An official website of the United States government.

We've made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

National Pollutant Discharge Elimination System (NPDES)

Pretreatment Standards and Requirements

Pretreatment standards are pollutant discharge limits which apply to industrial users (IUHelpIUA source of indirect discharge. [40 CFR 403.3(j)]s). Pretreatment requirements are substantive or procedural requirements applied to IUs.

Applicability of Pretreatment Standards and Requirements

The national pretreatment program objectives are achieved by applying and enforcing three types of pretreatment standards:

  • General and specific prohibitions
  • Categorical pretreatment standards
  • Local limits

All three types of standards can be enforced by EPA, the state, and local government, even though they are developed at different levels of government (i.e., federal, state, and local). Pretreatment standards and requirements can be expressed as numeric limits, narrative prohibitions, and best management practicesHelpbest management practicesThe most effective and practical ways to control pollutants and meet environmental quality goals. BMPs exist for forestry, agriculture, stormwater and many other sectors. (BMPsHelpBMPsThe most effective and practical ways to control pollutants and meet environmental quality goals. BMPs exist for forestry, agriculture, stormwater and many other sectors.).

IUs should be aware of the standards that apply to them. The control authorityHelpcontrol authorityThe POTW, in the case of a POTW with an approved pretreatment program, or the Approval Authority, in the case of a POTW without an approved pretreatment program. [paraphrased from 40 CFR 403.3(f)] is responsible for identifying standard(s) applicable to each IU and applying the most stringent requirements where multiple provisions exist. The different pretreatment standards are applied to IUs, significant industrial users (SIUHelpSIU(1) All users subject to categorical pretreatment standards under 40 CFR 403.6 and 40 CFR chapter I, subchapter N, except those designated as NSCIUs; and (2) Any other IU that discharges an average of 25,000 gallons per day or more of process wastewater to the POTW (excluding sanitary, noncontact cooling, and boiler blowdown wastewater); contributes a process wastestream that makes up 5 percent or more of the average dry-weather hydraulic or organic capacity of the POTW treatment plant; or is designated as such by the POTW on the basis that the IU has a reasonable potential for adversely affecting the POTW’s operation or for violating any pretreatment standard or requirement [in accordance with 40 CFR 403.8(f)(6)]. [40 CFR 403.3(v)]s), and categorical industrial users (CIUHelpCIUAn industrial user subject to national categorical pretreatment standards.s) as follows:

General and Specific Prohibitions

Categorical Pretreatment Standards

Local Limits

All IUs

X

May apply; depends on publicly owned treatment works (POTW) ordinance and permit provisions

SIUs

X

Generally apply; may depend on allocation method

CIUs

X

X

Generally apply; may depend on allocation method

Top of Page

General and Specific Prohibitions

General and specific prohibitions are national standards. These standards apply to all nondomestic dischargers that discharge wastewater to a publicly owned treatment works (POTW). They apply whether or not the POTW has an approved pretreatment program and also whether or not the nondomestic discharger has been issued a control mechanism or permit. EPA developed these standards with the intent to provide protection for POTWs, which include a treatment plant’s collection system.

On this page:You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.

General Prohibitions

The general prohibitions at 40 CFR Part 403.5(a) (PDF)(2 pp, 204 K) forbid the discharge of any pollutant(s) to a POTW that can cause pass through or interference:

Pass through (40 CFR Part 403.3(p)) (PDF)(4 pp, 192 K) – “A discharge that exits the POTW into waters of the United States in quantities or concentrations that, alone or in conjunction with a discharge or discharges from other sources, is a cause of a violation of any requirement of the POTW's NPDES [National Pollutant Discharge Elimination System] permit (including an increase in the magnitude or duration of a violation).”

Interference (40 CFR Part 403.3(k)) (PDF)(4 pp, 192 K) – “A discharge that, alone or in conjunction with a discharge or discharges from other sources, both (1) inhibits or disrupts the POTW, its treatment processes or operations, or its sludge processes, use, or disposal; and (2) therefore is a cause of a violation of any requirement of the POTW's NPDES permit (including an increase in the magnitude or duration of a violation) or of the prevention of sewage sludge use or disposal in compliance with the following statutory provisions and regulations or permits issued thereunder (or more stringent state or local regulations): Section 405 of the Clean Water Act, the Solid Waste Disposal Act (SWDA) (including title II, more commonly referred to as the Resource Conservation and Recovery Act (RCRA), and including state regulations contained in any state sludge management plan prepared pursuant to subtitle D of the SWDA), the Clean Air Act, the Toxic Substances Control Act, and the Marine Protection, Research and Sanctuaries Act.”

Top of Page


Specific Prohibitions

The specific prohibitions at 40 CFR Part 403.5(b) (PDF)(2 pp, 204 K) are intended to “enhance control of hazardous wastes entering POTWs.” (55 FR 30082) These provisions forbid eight categories of pollutant discharges:

(1) Pollutants which create a fire or explosion hazard in the POTW, including, but not limited to, wastestreams with a closed cup flashpoint of less than 140 degrees Fahrenheit or 60 degrees Centigrade using the test methods specified in 40 CFR Part 261.21 (PDF)(2 pp, 204 K).

(2) Pollutants which will cause corrosive structural damage to the POTW, but in no case discharges with pH lower than 5.0, unless the works is specifically designed to accommodate such discharges.

(3) Solid or viscous pollutants in amounts which will cause obstruction to the flow in the POTW resulting in interference.

