Potential Discharge Identification & Risk Reduction

Potential illicit discharge identification and risk reduction techniques

Illicit discharges are those wastes and wastewaters from non-stormwater sources which MS4s cannot legally discharge down storm drains. 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 (see Additional Resources) 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 / 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 & 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).

This image shows a labeled stormdrain
Labeled stormdrain

Detect and Address Illicit Discharges

A program to detect and address illicit discharges is central to the ultimate elimination of illicit discharges. EPA recommends (see Additional Resources) 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) (see Additional Resources).

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 (see Additional Resources) 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

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