Total Maximum Daily Load (TMDL) / Impaired Waters
Under Section 303(d) of the Clean Water Act, states, territories, and authorized tribes (referred to as "states" below) are required to develop:
- A list of impaired and threatened waters still requiring Total Maximum Daily Loads (TMDLs)
- Identification of the impairing pollutant(s)
- Priority ranking of these waters, including waters targeted for TMDL development within the next two years
A Total Maximum Daily Load (TMDL) is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet water quality standards. Developing and prioritizing TMDLs is an important step in solving water quality problems.
Impaired waters are waters that do not meet water quality standards even after point sources of pollution (such as municipal and industrial dischargers) have installed required levels of pollution controls.
States must consider "all existing and readily available information" when developing their Section 303(d) Lists for submission to EPA every two years. Along with the list, each state submits a listing methodology to EPA. At EPA's request, states must provide "good cause" for not including or removing a water body from the list. EPA may add waters to a state's list, based on EPA's review of the water quality data.
More information about TMDLs
Section 303(d) of the Clean Water Act requires that a TMDL be developed for the pollutant(s) responsible for impairing a water body. Each state compiles Section 303(d) lists, which identify the impaired water bodies within that state. States include priorities on their Section 303(d) lists by assigning each impaired water body a timeline for TMDL development.
To develop TMDLs, each state identifies the sources of pollutant loadings within an impaired water body, estimates the existing loads, and allocates load reductions from each source in order to attain and maintain water quality standards. This process includes an opportunity for public participation.
A TMDL provides states with an outline of the pollutant reductions necessary to meet the required water quality standards in an impaired water body. TMDLs are submitted to EPA for review and approval. EPA's reviewer ensures that:
- TMDLs are designed to implement applicable water quality standards.
- TMDLs include a total allowable load, as well as individual wasteload allocations and load allocations.
- TMDLs consider the impacts of background pollutant contributions.
- TMDLs consider critical environmental conditions.
- TMDLs consider seasonal environmental variations.
- TMDLs include a margin of safety.
- TMDLs have been subject to public participation.
- There is reasonable assurance that the TMDLs can be met.
EPA Region 7 Contacts
Tabatha Adkins, Regional TMDL Coordinator, can be contacted at 913-551-7128 or firstname.lastname@example.org.
Bruce Perkins, Region 7 Integrated Reporting Coordinator, can be contacted at 913-551-7056 or email@example.com.