EPA/600/A-14/127
Greening CSO Plans: Planning and
Modeling Green Infrastructure (Gl) for
Combined Sewer Overflow (CSO) Control
Collaborative effort of U.S. EPA's Office of Water,
Office of Research and Development, Office of Enforcement and Compliance
Assurance, and Region 5
(http://water.epa. gov/infrastructure/greeninfrastructure/upload/Greening_CSO_Plans. PDF)
3/26/2014
U.S. Environmental Protection Agency
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Greening CSO Plans: Planning and Modeling Green
Infrastructure (Gl) for Combined Sewer Overflow (CSO)
Control
Purpose of this technical resource:
- Assist communities in developing and evaluating Combined Sewer
Overflow (CSO) control alternatives that include green infrastructure
- Provide municipal officials as well as sewer authorities with tools to help
quantify green infrastructure contributions to an overall CSO control plan
Intended Audience:
Policy-oriented and technical professionals incorporating Gl into
CSO Long Term Control Plans (LTCPs)
U.S. Environmental Protection Agency
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Three Main Topics in the Resource
1) Regulatory and policy context - for incorporating Gl into
CSO control programs.
2) Process - how municipalities can use tools & models to
assess Gl alternatives
3) Tool demo - of a modeling tool that can help quantify Gl
contributions to a CSO control plan.
U.S. Environmental Protection Agency
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Integrating Green Infrastructure into the Federal
Regulatory Framework for CSO Control
Combined Sewer Overflow
(CSO) Control Policy (59 FR
18688(1994)).
Guidance to municipalities and State
and Federal permitting authorities on
controlling discharges from CSOs
through the National Pollutant
Discharge Elimination System
(NDPES) permit program under the
Clean Water Act. (Chapt. 2)
U.S. Environmental Protection Agency
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Implement the Nine Minimum Controls
Develop Long Term Control Plan
Characterize the combined sewer system and
receiving waters
Define CSO control targets to meet water
quality standards
Develop alternatives to meet CSO control
targets
Evaluate alternatives to meet CSO control
targets
Select cost-effective alternatives, analyze
financial capability, and develop schedule
Process for meeting CSO
Policy requirements with
gray infrastructure is
generally well
understood.
Process for meeting them
with a combination of
gray and green
infrastructure is less well
defined.
Implement Long Term Control Plan
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Phase I: Nine Minimum Controls
Proper operation and regular maintenance programs for sewer system and CSOs
Maximum use of collection system for storage
Review and modification of pretreatment requirements to assure CSO impacts are
minimized
Maximization of flow to publicly owned treatment works
Prohibition of CSOs during dry weather
Control of solid and floatable materials in CSOs
Pollution prevention
Public notification to ensure that public receives adequate notification of CSO
occurrences and CSO impacts
Monitoring to effectively characterize CSO impacts and efficacy of CSO controls
U.S. Environmental Protection Agency
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Phase II: Developing the Long Term Control Plan
• Develop and evaluate control alternatives, which can include Gl as a "Source
Control" measure (1995 EPA Guidance for LTCPs, Section 3.3.5.1)
• Implementing the Long Term CSO Control Plan
If LTCP includes Gl, adaptive management can be employed to monitor and
evaluate Gl projects. Opportunity to adapt or revise plans as needed based on
lessons learned
U.S. Environmental Protection Agency
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Quantifying Green Infrastructure Control Measures
as a Component of CSO Long Term Control Plans
Hydrologic and hydraulic models
(H&H, or stormwater mgt. models) -
used to simulate impact of
infrastructure changes on sewer
system and CSOs.
Complex H&H modeling tools
needed that simulate:
- Hydrology - Where does rainwater
go? How much flows into sewer
network?
- Hydraulics - volume and velocity of
flow in sewer network. How will
constructed infrastructure manage
and treat flows?
U.S. Environmental Protection Agency
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Choosing Gl Sites and Measures
A proposal for including Gl in LTCP must address (1) community and
political support, and (2) realistic potential for Gl implementation:
- Soil characteristics
- Land use/ownership
- Topography
- Property owner buy-in
- Financing and institutional factors
- Redevelopment rate
Once Gl sites and control measures have been selected, H&H
modeling can quantify how Gl will affect runoff and, in combination with
gray infrastructure, help reduce CSOs.
U.S. Environmental Protection Agency
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H & H / Stormwater Management Models
SWMM and related commercial products
(http://www.innovyze.com/products/infoswmm/), PCSWMM
(http://www. chiwater. com/Software/PC SWMM. NET/index. asp), XP-SWMM
(http://www.xpsoftware.com/products/xpswmm/), and MikeSWMM
(http://www. dhisoftware. com/mi keswmm/index. htm)
Info Works (http://www. innovyze. com/prod ucts/infoworks_cs/)
Mike Urban (http://www. dhisoftware. com/Prod ucts/Cities/MIKE URBAN, aspx)
SewerGems (http://www.bentley.com/en-US/Products/SewerGEMS/
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U.S. Environmental Protection Agency
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Case Study
Step 1 - Characterize the Combined Sewer System
Step 2 - Determine Baseline Scenario
Step 3 - Develop Gray Infrastructure Control Scenarios
Step 4 - Develop Green Infrastructure Alternatives
Step 5 - Analyze Gray/Green CSO Control Scenarios
U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEP1
Characterize the Combined
Sewer System
Imperviousness
20.00
40.00
60.00
80.00
RainGage
Pipe Diameter
U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEP 2
Determine Baseline scenario
Determine frequency and
magnitude of overflows under
current baseline conditions with
no CSO controls applied.
Annual Statrstk
Drv Weather Inflow (MG)
Stormwater Inflow (MG)
ifi6
70
Combined Systranfafbw (MG)
Treated Outf I oxv(MG)
456
428
Untreated Overflow f MG]
Plumber of Dayswrth Overflows
?B
64
CSS flow volumes for the case study area
in a typical year.
U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEPS
Develop a gray infrastructure
control scenario
Sewer separation, treatment
plant expansion, in-line storage,
and off-line storage/treatment
Add to, replace or modify
existing wastewater collection
and treatment system to
provide more capacity to handle
wet weather flows
Conceptual drawing of a CSO storage
facility.
U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEP 4
Develop Green Infrastructure
Alternatives
- Select an appropriate sub-set of Gl practices.
Establish design template for each
- For each CSS model sub-area, determine
total amount of impervious area that will be
treated by each Gl design
- Add this information into CSS model
- Run Gl-augmented CSS model with varying
levels of gray control to see combined effect of
green/gray on CSO
- Modify choices in step 2. Repeat steps 3 and 4
to see how different green control scenarios
reduce CSOs
U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEPS
Analyze Gray/Green CSO
Control Scenarios
Number of overflows with
varying gray infrastructure
storage volumes with different
gray and green CSO controls
I Gray Only Gray + Public Green «Gray+Full Green
1.2 1.6 2 3
Gray Infrastructure Storage Volume (MGal)
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U.S. Environmental Protection Agency
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Detailed Case Study of Incorporating Gl into a CSO
Model using EPA SWMM v. 5.0
STEP 5 cont.
Example: some options to meet a <
4 CSO requirement:
- 2 MGal storage + no Gl (gray only)
- 1.6 MGal storage + Gl on public property
- 1.2 MGal storage + Gl on public & private
property
I Gray Only Gray + Public Green «Gray+Full Green
1.2 1.6 2 3
Gray Infrastructure Storage Volume (MGal)
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U.S. Environmental Protection Agency
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