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Effluent Guidelines

Learn About Effluent Guidelines

Photo - electric power plant and pondsEffluent Guidelines are national wastewater discharge standards that are developed by EPA on an industry-by-industry basis. These are technology-based regulations, and are intended to represent the greatest pollutant reductions that are economically achievable for an industry. The standards for direct dischargers are incorporated into National Pollutant Discharge Elimination System (NPDES) permits issued by States and EPA regional offices, and permits or other control mechanisms for indirect dischargers (see Pretreatment Program).

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Development of Effluent Guidelines

To develop Effluent Guidelines, EPA first gathers information on:
  • industry practices
  • characteristics of discharges (pollutants and stormwater flows)
  • technologies or practices used to prevent or treat the discharge
  • 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.

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Levels of Control

National regulations for industrial wastewater discharges set technology-based numerical limitations for specific pollutants at several levels of control: BPTBATBCTNSPSPSNS or PSES. Each of these terms is defined below. Effluent limitations are based on performance of specific technologies, but the 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  
Conventional Pollutants      
Nonconventional Pollutants  


Best Practicable Control Technology Currently Available is defined at section 304(b)(1) of the Clean Water Act (CWA). EPA sets 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 (TSS), fecal coliform, pH, and any additional pollutants EPA defines as conventional. The Agency 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. All other pollutants are considered to be "nonconventional."
In specifying BPT, EPA looks at a number of factors:
  • the total cost of applying the control technology in relation to the effluent reduction benefits
  • age of the equipment and facilities
  • processes employed by the industry and any required process changes
  • engineering aspects of the control technologies
  • non-water quality environmental impacts, including energy requirements
  • other factors as EPA 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. are based on performance of specific technologies, but regulations do not require use of a specific control technology.


Best Conventional Pollutant Control Technology, defined at CWA section 304(b)(4), addresses conventional pollutants from existing industrial point sources. In addition to considering the other factors specified in section 304(b)(4)(B), EPA establishes BCT limitations after consideration of a two part "cost-reasonableness" test. This methodology was published in a Federal Register notice on July 9, 1986 (51 FR 24974).


Best Available Technology Economically Achievable is defined at CWA section 304(b)(2). In general, BAT represents the best available economically achievable performance of plants in the industrial subcategory or category. Factors considered in assessing BAT include:
  • cost of achieving BAT effluent reductions
  • age of equipment and facilities involved
  • the processes employed by the industry and potential process changes
  • non-water quality environmental impacts, including energy requirements
  • other factors as EPA deems appropriate


New Source Performance Standards, defined at CWA section 306, apply to direct dischargers. 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.
  • Definition of "new source" for direct dischargers: 40 CFR 122.2, 122.29


Pretreatment Standards for New Sources is defined at CWA section 307(c). 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.

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.


Pretreatment Standards for Existing Sources is defined at CWA section 307(b). Like PSNS, PSES are national, uniform, technology-based standards that apply to indirect dischargers. They are designed to prevent the discharge of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of POTWs.

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.


Best Management Practices 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 EPA to prescribe BMPs as part of Effluent Guidelines and Standards or as part of a permit.
CWA section 304(e) authorizes EPA to include BMPs in Effluent 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 40 CFR 122.44(k) also provide for BMPs to control or abate the discharge of pollutants when numeric limitations and standards are infeasible.

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Effluent Guidelines Program Plans

CWA section 304(b) requires EPA to annually review and, if appropriate, revise Effluent Guidelines. EPA publishes a plan every other year, establishing a schedule for annual review and revision, pursuant to section 304(m). This plan also identifies 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 is required to establish a schedule for completing effluent guidelines for these industries within three years, and the Agency must take public comment on its proposed plan prior to issuing a final plan. 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 under a separate planning process, required by CWA section 304(g). 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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Effluent guidelines are implemented through the NPDES permit program. Direct dischargers are regulated by permits that specify limits using BPT, BAT, BCT and NSPS.

Pretreatment standards are implemented through the national pretreatment program Indirect dischargers are regulated through categorical standards issued based on PSNS and PSES.

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Industries and/or Pollutants Not Specifically Regulated By Effluent Guidelines

For direct dischargers, the permit writer utilizes "best professional judgment" to establish technology-based limits or determine other appropriate means to control its discharge.
For indirect dischargers, the state or local regulatory agency develops local limits, either technology-based or other appropriate means to control the discharge.

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