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National Pollutant Discharge Elimination System (NPDES)
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NPDES Topics Alphabetical Index Glossary About NPDES

NPDES Glossary

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  • Acute
    A stimulus severe enough to rapidly induce an effect; in aquatic toxicity tests, an effect observed in 96 hours or less is typically considered acute. When referring to aquatic toxicology or human health, an acute effect is not always measured in terms of lethality.

  • Aerobic treatment unit (ATU)
    A mechanical wastewater treatment unit that provides secondary wastewater treatment for a single home, a cluster of homes, or a commercial establishment by mixing air (oxygen) and aerobic and facultative microbes with the wastewater. ATUs typically use a suspended growth process (such as activated sludge-extended aeration and batch reactors), a fixed-film process (similar to a trickling filter), or a combination of the two treatment processes.

  • Animal Feeding Operation (AFO)
    Lot or facility (other than an aquatic animal production facility) where the following conditions are met:
    • Animals (other than aquatic animals) have been, are, or will be stabled or confined and fed or maintained for a total of 45 days or more in any 12-month period, and
    • Crops, vegetation, forage growth, or post-harvest residues are not sustained in the normal growing season over any portion of the lot or facility.
    [40 CFR 122.23(b)(1)]

  • Anti-backsliding
    A provision in the Federal Regulations [CWA 303(d)(4); CWA 402(c); CFR 122.44(l)] that requires a reissued permit to be as stringent as the previous permit with some exceptions.

  • Antidegradation
    Policies which ensure protection of water quality for a particular water body where the water quality exceeds levels necessary to protect fish and wildlife propagation and recreation on and in the water. This also includes special protection of waters designated as outstanding natural resource waters. Antidegradation plans are adopted by each state to minimize adverse effects on water.

  • Applicant Type
    Indicate whether you, the applicant, are a federal, state, tribal, private, or other public entity. This question does not refer to the where the facility is located. For example, if this is a privately owned facility that is located in Indian country, select "private" from this list.

  • Authorized Program or Authorized State
    A state, Territorial, Tribal, or interstate NPDES program which has been approved or authorized by EPA under 40 CFR Part 123.

  • Average Monthly Discharge Limitations
    The highest allowable average of daily discharges over a calendar month, calculated as the sum of all daily discharges measured during that month divided by the number of days on which monitoring was performed (except in the case of fecal coliform).

  • Average Weekly Discharge Limitation
    The highest allowable average of daily discharges over a calendar week, calculated as the sum of all daily discharges measured during a calendar week divided by the number of daily discharges measured during that week.

  • Best Available Technology Economically Achievable (BAT)
    Technology-based standard established by the Clean Water Act (CWA) as the most appropriate means available on a national basis for controlling the direct discharge of toxic and nonconventional pollutants to navigable waters. BAT effluent limitations guidelines, in general, represent the best existing performance of treatment technologies that are economically achievable within an industrial point source category or subcategory.

  • Best Conventional Pollutant Control Technology (BCT)
    Technology-based standard for the discharge from existing industrial point sources of conventional pollutants including BOD, TSS, fecal coliform, pH, oil and grease. The BCT is established in light of a two-part "cost reasonableness" test which compares the cost for an industry to reduce its pollutant discharge with the cost to a POTW for similar levels of reduction of a pollutant loading. The second test examines the cost-effectiveness of additional industrial treatment beyond BPT. EPA must find limits which are reasonable under both tests before establishing them as BCT.

  • Best Management Practices (BMPs)
    Schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the discharge of pollutants to waters of the United States. BMPs also include treatment requirements, operating procedures, and practice to control plant site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage. (Source: Appendix A of the 2003 Construction General Permit [PDF Format])

  • Best Practicable Control Technology Currently Available (BPT)
    The first level of technology-based standards established by the CWA to control pollutants discharged to waters of the U.S. BPT effluent limitations guidelines are generally based on the average of the best existing performance by plants within an industrial category or subcategory.

  • Best Professional Judgment (BPJ)
    The method used by permit writers to develop technology-based NPDES permit conditions on a case-by-case basis using all reasonably available and relevant data.

  • Bioassay
    A test used to evaluate the relative potency of a chemical or a mixture of chemicals by comparing its effect on a living organism with the effect of a standard preparation on the same type of organism.

  • Biochemical Oxygen Demand (BOD)
    A measurement of the amount of oxygen utilized by the decomposition of organic material, over a specified time period (usually 5 days) in a wastewater sample; it is used as a measurement of the readily decomposable organic content of a wastewater.

  • Biosolids
    Sewage sludge that is used or disposed through land application, surface disposal, incineration, or disposal in a municipal solid waste landfill. Sewage sludge is defined as solid, semi-solid, or liquid untreated residue generated during the treatment of domestic sewage in a treatment facility.

