Under what conditions is a Total Maximum Daily Load (TMDL) required?

A Total Maximum Daily Load (TMDL) is a regulatory tool used to ensure that water bodies meet water quality standards. It is specifically required when a water body is found to be impaired, meaning it does not meet the water quality criteria. This situation typically arises when the existing Best Available Technologies (BAT) applied to point source discharges are not sufficient to reduce pollutant concentrations to levels that comply with state water quality standards.

The determination for requiring a TMDL is typically based on monitoring and assessment of water quality. If it is found that the controls in place, such as BAT, do not adequately address the levels of pollutants entering a water body, a TMDL is mandated to set limits on the maximum allowable pollutant load that can be discharged to ensure the water body can eventually meet its criteria.

In contrast, the other scenarios presented do not specifically trigger a TMDL requirement. Inadequacies in state water quality criteria, or issues with corrosion control for specific contaminants like lead, while they may indicate problems in water quality management, do not alone necessitate the establishment of a TMDL unless the point source discharges are deemed insufficient in controlling those pollutants. Thus, the application of a TMDL is directly linked to