United States
Environmental Protection
M % Agency
2012 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
CITY OF OMAHA, NEBRASKA
Support Process Development for Assessing
Green Infrastructure in Omaha
JANUARY 2017
EPA 832-R-17-009
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, soil and plants absorb and filter the water. When rain falls on our roofs, streets, and parking lots,
however, the water cannot soak into the ground. In most urban areas, stormwater is drained through
engineered collection systems (storm sewers) and discharged into nearby water bodies. The stormwater
carries trash, bacteria, heavy metals, and other pollutants from the urban landscape, polluting the
receiving waters. Higher flows also can cause erosion and flooding in urban streams, damaging habitat,
property, and infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. At the scale of a city or county, green infrastructure refers to the patchwork of
natural areas that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a
neighborhood or site, green infrastructure refers to stormwater management systems that mimic
nature by soaking up and storing water. These neighborhood or site-scale green infrastructure
approaches are often referred to as low impact development.
EPA encourages the use of green infrastructure to help manage stormwater runoff. In April 2011, EPA
renewed its commitment to green infrastructure with the release of the Strategic Agenda to Protect
Waters and Build More Livable Communities through Green Infrastructure. The agenda identifies
technical assistance as a key activity that EPA will pursue to accelerate the implementation of green
infrastructure.
In February 2012, EPA announced the availability of $950,000 in technical assistance to communities
working to overcome common barriers to green infrastructure. EPA received letters of interest from
over 150 communities across the country, and selected 17 of these communities to receive technical
assistance. Selected communities received assistance with a range of projects aimed at addressing
common barriers to green infrastructure, including code review, green infrastructure design, and cost-
benefit assessments. The City of Omaha was selected to receive assistance in developing a process for
assessing green infrastructure.
For more information about Green Infrastructure, visit http://www.epa.gov/greeninfrastructure.
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Acknowledgements
Principal EPA Staff
Kerry Herndon, USEPA Region 7
Mandy Whitsitt, USEPA Region 7
Tamara Mittman, USEPA
Christopher Kloss, USEPA
Community Team
Jim Theiler, CSO and Sanitary Wet Weather, City of Omaha
Nina Cudahy, Stormwater Program Coordinator, City of Omaha
Marty Grate, Environmental Services Manager, City of Omaha
Kirk Pfeffer, Design Division Manager, City of Omaha
Selma Kessler, Stormwater Plans Review, City of Omaha
Pat Nelson, Omaha CSO Program Management Team
Perrin Niemann, Omaha CSO Program Management Team
Consultant Team
Carol Hufnagel, Tetra Tech
Dan Christian, Tetra Tech
Anne Thomas, Tetra Tech
John Kosco, Tetra Tech
Cover photo credits: Tetra Tech
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2012 EPA Green
Infrastructure Community Partner Program.
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Contents
About the Green Infrastructure Technical Assistance Program ii
Acknowledgements iii
Executive Summary 1
1 Project Summary 2
1.1 Project Goals and Objectives 2
1.2 Background 2
1.3 Report Contents 4
2 Assessment of Green Infrastructure Costs and Benefits 5
2.1 Objective 5
2.2 Methodology 6
2.2.1 Definition of Goals and Objectives 6
2.2.2 City of Omaha Document Review 6
2.2.3 Local Community Concerns 6
2.2.4 Project Types 7
2.2.5 Process Approaches 7
2.2.6 Project Costs 7
2.2.7 Qualitative Benefits 8
2.2.8 Case Study 8
2.2.9 Future Steps 8
2.3 Results 8
2.3.1 Project Type Gap Analysis 8
2.3.2 Process Approaches 11
2.3.3 Design Criteria 17
2.3.4 Project Cost Development 18
2.3.5 Project Qualitative Benefits 19
2.4 Sample Project Process Application 22
2.4.1 Project Data 22
2.4.2 Cost-Effectiveness Comparison 23
2.4.3 Qualitative Comparison 26
2.5 Next Steps 27
3 Design Standards and Standard Details that Incorporate Green Infrastructure 28
3.1 Purpose and Objectives 28
3.2 Methodology 28
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3.2.1 Stormwater Design Criteria within the Right-of-Way 28
3.2.2 Water Quality, Channel Protection, Flood Control, and Conveyance Standards 28
3.2.3 Green Infrastructure Guidance 28
3.3 Results 29
3.3.1 Stormwater Design Criteria within the Right-of-Way 29
3.3.2 Water Quality, Channel Protection, Flood Control, and Conveyance Standards 29
3.3.3 Green Infrastructure Guidance 30
4 Conclusions 31
5 References 32
I .sbles
Table 1. Stormwater Management Incorporated into the Omaha CSO program 3
Table 2. Gap Analysis for Green Infrastructure Evaluation 11
Table 3. Potential Investments for Qualitative Benefits 15
Table 4. Non-Monetary Benefits (Table 3-9 of 2009 LTCP) 19
Table 5. Non-Monetary Benefits (Program Sustainability Goals) 21
Table 6. Additional Non-Monetary Benefits (Triple Bottom Line Goals) 22
Table 7. 26th and Corby Phase I: Base Project Data 23
Table 8. Gray/Green Project Cost Comparison (Tunnel Only) 24
Table 9. Gray/Green Project Cost Comparison (Tunnel and Dropshaft) 25
Table 10. Gray/Green Project Cost Comparison 25
Table 11. Example Qualitative Benefit Scoring 26
Table 12. Tools to Support Evaluation Process 27
Figures
Figure 1. Project Type Gap Analysis 9
Figure 2. Original Flow Chart for Incorporation of Green Solutions into Combined Sewer Separation
Projects 12
Figure 3. Modified Green Infrastructure Evaluation Flow Chart 16
Figure 4: Median Weights of Non-Monetary Criteria (reference Table 4) 21
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Appendices
Appendix A Green Infrastructure in Coordination with Long Term Control Plan Projects
Appendix B Technical Memorandum - Existing Practices for Green Infrastructure and Stormwater
Management, City of Omaha
Appendix C Green/Gray Cost Comparison Process Table
Appendix D Financial and Non-financial Benefits Table
Appendix E Design Standards Comparison Tables
Appendix F Green Infrastructure Construction Details and Photos
Appendix G Pervious Concrete Pavement Design References
Appendix H Green Block Cost Calculation
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Executive Summary
The City of Omaha, with approximately 415,000 residents, covers an area of 130 square miles that
includes approximately 43 square miles of combined sewer area. The city is currently implementing a
combined sewer overflow (CSO) control program based on a Long Term Control Plan (LTCP; City of
Omaha 2009 and 2014a) approved by the State of Nebraska in 2009 and updated in 2014. The city's CSO
Control Program is estimated to cost approximately $2 billion (in 2012 dollars).
The goal of this project was to help the city compare green and gray infrastructure so that it can
understand costs and benefits. The city also wanted to understand the costs associated with routinely
treating the first Vz inch of runoff from all municipal projects, and assess how other municipalities
address runoff from municipal projects.
The project team reviewed the city's current process for evaluating green infrastructure in CSO projects
and made recommendations to improve the comparison of green and gray infrastructure. The team also
reviewed the city's design criteria to compare it to the requirements from other cities. The cost/benefit
approach was applied to an example 87-acre project area. A gray to green project cost comparison
found, for this 87-acre area, that green infrastructure was 2 percent less than gray infrastructure
assuming green infrastructure implemented throughout the project area.
Finally, the project team reviewed design standards and design details from 16 municipalities across the
United States to assess which programs had design criteria for rights-of-way. Only five of the reviewed
municipalities specifically addressed rights-of-way, with most requiring the area to follow the same
post-construction requirements as other projects (with some exceptions). The project team also
collected information on treatment requirements and design standards from these municipalities.
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1 Project Summary
The City of Omaha, Nebraska sought to implement cost-effective stormwater management practices
and green infrastructure more broadly as part of its municipal projects, and in the new and
redevelopment projects within its jurisdictional control. This project was intended to aid the city in the
development of processes and tools to improve consistency in decision making and reduce barriers for
inclusion of these practices.
The analysis documented in this report was primarily conducted in 2012 - 2013. Subsequent to the
efforts documented herein, the city implemented activities to more broadly evaluate the potential for
green infrastructure as part of the CSO control program. Those results were published in the document
"Conceptual Green Infrastructure Project Development Technical Memorandum," October 2014. The
findings of this report were also included in the Long Term Control Plan Update, completed in 2014.
I I lis and Objectives
Omaha's primary goal for this study was to facilitate additional green infrastructure implementation as
part of its CSO Control Program and other municipal projects. The city found that green infrastructure is
often excluded because it is not shown to be cost effective or because the normal implementation
process for a project does not have a clear point when green infrastructure is considered. This study was
designed to answer the following questions to achieve Omaha's green infrastructure implementation
goals:
1. How can the city compare the green and gray infrastructure so that it a) provides a more
comprehensive understanding of costs and benefits, and b) can be communicated to the
ratepayer or taxpayer?
2. What are the costs associated with routinely treating the first Vz inch of runoff from all municipal
street or sewer projects? How do other municipalities retrofit established streets with green
infrastructure?