  • Bypass
    The intentional diversion of wastestreams from any portion of a treatment (or pretreatment) facility.

  • Categorical Industrial User (CIU)
    An industrial user subject to national categorical pretreatment standards.

  • Categorical Pretreatment Standards
    Limitations on pollutant discharges to publicly owned treatment works promulgated by EPA in accordance with Section 307 of the Clean Water Act that apply to specified process wastewaters of particular industrial categories [40 CFR 403.6 and Parts 405-471].

  • Centralized Wastewater Treatment System
    A managed system consisting of collection sewers and a single treatment plant used to collect and treat wastewater from an entire service area. Traditionally, such a system has been called a publicly owned treatment works (POTW) as defined at 40 CFR 122.2.

  • Certifying Official
    All applications, including NOIs, must be signed as follows:
    1. For a corporation: By a responsible corporate officer. For the purpose of this Part, a responsible corporate officer means: (i) a president, secretary, treasurer, or vice-president of the corporation in charge of a principal business function, or any other person who performs similar policy- or decision-making functions for the corporation, or (ii) the manager of one or more manufacturing, production, or operating facilities, provided, the manager is authorized to make management decisions which govern the operation of the regulated facility including having the explicit or implicit duty of making major capital investment recommendations, and initiating and directing other comprehensive measures to assure long term environmental compliance with environmental laws and regulations; the manager can ensure that the necessary systems are established or actions taken to gather complete and accurate information for permit application requirements; and where authority to sign documents has been assigned or delegated to the manager in accordance with corporate procedures.
    2. For a partnership or sole proprietorship: By a general partner or the proprietor, respectively; or
    3. For a municipality, state, federal, or other public agency: By either a principal executive officer or ranking elected official. For purposes of this Part, a principal executive officer of a federal agency includes (i) the chief executive officer of the agency, or (ii) a senior executive officer having responsibility for the overall operations of a principal geographic unit of the agency (e.g., Regional Administrator of EPA).

  • Chemical Oxygen Demand (COD)
    A measure of the oxygen-consuming capacity of inorganic and organic matter present in wastewater. COD is expressed as the amount of oxygen consumed in mg/l. Results do not necessarily correlate to the biochemical oxygen demand (BOD) because the chemical oxidant may react with substances that bacteria do not stabilize.

  • Chronic
    A stimulus that lingers or continues for a relatively long period of time, often one-tenth of the life span or more. Chronic should be considered a relative term depending on the life span of an organism. The measurement of a chronic effect can be reduced growth, reduced reproduction, etc., in addition to lethality.

  • Class V Injection Well
    A shallow well used to place a variety of fluids at shallow depths below the land surface, including a domestic onsite wastewater treatment system serving more than 20 people. USEPA permits these wells to inject wastes below the ground surface provided they meet certain requirements and do not endanger underground sources of drinking water.

  • Code of Federal Regulations (CFR)
    A codification of the final rules published daily in the Federal Register. Title 40 of the CFR contains the environmental regulations.

  • Combined Sewer Overflow (CSO)
    A discharge of untreated wastewater from a combined sewer system at a point prior to the headworks of a publicly owned treatment works. CSOs generally occur during wet weather (rainfall or snowmelt). During periods of wet weather, these systems become overloaded, bypass treatment works, and discharge directly to receiving waters.

  • Combined Sewer System (CSS)
    A wastewater collection system which conveys sanitary wastewaters (domestic, commercial and industrial wastewaters) and stormwater through a single pipe to a publicly owned treatment works for treatment prior to discharge to surface waters.

  • Compliance Schedule
    A schedule of remedial measures included in a permit or an enforcement order, including a sequence of interim requirements (for example, actions, operations, or milestone events) that lead to compliance with the CWA and regulations.

  • Composite Sample
    Sample composed of two or more discrete samples. The aggregate sample will reflect the average water quality covering the compositing or sample period.

  • Concentrated Animal Feeding Operation (CAFO)
    An AFO that is defined as a Large CAFO or as a Medium CAFO. . ., or that is designated as a CAFO. . . Two or more AFOs under common ownership are considered to be a single AFO for the purposes of determining the number of animals at an operation, if they adjoin each other or if they use a common area or system for the disposal of wastes.
    [40 CFR 122.23(b)(2)]

  • Conventional Pollutants
    Pollutants typical of municipal sewage, and for which municipal secondary treatment plants are typically designed; defined by Federal Regulation [40 CFR 401.16] as BOD, TSS, fecal coliform bacteria, oil and grease, and pH.

  • Conventional Septic System
    A wastewater treatment system consisting of a septic tank and a typical trench or bed subsurface wastewater infiltration system.

  • Criteria
    The numeric values and the narrative standards that represent contaminant concentrations that are not to be exceeded in the receiving environmental media (surface water, ground water, sediment) to protect beneficial uses.

  • Daily Discharge
    The discharge of a pollutant measured during any 24-hour period that reasonably represents a calendar day for purposes of sampling. For pollutants with limitations expressed in units of mass, the daily discharge is calculated as the total mass of the pollutant discharged during the day. For pollutants with limitations expressed in other units of measurement (e.g., concentration) the daily discharge is calculated as the average measurement of the pollutant throughout the day (40 CFR 122.2).

  • Daily Maximum Limit
    The maximum allowable discharge of pollutant during a calendar day. Where daily maximum limitations are expressed in units of mass, the daily discharge is the total mass discharged over the course of the day. Where daily maximum limitations are expressed in terms of a concentration, the daily discharge is the arithmetic average measurement of the pollutant concentration derived from all measurements taken that day.

  • Development Document
    A report prepared during the development of an effluent limitation guideline by EPA that provides the data and methodology used to develop limitations guidelines and categorical pretreatment standards for an industrial category.

  • Director
    The Regional Administrator or State Director, as the context requires, or an authorized representative. When there is no approved state program, and there is an EPA administered program, Director means the Regional Administrator. When there is an approved state program, "Director" normally means the State Director.

  • Discharge Monitoring Report (DMR)
    The form used (including any subsequent additions, revisions, or modifications) to report self-monitoring results by NPDES permittees. DMRs must be used by approved states as well as by EPA.

  • Draft Permit
    A document prepared under 40 CFR 124.6 indicating the Director's tentative decision to issue, deny, modify, revoke and reissue, terminate, or reissue a permit. A notice of intent to terminate a permit, and a notice of intent to deny a permit application, as discussed in 40 CFR 124.5, are considered draft permits. A denial of a request for modification, revocation and reissuance, or termination, as discussed in 40 CFR 124.5, is not a draft permit.

  • Effluent Limitation
    Any restriction imposed by the Director on quantities, discharge rates, and concentrations of pollutants which are discharged from point sources into waters of the United States, the waters of the contiguous zone, or the ocean.

  • Effluent Limitations Guidelines (ELG)
    A regulation published by the Administrator under Section 304(b) of CWA that establishes national technology-based effluent requirements for a specific industrial category.

  • Fact Sheet
    A document that must be prepared for all draft individual permits for NPDES major dischargers, NPDES general permits, NPDES permits that contain variances, NPDES permits that contain sewage sludge land application plans and several other classes of permittees. The document summarizes the principal facts and the significant factual, legal, methodological and policy questions considered in preparing the draft permit and tells how the public may comment (40 CFR 124.8 and 124.56). Where a fact sheet is not required, a statement of basis must be prepared (40 CFR 124.7).

  • Federal Facility
    Any buildings, installations, structures, land, public works, equipment, aircraft, vessels, and other vehicles and property, owned by, or constructed or manufactured for the purpose of leasing to, the federal government. (Source: Appendix A of the 2003 Construction General Permit [PDF] )

  • Four-Zero-One (401) (a) Certification
    A requirement of Section 401(a) of the Clean Water Act that all federally issued permits be certified by the state in which the discharge occurs. The state certifies that the proposed permit will comply with state water quality standards and other state requirements.

  • Fundamentally Different Factors (FDF)
    Those components of a petitioner's facility that are determined to be so unlike those components considered by EPA during the effluent limitation guideline and pretreatment standards rulemaking that the facility is worthy of a variance from the effluent limitations guidelines or categorical pretreatment standards.

  • General Permit
    An NPDES permit issued under 40 CFR 122.28 that authorizes a category of discharges under the CWA within a geographical area. A general permit is not specifically tailored for an individual discharger.

  • Grab Sample
    A sample which is taken from a wastestream on a one-time basis without consideration of the flow rate of the wastestream and without consideration of time.

  • Hazardous Substance
    Any substance, other than oil, which, when discharged in any quantities into waters of the U.S., presents an imminent and substantial danger to the public health or welfare, including but not limited to fish, shellfish, wildlife, shorelines and beaches (Section 311 of the CWA); identified by EPA as the pollutants listed under 40 CFR Part 116. Any substance, other than oil, which, when discharged in any quantities into waters of the U.S., presents an imminent and substantial danger to the public health or welfare, including but not limited to fish, shellfish, wildlife, shorelines and beaches (Section 311 of the CWA); identified by EPA as the pollutants listed under 40 CFR Part 116.

  • Indian Country
    Defined at 40 Code of Federal Regulations (CFR) 122.2 to mean:
    1. All land within the limits of any Indian reservation under the jurisdiction of the United States government, notwithstanding the issuance of any patent, and, including rights-of-way running through the reservation;
    2. All dependent Indian communities with the borders of the United States whether within the originally or subsequently acquired territory thereof, and whether within or without the limits of a state; and
    3. All Indian allotments, the Indian titles to which have not been extinguished, including rights-of-ways running through the same.

