This website has been authorized by the Palm Beach County MS4 NPDES (PBC NPDES) Steering Committee as a resource for all permittees within the county. It is intended that this site will provide the permittee with helpful information on understanding and complying with the requirements of the MS4 NPDES permit.

MS4 NPDES Definitions

The following terms are defined for your reference.

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Best Management Practices (BMPs) means schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the pollution of waters of the United States.  BMPs also include treatment requirements, operating procedures, and practices to control facility site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.


Clean Water Act (CWA), also referred to as "the Act" (formerly referred to as the Federal Water Pollution Control Act or Federal Water Pollution Control Act Amendments of 1972) Pub.L. 92-500, as amended Pub. L. 95-217, Pub. L. 95-576, Pub. L. 6-483 and Pub. L. 97-117, 33 U.S.C. 1251 et.seq., as amended by the WQA of 1987, P.L. 100-4, the "Act."


Discharge for the purpose of this permit, unless indicated otherwise, refers to discharges from the Municipal Separate Storm Sewer System (MS4).



Flow weighted composite sample means composite sample consisting of a mixture of alliquots collected at a constant time interval, where the volume of each aliquot is proportional to the flow rate of the discharge at the time of sampling.



High risk facility for the purpose of this permit, refers to any of the following:  a) operating municipal landfill; b) hazardous waste treatment, storage, disposal or recovery facility; c) facility that is subject to EPCRA Title III, Section 313 and d) any industrial or commercial facility that the permittee(s) determines is contributing a substantial pollutant loading to the MS4.


Illicit connection means any man-made conveyance connecting a non-stormwater discharge directly to a municipal separate storm sewer system.

Illicit discharge means any discharge to a municipal separate storm sewer that is not composed entirely of stormwater except discharges pursuant to a NPDES permit (other than the NPDES permit for discharges from the municipal separate storm sewer) and other discharges as stipulated in individual permits.

Industrial Land Use means land utilized in connection with manufacturing, processing, or raw materials storage at facilities identified under 40 CFR 122.26(b)(14).




Landfill means an area of land or an excavation in which wastes are placed for permanent disposal, and which is not a land application unit, surface impoundment, injection well, or waste pile.

Large Municipal Separate Storm Sewer System means all municipal separate storm sewers that are either:

  1. located in an incorporated place (city) with a population of 250,000 or more as determined by the latest Decennial Census by the Bureau of Census (these cities are listed in Appendices F and G of 40 CFR Part 122); or
  2. located in the counties with unincorporated urbanized populations of 250,000 or more, except municipal separate storm sewers that are located in the incorporated places, townships or towns within such counties (these counties are listed in Appendices H and I of 40 CFR Part 122); or
  3. owned or operated by a municipality other than those described in paragraph 1 or 2 and that are designated by the Director as part of the large municipal separate storm sewer system.


Major Outfall means a municipal separate storm sewer outfall that discharges from a single pipe with an inside diameter of 36 inches or more or its equivalent (discharge from a single conveyance other than circular pipe which is associated with a drainage area of more than 50 acres); or for municipal separate storm sewers that receive stormwater from lands zoned for industrial activity (based on comprehensive zoning plans or the equivalent), an outfall that discharges from a single pipe with an inside diameter of 12 inches or more or from its equivalent (discharge from other than a circular pipe associated with a drainage area of 2 acres or more). Rule 62-624.200(5), F.A.C.

MEP is an acronym for "Maximum Extent Practicable,"  the technology-based discharge standard for Municipal Separate Storm Sewer Systems established by CWA §402(p).

Municipal is defined to include cities, towns, villages, special districts and water control districts within Palm Beach County covered under this Permit and unincorporated Palm Beach County.

Municipal Separate Storm Sewer (MS4) means a conveyance, or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, and storm drains):

  1. owned or 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 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) as defined at 40 CFR 122.2.


Non-Point Source is water pollution affecting a water body from diffuse sources, not a single location.

NPDES is the National Pollutant Discharge Elimination System, a federal program designed to eliminate stormwater pollutant discharges to receiving waters of the United States



Permittee means each individual co-applicant for an NPDES permit who is only responsible for permit conditions relating to the discharge that they own or operate. (See 40 CFR 122.2)

Point Source means 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, 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.




Storm Sewer, unless otherwise indicated, refers to a municipal separate storm sewer (MS4).

Stormwater means stormwater runoff, snow melt runoff, surface runoff and drainage.

Stormwater Discharge Associated with Industrial Activity is defined at 40 CFR 122.26(b)(14).

Stormwater Management Program refers to a comprehensive program to manage the quality of stormwater discharged from the municipal separate storm sewer system.  For the purposes of this permit, the Stormwater Management Program is considered a single document, but may actually consist of separate programs.

Structural Control refers to any stormwater device designed and/or used to control stormwater flow in order to meet water quality and/or flood criteria including but not limited to pump stations, spillways, embankments, control structures, retention/detention basins, ponds, and pollution control devices.

SWMP is an acronym for "Stormwater Management Program."


Time weighted composite means a composite sample consisting of a mixture of equal aliquots collected at a constant time interval.




Waters of the United States is defined at 40 CFR 122.2.




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