United States Office of Water EPA 833-F-99-002

Environmental Protection (4203) April 1999

Agency Fact Sheet 2.0

Storm Water Phase II

Proposed Rule

Small MS4Storm Water Program Overview

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.

Polluted storm water runoff is often transported to municipal separate storm sewer systems (MS4s)

and ultimately discharged into local rivers and streams without treatment. EPA’s Storm Water

Phase II Proposed Rule would establish an MS4 storm water management program that is intended to

improve the Nation’s waterways by reducing the quantity of pollutants that storm water picks up and

carries into storm sewer systems during storm events. Common pollutants include oil and grease from

roadways, pesticides from lawns, sediment from construction sites, and carelessly discarded trash,

such as cigarette butts, paper wrappers, and plastic bottles. When deposited into nearby waterways

through MS4 discharges, these pollutants can impair the waterways, thereby discouraging

recreational use of the resource, contaminating drinking water supplies, and interfering with the

habitat for fish, other aquatic organisms, and wildlife.

In 1990, EPA promulgated rules establishing Phase I of the National Pollutant Discharge Elimination

System (NPDES) storm water program. The Phase I program for MS4s requires owners or operators

of “medium” and “large” MS4s, that is, those that typically serve populations of 100,000 people or

more, to implement a storm water management program as a means to control polluted discharges

from these MS4s. The Storm Water Phase II Proposed Rule would extend coverage of the NPDES

storm water program to certain “small” MS4s but takes a slightly different approach to how the storm

water management program would be developed and implemented.

What Is A Phase II Small MS4?

Asmall MS4 is any MS4 not already covered by the Phase I program as a medium or large MS4. 

The Phase II Proposed Rule would automatically cover on a nationwide basis all small MS4s

located in “urbanized areas” (UAs) as defined by the Bureau of the Census, and on a case-by-case

basis those small MS4s located outside of UAs that are designated by the NPDES permitting authority. 

For more information on Phase II small MS4 coverage, see Fact Sheets 2.1 and 2.2.

What Would Be the Phase II Small MS4 Program Requirements?

Owners or operators of regulated small MS4s would be required to design their programs to:

 Reduce the discharge of pollutants to the “maximum extent practicable” (MEP); and

 Protect water quality.

The successful implementation of approved best management practices (BMPs) is considered

compliance with the technical standard of MEP. The Phase II Proposed Rule would consider

narrative effluent limitations that require the implementation of BMPs and the achievement of

measurable goals as the most appropriate form of effluent limitations to achieve the protection of

water quality, rather than requiring storm water discharges to meet numeric effluent limitations.

The Phase II Proposed Rule outlines a small MS4 storm water management program comprising six

required program elements that, when implemented in concert, are expected to result in significant 

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
Fact Sheet 2.0 – An Overview of the Small MS4 Storm Water Program Page 2

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

reductions of pollutants discharged into receiving waterbodies. 

The proposed six program elements, termed “minimum control

measures,” are outlined below. For more information on each of

these required control measures, see Fact Sheets 2.3 through 2.8.

 Public Education and Outreach

Distributing educational materials and performing outreach

to inform citizens about the impacts polluted storm water

runoff discharges can have on water quality.

Public Participation/Involvement

Providing opportunities for citizens to participate in program

development and implementation, including effectively

publicizing public hearings and/or encouraging citizen

representatives on a storm water management panel.

 Illicit Discharge Detection and Elimination

Developing and implementing a plan to detect and eliminate

illicit discharges to the storm sewer system (includes

developing a system map and informing the community

about hazards associated with illegal discharges and

improper disposal of waste).

 Construction Site Runoff Control

Developing, implementing, and enforcing an erosion and

sediment control program for construction activities that

disturb 1 or more acres of land (controls could include silt

fences and temporary storm water detention ponds).

 Post-Construction Runoff Control

Developing, implementing, and enforcing a program to

address discharges of post-construction storm water runoff

from new development and redevelopment areas. 

Applicable controls could include preventative actions such

as protecting sensitive areas (e.g., wetlands) or the use of

structural BMPs such as grassed swales or porous pavement.

 Pollution Prevention/Good Housekeeping

Developing and implementing a program with the goal of

preventing or reducing pollutant runoff from municipal

operations. The program must include municipal staff

training on pollution prevention measures and techniques

(e.g., regular street sweeping, reduction in the use of

pesticides or street salt, or frequent catch-basin cleaning).

What Information Would Be Included in the

NPDES Permit Application?

Rather than individual permits, which were required for the

Phase I MS4s, the proposed Phase II program for MS4s is

designed to accommodate a general permit approach using a

Notice of Intent (NOI) as the permit application. The owner/

operator of a regulated small MS4 would need to include in its

permit application, or NOI, its chosen BMPs and measurable

goals for each minimum control measure. To help permittees

identify the most appropriate BMPs for their programs, the

proposed rule would require the NPDES permitting authority to

issue a list, or “menu,” of BMPs to serve as guidance. For more

information on application requirements, see Fact Sheet 2.9.

Would There Be Implementation Options?

Yes. The proposed rule would allow for a number of

implementation options to be chosen by the regulated small

MS4 owners or operators responsible for developing Phase II

municipal storm water programs. Such options would include

sharing responsibility for program development with a nearby

regulated small MS4, taking advantage of existing local or State

programs, or participating in the implementation of an existing

Phase I MS4’s storm water program as a co-permittee. These

options are intended to promote a regional approach to storm

water management coordinated on a watershed basis.

What Kind of Program Evaluation/Assessment

Would Be Required?

Permittees would need to evaluate the effectiveness of their

chosen BMPs in terms of reducing the discharge of pollutants

from their systems to the “maximum extent practicable” and in

terms of protecting water quality. Permittees also would be

required to assess their progress in achieving the program’s

measurable goals. The evaluation would not be based on

monitoring data, since permittees are expected to meet only

narrative, rather than numeric, effluent limitations. Monitoring

is not required under the proposal but the NPDES permitting

authority would have the discretion to require monitoring if

deemed necessary. If there is an indication of a need for

improved controls, permittees could revise their mix of BMPs to

provide for a more effective program. For more information on

program evaluation/assessment requirements, see Fact Sheet 2.9.