GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 2

                                                                            United States
                                                                            Environmental Protection
                                                                            Agency
                                                                            EPA832F12013
                     Combined  Sewer
                                     Overflows
          This factsheet is the second in a series of six on integrating green
                  infrastructure concepts into permitting, enforcement, and
                                    water quality standards actions.
Introduction
Evaluating the Potential of
Green Infrastructure for CSO Control

Developing Quantitative
Implementation Targets
                                                                      Incorporating Green Infrastructure     Page 5
                                                                      Approaches into Long-Term Control Plans

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Integrating Green Infrastructure Concepts into
Permitting, Enforcement, and Water Quality
Standards Actions

This factsheet is the second 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/infrastructure/greeninfrastructure/
gLpolicy.cfm.
          Combined Sewer Overflows (CSOs)
          Introduction
          Green infrastructure can reduce the volume of water going
          into combined systems during precipitation events, which
          may reduce numbers and volumes of overflows. Green
          infrastructure can also slow the delivery of wet weather
          flows to sewer systems, helping to mitigate peak flows
          while providing filtration through soil for some portion of the
          release into the sewer system, thereby reducing pollutant
                            =  loads. The implementation of
                                green infrastructure practices
                                may allow communities
                                to downsize certain grey
                                infrastructure components of
                                their CSO control plans. This may
                                provide some CSO communities
                                with significant cost savings.
EPA GUIDANCE: CONSIDER
SOURCE CONTROLS
Existing EPA guidance
states that, as part of the
"Identification Control
Alternatives" for inclusion in
CSO LTCPs, CSO communities
must consider source controls,
which are defined specifically
to include green infrastructure
approaches (Combined Sewer
Overflows Guidance for Long-
Term Control Plan, EPA832-B-
95-002, at pp. 3-31 -3-33).
                                Under the Clean Water Act
                                and EPA's 1994 CSO Control
                                Policy, most CSO communities
                                are required to develop and
                                implement a Long-Term Control
                                Plan(LTCP)to restore and
                                protect water quality. National
          Pollutant Discharge Elimination System  (NPDES) permits
          and administrative or judicial orders establish requirements
          for developing and implementing LTCPs. There is also
          existing guidance on development and implementation of
          LTCPs (see sidebar below).

      Existing Guidance on Development and Implementation of LTCPs
    PERMITTING: http://cfpub.epa.gov/npdes/home.cfm?program_id=5
ENFORCEMENT: http://www.epa.gov/compliance/resources/policies/civil/cwa/
                      csosso-guidelines-enf.pdf
         CSO POLICY: http://cfpub.epa.gov/npdes/cso/cpolicy.cfm

