Wastewater Treatment and the Duwamish River

  • By Jennifer Ott
  • Posted 7/14/2016
  • HistoryLink.org Essay 11250

The Duwamish River, located in King County, has borne the burden of municipal and regional development over the past century. Its channel straightened and dredged, tributaries rerouted, and floodwaters controlled and contained, the river's hydrology has been fundamentally altered. At the same time, the river has been a dumping ground for received human and industrial wastes -- peaking with a burst of unfettered industrial and sewage discharges in the 1940s and 1950s. Beginning in the 1960s, pollution-control measures began to reduce the load of chemical and wastewater contaminants in the river. Over the past half-century, the City of Seattle and the Municipality of Metropolitan Seattle (later superseded by the King County Wastewater Treatment Division) have built treatment plants and a network of sewer lines to remove raw sewage and treated effluent from the river, and work continues to clean up the last of the combined sewer overflows that pollute the river.

The Problem of Sewage

The sewage problem is largely one of population density. In communities with very low density, sewage can be handled at the source if the contamination of drinking-water supplies can be prevented. But as the population grows denser, dealing with human and industrial waste becomes imperative to prevent the spread of disease. As Seattle reached that density in the later decades of the nineteenth century, the open ditches and cesspools that residents were relying on did not suffice and sewage contaminated drinking-water sources. In 1883 the first wooden-box sewers were built and an 1884 city ordinance required residents to connect to the sewer system.

In the 1880s, the city hired Colonel George Waring (1833-1898) and then Benezette Williams (1844-1914) to design a sewage system. Waring's plan featured tunnels to carry waste and dismissed the need to provide drainage pipes for stormwater. Williams' plan combined sewage and stormwater in the same pipes. While neither plan was fully implemented, both would shape the system developed by City Engineer Reginald H. Thomson (1851-1949) in the early 1900s.

Most importantly for the Duwamish River, all of the engineers relied on waterways for the ultimate disposal of wastewater, utilizing the city's lake and rivers and some direct outfalls into saltwater where tides dispersed waste out to the larger ocean. While water-based systems predominated in cities in the 1890s and early 1900s, this was not the only method available for handling sewage. Jamie Benidickson's The Culture of Flushing: A Social and Legal History of Sewage details efforts to find land-based solutions to sewage management, including earth toilets, which operated much like composting toilets, and sewage farms, where wastewater was spread across thousands of acres of land to dry and compost.

Piping Sewage to Lakes and Rivers

While these land-based solutions were technically possible, and even promoted by Waring for a time, they were not considered in Seattle. Instead, Thomson's system utilized enormous trunk lines running through the city, receiving sewage and stormwater from a network of smaller neighborhood sewer lines, to carry wastewater to outfalls along Lake Washington, Lake Union, the Duwamish River, Elliott Bay, and Puget Sound.

Thomson and other city officials were aware of the issues involved in using waterways to dispose of untreated sewage. According to a history of Seattle's engineering department, "The engineers had known since early in the 1890s that the City must ultimately stop discharging sewage into the lakes, rivers, and Sound, but lack of money and public indifference prevented any definite action being taken for many years" (Phelps, 191).

As towns grew around King County, more systems carried wastewater to the region's waterways. In 1910, Auburn and Renton built sewer systems that discharged into the Green (the upstream portion of the river known as the Duwamish nearer its mouth) and Cedar rivers. Kent's system, built before 1930, also discharged into the Green River.

In some respects, use of waterways, particularly rivers, was sound given the science and circumstances of the time. Rivers were considered self-cleansing. River water moved at a high-enough volume to dilute and flush wastewater before it could accumulate or fester. Also, until about the 1930s, wastewater carried primarily biodegradable waste.

As county population grew from about 504,000 in 1940 and to almost 733,000 in 1950, the most severe problems developed first in Lake Washington. The lake had a relatively low turnover rate, so it did not effectively flush out wastewater. Also, it was used for recreation and drinking water, limiting how much wastewater it could handle without causing harm to people.

Early Treatment Plants

In 1925, Seattle officials developed a plan for 16 sewage treatment plants on Lake Washington to deal with sewage and stormwater along the western shoreline of the lake, three of which were built. The King County Board of Health and the Board of County Commissioners both rejected the use of Lake Washington for sewage -- treated or otherwise -- but they could not stop the effluent from entering the lake because the state Board of Health had the ultimate jurisdiction and its standards were lower.

