United States
Environmental Protection
Agency
EPA/600/X-09/003 | April 2007 | www.
earch for Wate
Infrastructure for the 21st Century
RESEARCH PLAN
Office of Research and Development
National Risk Management Research
- Water Supply and Water Resources Division
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EPA/600/X-09/003
April 2007
U.S. Environmental Protection Agency
Office of Research and Development
Innovation and Research for Water Infrastructure for the 21st Century
Research Plan
(4/30/07)
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Table of Contents
Executive Summary iii
Introduction 1
Condition Assessment of Wastewater Collection Systems 12
Condition Assessment of Water Distribution Systems 18
Rehabilitation of Wastewater Collection Systems 29
Rehabilitation of Water Distribution Systems 35
Advanced Concepts -Wastewater Collection-Treatment Systems 40
Advanced Concepts -Drinking Water Distribution Systems 63
Innovative Treatment Technologies for Wastewater and Water Reuse 69
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Executive Summary
Beginning in Fiscal Year 2007, the U.S. Environmental Protection Agency's (EPA) Office of
Research and Development (ORD) will be supporting a new research program to generate the
science and engineering to improve and evaluate promising innovative technologies and
techniques to reduce the cost and improve the effectiveness of operation, maintenance, and
replacement of aging and failing drinking water and wastewater treatment and conveyance
systems. This research program directly supports the Agency's Sustainable Water Infrastructure
Initiative (www.epa.gov/waterinfirastructure).
The program has been identified in the President's Fiscal Year 2007 Budget to receive $7 million
per year ($5 million wastewater, $2 million drinking water). The outputs from this program will
assist EPA's program and regional offices, states and tribes to meet their programmatic
requirements and utilities to more effectively implement comprehensive asset management,
provide reliable service to their customers, and meet their Clean Water Act and Safe Drinking
Water Act requirements. This research program recognizes that an essential component of
planning for water infrastructure is incorporating security aspects. Thus, the program will
coordinate with the water security program at the National Homeland Security Research Center.
This plan was developed in collaboration with key internal and external stakeholders. Key
internal stakeholders include the Office of Water and the EPA's Regional Offices. Important
external stakeholders include drinking water and wastewater utilities, the Water Environment
Research Foundation, the American Water Works Association Research Foundation and many
other federal, state and local agencies and departments, professional and trade associations, and
academia. The plan recognizes that stakeholder involvement and collaboration are critical to the
success of the planning, implementation and communication of this research program.
In March 2006, over 50 individuals representing key stakeholder organizations and considered
technical experts in the field were brought together for a two-day workshop to identify research
needs relating to drinking water and wastewater infrastructure. The products from that workshop
were a detailed meeting report (EPA, 2006a) and a comprehensive research issues report (EPA,
2006b) that served as foundation documents and helped to identify critical research gaps that led
to the recommendations in this plan.
The plan proposes work relating to condition assessment, system rehabilitation, advanced
concepts and innovative treatment technologies. Each section of this plan presents important
background information; analyzes the "state of the technology" and poses important research
questions that need to be answered to move the "state of the technology" forward through
innovation. The following high priority research, demonstration and technology transfer projects
are some that are proposed to help address the research questions:
in
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Condition Assessment of Wastewater Collection Systems:
- Technology Demonstration Program: Emerging and Innovative Technologies for the
Inspection of Wastewater Collection Systems
- Technology Transfer Product: Optimization of Closed Circuit Television Inspection
Data and Information for Effective Condition Assessment
Condition Assessment of Water Distribution Systems:
- Project Selection Tools: Value of Condition Assessment
- Basic and Applied Research: Investigations of Causes, Mechanisms and Predictability
of Failure to Enhance Condition Assessment Capability
System Rehabilitation of Wastewater Collection Systems:
- Technology Transfer Products: Collection System Rehabilitation Methods and
Technologies - State of the Technology
- Technology Demonstration Program: Emerging and Innovative Technologies for
Wastewater Collection System Rehabilitation
System Rehabilitation of Water Distribution Systems:
- Applied Research: Rehabilitation vs. Replacement Decision-making
- Technology Demonstration/Verification Program: Emerging and Innovative
Technologies for Pressure Pipe Rehabilitation
Advanced Concepts for Wastewater Collection-Treatment Systems:
- Develop and demonstrate innovative integrated sewerage system designs for new urban
areas, retrofitting existing urban areas, retrofitting existing combined sewer systems
(CSS), and upstream additions to existing CSS
- Conduct a worldwide search of the literature (including grey literature1), WERF,
AWWARF, EU, and other international organizations covering advanced sewerage-
system design and technology and from that effort, develop a refined research,
development and demonstration strategy
Grey literature - "Non -conventional literature (NCL, also called 'grey literature') comprises scientific and
technical reports, patent documents, conference papers, internal reports, government documents, newsletters,
factsheets and theses, which are not readily available through commercial channels. NCL specifically does not
include normal scientific journals, books or popular publications that are available through traditional commercial
publication channels." en.wikipedia.org/wiki/Grey_literature
IV
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Advanced Concepts for Drinking Water Distribution Systems:
- Retrospective and Prospective Assessments of Dual Systems for Potable and Non-
potable Uses
- Evaluate and Improve Distribution System Models
Innovative Treatment Technologies for Wastewater and Water Reuse:
- Nitrogen Control and Phosphorus Removal Technology Design Manuals
- Water Reuse Applications of Wastewater Treatment Technologies
- Wastewater Treatment Technology Evaluations
In addition, the proposed research, demonstration and technology transfer projects presented will
include work in several cross-cutting areas. Addressing these areas may require focused research
efforts or may require issue integration into broader research projects. These cross-cutting areas
include:
- Cost, cost effectiveness, cost benefit, and life-cycle costing
- Performance and outcome measurement
- Technology baseline development and "state of the technology" evaluations
- Decision support systems
- Systems modeling
- Integrated management systems
The plan recognizes that accountability is critical to the success of the program. Throughout the
implementation of the plan, clear and concise project performance indicators and programmatic
outcome measures will be developed and tracked. It is anticipated that these gauges of success
will include a range of human health, environmental, cost-effectiveness, infrastructure
performance, and customer service criteria. Also, the utility of program products will be
evaluated through interaction with customers, including the Office of Water, EPA Regional
Offices, state drinking water and water quality departments, and drinking water and wastewater
utilities. It is anticipated that project performance indicators will be project-specific and
developed as part of project planning. Programmatic outcome measures will be developed and
identified during the early stages of program implementation. To the extent possible, these
outcome measures will utilize data and information currently being collected that can provide
baselines and comparative analysis for a comprehensive, national view of program effectiveness.
The plan also provides preliminary sequencing of projects and resource estimates for a 5-year
time period. The implementation of this plan and final project timelines and resource
requirements will be the product of a dynamic process that will permit modifications to the plan,
as needed. As this plan is implemented and internal and external stakeholders are engaged and
new knowledge of ongoing research is attained, this plan will be reshaped to keep it current.
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This plan will become a tool for the Agency and ORD to demonstrate national leadership
through collaboration with our many stakeholders. One means to show national leadership
would be the establishment of a sustainable water infrastructure management and design research
center. This center of excellence in research for drinking water distribution systems and
wastewater collection systems infrastructure would be a competitively awarded, academic
research center. It is anticipated that this center will be a collaboration between several
universities that will come together to establish nationally recognized expertise to conduct
cutting edge research. This research center would establish a robust research program in
cooperation with ORD and key stakeholders. ORD has engaged the National Science
Foundation (NSF) and has established shared goals of collaborative research efforts, including
the potential for establishing an EPA-NSF engineering research center.
References
U.S. Environmental Protection Agency. 2006a. Innovation and Research for Water Infrastructure
for the 21st Century - EPA Research Planning Workshop - Draft Meeting Report, March.
U.S. Environmental Protection Agency. 2006b. Innovation and Research for Water
Infrastructure for the 21st Century - Water and Wastewater Infrastructure Draft Research Issues
Report, June.
VI
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Introduction
Purpose
This plan has been developed to provide the Office of Research and Development (ORD) with a
guide for implementing a research program that addresses high priority needs of the Nation
relating to its drinking water and wastewater infrastructure. By identifying these critical needs
through an inclusive process with internal and external stakeholders, ORD can select technology
research, development and demonstration projects for resource investment and can play a
national and international leadership role by cooperating and collaborating with its federal,
national and international research partners.
Background
In 2002, the Office of Water (OW) carried out a study to gain a better understanding of the
challenges facing the Nation's drinking water and wastewater utilities. In September 2002, the
Agency published "The Clean Water and Drinking Water Infrastructure Gap Analysis" (EPA-
816-R-02-020), also known as the "Gap Analysis" report. The report identified several issues
that raised concern as to the ability of utilities to keep up with their infrastructure needs in the
future:
- Our wastewater and drinking water systems are aging, with some system components
exceeding 100 years in age.
- The U.S. population is increasing and shifting geographically. This requires investment
for new infrastructure in growth areas and "strands" existing infrastructure in areas of
decreasing population.
- Current treatment may not be sufficient to address emerging issues and potentially
stronger regulatory requirements.
- Investment in research and development has declined.
In the report, the Agency estimated that if spending for capital investment and operations and
maintenance (O&M) remained at current levels, the potential gap in funding for the years 2000
through 2019 would be approximately $270 billion for wastewater infrastructure and $263
billion for drinking water infrastructure2.
In an introduction to the Gap Analysis report, the Assistant Administrator for Water stated,
"While much of the projected gap is the product of deferred maintenance, inadequate capital
replacement, and a generally aging infrastructure, it is in part a consequence of future trends we
2 The analysis estimated a 20-year capital gap for clean water of $ 122 billion ($6 billion per year) in 2001 dollars.
For drinking water, we estimated a capital gap of $ 102 billion ($5 billion per year). The O&M gaps for clean water
and drinking water were estimated at $148 billion ($7 billion per year) and $161 billion ($8 billion per year),
respectively. The report also estimated the capital and O&M gaps under a "revenue growth" scenario whereby
spending levels by the water industry are projected to increase at a real rate of 3 percent per year, which is consistent
with the economic growth forecast in the President's budget. Under the growth scenario, the capital gaps for clean
water and drinking water were $21 billion and $45 billion, respectively.
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can anticipate today, such as continuing population growth and development pressures. Yet,
funding gaps need not be inevitable. They will only occur if capital and operations and
maintenance spending and practices remain unchanged from present levels."
The Gap Analysis report and other work have helped focus more attention on the importance of
sustainable water infrastructure. EPA has acknowledged that some communities may have a
difficult time meeting future water infrastructure challenges. However, EPA also realizes that a
much bigger challenge is changing how the Nation views, values, manages and invests in its
water infrastructure. EPA's Sustainable Water Infrastructure Initiative (SI) acknowledges that
through the use of effective and innovative approaches and technologies, a commitment to long-
term stewardship of our water infrastructure, and collaboration with all key stakeholders, we can
make better use of our resources, potentially reduce the funding gap and move the Nation's water
infrastructure down a pathway toward sustainability. This is clearly stated in the SI vision
statement:
We will collaborate with our external stakeholders and,
through research and development, seek innovative
approaches and new technologies to help ensure that the
Nation's water infrastructure is sustainable through better
management and operations, improvements in water
efficiency, full cost pricing of water supply and wastewater
treatment, and watershed-based approaches to solving
water quality and water quantity problems.
The Agency views its primary role as that of an advocate for sustainable water infrastructure.
Led by the Office of Water and supported by many other Program Offices and the Regions, SI
represents a collaboration with public and private utilities and municipal governments that
provide drinking water and wastewater services; state and tribal water and wastewater programs;
drinking water and wastewater equipment manufacturers and consultants; academia; and
environmental advocacy groups.
The Office of Water has taken the leadership role in implementing SI and is relying on key
support from other EPA Program Offices and Regions, especially ORD, which can provide
critical support in identifying new and innovative approaches and technologies, and in
transferring the results of its research in a form most useful to the wide range of stakeholders.
While the Agency has initiated SI to focus its efforts on addressing the needs of the Nation's
water infrastructure, there is an emerging movement within the drinking water and wastewater
industry towards the adoption of comprehensive asset management. A recent U.S. Government
Accountability Office (GAO) report recognizes that utilities that have started adopting
comprehensive asset management are reporting several beneficial aspects to their operations. In
particular, by collecting, sharing, and analyzing data and information on their capital
infrastructure assets, utilities are allocating their resources more effectively and making better
decisions on the level of investigation needed and whether to rehabilitate or replace aging assets.
(GAO, 2004)
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The Agency recognizes the value of comprehensive asset management and OW currently
sponsors many initiatives that encourage its application by water utilities through partnerships
with industry associations, state and university-based training programs, and the establishment of
technical assistance centers. Clearly, drinking water and wastewater utilities are beginning an
"asset management paradigm shift" and this research plan has been developed recognizing the
changing nature of water infrastructure management.
ORD has long recognized the need for research and development in the area of drinking water
and wastewater infrastructure. Most recently, during the summer of 2005, in support of the
Agency's SI activities, ORD put forth a proposal for a new research and development program
entitled, "Innovation and Research for Water Infrastructure in the 21st Century."
The purpose of this program is to generate the science and engineering to improve and evaluate
promising innovative technologies and techniques to reduce the cost and improve the
effectiveness of operation, maintenance, and replacement of aging and failing drinking water and
wastewater treatment and conveyance systems. The outputs from this program will assist
utilities to more effectively implement comprehensive asset management, provide reliable
service to their customers, and meet their Clean Water Act and Safe Drinking Water Act
requirements. This research program recognizes that an essential component of planning for
water infrastructure is incorporating security aspects. Thus, the program will coordinate with the
water security program at the National Homeland Security Research Center.
The program will be based on a public-private research approach and will be conducted in
cooperation with key stakeholders to ensure that outputs meet users' needs, and to optimize
collaboration and technology transfer. ORD is best suited to provide the overall leadership of
this research program. This recognition is based on ORD's mission, breadth of perspective,
impartiality, objectivity, experience, and scientific and technical capability. A renewed ORD
presence in water infrastructure research will serve as a catalyst for innovation and will enhance
the opportunities for collaboration and leveraging with relevant Federal and international
research programs, states, academia, and utilities.
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In the 2005 research proposal, two major program areas were identified. The first was "Better
Management of Existing Wastewater Collection System Infrastructure" and includes the
following:
- Research and evaluation of inspection, condition assessment, and cost estimating tools
for existing collection systems to: enable more optimized repair, rehabilitation, and
replacement scheduling and budgeting; extend the service life of installed wastewater
infrastructure; reduce failures and their adverse public health, collateral damage,
economic, and other effects; and foster improvements in precision repair and
rehabilitation equipment and procedures
- Research and evaluation of performance and cost of innovative repair, rehabilitation,
and replacement technologies and procedures for wastewater collection systems to
expand and accelerate the technical options and data available for utilities to select
optimal, timely, efficient, and durable repair, rehabilitation, and replacement for
deteriorating wastewater infrastructure
- Investigation of advanced design concepts for wastewater collection systems such as
real-time control options and advanced drainage concepts (e.g., upland attenuation
before sewer system entry) that reduce construction costs and increase carrying
capacity and storage capabilities
- Evaluation of novel techniques to improve performance and extend service life of
existing systems by addressing problems associated with factors such as: sediments;
fats, oils, and grease; pH; corrosion, etc.
- Limited full-scale demonstration of most promising technologies and techniques
The second program area was "Increasing Water Efficiency in Drinking Water Distribution
Systems" and includes the following:
- Research and evaluation of innovative approaches to detect, locate, characterize, and
repair leakage in distribution systems to conserve source water, reduce capital and
operating costs, and reduce contaminant intrusion potential during low pressure
conditions
- Research and evaluation of innovative approaches to inspect and assess the condition of
high risk water mains to enable more optimized repair, rehabilitation, and replacement
scheduling and budgeting; extend the service life of installed drinking water mains;
reduce failures and their adverse public health, collateral damage, economic, and other
effects; and foster improvements in precision repair and rehabilitation equipment and
procedures
- Limited full-scale demonstration of the most promising technologies and approaches
Research Issues
As this plan has been developed, research issues have emerged that reflect the current technical
challenges that face drinking water and wastewater utilities. These challenges have also driven
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the Agency to launch and implement its SI program, as described earlier. In addition, the general
move of utilities towards the use of comprehensive asset management is transforming
infrastructure management and will impact the application of innovative technologies and
techniques that will emerge from this program.
The research issues presented in this plan have evolved into four major areas. These areas
generally conform to and support comprehensive asset management. The research issue areas
are condition assessment; system rehabilitation; advanced concepts; and emerging and
innovative treatment technologies for wastewater and water reuse.
Condition assessment encompasses the collection of data and information through direct
inspection, observation and investigation and in-direct monitoring and reporting, and the analysis
of the data and information to make a determination of the structural, operational and
performance status of capital infrastructure assets. Research issues in this area relate to the
collection of reliable data and information and the ability of utilities to make technically sound
judgments as to the condition of their assets. Condition assessment also includes the practice of
failure analysis which seeks to determine the causes of infrastructure failures in order to prevent
future failures.
System rehabilitation is the application of infrastructure repair, renewal and replacement
technologies in an effort to return functionality to a drinking water or wastewater system or sub-
system. The decision-making process for determining the proper balance of repair, renewal and
replacement is a function of the condition assessment, the life-cycle cost of the various
rehabilitation options, and the related risk reductions.
