The early days of sewage treatment and disposal

In the late 1890s and early 1900s, the chief engineer for the City of Seattle, R. (Reginald) H. Thomson (external link), led the design and construction of the city's sewer system. In planning the system for future growth, Thomson designed a brick sewer 12 feet in diameter across the north end of Seattle that went beyond needs of the time. Some huge sewer lines he designed are still in use today.

But back in Thomson's time, sewage treatment was not an issue. So the North Trunk Sewer discharged untreated sewage into Puget Sound. Finished in 1918, it reached Puget Sound at the base of the bluff at West Point. A dam blocked the lower half of the sewer line where it came through the bluff, but a smaller pipe exited the dam.

Outfall for sewage on Seattle's Magnolia Bluff, 1932. Source: Seattle Municipal Archives, Item No: 38497

In the mid-1950s, the pipe carried 40 million gallons a day of city sewage through an outfall that ended a short distance offshore, about 25 feet deep. At any tide, the sewage caused a fan-shaped stain in the water of Puget Sound that was easily seen from the air.

At certain tides, the sewage washed aback onto shore. When it rained hard, sewage spilled over the dam in the North Trunk Sewer and spread across the beach. The sandy spit was coated with a dark slime, and health official closed nearby beaches because of bacterial contamination. And above West Point was Fort Lawton, a U.S. Army base, which prohibited public access to the West Point beach.

Throughout the Seattle-King County region in those days, only about 47 percent of all sewage got any treatment. Sixty outfalls discharged untreated waste into the Duwamish Waterway, Elliott Bay and Puget Sound.

And around Lake Union, Green Lake and Lake Washington, sewers carrying a combination of sewage and stormwater overflowed in rainy weather, contaminating those lakes and often forcing closure of swimming beaches.

As population grew in communities surrounding Lake Washington, 10 small sewage-treatment plants discharged 20 million gallons of effluent into the lake daily. Although the plants provided secondary treatment, scientists in the early 1950s began suspecting their phosphorus-rich effluent was damaging the lake. The effluent stimulated the growth of algae that deprived the lake of light and consumed oxygen from the water.

That led to a decline in water transparency. Green scum could often be seen on the lake surface, and in summer the unpleasant odor of dying algae was in the air.