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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 2
  Evaluating the Potential of Green Infrastructure for CSO Control
  In many cases planning for the use of green and grey
  infrastructure will be most effective if both elements
  are integrated throughout the planning and engineering
  design processes. Therefore, it is recommended that
  communities carry out integrated green/grey planning
  to identify opportunities to use green infrastructure in
  cost-effective combinations with grey infrastructure. This
  can help lower upfront and/or operational costs. If, for
  example, a community does engineering analyses to plan
  grey infrastructure, sized to achieve high levels of control,
  and then adds green infrastructure as a layer near the
  end of the planning process, the community may conclude
  that green infrastructure does not appreciably increase
  the level of control. However, if planning specifically
  encompasses green and grey infrastructure together
  throughout the process, it is likely the planning will reveal
  many opportunities to use green infrastructure to keep
  water out of the system in some or all sewersheds. By
  capitalizing on opportunities to place  green infrastructure in
  sewersheds, communities may be able to reduce the size of
  grey infrastructure controls.
  This is not meant to imply that grey infrastructure controls
  are not needed; in most communities  green infrastructure
  alone will not resolve CSO problems for large  storms.
  Depending on land uses, land owners, and other variables,
  some sewersheds are well-suited for green solutions
  whereas others may provide less opportunity. Therefore,
  stormwater reduction analyses typically should be
  considered sewershed by sewershed. Estimating the
maximum or optimal amount of green infrastructure that
can be implemented in a sewershed requires an analysis
of land use and technical/environmental factors such
as soil types and topography, as well as institutional
considerations, such as the need to develop incentives to
facilitate implementation of green infrastructure features
on private property.
Development of CSO LTCPs involves analysis of the
financial capability of the community and analysis of
alternatives for reducing CSO frequencies, volumes, and
pollutant loads. Historically, grey infrastructure  approaches
and operational enhancements have been the key
components of LTCPs. Recently, there has been greater
interest in using green infrastructure approaches, often
in combination with grey infrastructure and operational
enhancements, to meet CSO control needs. This approach
may have the advantage of distributing the cost of control
more broadly, rather than relying solely on utility ratepayers.
For  example, if a green streetscapes project is implemented
it may be possible to cost-share between the stormwater
or CSO authority and a transportation organization. In
other cases a school or park district may cost-share with
the  local stormwater/CSO authority. Additionally, several
recent CSO consent decrees have required the  retrofitting
of sizeable areas with green infrastructure as part of holistic
approaches to CSO reduction.
(See Supplement 1).
 Case Study of the Impacts of Trees and Green Roofs on Stormwater Runoff
 Various organizations and communities have recently conducted studies to estimate the potential for
 reducing flows into combined sewer systems through systematic use of green infrastructure practices.
 In 2007, Casey Trees and LimnoTech, with funding from EPA, conducted a modeling study of the impacts
 of trees and green roofs on stormwater runoff in the Washington, DC area (http://caseytrees.org/
 programs/policyadvocacy/). The Casey Trees modeling estimated, upon completion of implementation
 of green infrastructure projects:
 •  For an average year, the intensive greening scenario would prevent over 1.2 billion gallons of stormwater
    from entering the sewer systems, resulting in a reduction of over 1 billion gallons in discharges to local
    rivers.
 •  For an average year, the moderate greening scenario would prevent over 311 million gallons of
    stormwater from entering the sewer systems, resulting in a reduction of 282 million gallons in discharges to local waterways.
 •  With the intensive greening scenario, installing 55 million square feet of green roofs in the Combined Sewer System (CSS) area
    would reduce CSO discharges by 435 million gallons, or 19%, each year.
 The initial round of modeling focused onlyongreen roofs and enhancing the urban tree canopy. Further work was then done to model
 the effects of other green infrastructure components in the Washington D.C. service area. Other communities and regional sewer
 authorities that have  incorporated green infrastructure  controls in their CSO planning include New York, Cincinnati, Louisville,, Omaha,
 San Francisco, Kansas City, and Cleveland.
                                      Figure 1: A bioretention cell
                                      absorbs runoff.

