This image shows a labeled stormdrain
Labeled stormdrain

Illicit discharges are those wastes and wastewaters from non-stormwater sources which cannot legally be discharged down storm drains to a Municipal Separate Storm Sewer System (MS4). Sources include:

  • Sanitary wastewater illegally connected to the storm drain system
  • Residential laundry washwaters
  • Effluent from septic tanks
  • Industrial wastewaters
  • Auto and household toxics such as used motor oil
  • Liquid fertilizers and pesticides
  • Pet waste
  • Drained pool water
  • Spills from roadways
  • Paint waste
  • Anything that isn’t rain down the storm drain is a potential illicit discharge.

The result of illicit discharges entering the storm drain is untreated discharges to receiving water, contributing high levels of pollutants including heavy metals, toxics, oil and grease, solvents, nutrients, viruses, and bacteria. Pollutant levels from these illicit discharges have been shown in EPA studies to be high enough to significantly degrade receiving water quality and threaten aquatic, wildlife and human health.

This fact sheet provides guidance on identification of potential illicit stormwater discharges and techniques to reduce the risk of illicit discharges.

Benefits and pollution reduction

Reduction of illicit discharges results in minimization of the discharge of pollutants down storm drains or water conduits and, ultimately to downstream lakes, streams and wetlands. Reducing discharge of pollutants improves water clarity, coloration and odor, as well as fish and wildlife habitat.

Program development and implementation

Programs designed to identify illicit discharges and reduce the risk of such discharges are dependant upon several factors including the MS4’s available resources, size of staff, and degree and character of its illicit discharges. Ultimately, effective source control is dependent upon applying a mixture of education, incentives and regulation.

The Center for Watershed Protection identifies some strategies for education and incentives: passive education, active training, provision of direct MS4 services, subsidies and discounts, home/business-owner recognition programs, stewardship group formation. Regulations might include: adoption of a local ordinance, notifications/signs /hotlines, restrictions or bans, enforcement, utility pricing. An effective program applies some combination of the above strategies, many of which are discussed below. For greater detail, see the Additional Resources section.

Awareness campaigns

Awareness campaigns inform public employees, businesses, property owners, and elected officials of the ways to detect and eliminate illicit discharges and the hazards associated with illegal discharges and improper disposal of waste. Illicit discharge education actions may include programs to promote, publicize and facilitate public reporting of illicit connections or discharges, distribution of outreach materials and storm drain stenciling. Suggested educational methods include:

  • Brochures - Develop informative brochures, guidance for specific audiences (i.e. carpet cleaning businesses that might dump their wastewater into a convenient manhole) and school curricula. Tips might include:
    • Direct wash water onto your lawn to soak up soap when washing your car or truck
    • Fertilize established lawns with phosphorous-free fertilizer and don’t overspray fertilizer into the street
    • Rake leaves and sweep grass clippings away from curbs. Clean curbs mean clean water.
    • Dispose of all spent auto fluids properly; recycle where programs exist
  • Public watch campaign - Design a program to publicize and facilitate public reporting of illicit discharges. Establish a 24-hour call-in line for pollution complaints.
  • Volunteer storm drain inspections and stenciling - Coordinate volunteers for locating and visually inspecting outfalls or to stencil storm drains (see the Storm Drain Stenciling fact sheet).

Detect and address illicit discharges

A program to detect and address illicit discharges is central to the ultimate elimination of illicit discharges. EPA recommends that the program include the following four components:

  • Locate problem areas - Some methods that can be used to locate problem areas include: public complaints, visual screening, routine or targeted water sampling from manholes and outfalls during dry weather, and use of infrared and thermal photography. EPA recommends visually screening outfalls during dry weather and conducting field tests of selected pollutants (such as total solids, chlorine, nutrients, metals) as part of the procedures for locating priority areas. The Center for Watershed Protection and the University of Alabama recommend conducting an Outfall Reconnaissance Inventory (ORI). An ORI is a field screening technique that entails a stream walk to inventory and measure storm drain outfalls to identify continuous and intermittent discharges without in-depth laboratory analysis. The Center for Watershed Protection’s Urban Subwatershed Restoration Manual No. 8 identifies three additional field methods to identify individual pollution source areas:
    • the Neighborhood Source Assessment (NSA)
    • the Hotspot Site Investigation (HSI) and
    • the Discharge Prevention Investigation (DPI).
Hotspot facilities produce higher levels of stormwater pollutants and/or present a higher potential risk for spills, leaks or illicit discharges. Common hotspot facilities are those that handle solid waste, wastewater, road and vehicle maintenance, and yard waste.
  • Find the source Once a problem area or discharge is found, additional efforts should be made to determine the source of the problem. Some methods include dye-testing buildings in problem areas; dye or smoke testing buildings at the time of sale; tracing the discharge upstream in the storm sewer; employing a certification program that shows that buildings have been checked for illicit connections; implementing an inspection program of existing septic systems; and using video to inspect the storm sewers.
  • Remove/correct illicit connections - Once the source is identified, the offending discharger should be notified and directed to correct the problem. Education efforts and working with the discharger can be effective in resolving the problem before taking legal action (see Awareness Campaigns above).
  • Document actions taken - Documenting actions illustrates that progress is being made to eliminate illicit connections and discharges. Actions should be documented in the MS4 annual report and should include the following: number of outfalls screened, any complaints received and corrected, the number of discharges and quantities of flow eliminated, and the number of dye or smoke tests conducted.

Recycling program

Initiate recycling programs for commonly dumped wastes, such as motor oil, antifreeze and pesticides. Provide sufficient public notification of any newly established programs or increase public awareness of existing programs. For more detailed information on ways to keep yard debris out of the street, see the Residential Waste Collection & Clean-up Programs fact sheet.

Maintenance considerations

Recycling collection services may be provided in a recycling program (see Recycling Program above), but are not necessary if the public is properly notified of recycling drop-off locations and materials accepted. For maintenance associated with storm drain stenciling, see the Storm Drain Stenciling fact sheet.

Typical cost

The cost of detecting and reducing the risk of illicit discharges will vary depending on the intensity of the effort and the approach(es) chosen. Costs attributable to detection and correction of illicit discharges are based on the total staff involvement driven by the problem area identification methods employed and the number and extent of discharge incidences. Public education program costs are determined by the type of materials produced and the method of distribution selected. Volunteer efforts can reduce program costs, as determined by staff hours required for program implementation and leadership of volunteers. An important consideration is that prevention of illicit discharges is much less costly than detection and subsequent correction.

This page was last edited on 29 September 2021, at 12:38.


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