In the end, it was public uproar that prevented the construction of more of the planned treatment plants. Instead, several interceptor pipelines were built along the western lakeshore in the 1930s. One carried sewage to the North Trunk, which discharged to Puget Sound at West Point in Seattle's Magnolia neighborhood (where Discovery Park was later developed), and two carried it into the Duwamish River. By 1936, raw sewage was largely eliminated from the city's outfalls into Lake Washington, except for during storms when the overflow, including raw sewage, drained into the lake via 30 outfalls.

Recognizing that the interceptor pipes from the lake, and another one carrying wastewater from the Rainier Valley, were harming the Duwamish, the city built the East Marginal Way interceptor in the 1930s to carry wastewater from the western shore of Lake Washington to Diagonal Avenue, where a treatment plant on the riverbank began operating in 1940. It provided primary treatment before discharging the liquid effluent into the river. The plant also had an overflow outfall that discharged raw sewage and stormwater during heavy rainfalls. The combined sewage and stormwater system had created a problem that plagued waterways.

While the situation was less than ideal in the 1920s and 1930s, the population boom that started during World War II made conditions in local waterways untenable. The Lake Washington Floating Bridge, opened in 1940, encouraged development of suburban towns in King County. Soon, 10 treatment plants discharged treated effluent into Lake Washington. Lake Union received untreated sewage from outfalls and overflows, along with polluted wastewater from industrial businesses ringing the lake. The North Trunk Sewer outfall off West Point did not extend out to deep water and city staff had to go out periodically and clear built up solids that blocked it.

The lower Duwamish River, which had been straightened and deepened in the 1910s, was lined with various industries, many of which contributed to the war effort. Boeing released chromic acid, cutting oils, sodium nitrate, and acetylene as part of its airplane production; Laucks Laboratories released paint, glue, and caustic soda; and Crown Zellerbach disposed of charcoal and copper ammoniate, used to make filters for gas masks, into the river and onto adjacent land, to name just a few. ("Seattle Women Train ...")

The river also received raw sewage from 14 outfalls and from the land west of the river, up to the crest of West Seattle. Upriver, at Auburn, Kent, and Renton, untreated sewage was discharged into the Green River.

Studies and Warnings

The 1940s saw a number of studies of the sewage-disposal problem in King County. University of Washington engineers looked at West Seattle's growing neighborhoods and recommended improvements, which eventually lead to the 1958 construction of a treatment plant at Alki Point to serve the west side of West Seattle. By 1945, all saltwater beaches in Seattle were declared unsafe for bathing after tests showed high levels of coliform in shoreline waters. The City of Seattle in 1948 brought Abel Wolman (1892-1989), a sanitary engineer, in to assess the situation. He recommended using Puget Sound for sewage disposal and called for a regional plan that would encompass the entire county.

No concerted effort was made, however. In 1952 Robert O. Sylvester (1914-2011) studied the area for the Washington Pollution Control Commission (precursor to the Department of Ecology) and outlined the reasons for the growing pollution problem in Lake Washington and the Duwamish River. These included the large number of small, isolated sewerage districts, the fact that those districts were only formed once conditions had significantly deteriorated (in areas where population density increased in fits and starts, not as the result of planned subdivisions), no coordination with the larger systems, and the high cost of pipelines to waterways for landlocked districts. Additionally, as development increased, it became more challenging to find sites for treatment plants and outfalls.

Forty-one jurisdictions covered the territory that drained into Lake Washington and the Duwamish, including cities and sewerage districts. Twenty-five treatment plants treated the sewage, but there were still 60 raw-sewage outfalls carrying the wastewater from about 425,000 people into the region's waterways. In 1956 the Pollution Control Commission wrote:

"People of Seattle cannot safely delay taking action to clean up the waters surrounding their city. Lake Washington, Elliott Bay, Alki Beach, the Duwamish River and other areas can be returned to a clean and healthy condition. The future of Seattle depends on action today. Tomorrow will be too late" ("For the Whole Lake Basin").

