Stormwater

Scope

Stormwater discharges are generated by rainwater and snowmelt runoff from land and impervious areas such as paved streets, parking lots, and building rooftops. This runoff often contains pollutants in quantities that could adversely affect water quality.

Most stormwater discharges are considered point sources and require coverage by a permit under the National Pollutant Discharge Elimination System (NPDES). The primary method to control stormwater discharges is through the use of best management practices. The NPDES stormwater permitting program is organized according to the three types of regulated stormwater discharges:

Regulatory citations

• 40 CFR 122.26 — Storm water discharges (applicable to State NPDES programs, see 123.25). 

Key definitions

• Average monthly discharge limitation: The highest allowable average of daily discharges over a calendar month, calculated as the sum of all “daily discharges” measured during a calendar month divided by the number of daily discharges measured during that month.
• Best management practices (BMPs): 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 plant site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.
• Combined sewer system (CSS): A wastewater collection system owned by a state or municipality (as defined by section 502(4) of the CWA) which conveys sanitary wastewaters (domestic, commercial and industrial wastewaters) and stormwater through a single-pipe system to a Publicly Owned Treatment Works (POTW) Treatment Plant.
• Continuous discharge: A “discharge” which occurs without interruption throughout the operating hours of the facility, except for infrequent shutdowns for maintenance, process changes, or other similar activities.
• Daily discharge: The “discharge of a pollutant” measured during a calendar day or any 24-hour period that reasonably represents the 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 over the day. For pollutants with limitations expressed in other units of measurement, the “daily discharge” is calculated as the average measurement of the pollutant over the day.
• Direct discharge: The discharge of a pollutant.
• Discharge of a pollutant: 
  • Any addition of any “pollutant” or combination of pollutants to “waters of the United States” from any “point source,” or
  • Any addition of any pollutant or combination of pollutants to the waters of the “contiguous zone” or the ocean from any point source other than a vessel or other floating craft which is being used as a means of transportation. This definition includes additions of pollutants into waters of the United States from: surface runoff which is collected or channeled by man; discharges through pipes, sewers, or other conveyances owned by a State, municipality, or other person which do not lead to a treatment works; and discharges through pipes, sewers, or other conveyances, leading into privately owned treatment works. This term does not include an addition of pollutants by any “indirect discharger.”
• Discharge Monitoring Report (DMR): The EPA uniform national form, including any subsequent additions, revisions, or modifications for the reporting of self-monitoring results by permittees. DMRs must be used by “approved states” as well as by EPA. EPA will supply DMRs to any approved state upon request. The EPA national forms may be modified to substitute the State Agency name, address, logo, and other similar information, as appropriate, in place of EPA’s.
• 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: A regulation published by the Administrator under section 304(b) of CWA to adopt or revise “effluent limitations.”
• Indirect discharger: A nondomestic discharger introducing “pollutants” to a “publicly owned treatment works.”
• Municipality: A city, town, borough, county, parish, district, association, or other public body created by or under State law and having jurisdiction over disposal of sewage, industrial wastes, or other wastes, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of CWA.
• National Pollutant Discharge Elimination System (NPDES): The national program for issuing, modifying, revoking and reissuing, terminating, monitoring and enforcing permits, and imposing and enforcing pretreatment requirements, under sections 307, 402, 318, and 405 of CWA. The term includes an “approved program.”
• 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, 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. It does not mean:
  • Sewage from vessels; or
  • Water, gas, or other material which is injected into a well to facilitate production of oil or gas, or water derived in association with oil and gas production and disposed of in a well, if the well used either to facilitate production or for disposal purposes is approved by authority of the State in which the well is located, and if the State determines that the injection or disposal will not result in the degradation of ground or surface water resources.
    Note: Radioactive materials covered by the Atomic Energy Act are those encompassed in its definition of source, byproduct, or special nuclear materials. Examples of materials not covered include radium and accelerator-produced isotopes. See Train v. Colorado Public Interest Research Group, Inc., 426 U.S. 1 (1976).
• 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.
• Sewage sludge: Any solid, semi-solid, or liquid residue removed during the treatment of municipal waste water or domestic sewage. Sewage sludge includes, but is not limited to, solids removed during primary, secondary, or advanced waste water treatment, scum, septage, portable toilet pumpings, type III marine sanitation device pumpings (33 CFR 159), and sewage sludge products. Sewage sludge does not include grit or screenings, or ash generated during the incineration of sewage sludge.
• Stormwater: Atormwater runoff, snow melt runoff, and surface runoff and drainage.

Summary of requirements

Industrial facilities

• Determine if your facility’s SIC code or industrial activity is subject to NPDES stormwater permitting.
• Determine if your facility is located in a state that runs its own NPDES stormwater permitting program, or if you must apply for a Multi-Sector General Permit.
• Test for the contaminants that are found in your stormwater/snowmelt discharges.
• Apply for the proper permit (general, specific, MSGP, construction, construction MSGP, or other.
• Comply with the terms and conditions listed in the permit.

Construction activities

• Determine if your construction activities will disturb one or more acres of land or are part of a larger construction project that will disturb five or more acres of land.
• Determine if you are eligible for a Construction General Permit.
• Apply for a stormwater construction permit.
• Comply with the terms and conditions in the permit.