Advanced concepts relate to the application or adoption of new and innovative infrastructure
designs, management procedures and operational approaches. The infusion of these advanced
concepts into an established drinking water distribution or wastewater collection system is
especially challenging. These innovative concepts can "evolve" in existing systems through
system retrofit opportunities, but their compatibility with the in-place infrastructure system is
critical. As existing systems expand with new development, the opportunity for the application
of advanced concepts grows. These new sub-systems become opportunities for demonstrating
the effectiveness of new and innovative concepts. The advanced concepts relating to integrated
management go beyond comprehensive asset management and include maximizing benefits from
low impact development, water reuse, source water protection and watershed management. For
utilities with responsibilities for and jurisdiction over both drinking water and wastewater
systems, the institutional challenges to integrated management may be reduced. These utilities
may be potential test beds for these integrated water resources and infrastructure management
approaches.
Innovative treatment technologies for wastewater and water reuse address the dynamic
requirements for improved water quality and the growing demands for safe and reliable
reclaimed wastewater and stormwater. The need for more cost-effective wastewater treatment
technologies is being driven by many factors. There is a growing challenge to more effectively
manage and treat peak wet weather flows at wastewater treatment plants, especially focusing on
the effectiveness of pathogen reduction. New and emerging contaminants, such as endocrine
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disrupting compounds (EDCs), pharmaceuticals and personal care products, present challenges
not only relating to their fate through a wastewater treatment plant, but to their potential capacity
to interfere and inhibit treatment effectiveness. The control of nitrogen and phosphorus is a
growing priority, especially in the basins that drain to the Mississippi River, Great Lakes and the
Chesapeake Bay. There is an ever present demand for wastewater treatment technologies that
are more energy efficient and produce smaller volumes of residuals. The use of reclaimed
wastewater and stormwater is increasing at a rapid pace around the country, especially in the arid
Southwest, California and Florida. Depending on the nature of the "source" water and the
intended reuse application, treatment requirements may exceed tertiary levels and demand the
use of advanced filtration and membrane technologies.
Partnership Research Organizations
The development of this plan included the participation of several research organizations that are
actively involved in a wide range of programs relating to drinking water and wastewater
infrastructure, and many other related water resources and water quality issues. These
organizations represent national and international research interests, as well as many academic
institutions. The following are brief descriptions of the research organizations engaged in the
development of this plan:
Water Environmental Research Foundation (WERF) - This organization is the research arm
of the Water Environment Federation (WEF), a not-for-profit technical and educational
organization with members from varied disciplines who work toward the preservation and
enhancement of the global water environment. Formerly known as the Water Pollution Control
Association, WEF is the leading professional organization representing the interests of the
wastewater collection and treatment industry. WERF manages water quality research through a
public-private partnership between municipal utilities, corporations, academia, industry, and the
federal government. WERF has a research portfolio valued at nearly $60 million with more than
200 completed and ongoing research projects. WERF research supports more than 250
subscribers, including local municipal wastewater and stormwater agencies in 40 states
representing nearly 70 percent of the sewered U.S. population and several agencies in other
countries. WERF typically funds nearly $7 million in new projects each year.
American Water Works Association Research Foundation (AwwaRF) - This organization is
the research arm of the American Water Works Association (AWWA), an international nonprofit
scientific and educational society dedicated to the improvement of drinking water quality and
supply. AWWA is the largest organization of water supply professionals in the world. Its more
than 57,000 members represent the full spectrum of the water community: treatment plant
operators and managers, scientists, environmentalists, manufacturers, academicians, regulators,
and others who hold genuine interest in water supply and public health. Membership includes
more than 4,700 utilities that supply water to roughly 180 million people in North America.
AwwaRF is a member-supported, international, nonprofit organization that sponsors research to
enable water utilities, public health agencies, and other professionals to provide safe and
affordable drinking water to consumers. AwwaRF is largely funded by member organizations
that voluntarily subscribe in order to support and benefit from the water-related research. Almost
900 water utilities and more than 50 water-related consulting firms and manufacturing
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companies currently subscribe to AwwaRF. AwwaRF has sponsored more than $370 million in
research, represented by more than 600 completed research projects while subscribers provide
more than $10 million annually to fund research.
Global Water Research Coalition (GWRC) - Founded in 2002, GWRC is an international
water research alliance made up of some of the world's leading water research organizations.
GWRC is a non-profit organization that serves as the mechanism for collaborative water research
across the globe. GWRC focuses on urban water supply and wastewater issues and renewable
water resources, and leverages funding and expertise among the participating research
organizations, coordinates research strategies, secures additional funding not available to single
research foundations, and actively manages a centralized approach to global water issues.
GWRC members are:
- Awwa Research Foundation (United States)
- Cooperative Research Center for Water Quality and Treatment (Australia)
- EAWAG - Swiss Federal Institute for Aquatic Science and Technology (Switzerland)
- Kiwa (Netherlands)
- PUB (Singapore)
- Suez Environmental - International Research Center on Water and Environment-
CIRSEE (France)
- Stowa - Foundation for Applied Water Research (Netherlands)
- DVGW TZW - German Waterworks Association - Water Technology Center
(Germany)
- United Kingdom Water Industry Research (United Kingdom)
- Anjou Recherche - Veolia Water (France)
- Water Environment Research Foundation (United States)
- Water Research Commission (South Africa)
- WateReuse Foundation (United States)
- Water Services Association of Australia
The U.S. Environmental Protection Agency is the first partner of the GWRC. A partnership
agreement was signed in July 2003.
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U.S. Department of Transportation, Pipeline and Hazardous Materials Safety
Administration (PHMSA), Office of Pipeline Safety (OPS) - OPS conducts and supports
research to support PHMSA regulatory and enforcement activities and to provide the technical
and analytical support for planning, evaluating, and implementing the OPS programs. OPS
sponsors research and development projects focused on providing near-term solutions that will
increase the safety, cleanliness, and reliability of the Nation's oil, gas and hazardous materials
pipeline systems. Recent R&D projects are focused on, leak detection; detection of mechanical
damage; damage prevention; improved pipeline system controls, monitoring, and operations;
and, improvements in pipeline materials. These projects are addressing technological solutions
that can quickly be implemented to improve pipeline safety.
National Research Council Canada, Institute for Research in Construction (NRC-IRC) -
NRC-IRC is the leading construction research agency in Canada. Equipped with world-class
facilities, NRC-IRC carries out applied and contract research on issues of strategic importance to
the Canadian construction sector. Through an integrated, multidisciplinary approach, NRC-IRC
assists the sector to become more competitive through innovation and to foster the provision of
safe and sustainable built environments. NRC-IRC's Urban Infrastructure Research Program
develops technologies for the design and rehabilitation of infrastructure systems, and innovative
tools and techniques for the evaluation and management of these systems. The research focuses
on buried utilities, urban roads and concrete structures and sustainable infrastructure for water
and wastewater systems.
University Research Organizations - Several universities conducting research and
development in the areas of drinking water and wastewater infrastructure have participated in
activities leading to the development of this plan. Examples include:
- Penn State University, Pipeline Infrastructure Research Center
- University of Houston, Center for Innovative Grouting Materials and Technology
- Louisiana Tech University, Trenchless Technology Center
- Polytechnic University of New York, Department of Civil Engineering
Evaluation Criteria
In formulating this plan, criteria were developed to guide the evaluation and selection of the
programmatic areas in which to conduct research. As mentioned above, the overall goal of this
research plan is to generally support the Agency's efforts to address the wide range of problems
and issues relating to the Nation's aging water infrastructure. While it is a given that research
programs and projects conducted as a result of this plan will support sustainable water
infrastructure, more discriminating selection criteria were needed to make program and project
prioritization and investment decisions.
The following criteria are based on strategic directions set in plans established at the Agency,
ORD and national laboratory levels. These plans set environmental and institutional goals to
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guide our organizations and professional staff. For this ORD research plan, these goals have
been translated into selection and evaluation criteria.
- Client and Stakeholder Needs: The program or project meets specific needs articulated
by clients and stakeholders.
- Cost Effectiveness: The program or project leads to innovations in management,
science, or technology that provide added value (i.e., overall, long-term benefits of
implementation exceed costs).
- Programmatic Impact: The program has the potential to produce significant,
measurable outcomes supporting environmental goals.
- Collaboration: The program or project can be conducted in collaboration and
cooperation with other research and stakeholder groups.
- National Leadership and Visibility: The program or project exhibits national leadership
within the Agency and with external research and stakeholder groups.
- Technical Expertise: The program or project builds on existing ORD technical
capabilities or, through its conduct, helps to develop new capabilities.
Program Guidance and Outcomes
It will be very important to the success of this research program to develop program guidance
and outcome measures. Several internal and external stakeholders suggested that we further
develop and apply criteria through infrastructure assessments to help refine our research
priorities and infrastructure research needs. Within research areas identified in this plan, these
criteria will help further delineate research priorities by providing insights into which
infrastructure assets and systems may be most vulnerable to high risk failures. It is planned that
assessments of water infrastructure will be conducted on national and regional levels. For
example, if a predominance of wastewater force mains overlay sensitive groundwater resources
and these force mains are identified to be highly susceptible to failure, then these types of assets
would be addressed early in the program. Some example criteria for these assessments could
include:
- Systems experiencing high growth
- The age of systems and assets
- Local geological conditions, including earthquake prone areas
- Proximity to sensitive ecological systems
- Systems with the potential to affect bathing beaches or shellfish beds
- Infrastructure assets particularly prone to rising sea levels
- Systems that affect sensitive water cycles
Early in the program, we will expedite the development and application of these types of
assessment criteria. The results of this effort will provide further insights into the nature of the
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challenges that our aging and deteriorating water infrastructure present. As mentioned above, it
is expected that this effort will provide information that will help develop national assessments
and will provide more regionally focused assessment information. For example, an assessment
of the most critically important water infrastructure in our coastal regions will provide direction
to our research program as well as internal and external stakeholders responsible for the
protection of our valuable coastal resources and the health of those enjoying those resources.
The application of these types of criteria and the conduct of assessments will also support the
definition of outcome measures and accountability for the program. When program priorities are
established and refined as mentioned above, outcome measures that can be used to gauge
program accountability will naturally follow. For example, an outcome of this program could be
a measurable reduction of wastewater force main failures and resultant decrease in the incidence
of contamination of water resources. These accountability measures could relate to both
programmatic and project level outcome tracking. These outcome measures could include:
- Reducing of life-cycle costs for water infrastructure management
- Extending service life of installed infrastructure
- Reducing sewer overflows, back-ups, failures
- Reducing I&I and peak wet weather flows to treatment plants
- Reducing high risk water main breaks
- Improving condition assessment and decision-making capabilities
- Reducing potable water leakage and intrusion potential
- Increased adoption of asset management and the use of performance and cost data for
decision support
- Increasing the adoption of innovative technologies
As program implementation begins and national and regional assessments are conducted, a suite
of key outcome measures which will provide feedback on the success of the program will be
identified. In addition, project specific outcome measures will be developed for each project. To
the extent possible, outcome measures will be built on data and information currently collected
and available. This will allow comparison of program progress and project results with historical
trends. For those outcome measures for which historical information may be lacking, baseline
data will be collected against which program and project results will be compared. It is
anticipated that as the program matures, experience with the development and deployment of
outcome measures will improve, leading to more effective and efficient reporting of progress.
References
U.S. Environmental Protection Agency. 2006a. Innovation and Research for Water Infrastructure
for the 21st Century - EPA Research Planning Workshop - Draft Meeting Report, March.
U.S. Environmental Protection Agency. 2006b. Innovation and Research for Water Infrastructure
for the 21st Century - Water and Wastewater Infrastructure Draft Research Issues Report, June.
10
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U.S. Government Accountability Office, Water Infrastructure - Comprehensive Asset
Management Has Potential to Help Utilities Better Identify Needs and Plan Future Investments,
GAO-04-461, March 2004.
11
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Condition Assessment of Wastewater Collection Systems
Background
Since the passage of the Water Pollution Control Act Amendments, better known as the Clean
Water Act (CWA), in 1972, the major focus of sewer system condition assessment and
rehabilitation has been the reduction of infiltration and inflow (I&I). Requirements for sewer
system assessments were codified in the Rules and Regulations for Sewer Evaluation and
Rehabilitation (40CFR35.927) and stated that U.S. EPA construction grants could not be
approved unless there was documentation that sewer systems contributing to municipal
wastewater treatment plants were not exhibiting "excessive infiltration and inflow." (EPA, 1991)
The focus of sewer system condition assessment and rehabilitation on the reduction of I&I,
almost exclusively targeted excessive hydraulic loading in collection systems and at treatment
facilities to lower capital and operation and maintenance costs, and to prolong the lifetime-
capacity of the treatment facility. (EPA, 1991) While I&I still plague our current wastewater
collection systems and is linked to our current challenges relating to sanitary sewer overflows
(SSOs) and wastewater blending, comprehensive asset management is broadening the focus of
sewer system condition assessment. In addition to condition assessment that seeks to determine
excessive hydraulic loading and I&I, currently practiced comprehensive asset management
assesses the likelihood that a capital infrastructure will deteriorate and potentially fail, and the
consequences of that deterioration and failure in terms of costs and effect on the system's ability
to deliver desired services and meet performance measures. (GAO, 2004)
As the focus of condition assessment continues to broaden to include targets beyond the
reduction of excessive hydraulic loading due to I&I, sewer system inspection technologies and
investigation approaches must evolve. More innovative technologies will take advantage of
observation and detection technologies, such as sonar, laser, ultrasonic, and infrared, not
traditionally applied to sewer system investigation. In addition, the deployment of these non-
traditional technologies will be supported by emerging digital, modular, and robotics
technologies to greatly expand the "reach" of sewer system inspection techniques.
Corrosion of wastewater collection infrastructure, especially concrete sewers, is a significant
cause of deterioration and premature failure. When exposed to the internal atmosphere of
gravity sewers which is characterized by high humidity and the presence of hydrogen sulfide,
sulfuric acid corrosion negatively affects concrete surfaces, mortar, and metal reinforcement
material. Given this universal challenge for wastewater utilities, this research program will look
into innovative inspection technologies and condition assessment methods that address
corrosion-related wastewater infrastructure issues.
Deteriorating collection systems can result in excessive infiltration of rising ground water during
high water table seasons and wet-weather events, and the export of recharge water from
watersheds. When this is combined with increased impervious surfaces and water withdrawals
resulting from urban growth, the effect of these man-made influences on the natural water
balance can result in reduced flows in streams affecting aquatic ecosystems and decreased water
availability. The application of isotope hydrology could provide innovative assessment
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techniques to determine relationships between aging infrastructure and altered water balances,
leading to measures to reduce or mitigate resulting adverse consequences.
Force mains are a relatively small, but important, segment of the wastewater collection system
infrastructure. Force mains convey pumped sewage. There are about 30,000 miles offeree
mains in the nation. Based on a sewer pipe inventory of approximately 600,000 miles, force
mains comprise about 5% of the total, by length. Because of hydrogen sulfide generation in
wastewater collection systems, force mains are more prone than drinking water pipes to
corrosion at the crown of the pipe. The average length offeree mains is around 3600 ft. About
60% of the total length offeree mains is constructed of ferrous materials, with ductile iron being
the dominant material. A significant percentage of ductile iron installed has an internal lining
that is most commonly cement mortar. For diameters of 36 inches and greater, pre-stressed
concrete cylinder pipe (PCCP) and concrete cylinder pipe (CCP) are the dominant types. For
diameters up to 20 inches, asbestos cement has a small but not insignificant percentage. For
diameters less than 12 inches, poly vinyl chloride (PVC) and polyethylene (PE) account for about
a third of the length installed. Most force mains are in constant service and cannot be accessed
internally for inspection without expensive by-passing arrangements.
Related to wastewater collection system inspection and condition assessment is the evaluation of
sewer system security vulnerabilities. In today's climate, vulnerability assessment of the
collection system should be an integral part of an overall system condition assessment program.
A recent GAO report found that few utilities have or are planning to install monitoring or
security devices to detect and prevent system intrusions. (GAO, 2006) Recent work, funded by
EPA, has been conducted by ASCE and WEF on monitoring systems and physical security
enhancements, including security measures for wastewater collection systems. This program
will coordinate with EPA's Water Security Division and National Homeland Security Research
Laboratory to leverage resources, identify collaboration opportunities, and assist wastewater
utilities in developing and implementing comprehensive inspection and condition assessment
programs.
State of the Technology
The ability to visually examine the internal condition of a gravity sewer using internal cameras,
usually closed circuit television (CCTV) has been the most important development in the area of
inspection and condition assessment, leading to the current operation, maintenance and
rehabilitation techniques employed by wastewater utilities. Incremental improvements continue
to be made to CCTV technology and as electronic components become more affordable, this
technology can be applied by most contractors and plumbers. Basic CCTV systems which can
inspect small-diameter sewer and drain pipes can be purchased for less than $1500. Also, a
standard investigation of a sewer line can cost a utility no more than $1 per foot. (WERF, 2004)
In addition, the National Association of Sewer Service Companies (NASSCO) provides a wide
range of training programs that is attempting to standardize the application of condition
assessment techniques. NASSCO's programs address the assessment of sewer pipe, manholes
and service laterals.
