OAR 340-042-0040
Establishing Total Maximum Daily Loads (TMDLs)


The Department will establish TMDLs for pollutants in waters of the state that are listed in accordance with the Federal Water Pollution Control Act Section 303(d) (33 USC Section 1313(d)).


The Department will group stream segments and other waterbodies geographically by subbasin and develop TMDLs for those subbasins, unless it determines another approach is warranted.


The Department will prioritize and schedule TMDLs for completion considering the following factors:


Severity of the pollution,


Uses of the water,


Availability of resources to develop TMDLs,


Specific judicial requirements, and


Any other relevant information.


A TMDL will include the following elements:


Name and location. This element describes the geographic area for which the TMDL is developed and includes maps as appropriate.


Pollutant identification. This element identifies the pollutants causing impairment of water quality that are addressed in the TMDL.


Water quality standards and beneficial uses. This element identifies the beneficial uses in the basin and the relevant water quality standards, including specific basin standards established in OAR 340-041-0202 through 340-041-0975. The beneficial use that is most sensitive to impairment by the pollutant or pollutants addressed in the TMDL will be specified.


Loading capacity. This element specifies 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. Flow assumptions used in the TMDL will be specified.


Excess load. This element evaluates, to the extent existing data allow, the difference between the actual pollutant load in a waterbody and the loading capacity of that waterbody.


Sources or source categories. This element identifies the pollutant sources and estimates, to the extent existing data allow, the amount of actual pollutant loading from these sources. The TMDL will establish wasteload allocations and load allocations for these sources. The Department will use available information and analyses to identify and document sources.


Wasteload allocations. This element determines 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. This element determines 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 anthropogenic 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. This element is 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.


Water quality management plan (WQMP). This element provides the framework of management strategies to attain and maintain water quality standards. The framework is designed to work in conjunction with detailed plans and analyses provided in sector-specific or source-specific implementation plans. The WQMP will address the following:


Condition assessment and problem description.


Goals and objectives.


Proposed management strategies designed to meet the wasteload allocations and load allocations in the TMDL. This will include a categorization of sources and a description of the management strategies proposed for each source category.


Timeline for implementing management strategies including:
Schedule for revising permits,
Schedule for achieving appropriate incremental and measurable water quality targets,
Schedule for implementing control actions, and
Schedule for 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 (DMAs), responsible for implementing the management strategies and developing and revising sector-specific or source-specific implementation plans.


Identification of sector-specific or source-specific implementation plans that are available at the time the TMDL is issued.


Schedule for preparation and submission of sector-specific or source-specific implementation plans by responsible persons, including DMAs, and processes that trigger revisions to these implementation plans.


Description of reasonable assurance that management strategies and sector-specific or source-specific 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. Sector-specific or source-specific 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.


To determine allocations for sources identified in the TMDL, the Department:


Will use water quality data analyses, which may include statistical analyses or mathematical models.


May use surrogate measures to estimate allocations for pollutants addressed in the TMDL. The Department may use one or more surrogate measures for a pollutant that is difficult to measure or highly variable. A surrogate measure will be closely related to the pollutant, and may be easier to monitor and track. The TMDL will establish the correlation between the surrogate measure and pollutant.


The Department will distribute wasteload and load allocations among identified sources and in doing so, may consider the following factors:


Contributions from sources;


Costs of implementing measures;


Ease of implementation;


Timelines for attainment of water quality standards;


Environmental impacts of allocations;


Unintended consequences;


Reasonable assurances of implementation; and


Any other relevant factor.


After issuing the TMDL, the Department may revise the loading capacity and allocations to accommodate changed needs or new information. In making these revisions, the Department will comply with the public notice provisions in OAR 340-042-0050 (Public Participation)(2) and procedures for issuing TMDL orders in OAR 340-042-0060 (Issuing a Total Maximum Daily Load).


If the Environmental Protection Agency establishes a TMDL addressing waterbodies in Oregon, the Department may prepare a WQMP to implement that TMDL
[Publications: Publications referenced are available from the agency.]

Source: Rule 340-042-0040 — Establishing Total Maximum Daily Loads (TMDLs), https://secure.­sos.­state.­or.­us/oard/view.­action?ruleNumber=340-042-0040.

Last Updated

Jun. 8, 2021

Rule 340-042-0040’s source at or​.us