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New Hampshire Department of Environmental Services

Storm Water Management Program
Minimum Control Measure 3
Illicit discharge detection and elimination

Photo of Illicit discharge What is an illicit discharge?
An illicit discharge is any discharge to the storm sewer system that is not composed entirely of storm water, except discharges that have a NPDES permit and discharges resulting from fire-fighting activities. There are also several categories of discharges that are exempt unless the municipality determines that they are a significant contributor of pollutants.

Categories of Discharges That Are Exempt

  • water line flushing
  • landscape irrigation
  • diverted stream flows
  • rising ground waters
  • uncontaminated ground water infiltration
  • discharges from potable water sources
  • foundation drains
  • air conditioning condensation
  • irrigation water
  • springs
  • water from crawl space pumps
  • footing drains
  • lawn watering
  • individual residential car washing
  • flows from riparian habitats and wetlands
  • dechlorinated swimming pool discharges
  • street wash water

What are some examples of illicit discharges?

The following are the most common examples of illicit discharges that NHDES has seen in New Hampshire

  • The sewage line from a house or business is incorrectly connected to the storm system.
  • There is a cross-connection between the sewer line and storm drainage system. This can be from an old connection that was never plugged or the plug has deteriorated, or it can be caused by exfiltration from leaking or cracked pipes.
  • Improper disposal of auto and household toxics (for example, pouring used automotive oil into a drain on the street).
  • Laundry or car wash discharge flows or is directly connected (floor drain etc.) to the storm sewer system.

What are the requirements of an illicit discharge detection and elimination program?

EPA's regulations state that the program must incorporate the following four components:

  1. Develop (if not already completed) a storm sewer system map showing at a minimum the location of all outfalls and the names and locations of all waters of the United States that receive discharges from those outfalls.

    Technically, the map is required for only the urbanized areas of small MS4s, but municipalities may find it beneficial to map the entire town or city. Also, many municipalities that have already created storm sewer system maps have included other details such the drainage lines (as ditches above ground or the underground system), locations of catch basins and manholes, and the flow direction.

  2. To the extent allowable under state or local law, effectively prohibit illicit discharges through an ordinance or other regulatory mechanism.
  3. Develop and implement a plan to detect and address illicit discharges (including illegal dumping).

    EPA recommends that the plan include the following four components:

    • procedures for locating priority areas likely to have illicit discharges
    • procedures for tracing the source of an illicit discharge
    • procedures for removing the source of the discharge
    • procedures for program evaluation and assessment

    EPA recommends visually screening outfalls during dry weather and conducting field tests of selected pollutants as part of the procedures for locating priority areas.

  4. Inform public employees, businesses, and the general public of the hazards associated with illegal discharges and improper disposal of waste.

    Illicit discharge education BMPs may include storm drain stenciling; a program to promote, publicize, and facilitate public reporting of illicit connections or discharges; and distribution of outreach materials.

More Information on General Best Management Practices

New Hampshire

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