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Water: Industry Effluent Guidelines

Frequent Questions

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What are effluent guidelines?

Effluent guidelines are national standards that are developed by EPA on an industry-by-industry basis, and are intended to represent the greatest pollutant reductions that are economically achievable for an industry. To develop these technology-based regulations, EPA first gathers information on the industry's practices; characteristics of discharges (stormwater flows and pollutants); technologies or practices used to prevent or treat the discharge; and economic characteristics. EPA identifies the best available technology that is economically achievable for that industry and sets regulatory requirements based on the performance of that technology. The effluent guidelines do not require facilities to install the particular technology identified by EPA; however, the regulations do require facilities to achieve the regulatory standards which were developed based on a particular model technology. The standards are then incorporated into National Pollutant Discharge Elimination System (NPDES) permits issued by States and EPA regional offices.

National regulations for industrial wastewater discharges set technology-based numerical limitations for specific pollutants at several levels of control: BAT, BPT, BCT, NSPS, PSNS, or PSES. Each of these terms is defined below. Effluent limitations are based on performance of specific technologies, but regulations do not require use of a specific control technology.

Type of Sites Regulated BPT BCT BAT NSPS PSES PSNS
Existing Direct Dischargers


New Direct Dischargers




Existing Indirect Dischargers




New Indirect Dischargers




Pollutants Regulated BPT BCT BAT NSPS PSES PSNS
Priority Pollutants
Nonconventional Pollutants
Conventional Pollutants


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What is BPT?

Best Practicable Control Technology Currently Available (BPT) is defined at Section 304(b)(1) of the Clean Water Act (CWA). EPA sets Best Practicable Control Technology Currently Available (BPT) effluent limitations for conventional, toxic, and non-conventional pollutants. Section 304(a)(4) designates the following as conventional pollutants: biochemical oxygen demand (BOD5), total suspended solids, fecal coliform, pH, and any additional pollutants defined by the Administrator as conventional. The Administrator designated oil and grease as an additional conventional pollutant on July 30, 1979 (see 44 FR 44501).

EPA has identified 65 pollutants and classes of pollutants as toxic pollutants, of which 126 specific substances have been designated priority toxic pollutants (see Appendix A to part 403, reprinted after 40 CFR 423.17). All other pollutants are considered to be non-conventional.

In specifying BPT, EPA looks at a number of factors. EPA first considers the total cost of applying the control technology in relation to the effluent reduction benefits. The Agency also considers the age of the equipment and facilities, the processes employed and any required process changes, engineering aspects of the control technologies, non-water quality environmental impacts (including energy requirements), and such other factors as the EPA Administrator deems appropriate. Traditionally, EPA establishes BPT effluent limitations based on the average of the best performance of facilities within the industry of various ages, sizes, processes or other common characteristics. Where existing performance is uniformly inadequate, BPT may reflect higher levels of control than currently in place in an industrial category if the Agency determines that the technology can be practically applied.

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What is BCT?

Best Conventional Pollutant Control Technology (BCT) is defined at Section 304(b)(4) of the CWA. The 1977 amendments to the CWA required EPA to identify effluent reduction levels for conventional pollutants associated with BCT for discharges from existing industrial point sources. In addition to the other factors specified in section 304(b)(4)(B), the CWA requires that EPA establish BCT limitations after consideration of a two part "cost-reasonableness" test. EPA explained its methodology for the development of BCT limitations in a Federal Register notice on July 9, 1986 (51 FR 24974).

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What is BAT?

Best Available Technology Economically Achievable (BAT) is defined at Section 304(b)(2) of the CWA. In general, Best Available Technology Economically Achievable (BAT) represents the best available economically achievable performance of plants in the industrial subcategory or category. The factors considered in assessing BAT include the cost of achieving BAT effluent reductions, the age of equipment and facilities involved, the process employed, potential process changes, non-water quality environmental impacts, including energy requirements and other such factors as the EPA Administrator deems appropriate. EPA retains considerable discretion in assigning the weight according to these factors. BAT limitations may be based on effluent reductions attainable through changes in a facility's processes and operations. Where existing performance is uniformly inadequate, BAT may reflect a higher level of performance than is currently being achieved within a particular subcategory based on technology transferred from a different subcategory or category. BAT may be based upon process changes or internal controls, even when these technologies are not common industry practice.

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What is NSPS?

New Source Performance Standards (NSPS) is defined at Section 306 of the CWA. New Source Performance Standards (NSPS) reflect effluent reductions that are achievable based on the best available demonstrated control technology. New sources have the opportunity to install the best and most efficient production processes and wastewater treatment technologies. As a result, NSPS should represent the most stringent controls attainable through the application of the best available demonstrated control technology for all pollutants (i.e., conventional, non-conventional, and priority pollutants). In establishing NSPS, EPA is directed to take into consideration the cost of achieving the effluent reduction and any non-water quality environmental impacts and energy requirements.

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What is PSNS?

Pretreatment Standards for New Sources (PSNS) is defined at Section 307(c) of the CWA. Pretreatment Standards for New Sources (PSNS) are national, uniform, technology-based standards that apply to dischargers to publicly owned treatment works (POTWs) from specific industrial categories (i.e. indirect dischargers). They are designed to prevent the discharges of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of POTWs. PSNS are to be issued at the same time as NSPS. The Agency considers the same factors in promulgating PSNS as it considers in promulgating NSPS.

