United States Office of Water EPA 833-F-99-007

Environmental Protection (4203) April 1999

Agency Fact Sheet 2.5

Storm Water Phase II

Proposed Rule

Illicit Discharge Detection and 

Elimination Minimum Control Measure

This fact sheet is based on the Storm Water Phase II Proposed Rule. Therefore, the information provided herein is subject to

change upon publication of the final Phase II rule in November 1999. A revised series of fact sheets will be provided at that

time. A comprehensive list of the current fact sheets is in the text box at left.

This fact sheet profiles the proposed Illicit Discharge Detection and Elimination minimum control

measure, one of six measures the owner or operator of a Phase II regulated small municipal separate

storm sewer system (MS4) would be required to include its storm water management program to meet

the conditions of its National Pollutant Discharge Elimination System (NPDES) permit. This fact

sheet outlines the Phase II Proposed Rule requirements and offers some general guidance on how to

satisfy them. It is important to keep in mind that the small MS4 owner or operator would have a great

deal of flexibility in choosing exactly how to satisfy the minimum control measure requirements.

What Is An “Illicit Discharge”?

Federal regulations define an illicit discharge as “...any discharge to an MS4 that is not composed

entirely of storm water...” with some exceptions. These exceptions include discharges from

NPDES-permitted industrial sources and discharges from fire-fighting activities. Illicit discharges

(see Table 1) are considered “illicit” because MS4s are not designed to accept, process, or discharge

such non-storm water wastes.

Why Are Illicit Discharge Detection and

Elimination Efforts Necessary?

Discharges from MS4s often include wastes and

wastewater from non-storm water sources. A study

conducted in 1987 in Sacramento, California, found that

almost one-half of the water discharged from a local MS4

was not directly attributable to precipitation runoff. A

significant portion of these dry weather flows were from

illicit and/or inappropriate discharges and connections to

the MS4.

Illicit discharges enter the system through either direct

connections (e.g., wastewater piping either mistakenly or

deliberately connected to the storm drains) or indirect

connections (e.g., infiltration into the MS4 from cracked

sanitary systems, spills collected by drain outlets, or paint

or used oil dumped directly into a drain). The result is

untreated discharges that contribute high levels of

pollutants, including heavy metals, toxics, oil and grease, solvents, nutrients, viruses, and bacteria to

receiving waterbodies. 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.

Storm Water Phase II

Proposed Rule 

Fact Sheet Series

Overview

1.0 – Storm Water Phase II

Proposed Rule Overview

Small MS4 Program

2.0 – Small MS4 Storm Water

Program Overview

2.1 – Who’s Covered? Designation

and Waivers of Regulated Small

MS4s

2.2 – Urbanized Areas: Definition

and Description

Minimum Control Measures

2.3 – Public Education and

Outreach Minimum Control

Measure

2.4 – Public Participation/

Involvement Minimum Control

Measure

2.5 – Illicit Discharge Detection and

Elimination Minimum Control

Measure

2.6 – Construction Site Runoff

Control Minimum Control Measure

2.7 – Post-Construction Runoff

Control Minimum Control Measure

2.8 – Pollution Prevention/Good

Housekeeping Minimum Control

Measure

2.9 – Permitting and Reporting:

The Process and Requirements

2.10 – Federal and State-Owned

MS4s: Program Implementation

Construction Program

3.0 – Construction Program

Overview

Industrial “No Exposure”

4.0 – Conditional No Exposure

Exemption for Industrial Activity

Sources of

Illicit Discharges

Sanitary wastewater

Effluent from septic tanks

Car wash wastewaters

Improper oil disposal

Radiator flushing disposal

Sump pump discharges

Laundry wastewaters

Spills from roadway accidents

Improper disposal of auto and

household toxics

Table 1
Fact Sheet 2.5 – Illicit Discharge Detection and Elimination Minimum Control Measure Page 2

What Is EPA Proposing?