(4) Any pollutant, including oxygen demanding pollutants (biochemical oxygen demand, etc.) released in a discharge at a flow rate and/or pollutant concentration which will cause Interference with the POTW.

(5) Heat in amounts which will inhibit biological activity in the POTW resulting in Interference, but in no case heat in such quantities that the temperature at the POTW treatment plant exceeds 40 °C (104 °F) unless the approval authority, upon request of the POTW, approves alternate temperature limits.

(6) Petroleum oil, nonbiodegradable cutting oil, or products of mineral oil origin in amounts that will cause interference or pass through.

(7) Pollutants which result in the presence of toxic gases, vapors, or fumes within the POTW in a quantity that may cause acute worker health and safety problems.

(8) Any trucked or hauled pollutants, except at discharge points designated by the POTW.”

Top of Page


Additional Information

Top of Page

Categorial Pretreatment Standards

Effluent limitations guidelines and pretreatment standards, also called effluent guidelines (“ELGs”), are uniform national standards developed by EPA for specific industrial categories. EPA bases these standards on the greatest pollutant reductions economically achievable for each industry. ELGs cover specific industrial processes and limit specific pollutants.

The standards applicable to indirect dischargers (also called categorical pretreatment standardsHelpcategorical pretreatment standardsStandards specifying the quantity, concentration, or pollutant properties of pollutants that may be discharged to POTWs. EPA promulgates pretreatment standards for specific industry categories in accordance with CWA section 307. These standards are codified in 40 CFR chapter I, subchapter N, Parts 405–471. [paraphrased from 40 CFR 403.6]) are listed under each ELG as pretreatment standards for existing sourcesHelppretreatment standards for existing sourcesCategorical standards and requirements applicable to industrial sources that began construction before the publication of the proposed pretreatment standards for that industrial category (see individual standards at 40 CFR Parts 405–471) or on a date specifically provided in promulgation of the pretreatment standard. (PSES) and pretreatment standards for new sourcesHelppretreatment standards for new sourcesCategorical standards and requirements applicable to industrial sources that began construction after the publication of the proposed pretreatment standards for that industrial category (see individual standards at 40 CFR Parts 405–471) or on a date specifically provided in promulgation of the pretreatment standard. (PSNS). Not all ELGs contain PSES and PSNS; EPA implements PSES and PSNS for 35 (out of 58) industrial categories.

These technology-based standards apply regardless of whether or not the publicly owned treatment works (POTW) has an approved pretreatment program or whether or not the nondomestic discharger has been issued a control mechanism or permit. Nondomestic dischargers subject to categorical pretreatment standards are categorical industrial users (CIUs).

Learn more about the development and implementation of current and future ELGs.

Learn more about specific industrial effluent guidelines.

Title 40 of the CFR contains regulations for all ELGs:

Learn more about variances from pretreatment standards and limits. Under certain circumstances, the control authority might grant variances to IUs from individual pretreatment standards.

Top of Page

Local Limits

Local limits address the specific needs and concerns of a publicly owned treatment works (POTW), its sludge, and its receiving waters. Most of the general prohibited discharge standards specified at 40 CFR Part 403.5 (PDF)(2 pp, 204 K) are not specific pollutant limitations. As a result, a POTW must evaluate its facility’s capabilities and establish local limits to protect it from receiving wastes that pass throughHelppass throughA discharge that exits the POTW into waters of the United States in quantities or concentrations that, alone or in conjunction with a discharge or discharges from other sources, is a cause of a violation of any requirement of the POTW's NPDES permit (including an increase in the magnitude or duration of a violation). [40 CFR 403.3(p)] or interfereHelpinterferenceA discharge that, alone or in conjunction with a discharge or discharges from other sources, both (1) inhibits or disrupts the POTW, its treatment processes or operations, or its sludge processes, use, or disposal; and (2) therefore is a cause of a violation of any requirement of the POTW's NPDES permit (including an increase in the magnitude or duration of a violation) or of the prevention of sewage sludge use or disposal in compliance with ... [applicable] statutory provisions and regulations or permits issued thereunder (or more stringent state or local regulations). [paraphrased from 40 CFR 403.3(k)] with operations (including sludge management).

These local limits are intended to protect:You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.

  • the POTW (including collection system infrastructure),
  • receiving waters,
  • workers’ health and safety, and
  • sludge disposal practices.

Local limits are site-specific and can be numeric or narrative effluent discharge limits, including BMPs. EPA identifies in 40 CFR Part 403.5(c) (PDF)(2 pp,  204 K) which POTWs must develop local limits:

  • POTWs required to develop a POTW pretreatment program per 40 CFR Part 403.8 (PDF)(7 pp, 232 K).
  • POTWs without a pretreatment program where pollutants from nondomestic dischargers might result in interference or pass through and such violation is likely to recur.
Evaluation of local limits is a required element of an approved POTW pretreatment program:
POTWs must evaluate their local limits following each NPDES permit issuance or reissuance:

POTWs impose local limits at the end-of-pipe discharge from an industrial user (i.e., at the point of connection to the POTW's collection system). EPA can enforce local limits that are developed and approved in accordance with 40 CFR Part 403.5(c) (PDF)(2 pp, 204 K) as pretreatment standards.

Additional Information

EPA provides guidance to municipalities on how to develop local limits. The guidance includes how to calculate maximum allowable loadings, collect and analyze data, design and implement local limits, determine pollutants of concern, and perform annual reviews and periodic reevaluations of local limits:

Top of Page