1.2 Background
Omaha, population approximately 415,000 people, covers an area of 130 square miles that includes
approximately 43 square miles of combined sewer area., It is currently implementing a combined sewer
overflow (CSO) control program, based on a Long Term Control Plan (LTCP; City of Omaha 2009 and
2014a) approved by the State of Nebraska in 2009 and updated in 2014.1 The city's CSO Control Program
is estimated to cost approximately $2 billion (in 2012 dollars).
Traditionally, Omaha's stormwater management has been focused on water quantity control.
Stormwater practices that address both quantity and quality more recently have been incorporated into
the city's practices. This shift is due to a number of reasons, including the city's sustainability objectives,
Municipal Separate Storm Sewer System (MS4) requirements, and the desire to apply a variety of cost-
effective options for CSO control. This has led to a change from the traditional emphasis on flood control
to a stormwater quality and green infrastructure approach. This results in the need for various decision-
making methodologies to support the goals of more localized management of stormwater. Each project
1 See http://omahacso.com/resources/ltcpdocs/.
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type has a unique decision-making process. These project types include public and private projects, new
development and redevelopment, CSO- and non-CSO-related activities.
The City of Omaha evaluated the potential for green infrastructure as part of their CSO LTCP and
subsequently began to incorporate green infrastructure into a series of projects. Many of the projects
implemented include regional stormwater management areas, which provide detention and water
quality treatment to tributary areas of between 30 and 300 acres. Also, projects at specific city-owned
parcels (e.g. at wastewater treatment plant (WWTP) and pump stations) have included green
infrastructure. As of 2012, 14 of 29 sewer separation projects also included green infrastructure
components (since 2012, the city has implemented a significant number of additional green
infrastructure practices including large regional practices as all as traditional LID practices). As seen in
Table 1 below, parcel-based projects tend to be larger and more comprehensive, given the larger area
with which to implement green infrastructure practices. Sewer separation projects may be limited to
modifications within the right of way. Appendix A provides a list of all CSO projects under the LTCP,
including an explanation for projects where green infrastructure is not included.
Table 1. Stormwater Management Incorporated into the Omaha CSO program
CSO Project Type
Number of Projects with
Green Infrastructure/Total
Number of Projects (for that
CSO Project Type)
Description*
Type of Practices
Implemented
Parcel-Based
Projects (WWTP,
pump station, etc.)
4/4
Includes two pump
stations, a WWTP and a
CSO facility.
Bioretention, rain gardens,
permeable pavement, dry
detention, vegetated
swales, other.
Sewer Separation
Projects
14/29
7 new regional and LID
practices in parks.
5 expansions and
modification of existing
stormwater detention for
additional flow and water
quality benefits.
4 additional projects in
rights-of-way or on non-
park parcels.
Regional practices:
Detention basins (dry and
wet), constructed
wetlands, bioretention,
rain gardens, vegetated
swales, stream daylighting.
In other areas:
Curb extension
bioretention and
boulevard bioretention.
* Note: Some projects include multiple elements.
The city has also promoted green infrastructure through the MS4 program. This includes requirements
in the City of Omaha municipal code calling for water quality control of the first Vz inch of runoff for new
development or redevelopment projects. As a result, best management practices (BMPs), including
green infrastructure, have been incorporated into most new or redevelopment projects on individual
parcels. Municipal linear projects - such as road or utility projects - have been less consistent in
incorporating green infrastructure. Exceptions to the Vz inch of runoff standard apply when
imperviousness is not increased and where the runoff standard is deemed infeasible.
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1.3 Repi i tents
This report summarizes methods and findings for each of the questions identified under the objectives.
The major emphasis of the study was on methodologies to compare green infrastructure with traditional
controls to assist in decision-making and facilitate implementation. The report presents draft
methodologies that the city will further evaluate and refine for the assessment of green infrastructure in
Omaha (Section 2). The methods provided to assess green infrastructure within Omaha will also benefit
municipalities across the country, providing insights and lessons learned in the comparison of green and
gray infrastructure. Secondary activities included a review of approaches in other communities to
incorporating green infrastructure practices within the right-of-way, and technical and cost information
for right-of-way practices (Section 3).
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2 Assessment of Green Infrastructure Costs and Benefits
2.1 Objective
The goal of this component of the study was development of a structured method for comparing green
and gray infrastructure costs and benefits of city projects, particularly the city's CSO control program.
With significant investments in public works infrastructure, the city is implementing cost-effective green
infrastructure into CSO control projects and stormwater management practices in city parks and facility
projects (i.e., parcel-based projects). A major component of the city's CSO program includes sewer
separation projects within the existing combined sewer system that are a significant opportunity to use
green infrastructure. Some are localized projects to protect against basement backups and others are
system upgrades to remove stormwater from the combined sewer system. A method for evaluating
green infrastructure will contribute to maximizing the implementation opportunities when they can be
justified financially.
There are three objectives for this cost/benefit analysis and evaluation:
1. Consider costs and benefits from the perspective of the funding source used for project
implementation. These sources generally are wastewater ratepayers (for CSO projects) or
taxpayers (for road or stormwater projects). City departments need to be able to demonstrate
that investments are made wisely and are consistent with the core mission of the funding. As a
result, the identified financial benefits of green infrastructure in this study were more limited
than have been included in many triple bottom line analyses (a triple bottom line analyses
incorporates economic, social, and environmental benefits). Additional social, environmental
and financial benefits remain important, but are not quantified. These benefits may trigger
additional investment when the additional costs are relatively small or where other funding
sources are available.
2. Clarify the process by which decisions are made. While Omaha has implemented a number of
green infrastructure projects, at the time of this report the city was primarily limited to green
infrastructure regional practices. The city is interested in a broader application of green
infrastructure, which could require a change in the city's financial and technical decision-making
process to ensure that the impacts of selecting green infrastructure are perceived as beneficial.
The natural inclination in any decision-making process is to maintain the status quo in the
absence of a clear reason to change. Without a convincing reason to implement green
infrastructure, the tendency has been to exclude or limit its application. Therefore a study
objective was to better understand the decision points where the choice for green
infrastructure was being limited.
3. Develop processes that work within the existing framework of ordinances, standards and
policies that have been adopted by the city. These elements of city governance can require
relatively long lead times to modify. Retaining consistency with current language will simplify
the ability to move from concept to practice. The current standards include various exceptions
that apply when imperviousness is not increased or when green infrastructure is "infeasible."
Since many city projects (such as road or utility projects) do not impact the amount of
imperviousness, and when there is a lack of clear financial benefit demonstrated, green
infrastructure implementation is either limited or not included on the project. Thus, better
quantification of financial benefits will enable greater green infrastructure implementation.
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2,2 Methodology
In order to define an approach that would facilitate greater implementation of green infrastructure, city
staff conducted several workshops with various city staff in the environmental sector of city operations
to understand concerns and define objectives. Participants reviewed the current processes and
identified methods that would more comprehensively value the costs and benefits associated with
green infrastructure. A case study was performed to test the proposed methodology. Participants also
identified future actions. The following sections describe the steps in the process.
2.2.1 Definition of Goals and Objectives
Goals and objectives were developed early in the study and continually revisited. Goals and objectives
were developed in the context of the city's varied responsibilities that include ensuring compliance with
regulatory requirements (e.g. CSO control and MS4), making wise investments with ratepayer/taxpayer
funds, and retaining consistency with existing processes. These were incorporated into the previously
identified objectives.
2.2.2 City of Omaha Document Review
Prior to developing a process to evaluate green/gray cost effectiveness for the City of Omaha, a better
understanding of the local city standards and processes was required. In order to accomplish this, a
variety of city documents were reviewed and their application was discussed with city staff.
Thirteen documents identified by the city were reviewed for stormwater-related requirements and
recommendations, as well as policies and procedures applied in the CSO program. Of these, six
contained authoritative requirements. The six documents were primarily based on the authority of the
Municipal Code Section 32, Article V (City of Omaha 2015) and the Papillion Watershed Management
Plan. (Papillion Creek Watershed Partnership 2009) The document with the most extensive definition of
requirements is the city's Post-Construction Stormwater Management Planning Guidance (City of
Omaha 2011). The primary criterion relative to green infrastructure is treatment of the first Vz inch of
runoff. Generally this is applied to development projects that occur after 2008. This has not been
treated as a requirement for city projects implemented in the right-of-way, although it is identified as an
objective for sewer separation projects. Appendix B contains a technical memorandum detailing the
document review.
2.2.3 Local Community Concerns
City staff are expected to perform their responsibilities in a manner that considers the following:
Ensures compliance with regulatory programs (CSO and MS4).
Provides value to the ratepayer/ taxpayer.
Considers the long-term performance of constructed infrastructure.
