Total Maximum Daily Loads

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What is a TMDL?

The Total Maximum Daily Load, or clean water plan, is a science-based approach to cleaning up polluted water so that it meets state water quality standards. A TMDL is a numerical value that represents the highest amount of a pollutant a surface water body can receive and still meet the standards.

The federal Clean Water Act requires states, or the U.S. Environmental Protection Agency, to develop a TMDL for each water body on the state's polluted waters list, also known as the 303(d) list (Integrated Report). The TMDL process is just one strategy used to clean up polluted waters.

In progress TMDL projects

Recently issued TMDLs

The TMDL process in Oregon

​The TMDL process starts with the Integrated Report. The Integrated Report (305(b) and 303(d) list required by the Clean Water Act) is an assessment of water quality data from the state's water bodies. We put assessed water bodies into categories based on the level of impairment. Those water bodies identified as impaired through the assessment method (not meeting water quality standards) go into the impaired category, known as the 303(d) list, (Category 5 in the Integrated Report) named for the section of the federal Clean Water Act that establishes this overall process. The 303(d) list shows us which waterbodies are impaired.

TMDL development projects are prioritized based on a variety of factors including risk to beneficial use, court ordered schedules, and permit issuance priorities. TMDL development priorities are documented in the Integrated Report and in the Performance Partnership Agreement between DEQ and EPA.

Each TMDL project is unique, but there are essential elements to all TMDLs. These elements are identified in the Federal Code of Regulations at 40 CFR § 130.7 and in Oregon Administrative Rules at OAR 340-042-0040.

We begin by identifying the 303(d) listings, waterbodies, water quality standards and beneficial uses in the project area that the TMDL will be developed.   

TMDL development includes analysis, then monitoring, followed by more technical analysis. The analysis and monitoring helps identify sources and amounts of pollutants causing the water quality problem. The technical analysis determines the pollution reductions sources must make for the waterbody to meet standards and to protect the uses of the waterbody. Any amount of pollution over the TMDL level needs to be reduced or eliminated to achieve clean water. We developed the following TMDL elements based on the results of the study:

  • Loading capacity: The amount of a pollutant or pollutants that a waterbody can receive and still meet water quality standards. The TMDL will be set at a level to ensure that loading capacity is not exceeded.

  • Excess load: The difference between the actual pollutant load in a waterbody and its loading capacity.

  • Sources: The pollutant sources and estimates, to the extent the existing data allow, of the amount of actual pollutant loading from these sources.

  • Wasteload allocations: The portions of the receiving water's loading capacity that are allocated to existing point sources of pollution, including all point source discharges regulated under the Federal Water Pollution Control Act Section 402 (33 USC Section 1342).

  • Load allocations: The portions of the receiving water's loading capacity that are allocated to existing nonpoint sources, including runoff, deposition, soil contamination and groundwater discharges, or to background sources. Load allocations are best estimates of loading, and may range from reasonably accurate estimates to gross allotments depending on the availability of data and appropriate techniques for predicting loading. Whenever reasonably feasible, natural background, long-range transport and human nonpoint source loads will be distinguished from each other.

  • Margin of safety: This element accounts for uncertainty related to the TMDL and, where feasible, quantifies uncertainties associated with estimating pollutant loads, modeling water quality and monitoring water quality. The TMDL will explain how the margin of safety was derived and incorporated into the TMDL.

  • Seasonal variation: This element accounts for seasonal variation and critical conditions in stream flow, sensitive beneficial uses, pollutant loading and water quality parameters so that water quality standards will be attained and maintained during all seasons of the year.

  • Reserve capacity: An allocation for increases in pollutant loads from future growth and new or expanded sources. The TMDL may allocate no reserve capacity and explain that decision.

  • Reasonable Assurance: A demonstration that a TMDL will be implemented by federal, state or local governments or individuals through regulatory or voluntary actions including management strategies or other controls.

  • Water Quality Management Plan (WQMP): A general plan and framework for implementation of the TMDL. The framework is designed to work in conjunction with detailed plans and analyses provided in sector-specific or source-specific implementation plans The water quality management plan will address the following as outlined in OAR 340-042-0040(I):

    • Proposed management strategies designed to meet the wasteload allocations and load allocations in the TMDL.

    • Timeline for implementing management strategies including the schedule for revising permits, achieving appropriate incremental and measurable water quality targets, implementing control actions, and completing other measurable milestones.

    • Explanation of how implementing the management strategies will result in attainment of water quality standards.

    • Timeline for attainment of water quality standards.

    • Identification of persons, including Designated Management Agencies  responsible for implementing the management strategies and developing and revising implementation plans.

    • Identification of implementation plans that are available at the time the TMDL is issued.

    • Schedule for preparation and submission of implementation plans by responsible persons, including management agencies, and processes that trigger revisions to these implementation plans.

    • Description of reasonable assurance that management strategies and implementation plans will be carried out through regulatory or voluntary actions.

    • Plan to monitor and evaluate progress toward achieving TMDL allocations and water quality standards including identification of persons responsible for monitoring and plan and schedule for reviewing monitoring information and revising the TMDL.

    • Plan for public involvement in implementing management strategies.

    • Description of planned efforts to maintain management strategies over time.

    • General discussion of costs and funding for implementing management strategies. Implementation plans may provide more detailed analyses of costs and funding for specific management strategies.

    • Citation of legal authorities relating to implementation of management strategies

  • Public Process: A public process and administrative record for development of the TMDL.

The Water Quality Management Plan is a part of the TMDL that is issued with the TMDL. The plan provides the framework of management strategies to implement the TMDL allocations and attain and maintain water quality standards. The plan is designed to work in conjunction with detailed implementation plans and analyses provided in sector-specific or source-specific implementation plans developed by a Designated Management Agency and responsible persons. DEQ works with management agencies, which are a federal, state or local governmental agency that has legal authority over a sector or source contributing pollutants, or a person(s)  responsible for their own activities that cause or contribute the pollutant, and who are identified in a TMDL.

Typically, assessment and monitoring is conducted to support evaluation of TMDL implementation.  This assessment is used to determine current status and evaluate if any changes are needed to implementation.

When monitoring data shows the water body attains water quality standards, DEQ will update the 305(b) and 303(d) list. The assessment status is changed from Category 4: Water quality limited to Category 2: Attaining. We continue periodic monitoring to ensure that the water body maintains state water quality standards and TMDL allocations or surrogates.

​The TMDL process includes getting feedback from watershed residents, local governments and other stakeholder groups. If entities or a person disagree, we attempt to resolve the disagreements through the local advisory group process or during response to comment. If the matter remains unresolved, an entity or person can petition the DEQ director for reconsideration or file for judicial review. These processes are provided to help solve technical, policy, procedural, or other disagreements regarding the TMDL project.

​TMDL development and implementation is a public process. That means we work to keep people informed and to consider their concerns and ideas. DEQ establishes a local advisory group to provide information and feedback on the TMDL during development. We coordinate with local and tribal governments and we incorporate environmental justice practices to make participation as open and accessible as possible. Community members and organizations can participate in TMDL project development and implementation in a number of ways. We strive to include local input as we plan and carry out TMDL projects.  In addition, we have a formal public comment period where anyone can provide comments. DEQ develops a response to comment document that is available to the public.