Section 303(d) of the Clean Water Act (CWA) and the United States Environmental Protection Agency's Water Quality Planning and Management Regulations (40 CFR Part 130) require states to develop total maximum daily loads (TMDLs) for water bodies that are exceeding water quality standards. The TMDL process establishes the allowable loadings of pollutants for a water body based on the relationship between pollution sources and in-stream water quality conditions.

In some cases during TMDL development, there is no identifiable most probable stressor for the impaired water.  In such cases, Virginia submits a Stressor Analysis report to EPA documenting the stressor identification process and justification for reclassifying the water as "no TMDL required".  Following EPA's approval of the Stressor Analysis report, Virginia's subsequent 305(b)/303(d) Water Quality Integrated Report is updated to categorize the water as one of the following:

•  4A (water is impaired but does not need a TMDL because one or more TMDLs for the identified pollutants have already been completed and approved by EPA),
• 4B (water is impaired or threatened for one or more designated uses but does not require the development of a TMDL because other pollution control requirements are reasonably expected to result in attainment of the water quality standard), or
• 4C (water is impaired due to natural conditions). 

Approved Stressor Analysis Reports - No TMDL Required