  • Indirect Discharge
    The introduction of pollutants into a municipal sewage treatment system fro any nondomestic source (i.e., any industrial or commercial facility) regulated under Section 307(b), (c), or (d) of the CWA.

  • Industrial Sources
    Non-municipal, or industrial sources, often generate wastewater that is discharged to surface waters. The types of wastewaters generated at a facility depend on the specific activities undertaken at a particular site, and may include manufacturing or process wastewaters, cooling waters, sanitary wastewater, and stormwater runoff.

  • Instantaneous Maximum Limit
    The maximum allowable concentration of a pollutant determined from the analysis of any discrete or composite sample collected, independent of the flow rate and the duration of the sampling event.

  • Large Concentrated Animal Feeding Operation (Large CAFO)
    An AFO is defined as a Large CAFO if it stables or confines as many or more than the numbers of animals specified in any of the following categories:
    • 700 mature dairy cows, whether milked or dry;
    • 1,000 veal calves;
    • 1,000 cattle other than mature dairy cows or veal calves. Cattle includes but is not limited to heifers, steers, bulls and cow/calf pairs;
    • 2,500 swine, each weighing 55 pounds or more;
    • 10,000 swine, each weighing less than 55 pounds;
    • 500 horses;
    • 10,000 sheep or lambs;
    • 55,000 turkeys;
    • 30,000 laying hens or broilers, if the AFO uses a liquid manure handling system;
    • 125,000 chickens (other than laying hens), if the AFO uses other than a liquid manure handling system;
    • 82,000 laying hens, if the AFO uses other than a liquid manure handling system;
    • 30,000 ducks (if the AFO uses other than a liquid manure handling system); or
    • 5,000 ducks (if the AFO uses a liquid manure handling system)
    [40 CFR 122.23(b)(4)]

  • Large Construction Activity
    As defined at 40 CFR 122.26(b)(14)(x), a large construction activity includes clearing, grading, and excavating resulting in a land disturbance that will disturb equal to or more than five acres of land or will disturb less than five acres of total land area but is part of a larger common plan of development or sale that will ultimately disturb equal to or more than five acres. Large construction activity does not include routine maintenance that is performed to maintain the original line and grade, hydraulic capacity, or original purpose of the site. (Source: Appendix A of the 2003 Construction General Permit [PDF Format])

  • Local Limits
    Conditional discharge limits imposed by municipalities upon industrial or commercial facilities that discharge to the municipal sewage treatment system.

  • Major Facility
    Any NPDES facility or activity classified as such by the Regional Administrator, or in the case of approved state programs, the Regional Administrator in conjunction with the State Director. Major municipal dischargers include all facilities with design flows of greater than one million gallons per day and facilities with EPA/State approved industrial pretreatment programs. Major industrial facilities are determined based on specific ratings criteria developed by EPA/State.

  • Mass-Based Standard
    A discharge limit that is measured in a mass unit such as pounds per day.

  • Medium Concentrated Animal Feeding Operation (Medium CAFO)
    The term Medium CAFO includes any AFO with the type and number of animals that fall within any of the ranges listed below and which has been defined or designated as a CAFO. An AFO is defined as a Medium CAFO if:
    • The type and number of animals that it stables or confines falls within any of the following ranges:
      • 200 to 699 mature dairy cows, whether milked or dry;
      • 300 to 999 veal calves;
      • 300 to 999 cattle other than mature dairy cows or veal calves. Cattle includes but is not limited to heifers, steers, bulls and cow/calf pairs;
      • 750 to 2,499 swine each weighing 55 pounds or more;
      • 3,000 to 9,999 swine each weighing less than 55 pounds;
      • 150 to 499 horses;
      • 3,000 to 9,999 sheep or lambs;
      • 16,500 to 54,999 turkeys;
      • 9,000 to 29,999 laying hens or broilers, if the AFO uses a liquid manure handling system;
      • 37,500 to 124,999 chickens (other than laying hens), if the AFO uses other than a liquid manure handling system;
      • 25,000 to 81,999 laying hens, if the AFO uses other than a liquid manure handling system;
      • 10,000 to 29,999 ducks (if the AFO uses other than a liquid manure handling system); or
      • 1,500 to 4,999 ducks (if the AFO uses a liquid manure handling system); and
    • Either one of the following conditions are met:
      • Pollutants are discharged into waters of the United States through a man-made ditch, flushing system, or other similar man-made device; or
      • Pollutants are discharged directly into waters of the United States which originate outside of and pass over, across, or through the facility or otherwise come into direct contact with the animals confined in the operation.
    [40 CFR 122.23(b)(6)]

  • Method Detection Limit (MDL)
    Defined as the minimum concentration of a substance that can be measured and reported with 99 percent confidence that the analyte concentration is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte.

