Tacoma stormwater system cleaning for legacy pollutants

Erasing a legacy of pollution

The Thea Foss Waterway in Commencement Bay includes three miles of nearshore habitat important for fish and wildlife. This area was contaminated by over a century of industrialization and was identified by the Environmental Protection Agency as a Superfund site in 1983. In 2006, the City of Tacoma completed a nearly 20-year effort to clean up the contaminated sediments in the Waterway. Currently, low-level contaminants from urban activities and other sources are carried to the Waterway by stormwater draining off paved areas. Pollutants from these sources contaminate the water and settle into bottom sediments where fish and wildlife find their food.

In 2001, the City of Tacoma expanded efforts to reduce pollution and improve stormwater quality. The City took a strategic approach to the clean-up by evaluating a variety of cost-effective methods to reduce stormwater pollutants entering waterways. By carefully monitoring pollution reduction effectiveness against cost, the City determined that cleaning stormwater pipes and increasing street sweeping were the most cost-effective actions for preventing further pollution to the Waterway. Initial cleaning of 230,500 feet of stormdrain pipes reduced pollutants entering the waterways by 67%-79%. Over 14 years of monitoring, bottomfish exposure to the toxic chemicals carried in stormwater has declined 65%. Tacoma’s long-term effort to clean the Waterway adds significant economic value to the city by supporting development, public access, and watershed health.

What worked:

Cleaning 230,500 feet of stormdrain pipes reduced pollutants by 67%-79%, improving water quality for fish and wildlife.
Reducing pollutants in waterways and sediments reduced exposure of bottomfish to pollutants by 65%.
Using vacuum street sweepers was 10-30% more effective at pollutant removal than mechanical street sweepers.
Using water quality and biological data collection to compare the cost-effectiveness of different stormwater management practices ensures public funds are spent efficiently.

Benefits: