NPDES Permit Glossary: Key Terms & Definitions for Developers and Consultants

NPDES Permit Key Terms & Definitions

Administrative Orders: Formal enforcement actions issued by the EPA or state regulatory agencies to address NPDES permit violations or other non-compliance. These orders typically require the permittee to take specific corrective actions and may impose penalties or other sanctions. (40 C.F.R. § 122.41(a)(2))

Antidegradation: A policy and regulatory framework that aims to protect and maintain existing water quality in surface waters, particularly in waters that exceed the levels necessary to support designated uses. Antidegradation requirements may affect NPDES permit conditions and effluent limitations. (40 C.F.R. § 131.12)

Best Available Technology Economically Achievable (BAT): A technology-based standard for setting effluent limitations in NPDES permits for industrial dischargers. BAT represents the best available technology that is economically achievable for a particular industry category or subcategory. (CWA § 301(b)(2)(A))

Best Conventional Pollutant Control Technology (BCT): A technology-based standard for setting effluent limitations in NPDES permits for conventional pollutants, such as BOD, TSS, pH, oil and grease, and fecal coliform. BCT is based on the performance of the best conventional pollution control technologies. (CWA § 301(b)(2)(E))

Best Management Practices (BMPs): Schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce pollution. BMPs may be required in NPDES permits to control or abate the discharge of pollutants. (40 C.F.R. § 122.2)

Clean Water Act (CWA): The primary federal law in the United States governing water pollution, enacted in 1972. The CWA establishes the NPDES permit program and sets the basic structure for regulating discharges of pollutants into waters of the United States. (33 U.S.C. § 1251 et seq.)

Concentrated Animal Feeding Operation (CAFO): An animal feeding operation that meets certain regulatory thresholds for the number of animals confined and the duration of confinement. CAFOs are considered point sources under the CWA and may be required to obtain NPDES permits. (40 C.F.R. § 122.23)

Designated Uses: The uses specified for each water body or segment under state water quality standards, such as public water supply, recreation, aquatic life support, or agriculture. NPDES permit conditions must be designed to protect and maintain designated uses. (40 C.F.R. § 131.3(f))

Discharge Monitoring Report (DMR): A report submitted by NPDES permit holders to the regulatory agency, containing self-monitoring results and other compliance information. DMRs are typically submitted on a monthly or quarterly basis. (40 C.F.R. § 122.41(l)(4))

Effluent Limitation: Any restriction imposed by the permitting authority on quantities, discharge rates, and concentrations of pollutants discharged from point sources into waters of the United States. Effluent limitations may be based on technology standards or water quality standards. (CWA § 502(11))

Fact Sheet: A document prepared by the permitting authority that summarizes the principal facts and the significant factual, legal, methodological, and policy questions considered in preparing the draft NPDES permit. The fact sheet is a key component of the administrative record. (40 C.F.R. § 124.8)

General Permit: An NPDES permit issued for a category of dischargers within a specific geographic area, rather than an individual discharger. General permits typically cover discharges with similar characteristics and require similar permit conditions. (40 C.F.R. § 122.28)

Individual Permit: An NPDES permit issued to a single discharger, tailored to the specific characteristics and requirements of that facility. Individual permits are issued when a facility does not qualify for coverage under a general permit or requires more stringent or site-specific conditions. (40 C.F.R. § 122.21)

Maximum Daily Discharge Limitation: The highest allowable daily discharge of a pollutant, calculated as the average measurement over a day. NPDES permits typically include maximum daily discharge limitations for specific pollutants. (40 C.F.R. § 122.2)

Municipal Separate Storm Sewer System (MS4): A conveyance or system of conveyances owned or operated by a public entity that discharges to waters of the United States and is designed or used for collecting or conveying stormwater. MS4s may be required to obtain NPDES permits. (40 C.F.R. § 122.26(b)(8))

National Pollutant Discharge Elimination System (NPDES): The national program for issuing, modifying, revoking and reissuing, terminating, monitoring, and enforcing permits for the discharge of pollutants from point sources into waters of the United States. (40 C.F.R. § 122.2)

Navigable Waters: A term used in the CWA to describe waters of the United States, including the territorial seas. Discharges to navigable waters are subject to NPDES permit requirements. (CWA § 502(7))

Point Source: Any discernible, confined, and discrete conveyance from which pollutants are or may be discharged, such as a pipe, ditch, channel, or concentrated animal feeding operation. Point sources are subject to NPDES permit requirements. (CWA § 502(14))

Pollutant: Dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water. (CWA § 502(6))

Pretreatment Standards: Pollutant discharge limits that apply to industrial users discharging to publicly owned treatment works (POTWs). Pretreatment standards are designed to prevent the introduction of pollutants that may interfere with POTW operations or pass through the treatment process. (CWA § 307(b))

Publicly Owned Treatment Works (POTW): A treatment works owned by a state or municipality that treats municipal sewage or industrial wastes. POTWs are subject to NPDES permit requirements and may also implement pretreatment programs for industrial users. (40 C.F.R. § 403.3(q))

Section 401 Certification: A certification issued by a state, territory, or authorized tribe stating that a proposed discharge will comply with applicable water quality standards and other requirements. NPDES permits may not be issued without a Section 401 certification or waiver. (CWA § 401)

Stormwater: Runoff generated from rain and snowmelt events that flows over land or impervious surfaces and does not soak into the ground. Stormwater discharges from certain sources, such as construction sites and industrial facilities, may be subject to NPDES permit requirements. (40 C.F.R. § 122.26(b)(13))

Technology-Based Effluent Limitations: Effluent limitations based on the performance of available pollution control technologies, rather than the impact of the discharge on the receiving water body. Technology-based effluent limitations are developed for specific industry categories and serve as the minimum level of control for NPDES permits. (CWA § 301(b))

Total Maximum Daily Load (TMDL): The maximum amount of a pollutant that a water body can receive and still meet water quality standards. TMDLs are developed for impaired waters and may result in more stringent effluent limitations in NPDES permits for dischargers to those waters. (CWA § 303(d))

Water Quality-Based Effluent Limitations: Effluent limitations based on the impact of the discharge on the receiving water body, designed to ensure that water quality standards are met. Water quality-based effluent limitations are developed when technology-based limitations are not sufficient to protect water quality. (40 C.F.R. § 122.44(d))

Water Quality Standards: The foundation of the water quality-based pollution control program under the CWA. Water quality standards define the goals for a water body by designating its uses, setting criteria to protect those uses, and establishing antidegradation provisions. NPDES permit conditions must be consistent with water quality standards. (CWA § 303(c))

Whole Effluent Toxicity (WET): The aggregate toxic effect of an effluent on aquatic organisms, measured through standardized toxicity tests. NPDES permits may include WET testing requirements to assess the overall toxicity of the discharge. (40 C.F.R. § 122.2)

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