The city staff work to balance these responsibilities, and this is reflected in a measured approach to
green infrastructure. One of the primary concerns relates to funding sources and availability of funds for
green infrastructure. The city is currently implementing a $2 billion (2012 dollars) CSO control program
that has resulted in a significant increase in wastewater rates. Typical residential rates increased from
approximately $10 to $37/month between 2006 and 2014. These rate increases have been applied to
customers throughout the wastewater service area, which includes both the City of Omaha and areas
served outside the city. While still below the national average, the rate of increase has resulted in
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scrutiny relative to the use of funds in the program. Funding sources for projects also include a mix of
sources based on the project purpose. This results in a need to understand and justify expenditures
relative to the core mission of the project funding source. Specifically, CSO program projects need to use
funds primarily to benefit the CSO program objectives. The cost/benefit evaluation needs to objectively
compare the options and inform decision makers on the relative costs and benefits that are provided in
the alternatives.
For MS4 compliance, the city has a modest stormwater fee that finances staff efforts associated with the
program. It does not fund capital projects. Therefore, green infrastructure implementation on MS4
projects is funded through non-stormwater sources. One source of funds the city has used is grant funds
from the State of Nebraska. This includes a grant program that assists MS4 communities. These funds
have been used by Omaha for demonstration projects and water quality features, as well as more
traditional stormwater management projects.
2.2.4 Project Types
A variety of project types are implemented in the City of Omaha. The city is responsible for CSO Program
projects and other city infrastructure projects (such as road improvements, streetscape and traffic
enhancement projects). Private entities implement development or redevelopment projects including
those at the site or subdivision scale. As part of the study, a review of various project types and how
green infrastructure is considered was evaluated. A gap analysis identified where green infrastructure
implementation could be expanded.
2.2.5 Process Approaches
The city has an established process for evaluating green infrastructure for CSO projects. Guidance is
provided for sewer separation projects in the Omaha Green Solutions Site Suitability Assessment and
BMP Selection Process Guidance Document (City of Omaha 2014a). Because the area of focus for the
cost/benefit evaluation was on sewer separation or linear project efforts, this was the primary guidance
document considered. The process described in this document was used as a foundation for a broader
assessment.
Since the existing process may not consider all costs and benefits, a review of the existing methodology
was undertaken to better understand which elements either encouraged or discouraged the use of
green infrastructure in projects. Aspects considered included the following:
Clear guidance for evaluating green infrastructure by project type.
Design criteria that are used to assess green infrastructure.
How costs and avoided costs over the project life-cycle are identified.
Methodology to account for semi-quantitative or qualitative benefits.
2.2.6 Project Costs
In order to develop a comprehensive cost-benefit analysis, all direct, indirect and avoided costs
associated with a given project need to be identified. The study identified the various cost components.
These were quantified for the specific case study. Additional discussion about costs can be found in
section 2.4.1.
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2.2.7 Qualitative Benefits
Qualitative benefits associated with a project may influence the alternative selection if the financial
analysis is relatively comparable. As used in this study, the term "qualitative" does not suggest that a
cost cannot be quantified. It is intended to indicate that the value of the benefit is either difficult to
determine or is not directly relevant to the core mission of the funding source. Qualitative benefits were
based on prior work by the city. As part of the LTCP development and implementation, community
values were defined and considered in the evaluation of alternatives. These community values relate to
some of the qualitative project benefits. In addition, the triple bottom line values used in methods such
as The Value of Green Infrastructure: A Guide to Recognizing Its Economic, Environmental and Social
Benefits from the Center for Neighborhood Technology (CNT) and American Rivers (2010) were
consulted to consider whether additional items were relevant in Omaha.
2.2.8 Case Study
An example project was evaluated in order to test the process that was developed. For this case study,
specific financial data were determined. The case study helped to identify information that would be
needed for a more consistent application of the process. The case study drew from one of the CSO LTCP
sewer separation projects, 26th and Corby Phase I. It was also supported by information from the
program management team (PMT) for the city's CSO program. This case study provided an opportunity
to test the process and evaluate process strengths and weaknesses.
2.2.9 Future Steps
Comparison of costs and benefits across multiple projects will require that the city have a structured
way of comparing the information. Much of the information required is outfall specific and difficult to
quantify. Future steps relate to development of a standard method of quantifying these benefits so they
can be considered in the project level analysis. A series of potential tools could assist in the analysis. The
content of these tools is described. Not all information can be simplified, and the ability to define the
process in an easy-to-apply tool may be limited.
23 Results
2.3.1 Project Type Gap Analysis
Green infrastructure can be a fundamental driver in the identification of a project or it can be included
as an enhancement to a project that has been identified to achieve a different primary purpose. Various
categories of projects were considered along with the method of assessing green infrastructure. Figure 1
shows the various project types and differences in how projects are approached.
The primary project types were identified based on the project purpose. Projects could include those
where green infrastructure is the main goal (both for CSO control or another objective), as well as
projects where stormwater management/green infrastructure was not the primary purpose, but rather
an enhancement. These project types include CSO program-related projects, such as sewer separation
(see item 5 in Figure 1 below); city infrastructure projects not directly related to the CSO control
program (item 6); and parcel-based projects through private or public development (item 7). Shaded
items on the figure identify processes that either need to be developed or could be strengthened.
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1. Project
Definition
2. Project
Type
3. Non Gl
driven
projects
4. Project
Type
7a. Apply
Established
Stormwater
Criteria
5a. Gl Cost
effectiveness
evaluation within
project limits
6b. Cost
effectiveness
evaluation outside
project limits
6c. Qualitative
Benefit Evaluation
6a. Cost
effectiveness
evaluation within
project limits
7. Parcel based
project in CSO or
non-CSO area
5c. Qualitative
Benefit Evaluation
5b. Gl Cost
effectiveness
evaluation outside
project limits
6. City
infrastructure
project in CSO/
Non-CSO area
2a. Specific Gl
project to aid in
CSO Control or
Other Purpose
5. CSO program
related project
upstream of outfall
in CSO area. Or RNC
project
Figure 1. Project Type Gap Analysis
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Stand-alone stormwater management/green infrastructure projects to support CSO control were
identified as part of the LTCP. Additional stormwater management projects can be identified to support
the LTCP throughout its implementation. Due to the effort required to develop an LTCP, most
communities do not attempt to make significant changes to the projects described in the LTCP, unless it
is part of a formal adaptive management process or it results from a wholesale review of the LTCP
approach. This can be problematic for integrating green infrastructure into the community, as a number
of otherwise appropriate projects may be installed before planners are able to consider green
infrastructure as part of the solution. In the City of Omaha, this barrier was addressed by the
commissioning of a green infrastructure study with the specific intention of identifying additional green
infrastructure projects and potential projects. In June 2013, the city selected a consultant to review
portions of the CSS and evaluate whether there are additional opportunities to reduce the CSO volumes,
magnitudes, or durations through the implementation of green infrastructure. A summary of this
analysis is included in section 3.3.2 of the 2014 LTCP update.
Sewer separation projects implemented within combined sewer areas are evaluated for green
infrastructure. Two limitations of this analysis were identified that hamper the use of green
infrastructure. The first is that full financial benefits associated with green infrastructure are not
quantified. Financial analysis is typically limited to the local project costs using a green infrastructure or
more traditional approach. The analysis is developed and documented by the project design engineer
who is not able to fully identify the costs and benefits associated with the project. Therefore, the
potential for green infrastructure to reduce costs in downstream projects are not defined. While
qualitative benefits are considered, there is not a specific approach to document or value these, limiting
the influence of qualitative benefits. The effective outcome is that decision makers do not have
complete information to use in making decisions about green infrastructure implementation. Activities
to enhance the process of quantifying benefits are identified in items 5b and 5c in Figure 1.
The second limitation is related to the methodology of the cost/benefit analysis. The sizing of green
infrastructure is based on a different criterion than what is used for evaluation of benefits. Size of green
infrastructure practices is based on controlling runoff from a 1-inch precipitation event. However, the
assessment of benefits is tied to the Omaha Regional Stormwater Design Manual, which is based on
managing flows from a 10-year event (City of Omaha 2014b). The general effect of this is that green
infrastructure provides minimal beneficial impact on the storm sewer design included in the project.
Since the completion of this EPA project in 2012, the city has worked to improve the evaluation of green
infrastructure and its benefits associated with CSO control, which has broadened the beneficial review
of green infrastructure.
City infrastructure projects (e.g. roadways) do not have a systematic approach for the evaluation of
green infrastructure based on a consideration of project cost, broader costs or non-financial benefits.
Process elements to address this gap are shown in items 6a, 6b, and 6c in Figure 1.
The proposed approach is intended to address the identified gaps as summarized in Table 2 below. The
questions that are pertinent to green infrastructure consideration include the following:
Is green infrastructure routinely evaluated for inclusion in the project?
Is green infrastructure the default choice for stormwater management prior to application of a
financial test?
Are the benefits associated with green infrastructure quantified only for the project area or are
they quantified for downstream impacts?
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Is the design criteria for green infrastructure clearly identified and is its performance evaluated
relative to that criteria?
Is there a consideration of other benefits from green infrastructure?
Table 2. Gap Analysis for Green Infrastructure Evaluation
Project Type
Primary
Purpose
Green Infrastructure
Routinely Evaluated
Green Infrastructure
Default Stormwater
Management
Approach
Comprehensive
Financial Benefits?
