Building a TMDL to Better Support Water Quality Trading

If water quality trading is a possibility in a watershed, a TMDL can help inform the science, policy, and overall goals for a trading program. This report provides information on how a total maximum daily load (TMDL) can be developed to better support water quality trading.

Understanding watershed dynamics is key to making water quality trading a viable, accountable, and legitimate means to improve water quality. A total maximum daily load (TMDL), at its core, is a watershed planning document that characterizes the sources of pollution in a watershed, the specific water quality goals, and what pollution reductions are needed to achieve those goals. More specifically, a TMDL is the sum of individual pollutant waste-load allocations (WLAs) for point sources, load allocations (LAs) for nonpoint sources and natural background, and a margin of safety (MOS). This report examines these concepts and provides suggestions on how TMDLs and their associated implementation documents can be developed to better support water quality trading.

This report represents the views of the authors and is not meant as any legal interpretation of TMDL requirements or as formal guidance in any way.

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