v>EPA
United States
Environmental Protection
Agency
Office of Water EPA 833-F-00-009
(4203) January 2000 (revised December 2005)
Fact Sheet 2.7
Storm water Phase II
Final Rule
Stormwater Phase II
Final Rule
Fact Sheet Series
Overview
1.0 - Stormwater Phase II Final
Rule: An Overview
Small MS4 Program
2.0 - Small MS4 Stormwater
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
2.4-Public Participation/
Involvement
2.5 - Illicit Discharge Detection
and Elimination
2.6 - Construction Site Runoff
Control
2.7 - Post-Construction Runoff
Control
2.8 - Pollution Prevention/Good
Housekeeping
2.9 - Permitting and Reporting:
The Process and Requirements
2.10 - Federal and State-Operated
MS4s: Program Implementation
Construction Program
3.0 - Construction Program
Overview
3.1 - Construction Rainfall
Erosivity Waiver
Industrial "No Exposure"
4.0 - Conditional No Exposure
Exclusion for Industrial Activity
Post-Construction Runoff Control
Minimum Control Measure
This fact sheet profiles the Post-Construction Runoff Control minimum control measure, one
of six measures that the operator of a Phase II regulated small municipal separate storm
sewer system (MS4) is required to include in its Stormwater management program in order to
meet the conditions of its National Pollutant Discharge Elimination System (NPDES) permit.
This fact sheet outlines the Phase II Final Rule requirements for post-construction runoff control
and offers some general guidance on how to satisfy those requirements. It is important to keep
in mind that the small MS4 operator has 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 Stormwater management in areas undergoing new development or
redevelopment is necessary because runoff from these areas has been shown to significantly
affect receiving waterbodies. Many studies indicate that prior planning and design for the
minimization of pollutants in post-construction Stormwater discharges is the most cost-effective
approach to Stormwater 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 Stormwater 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 offish 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 (e.g., parking lots, driveways, and rooftops)
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 Required?
The Phase II Final Rule requires an 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 operator is required to:
Q Develop and implement strategies which include a combination of structural and/or non-
structural best management practices (BMPs);
Q Have an ordinance or other regulatory mechanism requiring the implementation of post-
construction runoff controls to the extent allowable under State, Tribal or local law;
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Fact Sheet 2.7 - Post-Construction Runoff Control Minimum Control Measure
Page 2
Q Ensure adequate long-term operation and maintenance
of controls;
Q Determine the appropriate best management practices
and measurable goals for this minimum control measure.
What Is Considered a "Redevelopment" Project?
The Phase II Final Rule applies to "redevelopment" projects
that alter the "footprint" of an existing site or building in
such a way that there is a disturbance of equal to or greater than
1 acre of land. Redevelopment projects do not include such
activities as exterior remodeling. Because redevelopment
projects may have site constraints not found on new
development sites, the Phase II Final Rule provides flexibility
for implementing post-construction controls on redevelopment
sites that consider these constraints.
What Are Some Guidelines for Developing and
Implementing This Measure?
This section includes some non-structural and structural
BMPs that could be used to satisfy the requirements of the
post-construction runoff control minimum measure. It is
important to recognize that many BMPs are climate-specific,
and not all BMPs are appropriate in every geographic area.
Because the 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
operators develop and implement these two measures in
tandem.
Q Non-Structural BMPs
• Planning Procedures. Runoff problems can be
addressed efficiently with sound planning procedures.
Local master plans, comprehensive plans, and zoning
ordinances can promote improved water quality in many
ways, such as guiding the growth of a community away
from sensitive areas to areas that can support it without
compromising water quality.
• Site-Based BMPs. These BMPs can include buffer
strip and riparian zone preservation, minimization of
disturbance and imperviousness, and maximization of
open space.
G Structural BMPs
• Infiltration BMPs. Infiltration BMPs are designed
to facilitate the percolation of runoff through the soil
to ground water, and, thereby, result in reduced
stormwater runoff quantity and reduced mobilization of
pollutants. Examples include infiltration
basins/trenches, dry wells, and porous pavement.
• Vegetative BMPs. Vegetative BMPs are landscaping
features that, with optimal design and good soil
conditions, remove pollutants, and facilitate percolation
of runoff, thereby maintaining natural site hydrology,
promoting healthier habitats, and increasing aesthetic
appeal. Examples include grassy swales, filter strips,
artificial wetlands, and rain gardens.
What Are Appropriate Measurable Goals?
Measurable goals, which are required for each minimum
control measure, are intended to gauge permit compliance
and program effectiveness. The measurable goals, as well
as the BMPs, should reflect needs and characteristics of the
operator and the area served by its small MS4. Furthermore,
the measurable goals 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
the 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 program goal might be to reduce by 30
percent the road surface areas directly connected to storm sewer
systems (using traditional curb and gutter infrastructure) in new
developments and redevelopment areas over the course of the
first permit term. Using "softer" stormwater conveyance
approaches, such as grassy swales, will increase infiltration and
decrease the volume and velocity of runoff leaving
development sites. Progress toward the goal could be measured
by tracking the linear feet of curb and gutter not installed in
development projects that
historically would have been used.
Stormwater Retention/Detention BMPs. Retention or
detention BMPs control stormwater by gathering runoff
in wet ponds, dry basins, or multichamber catch basins
and slowly releasing it to receiving waters or drainage
systems. These practices can be designed to both
control stormwater volume and settle out particulates for
pollutant removal.
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Fact Sheet 2.7 - Post-Construction Runoff Control Minimum Control Measure
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For Additional Information
Contacts
"^ U.S. EPA Office of Wastewater Management
http://www.epa.gov/npdes/stormwater
Phone: 202-564-9545
"^ 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:
Alaska
District of Columbia
Idaho
Massachusetts
New Hampshire
New Mexico
American Samoa
Guam
Johnston Atoll
Midway and Wake Islands
Northern Mariana Islands
Puerto Rico
Trust Territories
"^ A list of names and telephone numbers for each EPA
Region and State is located at http ://www. epa. gov/
npdes/stormwater (click on "Contacts").
Reference Documents
"^ EPA's Stormwater Web Site
http://www.epa.gov/npdes/stormwater
• Stormwater Phase II Final Rule Fact Sheet Series
• Stormwater Phase II Final Rule (64 FR 68722)
• National Menu of Best Management Practices for
Stormwater Phase II
• Measurable Goals Guidance for Phase II Small
MS4s
• Stormwater Case Studies
• And many others
V& Other EPA Web sites
• Ordinance Database
www.epa. gov/owow/nps/ordinance
• Urban Nonpoint Source Guidance
www. epa. gov/owow/nps/urbanmm/index. html
• Low Impact Development Web site
www.epa. gov/owow/nps/lid
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