Columbia Slough - Pollution

Pollution

After years of piping raw sewage directly into the waterway, Portland built its first sewage treatment plant next to the lower slough in 1952. The Columbia Boulevard Wastewater Treatment Plant handled a combination of raw sewage and storm runoff that flowed into the sanitary sewer system from all over the city and piped the treated water into the Columbia River. When runoff exceeded the plant's capacity during heavy rains, sewage still entered the slough from combined sewer overflows (CSO)s at 13 outfalls.

The city closed the St. Johns Landfill, adjacent to the lower slough, in 1991. Pressed by citizen action groups, it agreed in 1993 to establish a 50-foot (15 m) environmental conservation zone along the slough. In response to a threatened lawsuit, the city began a comprehensive cleanup of the slough in 1994, and a year later it received a $10 million grant from the EPA for the purpose.

Of the streams monitored in the lower Willamette basin by the Oregon Department of Environmental Quality (DEQ) between 1986 and 1995, the Columbia Slough had the worst pollution scores. DEQ's measurements came from the slough at Landfill Road, 2.6 miles (4.2 km) from the mouth. On the Oregon Water Quality Index (OWQI) used by DEQ, water quality scores can vary from 10 (worst) to 100 (ideal). The average for the Columbia Slough was 22, or "very poor". By comparison, the average in the Willamette River at the Hawthorne Bridge in downtown Portland was 74 during the same years. Measurements of water quality at the Landfill Road site during the years covered by the DEQ report showed high concentrations of phosphates, ammonia and nitrates, fecal coliform bacteria, and suspended solids, and a high biochemical oxygen demand. High temperatures enhanced extreme eutrophication in the summer.

The Port of Portland began efforts in 1997 to reduce the flow of aircraft deicing chemicals from the airport into the waterway, though it still diverts concentrated chemicals (mostly glycol) directly into the slough during rare times of reservoir overflow. By 2000 the City of Portland had spent about $200 million to nearly eliminate CSOs from entering the slough. It also replaced septic tank and cesspool systems near the middle and upper slough with sanitary sewers. BES analysis of water samples taken between 1995 and 2002 showed that by the end of this period DEQ water quality standards for Escherichia coli, the indicator organism for fecal contamination, were nearly always being met in the upper and middle sloughs and generally being met in the lower slough. Despite these and other improvements in water quality, the slough is not a safe source of edible fish. The Multnomah County Health Department and other agencies have advised people to avoid or greatly reduce consumption of fish and crayfish from the slough because they contain polychlorinated biphenyls (PCB) and pesticides.