Total Maximum Daily Loads (TMDLs)

TMDL prioritization

Development

For a Water Quality Limited stream segment that requires a Total Maximum Daily Load (TMDL), the pollutant sources and allocate allowable loads to the contributing sources, both point and nonpoint, must be qualified so water quality standards can be attained for that segment. TMDL development is a rational method for weighing the competing pollution interests and developing an integrated pollution reduction strategy for point and nonpoint sources.

TMDL development includes these five basic steps:

Select the pollutant to consider.
Estimate the water body assimilative capacity.
Identify the contribution of that pollutant from all significant sources.
Analyze information to determine the total allowable pollutant load.
Allocate (with a margin of safety) the allowable pollution among the sources so water quality standards can be achieved.

The complexity of the TMDL development is determined by water body, the sources and the pollutant being considered. While not all segments and TMDLs require complex computer modeling, some do.

Implementation of control information

Implementation of the Total Maximum Daily Load (TMDL) is the final step. It requires participation from all the stakeholders, as TMDLs are not self-implementing.

The waste load allocation portion of the TMDL can be implemented through effluent limits in discharge permits. In the case of non-point sources, voluntary controls or locally enacted controls are necessary to implement the load allocations.

We rely on authority already granted by the federal Clean Water Act to implement TMDLs.