The Total Maximum Daily Load (TMDL) Program is a Federal program authorized under the Clean Water Act to address waters that are not meeting water quality standards. A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. The TMDL is then used to establish limits on sources of the pollutant which are classified as either point sources (waste load allocation), and non point sources (load allocation). The TMDL must account for seasonal variation in water quality and include a margin of safety to ensure that the TMDL allocations will adequate to protect the body of water.
The Modeling/TMDL Unit with the Division of Water Quality (DWQ) publishes the 303(d) list and develops TMDLs based on EPA guidance.
Please visit EPA's Introduction to TMDLs for more information on the TMDL development process.
Addressing Point Sources:
Once a TMDL is approved by the US EPA the pollution limits calculated for the waste load allocation (point sources) are enforced under the National Pollutant Discharge Elimination System (NPDES). For example, if there are two point sources discharging a pollutant on interest, the TMDL will assign each of the point sources a waste load allocation which will be reflected in the new NPDES permit for the facility. This may require wastewater treatment plants to implement additional and sometimes costly new treatment technology.
Addressing Non-Point Sources:
The TMDL load allocation is calculated for all non-point sources that are contributing to the pollution. Depending on the sources identified in the TMDL, the load allocation may apply to septic tanks, fertilizer runoff from agricultural and residential areas, or sediment runoff from new construction sites. Unlike point sources, the TMDL does not have authority in most cases to force a reduction of pollutants from non-point sources. In this case a TMDL Implementation Plan will outline a set of recommendations to improve the non-point source pollution identified in the TMDL. These plans are the basis for initiating local, regional, and state actions that reduce pollutant loads to levels established in TMDLs for non point sources.
Local input in the TMDL process is essential to determining which controls will be the most effective to implement. Additional 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. The plans may ask farmers and ranchers to use new practices which prevent fertilizers, manure, and pesticides from reaching lakes and rivers. Cities may need to enact new zoning ordinances.
TMDLs are usually only effective at addressing non point sources when enough interest is present from the community, local governments, or water quality advocacy groups, to carry out the implimentation plan.
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.
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:
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.