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Most utilities have established fairly simple rating systems which use the results from CCTV
investigations to make an overall assessment of each section of sewer being inspected. This
rating can then be combined with other data and information, such as results from hydraulic
evaluations, sewer location, known soil conditions, and operational records, to determine
maintenance and system rehabilitation priorities. However, CCTV assessments are qualitative
and rely heavily on the skill of the investigation personnel to make judgments on the condition of
the sewer. Also, this technology does not provide quantitative data to determine variations in
sewer dimensions, subtle deformations, or debris level. Also, CCTV does not permit assessment
of pipe condition below the water line within a sewer. While many sewers can be inspected
during dry weather conditions to limit this issue, most trunk sewers maintain a fairly high flow
and diverting these flows for inspection purposes is difficult. (WERF, 2004)
The application of CCTV in combination with newer technologies is currently being used in
sewer inspections. Sonar technology, which uses high-frequency sound waves, can identify
defects, especially large cracks, in the wall of sewer pipes and because it is almost exclusively
designed to work underwater, it can overcome one of the shortcomings of CCTV. Laser
technology can be used to identify variations in sewer pipes above the water line. Comparison of
laser images of the interior dimensions of a sewer over time can be an effective method to
determine temporal deterioration. (WERF, 2004)
One potential research issue emerges from this analysis of the state of technology for condition
assessment. Given the ubiquitous application of CCTV for sewer inspections and condition
assessment, a state of the art evaluation and technology transfer product on optimized application
of CCTV results for condition assessment could be generated in the early phases of this research
program. Wastewater utilities that are well known for their innovative application of CCTV
could be identified and a best practices assessment and tool produced. In addition, this effort
could include optimizing the use of existing and historical data and information, in combination
with CCTV information to establish baseline assessments.
Research Questions
The following key research questions relating to gravity sewer inspection and condition
assessment have emerged from the research issues meeting (EPA, 2006a) and the expanded
research issues evaluation conducted to develop the research issues report (EPA, 2006b). These
key research questions reflect critical gaps in our knowledge of the performance of innovative
inspection technologies, our understanding of proven condition assessment techniques, and our
ability to diagnose and predict infrastructure failures.
- Can emerging and innovative inspection technologies, for both sewer and non-sewer
assets, including force mains and service laterals, be identified and demonstrated in
field settings to improve our understanding of their cost-effectiveness, technical
performance, and reliability?
- Can advances in remote monitoring and wireless technologies be applied to develop in-
system and in-pipe sensor systems, including real-time data collection, reporting and
assessment, to reduce confined-space entry requirements for sewer system inspection
and investigation?
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- Can correlations be established between the assessed condition and measures of the
performance, operation, or internal environment of sewers and non-sewer assets which
could lead to the use of innovative indicators to determine and track the condition of
assets over time?
- Can standard technical guidelines, uniform data requirements and indicators be
developed for condition assessment of sewers and non-sewer assets, including
manholes, service laterals and pipe joints?
- Can technical guidance be developed for establishing an overall wastewater
infrastructure inspection program, including inspection prioritization, inspection
frequency, inspection type (physical vs. visual, maintenance vs. structural), inspection
by asset type, and inspection cost-effectiveness?
- Can cost-effective and reliable methods for the identification and assessment of the
impact of deteriorating collection systems on urban water budgets be developed?
- Can the dynamics of wastewater collection system infrastructure failure be better
understood, diagnosed, and learned from to model and forecast the remaining life of
assets, prioritize the investigation of asset failures of high consequence, and conduct
reliable infrastructure failure risk assessments in support of comprehensive asset
management?
Proposed Research
Based upon the key research questions presented above and the known research projects that are
ongoing or recently completed by other stakeholders, the following research, demonstrations and
technology transfer products are proposed. Each proposal indicates the estimate time frame for
the work. While these proposals address the issues in the questions above, modified, alternative
or additional projects may evolve as this plan is implemented.
1.Technology Transfer Product: Optimization of Internal Camera Inspection Data
and Information for Effective Condition Assessment - A comprehensive evaluation
of the state of the art of internal camera inspection of wastewater collection systems.
(12-15 months)
2.Technology Demonstration/Verification Program: Emerging and Innovative
Technologies for the Inspection of Wastewater Collection Systems - An inspection
technology demonstration/verification program, conducted in cooperation with
wastewater utilities and other research organizations. In 2004, WERF published a
report titled, "An Examination of Innovative Methods Used in the Inspection of
Wastewater Systems," which identified many innovative inspection technologies that
were emerging to support collection system condition assessment. This
demonstration/verification program will be a collaboration between EPA, other
research organizations, and wastewater utilities, to gather technically reliable cost and
performance data during applications of these technologies in a wide range of field
conditions. (48-60 months)
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3 Applied Research Review and Evaluation: Understanding the Forensics of Sewer
Failures to Support Failure Forecasting Model Development - A comprehensive
review of the research literature to determine our understanding of the critical factors
that cause sewer system failures and an evaluation of current ability to conduct forensic
studies of sewer failures to enhance our ability to model and forecast future failures to
support risk assessments. This effort will be conducted in close collaboration with
related work under condition assessment for drinking water distribution systems. (36-
48 months)
4.Technology Transfer and Development Program: Cross-Sector Transfer and
Application of Advanced and Remote Sensing Technologies for Wastewater
Collection System Monitoring - A comprehensive review of new, innovative pipeline
monitoring technologies that apply advanced and remote sensing approaches. Many of
these innovative pipeline monitoring technologies have been developed for application
in sectors other than the drinking water and wastewater industries, such as the gas and
petroleum pipeline industry. This program could be a cooperative effort with other
Federal departments, such as the Department of Transportation's Office of Pipeline
Safety, to identify these technologies, assess their transferability to drinking water and
wastewater applications, and support technology development. (24-36 months)
5 Innovative Condition Investigation Method Development: Advanced Techniques
for Detecting Exfiltration and Crown Corrosion Conditions - The exploration of
using advanced molecular/microbiological techniques for identifying the presence of
sulfate-reducing bacteria (Desulfovibrio desulfuricans) to assess the probability of
crown corrosion in sewers. (24-36 months)
6 Innovative Condition Investigation Method Development: Identification and
Evaluation of Urban Water Balance Impacts Due to Deteriorating Collection
Systems - The exploration of using isotope hydrology techniques to identify and
evaluate the effects of deteriorating collection systems on urban water budgets. (24-36
months)
7 Technology Application Methodology Development: Asset Management Guidance
and Tools - Guidance and tools for assisting wastewater utilities in applying inspection
and condition assessment technologies in support of asset management decision-
making. This will include a tool for prioritizing sewer inspections, selecting the
appropriate technology and inspection technique, and establishing inspection frequency
based on a risk-based methodology. Currently applied approaches, including the
WERFs SCRAPS (Sewer Cataloging, Retrieval, and Prioritization System) and Seattle
Public Utilities" Sewer Pipe Risk Model will be evaluated and further enhanced to
develop a "next generation" approach. (18-60 months)
References
U.S. Environmental Protection Agency, Handbook - Sewer System Infrastructure Analysis and
Rehabilitation, EPA/625/6-91/030, October 1991.
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U.S. Environmental Protection Agency, Innovation and Research for Water Infrastructure for the
21st Century - EPA Research Planning Workshop - Draft Meeting Report, March 2006.
U.S. Environmental Protection Agency, Innovation and Research for Water Infrastructure for the
21st Century - Water and Wastewater Infrastructure Draft Research Issues Report, June 2006.
U.S. Government Accountability Office, Water Infrastructure - Comprehensive Asset
Management Has Potential to Help Utilities Better Identify Needs and Plan Future Investments,
GAO-04-461, March 2004.
U.S Government Accountability Office, Securing Wastewater Facilities - Utilities Have Made
Important Upgrades but Further Improvements to Key System Components May Be Limited by
Costs and Other Constraints, GAO-06-390, March 2006.
Water Environment Research Foundation, An Examination of Innovative Methods Used in the
Inspection of Wastewater Systems, Ol-CTS-7, 2004.
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Condition Assessment of Water Distribution Systems
Background
This portion of the research plan addresses condition assessment of drinking water transmission
and distribution mains. Condition assessment is the collection of data and information through
direct and/or indirect methods, followed by analysis of the data and information, to make a
determination of the current and/or future structural, water quality, and hydraulic status of the
pipeline. Where it is applicable and cost-effective, condition assessment is a vital component in
effective water infrastructure asset management. A good understanding of pipeline condition
can help a utility to optimize operations, maintenance, and capital improvement decisions. This
helps to reduce structural, water quality, and hydraulic failures and their adverse effects, and to
minimize life-cycle costs. However, condition assessment may also be technically and/or
economically infeasible in many cases, and it may be preferable to perform reactive or scheduled
maintenance, rather than condition-based maintenance. Therefore, the ability to rapidly,
thoroughly, and objectively assess and rank condition assessment versus alternative approaches
for a range of pipe materials and failure mechanisms is also very important for its efficient
development and use.
The primary research emphasis in this program will be structural condition assessment, as
opposed to hydraulic or water quality condition assessment. Structural condition of the pipeline
is narrowly defined here as the presence/absence of holes, cracks, breaks, or conditions leading
to their formation, in the transmission or distribution pipe wall, lining, coating, and joints.
Structural condition does not, as defined here, generally include occlusion of the pipe bore by
tuberculation, scale, or other deposits. Structural condition assessment involves: (1) development
of a formal or informal structural-condition-rating approach that links pipeline parameter data to
the likelihood of structural failure (i.e., holes, cracks, and breaks) for the time period of interest;
(2) collection of data (e.g., physical, environmental, and operational characteristics; failure
history, processes, and associated indicators) by applicable direct and/or indirect methods,
necessary to characterize the pipeline's current and future structural integrity; and, (3) analysis of
the pipeline data and information to categorize pipe structural condition, based on the structural
condition rating approach, as to its likelihood of failure for the pipeline sections and time periods
of interest. The structural condition assessment results are used as input to an informal or formal
decision-support system. The decision support system considers not only condition assessment
results, but also other factors (e.g., consequences of failure, available options and their cost, level
of service targets, and hydraulic and water quality conditions, etc.) to determine whether, when,
where, and/or how the pipeline should be inspected in greater detail, repaired, rehabilitated,
replaced, or whether operating conditions (e.g., pressure, flow control, or corrosion protection)
should be changed.
The demand for, and value from, cost-effective structural condition assessment of moderate-risk
and high-risk pipes should increase significantly over the next 20+ years. Pipes installed during
construction booms in the 1920s and 30s as well as the post WWII boom are likely to begin to
fail en masse, and the ability to determine pipe condition will enable the worst-condition pipes to
be addressed first, which helps minimize failures and associated risks, damages, and costs. It
will also help avoid premature replacement of sound pipe, which will save resources and time.
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The annual replacement rate is projected to peak around 2035 at about 2% (i.e., 16,000 to 20,000
miles of pipe replaced/year), which is more than four times the current replacement rate. (U.S.
EPA, 2002 a and b). The sooner that useful, cost-effective structural condition assessment
devices and procedures are developed and brought into common use for supporting water
infrastructure decision-making, the greater the benefit to drinking water utilities and their
customers.
It's difficult to precisely inventory water mains, due to the time and cost involved, but a 2004
estimate (U.S. EPA, 2007) is approximately 1,000,000 miles of water mains in the United States.
About 57 % of drinking water mains are made of ferrous materials, with lined and unlined grey
cast iron mains representing nearly 29 % of the total, ductile iron (predominantly cement-lined)
about 24%, and steel (both unlined and cement-lined) about 4%. Other significant materials
include polyvinyl chloride (PVC) (17 %)3, asbestos cement pipe (15%), prestressed concrete
cylinder pipe (PCCP) (2%), and polyethylene (1%). About 6% of the pipe materials were either
used in < 1% of total length of mains or the material type was unknown/unreported. A 1994
estimate (U.S. EPA, 2007), indicates that new systems were most commonly installing ductile
iron pipe (48%), and PVC pipe (38%), and the total annual rate of expansion was 13,200 mi/yr.
Because of the range of pipe materials and failure modes, there are differing characteristics and
defects that often require specific investigation approaches. One common defect for all types of
pipe is leakage through the pipe wall, joints, or connections, which can not only release water or
allow intrusion during low-pressure events, but can also lead to soil erosion and loss of support.
Even leakage investigation approaches need to be tailored to differences, for example, in leakage
volume and rate or in sound attenuation due to pipe diameter, pressure, materials, or backfill.
Particular needs in assessing ferrous pipe include: the condition of pipe wall and joints
(specifically external and internal corrosion, pitting, graphitization and fractures), and the
condition of internal lining. Particular needs in assessing prestressed concrete cylinder pipe
(PCCP) (e.g., lined cylinder pipe (LCP) and embedded cylinder pipe (ECP)) include: detection
of wire breakage arising from corrosion, embrittlement or excessive pressure, and corrosion of
joints. Particular needs in assessing flexible plastic pipe include: detection of deformation and
material degradation. Particular needs in assessing asbestos cement pipes include: detecting
abrasion and decomposition of the pipe wall.
The user community strongly desires that condition assessment approaches should be non-
disruptive, i.e., they don't require excavation, de-watering, or entry into the pipeline. Non-
disruptive technologies provide not only economic and customer convenience benefits, but they
also reduce the risk of entry of contaminants or of dislodging sediments, biofilm, or tuberculation
already in the system.
In order to effectively assess the structural condition of a pipeline, reliable correlations must
exist and be recognized between data and information that can be collected about the pipeline,
and its structural integrity status. Much progress has already been made in this area, but a better
3 Based on personal communication with Robert Walker of the Uni-Bell PVC Pipe Assocation, who cited a
confidential industry study, the length of PVC pipe installed in rural systems is seriously undercounted in the
distribution system inventory cited above. The industry study estimates that the actual miles of PVC installed are
many times greater than the estimate above.
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understanding of the correlation between measurable data and information will improve the
understanding of the range of situations where condition assessment can or cannot be applied.
Since many water transmission and distribution pipelines have been successfully designed,
manufactured, installed, and operated up to, or beyond, their design service lives, the relevant
structural integrity factors and associated safety margins for new pipelines are often being
effectively addressed. On the other hand, there are an estimated 240,000 main breaks/year), and
a portion of these are catastrophic, which indicates that the technical and/or economic feasibility
of measuring the right parameters, and/or the ability to interpret the data, are not adequate for
high-risk mains.
The scope and goals for structural condition assessment can vary substantially, and they strongly
influence the type, quantity, quality, and cost of acquiring and analyzing the data required to
complete the assessment. Three examples follow that illustrate a range of combinations of
scopes and goals. Example Scope and Goal 1: Establish a preliminary investment plan for
future replacement of a class of pipe in similar environmental and operating conditions. In this
case limited pipeline data (e.g. installation date, and characteristics of pipe, soil, and climate),
plus service life history or deterioration curves from similar pipelines in similar settings, would
be sufficient condition data to support this goal. Example Scope and Goal 2: Economically and
promptly detect and locate potentially serious deterioration during operation of a prestressed
concrete cylinder pipeline (PCCP). A potential option for meeting this goal would be minimally
invasive acoustic emission monitoring to detect the number and location of prestressed wire
breaks. Example Scope and Goal 3: Make a final decision about the correct option (i.e., no
action, repair, rehabilitation, or replacement) for the potential problem areas identified in
Example 2. Achieving this goal may require de-watering and/or excavating the pipe at the
locations identified during acoustic emission screening, followed by detailed direct inspections
by destructive or non-destructive methods.
Condition assessment depends on the quantity, quality, and availability of data, and three broad
approaches were identified at the workshop for improving condition assessment data.
- Improve the consolidation, organization, and use (within and between utilities) of data
and information that already exist, but are under-utilized. The data and information are,
for example, installation, environmental, operating, and maintenance records, and
failure case histories for various types of pipe, environmental, and loading conditions.
A desire was expressed for the development of a database for these types of data.
- Improve the acquisition and analysis of additional condition assessment data from
existing technologies (e.g., automatic meter reading, SCAD A, and statistical analysis).
This approach may have important economic advantages, if the new condition
assessment data adds value with little additional expense to the utility.
- Improve the type, quality, spatial density, frequency, speed, and economics of pipe
condition data acquisition by utilizing new technologies (e.g., sensors, transmitters, data
storage, computers, robotics, software). This approach attempts to leverage a broad
range of new technologies. The key to acceptance of new technologies will be the
physical or logical demonstration of substantial value-added to utilities.
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Workshop attendees and research plan reviewers recommend that EPA structural condition
assessment research activities for water mains should emphasize a coordinated, collaborative
approach. Numerous options already exist for collecting and analyzing condition data for
drinking water mains, but these options have limitations, which represent potential research
needs. There are a large number of combinations of pipe materials, configurations, and failure
modes, and many cannot be adequately or economically characterized by existing structural
condition assessment approaches. However, there aren't sufficient resources to address all
combinations, so it's important to focus on scenarios of greatest interest to utilities and
regulators. Improved technologies must provide value-added for utilities and be both technically
and economically competitive with alternative approaches. A substantial amount of relevant
research, development, testing, and verification (R,D,T,&V) is recently completed, underway or
planned by, for example, the American Water Works Association Research Foundation
(AwwaRF), the Water Environment Research Foundation (WERF), the Global Water Research
Coalition (GWRC), the European Commission (EC), National Research Council Canada
(NRCC), and Commonwealth Scientific and Research Organization (CSIRO/Australia). Many
structural condition assessment improvement efforts involve applying recent advances in
technology (e.g., sensors; probe signal generation; data transmittal, storage, and analysis; and
robotics) to the creation of better, cheaper, and faster ways of acquiring and analyzing structural
integrity data. It is important not to duplicate this research, and also to take advantage of
opportunities for parallel or joint research at desktop-, laboratory-, pilot-, or full-scale. A
substantial amount of research, development, testing, and verification (R,D,T,&V) is also
completed, underway, or planned for structural condition assessment for non-drinking water
applications, such as oil and natural gas pipelines, nuclear power plants, large buildings, bridges,
and aircraft. This research may offer potential for technology transfer to the water sector.
