Total Maximum Daily Load (TMDL)

The Clean Water Act (CWA) requires states to protect the nation's waters so that they can be used for various designated purposes such as drinking water, fishing, swimming, irrigation, or industrial use. Depending on the designated use of a particular stream, river or lake, a water quality standard is established. Logically, the water quality standards for a river used as drinking water supply are more stringent than the standards for a stream used primarily for irrigation or industrial use.

For each pollutant that causes a water body to fail to meet water quality standards, the state must conduct a Total Maximum Daily Load (TMDL) study. A TMDL study identifies point and non-point sources of each pollutant that fails to meet water quality standards. Water quality sampling and computer modeling are then employed to determine how much each pollutant source must reduce its contribution to assure that the water quality standard is met. Rivers and streams may have several TMDLs, each one determining the limit for a different pollutant.

Why are TMDLs important to builders, developers and landowners?

• If your construction site runoff enters a water body that has a TMDL, then, in some states, you must consider the effects of your construction site runoff on water quality before you can receive coverage under the general stormwater permit.
• Some states have adopted permit waivers for small construction sites (1 to less than five acres) that discharge to waters not covered by a TMDL.

TMDL State Program Tool
Use this tool to find out more about the TMDL program in your state and to identify and locate impaired waters in your state. Use the pulldown or sensitive map to select a state.