Clear Design Criteria
for Green
Infrastructure?
Assessment of Other
Community Benefits
Included?
Green
Infrastructure
Stand Alone
project for CSO
Control (2a)
CSO control
Not applicable
(N/A)
N/A
Yes
May include:
1-inch storm,
2-year and
10-year
control level,
as well as
water quality
(0.5" runoff)
Unclear
CSO Program-
Related (5b, 5c)
Sewer
separation
(CSO
Control or
Combined
Sewer
Renovation)
Yes
No
Financial
evaluation in
project area
only.
Expand to
outside of
project limits
(item 5b,
Figure 1)
May include:
1-inch storm,
2-year and
10-year
control level
Unclear.
Formalize,
(item 5c,
Figure 1)
City
Infrastructure
Project (6a, 6b,
6c)
Various
(e.g.
transportati
on)
No
No
No. Include
analysis
(items 6b and
6c, Figure 1)
No structured
process
Include, (item
6d, Figure 1)
Parcel-Based
Project (public or
private)
CSO or non-
CSO
Yes
Yes
Not required
% inch of
runoff
management
Not Required
2.3.2 Process Approaches
As part of the CSO LTCP, the city developed a process for assessing green infrastructure as an
enhancement to CSO control projects. The primary process was included in a flow chart entitled
"Incorporation of Green Solutions into Combined Sewer Separation Projects" (City of Omaha 2014a). As
part of this study, the process (Figure 2) was reviewed to better understand any barriers to
implementation of green infrastructure. Modifications were developed to enhance the process,
including clarification of design criteria, more comprehensive financial evaluation, and better description
and utilization of qualitative benefits.
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City of Omaha, Public Works Department
Green Solutions Implementation Flowchart
Already Identified
High Suitability Area
Yes
No
Assess Other Sites for
S ere e n i ng Le ve IS u ita b ility
Soils {high perm)
FP (proximity)
Topo (flatordepressions)
Cover (grass, pavements)
Ownership (public)
Yes
No
Document Findings
and Obtain City
Approval
No
Review Runoff Sources
Overland Flow
Concentrated Flow
Identify Potential BMP Controls
r
Conduct Engineering Evaluations
Update Hydrology
3Z
Abstractions
Storage
Timing
Storage
Timing
Refine Hydraulics
Downstream Infrastructure
BenefitsorReduced Potential
for Overflow
Yes
Quantify Relative Capital Cost
Impacts for Benefits of Savings
No
Document Finding
and Obtain City
Approval
No
Yes
Yes
No Green Solutions
Implemented
Yes
No Green Solutions
Implemented
Incorporate Design Elements
Figure 2. Original Flow Chart for Incorporation of Green Solutions into Combined Sewer Separation
Projects
12
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The most developed process is that used for evaluation of green infrastructure in CSO control projects.
This process is not currently applied to non-CSO city projects (such as road projects), but could be. Areas
for enhancement in the existing approach include the following.
2.3.2.1 Policy
Two fundamental policy items should be addressed in the approach to green infrastructure evaluation.
These include the following:
Ability of Green Infrastructure to Reduce or Replace CSO Facilities. Appendix O of the 2009 LTCP
(titled Green Solutions Guidance) stated that "[t]he incorporation of Green Solution projects into
the LTCP [was] not anticipated to have a significant impact on the structural CSO controls
proposed since these are designed to address large events." In other words, green solutions
were expected to enhance rather than modify structural controls. Appendix B recognized the
ability of green solutions to result in downsized facilities, however the benefits are not
quantified from a cost perspective. It is the recommendation of this review that the city affirm
the ability of green infrastructure to reduce required downstream CSO controls. Where
questions exist related to the ability to ensure long-term performance, or where the extent of
implementation is unclear, these concerns should be clarified and reasonable safety factors
applied. However, these safety factors should be approached in a manner that is consistent with
safety factors applied to other technologies.
MS4 Application to New Stormwater Discharges. Appendix O indicates that "there is the
potential to maximize [green solutions] benefit by making sure the projects conform to the city's
municipal separate sewer system (MS4) program requirement." The MS4 requirement is
generally to treat the water quality volume (first Vz inch) of runoff from new development. This
standard has not been applied in all city-owned projects. It is recommended that the city
consider all newly separated stormwater (e.g., that which discharges through a stormwater
outfall) as new development. For these flows, treatment of the first Vz inch of stormwater runoff
from the tributary area should be considered a fundamental part of the project.
2.3.2.2 Opportunity Identification
Current language for site location of green infrastructure indicates, "Site location criteria will generally
focus on sites that may be suitable for BMP implementation by virtue of their proximity to runoff
sources, their ability to capture and control large areas or the fact that they may present attractive
ownership potential." Practices that can control larger areas are preferred: "Very small basins (such as
single lots) may be suitable for some local controls but aren't likely to have a material runoff reduction."
Publically owned sites are also more feasible: "The ownership of the site will have a significant influence
on the site suitability." The net result is that the primary green infrastructure implementation has been
larger practices in parks, rather than distributed green infrastructure practices or those that require
work on private property.
Recommendation: Revised language that would help facilitate greater inclusion of distributed green
infrastructure includes:
Clarify potential and interest in implementing green infrastructure on private property where
property owners can act as partners.
Clarify street right-of-ways as potential locations for green infrastructure practices.
13
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2.3.2.3 Hydrologic Evaluation
The Green Solutions in Facility Design Guidance Document (City of Omaha 2014a, Appendix B) identifies
a 1.0 inch event as the design criteria for green infrastructure, and then refers the engineer to the
Omaha Regional Stormwater Design Manual (City of Omaha 2014b) to assess the runoff reduction
benefits. The hydrologic evaluation in the Manual is based on larger storm events than used for CSO
control, primarily the 10-year event. The 10-year event drives the sizing of storm sewer at the project
level and therefore cost savings within the project are difficult to quantify.
Recommendation: Revised language is suggested to clarify that the hydrologic objective for stormwater
management within the project is CSO control or water quality management. The CSO control objective
(control of the 1.0 inch storm event) would directly support downsized CSO facilities at the downstream
end of the system. These provide a direct cost benefit to the CSO program. The stormwater objective {Vz
inch of runoff control) should apply whenever stormwater is being removed from the combined system
(see Policy discussion above). This is to provide water quality treatment of newly separated stormwater
that previously received some treatment at the WWTP.
2.3.2.4 Cost Identification
The current approach includes a definition of life-cycle costs at the project level with and without green
infrastructure. Possible increases in level of service, reduction in gray infrastructure outside of the
project area, and community enhancement benefits are considered qualitatively. Typically, green
infrastructure must be shown to be cost effective or cost neutral to be included in the project. The CSO
program Green Solutions in Facility Design Guidance Document (City of Omaha 2009) recognizes that
"[green solutions] will reduce the overall runoff and result in smaller downstream infrastructure and
fewer sewer overflows" (p2), however, the value of this benefit is not defined. Without a comprehensive
cost accounting of the benefits, decision makers cannot fully appreciate the total financial benefits
associated with green infrastructure.
The project design consultant is assigned the responsibility of developing the financial analysis, including
the full life-cycle cost of green infrastructure and other infrastructure within the project area. If gray
infrastructure within the project area is reduced through the use of green infrastructure, this can be
assessed quantitatively. However, some of the complete cost effectiveness evaluation would require an
assessment of costs outside of the immediate project area. The project design consultant is not in
possession of the information necessary to quantify these potential cost savings. As a result, these
potentially significant financial benefits are not included in the cost/benefit analysis. Impact of green
infrastructure on downstream infrastructure is therefore limited to a qualitative assessment, which
carries much less weight in the decision-making process.
Recommendation: Revised language is suggested to expand the financial analysis beyond the costs of
the specific separation project. The objective is to identify comprehensive costs with and without green
infrastructure. These costs include capital, life-cycle and avoided costs.
2.3.2.5 Qualitative Benefits
The city has considered community enhancement and other environmental and social benefits in CSO
project definition, but has no specific criteria to determine whether this justifies funding of green
infrastructure practices that are not otherwise cost effective. Qualitative benefits could be considered
based on the public works mission of the city, or broader benefits.
14
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Public Works Benefits. Some public works benefits associated with green infrastructure are difficult to
quantify. Examples include the benefit provided by green infrastructure toward the level of service.
Green infrastructure helps to control a portion of the runoff volume. This is not apparent in standard
flow calculations because the peak of the hydrograph occurs after the storage capacity associated with
green infrastructure is full.
Recommendation: Revised language is suggested to identify and score the aspects of green
infrastructure that are relevant to the public works and wastewater core mission. Specifically, drainage
enhancements (which may provide additional basement backup protection), traffic calming (through
curb extensions) and reduced infrastructure (through road narrowing) are examples of improvements
that may be provided by green infrastructure and are relevant to public works.
