GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 4
When rain falls on natural landscapes, much of it is intercepted
by vegetation or absorbed into the soil.
United States
Environmental Protection
Agency
EPA832F12015
Stormwater
Introduction
This factsheet is the fourth in a series of six on integrating green
infrastructure concepts into permitting, enforcement, and
water quality standards actions.
Permit Language
Example Permits
Stormwater Program Elements
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Introduction
Integrating Green Infrastructure Concepts into
Permitting, Enforcement, and Water Quality
Standards Actions
This factsheet is the fourth in a series
of six factsheets in the U.S. EPA Green
Infrastructure Permitting and Enforcement
Series (http://water.epa.gov/infrastructure/
greeninfrastructure/gi_regulatory.
cfm#permittingseriesA This series
describes how EPA and state permitting and
enforcement professionals can incorporate
green infrastructure practices and approaches
into National Pollutant Discharge Elimination
System (NPDES) wet weather programs,
including stormwater permits, Total
Maximum Daily Loads (TMDLs), combined
sewer overflow (CSO) long-term control
plans (LTCPs), and enforcement actions.
This series builds upon EPA's continued
investment in green infrastructure and low
impact development. Existing EPA authority,
guidance, and agreements enable EPA
Regions and state agencies to work with
permittees to include green infrastructure
measures as part of control programs.
For additional resources on green infrastructure,
go to the EPA Green Infrastructure Web
page: http://water.epa.gov/infrastructure/
greeninfrastructure/index.cfm.
Key green infrastructure guidance issued
to date can be found at: http://water.epa.
gov/infrastructu re/green infrastructure/
gLpolicy.cfm.
The Clean Water Act and applicable regulations require that
stormwater discharges from regulated construction sites,
industrial sites, and Municipal Separate Storm Sewer System
(MS4) communities can only occur if covered by a NPDES
stormwater permit. Stormwater permits typically require
implementation of control measures and Best Management
Practices (BMPs)to limit or minimize pollutant discharges.
While the implementation of structural and nonstructural
BMPs has helped reduce pollutant loadings, in many cases
stormwater has nevertheless been found to contribute to water
quality impairments. Adverse impacts have been identified
which are due to the volume of stormwater discharges and
the associated energy, which erode stream channels and lake
shorelines and otherwise degrade habitat and water quality.
The recent report of the National Research Council ("Urban
Stormwater Management in the United States," National
Academy of Sciences Press, 2008) recommends thatthe NPDES
stormwater program treat flow as a pollutant and as a proxy
for other pollutants, and include appropriate volume control
requirements in stormwater permits:
"Flow and related parameters like impervious cover
should be considered for use as proxies for stormwater
pollutant loading. These analogs for the traditional focus
on the 'discharge' of 'pollutants' have great potential as
a federal stormwater management tool because they
provide specific and measurable targets, while atthe
same time they focus regulators on water degradation
resulting from the increased volume as well as
increased pollutant loadings in stormwater runoff."
The report emphasizes that the current program fails to
effectively reduce stormwater pollutant discharges. It also
describes how many traditional stormwater practices, and the
permit language that drives them, fail to address the hydrologic
modifications that increase stormwater runoff quantity, and
cause excessive erosion and stream channel degradation.
Frequently the most serious degradation to aquatic systems
caused by stormwater is attributable to discharge volumes,
durations and velocities. To protect and restore the physical,
chemical and biological integrity of receiving waters, flow
controls should be an important element of stormwater permits.
Green infrastructure will be an important component of most
stormwater volume control strategies. Green infrastructure
practices help reduce stormwater discharge volumes through
infiltration, evapotranspiration, and capture and use. Permitting
agencies can advance implementation of green infrastructure
practices through stormwater permits.
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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 4
Permit Language
Permits can be written to foster green infrastructure
implementation in a number of ways, including:
• Establishing performance standards for post-
construction stormwater volume control for sites
undergoing development/redevelopment. Performance
standards to control the volume of discharges and to
mimic the pre-construction hydrology of a site will lead
to implementation of BMPs and green infrastructure
to infiltrate, evapotranspirate, and/or harvest and
beneficially use stormwater.
• Requiring that green infrastructure/low impact
development measures be considered/ implemented
as part of local building and site development approval
processes.
• Establishing ceilings on effective impervious area.
