A TMDL or Total Maximum Daily Load is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that amount to the pollutant's sources.
Water quality standards are set by States, Territories, and Tribes. They identify the uses for each waterbody, for example, drinking water supply, contact recreation (swimming), and aquatic life support (fishing), and the scientific criteria to support that use.
A TMDL is the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources. The calculation must include a margin of safety to ensure that the waterbody can be used for the purposes the State has designated. The calculation must also account for seasonal variation in water quality.
The Clean Water Act, section 303, establishes the water quality standards and TMDL programs.
Over 40% of our assessed waters still do not meet the water quality standards states, territories, and authorized tribes have set for them. This amounts to over 20,000 individual river segments, lakes, and estuaries.
These impaired waters include approximately 300,000 miles of rivers and shorelines and approximately 5 million acres of lakes -- polluted mostly by sediments, excess nutrients, and harmful microorganisms. An overwhelming majority of the population - 218 million - live within 10 miles of the impaired waters.
A TMDL specifies the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and allocates pollutant loadings among point and nonpoint pollutant sources. By law, EPA must approve or disapprove lists and TMDLs established by states, territories, and authorized tribes. If a state, territory, or authorized tribe submission is inadequate, EPA must establish the list or the TMDL. EPA issued regulations in 1985 and 1992 that implement section 303(d) of the Clean Water Act - the TMDL provisions.
While TMDLs have been required by the Clean Water Act since 1972, until recently states, territories, authorized tribes, and EPA have not developed many. Several years ago citizen organizations began bringing legal actions against EPA seeking the listing of waters and development of TMDLs. To date, there have been about 40 legal actions in 38 states. EPA is under court order or consent decrees in many states to ensure that TMDLs are established, either by the state or by EPA.
States, territories, and authorized tribes must list waters that are both impaired and threatened by pollutants.
The list is composed of waters that need a TMDL.
At the state's, territory's, or authorized tribe's discretion, the waterbody may remain on the list after EPA approves the TMDL, or until water quality standards are attained.
States, territories, and authorized tribes are to submit their list of waters on April 1 in every even-numbered year, except in 2000. In March 2000, EPA issued a rule removing the requirement for the 2000 list - though some states are choosing to submit such lists on their own initiative.
States, territories, and authorized tribes must consider "all existing and readily available water quality-related information" when developing their lists.
Monitored and evaluated data may be used.
The methodology must be submitted to EPA at the same time as the list is submitted.
At EPA's request, the states, territories, or authorized tribes must provide "good cause" for not including and removing a water from the list.
A TMDL is the sum of allocated loads of pollutants set at a level necessary to implement the applicable water quality standards, including -
Wasteload allocations from point sources, and
Load allocations from nonpoint sources and natural background conditions.
A TMDL must contain a margin of safety and a consideration of seasonal variations.
States, territories, and authorized tribes must establish a priority ranking of the listed waterbodies taking into account the severity of pollution and uses to be made of the water, for example, fishing, swimming, and drinking water.
The list must identify for each waterbody the pollutant that is causing the impairment.
States, territories, and authorized tribes must identify waters targeted for TMDL development within the next 2 years.
Calculations to establish TMDLs are subject to public review as defined in the state's continuing planning process.
EPA has 30 days in which to approve or disapprove a state's, territory's, or authorized tribe's list and the TMDLs.
If EPA disapproves either the state's, territory's, or authorized tribe's list or an individual TMDL, EPA has 30 days to establish the list or the TMDL. EPA must seek public comment on the list or TMDL it establishes.
EPA issued guidance in August, 1997, to respond to some of the issues raised as the program developed. The guidance includes a number of recommendations intended to achieve a more nationally consistent approach for developing and implementing TMDLs to attain water quality standards. These recommendations include: States, territories, and authorized tribes should develop schedules for establishing TMDLs expeditiously, generally within 8-13 years of being listed. EPA Regions should have a specific written agreement with each state, territory or authorized tribe in the Region about these schedules. Factors to be considered in developing the schedule could include: Number of impaired segments;
- Length of river miles, lakes, or other waterbodies for which TMDLs are needed;
- Proximity of listed waters to each other within a watershed;
- Number and relative complexity of the TMDLs;
- Number and similarities or differences among the source categories;
- Availability of monitoring data or models; and
- Relative significance of the environmental harm or threat.
States, territories, and authorized tribes should describe a plan for implementing load allocations for waters impaired solely or primarily by nonpoint sources, including - Reasonable assurances that load allocations will be achieved, using incentive-based, non-regulatory or regulatory approaches. TMDL implementation may involve individual landowners and public or private enterprises engaged in agriculture, forestry, or urban development. The primary implementation mechanism may include the state, territory, or authorized tribe section 319 nonpoint source management program coupled with state, local, and federal land management programs and authorities,
Recognition of other watershed management processes and programs, such as local source water protection and urban storm water management programs, as well as the state's section 303(e) continuing planning process.
