The CWA contains both “water-quality based” regulatory controls, which vary according to the designated use (., drinking water source, fishable, swimmable) and attributes (., volume and rate of flow) of the receiving water body, and “technology- based” effluent standards that are achievable using available pollution control technology. Legally, the environmental quality standards dominate the technology-based standards in the sense that additional regulatory action may be required if the technology-based limits do not achieve the ambient quality standard in a specific location. In practice, the technology-based standards are emphasized. This is due in part to the practical difficulties experienced prior to 1972 with state attempts to control.
