Water Quality Criteria Two

Relating water quality criteria to permit limits

Water quality criteria apply to a water body itself — not to the quality of water that is discharged into it. However, water quality criteria and the status of the water body should influence pollution limits for individual permits.

For example, if a state finds that a discharger meeting only the minimum, end-of-pipe discharge standards would cause or contribute to a violation of water quality standards for the “receiving water,” the state must then require the discharger to apply as much additional treatment as necessary to avoid violating the water quality standards and to protect the water body. The pollution limits in each discharge permit must be calculated to ensure that all water quality standards for the receiving water body will be met.

Relating water quality criteria to watershed restoration plans (TMDLs)

Water quality criteria should be the targets or goals for watershed restoration plans (Total Maximum Daily Loads/TMDLs -- see Lesson 4). TMDLs must lay out a plan to prevent or reduce contributions of pollution into each water body sufficiently to meet water quality criteria and support uses.

Because these plans are based on the strength and comprehensiveness of water quality standards, the value of employing a variety of water quality criteria to fully protect each use is underscored. Monitoring and assessment of many criteria is extremely useful in identifying problems, correcting them and maintaining chemical, physical and biological integrity.

If any one criterion is not met, the water body is only partially meeting uses, at best, and it is considered “impaired” even if all other criteria are met.

States develop criteria with guidance from U.S. EPA

States may do their own research and policy work to develop criteria. Because this can be a substantial technical and financial burden, most states rely heavily on EPA guidance documents when dealing with common pollutants and some pollutants of special concern.

States use EPA guidance documents as starting points. They may select criteria from within a range of variables established by the EPA. The choices made can result in huge differences in the pollutant levels considered acceptable in a state. It is worth examining your state’s methods for establishing criteria to see what assumptions go into setting these limits.