The definition of "new source" is set out in 40 CFR §403.3(m) of the General Pretreatment Regulations. New indirect dischargers have the opportunity to incorporate into their plants the best available demonstrated technologies. Users subject to PSNS are required to achieve compliance within the shortest feasible time, not to exceed 90 days from commencement of discharge.

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What is PSES?

Pretreatment Standards for Existing Sources (PSES) is defined at Section 307(b) of the CWA. Like PSNS, Pretreatment Standards for Existing Sources (PSES) are national, uniform, technology-based standards that apply to dischargers to publicly owned treatment works (POTWs) from specific industrial categories (i.e. indirect dischargers). They are designed to prevent the discharge of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of POTW.

Dischargers subject to PSES are required to comply with those standards by a specified date, typically no more than three years after the effective date of the categorical standard.

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What are BMPs?

Best Management Practices (BMPs) are defined as a Permit condition used in place of or in conjunction with effluent limitations to prevent or control the discharge of pollutants. BMPs may include a schedule of activities, prohibition of practices, maintenance procedure, or other management practice.

Sections 304(e), 308(a), 402(a), and 501(a) of the CWA authorize the Administrator to prescribe BMPs as part of effluent limitations guidelines and standards or as part of a permit. EPA's BMP regulations are found at 40 CFR 122.44(k). Section 304(e) of the CWA authorizes EPA to include BMPs in effluent limitations guidelines for certain toxic or hazardous pollutants for the purpose of controlling "plant site runoff, spillage or leaks, sludge or waste disposal, and drainage from raw material storage." Section 402(a)(1) and NPDES regulations (40 CFR 122.44(k)) also provide for best management practices to control or abate the discharge of pollutants when numeric limitations and standards are infeasible.

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Why does EPA publish effluent guidelines program plans?

Section 304(b) of the Clean Water Act requires EPA to annually review and, if appropriate, revise its technology-based regulations, called "effluent limitations guidelines" or "effluent guidelines," that limit the discharge of pollutants from various categories of industrial facilities. Every other year, Section 304(m) of the Clean Water Act requires EPA to publish a plan establishing a schedule for the annual review and revision of effluent guidelines required by Section 304(b). This plan must also identify industries discharging more than trivial amounts of toxic or "nonconventional" pollutants, such as nutrients, for which the Agency has not yet promulgated effluent guidelines. EPA must establish a schedule for completing effluent guidelines for these industries within three years. Section 304(m) also requires EPA to take public comment on its plan prior to issuing a final plan. See the planning page.

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How often are effluent guidelines updated?

Section 304(b) of the Clean Water Act requires EPA to annually review and, if appropriate, revise effluent guidelines. Section 304(m) of the Clean Water Act requires EPA to publish a plan establishing a schedule for the annual review and revision of effluent guidelines required by Section 304(b). The plan announces any EPA decisions to proceed with rulemakings which may lead to new requirements for direct discharging facilities covered by existing effluent guidelines. EPA reviews pretreatment standards (see sections 307(b) and 307(c) of the CWA) under a separate planning process, required by Section 304(g) of the CWA, EPA generally evaluates discharges from indirect dischargers as part of the 304(m) plan when industrial categories discharging toxic or non-conventional pollutants are composed of both direct and indirect dischargers.

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How are effluent guidelines for direct dischargers implemented?

Effluent limitations guidelines are implemented through the National Pollutant Discharge Elimination System (NPDES) permit program. Discharges from direct dischargers (i.e. facilities that discharge wastewaters directly into waters of the U.S.) are regulated in permits that specify limits using 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).

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How are pretreatment standards for indirect dischargers implemented?

Pretreatment standards are implemented through the national pretreatment program. Discharges from indirect dischargers (i.e. facilities that discharge their wastewaters to a publicly owned treatment works) are regulated through categorical standards issued based on Pretreatment Standards for New Sources (PSNS) and Pretreatment Standards for Existing Sources (PSES).

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If a pollutant is not specifically regulated by the applicable effluent guidelines, how is that pollutant discharge regulated?

When a pollutant discharged by a direct discharging industry is not specifically limited in an effluent guideline, it is up to the permit writer to utilize best professional judgment to establish technology based limits or determine other appropriate means to control its discharge. See NPDES Permit Writers Guide.

When a pollutant discharged by an indirect discharging industry is not specifically limited by pretreatment standards, it is up to the state or local regulatory agency to develop local limits to establish technology based limits or to determine other appropriate means to control its discharge. See EPA's NPDES Permit Writers' Guide.

When a pollutant discharged by an indirect discharging industry is not specifically limited by pretreatment standards, it is up to the state or local regulatory agency to develop local limits to establish technology based limits or to determine other appropriate means to control its discharge. See EPA's Local Limits Development Guidance (PDF) (134 pp, 2.3MB) and Appendices (PDF) (128 pp, 1.9MB).

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If there are no effluent guidelines or pretreatment standards for a specific industrial category, how are the discharges regulated?

When there are no national standards for an industrial category, it is up to the permit writer to establish site-specific technology based limits or determine other appropriate means to control the discharge. See EPA's NPDES Permit Writers' Guide for the direct discharges. When a pollutant, discharged by an indirect discharging industry, is not specifically limited by pretreatment standards, it is up to the state or local regulatory agency to develop local limits to establish technology based limits or to determine other appropriate means to control its discharge. See EPA's Local Limits Development Guidance (PDF) (134 pp, 2.3MB) and Appendices (PDF) (128 pp, 1.9MB).

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