Total Maximum Daily Load Program

Background & Information


The Federal Clean Water Act (CWA), contains two strategies for managing water quality. One, a technology-based approach that envisions requirements to maintain a minimum level of pollutant management using the best available technology, was the great innovation of the 1972 Act. The other, a water quality-based approach, relies on evaluating the condition of surface waters and setting limitations on the amount of pollution that the water can be exposed to without adversely affecting the beneficial uses of those waters. Section 303(d) of the CWA bridges these two strategies. Section 303(d) requires that the states make a list of waters that are not attaining standards after the technology-based limits are put into place. For waters on this list (and where the US EPA administrator deems they are appropriate) the states are to develop total maximum daily loads or TMDLs. A TMDL must account for all sources of the pollutants that caused the water to be listed. Federal regulations require that the TMDL, at a minimum, account for contributions from point sources (federally permitted discharges) and contributions from nonpoint sources. US EPA is required to review and approve the list of impaired waters and each TMDL. If US EPA cannot approve the list or a TMDL they are required to establish them for the state.

TMDLs are established at the level necessary to implement the applicable water quality standards. A TMDL requires that all sources of pollution and all aspects of a watershed's drainage system be reviewed, not just the pollution coming from discrete conveyances (known as point sources), such as a discharge pipe from a factory or a sewage treatment plant. Point sources are defined in the Clean Water Act, Section 502.

"Nonpoint source" pollution (also called polluted runoff) is the release of pollutants from everything other than point sources. These include landscape scale sources such as storm water and agricultural runoff, and dust and air pollution that find their way into water bodies. Nonpoint source pollution is not typically associated with discrete conveyances. Nonpoint sources are not defined in statute, but are considered everything that is not covered under the point source definition.

The Clean Water Act does not expressly require the implementation of TMDLs. Section 303(d), 303(e), and their implementing regulations require that approved TMDLs be incorporated into water quality control plans. The U.S. Environmental Protection Agency (USEPA) has established regulations (40 CFR 122) requiring that National Pollutant Discharge Elimination System (NPDES) permits be revised to be consistent with any approved TMDL. A new federal regulation, established in August 2000 and set to become effective in October 2001, requires that implementation plans be developed along with the TMDLs.

In California, the SWRCB has interpreted state law (Porter-Cologne Water Quality Control Act, California Water Code Section 13000 et. seq.) to require that implementation be addressed when TMDLs are incorporated into Basin Plans (water quality control plans). The Porter-Cologne Act requires each Regional Board to formulate and adopt water quality control plans for all areas within its region. It also requires that a program of implementation be developed that describes how water quality standards will be attained. TMDLs can be developed as a component of the program of implementation, thus triggering the need to describe the implementation features, or alternatively as a Water Quality Standard. When the TMDL is established as a standard, the program of implementation must be designed to implement the TMDL. Typically a revision to the program of implementation is needed whenever a new standard is adopted.

The requirement to develop TMDLs has been in the Clean Water Act since 1972. In the 1970's, point source pollution was considered the most significant problem affecting water quality in rivers and streams. The innovations in the Clean Water Act established extensive programs to address point sources, and the vast majority of federal dollars went to implement point source controls. State funding priorities mirrored the federal effort. During the 25 years following the enactment of the Clean Water Act, the technology-based effort received the highest priority and the vast majority of funding. In California, the State and Regional Boards also used state authorities provided by the Porter-Cologne Act to implement smaller scale corrective actions for nonpoint source pollution problems. Most of these efforts were not formally submitted to the USEPA as TMDLs.

By the late 1980s programs focusing on treatment facilities resulted in better controls of point source pollution. However, the concerns over general water quality were elevated again due to the growing impacts of nonpoint source pollution. Many environmental groups looked to the TMDL requirements to address the continuing water quality problems. A series of lawsuits ensued to compel regulatory agencies to take an assertive approach to TMDL developments. To date, over 40 lawsuits have been filed throughout the country, mostly brought by environmental groups. The TMDL lawsuits were generally filed against USEPA due to its responsibility to approve TMDLs. Some of the lawsuits have resulted in negotiated settlements and consent decrees that are supervised by the courts. California is currently operating under three consent decrees covering most of the North Coast Region, all of the Los Angeles Region, and Newport Bay and its tributaries in the Santa Ana Region. Additional statewide suits are under litigation.

