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National Pollutant Discharge Elimination System (NPDES)
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Pretreatment Standards & Limits
- Prohibited Discharge Standards
- Categorical Standards
- Local Limits
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Pretreatment Standards & Limits

The National Pretreatment Program identifies specific requirements that apply to all Industrial Users (IUs) or nondomestic sources of wastewater to a Publicly Owned Treatment Works (POTW), additional requirements that apply to all Significant Industrial Users (SIUs), and certain requirements that only apply to Categorical Industrial Users (CIUs). The objectives of the National Pretreatment Program are achieved by applying and enforcing three types of discharge standards:

Prohibited Discharge Standards forbid the discharge of any pollutant(s) to a POTW that cause pass through or interference. These national standards apply to all IUs to a POTW, regardless of whether or not the POTW has an approved pretreatment program or whether the industrial user has been issued a control mechanism or permit. These standards are intended to provide general protection for POTWs. However, their lack of specific pollutant limitations creates the need for additional controls, namely Categorical Pretreatment Standards and Local Limits. The Prohibited Discharge Standards are listed in 40 CFR 403.5 Exit EPA Site

Categorical Pretreatment Standards limit the pollutant discharges to POTWs from specific process wastewaters of particular industrial categories. These national technology-based standards apply regardless of whether or not the POTW has an approved pretreatment program or the IU has been issued a control mechanism or permit. Such industries are called Categorical Industrial Users. The standards are promulgated by EPA in accordance with Section 307 of the Clean Water Act and are designated in the Effluent Guidelines & Limitations [Parts 405-471] by the terms "Pretreatment Standards for Existing Sources (PSES)" and "Pretreatment Standards for New Sources (PSNS)".

Note: The Effluent Guidelines & Limitations designated by the terms "Best Practicable Control Technology Currently Available (BPT)", "Best Available Technology Economically Achievable (BAT)", "Best Conventional Pollutant Control Technology (BCT)", and "New Source Performance Standards (NSPS)" apply to discharge process wastewater to waters of the U.S. and should have a National Pollutant Discharge Elimination System (NPDES) Permit.

Regulations for all Effluent Guidelines and Standards are located at:

Additional information on ongoing Categorical Standards is located at:

Local Limits reflect the specific needs and capabilities at individual POTWs and are designed to protect the POTW, its receiving waters, and its sludge disposal practices. Regulations at 40 CFR 403.8(f)(4) state that POTW Pretreatment Programs must develop Local Limits or demonstrate that they are unnecessary; 40 CFR 403.5(c) states that Local Limits are needed when pollutants are received that could result in pass through or interference at the POTW. Essentially, Local Limits translate the General Prohibited Discharge Standards of 40 CFR 403.5 to site-specific needs.

Assistance for municipalities on how to develop local limits may be found in the Local Limits Development Guidance, July 2004 (PDF) (134 pp, 2.269MB) and its Appendices (PDF) (128 pp, 1.92MB).

This manual provides guidance to municipalities on the development and implementation of local controls for discharges of industrial or commercial wastes to sewage treatment facilities. This manual provides technical assistance and guidance on:

  • Determining pollutants of concern
  • Collecting and analyzing data
  • Calculating maximum allowable loadings
  • Designating and implementing local limits to protect wastewater treatment and collection systems
  • Performing annual reviews and periodic re-evaluations

EPA Supplemental Manual on the Development And Implementation of Local Discharge Limitations Under the Pretreatment Program: Residential and Commercial Toxic Pollutant Loadings and POTW Removal (PDF) (117 pp, 5.09MB) published May 1, 1991 provides information related to residential and commercial sources of toxic pollutants and estimated removal efficiencies of municipal treatment processes.

Local Limits Development Guidance

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Last updated on September 14, 2011 10:23 AM