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TMDL Allocations, continued

The figure to the left shows a conceptual diagram showing how loads under a TMDL might be allocated to various kinds of sources and other factors.

Margin of Safety (MOS)— Obviously, the bigger the slice of the pie, the less load that can be “given” to current or future sources.

Reserve Capacity—Deciding how much of the allowed load to assign to future growth and development presents some very interesting issues. There is an inevitable tradeoff between the interests of existing sources and those of future sources. If a TMDL does not set aside anything for the future, it will be harder to accommodate development that generates new loads of the pollutant in question. But if a relatively large amount is set aside for growth, then existing sources will get lower allocations and, therefore, will have to achieve greater reductions. A reserve capacity is optional and at the state’s discretion.

Natural Background—Allocation of the total allowed load must reflect the contribution from truly natural sources, such as areas where the soil is naturally high in a particular metal, for example.

Nonpoint Source Categories—The next two wedges illustrate that loads can be assigned to entire categories of nonpoint sources, such as all of a certain type of farming operation.

Individual Waste Load Allocations for Point Sources—A TMDL can assign different-size slices to each of these sources. These allocations in the TMDL would be the basis for each source’s NPDES permit discharge limit for the pollutant addressed by the TMDL.

Load Allocation to Specific Subbasins—This could be an option in situations where there are no significant individual point sources and the subwatershed is not dominated by one or two categories of nonpoint sources.

TMDLs are not "self-implementing". Hence, other authorities and programs must be used to implement the pollutant reductions called for by a TMDL or other strategy to achieve water quality standards. The exact authorities and programs a state, territory, or authorized tribe uses will depend on the type of sources present, as well as on social, political, and economic factors. A variety of federal, state, local, and tribal authorities and programs can be brought to bear, together with initiatives from the private sector.

The CWA provides many regulatory and voluntary tools that can be useful in achieving needed reductions. (It is likely, however, that the CWA tools alone might not be sufficient to achieve needed reductions, especially in situations where nonpoint sources dominate loadings. Other tools might be available from other federal programs, state and local government programs, academic institutions, the business community, nongovernmental organizations such as land trusts, and other sources)

Web Resources

• EPA’s website on TMDLs
• Each of the CWA tools listed in the figure to the left is covered in this module. The NPDES permit program, established in section 402 of the Clean Water Act, regulates a wide array of pollutant loads falling under the CWA’s definition of “point” sources.
• The permit program established by section 404 of the CWA deals with the placement of dredged or fill materials into wetlands and other “waters of the United States.”
• Section 401 of the CWA requires that before a federal agency can issue a license or permit for a project that might result in a discharge to waters of the US, it must have received from the state, in which the discharge would occur, a written certification. That certification must indicate that the activity would not cause an exceedence of water quality standards and would be consistent with effluent guidelines and certain other CWA provisions. Downstream states whose WQS might be exceeded as a result of federal approval of the activity also play a role in the 401 process. CWA section 319 created a federal program that provides money to states, tribes, and territories for developing and implementing programs aimed at reducing pollution from “nonpoint” sources of pollution. The CWA provides no federal regulatory authority over nonpoint sources, in contrast to point sources.
• By far, the largest federal source of money from the CWA comes through federal grants to states for the capitalization and operation of Clean Water State Revolving Loan programs. (In 1996, Congress created a Drinking Water State Revolving Loan Program under the Safe Drinking Water Act.) For more information on these and other funding sources, see EPA’s Watershed Funding Web page
• CWA section 106 authorizes federal grants to states, tribes, and territories to support the development and operation of state programs implementing the CWA.