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Total Maximum Daily Load (TMDL):
A Primer
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Our work in the
Chesapeake Bay
BMP Challenge
for Reduced Nitrogen
Water Quality

Get the Down Low on TMDL –Your Total Maximum Daily Load of Water Quality Terminology

So, what is a TMDL?

TMDL stands for Total Maximum Daily Load. TMDL is an assessment of the highest amount of a pollutant that a body of water can contain, while still maintaining a healthy ecosystem. A TMDL can measure a pollutant in pounds per gallon, or grams per liter. A pollutant can be anything from toxic industrial chemicals or harmful bacteria, to something as simple as disturbed sediment from stream bottoms. Just like we have fishing permits to make sure someone doesn’t take too many fish out a favorite fishing hole (leaving none for anyone else), a TMDL helps us make sure some of us aren’t putting too many nutrients into the water so that the water stays clean enough for everyone to enjoy for recreation, for its scenic beauty, and for wildlife to thrive. TMDL’s are used by regulating authorities – like the EPA, or state environmental agencies – as a fair way to achieve goals for cleaning up polluted waters.

How does this affect farms and farmland?

The United States Environmental Protection Agency is developing new Total Maximum Daily Load’s for three of the most common pollutants in the Chesapeake Bay Watershed – nitrogen, phosphorous and sediment. Agriculture accounts for 25% of the land-use in the watershed, and are responsible for a portion of these excess nutrients in the water ways and will have to be a part of the proposed solution to cleaning up the bay. States and counties will face stiff federal penalties if they don’t reduce pollution below the new Total Maximum Daily Load’s in their parts of the watershed. However, regulations will have to take farmers’ economic realities into account if they are to achieve ambitious the Environmental Protection Agency’s goals. Putting farms out of business with regulations requiring farmers to meet unattainable goals will ensure that nutrient reduction goals will be harder and more expensive to achieve. Replacing a farm with pavement will not help feed us or clean up the water!

How is this going to work? Let’s Tackle it in a Little Mathematical Word Problem.

Picture an imaginary river that runs through Eastville, Weston, and Northburg until it reaches imaginary Big Bay. All of the fish in Big Bay have been dying at an increasingly rapid rate. The EPA studies Big Bay and the rivers that empty into it and determines that there is 3 pounds of nitrogen for every gallon of water in Big Bay. The EPA determines that for the fish to come back, the Total Maximum Daily Load or TMDL for nitrogen in Big Bay is 1 pound of nitrogen per gallon. The EPA then tells everyone in Eastville, Weston, and Northburg that they have to reduce the amount of nitrogen being released into the Imaginary River, because it’s ending up in Big Bay. If they don’t, they will have to pay $50 for every pound of nitrogen they release into the Imaginary River. Now put together a plan for how the community will make their reductions assuming that some of the reductions will have to be made by the city and some will have to be made by citizens, pet owners, and farmers.

Sound easy? It won’t be!

Communities are going to have to work together to find the most efficient equitable way to reduce nutrients in the bay. Farmers, environmentalists, politicians, scientists, homeowners, pet-owners (yes Ms. Kitty is part of the problem too!) will have to figure out how they are going to work together to protect the bay that provides beauty and recreation in their backyard.  Whatever solution is chosen, it will have to be one that is feasible for farmers. Farms can implement conservation plans on their farms to reduce nutrients, but not when they have to risk their whole farm enterprise in the undertaking! We need to help farmers manage the risks they face when they help improve the environment so that everyone can benefit from their conservation commitments!

American Farmland Trust