oEPA
Stormwater Phase II Final Rule
September 2018
Illicit Discharge Detection and Elimination
Minimum Control Measure
Photo by U.S. EPA
This fact sheet profiles the Illicit Discharge Detection and Elimination
minimum control measure, one of six measures the operator of a
Phase II regulated small municipal separate storm sewer system (MS4)
is required to include in its stormwater management program to meet
the conditions of its National Pollutant Discharge Elimination System
(NPDES) permit. This fact sheet outlines the Phase II Final Rule
requirements modified December 9, 2016 and effective on January 9,
2017. It offers some general guidance on how to satisfy them. It is
important to keep in mind that the small MS4 operator typically has a
great deal of flexibility in choosing exactly how to satisfy the minimum
control measure requirements in its NPDES permit.
United States
Environmental Protection Agency
Office of Water
(4203)
Factsheet 2.5

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Illicit Discharge Detection and Elimination Minimum Control Measure
What Is an "Illicit Discharge"?
Federal regulations define an illicit discharge as "...any
discharge to an MS4 that is not composed entirely of
stormwater..." 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-
stormwater wastes.
Why Are Illicit Discharge Detection and
Elimination Efforts Necessary?
Discharges from MS4s often include wastes and
wastewater from non-stormwater 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.
What Is Required?
Recognizing the adverse effects illicit discharges can have on receiving waters, the Phase II
Final Rule requires an operator of a regulated small MS4 to develop, implement and
enforce an illicit discharge detection and elimination program. This program must include the
following:
¦	A storm sewer system map, showing the location of all outfalls and the names and
location of all waters of the United States that receive discharges from those outfalls.
¦	Through an ordinance, or other regulatory mechanism, a prohibition (to the extent
allowable under State, Tribal, or local law) on non-stormwater discharges into the MS4,
and appropriate enforcement procedures and actions.
¦	A plan to detect and address non-stormwater discharges, including illegal dumping, into
the MS4.
Table 1. Pollutants
Associated with Illicit
Discharges
TSS (Total Suspended Solids)
VSS (Volatile Suspended Solids)
TOC (Total Organic Carbon)
COD (Chemical Oxygen Demand)
NO3/NO2 (Nitrate + Nitrite)
TKN (Total Kjeldahl Nitrogen)
Phosphorus as P04
Cu (Total Copper)
Pb (Total Lead)
Zn (Total Zinc)
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Illicit Discharge Detection and Elimination Minimum Control Measure
The education of public employees, businesses, and the general public about the
hazards associated with illegal discharges and improper disposal of waste.
The determination of appropriate best management practices (BMPs) to meet permit
requirements for this minimum control measure. Some program implementation
approaches, BMPs (i.e., the program actions/activities), and measurable goals are
suggested below.
Does This Measure Need to Address All Illicit Discharges?
No. The illicit discharge detection and elimination program does not need to address the
following categories of non-stormwater discharges or flows unless the 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.
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 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 needed 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. An existing map, such as a topographical map, on which the
location of major pipes and outfalls can be clearly presented demonstrates such awareness.
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Illicit Discharge Detection and Elimination Minimum Control Measure
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. More than one
trip may be needed to locate all outfalls.
Legal Prohibition and Enforcement
EPA recognizes that some permittees may have limited authority under State, Tribal or local law
to establish and enforce an ordinance or other regulatory mechanism prohibiting illicit
discharges. In such a case, the permittee is encouraged to obtain the necessary authority, if
possible.
The Plan
The plan to detect and address illicit discharges is the central component of this minimum
control measure. The plan is dependent upon several factors, including the permittee's
available resources, size of staff, and degree and character of its illicit discharges and NPDES
permit requirements. 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). Methods that
can locate problem areas include: visual screening; water sampling from manholes and outfalls
during dry weather; the use of infrared and thermal photography, cross-training field staff to
detect illicit discharges, and public complaints.
Find the Source
Once a problem area or discharge is found, additional efforts usually are necessary to
determine the source of the problem. Methods that can 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 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.
Document Actions Taken
As a final step, all actions taken under the plan should be documented. This illustrates that
progress is being made to eliminate illicit connections and discharges. Documented actions
should be included in annual reports and include information such as: the number of outfalls
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Illicit Discharge Detection and Elimination Minimum Control Measure
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
The Center for Watershed Protection and Robert Pitt (2004) researched the most cost-effective
and efficient techniques that can be employed to identify and correct inappropriate discharges.
Data from Montgomery County, Maryland, was analyzed and it was determined that staff
identify and correct about six inappropriate discharges per year as a result of regular screening.
By contrast, over 185 inappropriate discharges are corrected each year in Montgomery County
as a direct result of citizen complaints and calls to a storm water compliant hotline. Public
education and labeling of outfalls and other storm drain infrastructure is an important element
of establishing a successful citizen hotline. Outreach to public employees, businesses, property
owners, the general public, and elected officials regarding ways to detect and eliminate illicit
discharges is an integral part of this minimum measure.
Suggested educational outreach efforts include:
¦	Developing informative brochures and guidance 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.
¦	Initiating recycling programs for commonly dumped wastes, such as motor oil,
antifreeze, and pesticides.
What Are Appropriate Measurable Goals?
The MS4 permit will specify any actions and deadlines that permittees must meet for permit
compliance. The permit may also require permittees to develop measurable goals that
guide implementation of your chosen actions to meet permit requirements and to determine
program effectiveness. The measurable goals, as well as the BMPs, should reflect the needs and
characteristics of the operator and the area served by its small MS4. Furthermore, they should
be chosen using an integrated approach that fully addresses the requirements and intent of the
minimum control measure.
EPA has developed a Measurable Goals Guidance for Phase II MS4s that is designed to help
program managers comply with any requirement to develop measurable goals. The guidance
presents an approach for MS4 operators to develop measurable goals as part of their
stormwater management plan. For example, an MS4 could establish a measurable goal of
responding to all complaints received by the citizen complaint hotline within 24 hours to
minimize water quality impacts or recurrent dumping. A complaint tracking system could be
used to log response and enforcement activity.
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Illicit Discharge Detection and Elimination Minimum Control Measure
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).
For Additional Information
Contacts
A list of names and telephone numbers
for the U.S. EPA's Office of Wastewater
Management (Headquarters), each EPA
Regional Office, and State Offices is
located at www.epa.gov/npdes/npdes-
stormwater-program (click on "Contact
Us" and then "Stormwater").
Your NPDES Permitting Authority
Most States and Territories are authorized to administer the
NPDES Program, except the following, for which EPA is the
permitting authority:
Guam
District of Columbia
Johnston Atoll
Idaho (until 7/1/2021,
which is the date when
Idaho becomes
authorized to
implement the
Stormwater NPDES
program)
Midway and Wake Islands
Massachusetts
Northern Mariana Islands
New Hampshire
Puerto Rico
New Mexico
Trust Territories
American Samoa
Reference Documents
EPA's Stormwater Web Site
o Phase II Final Rule Fact Sheet Series
o Stormwater Phase II Final Rule (64 FR 68722)
o National Menu of Best Management Practicesfor Stormwater Phase
o Measurable Goals Guidance for Phase II Small MS4s
Illicit Discharge Detection and Elimination: A Guidance Manual for Program Development
and Technical Assessments
Center for Watershed Protection and R. Pitt. (2004). Illicit Discharge Detection and Elimination: A
Guidance Manual for Program Development and Technical Assessments.
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.
Disclaimer: This information is guidance only and does not establish or affect legal rights or obligations. Agency
decisions in any particular case will be made by applying the law and regulations to the specific facts of the case.
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