Columbia Slough TMDL Fact Sheet
What and Where is the Columbia Slough?
The Columbia Slough, a complex of narrow and shallow channels is located on the southern floodplain of the Columbia River between Fairview Lake and the Willamette River. The Slough, originally a series of wetlands and marshes, is now a highly managed water system draining the most highly industrialized area of Portland.
What is a TMDL?
Total maximum daily loads (TMDLs) describe the amount of each pollutant a waterway can receive and still not violate water quality standards. These limits can be either numerical limits or corrective or protective actions that prevent pollution. TMDLs take into account the pollution from all sources, including discharges from industry and sewage treatment facilities; runoff from farms, forests and urban areas; and natural sources such as decaying organic matter or nutrients in soil. TMDLs include a safety margin for uncertainty and growth that allows for future discharges to a river or stream without exceeding water quality standards.
Water quality monitoring of the Columbia Slough has documented a variety of pollution problems impairing existing and future beneficial uses. The Oregon Department of Environmental Quality (DEQ) has designated the slough as “water quality limited” for:
· Toxics (lead, PCBs, DDEIDDT, dieldrin, dioxin);
· Eutrophication (pH, dissolved oxygen, phosphorous, chlorophyll a);
· Bacteria;
· Temperature.
TMDLs were established for these parameters except temperature. The TMDL limits the amount of pollutant input into the Columbia Slough to values, which will not exceed the assimilative capacity of the Slough and hence meet water quality criteria. The improvements in water quality are designed to protect designated beneficial uses, including salmonid fish rearing, resident fish and aquatic life; to enable the community to use the slough for water contact recreation, boating, fishing; and to see improvements to its aesthetic quality and overall wildlife habitats.
The TMDL process directs the designated management agencies (Cities of Portland, Gresham, Fairview, and Wood Village, the Port of Portland, Multnomah County, Oregon Department of Agriculture, Oregon Department of Transportation and Department of Environmental Quality to develop and implement projects and programs that will result in improvements of Slough water quality to meet water quality standards.
The Environmental Protection Agency accepted the Columbia Slough in November 1998. The City will prepare a Memorandum of Agreement (MOA) with DEQ and a TMDL implementation plan and will develop activities that will meet Portland�s obligations. This MOA will guide Phase I of the TMDL implementation process, stormwater management, and Slough flow management activities for the next 5 years. The main activities are:
· Removal of CSO�s and eliminate direct and illicit discharges to the slough
· Monitoring of in-stream water quality
· Implementation and monitoring of Best Management Practices (BMP)
During Phase II of the TMDL implementation, in-stream water quality will be reevaluated to determine whether the Columbia Slough meets water quality standards. If the Slough meets all water quality standards, the TMDL will be lifted and the Slough will be removed from the 303d list. In case the Slough does not meet water quality standards, the TMDL and the MOA have to be reviewed and updated and additional BMPs have to be implemented.
How will the TMDL affect landowners and businesses?
The City of Portland in connection with the other DMAs is responsible for meeting in-stream water quality standards. To improve water and sediment quality in the Slough, the City will implement programs designed to improve the quality of stormwater entering the Slough through its storm sewer system. It will also investigate options to mitigate contaminated sediments. DEQ will work with numerous businesses in the Slough watershed to reduce stormwater pollutant loads from various industrial and commercial activities.
Individual business and property owners may be required to
· Improve materials handling and storage
· Pretreat stormwater prior to discharge
· Detain and treat stormwater on-site for new developments or significant redevelopments
· Implement effective erosion control measures
· Reduce discharges of toxic materials
· Monitor for water quality in private discharges to the slough
For information contact:
Frank Wildensee, Environmental Specialist, 823-2926
