Total Maximum Daily Loads

A TMDL is the calculated pollutant amount that a waterbody can receive and still meet Oregon water quality standards.

Through the TMDLs development process, DEQ determines the amount of a pollutant that a water body can receive without violating the applicable water quality standard. Water monitoring for TMDLs is a collaborative effort among DEQ’s Laboratory and Environmental Assessment Division, Watershed Management section and regional water quality programs. DEQ develops and implements sampling and analysis plans to characterize water quality conditions. DEQ may subsequently perform monitoring once the TMDL plan has been implemented to assess whether water quality has improved and inform future actions.

Objectives of the TMDL Program include:
  • Conducting intensive watershed assessments
  • Characterizing pollutant sources and loads
  • Developing conceptual and mathematical models
  • Establishing assimilative capacity, limiting factors, and load/wasteload allocations

View Oregon TMDLs by basin



Extent of Monitoring

Depending on the TMDL data needs, some or all of the following data may be collected:

  • Hydrology: flow, time of travel, seasonal variability, groundwater affects
  • Chemistry: longitudinal sampling surveys, synoptic sampling surveys (for dissolved oxygen), source studies
  • Temperature: shading and channel characteristics, temperature

  • Biological: fish, macro-invertebrates, algae sampling

How data is used:

  • Characterize water quality conditions and inform assessment status
  • Develop and Calibrate TMDL Models
  • Fill in existing data gaps
  • Set load limits for listed water quality parameters
  • Help determine source controls needed to meet load limits

For more TMDL information:
Search the 303(d) list for water quality status of Oregon waters

DEQ/EPA Memorandum of Agreement

DEQ and EPA signed an MOA on Feb. 1, 2000. The purpose of the MOA is to formalize the commitment to complete TMDLs in Oregon on a 10 year schedule. In addition, the MOA describes the components of a TMDL and that an implementation strategy and plans will be included with TMDLs that DEQ develops.

Consent decree

A Consent Decree between the US Environmental Protection Agency and Northwest Environmental Defense Center, John R. Churchill, and Northwest Environmental Advocates was approved and signed on Oct. 17, 2000 regarding the establishment of TMDLs based upon the Feb. 1, 2000 MOA between EPA and DEQ. The Consent Decree lists the cumulative number of TMDLs to be established through 2010.



Basin Coordinator List

Gene Foster , Watershed Management Manager, 503-229-5325


More resources

Map: TMDL Development Status for 303(d) Listed Water

U.S. EPA Region 10 Total Maximum Daily Load Program



Oregon Administrative Rules Chapter 340 Division 042 - Total Maximum Daily Loads
Rules that guide TMDL implementation including elements required for every implementation plan

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