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Developing Quantitative Implementation  Targets
Once a community has evaluated the potential of green
infrastructure practices for CSO control, and determined
green infrastructure practices can be a cost-effective
component of an LTCP, it is important to identify the
locations for green infrastructure implementation and
to quantify the projected level of green infrastructure
implementation. A community can identify what green
infrastructure of what size/capacity can be put where in a
sewershed, and can then determine what level of reduction
that will achieve in terms of wet weather flows entering the
sewer system. The new flow information  can then be used
in the sizing of grey infrastructure. See Supplement 3 for
a summary of tools and calculators that are available to
help quantify the impacts of green infrastructure.
Once a community has completed a desktop analysis
identifying priority sewersheds for green  infrastructure
implementation, a more detailed analysis must be
completed to establish a quantitative green infrastructure
implementation target. A discussion of alternative analysis
methodologies is beyond the scope of this document. In
general, however, the methodology should first develop a
set of green infrastructure scenarios, and then assess  the
outcomes associated with each scenario. The scenario
that best meets the  community's needs may be adopted as
an implementation target. Ideally, the methodology should
allow the community to compare the cost-effectiveness
of each alternative in meeting CSO control targets, and
the range of environmental benefits provided  by each
alternative. The checklist on Page 5 provides  a general
methodology for establishing a quantitative green
infrastructure implementation target. Note that this is only
one of many approaches that a community might take.
The implementation target identified may call for many
decentralized green infrastructure practices.  In a permit
or enforcement action, it will be important to include
appropriate provisions to ensure the decentralized
practices (many of which will not be on land owned/
controlled by the sewer authority) are properly installed,
preserved overtime, and maintained.
Many communities  have identified municipally-owned
properties and road right-of-ways, and other parcels that
may be well-suited for green infrastructure practices, (e.g.,
corporate campuses, school campuses, and vacant  parcels
where there is no near-term demand for redevelopment).
These communities have quantified the flow volumes that
could be  managed at these sites, and then incorporated
the results into planning of the complementary grey
infrastructure controls.
Figure 2: Stormwater park at Saylor
Grove in Philadelphia
Also, important factors in some sub-watersheds may
be the preservation or enhancement of natural green
infrastructure, including features like riparian buffers, forest
preserves, floodplains, wetlands, and parks. In estimating
flows coming out of a sewershed, the capacity of such
areas to absorb stormwater flows needs to be considered. It
may be appropriate to incorporate the need to preserve, and
in some cases enhance such areas in  a LTCP.
In some urban areas, a
city or sewer authority
may determine that it will
focus on relatively larger
green infrastructure
practices, perhaps at
the block scale, and will
setup ownership and
operation of the sites
and practices underthe
direct control of the city
or sewer authority. An example of this would be where a city
constructs "stormwater parks" to store and infiltrate wet
weather flows (see Figure 2). With an approach like this, the
capacity of the practice can be readily determined, much
like a detention pond, and green infrastructure plans and
commitments can reflect the number, locations, and sizing
of the larger-scale green practices. Stormwater parks can
be planned at strategic locations in the sewer network,  and
where they fit well into the fabric of the community area.
Using larger scale  green infrastructure practices, where the
city or sewer authority retains control over the practices,
may be advantageous for a community in terms of assuring
the practices are properly built, preserved, and maintained.
Adaptive management approaches can be used during  LTCP
implementation to  ensure green infrastructure measures
are being implemented and  are working to the degree
expected (see further discussion below). Closely monitoring
green infrastructure implementation and performance is
important to ensure the projected levels of storage and
control are being achieved.  Mid-course adjustments  can be
made if necessary. The monitoring of implementation and
performance coupled with the use of adaptive management
approaches — making adjustments to future efforts
based on lessons learned — can help  alleviate possible
uncertainty or perceived risks about implementing green
solutions as part of a CSO control program.

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 GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 2
A General Methodology for Establishing a Quantitative Green Infrastructure Implementation Target
  ] Select a sample set of sewershedsthatare generally representative of the service area as a whole, in terms of land uses, land
    ownership, soils, and topography.
  ] Characterize existing land use/land cover in the subwatersheds; this can often be done using aerial photographs and/or a
    community's geographic information system (GIS) coverages.
Q Create templates for the various land uses in the sewersheds (e.g., typical single family residential lot, typical commercial/office
    site). Estimate the pervious and impervious areas for the templates.
  ] Identify green infrastructure opportunities for the different land use categories (templates) in the sewersheds, taking into account
    space needs, soil types, and slopes.
  ] Estimate the total green infrastructure that could be implemented in the sewershed by extrapolating from the templates to the
    sewershed as a whole. This estimate should take into account current and future zoning and institutional considerations, such as
    acceptance by property owners of green infrastructure features on private property. The level of buy-in to the green infrastructure
    program on the part of local property owners is an  important variable, and needs to be explicitly considered in CSO planning. The
    estimate should also consider public properties and parks that may be good candidates for green infrastructure practices.
  ] Examine the cost-effectiveness of green infrastructure approaches. Will the green solutions reduce upfront or operational costs?
    Experiment with various combinations of green and grey infrastructure to determine what combination results in the lowest costs.
  ] Estimate the green infrastructure opportunities for the CSO service area as a whole by extrapolating from the sample set of
    sewersheds studied.
  ] Estimate the stormwater volumes that can be kept  out of the system by the green infrastructure, taking into account the level of
    estimated  implementation and the size of the practices. Also consider if there should be a margin of safety to reflect actual green
    implementation that may vary from projections, especially for sites not underthe direct control of the sewer authority.
  Incorporating Green Infrastructure  Approaches  into Long-Term  Control Plans
  Green infrastructure components should be explicitly
  identified and accompanied by compliance schedules in
  LTCPs along with grey infrastructure components. A list of
  the items that should be included in a LTCP if a community
  chooses to utilize green infrastructure measures is
  provided in the checklist on Page 6.
  The timing for green infrastructure implementation should
  be expressly considered in CSO planning. Some green
  infrastructure benefits will probably be realized sooner than
  those for grey solutions, while others maytake longer. It is
  important to achieve a reasonable balance while keeping
  in mind the overall environmental objectives. Discussion
  of these items and how they will be addressed in the LTCP
  should be done jointly  between the community carrying out
  implementation and the permitting/enforcement authority.
  As a companion to LTCP implementation, CSO
  communities planning for significant green infrastructure
  implementation should:
  •   Develop strategies or standard operating procedures
      (SOPs) for green infrastructure implementation;
  •   Consider approaches for dealing with legal and
      institutional issues including updating codes and
      ordinances;
  •   Consider changes to fee structures to incentivize green
      infrastructure;
•  Consider how they will work to systematically install
   green infrastructure on different types of sites, e.g.,
   municipally-owned public sites, schools, park district
   sites, corporate sites, and residential properties. The
   issuesthatwill be encountered in putting rain gardens
   in parks or schools will  be very different from the issues
   to be dealt with in getting green roofs on public and
   private buildings.