Recognizing the adverse effects illicit discharges can have on

receiving waters, the proposed rule would require an owner

or operator of a regulated small MS4 to develop and implement

an illicit discharge detection and elimination program. This

program would need to include the following:

 A storm sewer system map showing the location of

major pipes, outfalls, and topography. In addition, if

such data exist, the map needs to show the areas of

concentrated activities that are likely to be sources of

pollution;

 Through an ordinance, order, or similar means, a

prohibition (to the extent allowable under State,

Tribal, or local law) on illicit discharges into the MS4,

and appropriate enforcement procedures and actions;

 A plan to detect and address illicit discharges,

including illegal dumping, into the MS4;

 The education of public employees, businesses, and

the general public about the hazards associated with

illegal discharges and improper disposal of waste; and

 The determination of appropriate best management

practices (BMPs) and measurable goals for this

minimum control measure. Some program

implementation approaches, BMPs (i.e., the program

actions/activities), and measurable goals are suggested

below. 

Would This Measure Need to Address All Illicit

Discharges?

No. The illicit discharge detection and elimination program

would not need to address the following categories of nonstorm water discharges or flows unless the owner or operator of

the regulated small MS4 identifies them as significant

contributors of pollutants to its MS4:

• Water line flushing;

• Landscape irrigation;

• Diverted stream flows;

• Rising ground waters;

• Uncontaminated ground water infiltration;

• Uncontaminated pumped ground water;

• 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; and

• Street wash water.

What Are Some Guidelines for Developing and

Implementing This Measure?

The objective of the illicit discharge detection and elimination

minimum control measure is to have regulated small MS4

owners and operators gain a thorough awareness of their systems. 

This awareness allows them to determine the types and sources of

illicit discharges entering their system, and establish the legal,

technical, and educational means to attempt to eliminate these

discharges. Permittees could meet these objectives in a variety of

ways depending on their individual needs and abilities, but some

general guidance for each requirement is provided below.

The Map

The storm sewer system map is meant to demonstrate a basic

awareness of the intake and discharge areas of the system. It is

needed to help determine the extent of discharged dry weather

flows, the possible sources of the dry weather flows, and the

particular waterbodies these flows may be affecting. Since the

location of the major pipes and outfalls could be indicated on an

existing topographical map, a new map would not need to be

created specifically for this purpose as long as the information is

clearly presented on the existing map. The permittee would be

allowed to choose the type and size of map that best fits its needs.

EPA recommends collecting all existing information on outfall

locations (e.g., review city records, drainage maps, storm drain

maps), and then conducting field surveys to verify locations. It

probably will be necessary to walk (i.e., wade through small

receiving waters or use a boat for larger waters) the streambanks

and shorelines for visual observation. It may take more than one

trip to locate all outfalls.

Legal Prohibition and Enforcement

EPA recognizes that some permittees may have limited authority

under State or Tribal law to establish and enforce an ordinance, or

similar means, prohibiting illicit discharges. In such a case, the

permittee would be encouraged to obtain the necessary authority,

if at all possible. Otherwise, the NPDES permitting authority

would assume the responsibility for implementation of this

component of the minimum measure, yet the permittee would

remain ultimately responsible for the quality of its MS4

discharge. Model ordinances, including examples of amendments

to local codes or existing ordinances, will be provided in the

Phase II storm water guidance for regulated small MS4s, which is

part of EPA’s planned implementation “tool box” for the final

rule (see Fact Sheet 1.0).
Fact Sheet 2.5 – Illicit Discharge Detection and Elimination Minimum Control Measure Page 3

The Plan

The plan to detect and address illicit discharges is the central

component of this minimum control measure. The plan would be

shaped by several factors, including the permittee’s available

resources, size of staff, and degree and character of its illicit

discharges. EPA envisions a plan similar to the one

recommended for use in meeting Michigan’s general storm water

NPDES permit for small MS4s. As guidance only, the four steps

of a recommended plan are outlined below:

 Locate Problem Areas

EPA recommends that priority areas be identified for detailed

screening of the system based on the likelihood of illicit

connections (e.g., areas with older sanitary sewer lines). 

