Two Decades of Work Result in Meeting Water Quality Standards for Bacteria in the Lower Columbia Slough

Photo: The Columbia Slough is a 19-mile-long complex of narrow, shallow channels located on the southern floodplain of the Columbia River between Fairview Lake and the Willamette River.

You might not know this, but keeping poop out of the water is a lot of work! The Department of Environmental Quality is responsible for keeping Oregon’s waters safe and healthy and restoring streams and lakes from sources of nonpoint source pollution, such as bacteria from human and animal waste. This is a long-term investment that takes a combination of resources, partnerships and time.

One such long-term investment recently paid off when 20 years of hard work and elbow grease reduced bacteria levels in an eight-mile segment of the Columbia Slough. A recent DEQ report found data collected between 2008–2017 indicate that the Columbia Slough has consistently met water quality standards – a major victory.

A dirty past

The Columbia Slough is a 19-mile-long complex of narrow, shallow channels located on the southern floodplain of the Columbia River. The U.S. Environmental Protection Agency identifies the Columbia as one of the nation’s seven “great water bodies” in need of heightened protection from environmental harm.

In the mid-1990s, Columbia Slough water quality routinely failed to meet standards for recreational use, prompting DEQ to add it to the impaired waters list. This decision meant DEQ had to develop a pollutant reduction plan for the watershed. These plans, called Total Maximum Daily Loads, or TMDLs, develop pollutant “loads” to meet water quality standards over time for various sources of pollution to the watershed, such as from urban stormwater runoff, or from agriculture or forestry practices.

DEQ’s TMDL modeling efforts indicated that the primary sources of bacteria were combined sewer overflows in the lower slough, poor connections and failing septic systems in the middle slough, and stormwater in the upper slough.

Power through Partnerships

Overflows of stormwater are particularly problematic when they mix with raw sewage during periods of heavy rain. To reduce sewer overflows, the City of Portland installed the “Big Pipe,” a massive stormwater system upgrade along the Willamette River, as well as in the Columbia Slough. This $1.4 billion investment, completed in 2011, collects the overflow from the combined sewers and stores it until it can be transported for treatment at the wastewater treatment plant. This has been nearly 100% effective in reducing the volume of stormwater and raw sewage overflows from reaching the slough’s waters.

Through DEQ State Revolving Loans, Portland also received approximately $500,000 for revegetation work. Planting trees and shrubs along the Columbia Slough and its tributaries act as natural filters to remove bacteria and other pollutants from runoff flowing into streams. Other organizations, such as the Port of Portland, Multnomah County Drainage District, and the Columbia Slough Watershed Council have also made considerable investments by planting trees and stabilizing streambanks in the watershed, and creating rain gardens in the Cully Neighborhood. These organizations and the partnerships formed were instrumental in reducing bacteria to the Lower Columbia Slough.

A success?

Photo: A rain garden installation by Multnomah Youth Cooperative in Portland’s Cully neighborhood, made possible by DEQ funding.

Was this a success story? Absolutely. Is the work completed? No.

There are other water quality impairments in the Columbia Slough and remaining bacteria exceedances in the Upper Columbia Slough. Restoration work is a marathon. Success in this case involved a combination of regulation, volunteer organization know-how, and individuals getting things done. Hopefully, there will be more success stories to tell in the not-too-distant future.

For more details on this story , or other nonpoint source success stories from across the nation, see EPA’s website.

Andrea Matzke, Lower Willamette Basin Coordinator

Published by Oregon Department of Environmental Quality

DEQ’s mission is to be a leader in restoring, maintaining and enhancing the quality of Oregon’s air, land and water.

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