As described above, improved condition assessment capability has potential for improving
structural asset management for water infrastructure, but it also has limitations, and there are
difficult challenges to overcome.
- One limitation of condition assessment is that it does not, and is not likely to, produce a
precisely accurate prediction of the time and location of failure. Pipe structural failure
occurs when the loading on the pipe exceeds the ability of the pipe to resist it. There
are a range of types and magnitudes of environmental conditions and loadings acting on
the pipe, so predicting exactly when and where the pipe will fail is very difficult. Also,
as a pipe deteriorates, failure may be triggered by smaller loads that would have been
resisted earlier in the pipe's lifetime, and this strength deterioration adds to the
difficulty of predicting time and location of failure. If the time and location of failure
prediction are not exact, then it becomes more difficult to quantify the value of
condition assessment. Nonetheless, if condition assessment can be conducted more
frequently and accurately because of technology performance and/or cost
improvements, it should enhance the capability of tracking pipe deterioration, and the
approach toward conditions that pose an unacceptable probability of failure.
- Cost is a very important consideration, and condition assessment is not economically
feasible for all situations. For example, for low-risk mains, the cost of condition
assessment may exceed the value of any damages prevented following failure. So, for
low-risk pipes, it may be better to repair after failure, and replace when the failure rate
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becomes unacceptable based on economics or service reliability considerations. For
moderate- and high-risk mains, there should be a greater willingness to pay for
structural condition assessment, but a structural condition assessment approach that far
exceeds its benefits is not likely to be widely used. On the other hand, if dramatic
reductions occur in inspection and rehabilitation costs, this will have a favorable
influence the economic feasibility of inspection.
- Some types of failures may not be preventable through more intensive structural
condition assessment. For example: the critical failure mechanisms and conditions may
be poorly understood; the failure mechanisms may provide too little pre-failure warning
to enable preventive action; or, the critical parameters may be technically or
economically infeasible to monitor.
- Documenting long-term value-added and reduced life-cycle costs for utilities will
require some long-term studies. For example, if condition assessment indicates that a
pipeline can be safely operated 10-yr longer than previously planned, it won't be
known if the prediction is actually correct for 10-yr. Surrogate measures, e.g., measure
deterioration, laboratory tests, modeling can be used to estimate accuracy of projections
in a shorter time period.
It will be important to keep these challenges and limitations in mind during project selection and
project and program progress reviews in order to focus on projects with good prospects for
providing value-added to utility asset managers.
State of the Technology
Indirect assessment: A great deal can be learned about the potential for defects in the system
from: (a) historical data such as the age of pipe, manufacturer, when and who laid it, and
experience of various pipe materials; (b) environmental data such as soil conditions, ground
water tables, surface conditions; and (c) operational data such as flow, maintenance and repair
records. This information, from which pipe and/or network condition can be inferred, coupled
with information about potential consequences of failure, is of great value in focussing an
investigation strategy to those sections in most need of assessment. Indirect methods are
generally less costly than direct methods. Indirect methods may not provide the level of detail,
timeliness, or confidence required for maintenance and renewal decisions about pipes with a high
consequence of failure. A number of decision support tools have been developed for prioritizing
investment, maintenance, and replacement schedules, e.g., Deb et al., 1998; Deb, et al., 2002a;
Deb et al., 2002b; Kleiner et al., 2005; O'Day, et al., 1986; Sagrov, 2003; Sagrov, 2005; Stone et
al., 2002; WERF, 2004. Evaluating the practicality and value of innovative decision support
tools will assist the user community to select appropriate options.
Direct Assessment: Direct methods include visual inspection, destructive methods, and
nondestructive methods. Visual inspection may be done in-person for larger diameter pipes or
the exterior of excavated pipes, or it may done by closed-circuit TV (CCTV) for the interior of a
wide range of pipe sizes. CCTV is used for both water main and force main inspections. CCTV
can be beneficial, but it inspects only the inner wall of the pipe, not wall thickness, the outer
wall, and pipe bedding voids. Destructive testing involves pipe coupon sampling (i.e. removal of
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a sample of the pipe wall) and analysis for thickness, defects, damage, and residual strength.
Hydrostatic testing (i.e. isolating pipe, filling, pressurizing, then observing pressure or fluid loss)
is a nondestructive evaluation except in cases where pressurizing the pipe causes failure at weak
spots. Hydrostatic testing is the most common (i.e., 20% of surveyed utilities) investigation
method for sewer force mains among surveyed utilities.
Nondestructive testing (NDT) methods measure various structural parameters without damaging
the inspected material. Evaluation and improvement of NDT methods for a range of water and
wastewater pipe scenarios has attracted considerable attention (e.g., Jackson et al., 1992; Hunaidi
et al., 1999; Mergelas and Kong, 2001; Dingus et al., 2002; Lilley et al., 2004; Reed et al., 2004;
Thomson et al., 2004).
- NDT methods available for pipes include penetrant testing for cracks (not common for
water pipes), x-ray inspection (not common for water pipes), acoustic emissions (e.g.,
for wire break events in PCCP), acoustic leak detection, remote field eddy current (for
ferrous pipe), remote field eddy current/transformer coupled (for broken wires in
PCCP), magnetic flux leakage (mostly for steel pipe), ultrasonic pulse velocity (for wall
thickness measurement), ultrasonic guided waves (primarily for pipe with welded steel
joints), and seismic methods (for PCCP defects).
- Except for acoustic leak detection and location, and acoustic wire break detection for
PCCP, NDT for pressure pipes is not in widespread use. One estimate is that current
NDT technology is only applicable to about 10% of U.S. drinking water mains (Dingus,
et al., 2002). Limited use of NDT methods can be attributed to several causes including
their high cost, disruptiveness, and for most methods the lack of a track record. Slow
development of NDT methods for water pipes may be attributed to small market size,
challenging testing conditions in water mains, and/or lack of understanding and
consensus regarding the requirements for pipe inspection.
- Current and expected improvements in NDT-related technologies such as sensors (e.g.,
sensitivity, miniaturization, durability), sensor platforms (e.g., robotics), sensor
networking, communications, data interpretation, and computing, indicate that NDT
capability, and its applicability to water mains can be substantially improved. Water
mains with moderate to high consequences of failure should be the focal point for NDT
improvement on the basis of risk reduction potential and economic feasibility.
Recent innovations: A number of innovative and effective new developments have occurred
that greatly improved the capability of providing the information needed to make an assessment.
- Leak Detection - Externally applied leak correlator tools have been in existence for
many years, but important advances have been in the development of in-line tools. A
hydrophone, either tethered or free, is inserted into an operational main and is moved
along by the pressure. The great advantage is that due to closeness of the hydrophone to
the leak, it can detect and pinpoint small leaks. The most advanced of these is Sahara,
which was developed for the water industry. Smartball is an innovative acoustic
acquisition device complete with power supply that is contained within an aluminum
casing and then placed inside a foam ball, which can float through the pipes with
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diameter > 10-in. and operate up 17 hours. Acoustic detection and recording modules
have been developed that can be placed at selected locations to monitor leakage at night
for several days or weeks, then the units are either retrieved or queried and the data are
analyzed to identify leaks. A leak detection monitoring system using long, acoustic
fiber optics is being tested in Arizona. Another innovative system integrates automatic
meter reading systems and leak detection.
Ferrous Pipe Investigation - Broadband Electro-Magnetic (BEM) is a patented
technology developed in Australia that is commercially available. It works by inducing
eddy currents to flow in close proximity to a transmitter. These currents migrate with
time and the collected data can provide an accurate profile of the pipe wall. It can see
through even significant linings and coatings without their removal, which is a major
advantage. Another advantage over ultrasonics is that it generates a contour plot of the
whole section of pipe. It can detect metal loss to 1/25" of an inch. To scan internally
the pipe has to be out of commission and a short section of pipe removed to allow
insertion of the BEM pig. BEM operating speed is low. Remote Field Technology
(RFT) - An RFT tool used in the oil and gas industry is the "See Snake" which is
stated to be suitable for pipeline diameters of 2" to 8" and is flexible and able to
negotiate bends and captures data and stores it on board. Magnetic Flux Leakage - A
UK company has developed MFL external inspection tools for small and medium sized
ferrous pipe. Sonics and Ultrasonics - An ultrasonics in-line intelligent pigs for water
and force mains was undertaken by the UK utility Thames Water. This is a prototype
and not commercially available. It is believed that there are similar developments
underway. Linear Polarization Resistance (LPR) - A device developed in Australia
utilizes working, counter and reference electrodes using a Ferguson-Nicholas cell. The
polarization resistance is used to determine the maximum pitting rate of a ferrous pipe
in that type of soil by reference to an established data base. It can be used in the
assessment of external corrosion of a ferrous pipeline.
Ferrous and other pipe materials investigation - Acoustics ~ A new acoustic
technology for measuring the remaining general wall thickness for water pipes has been
developed by National Research Council of Canada. This method is non-destructive
and does not require taking pipes out of service. The method uses acoustic signals
induced in pipes by releasing water from fire hydrants. These signals are measured by
acoustic sensors at two points 300 to 600 ft apart along a pipeline. In principle, this
new method can be used on all types of pipes including cast and ductile iron, steel,
PVC, asbestos cement and PCCP.
Research Questions
1. How can condition assessment decision support approaches be improved?
a. How can/should procedures be improved for setting pipeline investigation
priorities (i.e., determining whether, when, where, and how to assess pipe
condition)?
b. How can/should procedures be improved for utilizing outputs from condition
assessment to support asset management decisions?
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c. What is the estimated value of, and market for, condition assessment for key
pipe scenarios?
d. What existing types of condition assessment information and data could, if
collected and made readily available, support better decision-making among the
user community (e.g., utilities, inspection/condition assessment service
providers, inspection technology manufacturers, researchers, research funding
organizations)?
i. How can the quantity, quality, and accessibility of those data be
improved?
2. Can innovative technologies and procedures substantially improve condition-based
management of drinking water infrastructure assets?
a. Can innovative condition assessment technologies and procedures provide more
timely and reliable warning of impending failures in high risk mains (e.g., large
diameter cast iron, ductile iron, steel, PCCP, asbestos cement) so that a
substantial reduction can occur in currently unpreventable catastrophic failures?
b. Can correlations be substantially improved between measurable structural
parameters and pipe condition for key pipe scenarios?
c. How can the evaluation and acceptance of innovative, improved condition
assessment technologies be accelerated?
3. Can condition assessment for key pipe scenarios be improved through better
understanding of failure mechanisms and their indicators?
Proposed Drinking Water Pipe Condition Assessment Research
1 Applied Research: Decision Support Evaluation and Improvement - A rational
decision about whether it is worthwhile to implement or improve condition
assessment requires that estimates be made regarding the applicability, technical and
economic feasibility, and value of condition assessment for the approach and
application under consideration. This project will evaluate and develop procedures
and data to support selection decisions for both implementation and research
regarding condition assessment for water mains.
a. Value of condition assessment - The value of condition assessment will be
assessed and documented from several perspectives. Procedures will be
developed, reviewed by the user community and subject experts, and then
implemented for quantifying the cost and number of high consequence failures,
which will help establish the maximum value of direct condition assessment
and/or identify key data gaps. The relationship between the value of the asset
and the acceptable cost of investigation, which will assist in determining what
might be economically feasible with existing and future condition assessment
approaches, will be investigated. The cost-effectiveness of condition assessment
on a life-cycle basis will be determined for selected case histories. The
breakpoint between reactive vs. condition-based maintenance and between NDT
vs. indirect assessment approaches (e.g. use of historical, operational, and
environmental data) will be evaluated for high priority scenarios. Optimization
of inspection frequency based on a system for establishing risk of failure for
water pipes will be investigated. The feasibility will be explored of developing
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a condition rating system or scale, e.g., an infrastructure condition factor (ICF)
on a scale from 1 to 10 that can be used, together with information about the
rate of deterioration, for optimizing the cost of rehab and replacement programs.
This effort will build on WERF 03-CTS-20CO - Condition Assessment
Protocols, jointly sponsored by WERF, AwwaRF, and EPA, and other relevant
research.
b. Research awareness and priority-setting - The following products will be
generated to help ensure that condition assessment research leverages available
knowledge and collaboration opportunities, and meets high priority needs of the
user community. An annual review of condition assessment research will be
published. A condition assessment research database will be developed that
will help foster more efficient collaboration and reduce redundancy. We will
participate in updating research roadmaps for key water infrastructure condition
assessment needs.
c. Improving Quantity, Quality, and Accessibility of Condition Assessment
Data - This project will involve working with key stakeholders to develop a
condition assessment database for water and wastewater mains that contains
information on pipe failures and consequences; inspection procedures,
frequencies, results, and costs; and repair, rehabilitation, and renewal
methodologies and costs. The database is expected to support more effective
selection of pipe, pipe inspection, and pipe rehabilitation methods.
2. Technology Evaluation and Improvement: Condition Assessment Technology
Performance and Cost - Advances in, for example, sensing, sensor platforms,
computing, miniaturization, and communications are potentially enabling
improvements in inspection speed, spatial coverage, temporal coverage, failure mode
coverage, and cost. Independent performance and cost data for key pipe situations
help developers, users, researchers, and research funding organizations to make sound
decisions about application and development of innovative inspection devices for
more effective and efficient management of drinking water infrastructure.
a. Evaluate/demonstrate technologies - The project will evaluate/ demonstrate
innovative approaches for timely, accurate, reliable, and cost-effective detection
of pre-failure indicators for high-risk classes of water main breaks.
b Develop technology evaluation protocols and metrics - The project will also
develop protocols and metrics for demonstrating/verifying existing and
innovative condition assessment technologies' performance and cost for key
pipe situations.
c. Improve accessibility for in-line inspection - To help overcome in-line
inspection accessibility problems that limit their application, the project will
collaborate with relevant organizations to develop commonly accepted design
standards for new distribution system installation for ease of inspection and
assessment.
3. Basic and Applied Research: Causes, Mechanisms and Predictability of Failure
to Enhance Condition Assessment Capability - This project encompasses basic
research on pipe failure mechanisms and predictability of unacceptable conditions or
ultimate failure, as well as collection and analysis of failure case histories and
statistics. This project will be done in close cooperation with utility experts, pipe
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manufacturers, consultants, academia, AwwaRF, WERF, U.S. Bureau of
Reclamation, CSIRO, GWRC, NRC-Canada, and EU.
a. PCCP - The project will initially investigate embrittlement of prestressed
concrete cylinder pipe (PCCP), which can cause catastrophic failure of large
diameter transmission mains. While it is already known that overcurrent in
cathodically protected PCCP can cause damage to the prestressing wires, better
documentation about the rate of embrittlement and its effect on time to failure
will help improve maintenance scheduling, option selection, and failure
prevention. The influence of bonding on residual strength of broken pre-
stressing wires and the number of broken wires that will cause PCCP failure
will be explored. The correlation will be studied between RFEC/TC results and
actual prestressing wire damage in PCCP pipe without shorting straps, which
seem prone to false positives.
b. Plastic Pipe - The project will develop decay curves and prediction models for
estimating performance and remaining life of water mains, including small
diameter plastic pipe. Also, the effects of pressure transients on the degradation
and failure of plastic pipe will be evaluated.
c. Failure Documentation Guidelines - Guidelines regarding determining and
documenting causes of pipe failures will be developed.
d. Predictability and Preventability Indices - The correlation between measurable
parameters and probability of failure will be studied for high priority pipe
scenarios. Pipe failure predictability and preventability indices for high-priority
pipe failure scenarios will be considered and developed where feasible. These
indices will quickly indicate to the user, regulatory, and research communities
the relative level of difficulty involved in predicting and preventing key types of
failures. Changes in the indicators over time will also indicate progress (or lack
of it) toward enabling prevention of these types of failures.
e. CI/AC/Polywrapped DI - Pending results of ongoing AwwaRF projects,
additional future efforts may be undertaken on predictability and preventability
of failures of cast iron pipe bells, asbestos cement pipe, and polywrapped
Dl.pipe.
References
Deb, A.K.,Y.K. Hasit, P.M. Grablutz, R.K. Herz. 1998. Quantifying Future Rehabilitation and
Replacement Needs of Water Mains. Awwa Research Foundation. Denver, CO. 156 pp
Deb, A.K., Grablutz, F.M., Hasit, Y.J., Snyder, J.K., Loganathan, G.V., andN. Agbenowski.
2002a. Prioritizing Water Main Replacement and Rehabilitation. American Water Works
Association Research Foundation. Denver, CO. 234 pp
Deb, A.K., YJ. Hasit, H.M. Schoser, J.K. Snyder, G. V. Loganathan, P. Khambhammettu.
2002b. Decision Support for Distribution System Piping Renewal. Awwa Research
Foundation. Denver, CO. 278 pp.
Dingus, M., J. Haven, and R. Austin. 2002. Nondestructive, Noninvasive Assessment of
Underground Pipelines. Awwa Research Foundation. Denver, CO. 116.
Hunaidi, O., W. Chu, A. Wang, W. Guan. 1999. Leak Detection Methods for Plastic Water
Distribution Pipes. AWWA Research Foundation. Denver, CO. 142 pp
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Jackson, Rodney Z., C. Pitt, R. Skabo. 1992. Nondestructive Testing of Water Mains for
Physical Integrity. American Water Works Association Research Foundation. Denver,
CO. 109 pp.