Some methods that could be used to locate problem areas

include: public complaints and other input; visual screening;

water sampling from manholes and outfalls during dry

weather; and use of infrared and thermal photography.

Find the Source

Once a problem area or discharge is found, additional efforts

usually would be necessary to determine the source of the

problem. Some methods that could be used to find the source

of the illicit discharge 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 would

need to 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.

 Document Actions Taken

As a final step, all actions taken under the plan should be

documented. Doing so would illustrate that progress is being

made to eliminate illicit connections and discharges. 

Documented actions should be included in the required

annual reports and include information such as: the 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.

Educational Outreach

Educational outreach to public employees, businesses, property

owners, the general community, and elected officials would be

necessary to inform them of what they could do to detect and

eliminate illicit discharges, but it would also help to gain support

for the permittee’s storm water program. The educational

outreach efforts should, at a minimum, include:

• Providing training programs for public employees;

• Developing informative brochures, and guidances for

specific audiences (e.g., carpet cleaning businesses) and

school curricula;

• Designing a program to publicize and facilitate public

reporting of illicit discharges; 

• Coordinating volunteers for locating, and visually

inspecting, outfalls or to stencil storm drains; and

• Initiating recycling programs for commonly dumped

wastes, such as motor oil, antifreeze, and pesticides.

What Would Be Appropriate Measurable Goals?

Measurable goals, which would be required for each minimum

control measure, are meant to help gauge permit compliance

and program effectiveness. The measurable goals, as well as the

BMPs, would greatly depend on the needs and characteristics of

the owner/operator and the area served by its small MS4. The

measurable goals should be chosen using an integrated approach

that would fully address the requirements and intent of the

minimum control measure. An integrated approach for this

minimum measure could include the following measurable goals:

Target Date Activity

1 year............ Sewer system map completed; recycling

program for household hazardous waste in

place.

2 years.......... Ordinance in place; training for public

employees completed; a certain percentage of

sources of illicit discharges determined.

3 years.......... A certain percentage of: illicit discharges

determined; illicit discharges eliminated; and

households participating in quarterly household

hazardous waste special collection days.

4 years.......... Most illicit discharge sources determined and

eliminated.

The educational outreach measurable goals for this minimum

control measure could be combined with the measurable goals for

the Public Education and Outreach minimum control measure (see

Fact Sheet 2.3).
Fact Sheet 2.5 – Illicit Discharge Detection and Elimination Minimum Control Measure Page 4

For Additional Information

Contact

 U.S. EPA Office of Wastewater Management

• Phone : 202 260-5816

• E-mail: SW2@epa.gov

• Internet: www.epa.gov/owm/sw2.htm

Reference Documents

 Storm Water Phase II Proposed Rule Fact Sheet Series.

• Contact the U.S. EPA Water Resource Center at

202 260-7786 or at waterpubs@epa.gov 

• Internet: www.epa.gov/owm/sw2.htm

 Storm Water Phase II Proposed Rule, published on Jan.

9, 1998 in the Federal Register (63 FR 1536).

• Internet: www.epa.gov/owm/sw2.htm

Sources

Maryland Department of the Environment, Water

Management Administration. 1997. Dry Weather Flow

and Illicit Discharges in Maryland Storm Drain Systems.

Baltimore, Maryland.

U.S. EPA Office of Water. 1993. Investigation of

Inappropriate Pollutant Entries into Storm Drainage

Systems: A User’s Guide. EPA/600/R-92/238.

Washington, D.C.

Wayne County Rouge River National Wet Weather

Demonstration Project. 1997. Guidance for Preparing a

Program for the Elimination of Illicit Discharges.

Wayne County, Michigan.