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Effluent limitations
  • TBELs in NPDES permits require a minimum level of treatment of pollutants for point source discharges while allowing the discharger to use any available control technique to meet the limits.

Technology-based effluent limitations

Technology-based effluent limitations (TBELs) in National Pollutant Discharge Elimination System (NPDES) permits require a minimum level of treatment of pollutants for point source discharges based on available treatment technologies, while allowing the discharger to use any available control technique to meet the limits. For industrial (and other non-municipal) facilities, technology-based effluent limits are derived by:

  • Using national effluent limitations guidelines and standards established by the Environmental Protection Agency (EPA), and/or
  • Using best professional judgement (BPJ) on a case-by-case basis in the absence of national guidelines and standards.

Water quality-based effluent limitations and TMDLs

The Clean Water Act (CWA) establishes a process for states to identify waters within their boundaries where implementing technology-based controls isn’t enough to achieve water quality standards. States establish a priority ranking of these waters and, for the priority waters, develop Total Maximum Daily Loads (TMDLs). A TMDL identifies the amount of a specific pollutant or property of a pollutant, from point, nonpoint, and natural background sources, including a margin of safety, that may be discharged to a water body and still ensure that the water body attains water quality standards. The allocations of pollutant loadings to point sources are called wasteload allocations.

Effluent limits in NPDES permits must be consistent with the assumptions used to derive the wasteload allocations. Also, in the absence of a TMDL, permitting authorities still must assess the need for effluent limits based on water quality standards and, where necessary, develop appropriate wasteload allocations and effluent limits. This analysis could be done for an entire watershed or separately for each individual discharge.

Permit writers have to consider the potential impact of every proposed surface water discharge on the quality of the receiving water. If TMDLs are not sufficient to meet the water quality standards in the receiving water, the CWA and NPDES regulations require that the permit writer develop more stringent, water quality-based effluent limits.

Water quality planning and management

The regulations governing the TMDL program are found at 40 CFR 130.7. Once a state has identified its impaired waters, it must:

  • Set up TMDLs;
  • Set priorities for developing the loads;
  • Establish loads for segments identified, including water quality monitoring, modeling, data analysis, calculation methods, and the list of pollutants to be regulated;
  • Submit the list of segments identified, priority ranking, and loads established to EPA for approval;
  • Incorporate the approved loads into the state’s water quality management plans and NPDES permits; and
  • Describe the process in its State Continuing Planning Process.