Water: Water Quality Standards Academy
Basic Course: Supplemental Topics (NPDES Permit 7)
- Listing Impaired Waters and Developing TMDLs
- Monitoring & Assessment
- NPDES Permit Program
- Point Source Control
- Permitting Authority
- Types of Permits
- Categories of Permits
- Permit Components
- Key Considerations
- Technology-Based Determination
- Water Quality-Based Determination
- WQBELs Process
- Step 1: Identify WQSs
- Step 2: Assess Concentration
- Pollutants of Concern
- Critical Conditions
- Dilution/Mixing Allowance
- Step 3: Establish Need
- Step 4: Calculate Limits
- Human Health Ambient Water Quality Criteria
- Aquatic Life Criteria
Effluent Limits: Key Considerations
An NPDES permitting authority establishes the “effluent limits” of an NPDES permit based on two separate and unique approaches established in the CWA. The limits based on these approaches are referred to as:
- Technology-based effluent limits. Limits on pollutants of concern in discharges that have been established as being achievable by using available technology.
- Water quality-based effluent limits. Further limits on discharges of pollutants that may be necessary if the limits achievable using the available technology are not sufficient to prevent impacts from discharges into the receiving waters in regard to compliance with the State/Tribe’s water quality standards.
Technology-based effluent limits are required under the regulation as the “minimum level of control that must be imposed” in an NPDES permit. (Sec. 125.3) EPA establishes national technology-based standards for municipal dischargers and for various categories of non-municipal facilities. The standards and guidelines are based on the performance of actual treatment systems or other pollutant control technologies, such as process controls or material substitution. By not being site specific, the standards and guidance put all facilities within an identified category on an equal footing.
Key Point. A central concept built into the Act is that as technology improves, dischargers will move toward the goal of zero discharge of pollutants. Thus, technology-based effluent limits have their foundation in the CWA’s “zero-discharge” performance goal.
Resource. Linked listing of EPA-promulgated effluent standards and guidelines, sorted alphabetically by industry category.
Illustration. View a high-level diagram of the process for developing effluent limits. Proceed to the Illustration. » (Note: This link launches a pop-up window.)