Land development often includes the construction of
buildings, parking lots, roads, driveways, and other
impervious surfaces. The new impervious surfaces and
changes to landscapes alter the hydrology of sites or
neighborhoods, leading to higher stormwater discharge
volumes and higher pollutant loads. MS4 permits
and construction stormwater discharge permits can
include requirements for post-construction stormwater
management to reduce or eliminate the negative effects of
land development and new impervious surfaces.
Effective post-construction stormwater performance
standards should be centered on maintaining or restoring
stable hydrology in receiving waters by having post-
construction hydrology mimic the natural hydrology of the
area. One way of approach for this is to stipulate in permits
that pre-development (i.e., stable, natural) hydrographs
match post-development hydrographs. If this approach is
used, the permit must be very clear that all variables of the
hydrograph (volume, rate, duration, frequency) be matched.
and not just the discharge rate. Unfortunately, many current
hydrology standards focus only on discharge rate, which is
primarily a flood control approach, i.e., extended detention.
In addition, a pre-development condition should also be
defined, and that condition should be one that is reasonably
'natural', not simply the conditions (perhaps already fairly
impervious)that existed immediately priorto the current
development project. The "pre-post hydrograph match"
approach will generally involve an in-depth analysis for
each development project, which means that site plan
reviews by the municipality may also be more complicated
and time consuming.
A simpler, but reasonably approximate "mimicking the
natural hydrograph" approach can often be accomplished
by specifying in the permit that the volume of water from
a certain size storm be managed on site. An example
of this is to estimate a storm size that would generally
equate to the size of storm that would be managed in a
natural forest or grassland environment with no discharge,
and to require that this size of storm be managed on site
at new development/ redevelopment sites. Athorough
explanation of this approach can be found in the document
"Technical Guidance on Implementing the Stormwater
Runoff Requirements for Federal Projects under Section 438
of the Energy Independence and Security Act," available
at: http://www.epa.gov/owow/NPS/lid/section438/
pdf/final_sec438_eisa.pdf. This document covers in
detail the concept that managing a 95th percentile storm
would result in a site/neighborhood hydrology similar to a
natural condition, and how to plan site features, including
in particular green infrastructure, to effectively manage
stormwater on site.
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Example Permits
The following are some examples of stormwater permits with relevant performance provisions.
West Virginia
The West Virginia Department of Environmental Protection
has issued a small MS4 permit that includes the following
performance standard for new and redevelopment projects:
"Performance Standards. The permittee must
implement and enforce via ordinance and/or
other enforceable mechanism(s)the following
requirements for new and redevelopment: [...]
Site design standards for all new and
redevelopment that require, in combination or
alone, management measures that keep and
manage on site the first one inch of rainfall from
a 24-hour storm preceded by 48 hours of no
measurable precipitation. Runoff volume reduction
can be achieved by canopy interception, soil
amendments, evaporation, rainfall harvesting,
engineered infiltration, extended filtration, and/
or evapotranspiration and any combination of the
aforementioned practices. This first one inch of
rainfall must be 100% managed with no discharge to
surface waters."
The 1-inch stay-on volume requirement is based on an
analysis of 60 years of rainfall data in the state, which
indicated that, on average, 90% of the rainfall events in
West Virginia are 1 inch or less. Rainfall patterns do not
vary significantly across the state.
This permit also includes provisions for:
• Revising codes and ordinances accordingly.
• Reviewing planning policies for opportunities to protect
natural resources.
• Incentives for redevelopment, Brownfield
redevelopment, and other higher density urban
situations, i.e., disincentives for sprawl.
• options for payment-in-lieu and off site mitigation when
fulfillment of the 1" standard cannot be met.
• A requirement for road retrofits assessment when
standard road maintenance is occurring.
• Specific accountability provisions (operation and
maintenance, inspections, tracking, and reporting).
