Total maximum daily loads (TMDLs)

Scope

The CWA establishes a process for states to identify waters within their boundaries where implementing technology-based controls isn’t enough to achieve water quality standards. States establish a priority ranking of these waters and, for the priority waters, develop TMDLs. A TMDL identifies the amount of a specific pollutant or property of a pollutant, from point, nonpoint, and natural background sources, including a margin of safety, that may be discharged to a water body and still ensure that the water body attains water quality standards. The allocations of pollutant loadings to point sources are called wasteload allocations (WLAs).

Regulatory citations

• 40 CFR 130.7 — Total maximum daily loads (TMDL) and individual water quality-based effluent limitations

Key definitions

• Best Management Practices (BMPs): Methods, measures, or practices selected by an agency to meet its nonpoint source control needs. BMPs include but are not limited to structural and nonstructural controls and operation and maintenance procedures. BMPs can be applied before, during and after pollution-producing activities to reduce or eliminate the introduction of pollutants into receiving waters.
• Direct discharge: The discharge of a pollutant.
• Discharge of a pollutant:
  • Any addition of any “pollutant” or combination of pollutants to “waters of the United States” from any “point source,” or
  • Any addition of any pollutant or combination of pollutants to the waters of the shoreline or the ocean from any point source other than a vessel or other floating craft which is being used as a means of transportation.
  • This definition includes additions of pollutants into waters of the United States from: surface runoff which is collected or channeled by man; discharges through pipes, sewers, or other conveyances owned by a state, municipality, or other person which do not lead to a treatment works; and discharges through pipes, sewers, or other conveyances, leading into privately owned treatment works. This term does not include an addition of pollutants by any “indirect discharger.”
• Effluent limitation: Any restriction on quantities, discharge rates, and concentrations of “pollutants” which are “discharged” from “point sources” into “waters of the United States,” shorelines, or the ocean.
• Effluent limitations guidelines: Regulations published by EPA to adopt or revise effluent limitations.
• General permit: An NPDES permit issued under 122.28 authorizing a category of discharges under the CWA within a geographical area.
• Load allocation (LA): The portion of a receiving water’s loading capacity that is attributed either to one of its existing or future nonpoint sources of pollution or to natural background sources. Load allocations are best estimates of the loading, which may range from reasonably accurate estimates to gross allotments, depending on the availability of data and appropriate techniques for predicting the loading. Wherever possible, natural and nonpoint source loads should be distinguished.
• National Pollutant Discharge Elimination System (NPDES): The national program for issuing, modifying, revoking and reissuing, terminating, monitoring and enforcing permits, and imposing and enforcing pretreatment requirements, under the CWA.
• Nonpoint sources: Discharges of a pollutant that does not originate from a specific point, outfall, pipe, or other specific place. It can result from land runoff or seepage or be deposited from the atmosphere. Examples include excess fertilizers, herbicides, and pesticides from farms and lawns; oil, grease, and toxic chemicals from industrial sites and energy production; sediment from improperly managed construction sites; crop lands, forests, and eroding streambanks; bacteria and nutrients from animal waste and faulty septic systems; and atmospheric deposits from hydromodification (e.g., dams).
• Permit: An authorization, license, or equivalent control document issued by EPA or an approved state to meet effluent guidelines. The term includes a NPDES general permit, but does not include any permit which has not yet been the subject of final agency action, such as a draft permit or a proposed permit.
• Point source: Any discernible, confined, and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, landfill leachate collection system, vessel or other floating craft from which pollutants are or may be discharged. This term does not include return flows from irrigated agriculture or agricultural storm water runoff.
• Pollutant: Dredged spoil, solid waste, incinerator residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials (except those regulated under the Atomic Energy Act of 1954, as amended), heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water.
• Total maximum daily loads (TMDLs): The amount of a specific pollutant or property of a pollutant, from point, nonpoint, and natural background sources, including a margin of safety, that may be discharged to a water body and still ensure that the water body attains water quality standards.
• Wasteload allocation (WLA): The portion of a receiving water’s loading capacity that is allocated to one of its existing or future point sources of pollution. WLAs constitute a type of water quality-based effluent limitation.
• Water quality management (WQM) plan: A state or areawide waste treatment management plan developed and updated in accordance with the provisions of sections 205(j), 208 and 303 of the Clean Water Act and 40 CFR 130.

Summary of requirements

The regulations governing the TMDL program are found at 40 CFR 130.7. Once a state has identified its impaired waters, it must:

• Set up its TMDLs;
• Set priorities for developing the loads;
• Establish loads for segments identified, including water quality monitoring, modeling, data analysis, calculation methods, and the list of pollutants to be regulated;
• Submit the list of segments identified, priority ranking, and loads established to EPA for approval;
• Incorporate the approved loads into the state’s water quality management plans and NPDES permits;
• Describe the process in its State Continuing Planning Process.