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Water: Total Maximum Daily Loads (303d)


Overview | Glossary | Example TMDLs | Litigation

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Adaptive implementation
A process that allows for the evaluation of the adequacy of the TMDL in achieving the water quality standard. As stream monitoring continues to occur, staged or phased implementation enables water quality improvements to be recorded as they are being achieved, providing a measure of quality control and ensuring that the most cost-effective practices are implemented first.
Antidegradation policy
A required process for protecting all existing uses, keeping healthy waters healthy and giving strict protection to outstanding waters.

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Clean Water Act (CWA)
The series of legislative acts that form the foundation for protection of U.S. water resources, including the Water Quality Act of 1965, Federal Water Pollution Control Act of 1972, Clean Water Act of 1977, and Water Quality Act of 1987. CWA Secs. 305(b) and 303(d) deal specifically with water quality assessment and TMDL development.
Consent decree
Also referred to as a Consent Order, is a judicial decree expressing voluntary agreement between parties to a suit.

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Designated use
Those uses specified in water quality standards for each waterbody or segment. Recreational uses; the propagation and growth of a balanced, indigenous population of aquatic life; wildlife; and the production of edible and marketable natural resources are generally stated as "fishable and swimmable" uses. Other uses may be industrial water supply, irrigation, and navigation.

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Impaired waterbody
A waterbody (i.e., stream reaches, lakes, waterbody segments) with chronic or recurring monitored violations of the applicable numeric and/or narrative water quality criteria.
Implementation plan
The document or section of a document detailing the suite of corrective actions needed to reduce pollution and remediate an impaired waterbody. Once fully implemented, the plan should result in the waterbody achieving a "fully supporting" status. Current 303(d) regulations do not require implementation plans, though some state regulations do require an implementation plan for a TMDL.

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Loading capacity
The greatest amount of a pollutant that a water can assimilate and still meet water quality standards.
Load or loading
The total amount of pollutants entering a waterbody from one or multiple sources, measured as a rate, as in weight per unit time or per unit area.
Load allocation (LA)
The portion of the loading capacity attributed to (1) the existing or future nonpoint sources of pollution and (2) natural background sources. Wherever possible, nonpoint source loads and natural loads should be distinguished.

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Margin of safety (MOS)
A required component of the TMDL that accounts for the uncertainty in the response of the waterbody to loading reductions.
Periodic or continuous sampling and measurement to determine the physical, chemical, and biological status of a particular medium, such as air, soil or water.

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Narrative criteria
Non-numeric, qualitative guidelines that describe a desired water quality goal.
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 Section 307, 402, 318, and 405 of the Clean Water Act. Facilities subjected to NPDES permitting regulations include operations such as municipal wastewater treatment plants and industrial waste treatment facilities.
Natural background levels
Chemical, physical, and biological levels representing conditions that would result from natural processes, such as weathering and dissolution.
Nonpoint source pollution
Pollution that is not released through pipes but rather originates from multiple sources over a relatively large area. Nonpoint sources can be divided into source activities related either to land or water use including failing septic tanks, improper animal-keeping practices, forestry practices, and urban and rural runoff.
Numeric criterion
A measurable value determined for the pollutant of concern that, if achieved, is expected to result in the attainment of water quality standards in the listed waterbody.

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Point source pollution
Pollutant loads discharged at a specific location from pipes, outfalls, and conveyance channels from either municipal wastewater treatment plants or industrial waste treatment facilities. Point sources can also include pollutant loads contributed by tributaries to the main receiving water stream or river.
As defined in Clean Water Act Sec. 502(6), a pollutant means dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water.
The man-made or man-induced alteration of the chemical, physical, biological, and radiological integrity of water.

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Receiving water
Creeks, streams, rivers, lakes, estuaries, groundwater formations, or other bodies of water into which surface water, treated waste, or untreated waste are discharged.

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Section 305(b) CWA
Section of the Clean Water Act that requires states to submit a biennial report in even-numbered years to the U.S. Environmental Protection Agency describing the quality of the state's waters. The Sec. 305(b) report describes the overall water quality conditions and trends in the state.
Section 303(d) CWA
Section of the Clean Water Act that requires states periodically to identify waters that do not or are not expected to meet applicable water quality standards. These waters are identified on the Sec. 303(d) Impaired Waters List. A TMDL must be developed for each waterbody on the Sec. 303(d) list. If a listed waterbody has multiple impairments, a TMDL must be developed for each impairment.
Any person or organization with vested interest in TMDL development and implementation in a specific watershed.
Any substance or condition that adversely impacts the aquatic ecosystem.

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Third-party TMDL
A TMDL in which an organization or group other than the lead water quality agency or organization takes responsibility for developing the TMDL document and supporting analysis. Upon completion of the TMDL, the state is then responsible for submitting the TMDL document to EPA for approval.
Threatened waterbody
Any waterbody of the United States that currently attains water quality standards, but for which existing and readily available data and information on adverse declining trends indicate that water quality standards will likely be exceeded by the time the next list of impaired or threatened waterbodies is required to be submitted to EPA.
303(d) Threatened and Impaired Waters List
Under Section 303(d) of the Clean Water Act (CWA) or Act, states, territories, and authorized tribes are required to develop lists of impaired waters every two years (i.e., Section 303(d) list). The states identify all waters where required pollution controls are not sufficient to attain or maintain applicable water quality standards. States are required to establish priorities for development of TMDLs for waters on the 303(d) List (40C.F.R. §130.7(b)(4)).
303(d) and 305(b) Integrated Report
EPA recommended approach to integrating water quality conditions data submitted by states under Clean Water Act sections 303(d) and 305(b).  EPA guidance provides recommended organization for states' Integrated Report submittals.
Total maximum daily load (TMDL)
The sum of the individual wasteload allocations (WLAs) for point sources, load allocations (LAs) for nonpoint sources and natural background, and a margin of safety (MOS). TMDLs can be expressed in terms of mass per time, toxicity, or other appropriate measures that relate to a state's water quality standard.

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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 (e.g., permitted waste treatment facilities).
A geographically defined portion of navigable waters, waters of the contiguous zone, and ocean waters under the jurisdiction of the United States, including segments of rivers, streams, lakes, wetlands, coastal waters and ocean waters.
Water quality
The biological, chemical, and physical conditions of a waterbody. It is a measure of a waterbody's ability to support beneficial uses.
Water quality criteria
Elements of state water quality standards expressed as constituent concentrations, levels, or narrative statement, representing a quality of water that supports a particular use. When criteria are met, water quality will generally protect the designated use.
Water quality modeling
A system of mathematical expressions that describe both hydrologic and water quality processes. When used for the development of TMDLs, models can estimate the load of a specific pollutant to a waterbody and make predictions about how the load would change as corrective actions are implemented.
Water quality standards
State or federal law or regulation consisting of a designated use or uses for the waters of the United States, water quality criteria for such waters based upon such uses, and an antidegradation policy and implementation procedures. Water quality standards protect the public health or welfare, enhance the quality of water and serve the purposes of the Clean Water Act.
Area that drains or contributes water to a particular point, stream, river, lake, or ocean. Larger watersheds are also referred to as basins. Watersheds range in size from a few acres for a small stream to large areas of the country.

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