Kleiner, Y., B. Rajani, R. Sadiq. 2005. Risk Management of Large-Diameter Water
Transmission Mains. Awwa Research Foundation, Denver, CO and National Research
Council of Canada, Ottawa, ON, Canada. 119. pp.
Lillie, K. C. Reed, M.A.R. Rodgers, S. Daniels, and D. Smart. 2004. Workshop on Condition
Assessment Inspection Devices for Water Transmission Mains. Awwa Research
Foundation. Denver, CO. 140 pp.
Mergelas, B. and X. Kong. 2001. Electromagnetic Inspection of Prestressed Concrete Pressure
Pipe. Awwa Research Foundation. Denver, CO. 89 pp.
O'Day, K.D., R. Weiss, S. Chiavari, D. Blair. 1986. Water Main Evaluation for
Rehabilitation/Replacement. American Water Works Association Research Foundation.
Denver, CO. 182pp.
Reed, C., A. J. Robinson, and D. Smart. 2004. Techniques for Monitoring Structural Behavior of
Pipeline Systems. Awwa Research Foundation. Denver, CO. 246 pp.
Randall-Smith, M. A. Russell, R. Oliphant. 1992. Guidance Manual for the Structural
Condition Assessment of Trunk Mains. WRc. Swindon, UK.
Sagrov, Sveinung. 2003. Computer Assisted Rehabilitation for Water Systems (CARE-W).
European Commission under the Fifth Framework Programme, http://care-w.unife.it/
Sagrov, Sveinung.2005. Computer Assisted Rehabilitation for Sewers (CARE-S). European
Commission under the Fifth Framework Programme, http://care-s.unife.it/
Stone, S., EJ. Dzuray, D. Meisegeier, A.S. Dahlborg, M. Erickson. 2002. Decision-Support
Tools for Predicting the Performance of Water Distribution and Wastewater Collection
Systems. Logistics Management Institute for WSWRD, NRMRL, U.S. EPA. EPA/600/R-
02/029. 97 pp.
Thomson, J.C., P. Hayward, G. Hazelden, R.S. Morrison, and T. Sangster, D.S. Williams, and R.
Kopchynski. 2004. An Examination of Innovative Methods Used in the Inspection of
Wastewater Systems. Water Environment Research Foundation. Water Environment
Federation, Alexandria, VA and IWA Publishing, London, UK.
U.S. Environmental Protection Agency. 2002a. The Clean Water and Drinking Water
Infrastructure Gap Analysis. EPA-816-R-02-020. Office of Water. Washington, DC.
September. 50 pp.
U.S. Environmental Protection Agency. 2002b. The Clean Water and Drinking Water
Infrastructure Gap Analysis. EPA 816-F-02-017. EPA Office of Water. September. 2 pp.
U.S. Environmental Protection Agency. 2007. Distribution System Inventory, Integrity, and
Water Quality. Office of Water. Washington, DC. 24pp.
http://www.epa.gov/safewater/disinfecti on/tcr/pdfs/issuepaper_tcr_ds-inventory.pdf
WERF. 2004. Development of a Tool to Prioritize Sewer Inspections (SCRAPS). Water
Environment Research Foundation. Alexandria, VA. 123pp.
http://www.werf.org/AM/CustomSource/Downloads/uGetExecutiveSummary.cfm7FILE
=ES-97-CTS-7.pdf
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Rehabilitation of Wastewater Collection Systems
Background
The objective of system rehabilitation is to ensure the overall viability of the collection system to
maintain operational and structural integrity and to prevent or reduce infiltration, inflow and
exfiltration and their negative environmental impacts. There are several primary concerns
related to deteriorating sewers. On a daily basis, significant pipe defects can cause blockages
that lead to dry weather sewer overflows and backups into buildings. Water that flows into sewer
pipes through defects (holes, cracks, failed pipe joints) can weaken the critical soil-pipe
structure. Fine soil particles carried into the sewer can eventually reduce soil support to a point
causing pipe deformation and/or subsidence. Exfiltration of water from the sewer into the
surrounding soil can also weaken support provided by the soil. Soil movement due to traffic
movement can exceed design assumptions and result in soil-support related problems.
Deposition of material and sewer blockages can result in septic conditions due to flat grades,
high ambient temperatures and poor ventilation. These conditions are ideal for the development
of sulfuric acid and resulting crown corrosion which reduces the structural integrity of concrete
material and the reinforcing steel, commonly used sewer materials. High rates of infiltration and
inflow can lead to sewer overflows, basement backups, significant system capacity issues and
excessive peak flows at pumping stations and at the treatment plant. Although an infrequent
occurrence, exfiltration of sewage into the surrounding soil can lead to groundwater and soil
contamination. In some instances, water pressure drops in water distribution pipes adjacent to
exfiltrating sewers can result in contamination of the potable water supply. In many cases, these
problems are the result of faulty sewer designs. In addition, inadequate inspection, quality
assurance and poor construction workmanship during sewer installation can result in long-term
problems due to poor workmanship. (Tafuri and Selvakumar, 2002)
Generally, rehabilitation includes a broad spectrum of approaches, from repair to replacement
that attempt to return the system to near-original condition and performance. Rehabilitated
systems can be improved to provide hydraulic conditions and structural integrity better than the
original sewer. Repair techniques are used when the existing sewer is structurally sound,
provides acceptable flow capacity and can serve as the support or host of the repair method.
When the existing sewer is severely deteriorated, collapsed, or increased flow capacity is needed,
it is usually replaced. Current rehabilitation methods generally address unsound structural
conditions. A wide range of causes can be responsible for sewer line deterioration and failure.
These include:
- Inadequate or improper bedding material
- Chemical attack
- Traffic loadings
- Soil movements
- Root intrusion
- Compromised joint integrity
- Subsequent construction damage
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- Groundwater fluctuations
- Poor design and installation
- Inadequate maintenance (WERF, 2000)
Effective system rehabilitation programs require a complete understanding of the condition and
performance of the collection system, including factors that affect system integrity and
operations. Pipe age is a factor; however, pipe deterioration is very complex and it is usually a
combination of several factors that causes failures and influences rehabilitation decisions,
leading to a very complex decision-making process. Pipe materials, bedding and backfill
materials, surrounding soil conditions, loads and stresses on the pipe, groundwater levels, sewage
and soil acidity, sewage dissolved oxygen levels, and electrical and magnetic fields are factors
that negatively impact long-term integrity and operational performance of the collection system.
The results from a sound system inspection and condition assessment program provide critical
input to decision support tools that evaluate the condition of the system based on structural,
hydraulic, service delivery, water quality and economic factors.
Building connections to street sewers, referred to as house or service laterals, can contribute as
much as 70 to 80% of the infiltration to a sewer. Fluctuating ground water, variable soil
characteristics and conditions, traffic, erosion, washouts, etc., cause enormous stresses on
house/service lateral pipes and joints. Connectors and fittings in many cases do not retain their
watertight integrity while adjusting to these factors. Some connections react to soil acid and may
totally disintegrate in a few years. These conditions often result in generating major points of
infiltration at the connection of the house/service lateral to the street lateral or main. With
current technology, rehabilitating building connections has become technically feasible but,
because of the shear number of connections and cost for service renewals, is a significant
additional cost. Economics and conditions of service renewals may make this difficult to address
systematically. The problem is both critical and sensitive because of legal jurisdiction, private
ownership and costs associated with disturbance to the occupant and destruction of valuable
landscaping. Because of this, municipalities are often reluctant to address infiltration and inflow
problems from these sources. (Tafuri and Selvakumar, 2002)
State of the Technology
Collection system rehabilitation includes a wide range of repair and replacement options that can
be used to return the system to acceptable levels of performance. Pipeline rehabilitation
procedures are usually preceded by some form of cleaning to remove foreign materials before
other phases of rehabilitation. The removal of roots, sediments, and debris is also a critically
important practice for maintaining operational performance levels including ensuring proper
flow conditions, reducing infiltration and exfiltration and preventing structural damage to the
pipeline. Common repair methods of chemical and cement grouting address problems associated
with groundwater movement, washouts, soil settlements, collapses, and soil voids. Grouting is
marginally effective in reducing or eliminating infiltration but will not significantly improve the
structural condition and has a limited life-cycle. It does, however, help stabilize the surrounding
soil mass. Other system repair approaches include sliplining, spiral-wound pipe, segmented liner
pipes, cured-in-place pipe (CIPP), fold and form pipe, close-fit-pipe, coatings, mechanical
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sealing devices, and spot repair. Many rehabilitation methods marginally reduce pipe cross-
sectional area and can reduce hydraulic performance, but generally improve the system
hydraulics.
Trenchless technologies have moved to the forefront of sewer system rehabilitation. Many are
proprietary systems and the details of installation procedures and materials are trade secrets,
limiting the ability to compare and evaluate competing approaches. For some techniques, codes
and standards have been developed; however, because of the rapidly evolving technology in
rehabilitation, standards and codes often lag behind. Trenchless technologies are applied in both
repair and replacement situations. Pipe replacement technologies include pipe bursting, pipe
splitting, pipe reaming and pipe eating. These trenchless replacement techniques install a new
sewer in the location of the old pipe without total surface digging and accompanying traffic and
business disruptions.
It is significant to mention that past studies have found that rehabilitation of sewers at the street
alone does not completely solve the infiltration problem. Successive rainfalls can elevate the
groundwater table to levels where entry occurs through these service laterals.
When performed, rehabilitation of service laterals is generally done by point repair or
replacement; cured-in-place lining, sliplining and pipe bursting are sometimes used. These
approaches do not overcome the private ownership problem or the problems associated with the
location and configuration of the line (sharp bends/transitions) or the line condition (massive
roots).
System rehabilitation includes repairing or replacing appurtenances (manholes, pump stations,
wet wells, and siphons) which is an important component of a comprehensive program. About
30 to 50 percent of system infiltration and inflow is due to defects in or near appurtenances, in
particular, manholes. For example, manhole covers submerged in one inch of water can allow as
much as 75 gallons per minute to enter the system depending on the number and size of holes in
the cover. Rehabilitation of manholes, pump stations, and wet wells includes spray-on coatings,
spot repairs, structural liners, and replacement. Rehabilitation of siphons includes some of the
options available for pipelines such as grouting and lining. Many siphons have been
rehabilitated using either CIPP or high density polyethylene (FtDPE) liners. (Tafuri and
Selvakumar, 2002)
Selection of rehabilitation methods and materials suitable for various parts of the wastewater
collection system remains an issue, especially due to ever emerging new materials and methods
of construction. Uncertainty in the selection of appropriate repair and replacement techniques is
partly related to the lack of understanding of the capabilities of each methodology to solve the
problem in the long term. Reliable rehabilitation product performance under actual field
conditions, especially over longer periods of performance, is lacking. Data on the effectiveness
and longevity of rehabilitation technologies and materials and life-cycle cost information will be
useful in determining whether rehabilitation or replacement is more cost effective.
The introduction of sewer pipes made from plastic materials has replaced in the market the more
traditional sewer pipes constructed from concrete, clay and ductile iron. Plastic pipe has and
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continues to be an area of innovation for sewer pipes. The most commonly used materials for
wastewater applications are polyvinyl chloride (PVC), polyethylene (PE) and glass reinforced
plastic (GRP). Plastic pipe innovations include structured wall pipe and composite pipe that use
different pipe materials to address both structural and corrosion issues. The application of plastic
pipe in wastewater is becoming standard practice, resulting in the need for determining long-term
performance and related testing. In addition, raw materials and formulations can vary widely,
resulting in different quality pipe for the same plastic.
Research Questions
The following key research questions relating to sewer system rehabilitation have emerged from
the research issues meeting (EPA, 2006a) and the expanded research issues evaluation conducted
to develop the research issues report (EPA, 2006b). These key research questions reflect critical
gaps in our knowledge of the performance of innovative rehabilitation technologies, our
understanding of the long-term performance and cost of sewer pipe made from new materials,
and our ability to determine the most long-term cost effective rehabilitation methods for the
situation being addressed.
- Can emerging and innovative sewer system rehabilitation technologies, for both sewer
and non-sewer assets, including service laterals, be identified and demonstrated in field
settings to improve our understanding of their cost-effectiveness, technical performance
and reliability?
- Can approaches and methods be developed for determining the long-term performance
and life-cycle cost effectiveness of various system rehabilitation technologies,
including new and existing materials?
- Can guidance be provided for establishing a comprehensive system rehabilitation
program, including rehabilitation of non-sewer assets, selection of pipe and
rehabilitation materials, and testing and quality assurance of field installation and
application of rehabilitation technologies?
- Can guidance be provided for collection system operation and maintenance programs,
including procedures to assess and optimize maintenance practices that reduce the need
for rehabilitation?
- Can sewer and collection system design guidance based on lessons learned from system
rehabilitation be developed to enhance long-term performance and system integrity and
to allow for easier inspection, maintenance and rehabilitation?
- Can a sound, risk-based, decision-making process for selecting optimal system
rehabilitation technologies and methods be developed based on long-term effectiveness,
system performance, structural integrity, consequence of failure, and life-cycle cost?
Proposed Research
Based upon the key research questions presented above and the known research projects that are
ongoing or recently completed by other stakeholders, the following research, demonstrations and
technology transfer products are proposed. Each proposal indicates the estimated time frame for
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the work. While these proposals address the issues in the questions above, modified, alternative
or additional projects may evolve as this plan is implemented.
1. Technology Transfer Products: Collection System Rehabilitation Methods and
Technologies - State of the Technology. A series of products that present the
current state of the art in the rehabilitation of sewer and non-sewer assets. The first
phase of this project will be the conduct of an international technology forum to
develop a comprehensive inventory of rehabilitation technologies being applied
around the world. This could be conducted in conjunction with the Global Water
Research Coalition's Asset Management Work Group. The second phase of the
project will be the development of a series of technology capsule reports that will
transfer performance and cost information on rehabilitation technologies using case-
studies. (24-48 months)
2. Technology Evaluation Report: Sewer Liner Systems - This will be a
retrospective evaluation of liner systems installed in collection systems. This effort
will identify key parameters that will be evaluated to determine the performance,
durability, and longevity of these systems. This retrospective evaluation will also
provide input into potential demonstration and verification protocols rehabilitation
technologies. (18-24 months)
3. State of the Technology Report: Rehabilitation of Service Laterals - This
evaluation report will examine the state of the art in sewer lateral rehabilitation
techniques. The special challenges presented by sewer laterals will be identified and
innovative rehabilitation approaches will be described. Beyond the technical
challenges, the report will include examples of strategies to address legal
jurisdictional and private property issues relating to service laterals. (18-24 months)
4. Technology Demonstration Program: Emerging and Innovative Technologies
for Wastewater Collection System Rehabilitation - A rehabilitation technology
demonstration/verification program, conducted in cooperation with wastewater
utilities. In 2006, EPA's Office of Wastewater Management published a report titled,
"Emerging Technologies for Conveyance Systems - New Installations and
Rehabilitation," which identified many innovative inspection technologies that were
emerging to support collection system rehabilitation. This demonstration program
will be a collaboration between EPA and wastewater utilities, to gather technically
reliable cost and performance data during applications of these technologies in a wide
range of field conditions. (36-48 months)
5 Technology Transfer Product: Inspection and Quality Assurance Procedures
for Installation and Application of Collection System Rehabilitation Methods
and Technologies. This product will provide technical guidance on the development
and implementation of testing and quality assurance practices for field installation of
rehabilitation (repair and replacement) methods and technologies for sewer and non-
sewer assets. This guide will examine best practices selected from wastewater
utilities, vendors and industry. The goal of the product will be to improve installation
practices and collecting critically needed "as built" information for future
rehabilitation decision making. (12-24 months)
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6 Technology Transfer Products: New Materials Evaluation and Collection
System Sewer Pipe Selection Guide. These products will be an evaluation of new
sewer pipe materials and a comprehensive guide for the selection of sewer pipe for
use by wastewater utilities and consulting engineers. This guide will include both
traditional and new, emerging pipe materials. The selection matrix will present
advantages and disadvantages of various pipe materials and pipe designs for use in a
wide variety of conditions and applications. (18-48 months)
7. Applied Research and Review: Collection System Design Based on Lessons
Learned from System Rehabilitation. This research effort will look at experience
from sewer repair and replacement to determine if approaches for sewer designs can
be improved to enhance long-term performance and structural integrity. As collection
systems undergo inspection, condition assessment and rehabilitation, data and
information that could improve system designs is collected. This effort will review
and evaluate those data and information to identify trends and implications on system
design. The outcome will be technical guidance on using experiences from
rehabilitation to improve site-specific designs as well as general design practices
where possible. (24-36 months)
8 Updated Technology Transfer Product: Design Manual - Odor and Corrosion
Control in Sanitary Sewerage Systems and Treatment Plants. This will be an
update of the EPA design manual published in 1985 (EPA/625/1-85/018). This
updated manual will reflect changes in technologies and practices for controlling odor
and corrosion in existing and new collection and treatment systems developed over
the last twenty years. Especially important will be the application of new materials
that are designed to be corrosion resistant. (12-24 months)
References
Tafuri, Anthony, N. and Ariamalar Selvakumar, Wastewater Collection System Infrastructure
Research Needs in the USA, Urban Water, Vol. 4, Issue 1, 2002.