More details are available: http://www.dep.wv.gov/
WWE/Programs/stormwater/MS4/permits/
Documents/WV%20MS4%202009%20General%20
Permit.pdf
North Carolina
The North Carolina Permit to Construct, Operate and
Maintain Impervious Areas and BMPs Associated with
Residential Development Disturbing Less Than 1 Acre,
includes the following provisions for control of post-
construction stormwater runoff:
"Stormwater runoff shall be managed using any one
or combination of the following practices:
a. Install rain cisterns or rain barrels designed
to collect all rooftop runoff from the first one
and one-half inches of rain. Rain barrels and
cisterns shall be installed in such a manner asto
facilitate the reuse of the collected rainwater on
site and shall be installed in such a mannerthat
any overflow from these devices is directed to
a vegetated area in a diffuse flow. Construct all
uncovered driveways, uncovered parking areas,
uncovered walkways, and uncovered patios
out of permeable pavement or other pervious
materials.
b. Direct rooftop runoff from the first one and one-
half inches of rain to an appropriately sized and
designed rain garden. Construct all uncovered
driveways, uncovered parking areas, uncovered
walkways, and uncovered patios out of
permeable pavement or other pervious materials.
c. Install any other stormwater best management
practice that meets the requirements of 15A NCAC
02H .1008to control and treat the stormwater
runoff from all built upon areas of the site from the
first one and one-half inches of rain."
More details are available: http://portal.ncdenr.0rg/c/
document_library/get_file?uuid=724171cc-c208-4f39-
a68c-b4cd84022cd9&groupld=38364
New Jersey
The New Jersey Department of Environmental Protection
developed performance standards reflecting the concept of
mimicking natural hydrology, and based the measurement
of specifically for groundwater recharge.
The New Jersey Stormwater Management Rules at
N.J.A.C. 7:8 require that a "major development" project,
which is one that disturbs at least 1 acre of land or creates
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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 4
at least 0.25 acres of new or additional impervious surface,
must comply with one of the following groundwater
recharge requirements:
• "Demonstrate through hydrologic and hydraulic
analysis that the site and its stormwater
management measures maintain 100 percent
of the average annual preconstruction
groundwater recharge volume for the site; or
• Demonstrate through hydrologic and hydraulic
analysis that the increase of stormwater
runoff volume from pre-construction to post-
construction for the two-year storm is infiltrated."
The State has a spreadsheet for documenting how the
recharge rate requirement is being met. Chapter 6 of the
New Jersey Stormwater Best Management Practices
Manual discusses the groundwater recharge methodology,
the groundwater recharge design storm, and the details of
the New Jersey Groundwater Recharge Spreadsheet.
More details are available: http://www.state.nj.us/dep/
stormwater/tier_A/index.htm
Ohio
The Ohio Environmental Protection Agency has also
developed performance standards based on groundwater
recharge. The Ohio construction general permit forthe Big
Darby Creek Watershed near Columbus, where significant
growth is projected, includes post-construction infiltration
requirements. This permit requires that post-development
groundwater recharge be equal to or exceed the pre-
construction groundwater recharge.1 The permit specifies
thatthe Stormwater Pollution Prevention Plan (SWPPP)
must describe the conservation development strategies,
stormwater control measures and other practices deemed
necessary by the permittee to maintain or improve pre-
development rates of groundwater recharge. The permit
includes a formula and standard values for gauging
groundwater recharge rates, and includes provisions to
ensure preservation of open space where infiltration will
occur. Protection of open space (infiltration areas) is to be
achieved by binding conservation easements that identify
a third party management agency, such as a homeowners
1 Brown and Caldwell. Municipal NPDES Stormwater
Permits, http://depts.clackamas.cc.or.us/wet/
documents/MS4_Update.pdf
association, condominium association, political jurisdiction
or third party land trust. If the post-development recharge
volume will be less than the pre-construction recharge
volume, mitigation is required. This permit also has a
riparian buffer establishment and protection provision.
More details are available: http://www.epa.state.oh.us/dsw/
permits/GP_ConstructionSiteStormWater_Darby.aspx
California
There are examples in California of permits that establish
performance standards for runoff volumes from
development sites, and permits that establish requirements
addressing effective impervious area:
Performance Standards for Development Sites: California's
Santa Ana Regional Water Quality Control Board has issued
an MS4 permit for Orange County and the municipalities in
the County calling for permittees to:
"Require that each priority development project
infiltrate, harvest and reuse, evapotranspire, or
biotreat the 85th percentile storm event ("design
capture volume")... Any portion of the design
capture volume that is not infiltrated, harvested
and re-used, evapotranspired, or bio-treated onsite
by LID BMPs shall be treated and discharged in
accordance with the requirements set forth in
Section XII.C.7 and/or Section XII.E, below."
