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Modeling
and TMDL Unit : The NC TMDL Program
What Is a TMDL?
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.
A TMDL provides a detailed water quality assessment that provides the scientific foundation for an implementation plan. An implementation plan outlines the steps necessary to reduce pollutant loads in a certain body of water to restore and maintain human uses or aquatic life. The development of TMDLs and implementation plans are often the best method to improve water quality.
The Clean Water Act, section 303, establishes the water quality standards and TMDL programs.
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What is the NC TMDL Program?
The Total Maximum Daily Load (TMDL) Program is a Federal program authorized under the Clean Water Act to address waters that are not meeting uses. The program has two parts:
- The development of a list of all waters not meeting uses or where standards are violated. This list is referred to as the Section 303(d) list, after the section of the Clean Water Act which mandates it's development.
- The development of TMDLs or management plans, which can be used as a guide to restore uses of the impaired water bodies.
The Division of Water Quality (DWQ) has the responsibility of developing the 303(d) list and the subsequent TMDLs. The DWQ evaluates waters for multiple uses in each basinwide management plan. These uses include aquatic life support, primary and secondary recreation, fish consumption, water supply, and for coastal waters, shellfish harvesting. If data indicate that any one of these is sacrificed, the water body is included in the Section 303(d) list. Waters on the 303(d) list are scheduled for additional study and/or development of a TMDL.
The Modeling/TMDL Unit with the Division of Water Quality (DWQ) publishes the 303(d) list and develops TMDLs based on EPA guidance.
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Why Is North Carolina Developing TMDLs?
- The development of TMDLs and implementation plans are often the best method to improve water quality.
- All states are required by Section 303(d) of the 1972 Federal Clean Water Act (CWA) to develop TMDLs for water bodies that are impaired (too polluted to maintain their beneficial uses). The list of the lakes, rivers, streams, and estuaries in North Carolina that may need TMDLs and implementation plans is published in the report North Carolina Clean Water Act Section 303(d) List [or the North Carolina 303(d) List].
- Federal regulations prohibit the addition of certain new sources and new discharges of pollutants to waters listed on the North Carolina 303(d) List until a TMDL is established.
- Under federal law, if North Carolina does not develop its own TMDLs, the U.S. Environmental Protection Agency (EPA) must develop them.
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How Are TMDLs Developed?
TMDLs are developed by Modeling & TMDL Unit staff or independent contractors working for the agency through a scientifically rigorous process of intensive data collection and analysis. Upon adoption by the Modeling & TMDL Unit, the TMDLs are submitted for consideration for approval by the EPA.
Click here for the NC TMDL Presentation and FlowChart.
In 2002 the Modeling & TMDL Unit set a goal to develop TMDLs for all impaired waterbodies within 10 years of their first placement on the North Carolina 303(d) List.
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How Will TMDLs Be Funded?
Funding approaches being pursued include:
- Leveraging existing grants from other state and federal agencies by identifying common watershed management goals.
- Encouraging soil and water conservation districts, industry groups, local governments, and watershed groups to sponsor and locally coordinate TMDLs.
- Seeking in-kind services from other agencies, industries and conservation groups.
- Obtaining expertise, resources, and training from consulting firms and universities.
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What Happens When TMDLs Are Established?
Implementation plans are the basis for initiating local, regional, and state actions that reduce pollutant loads to levels established in TMDLs. An example of an action that might be taken is making wastewater permit limits more stringent. This may require wastewater treatment plants for communities and industry to implement additional and sometimes costly new treatment technology.
Alternatively, farmers and ranchers may be asked to use new practices which prevent fertilizers, manure, and pesticides from reaching lakes and rivers. Cities may be required to control and treat runoff from their streets.
Local input in the TMDL process is essential to determining which controls will be the most effective to implement. Additional water sampling will also be required to determine the effectiveness of the chosen controls. If the controls are found to be inadequate, then the implementation plan will be revised and more stringent measures may be adopted.
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Who Should Help Develop TMDLs?
Anyone whose interests may be affected by a TMDL project should be involved. Examples of participants include permitted wastewater dischargers, municipal and county governments, agricultural producers and groups, environmental and recreational groups, or other water users. State and federal agencies, as well as experts from universities, should also participate to provide technical and scientific support.
The TMDL process is an excellent opportunity for you to get involved in improving water quality in your local watershed. As a resident, you have unique insights into the conditions that influence water quality in your area. Your local expertise is needed to identify site-specific problems, target them for water quality cleanup, and help determine what measures will be most effective.
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How Can You Help?
Public participation is an integral part of the TMDL process. In fact it is a required part of the process. Here are a few of the ways you can get involved:
- TMDL documents are available for public review and comment. All TMDLs developed for the Division of Water Quality are available for comment for a period of 30 to 45 days.
- TMDL meetings are open to the public. The Modeling & TMDL Unit typically schedules meetings toward the end of a TMDL project. These meetings are noticed on our web site, through legal advertisements and through email list-serves.
- As the Modeling & TMDL Unit develops the current North Carolina 303(d) List, you are given a chance to review the report and provide comments.
One way to be involved is to read the North Carolina 303(d) List; identify waters in your area that are listed; find out what is being done, when, and what help is needed; and spread the word in your community.
Through careful planning and approaches like the Total Maximum Daily Load program, North Carolinians can restore and maintain the quality of North Carolina waters.
View TMDLs
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For More Information
Modeling & TMDL contacts
For more information please contact us at the number below.
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