United States Office of Water EPA 833-F-99-009

Environmental Protection (4203) April 1999

Agency Fact Sheet 2.7

Storm Water Phase II

Proposed Rule

Post-Construction Runoff Control

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 Post-Construction Runoff Control minimum control measure,

one of six measures that the owner or operator of a Phase II regulated small municipal separate storm

sewer system (MS4) would be required to include in its storm water management program in order 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.

Why Is The Control of Post-Construction Runoff Necessary?

Post-construction storm water management in areas undergoing new development or redevelopment

is necessary because runoff from these areas has been shown to significantly effect receiving

waterbodies. The Nationwide Urban Runoff Program study (Final Report of the Nationwide Urban

Runoff Program. U.S. EPA, Office of Water, 1983), and more recent studies indicate that prior

planning and design for the minimization of pollutants in post-construction storm water discharges is

the most cost-effective approach to storm water quality management.

There are generally two forms of substantial impacts of post-construction runoff. The first is caused

by an increase in the type and quantity of pollutants in storm water runoff. As runoff flows over areas

altered by development, it picks up harmful sediment and chemicals such as oil and grease, pesticides,

heavy metals, and nutrients (e.g., nitrogen and phosphorus). These pollutants often become

suspended in runoff and are carried to receiving waters, such as lakes, ponds, and streams. Once

deposited, these pollutants can enter the food chain through small aquatic life, eventually entering the

tissues of fish and humans. The second kind of post-construction runoff impact occurs by increasing

the quantity of water delivered to the waterbody during storms. Increased impervious surfaces

interrupt the natural cycle of gradual percolation of water through vegetation and soil. Instead, water

is collected from surfaces such as asphalt and concrete and routed to drainage systems where large

volumes of runoff quickly flow to the nearest receiving water. The effects of this process include

streambank scouring and downstream flooding, which often lead to a loss of aquatic life and damage

to property.

What Is EPA Proposing?

The Phase II Proposed Rule would require an owner or operator of a regulated small MS4 to

develop, implement, and enforce a program to reduce pollutants in post-construction runoff to

their MS4 from new development and redevelopment projects that result in the land disturbance of

greater than or equal to 1 acre. The small MS4 owner or operator would be required to:

 Have a plan to implement structural and/or non-structural best management practices (BMPs)

and ensure adequate long-term operation and maintenance of such BMPs;

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 2.7 – Post-Construction Runoff Control Minimum Control Measure Page 2

 Ensure that controls are in place that would prevent or

minimize water quality impacts; and

 Determine the appropriate best management practices

(BMPs) and measurable goals for this minimum control

measure.

What Would Be Considered a “Redevelopment”

Project?

The term “redevelopment” is intended to refer to alterations of

a property that change the “footprint” of a site or building in

such a way that the disturbance of equal to or greater than 1 acre

of land results. The term is not intended to include such activities

as exterior remodeling. To account for the various types of

redevelopment projects, the proposed rule contains enough

flexibility to allow post-construction controls for redevelopment

to be different than those for new development.

What Are Some Guidelines for Developing and

Implementing This Measure?

This section includes some sample non-structural and structural

BMPs that could be used to satisfy the requirements of the

post-construction runoff control minimum measure. Because the

proposed requirements of this measure are closely tied to the

requirements of the construction site runoff control minimum

measure (see Fact Sheet 2.6), EPA recommends that small MS4

owners or operators develop and implement these two measures

in tandem. Sample BMPs follow. 

 Non-Structural BMPs

• Planning and Procedures. Runoff problems can be

addressed efficiently with sound planning procedures. 

Master Plans, Comprehensive Plans, and zoning ordinances

can promote improved water quality by guiding the growth of

a community away from sensitive areas and by restricting

certain types of growth (industrial, for example) to areas that

can support it without compromising water quality.

• Site-Based Local Controls. These controls can include

buffer strip and riparian zone preservation, minimization of

disturbance and imperviousness, and maximization of open

space.

 Structural BMPs 

• Storage Practices. Storage or detention BMPs control storm

water by gathering runoff in wet ponds, dry basins, or

multichamber catch basins and slowly releasing it to

receiving waters or drainage systems. These practices both

control storm water volume and settle out particulates for

pollutant removal.

• Infiltration Practices. Infiltration BMPs are designed to

facilitate the infiltration of runoff through the soil to ground

water, and, thereby, result in reduced storm water quantity

and reduced mobilization of pollutants. Examples include

infiltration basins/trenches, dry wells, and porous pavement.

• Vegetative Practices. Vegetative BMPs are landscaping

features that, with optimal design and good soil conditions,

enhance pollutant removal, maintain/improve natural site

hydrology, promote healthier habitats, and increase aesthetic

appeal. Examples include grassy swales, filter strips,

artificial wetlands, and rain gardens.

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 goals:

Target Date Activity

1 year............ Strategies developed that include structural

and/or non-structural BMPs.

2 years.......... Strategies codified by use of ordinance or other

regulatory mechanism.

3 years.......... Reduced percent of new impervious surfaces

associated with new development projects.

4 years.......... Improved clarity and reduced sedimentation of

local waterbodies.

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