Total Maximum Daily Load (TMDL)

The U.S. Clean Water Act (CWA) requires that the Oregon Department of Environmental Quality establish water quality standards and monitor the health of water bodies and developed a list 'impaired' streams and other water resources. Water quality standards set limits for pollutants that impact the chemical, physical, and biological integrity goals. Streams including the Willamette River, Marys River, Long Tom River, Muddy Creek and many other seasonal and year-round flowing streams do not meet water quality standards in Benton County.

Regulations are developed for each listed water resource called Total Maximum Daily Load (TMDL), then developed to improve and protect listed streams. A TMDL is 1) a calculation of the amount of a pollutant that a water body can receive and still meet water quality standards; and 2) a method to allocate an acceptable load among the agricultural, forest, municipal and industrial organizations. 

Benton County is a 'designated management agency', and is required by the State of Oregon to develop and update a water quality implementation plan, to develop reduction strategies for all TMDLs within streams outside of incorporated cities of Benton County (Document Library).

Current TMDLs within Benton County that require pollutant load reduction strategies include bacteria, mercury, and temperature. Benton County has developed strategies to address all TMDLs where Benton County has authority to regulate land uses, while encourage positive actions countywide.  In addition, the long term Benton County Riparian and Wetlands Project started in 2009, to primarily address the temperature issues in addition to supporting local comprehensive plan goals for natural stream and riparian resources including stream associated wetlands.