U.S. Environmental Protection Agency. 2006a. Innovation and Research for Water Infrastructure
for the 21st Century - EPA Research Planning Workshop - Draft Meeting Report, March.
U.S. Environmental Protection Agency. 2006b. Innovation and Research for Water
Infrastructure for the 21st Century - Water and Wastewater Infrastructure Draft Research Issues
Report, June.
Water Environment Research Foundation, New Pipes for Old: A Study of Recent Advances in
Sewer Pipe Materials and Technology, 97-CTS-3, 2000.
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Rehabilitation of Water Distribution Systems
Background
When the hydraulic or structural condition of drinking water distribution mains deteriorate, then
cleaning, repair, rehabilitation, replacement, and installation of parallel mains are the available
options. Pipe rehabilitation is the option predominantly addressed in this research plan. Pipe
rehabilitation is done by one of several available lining processes, which are described in more
detail below. Pipe rehabilitation has the potential to substantially and economically increase the
life of, and improve water quality from, existing pipe infrastructure by reducing corrosion,
tuberculation, intrusion potential, leakage, and breaks. It can also reduce energy requirements
due to decreased roughness. Pipe rehabilitation/lining is primarily used for unlined ferrous
mains, which represent a substantial portion of drinking water transmission and distribution
mains. The decision to rehabilitate or replace a pipe is strongly influenced by factors such as the
remaining life of the main, the life extension from rehabilitation, the discount rate, replacement
unit cost, rehabilitation unit cost, and break repair costs. (O'Day, 1986)
State of the Technology
Rehabilitation by lining involves placing a watertight surface inside an existing pipe. Cleaning is
typically needed prior to lining to remove sedimentation, scale, tuberculation, and graphitization.
Thorough cleaning is critical to allow for intimate contact of the liner with the pipe. Surface
preparation significantly affects the strength and bonding of liners (Ashton et al., 1998). There
are three major categories of lining methods based on the structural capabilities and interaction
of the lining and the host pipe: nonstructural, semi structural, and fully structural (AWWA,
2001).
- Nonstructural lining involves placing a thin layer of corrosion-resistant material on the
inner surface of the pipe. The lining is applied to increase the service life by protecting
the inner surface of the pipe from corrosion. It does not increase the structural integrity
of the pipe, and does not substantially reduce leakage (AWWA, 2001). The two most
common linings for water distribution pipes are cement mortar and epoxy. The
cement-based systems depend partly on physical protection due to the lining and partly
on the alkaline passivation due to the pH increase caused by the cement. Epoxy
systems reduce corrosion by forming a thin, impermeable coating on the inside of the
pipe. Nonstructural liners, unlike semistructural and structural liners, do not require
excavation to disconnect and re-connect services lines. Nonstructural lining is the most
economical option where the host pipe is structurally sound. Recent AwwaRF research
projects (Deb et al., 2007 and AwwaRF, 2007) are addressing both epoxy lining and
cement mortar lining. Both of these projects are trying to establish a more technical
basis for the use of these materials using a combination of experience and laboratory
testing. Each project intends to develop an empirical or mechanistic understanding of
the deterioration of these materials in different environments, and produce either an
equation, look-up tables, or decay curves that can be used to better estimate the
projected lifespan of each lining material.
- Semistructural lining involves placing a watertight structure in immediate and
interactive contact with the inner surface of a cleaned pipe. "Since the stiffness of such
35
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a lining is less than that of the host pipe, all internal pressure loads are transferred to the
host piping, leading to their classification as interactive" (AWWA, 2001). A variety of
technologies are available, including: sliplining, close-fit pipe lining, fold and form
pipe, and cured-in-place pipe. For semi structural lining, disconnecting and re-
connecting services increases excavation and labor costs.
a) In sliplining, the liner pipe is inserted into the host pipe either by pulling with a
winch and cable or by pushing with a backhoe or with hydraulic equipment.
Before the liner is inserted into the host pipe, individual sections of pipe are
fused together to form a single pipe longer than the section to be lined. The
annulus between the new pipe and the host pipe is usually filled with grout.
b) Close-fit pipe lining utilizes a continuous pipe that has been deformed
temporarily [either by mechanical rolling (rolldown) or by drawing through a
reduction die (swagelining)] so that its profile is smaller than the inner diameter
of the host pipe. The deformed pipe is inserted into the host pipe and
subsequently expanded by applying pressure to form a tight fit against the wall
of the original pipe. Annulus grouting is not required as with conventional
sliplining.
c) The fold and form lining process utilizes a thermoplastic material (PVC or PE)
which is heated and deformed at the factory (from a circular shape to a "U"
shape) to produce a net cross-section that can be easily fed into the pipe to be
rehabilitated. The fold and form pipe is fed into the existing pipe where hot
water or steam is applied until the liner is heated enough to regain its original
circular shape and create a snug fit within the host pipe. The liner pipe, fully
intact, is then slowly cooled, maintaining the form of the host pipe.
d) Cured-in-place pipe lining involves placing a flexible tube impregnated with a
thermosetting resin into a cleaned host pipe using the inversion process. With
the aid of hot water or steam, the resin cures and stiffens the tube, forming a
new jointless pipe in close contact with the inner wall of the host pipe.
Structural lining involves placing a self-supporting, watertight structure inside a pipe.
Structural lining is typically used in situations requiring minimum disruption to repair
structurally unsatisfactory pipe where loss of flow capacity is acceptable. The resultant
lining is capable of sustaining the maximum allowable operating pressure of the pipe
section being renovated. The structural lining can be either continuous or discrete. For
structural lining, disconnecting and re-connecting services increases excavation and labor
costs.
(a) The continuous lining approach involves inserting a long section of continuous
pipe into the host pipe. The method can cause a significant reduction of the flow
area. Plastic pipe is normally used, although steel can be used. Before the liner is
pulled into the host pipe, individual sections are fused together. Grouting is
typically applied in the annular space between the host pipe and the replacement
pipe.
(b) Segmented pipe lining involves forming a new pipe inside the host pipe using
split pipe segments. The new pipe is constructed by making longitudinal and
circumferential joints of pipe segments. Segmented pipe lining is more common
for wastewater pipes. Segmented lining with a steel liner has been done for PCCP
drinking water mains (e.g., Kelso, et al., 2006). The steel liner sections have an
36
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unwelded longitudinal seam, and the section is compressed by steel bands to a
diameter several inches less than the host PCCP for ease of insertion. After
insertion in the PCCP, the bands are cut and the longitudinal seams and
circumferential joints are welded. The resultant annular space between the two
pipes is grouted. The steel liner also receives a cement mortar lining.
(c) Carbon fiber-epoxy lining has also been used for lining of PCCP. An AwwaRF -
U.S Bureau of Reclamation project, starting in 2007 (AwwaRF, 2007b) will seek
to develop a standard for use of carbon fiber reinforced polymers (CFRP) as a
repair technique for PCCP. This project will develop detailed specifications to
ensure use of appropriate materials and techniques for quality PCCP repairs.
(d) The potential of structural spray-on linings will be investigated in a global
literature review in an AwwaRF project initiated in 2007. An important
advantage of spray-on structural coating is that they significantly reduce the
problem of disconnecting and reconnecting service lines. This project will review
spray-on structural linings for pipeline rehabilitation, including technologies
existing or under development in other countries or industries. A detailed
technical assessment of the suitability of these technologies for application in
North America will be conducted. Methods of overcoming anticipated difficulties
with use of the technologies in North America will be presented.
A number of programs and procedures exist to aid in determining whether to rehabilitate or
replace pipe. More data regarding the applicability, effectiveness, and cost of these programs
and procedures are of interest to the user community. Infrastructure materials (i.e., pipe, liner,
and coating materials) research has been specifically identified by AwwaRF research planning
volunteers as an area of work for concentrated focus. In general, all of the projects addressing
materials have typically considered: improved understanding of the failure mechanisms, strong
and weak applications/characteristics of the materials, and water quality implications of a given
material. As indicated above, recent or ongoing projects are addressing epoxy lining and
cement-mortar lining of ferrous pipes, and carbon fiber-epoxy lining of PCCP. In 2007 a
preliminary investigation (i.e. literature review) of spray-on structural lining is planned by
AwwaRF, as well as an assessment of distribution system "optimization" goals that will include
structural integrity issues.
Research Questions
The research questions below reflect critical gaps in our knowledge of the performance of
innovative rehabilitation technologies, and our ability to determine the most long-term cost
effective rehabilitation methods for the situation being addressed.
1. Are decision-making processes for selecting optimal system rehabilitation technologies
and methods cost-effective, and do they adequately address relevant factors (e.g., long-
and short-term performance and cost, hydraulic effects, structural integrity, condition
assessment, maintenance, water quality, consequence of failure)?
2. Can emerging and innovative pressure system rehabilitation technologies, be identified
and demonstrated/verified in field settings to improve our understanding of their cost-
effectiveness, technical performance and reliability?
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Proposed Research
Based upon the key research questions presented above and the known research projects that are
ongoing or recently completed by other stakeholders, the following research, demonstration and
technology transfer products are proposed. These proposals are presented in priority order. Each
proposal indicates the time frame for the work.
1. Applied Research: Rehabilitation vs. Replacement Decision-making. The
capabilities, limitations, benefits, and costs of the principal, existing approaches for
determining whether to rehabilitate or replace pressure pipes for representative
situations will be identified and characterized. Critical gaps in applicability,
performance, data, and affordability will be identified. Case histories on the
utilization of rehabilitation vs. replacement decision-making approaches will be
collected. A state-of-the-art summary will be produced that will point users to either
existing, innovative approaches or to traditional approaches. The feasibility of
substantially improving upon existing approaches will also be assessed. Specific
recommendations will be made regarding the need for data from accelerated aging
tests and case histories.
2. Technology Demonstration/Verification Program: Emerging and Innovative
Technologies for Pressure Pipe Rehabilitation - A rehabilitation technology
demonstration/verification program will be conducted in cooperation with drinking
water utilities. This demonstration/verification program will gather technically
reliable cost and performance data during applications of these rehabilitation
technologies in a range of field conditions. This project will build on and update
previous field evaluations of water main rehabilitation technologies (Deb et al.,
1999). The initial candidate technology types, based on the EPA research needs
workshop, are: structural lining technologies that either avoid digging up service
connections, or that greatly reduce the time and effort to disconnect and reconnect
services; and, carbon fiber-epoxy lining. A broader survey will be conducted before
making the final selection.
3 Applied Research: Evaluation/improvement of Innovative Repair and
Rehabilitation Materials. This project will complement the
demonstration/verification project by generating or collecting data from, for example,
laboratory-, pilot-scale testing, or case histories for promising innovative materials.
These data will be used in the demonstration/ verification selection process, and will
also fill data gaps not addressed by demonstration/verification. Carbon fiber repair
patches and liners for PCCP and other pipe applications is a specific technology
recommended for further evaluation and improvement at the EPA workshop. There
is a need for retrospective evaluation of performance, evaluation of design issues, and
development and review of design standards. If carbon fiber is selected for study, the
research will be conducted in cooperation with the PCCP users' group, AwwaRF, and
US. Bureau of Reclamation.
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References
American Water Works Association. 2001. Rehabilitation of Water Mains - Manual of Practice
-M28. American Water Works Assocation. Denver, CO. 65pp.
American Water Works Association Research Foundation (AwwaRF). 2007. "Project Snapshot
- Life Expectancy of Field and Factory Applied Cement-Mortar Linings in Ductile-Iron
and Cast-Iron Water Mains-#3126". AwwaRF. Denver, CO.
http://www.awwarf.org/research/TopicsAndProiects/proiectSnapshot.aspx?pn=3126, 1 p.
American Water Works Association Research Foundation (AwwaRF). 2007b. "4114 - Fiber
Rehabilitation of Prestressed Concrete Pipe (US Bureau of Reclamation)."
http://www.awwarf.org/research/PlansAwardsFunding/PrintFriendly_Volunteer%20Opp
ortunities%20for%20AwwaRF%202007%20Proiects.pdf l.p.
Ashton, C.H., V.S. Hope, and J.A. Ockleston. (1998). The Effect of Surface Preparation in the
Repair of Pipes. Paper presented at the Proceedings of the International Conference on
Rehabilitation Technology for the Water Industry, Lille, France. March 23-25.
Deb, A.K. Y.K. Hasit, and C. Norris. 1999. Demonstration of Innovative Water Main Renewal
Techniques. American Water Works Research Foundation. Denver, CO. 113pp.
Deb, A..K., J.K. Snyder, J.O. Hammell, Jr., E. Tyler, L. Gray, and I. Warren. 2007. "Service
Life Analysis of Water Main Epoxy Lining. American Water Works Association
Research Foundation. Denver, CO. 180pp.
O'Day, K.D., R. Weiss, S. Chiavari, D. Blair. 1986. Water Main Evaluation for
Rehabilitation/Replacement. American Water Works Association Research Foundation.
Denver, CO. 182pp.
Kelso, B. A., B.A. Williams, and G. Schult. 2006. "City of Phoenix Embraces Five Year
Rehabilitation Program for the Val Vista Transmission Main." Arizona Water &
Pollution Control Association Newsletter. Vol. 23, No. 2.
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Advanced Concepts - Wastewater Collection-Treatment Systems
Background
Stormwater and wastewater collection systems are a critical link in the urban water cycle,
especially under wet-weather conditions. In the context of pollution control, these systems
transport sanitary wastewater, stormwater, industrial wastewater, irrigation and washwater, and
inflow/infiltration (I/I).
Research in the area of collection systems as means of wet-weather pollution control is showing
signs of renewed activity, especially in Europe and Japan (Henze et al. 1997, Sieker and
Verworn 1996, Ashley 1996, Bally et al. 1996). Case studies of recent applications of
innovations in this country are also receiving attention, as evidenced by recent Water
Environment Federation technical conferences (WEF 1994a, 1994b, 1995a, 1995, 1996) and a
recent EPA seminar (USEPA 1996b). By applying new technology and revisiting traditional
urban water problems with a fresh outlook, advances are being made in a wide variety of sewer-
related areas. By reviewing successful applications of research in recent projects, a vision of
successful wet-weather management of collection systems of the future may be formulated.
A historical review of collection systems in the United States helps with understanding the
problems associated with modern sewer collection systems. Many of the early sewers, including
some from before the turn of the century, are still in service. As cities grew, the need for
stormwater and wastewater conveyance became a necessity to protect human health. Stormwater
and sanitary waste were generally conveyed to the nearest natural water body. In fact, the
modern word "sewer" is derived from the old English word meaning "seaward" (Gayman 1996).
In the late 19th and early part of the 20th century, these conveyance systems were "intercepted"
into a smaller conveyance sized to accommodate a multiple of the estimated dry-weather sanitary
flow (Moffa 1990; Foil et al. 1993; Metcalf and Eddy 1914). The first construction of an
intercepting sewer for combined sewer systems (CSS) in this country was in Boston in 1876
(Foil et al. 1993). The intercepted sewage was usually transported to a primitive treatment plant
consisting of solids and floatables removal via screening and settling (Metcalf and Eddy 1914).
During this period there was considerable debate between proponents of separate systems and
those who favored CSS. The appeal of the combined system was one of economics, especially in
areas where rainfall intensity was high enough to regularly flush the sewers, greatly alleviating
the need for regular cleaning (Metcalf and Eddy 1914). Although engineers in England were
strongly advocating separate systems as early as 1842, primarily for sanitation reasons, engineers
in America were divided. An important engineering monograph of the time by Dr. Rudolph
Hering is quoted in "Design of Sewers" by Metcalf and Eddy (1914):
The advantages of the combined system over a separate one
depend mainly on the following conditions: Where rain-
water must be carried off underground from extensive
districts, and when new sewers must be built for the
purpose, it (combined sewers) will generally be cheaper.
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But more important is the fact that in closely build-up
sections, the surface washings from light rains would carry
an amount of decomposable matter into the rain-water
sewers, which, when it lodges as the flow ceases, will cause
a much greater storage of filth than in well-designed
combined sewers which have a continuous flow and
generally, also, appliances for flushing.
Thus problems associated with settled solids (e.g., maintenance costs and odor problems) were a
primary reason for the spread of combined sewers in this country at the turn of the century.
One of the first separate systems designed in this country was in Memphis, TN following a
yellow fever outbreak in 1873 when more than 2,000 people died. (Metcalf and Eddy 1914; Foil
et al. 1993). Separate sewer systems became more widely accepted as receiving water quality
decreased and potable water supplies were threatened. They were designed primarily for newer
urban areas, but later were also used as a means of doing away whit combined systems. Separate
systems, consisting of sanitary and storm sewers, remain the norm in the United States.
However, stormwater pollution has become more of a concern for urban areas (as well as in rural
agricultural areas); separate untreated stormwater conveyance is now being questioned as an
acceptable design practice. For example, sewer separation, common mitigative action for areas
with severe combined sewer overflow (CSO) problems, has been shown in many areas to be an
unfeasible solution for reducing water quality impacts. In Cincinnati, OH separation of the
combined system was evaluated as a design alternative and shown to be an ineffective means of
controlling the total solids load to the receiving water due to the polluted stormwater runoff from
the untreated separate storm sewers (Zukovs et al. 1996). In addition, national studies have
shown separation to be significantly more costly than other alternatives for CSO pollution
control (Field and Struzeski, 1972).