SOPs can help communities plan for and implement
effective approaches to place green infrastructure at
different types of sites within their service area.

Preservation of green infrastructure sites and  practices
In addition to including provisions for operation and
maintenance of green infrastructure practices,  permits, and
enforcement actions also need to consider mechanisms
to assure green infrastructure  is preserved (i.e., that
a site or green infrastructure practice is not changed
or removed at some point in the future). For example,
language in a general permit issued by Ohio EPA specifies
that protection (preservation) of infiltration areas shall be
by binding conservation easements that identify a third
party management agency, such as a homeowner or
condominium association, political jurisdiction,  orthird
party land trust. See: http://www.epa.state.oh.us/dsw/
permits/GP_ConstructionSiteStormWater_Darby.aspx.

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                     v-a
Including Green Infrastructure in LTCPs
Green infrastructure components should be explicitly identified and accompanied by compliance schedules in LTCPs along
with grey infrastructure components.
The following should be included in an LTCP with green infrastructure:
Q The planned (and quantified) level of green infrastructure implementation (what will be installed where, e.g.,
    number of infiltration practices to be installed and associated sizes/capacity);
Q Key implementation steps (actions);
Q Sequencing (ensure green and grey elements fit together; also in many cases it may work well to start in upstream
    areas and work toward downstream areas);
Q Schedule;
Q Methods and milestones for tracking and reporting on green infrastructure implementation (are the green
    infrastructure practices going in as planned and scheduled);
QJ Requirements to assure appropriate operation and management (O&M) of the green infrastructure;
n Methods for monitoring the performance and effects of green infrastructure implementation (e.g., are individual
    practices working as planned, are collections of practices in a sewershed keeping flows out of the sewer system
    as projected);
Q Provisions for adaptive management/corrective actions if green infrastructure performance (at the site scale and/
    orthe sewershed scale) does not meet expectations
Green for Grey Substitutions
In some cases much of the foundational planning and
engineering work on CSO controls may have focused on
grey infrastructure practices, but well into CSO planning
work the idea of incorporating green infrastructure
into the LTCP may have been raised. In these types of
situations it may be appropriate in a permit or enforcement
action to include provisionsthatwould govern a possible
substitution of green infrastructure control measures
for grey infrastructure control measures. The Consent
Decrees dealing with CSOs in the Kansas City, Missouri
and Cleveland, Ohio areas are examples of agreements
that include provisions for green for grey substitutions.
Supplement 2 provides example language which
addresses some of the issues that may be associated with
green for grey substitutions.