In September 1956, Seattle mayor Gordon S. Clinton (1920-2011) and the King County Board of County Commissioners appointed 48 citizens from around the county (later expanded to 75) to the Metropolitan Problems Advisory Committee. Local lawyer Jim Ellis (b. 1921) was named chair. Ellis had been part of an unsuccessful effort in 1952 to reform county government to address regional problems and would later lead other efforts to improve and protect King County's environment, including the Forward Thrust bond measures and the Mountains to Sound Greenways Trust.

The Metropolitan Problems Advisory Committee released its recommendations in August 1957, stating "There is a clear and present danger that sewage will destroy Lake Washington as a community recreational asset" and that "Pollution from the discharge of raw sewage and treated effluent into the Duwamish River threatens to destroy the valuable fishery which it supports" ("Report of Metropolitan Problems Advisory Committee," 2). The committee called for the complete removal of all raw and treated sewage from the river.

Creation of Metro

Recognizing that watersheds formed natural boundaries for sewage handling, the committee recommended a cross-jurisdictional organization to develop and operate a regional sewer system. Committee members helped draw up legislation enabling formation of metropolitan municipal corporations, which the state legislature was passed in March 1957. The municipal corporations could address sewage disposal, water supply, public transportation, garbage disposal, parks and parkways, and comprehensive planning within their boundaries upon approval by voters.

A March 1958 ballot measure would have created a Municipality of Metropolitan Seattle with broad authority to address sewage disposal, water-quality improvement, public transit, and comprehensive planning. The Seattle Times endorsed the measure, saying "This is the only agency conceived to date that could take the steps necessary to curb pollution of Lake Washington, the Duwamish River and other waterways" ("Proposals Vital to Community ..."). The measure won a majority in Seattle but failed in many suburban areas.

A reconfigured proposal was put before voters in September 1958. The new measure focused more narrowly on sewage disposal and water-quality improvement and reduced the municipality's boundaries primarily to the area draining to Lake Washington plus the entire city of Seattle. To its advantage, the weather during the summer of 1958 exacerbated all the symptoms of Lake Washington's eutrophication. Algae feeding off the high phosphorus content of the sewage-polluted water bloomed across the lake, making it murky. As the bloom died off in the latter part of the summer, it washed up on shore and created a stench. Numerous beaches were closed to swimming.

The campaign for the Municipality of Metropolitan Seattle, or "Metro," as the agency name was quickly shortened, emphasized Lake Washington and Puget Sound because they were most publicly visible and used most often by voters. While the Duwamish River's condition and the need to clean it up were referenced in nearly all the reports and statements related to the formation of Metro, the river, the Lake Washington Ship Canal, and Lake Union were not emphasized in the campaign. They were working waterfronts and did not garner the same public awareness as did Lake Washington and Puget Sound.

Regional Plan for Sewage Disposal

When the measure passed, Metro was ready to begin work. Concurrently with the work of the Metropolitan Problems Advisory Committee, engineers from the firm Brown and Caldwell and government officials had been studying the region's waterways and developing a regional plan for sewage disposal, which was issued in March 1958.

In preparing the plan, the Brown and Caldwell engineers operated under several assumptions. First, they concluded the river could absorb treated effluent better than the lake. They cited an Army Corps of Engineers report describing the lake's turnover rate. It took three years for water to completely flush out of the lake, in sharp contrast to the river's flush rate, which was four days, at the most, according to the United States Geological Survey.

Second, they identified commercial fishing and shipping on the lower river as the only uses relevant to the sewage discussion. Other waterways were valued also for recreational use or irrigation, which required higher water-quality standards but, as Seattle's industrial waterway, not an aesthetic or recreational amenity, the Duwamish did not merit the same standards.

Likewise, the significance of the river to people who lived in nearby neighborhoods, such as Georgetown or South Park, or Native communities, such as the Duwamish, Muckleshoot, and Suquamish tribes, with generations-old connections to the river, did not factor into the planning. Fishing by Native people was not specifically recognized as a beneficial use of the river. Quite the opposite -- in 1963 Metro officials complained to the Bureau of Indian Affairs, the Department of Fisheries, and other agencies about Muckleshoot Indians net-fishing on the Green River, arguing that the tribal fishery was taking fish that Metro was trying to protect for the commercial and sport fisheries. It would be more than a decade before courts reaffirmed tribal fishing rights. Fishing by other local residents was not part of the discussion either, despite the potential health effects of eating those fish. As more immigrants and low-income families moved into the neighborhoods in the 1960s and 1970s, this would become a more significant issue given that these residents sometimes depended on fish from the river as a low-cost resource.