  • Million Gallons per Day (mgd)
    A unit of flow commonly used for wastewater discharges. One mgd is equivalent to 1.547 cubic feet per second.

  • Mining (Coal)
    Coal mining employs basically the same traditional mining techniques used in hard rock mining - underground and surface ("strip") mining. One of the more efficient but environmentally destructive methods for mining coal involves "strip" mining. This technique is analogous to the open pit mining techniques used in hard rock mining whereby the soil and rock above the coal seam are removed to expose the seam. The seam is then blasted and the coal is scooped up by huge front end loaders or electric shovels and transported to a coal processing plant. These coal preparation plants use a variety of physical (e.g., screening) and chemical (e.g., flotation using high gravity liquids) methods to separate the raw coal from all of the non-combustible waste rock and minerals (e.g., pyrite). The coarser waste rock is piled up adjacent to the mined out area and the finer coal tailings coming from the preparation plant are discharged as a thick slurry into a man-made impoundment. After coal mining operations have ceased, the mine is reclaimed by dumping the waste rock into the pit, regrading the area to approximate the original contours of the land and then replanting the area using native grasses and trees.

  • Mining (Hardrock)
    Traditional hardrock mining usually involves digging tunnels and adits (horizontal entrances into hillsides) to reach lodes of mineral-rich ore. Traditional underground mining and open pit mining require that the ore-bearing rock be removed and then put through a milling and extraction plant to extract the desired minerals. After the ore body is exhausted, miners move on leaving behind huge mounds of finely-ground tailings and coarser waste rock, as well as an underground tunnel complex and/or open pit.

  • Mining (Mountaintop)
    A relatively new variant of strip mining technology. This mining technique is common West Virginia and eastern Kentucky where there is enough topographic relief that is highly dissected such that the adjacent valleys can serve as repositories for overburden (soil and waste rock). Bulldozers remove all topsoil and vegetation from the top of the mountain. The bedrock above the coal is then blasted to break it up for removal. Huge draglines (the bucket can hold 15-20 pickup trucks) then remove the overburden from on top of the coal seam and dump the waste rock ("spoil") into adjacent valleys. Once exposed, the coal seam is then blasted and front end loaders scoop up the coal and load it into huge dump trucks (capable of carrying 100 tons) that haul the raw coal to the coal preparation plant.

  • Mining (Non-metals)
    Non-metallic minerals include salt, gypsum, potash, phosphate, borax and other minerals used in the chemical industry. Sand and gravel extracted for glass making and construction (highways, buildings, and dams) is also regarded as a form of non-metal mining activity. These minerals are extracted primarily using open pit mining techniques, but may also employ underground mining techniques when the deposit is located hundreds or thousands of feet below the surface. Non-metal minerals and associated waste rock are generally of lower toxicity and more manageable than hardrock and coal mining wastes, but still have the potential to create environmental pollution from rainwater running off the piles.

  • Mixing Zone
    An area where an effluent discharge undergoes initial dilution and is extended to cover the secondary mixing in the ambient water body. A mixing zone is an allocated impact zone where water quality criteria can be exceeded as long as acutely toxic conditions are prevented.

  • Multi-Sector General Permit (MSGP)
    The Stormwater Multi-Sector General Permit (MSGP) authorizes the discharge of stormwater from industrial facilities, consistent with the terms of the permit, in areas of the United States where EPA manages the NPDES permit program. To download the current MSGP that was published 10/30/2000 and to view the MSGP addendiums, go to the Stormwater Example and General Permits page.

  • Municipal Separate Storm Sewer System (MS4)
    A conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains):
    1. Owned and operated by a state, city, town, borough, county, parish, district, association, or other public body (created by or pursuant to state law) having jurisdiction over disposal of sewage, industrial wastes, stormwater, or other wastes, including special districts under state law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the Clean Water Act (CWA) that discharges to waters of the United States;
    2. Designed or used for collecting or conveying stormwater;
    3. Which is not a combined sewer; and
    4. Which is not part of a publicly owned treatment works (POTW).
    [40 CFR 122.26(b)(8)].

  • Municipal Sources
    POTWs collect domestic sewage from houses, other sanitary wastewater, and wastes from commercial and industrial facilities. POTWs discharge conventional pollutants, and are covered by secondary treatment standards and state water quality standards. POTWs also produce biosolids during the treatment process.

  • National Pollutant Discharge Elimination System (NPDES)
    A national program under Section 402 of the Clean Water Act for regulation of discharges of pollutants from point sources to waters of the United States. Discharges are illegal unless authorized by an NPDES permit.

  • National Pretreatment Standard or Pretreatment Standard
    Any regulation promulgated by the EPA in accordance with Sections 307(b) and (c) of the CWA that applies to a specific category of industrial users and provides limitations on the introduction of pollutants into publicly owned treatment works. This term includes the prohibited discharge standards under 40 CFR 403.5, including local limits [40 CFR 403.3(j)].

