TMDLs: What are they?!

Impaired waters and their associated TMDLs are a topic that comes up in our SWPPP books, but not many people understand what this actually means. There are thousands of waters in the United States, Florida included, that are listed as impaired. Impairments can come from a variety of different sources, stormwater included. Pollutants that can be carried through stormwater include things like sediment, nutrients, different types of metals, and pathogens. In order to determine how much of a pollutant a water body can realistically hold while still maintaining water quality standards. The total maximum daily load, or TMDL, refers to the calculation used to determine what can be allowed while still maintaining these standards, as per the Clean Water Act. A TMDL functions not only to identify an impaired water, but also functions as a tool to begin working towards bring water quality back to acceptable levels.

Stormwater sources contribute to a large amount of water quality concerns throughout the United States. The runoff can come from urban and residential areas, including irrigation runoff from lawns and agriculture, pet and livestock runoff, and chemicals and liquid waste from construction sites and industry. The flat, impervious concrete and pavement that fills these areas helps to carry all kinds of pollutants through stormwater systems, unfiltered, into streams, and ultimately into lakes and even the ocean.

The EPA has established steps, using adaptive management, associated with implementing stormwater TMDLs:

  1. Investigate – Examine the existing conditions including impervious cover and its connectivity to local stream systems.
  2. Prioritize – Recognize trouble areas and make them a priority for mitigation actions.
  3. Mitigate – Take action to fix problems at prioritized sites, including utilizing appropriate BMPs
  4. Monitor – Determine the effectiveness of actions taken by monitoring water quality
  5. Assess and Repeat. – Assess water quality and repeat the process until impairments are removed or brought to an acceptable level.

Be sure to check out some of the tools that are available for learning more about impaired waters and water quality issues near you. Learning more about the issues surrounding water quality can help you make informed decisions when it comes to things like new projects, or even just the impact your lawn maintenance may have on local water bodies.

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