The Brown and Caldwell plan for sewerage in the metropolitan area built upon the existing trunk sewer lines in Seattle, some of which had 12-foot diameters and had seemed enormous when they were built in the first decade of the century, but were reaching capacity in the 1950s. The plan called for decommissioning most of the existing treatment plants, which were small and inefficient. They would be replaced with trunk pipelines that carried sewage to interceptor pipelines. Those interceptors would carry the sewage from huge areas to two treatment plants, one at West Point and one at Renton. The Renton plant would serve the east side of Lake Washington and the Green River valley. The West Point plant would treat wastewater from Seattle and the northern suburbs. The newly constructed Alki Treatment Plant continued to operate and plants on Puget Sound at Carkeek in North Seattle and Richmond Beach north of the city would be rebuilt because they could not be incorporated into the regional network effectively.

The Metro Council, the newly formed agency's governing board, adopted the Brown and Caldwell plan in April 1959. Work began to acquire land and permits for the treatment plants at Renton (also known as the South Treatment Plant), scheduled for completion in 1965, and at West Point, scheduled to be operational in 1966. Interceptor sewers were built, mostly underground, except along the north shore of Lake Washington where the Kenmore interceptor was installed underwater, supported above the lakebed by a trestle, to avoid tearing up neighborhoods.

Monitoring Water Quality and Controlling Toxic Discharges

In March 1960, the Pollution Control Commission held a hearing in Seattle on a permit for the Renton treatment plant. Plans for the plant called for discharge of liquid effluent into the Duwamish River and piping of solids to West Point for discharge to Puget Sound. Wastewater processed by the Renton plant would receive secondary treatment, which removes almost all the solids in sewage, with the resulting effluent disinfected with chlorine and released into the river. West Point would use only primary treatment processes to remove most of the solids from wastewater before discharging it into the Sound.

The commission issued the permit with conditions. Metro had to ensure that the amount of dissolved oxygen in the river did not drop below five milligrams per liter, then considered the minimum for aquatic life; control the amount of chlorine residue from the treatment process that entered the river; ensure that the river's water temperature did not increase; and prevent accumulation of sludge on the riverbed.

Metro was required to install water-quality monitors, one above the effluent outlet to the river and three downstream. The agency used of automatic water-quality monitors, which continuously fed readings of dissolved-oxygen levels, turbidity, chloride levels, and other data to Metro computers. When they were installed in 1963, only the Ohio River was monitored using this type of monitor. The Seattle Times called them "$9,000 Robots." Charles (Tom) Gibbs, then chief of the water-quality division and subsequently Metro's executive director, recalled how they were state-of-the-art and provided more comprehensive data on river conditions. Gibbs was later awarded the American Public Works Association's Charles Walter Nichols Award for his innovative work on the water-quality monitors and other projects.

Metro also had to control toxic discharges into the sewer system, which led to the development of an industrial wastewater pre-treatment program. To protect the treatment plant from contamination and disruption and to ensure no toxins passed through the plant and into the river, Metro developed a monitoring program requiring industrial customers to develop treatment facilities on-site for their wastewater. Depending on the type of chemicals handled, businesses had to develop processes to remove them from wastewater before it entered the sewer system. While chemicals still reached the river from spills and dumping and from leaching into groundwater, the industrial pre-treatment program reduced the number and volume of chemicals entering the river.

Other problems facing the Duwamish River were also discussed at the March 1960 hearing. Brown and Caldwell sanitary engineer John T. Norgaard had studied 22 fish kills (the time period when they occurred was not specified in the hearing statement, but fish kills happened regularly on the river once it became an industrial waterway) and identified their sources. Eighteen resulted from discharges of untreated industrial wastes. Norgaard noted that the Metro plan included industrial waste, much of which would be pretreated at its point of origin to prevent contamination of wastewater going into the plant and to protect the biological processes involved in decomposing the sludge, which could be interrupted or halted by toxins. He noted that treatment-plant discharges at Kent and Auburn caused three other fish kills and explained how the Renton treatment plant would remedy the circumstances involved in these fish kills because toxins in the effluent would be more diluted and subjected to more treatment.