Priority development projects are specifically defined in the
permit, and include redevelopment projects. Biofiltration
can only be used if infiltration, harvesting and re-use,
and evapotranspiration cannot be feasibly used atthe
project site. The permittees must submit both feasibility
criteria and design, operation, and maintenance criteria
for biotreatment systems for public review and Regional
Board approval. Sections XII.C.7 and Section XII.E, which
must be used if LID is infeasible on-site, include provisions
for implementing LID at another location away from the
project site (a mitigation measure), or achieving alternative
compliance by paying in-lieu fees.
More details are available: http://www.swrcb.
ca.gov/rwqcb8/board_decisions/adopted_orders/
orders/2009/09_030_OC_MS4_as_amended_
by_10_062.pdf.
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Effective Impervious Area: The California Los Angeles
Regional Water Quality Control Board has included the
following standard in the MS4 permit for Ventura County:
"New Development/Redevelopment Performance
Criteria
1. Integrated Water Quality/ Flow Reduction/
Resources Management Criterion
(a) ...Permittees shall require all New
Development and Redevelopment
projects identified in subpart 4.E.II to
control pollutants, pollutant loads, and
runoff volume emanating from impervious
surfaces through infiltration, storage for
reuse, evapotranspiration, or bioretention/
biofiltration by reducing the percentage of
Effective Impervious Area (EIA) to 5 percent
or less of the total project area."
More details are available: http://www.swrcb.ca.gov/
rwqcb4/water_issues/programs/stormwater/
municipal/ventura_ms4/Final_Ventura_County_MS4_
Permit_Order_No.09-0057_01-13-2010.pdf.
The Elmer Avenue Neighborhood Retrofit Project in Los Angeles reduced
effective impervious area by routing stormwaterfrom paved areas
to vegetated swales, rain gardens, rain barrels, and an underground
infiltration gallery. Photo Courtesy of Los Angeles and San Gabriel Rivers
Watershed Council.
Stormwater Program Elements
Permits should be as specific about expectations and
outcomes as possible.2 However, regardless of how
comprehensive the permit is, many of the activities and
projects will be detailed in the permittee's stormwater
plan and not in the permit itself. Stormwater permittees
are required to provide details of their programs in plans,
and permitting authorities should review those plans as
a facet of providing permit coverage, and/or as a facet of
evaluating permit compliance.
Permits should require many of the following elements as
part of a program with a solid green infrastructure focus.
In April of 2010, EPA released the "Municipal Separate
Storm Sewer System Permit Improvement Guide" to
assist permit writers in strengthening MS4 permits. The
guide is available at: http://www.epa.gov/npdes/
pubs/ms4permit_improvement_guide.pdf.
Policies and Standards
Stormwater programs should institutionalize changes in
order to be effective. There are a variety of issues to be
addressed. MS4 permittees should:
• Evaluate transportation design specifications,
plumbing codes, landscaping requirements, and other
standards that might prohibit the use of practices.
Identify language that may be incompatible with
green infrastructure and work with other municipal
departments to discuss the changes and identify
alternatives. Develop new code language and propose
changes to the relevant ordinance. This should include
the specified performance standard from the permit.
Communities can use the Water Quality Scorecard
to evaluate and modify local policies, codes, and
ordinances to address a number of issues that influence
environmental outcomes, (http://www.epa.gov/
smartgrowth/pdf/2009_1208_wq_scorecard.pdf).
Permits could include many of the following elements as part of a program with a solid green infrastructure focus:
Review and revise local policies and standards
Employ green infrastructure for capital improvement projects
Educate developers and maintenance crews
Establish a maintenance tracking system
Incentivize green infrastructure
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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 4
• Implement standards for construction site stormwater
runoff. Preservation of open space, trees, and other
natural features reduces the amount of area cleared
and graded, decreasing costs for erosion and sediment
control. Municipalities can include this practice as one
of their required or recommended control measures
for construction activities, and can incorporate this
practice into capital improvement projects.
• Provide guidance for implementing the performance
standards for new development and redevelopment.
Develop a standards manual or adopt the state manual
if it meets the community's needs. Wherever possible,
adapt existing resources to local situations in order to
conserve resources. Prince George's County, Maryland,
developed two design manuals with technical
specifications for green infrastructure practices: "Low-
Impact Development Design Strategies: An Integrated
Design Approach" and "Low-Impact Development
Hydrologic Analysis," both of which are available on
EPA's website at: www.epa.gov/owow/nps/lid. The
"Low Impact Development Manual for Michigan"
is another very good resource: http://library.
semcog.org/lnmagicGenie/DocumentFolder/
LIDManualWeb.pdf.