At this point in time the concerns over implementation have become a significant driving force in TMDL development. While these concerns fall largely outside of the requirements of Section 303)d), they are nonetheless fundamental to achieving water quality improvements from the development of TMDLs. It is possible to work through technical assessments of total load without concern for implementation. However, in developing allocations to various sources it is imperative to consider the possible mechanisms by which pollution can be reduced. Failing to consider implementation options can easily lead to allocation schemes that are far more costly than necessary or, in the worst case, unachievable. California has dedicated itself to pursuing TMDL development, including programs of implementation, in an open and public forum that enlists the opinions of all affected parties. The TMDL strategy in California relies on an adaptive process that matches management capabilities with scientific understanding. It relies heavily on engaging the public and cultivating an understanding of watershed issues.

Development of TMDLs

TMDLs in California are developed either by RWQCBs or by USEPA. TMDLs developed by RWQCBs are designed as Basin Plan amendments and include implementation provisions. TMDLs developed by USEPA typically contain the total load and load allocations required by Section 303(d), but do not contain comprehensive implementation provisions. This stems from the fact that USEPA authorities related to implementation of nonpoint source pollution control measures are generally limited to education and outreach as provided by CWA Section 319. TMDLs are currently required for all waters and pollutants on the 303(d) list. TMDLs must consider and include allocations to both point sources and nonpoint sources of listed pollutants. Although the abbreviation stands for "Total Maximum Daily Load," the limitations contained in a TMDL may be other than "daily load" limits. There also can be multiple TMDLs on a particular water body, or there can be one TMDL that addresses numerous pollutants. The basis for grouping is whether or not there can be a common analytical approach to the assessment or a common management response to the impairment.

Steps for Developing TMDLs

There are five steps in producing a TMDL:

  • Involve Stakeholders: Stakeholders can be the general public, business interests, government entities, environmental groups, or anyone concerned with a particular water body. Stakeholders are involved at the beginning of the process in order to provide input to the RWQCBs on the development of TMDLs.
  • Assess Water Body: In this step, pollution sources and amounts, or "loads," are identified for various times of the year. Then the overall effect of these loads on the water body is determined.
  • Define the Total Load and Develop Allocations: To ensure water quality standards are met and beneficial uses are attained, allocations of pollutant load to all sources are established for the pollutant(s) in question. TMDLs can address single pollutants or combinations of pollutants. The sum of the allocations must result in the water body attaining the applicable water quality standards. Federal regulations provide that TMDLs can be expressed as mass, thermal energy, toxicity or other appropriate measures. In California, toxicity and other appropriate measures often serve as the basis for TMDLs. As watershed management efforts mature it is likely that an increased dependence on measures other than mass or thermal energy will serve as the basis for TMDLs.
  • Develop Implementation Plan: This step is a description of the approach and activities to be undertaken to ensure the allocations are met and identification of parties responsible for carrying out the actions.
  • Amend the Basin Plan: Federal law requires that TMDLs be incorporated into the Basin Plans. The Basin Plan is a legal document that describes how a Regional Board would manage water quality. The TMDLs must be formally incorporated into the Basin Plan to be part of the basis for Regional Board actions. Basin Plan amendments are adopted through a public process that requires approval of the TMDLs by a Regional Board, the State Board, the Office of Administrative Law, and USEPA Region 9.

TMDL Elements

A complete TMDL must contain all of the following elements in order to be approved by the U.S.EPA:

  • Problem Statement: Describes 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.
  • Implementation Plan: 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).
  • 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.
  • 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.
  • 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).

Current TMDL Status

Technical issues and the number of combinable pollutants affect the exact number of TMDLs that will be necessary to address the State's water quality problems. Some multiple pollutants can be addressed in a single TMDL or multiple water bodies in a watershed may be addressed in a single TMDL project. Based on the current 303(d) list with over 1,883 water body/pollutant combinations, the State Board estimates that the total number of TMDLs needed is over 400 projects. The Regional Boards are currently engaged in developing over 120 TMDLs, many addressing multiple pollutants. Schedules have been developed for establishing all required TMDLs over a 13-year period. More detailed schedules of work to be undertaken in the 3- and 5-year periods have also been developed.