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GREEN INFRASTRUCTURE PERMITTING AND ENFORCEMENT SERIES: FACTSMEET 2
 Monitoring and Evaluating Green Infrastructure Performance
 Permits and enforcement actions that include green infrastructure measures should include provisions for evaluating
 the performance and effects of installed green infrastructure control measures. These provisions would be an essential
 component of post-construction  monitoring required for CSO control practices. It may also be appropriate to include
 requirements for corrective action implementation if green infrastructure practices do not perform as projected.
 Following is example language to address post-construction monitoring for green infrastructure practices: [http://www.
 ohioenvironmentallawblog.com/uploads/file/NEORSD%20Green%20infrastructure%20CO.pdf]
     "The Sewer District shall submit a plan for performing
     green infrastructure post-construction monitoring
     ("GIPCM") at two scales: (a) site or practice scale; and
     (b) sewershed scale. The monitoring shall be planned
     to evaluate the performance and effectiveness of
     the green infrastructure control measures, as further
     defined below. Once approved by EPA and the State,
     the District shall implement the GIPCM program in
     accordance with the approved GIPCM plan. The
     District shall submit green infrastructure post-
     construction monitoring reports providing the results of
     the GIPCM  programs to EPA and the State.

     a. The site or practice scale GIPCM program
        shall evaluate the effectiveness of the green
        infrastructure control measures on a site-specific
        scale. The GIPCM plan shall set forth the ways
        the various types of green infrastructure control
        measures to be implemented (e.g., constructed
        wetland, etc.) will function to control wet weather
        flows (e.g., through storage, infiltration, and/
        or evapotranspiration), and the monitoring/
        assessment methods that will be used to evaluate
        the performance and effectiveness of the various
        types of practices. The GIPCM plan shall set
        forth the District's methods and procedures for
        evaluating the performance of green infrastructure
        control measures on a site-specific scale, such as
        monitoring practices during and after rain events
        to gauge storage and/or infiltration performance.
        The GIPCM plan shall establish procedures for
        conducting performance evaluations on the fully
        constructed and operating green  infrastructure
        control measures. Underthe site-specific
        program, performance evaluations shall assess
        the effectiveness of the practices in terms of the
        functions the green infrastructure control measure
        was intended to fulfill (e.g., storage, infiltration).
        Each site-specific green infrastructure control
        measure (or a representative sample if similar
        practices are installed at similar sites) shall be
        monitored for a  minimum of 12-months immediately
        following implementation.

     b. The sewershed-specific GIPCM program shall
        set forth the steps the District shall take to
evaluate the performance and effectiveness of
green infrastructure measures on a sewershed
scale. Examples of such methods and procedures
include collecting rainfall and wet weather flow
data sufficient in scope and detail to allow: (i)
characterization of the performance of the green
infrastructure measures in a sewershed, and (ii)
hydrologic adjustment of the sewershed portion
of the collection system model to determine the
impacts of the green infrastructure  measures
on system performance within the subject
sewershed. The District shall adjust the hydrologic
model parameters directly related to the green
infrastructure control measures as  necessary to
accommodate changes in model parameterization
caused by shifts in runoff hydrology from the green
infrastructure measures. The District shall then
use both the appropriate CSO model without the
green infrastructure measures, and the model that
includes the green infrastructure measures, to
simulate the sewershed's typical year performance
both with and without the  green infrastructure
measures in order to demonstrate the CSO volume
reduction.

If the green infrastructure post-construction
monitoring report submitted by the  District fails to
demonstrate that the green infrastructure control
measures have met the performance criteria
specified for such control measures, then within
180 days of submission of the report, the District
shall submit to EPA and the State a corrective
action proposal. The corrective action proposal
shall define the green or grey infrastructure
enhancements/expansions to be carried out to
address performance shortcomings and ensure the
performance criteria are met. The proposal shall
include a schedule for completion of all corrective
action measures and an updated post-construction
monitoring plan to evaluate whether the corrective
actions have resulted in the performance criteria
being met. The performance criteria forthe green
infrastructure sites/practices must be achieved
within [XX] years of entry  of the Consent Decree."

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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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