NPDES Stormwater Permitting Basics

Posted on 9/9/2022 by Roger Marks

When water from rainfall, melting snow, flooding, or other weather events collects on an industrial site, the water can pick up chemical residues, oils, dirt, trash, and other pollutants. Those pollutants may then flow into nearby bodies of water, either directly or through sewer systems.

US EPA created the stormwater regulations to control the amount of polluted stormwater discharged from streets, paved lots, rooftops, and other surfaces at industrial facilities and other sites.

These stormwater regulations are a part of the National Pollutant Discharge Elimination System (NPDES) program. The NPDES program was established under the Clean Water Act and requires industrial facilities (and others) to obtain permits before they can discharge pollutants to the water through a “point source” such as a pipe or storm drain.

To comply with the NPDES requirements related to stormwater, an industrial facility must take some key steps:

  • Determine if the facility is covered by EPA’s definition of “industrial activity”
  • Identify areas of the facility that are “associated with industrial activity”
  • Identify “point sources” through which stormwater is discharged
  • Obtain a permit that sets limits on stormwater discharges
  • Implement control measures for stormwater runoff
  • Measure and monitor discharge volumes and pollution levels
  • Create and maintain a stormwater pollution prevention plan (SWPPP)

Part 1 of our stormwater compliance basics blog series covers how to determine whether the NPDES stormwater permitting regulations apply to your facility.

NPDES Stormwater Permitting Basics

What kind of “industrial activity” is covered by the NPDES stormwater regulations?

“Industrial activity” is one category of site that is required to obtain a permit for stormwater discharges. Others include large construction sites and municipal separate storm sewer systems (MS4s).

In the stormwater regulations, EPA’s definition of “industrial activity” covers eleven specific source categories, including:

  • Manufacturing facilities (Various SIC codes) 
  • Hazardous waste treatment storage, or disposal facilities
  • Recycling facilities, junkyards, and battery reclaimers
  • Airports and other transportation facilities
  • Landfills
  • Mining, Mineral, Oil, and Gas (SIC Codes 10-14)
  • Steam electric power plants (incl. coal handling sites)
  • Treatment works
  • Many forms of light industrial activity (based on SIC Code)
  • Small construction activities (i.e., disturbing less than 5 acres)

The full list of industry categories is found in 40 CFR 122.26(b)(14).

What areas of the facility are covered?

EPA defines “stormwater discharge associated with industrial activity” to mean:

“…discharge from any conveyance that is used for collecting and conveying stormwater and that is directly related to manufacturing, processing, or raw materials storage areas at an industrial plant…”

Areas of a facility that stormwater runoff may come into contact with include, but are not limited to:

  • Industrial plant yards
  • Material handling sites
  • Shipping and receiving areas
  • Manufacturing buildings
  • Raw material storage areas
  • Storage areas for intermediate and final products
  • Refuse sites
  • Sites used to store or maintain material handling equipment
  • Sites used for residual treatment, storage, or disposal
  • Sites used for application or disposal of wastewater

(40 CFR 122.26(b))

What is a “point source” for stormwater discharges?

The Clean Water Act regulations define a point source as:

"any discernible, confined, discrete conveyance…from which pollutants are or may be discharged." 

For the purpose of compliance with the NPDES stormwater regulations, a point source can be any natural or man-made feature that stormwater moves through to reach a receiving water—e.g., storm drains, pipes, street gutters, tunnels, wells, fissures, containers, ditches, channels, catch basins, etc.

Quick Recap:

Your facility will likely need a NPDES permit that covers stormwater discharges if:

  • Your facility is in one of the eleven source categories listed in 40 CFR 122.26(b)(14); and
  • You discharge stormwater through a point source from any area that is “associated with industrial activity.”

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Learn more about NPDES permitting requirements under the Clean Water Act and your responsibilities for compliance with other major EPA air, water, and chemical regulations during the two-day Complete Environmental Regulations Webinar

Discover what you must monitor, report, and keep on file to ensure compliance and keep your facility running smoothly. You will learn core requirements of the Clean Air Act, Clean Water Act, SDWA, TSCA, FIFRA, CERCLA/Superfund, and more—and what steps to take to achieve compliance.
September 19—20 Details
December 5—6 Details

Can't make a live webinar? Train at your own pace with the online course

Tags: Clean Water Act, NPDES, NPDES permitting, stormwater, stormwater permits

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