Total Maximum Daily Load (TMDL)

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Introduction

Section 303(d) of the Clean Water Act establishes the Total Maximum Daily Load (TMDL) program.

A TMDL is a study that:

1. Quantifies the amount of a pollutant in a stream,
2. Identifies the sources of the pollutant, and
3. Recommends regulatory or other actions that may need
   to be taken in order for the stream to cease being polluted.

Some of the actions that might be taken are:

• Re-allocation of limits on the sources of pollutants documented as impacting streams. It might be necessary to lower the amount of pollutants being discharged under NPDES permits or to require the installation of other control measures, if necessary, to ensure that water quality standards will be met.
• For sources the Division does not have regulatory authority over, such as ordinary agricultural or forestry activities, provide information and technical assistance to other state and federal agencies that work directly with these groups to install appropriate Best Management Practices.

TMDLs can also be described by the following equation:

TMDL = sum of nonpoint sources + sum of point sources + margin of safety

The Division of Water Pollution Control has structured monitoring and permitting activities on a rotating watershed basis. In keeping with this approach, Tennessee is developing TMDLs on a watershed basis, with each watershed examined at the appropriate time in the five-year watershed cycle.