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Cleaning Up the Columbia Slough’s Sediment

Photo shows waterway winding from left to right with trees, muddy banks, and piles of wood along the sides.
Environmental Services' Columbia Slough Sediment Program works closely with the Oregon Department of Environmental Quality to investigate environmental conditions in the slough and implement actions to prevent pollution and improve watershed health.

The contamination in the Columbia Slough's sediments is widespread and at relatively low concentrations. It reflects years of historic agricultural and industrial activities in the areas around the slough that contributed long-lasting pollutants to the sediments. With more than 200 stormwater outfalls that carry runoff from public streets and neighborhoods directly to the slough, the City also has a role in the cleanup of slough sediment.

The Columbia Slough Sediment Program is responsible for meeting the requirements of the state’s environmental cleanup law. The requirements are outlined in the 2005 Oregon Department of Environmental Quality Record of Decision for Slough Sediments. Since 1993, Environmental Services and the Oregon Department of Environmental Quality have been working together to investigate environmental conditions in the slough and implement actions to reduce contaminant discharges and improve watershed health.

Our Cleanup Approach

  • Identify and work with businesses to prevent pollution from industrial and commercial facilities.
  • Stop unauthorized and illegal discharges to storm sewers that flow directly to the slough.
  • Implement citywide actions to meet the requirements of the City’s Municipal Separated Stormwater Sewer permit and Total Maximum Daily Load Implementation Plan.
  • Install pollution reduction facilities, such as green streets and stormwater filters, to reduce contaminant levels in stormwater runoff from selected public roadways before discharge to the slough.
  • Test sediment quality and fish tissue in the slough over time to assess progress reducing pollutant levels.
  • Stop soil erosion.
  • Encourage property owners to landscape with native plants and reduce pesticide use.
  • Build and restore wetlands to filter stormwater.
  • Add native plants and trees along the banks of the slough to buffer the water from human activity.
  • Engage residents of the Columbia Slough watershed to ensure they know how they can help keep rivers and streams clean.
  • Eliminate sanitary waste overflows into the slough. In 2000, Environmental Services finished building the Columbia Slough combined sewer overflow projects, which eliminated combined sewer overflows to the slough.

Annual Report

This past year, we saw the completion of the East Whitaker Pond cleanup project and the Department of Environmental Quality’s evaluations/cleanup actions at more than 20 properties in the watershed to prevent sediment recontamination. The City continued source identification and testing in more than 35 stormwater outfall basins and preliminary design of stormwater treatment alternatives in 13 basins.

More Information