Community Benefits. Community benefits beyond the mission of public works include such items as
aesthetic and property value improvements. Broader social and environmental benefits (e.g. triple
bottom line considerations) relevant to Omaha should be listed for consideration. The financial benefits
of these items can be quantified with TBL calculators, such as the one developed by CNT and American
Rivers (2010). However, community benefits are expected to be considered primarily from a qualitative
perspective. In the event that the financial evaluation is relatively close, the community benefits
associated with green may warrant consideration of additional project investment.
Recommendation: The city could formalize a series of benefits and a relative value (expressed as project
cost percentage) that would trigger implementation of green infrastructure. This could be applied as
follows (values are for illustration only):
Table 3. Potential Investments for Qualitative Benefits
Community and Public Works
Benefit Ranking
Implement Green Infrastructure if within
XX percent of base project value
High
5%
Medium
3%
Low
1%
None
0%
In summary, the existing process flow diagram is displayed in Figure 2. The modified process flow chart
with recommended revisions is included in Figure 3.
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City of Omaha, Public Works Department
Green Solutions Implementation Flow Chart
Already Identified
High Suitability Area
Do any of the following exist:
Publically-owned sites in area
Vacant sites in area
Roads disturbed in project
Existing storm sewered areas
No
Document Findings
and Obtain City
Approval
No
Yes «-
Review Runoff Sources
Overland Flow
Concentrated Flow
Identify Potential BMP Controls
Conduct Engineering Evaluations
Update Hydrology
Abstractions
Storage
Timing
Storage
Timing
Refine Hydraulics
Downstream Infrastructure
Benefits or Reduced Potential
for Overflow
Yes
Quantify Capital, Life Cycle, and
Avoided Cost Impacts for
Benefits of Savings
Yes
Incorporate Design Elements
No
No
Document Findings
and Obtain City
Approval
No
No
Yes
No Green Solutions
Implemented
Yes
No Green Solutions
Implemented
Consider Qualitative Benefits to the
Community
Costs within XX% and qualitative benefits
identified
Yes
Figure 3. Modified Green Infrastructure Evaluation Flow Chart
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23.3 Design Criteria
Green infrastructure could be (and has been) applied for CSO control, stormwater quality, and design
storm flow management. The design criteria as applied in Omaha are contrasted with other design
criteria used elsewhere in the country. The city specifically requested input on stormwater criteria that
are applied (or could be applied in the future) as comparison against current standards.
2.3.3.1 CSO Control Criteria
Omaha's LTCP is based on a presumptive level of control per EPA policy.2 In general, the city estimates in
their LTCP that overflow control measures proposed in the 2009 LTCP achieve frequency targets of 4-6
overflows/year and 85% annual volume control. As part of the green solutions guidance document, the
1.0 inch rainfall event was identified as a "knee of the curve" level of control for green infrastructure.3
This precipitation event is also estimated to represent an 85% volumetric control. In several of the CSO
communities that have emphasized green infrastructure (e.g., Philadelphia, Cincinnati), the control level
has been defined by a percentage control rather than frequency targets. In other communities with
significant green infrastructure (e.g., Louisville, Kansas City) CSO control levels are based on frequency
targets.
2.3.3.2 Stormwater Quality Criteria
The city's post construction stormwater standards are based on treatment of the first Vz inch of runoff.
The preference is for this treatment to be accomplished using various stormwater BMPs that also
control volume. As green infrastructure is implemented, the city recognized that this standard may
change in the future. A range of potential control levels should be considered from a water quality
perspective. These could range from control of various rain events. One standard that has been
discussed is control of the 85th or 90th percentile precipitation event. For Omaha, the 90th percentile
event is approximately 1.5 inch.
2.3.3.3 Channel Protection
The channel protection criterion is intended to prevent detrimental impacts on receiving channels and
streams. Detrimental impacts include erosive flows that destabilize the streambanks. The criterion
applied for channel protection is the two-year storm event. For this size storm, flows following the
project are to be less than or equal to the pre-project flow rate.
2.3.3.4 Drainage Design
Conveyance design standards are intended to reduce the risk of flood damage or inconvenience. A series
of criteria are identified in the Omaha Regional Stormwater Design Manual (City of Omaha 2014b). The
criterion is for no adverse impact. The design event is the 10-year storm for most sewers.
2 EPA's CSO Control Policy is at http://water.epa.gov/polwaste/npdes/cso/CSO-Control-Policy.cfm. The
"presumptive" approach is one of two alternatives a city must select in developing an LTCP; the CSO program must
meet one of a series of performance measures and is therefore "presumed to provide an adequate level of
control." (59 FR 18692, April 19, 1994).
3 The knee of the curve is "an analysis to determine where the increment of pollution reduction achieved in the
receiving water diminishes compared to the increased costs." (59 FR 18693) It is a way to compare the cost of
control alternatives with their respective performance.
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2.3.4 Project Cost Development
In order to compare the financial impact of green infrastructure as an either partial or complete
replacement of more traditional alternatives, all relevant costs within or external to the project need to
be quantified. The development of costs is challenging since the relationship between the project level
capital components and the downstream facilities is complex. In the combined sewer system (CSS), the
hydrologic control of stormwater (project objective) cannot be directly related to changes in
downstream CSO facilities. The rate of change is unique for each level of control. For example, as
stormwater is managed through green infrastructure, some CSO control facilities may be reduced in
size. Ideally, if green infrastructure is implemented throughout a large portion of the tributary area, the
CSO facilities may be avoided altogether. Sizing of CSO control facilities is related to multiple factors,
including the regulatory control criteria, the extent of implementation of green infrastructure and the
unique hydrologic and hydraulic conditions that determine the behavior of the sewer system. Facility
sizing may relate to total volume, flow rate or a combination of the two. Some of the complexities
involve the following relationships:
The non-linear relationship between stormwater runoff control and CSO control. For example,
removal of 100 gallons of stormwater does not translate into 100 gallons of CSO reduction. The
ratio is dependent on the system, the type of stormwater control implemented, and the control
target.
The non-linear relationship between CSO facility size and cost. There are economies of scale that
result in the marginal cost of construction of CSO facilities being much less than the average
cost. This needs to be recognized in a credible cost comparison between gray and green
infrastructure.
2.3.4.1 Cost Components
Each alternative considered for a particular project results in a variety of cost elements. These cost
elements include capital, operation and maintenance, and avoided costs. To define a full life-cycle cost,
all cost elements need to be considered. Cost components include the following:
Green infrastructure (distributed): Application of low impact development or site-scale
practices near the source of flow generation. Capital and operation and maintenance (O&M)
costs would be relevant. Costs are dependent on the sizing criteria, the type of practice, and
whether green infrastructure is implemented as part of another project or as a retrofit. Funding
for green infrastructure may be either public or private or shared.
Regional stormwater practices: Larger stormwater management practices include those such as
previously identified in the LTCP and identified as cost effective. Capital and O&M costs would
be incurred. Costs are dependent on land availability and configuration, sewers required to
transport flows, any partial sewer separation required, type of practice, and land ownership.
Local capacity improvements for basement backup protection: Local separation or combined
sewer replacement to protect basements from sewage backup. Cost components include capital
cost. O&M costs are related to pipe length rather than size. A cost savings includes the
reduction in property damage due to basement backup, but this is not a quantified cost.
Local capacity improvements for storm drainage: When sewers are separated, newly
constructed storm sewers are sized based on the Omaha Regional Stormwater Design Manual
(City of Omaha 2014b). Absent sewer separation, stormwater capacity improvements are rarely
implemented due to lack of funding source. Cost components include capital cost. O&M costs
would be associated with length of pipe. Cost savings include the reduction in property damage
or inconvenience due to flooding, but this is not a quantified cost.
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Major trunk sewer conveyance improvements: some major trunk sewers have inadequate
capacity for design conditions. Absent new stormwater outlets for CSO control, stormwater
capacity improvements are rarely implemented due to lack of funding source. Cost components
include capital and O&M costs. A cost savings includes the reduction in property damage or
inconvenience due to flooding, but this is not a quantified cost.
CSO Control: Sewer separation (direct stormwater discharge to new outlets), storage facilities
(such as tanks or tunnels), and treatment facilities (such as retention treatment basins (RTBs)).
Includes capital and O&M cost. Capital costs are highly dependent on extent and size (sewers,
tunnels), overall volume (basins) or type and rate of treatment (treatment facilities). O&M costs
for sewers are based on length as previously indicated. O&M for tunnels is primarily related to
pumping costs.
Pumping and wastewater treatment: Captured combined sewage will be conveyed through the
collection system for treatment. These costs include system upgrades and operations for the
captured flows. WWTP improvements included in the LTCP are primarily headworks
improvements, wet weather treatment for flows in excess of secondary capacity, and dewatered
tunnel flows. It is generally assumed that the sizing of these facilities would not change due to
green infrastructure implementation. Therefore, the cost component used in this analysis is
O&M. This is a unit rate that is primarily comprised of power and chemical expense associated
with treatment.
2.3.5 Project Qualitative Benefits
In addition to quantifiable cost differences between alternatives, there are other environmental and
social benefits that can be considered in a more comprehensive analysis. The city is interested in
considering specific triple bottom line benefits that would be accepted by the community at large and
rate payers specifically. As with the process approach, non-financial benefits applicable to city projects
were based on prior work included in the LTCP.