  • New Discharger
    Any building, structure, facility, or installation: a. From which there is or may be a discharge of pollutants; b. That did not commence the discharge of pollutants at that particular site prior to August 13, 1979; c. Which is not a new source; and d. Which has never received a finally effective NPDES permit for discharges at that site.

  • New Source
    Any building, structure, facility, or installation from which there is or may be a discharge of pollutants, the construction of which commenced: a. After promulgation of standards of performance under Section 306 of the CWA which are applicable to such source; or b. After proposal of standards of performance in accordance with Section 306 of the CWA which are applicable to such source, but only if the standards are promulgated in accordance with Section 306 of the CWA within 120 days of their proposal. c. Except as otherwise provided in an applicable new source performance standard, a source is a new source if it meets the definition in 40 CFR 122.2; and i. It is constructed at a site at which no other source is located; or ii. It totally replaces the process or production equipment that causes the discharge of pollutants at an existing source; or iii. Its processes are substantially independent of an existing source at the same site. In determining whether these processes are substantially independent, the Director shall consider such factors as the extent to which the new facility is integrated with the existing plant; and the extent to which the new facility is engaged in the same general type of activity as the existing source.

  • New Source Performance Standards (NSPS)
    Technology-based standards for facilities that qualify as new sources under 40 CFR 122.2 and 40 CFR 122.29. Standards consider that the new source facility has an opportunity to design operations to more effectively control pollutant discharges.

  • Nonconventional Pollutants
    All pollutants that are not included in the list of conventional or toxic pollutants in 40 CFR Part 401. Includes pollutants such as chemical oxygen demand (COD), total organic carbon (TOC), nitrogen, and phosphorus.

  • Operator/Owner
    For the purpose of the 2003 Construction General Permit and in the context of stormwater associated with construction activity, any party associated with a construction project that meets either of the following two criteria:
    1. The party has operational control over construction plans and specifications, including the ability to make modifications to those plans and specifications
    2. The party has day-to-day operational control of those activities at a project which are necessary to ensure compliance with a SWPPP for the site or other permit conditions (e.g., authorized to direct workers at a site to carry out activities required by the SWPPP or comply with other permit conditions).
    (Source: Appendix A of the 2003 Construction General Permit [PDF Format])

  • Permitting Authority
    The United States Environmental Protection Agency (EPA), a Regional Administrator of the Environmental Protection Agency, or an authorized representative. Under the Clean Water Act, most states are authorized to implement the NPDES permit program. State Authorization Process describes the process for authorizing states to implement the NPDES permit program.

  • pH
    A measure of the hydrogen ion concentration of water or wastewater; expressed as the negative log of the hydrogen ion concentration in mg/l. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.

  • Point Source
    Any discernible, confined, and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock concentrated animal feeding operation (CAFO), landfill leachate collection system, vessel or other floating craft from which pollutants are or may be discharged. This term does not include return flows from irrigated agriculture or agricultural stormwater runoff.

  • Pollutant
    Dredged spoil, solid waste, incinerator residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials (except those regulated under the Atomic Energy Act of 1954, as amended (42 U.S.C. 2011 et seq.)), heat, wrecked or discarded equipment, rock, sand, cellar dirt, and industrial, municipal, and agricultural waste discharged into water [40 CFR 122.2].

  • Pollutant, Conservative
    Pollutants that do not readily degrade in the environment, and which are mitigated primarily by natural stream dilution after entering receiving bodies of waters. Included are pollutants such as metals.

  • Pollutant, Non-Conservative
    Pollutants that are mitigated by natural biodegradation or other environmental decay or removal processes in the receiving stream after in-stream mixing and dilution have occurred.

  • Practical Quantification Limit (PQL)
    The lowest level that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions.

  • Pretreatment
    The reduction of the amount of pollutants, the elimination of pollutants, or the alteration of the nature of pollutant properties in wastewater prior to or in lieu of discharging or otherwise introducing such pollutants into a publicly owned treatment works [40 CFR 403.3(q)].

  • Primary Industry Categories
    Any industry category listed in the Natural Resources Defense Council (NRDC) settlement agreement [( NRDC et al. v. Train, 8 E.R.C. 2120 (D.D.C. 1976), modified 12 E.R.C. 1833 (D.D.C. 1979)] for which EPA has or will develop effluent guidelines; also listed in Appendix A of 40 CFR Part 122.

  • Primary Treatment
    The practice of removing some portion of the suspended solids and organic matter in a wastewater through sedimentation. Common usage of this term also includes preliminary treatment to remove wastewater constituents that may cause maintenance or operational problems in the system (i.e., grit removal, screening for rags and debris, oil and grease removal, etc.).