Skokie, IL offers one example of a "new look." Faced with a massive basement flooding
problem caused by combined sewer surcharging, Skokie found traditional sewer separation to be
unacceptably costly. Accordingly, controlled and below street storage of stormwater was found
to be a cost-effective (one-third the cost of separation) solution. Flow and storage control is
achieved with a system of street berms and flow regulators. The premise of this retrofit system,
which is almost completely implemented throughout the 8.6-square mile community, is that "out
of control" stormwater is the root cause of combined sewer problems. As a side benefit, the
Skokie system includes numerous pollutant-trapping sumps (Walesh and Carr 1998).
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Problems Commonly Associated with Present Day Collection Systems
As described above, some collection systems in use today in the United States represent over 100
years of Infrastructure investment. During that period the technical knowledge of the nature of
wastewater has increased, and the public expectation of the performance and purpose of
collection systems has changed. What was considered state-of-the-art pollution control in 1898
is no longer acceptable. The societal goals that the engineer attempts to satisfy with a
combination of technical feasibility and judgment has undergone drastic changes in the last 30
years (Harremoes 1997). Present-day collection systems, many of which were designed and
constructed in older periods when performance expectations and technical knowledge were less
advanced than today, now must perform to today's elevated standards. At the same time,
sprawling urban growth has strained infrastructure in many areas, exacerbated by poor cradle-to-
grave project management (Harresmoes 1997). Designers of new collection systems must
recognize and address the problems of past designs.
The current status of collection system infrastructure in the United States represents a
combination of combined, sanitary and separate storm sewers. These collection systems vary in
age from over 100 years old to brand new. Although general design practices in the United
States today are not drastically different from 30 years ago, current innovative research in
Europe and Japan suggest that broad societal goals such as "sustainability" are not being
achieved by current design practices in the United States. Old combined sewers discharge raw
sewage to receiving waters. I/I is a costly and wasteful problem associated with sewers.
Sanitary sewer overflows (SSO) discharge raw sewage from failed or under-designed separate
systems. Stormwater pollution associated with urban areas is discharged from separate storm
sewers. Proper transport of solids in sewers is still a misunderstood phenomenon, causing
significant operational problems such as clogging, overflows, and surcharging.
This section provides n overview of the problems commonly associated with collection system
infrastructure currently in use in the United States. Designers of new collection systems must
recognize these problems and address them with modern tools. Unsustainable design practices
must not be allowed to be perpetuated in the field of urban water management. The useful life of
the infrastructure is too long to simply design big systems to compensate for uncertainty.
Following this section are sections describing innovative technologies being investigated and
ways they might be used in the 21st century.
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Combined Sewer Systems (CSS) CSS now constitute one of the remaining large-scale urban
pollution sources in many older parts of major cities (Moffa 1990). In large urban areas, raw
sewage, combined with stormwater runoff, regularly discharges to receiving waters during wet
weather. Water quality problems arise from the stormwater portion of the discharge mixing with
the sanitary wastes associated with the combined sewer. Low dissolved oxygen, high nutrient
loads, fecal matter pathogens, objectionable floatable material, toxins, and solids all are found in
abundance in combined sewage (Moffa 1990). This mixture has led to some of the more
difficult control problems in urban water management. However, CSS problems of today are the
result of technology dating back to 1900 and earlier.
Inflow and Infiltration (I/I) Separate sanitary sewers serve a large portion of the sewered area in
the United States. These sewers are generally of smaller diameter than combined or storm
sewers and serve residential, commercial, and industrial areas. Although sanitary systems are
not specifically designed to carry stormwater, per se, stormwater and groundwater do enter these
systems. This is a common and complicated problem for sewer owners, so common, in fact, that
the design of sanitary sewers must include I/I capacity, which may actually exceed pure sanitary
flow rates (ASCE/WPCF 1982). The capacities of many collection systems are being exceeded
well before the end of their design life, resulting in bypasses, overflows, surcharging and reduced
treatment efficiency (Merril and Butler 1994).
Sanitary Sewer Overflows (SSO) When the capacity of a sanitary sewer is exceeded, untreated
sewage may discharge to the environment. SSO may be due to excessive I/I, from an under
designed (or overdeveloped) area releasing more sanitary flow than the system was designed for,
from a sewer blockage, or from a malfunctioning pump station. The distribution of SSO causes
from a sample of six communities is show in Figure 5.1. An SSO can occur at the downstream
end of a gravity sewer near the head works of a WWTP or at relief points upstream in the
system. I/I is a significant cause of SSO. These relief points may have been designed into the
system, or retrofitted to alleviate the problem, or unexpected surcharging through manholes,
basements or sewer vents.
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Insufficient System
Capacity
Power
Failure
Infiltration
and Inflow
Pipe
Breaks
Based on a sample
of six communities.
The causes of SSOs can
vary significantly from
community to community.
Pipe
Blockages
Figure 5.1. Estimated occurrence of SSO by cause (U.S. EPA 1996b)
SSO are undesirable under any circumstance because they result in relatively high concentrations
of raw sewage flowing directly to surface waters. Wet-weather SSO may behave in a fashion
similar to CSOs in extreme cases, although rehabilitation of the system is different. Instead of
treating overflow (as is often the case of CSOs where the CSS provides primary drainage), wet-
weather SSO are more typically treated by attempting to remove wet-weather sources , enabling
higher flows to the WWTP, or removing hydraulic capacity bottlenecks.
State-of-the-Technology
Combined Sewer Systems (CSS)
The traditional way to control CSO is to first maximize the efficiency of the existing collection
system. This may include an aggressive sewer-cleaning policy to maximize conveyance and
storage properties of the system, reducing the rate of stormwater inflow, a reevaluation of control
points (frequently resulting in raised overflow weirs to maximize in-line storage in a static
sense), and alterations of the wastewater treatment plant's operating policy to better
accommodate short-term wet-weather flows (WWF) (Gross et al. 1994). These measures were
instituted as requirements for CSO discharge permits in 1994 by the EPA. The "Nine Minimum
Control (NMC) "Requirements" are (USEPA 1995b):
1. Proper operation and regular maintenance programs for the sewer system and CSO
points.
2. Maximum use of the collection system for storage.
3. Review and modification of pretreatment programs to ensure CSO impacts are
minimized.
4. Maximization of flow to the WWTP.
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5. Prohibition of dry-weather CSO discharges.
6. Control of solids and floatables.
7. Pollution prevention programs that focus on contaminant reduction activities.
8. Public notification to ensure that the public receives adequate notification of CSO
occurrences and impacts.
9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls.
In creating these permit requirements, the EPA has mandated that all owners must, at a
minimum, adhere to these relatively low-cost management activities.
These measures were frequently not enough, and less passive means of controlling CSO have
been adopted in many cities. Storage of combined sewage, both in-line and off-line, has been
used in a number of locations to capture frequent storms and the "first flush" of large events. As
the capacity in the collection system and treatment works increases when the runoff subsides, the
stored combined sewage is returned to the system for treatment (Field 1990). Although not
completely doing away with CSO (e.g., overflows occur when storage capacity is exceeded),
storage of combined sewage has been a cost-effective CSO control method (Walker et al. 1994).
An interesting development regarding CSS is that because of contaminated stormwater runoff
from urban areas that require treatment, combined systems are now at least being considered for
new urban areas in some parts of Europe. CSS may in fact discharge less pollutant load to
receiving water than separate systems where stormwater is discharged untreated and sanitary
wastewater is treated fully. In southern Germany, CSS are being designed with state-of-the-art
BMPs to reduce the volume of stormwater entering the system. With reduced stormwater input,
the number and volume of overflows are reduced over a traditional "old-fashioned" CSS, thus
only discharging CSO during large, infrequent events, when the receiving water is most likely to
be at high flow conditions also. This concept is discussed in more detail in subsequent sections
of this chapter titled, "Innovative Collection System Design - - The State of the Art" and "Future
Directions: Collection Systems of the 21st Century."
Separate Stormwater Collection Systems and Diffuse Sources
Separate storm sewers of one form or another can be found in virtually every municipality in the
United States. They are typically designed to collect stormwater from urban/suburban areas to
prevent nuisance flooding (e.g., usually storms with return frequencies less than 10 years). This
"level of protection" from flooding replaces an economic efficiency analysis that would ideally
be performed on the basis of the worth of the potential damages resultant from flooding
(ASCE/WEF 1993). The selection of return period is related to the exceedance probability of the
design storm and not the reliability (or probability of failure) of the drainage system
(ASCE/WEF 1993). Typical different levels of protection depending on the land use of the
service area are presented in Table 5.1.
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Table 5.1. Typical design storm frequencies (ASCE 1993).
Land Use
Minor Drainage Systems
Residential
High value commercial
Airports (terminals, roads, aprons)
High value downtown business areas
Major Drainage System Elements
Design Storm
Return Period
(years)
2-5
2-10
2-10
5-10
<100
A more thorough analysis of the expected performance of a drainage system would include a
continuous mathematical simulation of the response of the system over an extended period of
time using measured rainfall in the service area. This analysis would provide a more accurate
estimation of the expected return period at which the capacity of the drainage system would be
exceeded and the magnitude of the exceedences. This information may be used in conjunction
with property values to estimate the distribution of expected damages that result from system
overload, thus providing a more rational basis of design (USAGE 1994). In addition, the quality
of the discharged stormwater may be mathematically simulated, which would provide
information that could be used for receiving water management decisions. A detailed account of
the benefits of continuous storm drainage accounting is provided in Heaney and Wright (1997).
Typical elements of a stormwater system include curbs, gutters, catchbasins, subsurface
conveyance to receiving water, sometimes first passing through a passive treatment facility such
as a dry detention pond, a wet pond, and/or through a constructed wetland (ASCE/WEF 1993).
This typical system may have open channels or swales instead of catchbasins and pipes.
Separate storm sewers may transport various forms of diffuse or stormwater pollution to the
receiving water. The amount and type of contaminant transported is heavily dependent on the
land use of the tributary area, the rainfall/snowmelt characteristics of the area, and the type of
storm sewer. Recent studies have shown a relationship between the impervious tributary area
and receiving water quality. Although the volume and time to peak of storm hydrographs have
long been known to be adversely impacted by imperviousness, the water quality degradation
aspects of imperviousness are still not completely understood, and above all, can be mitigated by
stormwater management practices.
Solids and Their Effect on Sewer Design and Operation
The fundamentals of modern sewer design have not changed in many respects since the
beginning of the century. Review of "Design of Sewers" by Metcalf and Eddy (1914) indicates
that the fundamentals of minimum and maximum velocities, grade, flow rate prediction, and
solids transport were in place at the turn of the century after hundreds of years of trial and error
designs dating back to ancient civilizations. Modern design has significantly refined the
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information used in design, but the basic engineering criteria have remained, much to the credit
of early sanitary engineers.
The purpose of sewer collection systems has always been to safely transport unwanted water and
solids. Historically, sewer design has focused primarily on the volume and flow rate of the fluid
and has assumed solids will be carried with the fluid if certain "rules-of-thumb" regarding
velocity are followed. This imprecise method of designing for solids transport has been a costly
and significant source of maintenance needs over the years in the United States and elsewhere.
Recent research conducted in Europe (Ashley 1996) has focused on the age-old question of
transport of solids in sewers. The flow rate, velocity, and size of pipe are all important in
determining the amount and size distribution of solids a particular sewer will carry. Therefore,
along with flow rate, the solids transport question is one of the most fundamental questions that
must be addressed when calculating costs. It is a vexing question, because solids transport is a
function of flow rate, velocity, pipe size, pipe material, gradient, solids concentration, size and
settling velocity distribution of the solids, and the type of solid (e.g., colloidal or non-colloidal
and grit). Also important is the question of solids transformation in the collection system.
Fundamental research conducted in Europe has shed some light on this issue (Ashley 1996;
Sieker and Verworn 1996; Ackers et al. 1996).
A historic reference to a minimum design velocity is found in Metcalf and Eddy (1914), where
an early sewer design in London is cited as using a value of 2.2 ft/s to avoid unwanted deposition
in sewers. Other early work on minimum grades for various pipe sizes was done by Col. Julius
W. Adams in designing the Brooklyn, NY sewers in 1857 - 1859 (Metcalf and Eddy 1914). Col.
Adams' recommended sewer grades are shown in Table 5.2 and compared with modern values
found in Gravity Sanitary Sewer Design and Construction (ASCE/WPCF 1982). These early
designers recognized that the minimum mean velocity to avoid deposition was dependent on the
pipe diameter.
However, in the 1994 WEFTEC proceeding "Collection Systems: Residuals and Biosolids
Management," a paper entitled, "Two feet per second ain't even close" by P.L Schafer discusses
the problems associated with deposition in large diameter sewers due to using a "rule-of-thumb"
design value of 2.0 ft/s (Schafer 1994). Modern design guidelines still state: "Accepted
standards dictate that the minimum design velocity should not be less than 0.60 m/sec (2.0 ft/s)
or generally greater than 3.5 m/s (10 ft/s) at peak flow." (ASCE/WPCF 1982). One problem
with this recommendation is the lack of peak flow definition. Should this be the seasonal,
monthly, daily, or hourly peak flow? The frequency and duration of the flushing flow are critical
to the proper performance of the sewer. Ideally, a settled sewer particle at the furthest end of the
collection system will be reentered into the waste stream and carried to the WWTP. Clearly the
minimum velocity design problem has not been resolved.
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Table 5.2. Comparison of recommended minimum sewer grades and velocities over the years.
Source
Balzalgette, London, c.
1852(1)
Roe, London, c. 1840(1)
New Jersey Board of
Health, 1913 (1)
Metcalf and Eddy, 1914 (2)
WPCF/WEF, 1982 (3)
WEF/ASCE, 1992 (4)
Acker etal. 1996 (5)
Type of sewer and pipe diameter
Large intercepting sewers — combined
system
Large intercepting sewers — combined
system
8 in. - Sanitary sewer (n = 0.013)
12 in. - Sanitary sewer ( n = 0.013)
24 in. - Sanitary sewer (n = 0.013
Combined systems
Sanitary systems
Sanitary systems
Storm Sewers
150 mm (5. 9 in.)
225 mm (8.85 in.)
300 mm (11. 8 in.)
450 mm (17.7 in.)
600 mm (23. 6 in.)
750 mm (29.5 in.)
1000 mm (39.3 in.)
1800 mm (70.8 in.)
Minimum
Slope
(ft/ft)
0.002
0.004
0.0022
0.0008
0.0062
0.0043
0.0032
0.0024
0.0021
0.0022
0.0025
0.0028
Minimum
Velocity
(ft/s)
2.2
2.5
2.0
2.0
2-3
2.2
2.36
2.46
2.59
2.95
3.48
4.43
6.66
Note:
1. Col. Julius W. Adams (c. 1859) in Metcalf and Eddy (1914)
2. Metcalf and Eddy (1914)
3. ASCE/WPCF (1982)
4. ASCE/WEF (1992)
5. Ackers etal. (1996)
Sewers that exhibit sediment deposition are prone to a multitude of problems over time. Excess
sedimentation promotes clogging, backwater, and surcharging and may promote corrosion by
producing hydrogen sulfide (Schafer 1994). Because sedimentation problems are more likely to
occur in larger diameter sewers, such as trunk sewers, the associated costs of sewer failure may
be substantially greater than in a smaller diameter pipe. In combined systems, the storage
capacity that is taken up in a heavily sediment-laden trunk or interceptor sewer will tend to
increase the volume and frequency of overflow events (Mark et al. 1996). In addition, the
deposited sediments in combined systems represent a buildup of pollutants that may resuspend
during wet weather (Gent et al. 1996).
When considering sewer collection systems, the proper transport of solids is crucial to a correctly
functioning system. There are distinct areas where deposition should be avoided (e.g., the
conduit network) and also areas where deposition is desired (e.g., treatment works). The system
should function under a wide range of hydraulic conditions and under a wide range of solid
loadings. The solids may also vary widely in character, which may alter the performance of the
sewer.
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To avoid deposition, a common design method is to calculate the shear stress required to move
the largest size of particle expected in the sewer under average or high-flow conditions (Schafer
1994). This assumes that the frequency of the high flow is enough to avoid excessive deposition
and the subsequent creation of a permanent bed layer. The critical shear stress of a particle is
defined as the minimum boundary stress required to initiate motion (Schafer 1994). Chow
(1959) indicates that shear stress is a function of the specific weight of water and the hydraulic
radius and invert slope of the sewer. Various values of critical shear stress have been
recommended, depending on the maximum size of particle found in the sewer. Values of critical
shear stress recommended by various researchers are show in Table 5.3.
Table 5.3. Recommended critical shear stress to move sewer deposits (Schafer 1994).
Recommended critical
Shear stress
N/m2
4
4
1.5-2.0
1-2
3-4
2.5
6-7
lb/ft2
0.08
0.08
0.03-0.04
0.02-0.04
0.06-0.08
0.05
0.12-0.14
Reference
Lynse 1969
Paintal 1972
Schultz 1960
Yao 1974
Yao 1974
Nalluri 1992
Nalluri 1992
Conditions
Sanitary sewers
Sanitary sewers
German systems
Sanitary sewer with small grit size
Storm sewers
Sand with weak cohesiveness
Sand with high cohesiveness
Note: 1 N/m2 = 0.02064 lb/ft2
Schafter (1994) recommends that the lower end of the shear stress range in Table 5.3 is adequate
only for waste streams with small particle size and limited grit and when flushing flows may be
expected daily. The high end of the range is appropriate when the waste stream contains heavy
grit and gravel, as is common in combined or storm sewers (Schafer 1994). Table 5.3 indicates
that commonly used design values for the minimum flushing velocities in sewers are not
adequate to resuspend grit from large sewers. Consider, for example, a 48- in.-diameter sewer
transporting a reasonable load of grit. Minimum velocities in the range of 4.0 ft/s are required to
flush deposited grit, far greater than the 2.0 ft/s recommended in some design guidelines.