2.3.5. / Prior City Benefit Tool
Previously, the city developed a process for considering non-monetary benefits as part of the CSO LTCP,
which were developed with public input. The benefits were evaluated through the implementation of a
Decision Tool (2009 LTCP p 3-25). This Decision Tool included the non-monetary benefits identified in
Table 4 (Table 3-9 of 2009 LTCP).
Table 4. Non-Monetary Benefits (Table 3-9 of 2009 LTCP)
Category
Description
1. Water Quality
Improvement
Water quality improvements in the receiving streams above and beyond
the minimum requirements to comply with state and federal regulations.
This criterion also includes consideration for stormwater quality regulations
that may be required in the future. The water quality parameters include
bacteria, TSS, and floatables.
2. Reduction of Combined
Sewer Backups into
Basements and Existing
Odors
This category emphasizes those alternatives that in conjunction with
addressing the effects of CSOs on receiving streams, would either reduce
the number of sewer backups and/or reduce odors that occur at different
locations within the system.
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Category
Description
3. Reduction of Street
Flooding
This category emphasizes those alternatives that in conjunction with
addressing the effects of CSOs on receiving streams, would reduce the
backup of stormwater on to the city's streets.
4. Minimizing Community
Disruption
The minimization of community disruption that would occur during
construction of CSO solutions, including:
Minimizing neighborhood and business disruption
Minimizing community traffic impacts
5. Simplicity of Solutions
The simplicity of operations and maintenance of the proposed facilities and
the reliability of the facilities to function during wet weather events. This
category emphasizes proven technologies that are locally applicable.
6. Opportunities for
Infrastructure/Utility
Improvements
The potential for replacement of aging infrastructure, including:
Street and sidewalk improvements
Burying overhead power lines
Water main, gas main and sewer replacements
7. Compatibility with
Community
The long-term compatibility of an alternative with the community,
considering aesthetics and other benefits of the proposed facilities such as:
Consistency of solutions with existing zoning
Historic preservation of community
Remediated contamination
Compatibility with neighborhood
Restoration of property after project
Aesthetics of solution (footprint, noise, odors, traffic, and proximity)
Safety
8. Opportunities for
Community
Enhancements
This criterion includes the potential enhancements for the community
through construction of the projects. Enhancements could include green
space/parks, streetscapes, structures and other amenities and support of
future development in the community. Examples include:
Coordination with future development
Potential hiking/biking trail routes
Potential green space and parks
Enhancement of streetscapes
In the Decision Tool process, relative weights for each Non-Monetary Benefit were developed for the
CSO areas by the Community Basin Panel. Weights were applied by the Basin Advisory Panels for each
basin area. A review of these weighting factors suggests that values were relatively consistent, although
specific rankings were higher or lower based on unique characteristics of the individual basins. For
example, "reduction of sewer backups" and "infrastructure improvements" received higher weight in
the Minne Lusa basin and "reduction of street flooding" was scored highest in Saddle Creek.
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Median weighting for all basins is shown in Figure 4.
Alternatives were assessed by assigning a ranking of
1-5 for each benefit category (5 being highest
potential benefit). Once the total benefit score was
determined, it was divided by the present worth cost
of the alternative to determine a normalized project
benefit value.
2.3.5.2 City Sustainability Criteria
Sustainability criteria were considered In the LTCP,
and these criteria relate to non-financial goals. These
goals are discussed in the Omaha Green Solutions
Site Suitability Assessment and BMP Selection
Process Guidance Document (City of Omaha 2014a).
The City of Omaha has adopted broad sustainability
goals as part of the implementation of the CSO Figure 4. Median Weights of Non-Monetary Criteria
Control Program. It is the city's intention to (reference Table 4)
incorporate the concepts embodied by the goals into
projects implemented as part of the LTCP. The following Vision Statement has been established:
"The City of Omaha CSO Control Program will apply the principles of sustainability in a fiscally
responsible manner to add meaningful and lasting social, environmental, and economic benefits to the
implementation of the LTCP and serve as a model for the application of sustainability in the design,
construction, and operation of infrastructure." (City of Omaha 2009)
The process identified seven specific goals to support the implementation of the vision statement. Three
of the goals can be applied to infrastructure improvement projects. Those are listed in Table 5.
Table 5. Non-Monetary Benefits (Program Sustainability Goals)
Category
Description
1. Incorporate
Resource
Efficiency
Incorporate resource efficiency (e.g., energy efficiency, reduced construction
waste, reduced hazardous waste generation, recycling of concrete and asphalt)
into project design, construction and operation to reduce energy and material
use, reduce waste and provide economic benefit to rate-payers.
2. Incorporate
Multiple Benefits
Identify and implement opportunities for design practices that encourage
innovative thinking to produce multiple benefits, such as enhance
environmental protection, contribution to the control of CSOs and economic
benefit to rate-payers.
3. Natural Systems
Enhancements
Identify and implement natural system enhancements that contribute to the
control of CSOs, improve water quality and/or create valuable community
enhancements.
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2.3.5.3 Additional Benefit Considerations
As part of the EPA technical assistance project, other potential benefits were discussed. These benefits
were based on various triple bottom line calculators or tools such as published by CNT. These benefits
are identified in Table 6.
Table 6. Additional Non-Monetary Benefits (Triple Bottom Line Goals)
1. Environmental
Benefits
Additional environmental benefits such as air quality improvements, climate
change mitigation, energy savings, salt/ deicer use reduction, increased
infiltration, additional water quality benefits, ecosystem, habitat and wetland
improvements
2. Social Benefits
Recreation, aesthetic improvements, urban heat island reduction
3. Financial
Benefits (Indirect)
Energy savings, salt/ deicer use reduction, property value improvements,
landscape job creation
2,4 Sample Project Process Application
The cost/benefit approach was applied to the 26th and Corby Phase I project area. This is an 87-acre
project area within the CSO number 107 tributary area.
The purpose of the 26th and Corby Phase I Project is primarily to provide basement backup protection
for homes in the area. The design consultant (Tetra Tech) prepared project costs for this area. The
baseline alternative did not include a mechanism for stormwater management (other than conveyance).
The green infrastructure alternative assumed permeable pavement or bioretention to control
stormwater runoff from the critical CSO event.
The project team worked with the Omaha CSO Program Management Team (PMT) to define hydrologic
response and approximate costs associated with reductions in downstream CSO infrastructure
requirements.
2.4.1 Project Data
The 26th and Corby project area is located in the Burt Izard CSO basin. Flows from this area are tributary
to CSO 107. The system is interconnected with CSO 106.
The 26th and Corby project is a local sewer separation project that is being implemented to address
basement backup concerns. The project will effectively separate 87 acres of area internal to the
combined area. The stormwater outlet will be an existing combined sewer. Data for the 26th and Corby
Phase I project came from design memoranda that considered green infrastructure practices. At the
conceptual level, the project team selected permeable pavement with a storage layer for control of the
critical event that was associated with sizing of downstream CSO control facilities. Permeable pavement
was assumed in locations where pavement was disturbed due to sewer construction.
Downstream CSO infrastructure data was developed by the program management team (PMT). This
data included model results and assessment of reduced CSO facilities if the critical sizing event were
controlled. The impact of the 26th and Corby project was assumed to be the unit impact of a broader
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application of green infrastructure within the tributary area. Effectiveness of green infrastructure
presumes that it would be implemented broadly throughout the tributary area. The 26th and Corby
project on its own is not sufficient in magnitude to result in major change to the CSO controls.
Basic hydrologic data relative to the project area and the downstream CSO controls are shown in
Table 7. This analysis assumed a level of control equal to four residual overflows per year.
Table 7. 26th and Corby Phase I: Base Project Data
Description
Value
Unit
Area Tributary to CSO 107:
1413
acres
Precipitation volume (5th largest event)
0.95
inches
Total Precipitation volume (5th largest event)
36.46
MG
InfoWorks model predicted total runoff 5th largest event
0.24
inches
InfoWorks model predicted total runoff 5th largest event
9.23
MG
InfoWorks model predicted CSO volume 5th largest event
0.19
inches
InfoWorks model predicted CSO volume 5th largest event
7.20
MG
Annual runoff volume (to diversion)
286.5
MG
Total annual effective runoff volume
7.47
inches
Residual annual overflow volume (with four overflows)
40.5
MG
Net annual runoff to WWTP (following control)
246.0
MG
26th and Corby drainage area
87
acres
26th and Corby runoff volume 5th largest event
0.29
inches
Effective share of flow to tunnel (5th largest event)
0.44
MG
Annual 26th and Corby total runoff volume
18
MG
Annual runoff volume (that could reach treatment)
15.15
MG
2.4.2 Cost-Effectiveness Comparison
Four cost elements were defined and evaluated as part of the cost effectiveness comparison.
