Sound and the Environment
The West Point Treatment Plant was offline for 18 hours. The King County Wastewater Treatment Division estimated that 180 million gallons of wastewater, including stormwater and raw sewage, went into Puget Sound on the night of the event. During heavy rains the following week, with the plant only partially functioning, on February 15 and 16 an additional 55 million gallons of wastewater were released into Puget Sound.
King County closed beaches and began extra monitoring of water quality. Concentrations of fecal bacteria were high at the West Point beach and at the beaches at Carkeek Park to the north and Golden Gardens to the south. Over several days these concentrations declined rather quickly. Beaches were reopened on February 21, 2017. The Washington State Department of Ecology announced a decision to fine King County $361,000 for the period West Point was out of compliance with its water-quality requirements.
Cleaning It Up
Robert Waddle (b. 1956), divisions operations manager for the King County Wastewater Treatment Division, was called at 3 a.m. and arrived at the plant at 5 a.m. He found chaos. "We couldn't enter tunnels," he told a reporter, "You could get down the stairwells to the tunnels, but couldn't see the tops of the doors down the stairs" ("Seattle Operators Back on Track ...")
The plant staff along with 40 outside contractors worked day and night on the cleanup. It took three days to get wastewater out of the tunnels. Then the tunnels were hosed down, steam-cleaned by sanitation crews, and, finally, further sanitized. Only then could electrical and mechanical crews begin replacing wiring, motors, and control panels.
Two systems -- the digesters that treat solids drawn from the primary tanks and the secondary treatment tanks that treat partially treated wastewater drawn in the other direction from the primary tanks -- involve biological processes. These living organisms must be properly fed and kept warm. The secondary treatment tanks were not damaged but they had to be kept offline to protect the organisms that make them work, thus depriving the organisms of food. The digesters lost power and the organisms in them got cold. During the cleanup, both systems were the subjects of much attention and concern.
Partial treatment of wastewater was resumed after the 18-hour shutdown. It included trash removal and disinfection with sodium hypochlorite followed by dechlorination with sodium bisulphite.
But it was not until May 12 that the plant was back up and running to strict environmental standards with complete treatment in place.
Decisions and Revisions
On April 27, 2017, the King County Council commissioned an assessment by AECOM, an independent consulting firm. The firm's final report including suggestions was delivered on July 18, 2017. Improvements made to the plant infrastructure and its systems and procedures included:
- Drills and ongoing training to deal with emergencies, including tabletop modeling and actual drills, especially emphasizing actions that must be undertaken in an emergency that are not routine.
- Redundancy in electrical systems so that failure of a source of power will not knock out everything it serves, as happened to the effluent pumps on February 9. At that time, under peak flow conditions, the plant needed all systems to be fully functional.
- All float switches were replaced with a new type that was more reliable. Problems with the float switches had been chronic for years and it was generally agreed that this should have been done years ago.
- The alarm system was reconfigured so that priority alarms go on, are clearly visible on their own panel, and stay on until an operator turns them off.
- Better training in when it is imperative to open the emergency bypass gate. This training runs counter to the usual effort to prevent this gate from opening, since it releases raw sewage into Puget Sound.
- During wet weather an electrician will be on site and staff will walk the plant to watch for anything amiss.
- There is a "Process Safety Management" system required by industry regulations to be in place in chemical-systems areas of the plant (it was in place in those areas of West Point). AECOM recommended that West Point put this system in place in all areas of the plant.
The West Point Treatment Plant was built in 1966. It is constrained in that, ever since the secondary treatment tanks were installed in 1995, it has occupied all of its allotted space and cannot be expanded. Like many infrastructural systems, it is also constrained by decisions made decades ago, mainly the decision to include stormwater in the sewage treatment system instead of handling stormwater in a separate treatment facility. Climate change is making for more rain, and Seattle's rapid growth in population and building has resulted in more concrete and less vegetation and ground to absorb rainwater. West Point is likely to be running at full capacity more and more often during the rainy season.
Although AECOM reported that the operators did everything that could reasonably be expected of them (and all but the operator-in-training were highly trained), the plant faced ongoing staffing issues. Given Seattle's skyrocketing housing costs in the late 2010s, most operators could not afford to live anywhere near the plant and many commuted an hour or more each way. This on top of 12-hour shifts. Thus there were many requests for transfers to King County's other wastewater-treatment plants. In early 2018 officials were considering an increase in pay for West Point staff and help with vanpool commuting.
For 14 years in a row, West Point Treatment Plant managers had received platinum awards from their industry for perfect compliance with the plant's permit. The events of February 9, 2017, brought an end to that streak.