What total maximum daily load (TMDL) means to agriculture

TMDL is becoming a common term in rural communities. It’s important for farmers to understand how TMDLs affect nearby watersheds.

Within agriculture the acronym TMDL is surfacing as common nomenclature. TMDL--or total maximum daily load--is the maximum amount of a pollutant that a body of water can receive and still meet water quality standards. Concern over the nutrient loading to Lake Erie and its watershed has farmers, businesses and residents in southeast Michigan and northern Ohio concerned about the changes that may be necessary if new TMDLs are determined and implementation plans developed.

There are many other rural areas with water bodies that have been recognized as "impaired" by the Michigan Department of Environmental Quality (DEQ), and TMDLs have already been developed. Eventually these water bodies must be addressed and implementation plans developed. Agriculture depends on these waters for surface, and in some cases subsurface drainage. This relationship between farm practices, drainage and impaired water body restoration plans has the potential to impact farm practices. Farmers, their consultants and local Michigan State University Extension educators, need to be aware of the water body status area farm land drains towards and the impacts of potential TMDL implementation plans.

TMDLs are required when a surface water of the state (lake, river, stream, creek, etc.) fails to meet federal water quality standards (WQS). If a surface water body is determined to be below WQS, the federal clean water act requires the state environmental authority to complete a study determining the daily limits of the pollutant the waters may assimilate and still meet WQS. TMDLs are necessary, they are developed to assist watershed stakeholders address the pollutant loading in impaired or non-attainment waters.

Many of the water bodies currently identified on the list of TMDLs for Michigan name E. coli and phosphorus as the pollutants of concern, both of which may be associated with agricultural practices.

Once the TMDL for a pollutant has been determined by the state environmental agency, the report establishing the TMDL is submitted to the U.S. Environmental Protection Agency (EPA) for their approval. After the EPA has approved the TMDL, the next step is the development of an implementation plan. Local conservation groups and concerned citizens may be involved in the development of the plan but the state DEQ has ultimate authority. Both point and non-point discharges are included in the plan. Non-point discharges include run off from rural fields and farm land and non-collected urban runoff. The implementation plan will include allocating the daily limit of the pollutant to all contributing sources. Farmers with fields that drain into impaired waters with TMDLs for nutrient loading or E. coli should anticipate being included in the implementation plan.

Many of the currently listed TMDLs for Michigan are awaiting the development of implementation plans. This list of Michigan water bodies with TMDLs is available online.

Farmers, agronomists and farm consultants are encouraged to visit the list and determine the status of the water bodies within their area of influence. A second list of impaired waters in Michigan waiting the development of TMDL’s is also available online. Very few of the water bodies identified on this second list are associated with nutrient or E. coli pollution.

For further information on TMDLs see the EPA’s website Impaired Waters and Total Maximum Daily Loads.

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