Project capital costs were based on project data for the 26th and Corby Phase I area. Regardless of green
infrastructure implementation, new storm and sanitary sewers would be provided to essentially the
same extent. Green infrastructure would be an additional component intended to accomplish CSO
reduction. Green infrastructure costs were based on the control of the 0.95 inch event, which
corresponded to the critical event associated with control of the downstream outfall. Costs were
developed for project alternatives without and with green infrastructure. The effective unit cost of
green practice installed volume was $1.33/gallon in this scenario. This is an incremental cost relative to
construction of green practices versus traditional surface restoration. A total of 635,000 gallons of
volume were included in the green infrastructure concept.
Operation and maintenance costs were determined based on relative changes in O&M for the gray and
green projects in the 26th and Corby Area. The primary difference in O&M is related to additional costs
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for permeable pavement maintenance. All other cost differences were minor and were not included in
the final calculations. A 50-year present worth was determined.
Avoided capital costs were determined based on a reduction in the size of the tunnel associated with
comparable green infrastructure installation throughout the 1431 acre tributary area. Costs for this level
of control were prorated to the project area under review. Present worth cost was assumed equal to
construction cost. For the critical event which drives the sizing of the tunnel, approximately 78% of the
stormwater runoff is converted to CSO gallons. (CSO volume for this event for this regulator is 7.2 MG
out of 9.2 MG of runoff). Because the tunnel continuously directs flow to treatment during the event,
the extent to which the tunnel is decreased in size is less than the CSO volume. The estimated tunnel
size decrease for this condition was estimated as 5.5 MG. Thus, the effective green infrastructure to gray
infrastructure installed volume ratio for this scenario is 9.2 MG/5.5 MG = 1.67.
Reduced capital costs for the tunnel for the case study were determined to be at a marginal rate of
$1.03/gallon. This is because the net effect of controlling this outfall using green infrastructure would be
a decrease in tunnel diameter from 17 to 16 feet. Control of this location would not significantly reduce
the tunnel length, an approach that would have a much greater impact on the marginal cost.
Should sufficient control of area and volume be provided through the implementation of green
infrastructure, there would be a potential for a dropshaft to be removed. With that additional capital
facility reduction, the marginal capital cost for the gray infrastructure becomes $2.45/gallon.
Avoided operation and maintenance costs for wastewater collection and pumping were provided by the
PMT. The value of $500/MG treated is consistent with the city's rate model. For the gray alternative the
volume of flow captured in the CSO facilities would result in more flow treated. Green infrastructure
enhances the evaporation and infiltration of stormwater runoff. Evaluations of installed green
infrastructure with controlled underdrains have demonstrated an effective annual reduction in runoff to
the sewer system of approximately 65%. Thus, the green infrastructure alternative was assumed to
reduce the total volume to treatment.
Results of the analysis are summarized in Table 8 and Table 9. A proposed green/gray cost comparison
process table is included as Appendix C.
Table 8. Gray/Green Project Cost Comparison (Tunnel Only)
Element
Gray Present
Worth
Green Present
Worth
Comments
26th/Corby Phase 1
$5,596,000
$6,442,000
635,000 gallons of permeable
pavement storage added
O&M of green
infrastructure
$229,809
$357,480
Permeable pavement
maintenance
Reduce CSO facilities
0
($410,566)
400,000 gallon tunnel reduction
Change in flow to WWTP
$39,090
($77,597)
Increased/reduced volume per
option.
Total
$5,864,898
$6,311,317
Green is 108% of gray cost
(present worth)
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Table 9. Gray/Green Project Cost Comparison (Tunnel and Dropshaft)
Element
Gray Present
Worth
Green Present
Worth
Comments
26th/Corby Phase 1
$5,596,000
$6,442,000
635,000 gallons of permeable
pavement storage added
O&M of green
infrastructure
$229,809
$357,480
Permeable pavement maintenance
Reduce CSO facilities
0
($980,210)
400,000 gallon tunnel reduction
Drop shaft eliminated
Change in flow to
WWTP
$39,090
($77,597)
Increased/reduced volume per option.
Total
$5,864,898
$5,741,673
Green is 98% of gray cost (present
worth)
The results for the cost-benefit analyses are presented in Table 10. These summary costs demonstrate
the need to look outside of the immediate project area to quantify the full benefit of green
infrastructure. When looked at only at the project level, the cost of green infrastructure is calculated to
be 17% greater than no green infrastructure. However, when the downstream benefits are quantified,
the complete costs are more competitive and may represent a decrease.
Table 10. Gray/Green Project Cost Comparison
Element
Gray Present
Worth
Green Present
Worth
Relative Difference
26th/Corby Phase 1
Construction Cost only
$5,596,000
$6,442,000
635,000 gallons of permeable
pavement storage added (apparent
15% increase in project capital cost)
O&M of green
infrastructure
$229,809
$357,480
Permeable pavement maintenance
(apparent 55% increase in O&M)
Total Project Life Cycle
$5,825,809
$6,799,480
Green 17% greater at project level
Total Project with
downstream benefits
considered
$5,864,898
$6,311,317
Green 8% greater with
comprehensive costs considered
Total Comparison with
green assumed
implemented throughout
tributary area
$5,864,898
$5,741,673
Green is 2% less with widespread
implementation and comprehensive
cost
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The case study location was selected due to availability of information for the 26th and Corby project.
This location is a particularly challenging one for green infrastructure to offset gray. This is related to the
fact that the overall tributary area is large and the downstream control is shared with other outfalls.
Nevertheless, the consideration of downstream benefits significantly offset the additional costs to
implement green infrastructure.
2.4.3 Qualitative Comparison
A qualitative scoring of the case study project is presented in Table 11. This scoring was prepared for the
base project, green infrastructure controls with an emphasis on permeable pavement and green
infrastructure with an emphasis on bioretention.
Table 11. Example Qualitative Benefit Scoring
Criterion
Criteria
Weight
Separation
with
Tunnel1
Permeable
Pavement
Bioretention
Comments
1. Water Quality
Improvement
14
1
1.25
1.25
Green solutions
slightly reduce
pollutant load in
residual overflows
2. Reduction of Combined
Sewer Backups into
Basements and Existing
Odors
19
1
1.25
1.25
Green solutions
help to reduce
peaks to
downstream sewers
3. Reduction of Street
Flooding
11
1
1
1
All solutions
address
4. Minimizing Community
Disruption
13
0
0
0
All equally
disruptive to
implement
5. Simplicity of Solutions
6
0
-1
-1
Concern that green
infrastructure
solutions are more
complex
6. Opportunities for
Infrastructure/Utility
Improvements
15
1
1
1
All solutions
address
7. Compatibility with
Community
11
0
0
1
Bioretention adds
aesthetic appeal
8. Opportunities for
Community
Enhancements
12
0
0.5
1
24th Streetscape
Totals
59
67.25
84.25
Note 1: The base 26th and Corby project includes local sewer separation to reduce basement backup and a
downstream tunnel for CSO control.
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2.5 Next Steps
In developing this analysis, several challenges were encountered. These issues should be evaluated as
part of future work.
The most complex aspect of the cost comparison is related to the potential changes in CSO facilities that
might result from implementation. For the case study, these costs were developed based on the specific
project application. When considering a major CSO facility, such as a tunnel, the costs can be impacted
by total volume required, length of tunnel required, number of dropshafts, etc. The overall cost of the
facility cannot be expressed as a $/gallon that applies across all ranges of green infrastructure
implementation. However, to perform the comprehensive analysis, an estimate of the CSO facility
savings is required.
Green infrastructure can be optimized by sizing it relative to a precipitation event that is comparable to
that which drives the sizing of the CSO facility. The program is currently using a 1.0 inch event as a
surrogate for this critical event. The LTCP recognized that various outfalls behaved differently in terms of
discharge frequency and critical event. This control target could be evaluated on an outfall by outfall
basis. In addition, updates to the city's LTCP may result in a review of control levels at some outfalls. This
may also modify the control target.
A listing of potential tools and the associated objectives is included in Table 12.
Table 12. Tools to Support Evaluation Process
Tool Description
Objective
Avoided Cost Definition
for CSO Control Projects
Defines the step function associated with reducing the size or extent of
CSO control facilities. Provides marginal cost data at various levels of
implementation.
Critical Event Selection
Tool
Defines "surrogate" sizing event for green infrastructure. Event is
intended to be approximately equivalent to the critical event that
determines the sizing of CSO control facilities. This is unique for each CSO
regulator tributary area. This is a refinement on the presumed 1.0-inch
event.
Green Infrastructure
Costing and Performance
Tool
Defines the capital and lifecycle costs for green infrastructure on a
unitized basis by practice type and location.
Defines the hydrologic response by practice including such items as
storage effectiveness during critical events and amount of water totally
removed from the system due to infiltration/ evaporation.
Avoided Operational
Costs for Flow
Reductions to Collection
System
Methodology to evaluate the present worth of the reduced flows to
treatment.
Level of Service
Evaluation for
Downstream Capacity
Methodology to relate green infrastructure storage volume to increased
downstream level of service and apply a value.
Non-financial Benefits
Methodology to rank various non-financial benefits and relate this to
increased project capital or life cycle cost. See Appendix D.