• The use of native plants in landscaping reduces the
need for municipal crews to irrigate or use pesticides,
herbicides, or fertilizers. Municipalities can incorporate
selection of native plants into its landscaping guidelines
and can train its maintenance crews to use integrated
pest management.
• Evaluate constraints (areas of high groundwater, poorly
drained soils, etc.) and adapt local guidance to address
such site conditions.
Employ Green Infrastructure for Capital
Improvement Projects
A municipality can set a good example, show confidence
in the use of new technology, and demonstrate success
with projects in the public right-of-way. Municipalities
have jurisdiction over development activities in the right-
of-way and on public lands, which allows greater design
flexibility and more reliable maintenance using municipal
crews. Green infrastructure projects adapt well to linear
applications (streetscapes, courtyards, medians, etc.) and
small-scale open spaces. It will be necessary to work with
facilities management and landscaping crews because
maintenance of vegetated green infrastructure practices
sometimes requires special handling, such as hand-weeding
and prohibiting heavy equipment and pesticide use.
Educate Developers and Maintenance Crews
Allowtime and dedicate staff resources for bringing design
engineers and landscape architects up to speed on new
requirements. Provide checklists to help ensure compliance
with new procedures. Develop locally based coefficients
where appropriate in orderto streamline sizing calculations
and include example calculations to ensure consistency
and transparency in project submittals. Hold periodic
training sessions on green infrastructure applications, and
request that plan reviewers provide specific comments
when submitted designs do not meet standards.
Establish a Maintenance Tracking System
Communities need to determine whether property owners
or the municipality will be responsible for maintenance. If
property owners will be responsible, there are a number of
ways in which the municipality can assure maintenance:
• Require maintenance agreements, which are recorded
with the property deed, for new and existing control
measures.
• Require a performance bond for new controls.
• Perform spot inspections to identify maintenance
problems and check maintenance records.
• Require that property owners submit maintenance
records or other evidence that maintenance was
performed as prescribed.
Communities should maintain a database or geographic
information system to manage information on the design
parameters and locations of green infrastructure practices.
A database or other tracking system is critical for
maintenance assurance and can also be used for other
efforts, such as watershed modeling, stormwater master
planning, and inspection programs.
Incentivize Green Infrastructure
Communities can offer incentives to developers to preserve
open space, protect or plant trees, and implement green
infrastructure site design techniques by offering stormwater
credits and other incentives. Incentives can be in the form
of a density bonus, reduced size of required drainage
infrastructure, discounted utility fees, and tax credits. The
goal of the credits is to reduce the required capacity (and
therefore the cost) of stormwater treatment practices using
non-structural site design and conservation measures.
Credits can also be used to reduce the stormwater utility
rate or user fee, if applicable. A number of municipalities
across the nation offer some form of stormwater credit,
and some states have developed guidance to encourage
municipalities to adopt a credit system. For more
information on incentives, see "Incentive Mechanisms,"
an installment of EPA's "Managing Wet Weather with
Green Infrastructure Municipal Handbook Series": http://
water.epa.gov/infrastructure/greeninfrastructure/upload/
gi_munichandbook_incentives.pdf.
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Green Infrastructure Permitting and Enforcement Series
This series on integrating green infrastructure concepts into
permitting, enforcement, and water quality standards actions
contains six factsheets plus four supplemental materials
that can be found at http://water.epa.gov/infrastructure/
greeninfrastructure/gi_regulatory.cfm#permittingseries.
Factsheets
1. Potential Challenges and Accountability Considerations
2. Combined Sewer Overflows
3. Sanitary Sewer Overflows
b. Stormwater
5. Total Maximum Daily Loads
6. Water Quality Standards
Supplemental Materials
1. Consent Decrees that Include Green Infrastructure Provisions
2. Consent Decree Language Addressing Green for Grey
Substitutions
3. Green Infrastructure Models and Calculators
b. Green Infrastructure in Total Maximum Daily Loads (TMDLs)
United States
Environmental Protection
Agency
For additional resources on green infrastructure,
goto the EPA Green Infrastructure Web page:
http://www.epa.gov/greeninfrastructure/.
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