Colorado River Basin - What Are TMDLs?

Background:

Section 303(d)(A)(1) of the Federal Clean Water Act (CWA) requires states to identify waterbodies that do not meet water quality objectives and are not supporting their beneficial uses. Each state must submit an updated list, called the 303(d) List, to the U.S. Environmental Protection Agency (USEPA) every two years for approval. In addition, the law requires states to establish priority ranking for water bodies on the lists and develop control plans, called Total Maximum Daily Loads (TMDLs), to address the impairment. A TMDL serves as the means to attain and maintain water quality standards (WQSs) for the impaired water body.

CWA Section 303(d) and 40 Code of Federal Regulation (CFR) Section 130.2 et seq., specify the components and requirements of a TMDL. Essentially, the TMDL is a numeric target developed to achieve WQSs and must:

• Show how the TMDL will result in attainment of standards of concern in the specific water body;
• Identify and explain the basis for the total allowable load(s) such that the water body assimilation capacity is not exceeded;
• Identify and explain the basis for individual WLAs for point sources and LAs for nonpoint sources of pollution;
• Explain how an adequate margin of safety (MOS) is provided to account for uncertainty in the analysis;
• Account for seasonal variations and critical conditions concerning the flow, loading, and other water quality parameters.

If a State fails to develop a TMDL, or if USEPA rejects the State's TMDL, USEPA must develop one (CWA 303(d)(D)(2), 40 CFR 130.6(c)). Upon approval of the TMDL by USEPA, the State is required to incorporate the TMDL, along with appropriate implementation measures, into the State Water Quality Management Plan (40 CFR 130.6(c)(1), 130.7).

TMDL Development

The TMDL process involves working with stakeholders and coordinating with other programs within the Regional Water Board, such as the National Pollutant Discharge Elimination System (NPDES) and storm water programs, and the nonpoint source program. The five steps in producing a TMDL are:

1. Stakeholder involvement: Stakeholders are people (e.g., general public, business interests, government entities, local agencies, citizens, etc.) concerned about a particular water body. They become involved in TMDL development through local groups working with Regional Water Quality Control Board staff. Their interests range from pursuing the science to support TMDLs to figuring out how to implement new management approaches.
2. Water body assessment: Pollution sources and loads are determined, and their overall effect on the water body is assessed.
3. Develop allocations: Based on the assessment, pollutant loads are allocated for each source. A TMDL may address a single pollutant or many pollutants. The allocations must be designed so that the water body will attain the applicable water quality standards.
4. Develop an implementation plan: The plan describes the approach and activities required to ensure that the allocations are met.
5. Amend the Basin Plan: Before a TMDL is enforceable it must be incorporated into the appropriate Water Quality Control Plan (Basin Plan) by amending the Basin Plan in accordance with state law. If TMDLs are not incorporated into Basin Plans, they have no legal standing under state law and cannot be enforced by Regional Boards. A Basin Plan amendment requires approval by the appropriate Regional Board, the State Water Resources Control Board (State Board), the Office of Administrative Law, and the U.S. Environmental Protection Agency Region 9. A public hearing process is used for the Regional Board and State Board steps in the process.

TMDL Elements

Essential elements of a TMDL are:

Problem Statement: Describes the water body, which water quality standards are not being attained, which beneficial uses are impaired, and the nature of the impairment.

Numeric Targets: The Desired Future Condition: Defines measurements that will ensure recovery of the beneficial uses that are impaired, and attainment of standards. Numeric targets are usually not directly enforceable but are used to assess progress towards the attainment of standards.

Source Analysis: Identifies the amount, timing, and point of origin of pollutants of concern. Source analysis may be based on field measurements and/or models and estimations.

Allocations: Allocates responsibility, and identifies the parties to take the specified actions. The allocations may be specific to agencies or persons (businesses), or generally by source category or sector. Allocations of allowable pollutant burdens define TMDL endpoints (e.g., total sediment load from urban runoff). The sum of individual allocations must equal total allowable pollutant burden.

Linkage Analysis: How the Numeric Targets relate to the Problem: Describes how the actions to be taken will result in achievement of the relevant standards.

Margin of Safety: Describes how the required margin of safety was incorporated into the TMDL. The margin of safety may be implicit (i.e., using conservative assumptions), or explicit (i.e., a discrete allocation assigned to the margin of safety).

Implementation Plan: Identifies responsible parties and describes what actions will be undertaken to alleviate the impairments. The Implementation Plan identifies enforceable features (e.g., prohibition) and triggers for Regional Board action (e.g., performance standards).

Monitoring/ Re-evaluation: Describes the monitoring strategy that will be used to develop more refined information for performance evaluation and consideration of TMDL revisions, for phased TMDLs.

More information on the TMDL Program can be viewed at the State Water Board's Website:

( updated 04/16/08 )