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3 Design Standards and Standard Details that Incorporate Green
Infrastructure
Purpose and Objectives
The City of Omaha desired to gain some perspective on and knowledge of what other municipalities
have in place regarding stormwater design criteria, particularly within the right-of-way, to help guide
future modifications to their own stormwater design standards. This information would provide an
approach to follow for their internal projects. Additionally, they were interested in viewing construction
details for green infrastructure practices previously constructed within the right-of-way and references
regarding pervious concrete pavement design. This interest was related to the limited direct experience
with these practices by city engineering staff and their desire to understand more specifically how green
infrastructure practices are designed. This section provides this information as well as the estimated
cost of incorporating green infrastructure within a standard street block. The specific objectives include:
1. Investigating and documenting municipal ordinances and standards that address the
applicability of stormwater design criteria within the public right-of-way.
2. Investigating and documenting municipal ordinances and standards within the Great Plains
states, which address stormwater quality, channel protection, flood control and conveyance.
3. Providing green infrastructure implementation guidance for right-of-way projects including
design details and costs.
Methodology
3.2.1 Stormwater Design Criteria within the Right-of-Way
Sixteen municipalities from across the United States were selected for review relative to how
stormwater management design criteria were addressed within the public right-of-way. In particular,
roadway resurfacing and widening were considered. Resources used for the investigation included
online ordinances and design manuals. The selected municipalities included Kearney, NE; Philadelphia,
PA; Suffolk, VA; Seattle, WA; Madison, Wl; Boise, ID; Lake County, IN; Muldraugh, KY; Bloomfield Hills,
Ml; Burnsville, MN; Scott County, MN; Urbana, OH; Harrison, OH; Concord Township, OH; San Antonio,
TX; and Corpus Christi, TX.
3.2.2 Water Quality, Channel Protection, Flood Control, and Conveyance Standards
Large municipalities within the Great Plains states were selected for investigation into their stormwater
quality criteria. Resources used for the investigation included on-line ordinances and design manuals.
The selected municipalities included Des Moines, IA; Kansas City, KS; Wichita KS; Minneapolis, MN;
Springfield, MO; St. Louis, MO; Lincoln, NE; Oklahoma City, OK; Tulsa, OK; Fort Worth, TX; and
Lubbock, TX.
3.2.3 Green Infrastructure Guidance
Green infrastructure practice construction details and photos were compiled from right-of-way projects
throughout the country. In addition, references for pervious concrete design were compiled. The
incremental cost of incorporating green infrastructure along a city block in conjunction with road
reconstruction was estimated.
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mlts
3.3.1 Storm water Design Criteria within the Right-of-Way
Of the sixteen municipalities reviewed, five were found to address projects within the right-of-way. The
remaining municipalities either had limited on-line information or remained silent on right-of-way
projects, although several stated that resurfacing activities were exempt from stormwater
requirements. The five municipalities listed below recognize right-of-way or transportation-related
projects as development. Appendix E, Table 1 provides specific language from these municipalities
regarding stormwater design criteria within the right-of-way.
Kearney, NE requires that right-of-way applications meet the same stormwater runoff quality
requirements as all other construction activity and land developments. Projects related to maintaining
the original design purpose of the facility are exempt.
Philadelphia, PA considers public or private street construction to be "new development" or
"redevelopment" and must follow the same post-construction stormwater management requirements
as any human-induced change to improved or unimproved real estate. Replacement of impervious
surfaces is "redevelopment." Maintenance activities including top-layer grinding and repaving are not
considered "redevelopment."
Suffolk, VA exempts linear development projects that disturb less than one acre of land per outfall or
watershed; cause insignificant increases in the peak flow rates (<1 cfs); and are located upstream of
areas with no existing, or anticipated, flooding or erosion problems. If the exemptions do not apply, the
linear development project must follow the city's stormwater performance standards.
Seattle, WA defines activity requiring a right-of-way permit to be "development." A transportation
redevelopment project is a stand-alone transportation improvement project that proposes to add,
replace, or modify impervious surface within a public or private road right-of-way that has an existing
impervious surface of 35 percent or more. Maintenance-only projects do not apply. Flow rate and water
quality standards (as part of the Design Review) apply for any proposed project subject to a
development permit AND meeting various other conditions. Transportation redevelopment projects
must follow the flow rate and water quality drainage review requirements unless they meet the
exemption criteria.
Madison, Wl states that municipal road or county highway projects that are not exempted under local
erosion control ordinances under state or federal statute, are exempt from runoff rate control if all of
the following conditions are met: 1) The purpose of the project is only to meet current state or federal
design or safety guidelines, 2) All activity takes place within existing public right-of-way, 3) All other
requirements of the Stormwater Management Plan are met; and 4) The project does not include the
addition of new driving lanes. As part of the Stormwater Management Plan, street reconstruction
projects shall include design practices to retain soil particles greater than 20 microns on the site
resulting from a 1-year, 24-hour storm event with no sediment resuspension.
3.3.2 Water Quality, Channel Protection, Flood Control, and Conveyance Standards
Of the eleven municipalities reviewed, eight of them did not have stringent water quality requirements
leaving two with set requirements and one not found. The majority of the municipalities had flood
control and conveyance standards. Channel protection in several municipalities was addressed by
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requiring the 1-year or 2-year post-development peak flow to match pre-development rates. Appendix
E, Table 2 provides specific language, as applicable, regarding water quality treatment, channel
protection, flood control, and stormwater conveyance for these municipalities.
3,3.3 Green Infrastructure Guidance
An assortment of green infrastructure construction details and accompanying photos are provided for
reference in Appendix F to aid in the future development of Omaha's design standards. Appendix G
provides additional design guidance references for pervious concrete pavement design.
The added cost of incorporating green infrastructure into a standard 350 foot city block as part of a road
reconstruction project is included in Appendix H. This table provides separate costs for using pervious
concrete and curb extension bioretention along a city block to capture the first %-inch of runoff from the
right-of-way only.
Providing pervious concrete in the parking lanes with eight inches of aggregate sub-surface storage is
sufficient enough to store the required volume of runoff. The additional cost of constructing the
pervious concrete for one block is approximately $16,000.
Incorporating a curb extension that is five feet wide by 44 feet long on each side of the street will
provide sufficient storage for the required volume of runoff. The additional cost of constructing the curb
extension bioretention for one block is approximately $8,000.
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4 Conclusions
For cities with combined sewer systems, the ability to compare green infrastructure practices with
traditional gray infrastructure practices is important in order to choose controls that both minimize
costs and maximize benefits. The City of Omaha has developed a process to incorporate green solutions
into combined sewer separation projects with recommendations made to improve the process to clarify
design criteria, more comprehensively evaluate finances, and better describe qualitative benefits. For
example, a recommendation was made to expand the financial analysis beyond the cost of the specific
project to also include comprehensive costs such as capital, life-cycle and avoided costs.
The cost/benefit approach was applied to an 87-acre project area within the CSO tributary area where
the primary goal was to provide basement backup protection for homes in the area. The main control
was sewer separation with permeable pavement and bioretention considered as green infrastructure
controls. By considering all cost elements (such as project capital costs, operation and maintenance
costs, avoided capital costs, and reduced capital costs), the comparison found that the cost of a green
project was approximately 2 percent less than the cost of a gray project.
To incorporate green infrastructure into CSO designs, construction details and design criteria are
needed. A number of municipalities were reviewed to assess their current requirements, with
comparisons of design standards (Appendix E) included in the report along with construction and design
details (Appendix F).
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5 References
Center for Neighborhood Technology (CNT) and American Rivers. 2010. The Value of Green
Infrastructure: A Guide to Recognizing Its Economic, Environmental and Social Benefits.
http://www.cnt.org/sites/default/files/publications/CNT Value-of-Green-lnfrastructure.pdf.
City of Omaha. 2009. Long Term Control Plan for the Omaha Combined Sewer Overflow Control
Program. October 1, 2009. http://omahacso.com/resources/ltcpdocs/
City of Omaha CSO Control Program. 2009. Refinement Phase Task 3Develop Sustainability Guidance
Document. Technical memorandum from Refinement Task 3 team to T. Heinemann. August 17, 2009.
http://omahacso.com/files/9313/6620/5291/SustainabilityGuidanceTM.pdf
City of Omaha. 2011. Post Construction Stormwater Management Planning Guidance. November 2011.
http://omahastormwater.org/development/post-construction/
City of Omaha. 2014a. Update to Long-Term Control Plan for the Omaha Combined Sewer Overflow
Control Program. Appendix B: Omaha Green Solutions Site Suitability Assessment and BMP Selection
Process Guidance Document.
http://omahacso.com/files/6814/1450/8302/Final Omaha LTCPUpdate-Appendices Qct2014.pdf
City of Omaha. 2014b. Omaha Regional Stormwater Design Manual.
http://www.omahastorrnwater.org/orsdni/
City of Omaha. 2015. Code of Ordinances for the City of Omaha, Nebraska.
https://www.mynicode.com/librarv/rie/omaha/codes/code of ordinances
Papillion Creek Watershed Partnership. 2009. Papillion Watershed Management Plan. April 2009.
http://www.papiopartnership.org/resources/publicatioi .02865415.pdf
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