The Metro plan did not seek to eliminate entirely the release of sewage to area waterways. Given the uses of different areas, ranging from recreation to shellfish gathering to industry, the plan delineated the number of combined sewer overflows each waterway could tolerate. Lake Washington, east of the Montlake Bridge, could absorb one summer overflow. Puget Sound beaches would remain open to the public with up to 12 overflows per summer. The ship canal west of the Montlake Bridge (and, presumably, Lake Union), the Duwamish River, and Elliott Bay were believed to be able to tolerate unlimited summer overflows. Winter overflows, which were unavoidable unless a much larger trunk-sewer-and-treatment-plant system was developed, were not limited. This was tolerable because the waterways were hardly used for recreation in the winter months.

Diverting Sewage from Lakes and Rivers

The system Brown and Caldwell devised could handle the regular flow of sewage and stormwater. By February 1963, the first treated effluent was diverted from Lake Washington. In 1964, Metro built storm drains on Harbor Island to divert runoff from the highly polluted island into the sewer system and away from Elliott Bay. By April 1967, all treated water had been diverted out of Lake Washington. In August 1968, the Issaquah treatment plant closed and all treated wastewater was diverted out of Lake Sammamish.

The Renton Treatment Plant began operations in 1965. It handled the sewage from the east side of Lake Washington and the valley to the south. Interceptor pipes were built along the river to take sewage that had been discharged via outfalls into the river to the West Point Treatment Plant. In 1961, 70 million gallons per day of raw sewage was dumped into the river. By 1968 that number was down to 15 million gallons per day and it was nearly zero by 1970. That year, the Elliott Bay Interceptor was built to carry sewage from the mouth of the Duwamish north along the central waterfront and Metro was able to close the Diagonal Avenue plant. The interceptor replaced several outfalls, preventing the direct discharge of 22 million gallons of raw sewage into the river and bay each day.

The only raw sewage still discharging into the river came from combined sewer overflows during storms. In 1971 Metro developed the Computer Augmented Treatment and Disposal (CATAD) system to manage the flow of wastewater in interceptor pipes and trunk sewers. The computers could raise and lower gates to maximize the storage capacity of the pipes and reduce the number and frequency of overflows. The system was able to halt summertime overflows but did not eliminate them entirely, and combined sewer overflows remain a problem today. The federal Environmental Protection Agency (EPA) partially funded the program as a demonstration project. While not yet subject to federal regulations, Metro made the prevention of raw-sewage overflows an early priority in its overall effort to improve and protect water quality. In 1973 Metro employee Curtis P. Leiser wrote a report funded by EPA that explained the CATAD system and how it was implemented in Seattle for reference by other municipal sewage-disposal agencies.

In 1972, the Clean Water Act, passed by Congress, established new standards for discharging treatment-plant effluent in waterways. Additionally, a federal court decision recognized that habitat protection for salmon migratory waters was included in Indian tribes' treaty-reserved rights. These new rules became relevant for the Duwamish River because, as the region's population grew, the amount of effluent being discharged from the Renton treatment plant grew. By the early 1980s, the effluent made up 25 percent of the river's flow when the river's volume was lowest. The increased effluent volume also led to increases in nitrification, ammonia, and residual chlorine, all byproducts of the treatment processes.

In 1981, Metro began planning for piping the Renton treatment plant's effluent to Puget Sound, bypassing the river entirely. When the pipeline was completed in 1987, the impact on the river was significant. Ammonia was essentially eliminated; nitrites, cadmium, and other contaminants decreased. Dissolved oxygen in the river went up to 8 milligrams per liter.

Cleaning up the sewage in the Duwamish River took care of one of its challenges. Combined sewer overflows, pollution-carrying stormwater runoff, and toxin-laced sediments remain a threat to human and ecological health. Ongoing projects are addressing those problems, but the tension between protecting water quality in the midst of an urban industrial area will remain.


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