  • Priority Pollutants
    Those pollutants considered to be of principal importance for control under the CWA based on the NRDC consent decree settlement [( NRDC et al. v. Train, 8 E.R.C. 2120 (D.D.C. 1976), modified 12 E.R.C. 1833 (D.D.C. 1979)]; a list of these pollutants is provided as Appendix A to 40 CFR Part 423.

  • Process Wastewater
    Any water which, during manufacturing or processing, comes into direct contact with, or results from the production or use of any raw material, intermediate product, finished product, byproduct, or waste product.

  • Production-Based Standard
    A discharge standard expressed in terms of pollutant mass allowed in a discharge per unit of product manufactured.

  • Proposed Permit
    A state NPDES permit prepared after the close of the public comment period (and when applicable, any public hearing and administrative appeals) which is sent to EPA for review before final issuance by the state.

  • Publicly Owned Treatment Works (POTW)
    A treatment works, as defined by Section 212 of the CWA, that is owned by the state or municipality. This definition includes any devices and systems used in the storage, treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes sewers, pipes, and other conveyances only if they convey wastewater to a POTW treatment plant [40 CFR 403.3]. Privately-owned treatment works, Federally-owned treatment works, and other treatment plants not owned by municipalities are not considered POTWs.

  • Receiving Water
    The "Water of the United States" as defined in 40 CFR 122.2 into which the regulated stormwater discharges.

  • Sanitary Sewer
    A pipe or conduit (sewer) intended to carry wastewater or water-borne wastes from homes, businesses, and industries to the POTW.

  • Sanitary Sewer Overflows (SSO)
    Untreated or partially treated sewage overflows from a sanitary sewer collection system.

  • Secondary Industry Category
    Any industry category which is not a primary industry category.

  • Secondary Treatment
    Technology-based requirements for direct discharging municipal sewage treatment facilities. Standard is based on a combination of physical and biological processes typical for the treatment of pollutants in municipal sewage. Standards are expressed as a minimum level of effluent quality in terms of: BOD 5 , suspended solids (SS), and pH (except as provided for special considerations and treatment equivalent to secondary treatment).

  • Self-Monitoring
    Sampling and analyses performed by a facility to determine compliance with a permit or other regulatory requirements.

  • Significant Industrial User (SIU)
    An indirect discharger that is the focus of control efforts under the national pretreatment program; includes all indirect dischargers subject to national categorical pretreatment standards, and all other indirect dischargers that contribute 25,000 gpd or more of process wastewater, or which make up five percent or more of the hydraulic or organic loading to the municipal treatment plant, subject to certain exceptions [40 CFR 403.3(t)].

  • Small Concentrated Animal Feeding Operation (Small CAFO)
    An AFO that is designated as a CAFO and is not a Medium CAFO.
    [40 CFR 122.23(b)(9)]

  • Small Construction Activity
    Clearing, grading, and excavating resulting in a land disturbance that will disturb equal to or more than one acre and fewer than five acres of total land area but is part of a larger common plan of development or sale that will ultimately disturb equal to or fewer than five acres. Small construction activity does not include routine maintenance that is performed to maintain the original line and grade, hydraulic capacity, or original purpose of the site [40 CFR 122.26(b)(15)].

  • Spill Prevention Control and Countermeasure Plan (SPCC)
    A plan prepared by a facility to minimize the likelihood of a spill and to expedite control and cleanup activities should a spill occur.

  • Standard Industrial Classification (SIC) Code
    A code number system used to identify various types of industries. The code numbers are published by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. A particular industry may have more than one SIC code if it conducts several types of commercial or manufacturing activities onsite.

  • Statement of Basis
    A document prepared for every draft NPDES permit for which a fact sheet is not required. A statement of basis briefly describes how permit conditions were derived and the reasons the conditions are necessary for the permit [40 CFR 124.7].

    EPA's computerized STOrage and RETrieval water quality data base that includes physical, chemical, and biological data measured in waterbodies throughout the United States.

  • Stormwater
    Stormwater runoff, snow melt runoff, and surface runoff and drainage [40 CFR 122.26(b)(13)].

  • Stormwater Discharge-Related Activities
    Activities that cause, contribute to, or result in stormwater point source pollutant discharges, including excavation, site development, grading, and other surface disturbance activities; and measures to control stormwater, including the siting, construction, and operation of BMPs to control, reduce, or prevent stormwater pollution. (Source: Appendix A of the 2003 Construction General Permit [PDF Format])

  • Technology-Based Effluent Limit
    A permit limit for a pollutant that is based on the capability of a treatment method to reduce the pollutant to a certain concentration.

  • Tiered Permit Limits
    Permit limits that only apply to the discharge when a certain threshold (e.g., production level), specific circumstance (e.g., batch discharge), or timeframe (e.g., after 6 months) triggers their use.

  • Tiered Testing
    Any of a series of tests that are conducted as a result of a previous test's findings.

  • Total Maximum Daily Load (TMDL)
    The sum of the individual wasteload allocations (WLAs) for point sources and load allocations (LAs) for nonpoint sources and natural background. Additional information on TMDLs can be found at To determine if there is an approved or established TMDL on your project's receiving water, refer to for state and regional specific TMDL information related to the construction general permit. You may also have to contact your EPA regional office or state agency.

  • Total Organic Carbon (TOC)
    Measures the amount of organic carbon in water.

  • Total Suspended Solids (TSS)
    A measure of the filterable solids present in a sample, as determined by the method specified in 40 CFR Part 136.

  • Toxic Pollutant
    Pollutants or combinations of pollutants, including disease-causing agents, which after discharge and upon exposure, ingestion, inhalation or assimilation into any organism, either directly from the environment or indirectly by ingestion through food chains, will, on the basis of information available to the Administrator of EPA, cause death, disease, behavioral abnormalities, cancer, genetic mutations, physiological malfunctions, (including malfunctions in reproduction) or physical deformations, in such organisms or their offspring. Toxic pollutants also include those pollutants listed by the Administrator under CWA Section 307(a)(1) or any pollutant listed under Section 405(d) which relates to sludge management.

  • Toxicity Reduction Evaluation (TRE)
    A site-specific study conducted in a stepwise process designed to identify the causative agent(s) of effluent toxicity, isolate the sources of toxicity, evaluate the effectiveness of toxicity control options, and then confirm the reduction in effluent toxicity.

  • Toxicity Test
    A procedure to determine the toxicity of a chemical or an effluent using living organisms. A toxicity test measures the degree of effect on exposed test organisms of a specific chemical or effluent.

  • Treatability Manual
    Five-set library of EPA guidance manuals that contain information related to the treatability of many pollutants. This manual can be used in developing NPDES permit limitations for facilities and/or pollutants which, at the time of permit issuance, are not subject to industry-specific effluent guidelines. The five volumes that comprise this series include: Vol. I - Treatability Data (EPA-600/8-80-042a); Vol. II -Industrial Descriptions (EPA-600/8-80-042b); Vol. III - Technologies (EPA-600/8-80-042c); Vol. IV - Cost Estimating (EPA-600/8-80-042d); Vol. V - Summary (EPA-600/8-80-042e).

  • TSD
    Abbreviation for the Technical Support Document Water Quality-based Toxics Control (EPA-505/2-90-001), EPA Office of Water Enforcement and Permits, 1991. It contains procedures for water quality-based limitation development.

    Abbreviation for Treatment Works Treating Domestic Sewage. Includes all POTWs and other facilities that treat domestic wastewater, and facilities that do not treat domestic wastewater, but that treat or dispose of sewage sludge.

  • Upset
    An exceptional incident in which there is unintentional and temporary noncompliance with the permit limit because of factors beyond the reasonable control of the permittee. An upset does not include noncompliance to the extent caused by operational error, improperly designed treatment facilities, inadequate treatment facilities, lack of preventive maintenance, or careless or improper operation.

  • Variance
    Any mechanism or provision under Sections 301 or 316 of the CWA or under 40 CFR Part 125, or in the applicable "effluent limitations guidelines" which allows modification to or waiver of the generally applicable effluent limitations requirements or time deadlines of the CWA. This includes provisions which allow the establishment of alternative limitations based on fundamentally different factors.

  • Wasteload Allocation (WLA)
    The proportion of a receiving water's total maximum daily load that is allocated to one of its existing or future point sources of pollution.

  • Water Quality Criteria
    Comprised of numeric and narrative criteria. Numeric criteria are scientifically derived ambient concentrations developed by EPA or states for various pollutants of concern to protect human health and aquatic life. Narrative criteria are statements that describe the desired water quality goal.

  • Water Quality Standard (WQS)
    A law or regulation that consists of the beneficial use or uses of a waterbody, the numeric and narrative water quality criteria that are necessary to protect the use or uses of that particular waterbody, and an antidegradation statement.

  • Water Quality-Based Effluent Limit (WQBEL)
    A value determined by selecting the most stringent of the effluent limits calculated using all applicable water quality criteria (e.g., aquatic life, human health, and wildlife) for a specific point source to a specific receiving water for a given pollutant.

  • Waters of the United States
    All waters that are currently used, were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters subject to the ebb and flow of the tide. Waters of the United States include all interstate waters and intrastate lakes, rivers, streams (including intermittent streams), mudflats, sand flats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds. [See 40 CFR 122.2 for the complete definition.]

  • Wetlands
    Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. (Source: Appendix A of the 2003 Construction General Permit [PDF Format])

  • Whole Effluent Toxicity (WET)
    The total toxic effect of an effluent measured directly with a toxicity test.

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Last updated on March 23, 2004 3:51 PM