However, European research shows that bed stress is the most important criterion, and a
minimum bed shear stress of 2 N/m2 is required to ensure sediment transport (Ashley and
Verbanck, 1997).
Uncertainty in key design parameters is the source of unnecessary cost. If under designed,
operation and maintenance costs are likely to be high. If over designed, additional unnecessary
capital costs are incurred as are high-maintenance costs due to solids deposition at low flows.
However, in addition to the lack of high-quality frequency/duration information regarding flows,
the designer concerned with solids transportation must also contend with a physical process
about which only the rudimentary nature is known. The relationship between the solids
concentration, the distribution of settling velocities, and the dynamics of movement are not well
understood for gravity pipe flow. Operational costs will be incurred if the frequency and
49
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duration of velocities are not enough to regularly cleanse the pipes. Deposition in unclean
sanitary sewers will cause SSOs. Thus, environmental costs are also incurred. If over designed,
the sewers will remain clean; however, additional excavation and material costs will be incurred.
Although attempts have been made to estimate costs of I/I and SSO on a national basis, there are
no cost estimations of improperly designed sewers. It is likely that these costs, if known, would
dwarf those for I/I and SSO. As in the case with I/I estimation, new systems that record and
store operational data will be invaluable to improving design techniques for solids transport.
Innovative Collection System Design - The State-of-the-Art
Recent work in all aspects of sewer collection systems, from design and facilities-planning level
research to construction and operation and maintenance, shows promise for greatly improved
collection system performance for the next century. In addition, drastically new technologies
that may greatly affect the future configuration of urban water management are being considered.
Some innovators in the field are advancing ideas to replace water-intensive waste removal
systems.
This section provides an overview of many aspects of sewer concepts. It is generally organized
in terms of increasing innovation. In other words, the first examples remain closest to present-
day systems, and the last innovations described deviate farthest from current design concepts.
The reader is reminded that this section is an overview of innovative ideas in the field of waste
management. The section following this one attempts to provide these technologies in a future
scenario-type context.
Recent literature in the area of sewer innovation were surveyed from WEF (1994a), WEF
(1994b), WEF (1995a), WEF (1995b), WEF (1996), Sieker and Verworn 1996, Ashley 1996,
Bally et al. (1996), Henze et al. (1997), USEPA (1991a), and USEPA (1991b). Especially
important summary of vacuum, pressure, and small-diameter gravity sewers is presented in
USEPA (1991b).
Real-Time Control (RTC) Many fields, including that of urban water management, have barely
been able to keep up with the rapid technological and computational advances of the past decade.
This has been exacerbated in the United States by the relative longevity of civil infrastructure
works and the amount of infrastructure already in place, with most being constructed in the 20th
century. As the end of the project life of many of these works is approaching, and as new urban
areas are being contemplated for certain high-growth sections of the United States, practitioners
and researchers in the field of urban water management have a unique window of opportunity.
Now is the time to take advantage of the latest in technological advances and to use the past two
decades as a model to predict what the future may bring in terms of technology.
The information age has changed the way in which resources are managed. This fact will be
more apparent in new collection systems and waste management of the 21st century. New
systems will be operationally data-intensive because of a higher level of control. The current
level of control in WWTPs may be seen as extending into the collection system. The increase in
data quality and quantity will have positive effects on simulation for design, simulation for
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operation, and for real-time control of the system. These innovations should decrease costs and
environmental impacts and maximize utility of the system.
Seattle, WA was one of the first major municipal sewer owners in the United States to use real-
time measurements of the collection system in a control scheme (Gonwa et al. 1994; Vitasovic et
al. 1994). Vitasovic et al. (1994) describes the use of real-time control (RTC) in Seattle for CSO
control purposes. Vitasovic (1994) states the goal of the program succinctly:
.. .the idea behind RTC of CSO's is fairly straightforward:
the conveyance system is controlled in real time with the
objective of maximizing the utilization of in-line storage
available within the system. The cost of the control system
is often a fraction of the cost required for alternatives that
include construction of new storage facilities.
The Seattle experience highlights the need for some form of system simulation to test control
procedures off-line and to provide a higher level of system knowledge on-line than from data
measurement alone (Vitasovic et al. 1994). A supervisory control and data acquisition (SCADA)
system provides automation one level above manual process level control and interfaces data
retrieval systems with a relational database (Vitasovic et al. 1994; Dent and Davis 1995). Under
the SCADA level of control, operators usually manage the system from a centralized location
using man-machine interface (MMI) software, receiving data from the SCADA, while
maintaining a supervisory level of control over the system (Vitasovic et al. 1994, Dent and Davis
1995). A higher level of automation may be used if a computer controller is used to change
system operation. This can
include simple control algorithms, such as if-then and set-level points, or may be as advanced as
providing on-line nonlinear optimization (e.g., genetic algorithms).
Other successful applications of RTC in the United States include Lima, OH, Milwaukee, WI,
and Cleveland, OH. Gonwa et al. (1994) provide a summary of the Milwaukee upgrade of an
existing RTC. One new feature of the upgrade was additional control applied to the headworks
oftheWWTP.
The hydraulic grade line of the Milwaukee system modified by the RTC upstream of the WWTP
resulted in 1,500,000 m3 in-line storage volume during peak storm diversions after interceptor
storage is maximized. In other words, the RTC provides control of the system to maximize pipe
storage before diverting to the in-line storage system. RTC is used in combination with storage
facilities to minimize overflows.
Most applications of RTC, SCADA, automated system optimization and other advanced data
management techniques are currently used in collection systems designed before the
computer/information age revolution. For new collection system designs, it is imperative that
designers understand the physical/structural requirements of long-term high-quality data
measurement. Successful design will have adaptivity "built-in." The ability to change
operational procedures as technological advances become available will greatly extend the useful
life of future collection systems. In other words, future collection systems will have many
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critical "high information points" that, used in conjunction with control and simulation, will
facilitate operating the system for optimal utilization. The tools used to accomplish this task will
change during the project life of the system because of the longevity of infrastructure in contrast
with the rapidity of computer technological advances. A successful design will anticipate these
changes.
Sanitary Sewer Technology - Vacuum Sewers Hassett (1995) provides a summary of current
vacuum sewer technology. A typical vacuum sewer configuration is shown in Figure 5.2.
Centra! Vacuum and Pumping Station
Wastewater to
Treatment Plant
Figure 5.2. Typical vacuum sewer system schematic (Hassett 1995)
Vacuum sewers are typified by shallow pipelines that make them attractive for high-groundwater
areas and for alignments that would require expensive rock excavation for gravity lines. Such
systems are also useful in flat countries such as the Netherlands. Being completely sealed,
vacuum lines also do not have any I/I - a remarkable benefit that begs the question: If vacuum
sewer lines can be constructed water tight, why not gravity lines? Vacuum systems do show
promise, however, especially with recent advances in lifting capabilities. A recent installation in
an Amtrak station in Chicago, IL used a valve configuration that achieved over 20 ft of vacuum
lift (Hassett 1995). Another advantage of these systems is the vacuum toilets function with less
than a third of water per flush than do modern low-flush toilets, using only 0.3-0.4 gallons per
flush, compared to 1.5-6.0 gallons for toilets connected to gravity sewers
Hassett (1995) provides a cost comparison for vacuum sewers for an actual project location in
Virginia. The service area was assumed flat with a 3 ft depth to groundwater, an area of 750
acres (300 hectares) and approximately 750 residential units housing 3,000 people. The density
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was then varied to provide the construction cost information presented in Figure 5.3 and the
operating costs shown in Table 5.4. Hassett (1995) notes that the operating costs of any of the
system configurations is only 4-6% of the present value of the capital components and is,
therefore, unlikely to be a decision factor. This observation may not be true in countries with
higher energy cots.
Table 5.4. Annual operating costs of vacuum and gravity sewer systems as of 1995
(Hassett 1995)
Type of Sanitary
Sewer System
Gravity (Dry)
Gravity (Wet) 1
Modern Vacuum
High Lift Vacuum
Cost (1995$ U.S.)
Labor
26,000
28,000
42,000
34,000
Materials
3,000
28,000
10,000
3,000
Power
4,000
4,000
8,000
8,000
Total
33,000
60,000
60,000
45,000
Wet means that the system includes lift stations and is below the water table.
A major advantage of these systems (along with pressure sewers) is their adaptability to
monitoring and control. The use of pressure instead of gravity flow simplifies flow
measurement. Control of these systems is more exact than with gravity systems, thereby making
them suited for overall system optimization by RTC.
Sanitary Sewer Technology -Low-Pressure Sewers (LPS) Another modern collection system
technology that has been used in the United States is the low-pressure sewer used in conjunction
with a grinder pump (Farrell and Darrah 1994). These systems use a small grinder pump
typically installed at each residence. The grinder pump reduces solids to 0.25 - 0.5 in. maximum
dimension (Farrell and Darrah 1994). Like vacuum systems, these low-pressure grinder systems
feature watertight piping, thus virtually eliminating I/I. A full system in Washington County,
MD went on-line in 1991. Water use, rainfall and wastewater flows were monitored, and
wastewater flows were found to be 110-130 gpcd, with no measurable increase during or
following wet-weather events (Farrell and Darrah 1994).
A demonstration facility in Albany, NY was installed in 1972, where per capita flows were only
45 gpd. One purpose of this demonstration was to determine the effect of grinding solids on
settleability. The conclusion was that there was no effect on settleability and treatability
compared with solids transported via a traditional gravity sewer (Farrell and Darrah 1994).
Other demonstrations found no significant differences in grease concentrations (Farrell and
Darrah 1994). The LPS pipe was excavated after several years of service and significant
buildups of solids were noted in the pipes (Farrell and Darrah 1994).
LPS systems have more than a 20-year track record. As with most new technologies, engineers
were hesitant to specify these sewers despite smaller capital expenditures due to the lack of long-
term experience (Farrell and Darrah 1994). The reliability and costs of operating and
maintaining the pumps were a major impediment to widespread use. Reliability of LPS systems
has increased dramatically since the first commercial installation at a marina in the Adirondack
Mountains in NY (Farrell and Darrah 1994). In the 1972 Albany demonstration project (which
53
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only lasted 13 months), the mean time between service calls for pump maintenance was 0.9 years
(Farrell and Darrah 1994). An LPS system installed in 1986 in Bloomingdate, GA averaged 10.4
years between service calls (Farrell and Darrah 1994) over an 8-year period.
As with vacuum systems, LPS systems are well suited for control and monitoring because of the
use of pressure rather than gravity to drive the system. This may be significant advantage over
gravity systems in the future for RTC applications.
Sanitary Sewer Technology -Small-Diameter Gravity Sewers These systems consist of a system
of interceptor tanks, usually located on the property served, a network of small-diameter
collector gravity sewers (USEPA 1991b). The interceptor tanks remove settleable solids and
grease from the wastewater. Effluent from each tank is discharged to the collector sewer via
gravity or by pumping septic tank effluent pumping (USEPA 1991b). A typical system layout is
shown in Figure 5.3
Settteable Solids Soluble Bod Lateral
Inlet
Scum
Sludge
Outlet
Figure 5.3. Components of small-diameter gravity sewer systems (U.S. EPA 1991b)
This system has the advantage of not having to transport appreciable solids (USEPA 1991b).
Cost savings, therefore, result from having a lower required velocity and from less cleaning
54
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costs. Also, peak flows are attenuated in the tank. Therefore, the average to peak flow rate from
wastewater is far less than for a standard gravity sewer (USEPA 1991b)
Otherwise, these systems function much the same as traditional gravity sewers. They have been
used in rural areas to replace existing septic tank discharge. A problem associated with these
sewers are I/I. The use of old septic tanks tend to increase the amount of rainfall induced
infiltration (USEPA 1991b)
Blackwater/Graywater Separation Systems
A more drastic break with modern systems is that of water separation at the household level.
This has been a relatively active research area in recent years because of its appeal from a water
conservation standpoint. Water from faucets, showers, dishwashers and clothes washers drains
to a separate on-site filtration device. The filtered water is then typically used for outdoor
irrigation. This may be especially advantageous in arid areas where on-site stormwater detention
for outdoor use does not meet the evapo-transpiration needs on an average annual basis.
Waste/Source Separation
Recent research in Europe has focused on the separation of household waste in a variety of ways
(Henze et al. 1997). The goal of these systems is to promote nutrient recycling and limit entropy
gain (a goal for sustainability) via dilution. Urine separation is perhaps the most radical
departure, where urine is tanked on-site and converted to fertilizer (Hanaeus et al. 1997). Human
urine contains 70% of the phosphorus and 90% of the nitrogen found in wastewater from toilets
(Hanaeus et al. 1997). This technology is still in the formulation phase and has only been tested
on a limited basis. Research shows it may have applicability for certain waste management
applications.
High-Density Areas
Areas with the highest levels of urban stormwater pollution will require stormwater treatment,
much as they do today. A form of CSS, or an integrated storm-sanitary system (ISS) (Lemmen
et al. 1996) will capture a large portion of the annual runoff volume from dense urban areas.
Storm runoff will be reduced by source control and infiltration BMPs/LIDs, and the residual of
small events will be transported to the WWTP. Large events will be throttled out of the ISS,
before mixing with sanitary waste, and discharged to receiving waters. This new system will
have the best of both CSS and separate systems. The advantage of the combined system has
been treatment of small runoff-producing events, including snowmelt. However, the
disadvantage has always been the discharge of raw sewage to receiving waters during large
events. With the advantage of control technology, as the sewers and/or the WWTP reach
capacity, the stormwater is diverted directly to receiving waters, without mixing with sanitary
and industrial wastes. WWTP will be made larger to afford treating more stormflow.
This system will have a high degree of built-in control. The data stream begins with local radar
observations. This information is combined with real-time ground level measurements of
rainfall. These data will be used to predict the rainfall patterns over the catchments for the next
half hour. The SCAD A system receives information about the present state of the sanitary and
55
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storm portions of the waste stream. Quality and quantity are monitored. Performance of high-
rate treatment devices operating on the discharged stormwater is monitored. A critical
innovation is the integration of the WWTP performance, operation, and control into the system.
Operation of the WWTP now extends to the collection system. Rainfall information, in
conjunction with the state of the system and receiving water data, are used to predict potential
outcomes of the wet-weather event with a system simulation model. Coupled with a non-linear
optimization routine, and optimal control scheme is determined on-line, and changes in system
control are relayed back to the system via the SCADA system.
The system response is fed back to the SCADA, and continuous control is maintained throughout
the wet-weather event. This "feedback" loop provides the municipality with rapid response for
flashy summer events and provides urban flood control simultaneously with water quality
control. In addition, the time series of wet-weather data are now stored in a relational database,
spatially segregated to interface with static geography stored in a GIS.
Future Collection System Scenarios
Innovative Integrated Systems Although old CSS are considered a major source of urban
pollution, there is some recent activity in the area of new CSS. Where urban areas have
significant amounts of stormwater pollution that requires treatment, it may be possible to design
a CSS to capture most of the annual storm volume for treatment at a WWTP, without
discharging raw sewage during major events. Lemmen et al. (1996) describe a concept for a
sewer system in the Netherlands that has connections between the storm drainage network and
the sanitary collection system.
Walesh and Carr (1998) and Loucks and Morgan (1995) describe use of controlled storage of
stormwater on and below streets to control surcharging and solve basement flooding in a CSS.
The premise of this approach is that stormwater flow rate, not volume, is the principal cause of
surcharging of CSS and resulting basement flooding and CSO. On and below street storage of
stormwater, strategically placed throughout the CSS, reduces peak stormwater flows to rates that
can be accommodated in the CSS without surcharging. The two large-scale, constructed, and
cost-effective projects described by Walesh and Carr and by Loucks and Morgan were retrofits.
However, the success of these projects suggests integrating the design of streets and CSS in
newly developing high intensity areas.
Suburban Development Outlying from the new urban centers, suburban-type development still
exists. Although less dense than the city, new suburban development contains some of the
mixed land uses found in the urban center. The collection system serving this area is far
different from the city, however, because the stormwater pollution is not so severe as to warrant
full treatment at the WWTP. BMPs and source control innovations will reduce the stormwater
impacts on the receiving water. Regional detention is used for flood control and water quality
enhancement while possibly providing recreation.
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Sanitary wastes are transported via pressure sewers to collector gravity lines at the city's border.
The use of pressure sewers has reduced suburban I/I to near zero. In addition, the new sanitary
LPS sewers are very easy to monitor, because the age-old problem of open channel flow
estimation is avoided by using pressure lines. This provides added certainty in the flow
estimation and lends itself very well to control. Technology borrowed from the water
distribution field has achieved a great level of system reliability and control. In fact, the sewer
now mirrors the water distribution network, essentially providing the inverse service.
Research Questions
1. On a global basis, what is the state-of-the-technology in the field of sewerage system
design?
2. Is there a better way to design and operate sewerage systems given the concern for WWF
stressors and are there emerging technologies that can be used for treating and controlling
WWF at a reasonable cost?
3. What effective watershed management strategies are available and how do
communities/utilities select the most appropriate subset from these to match specific
watershed needs?
4. How can we effectively prevent and reduce pollutant discharges to receiving waters of
the urban watershed?
5. What are the best approaches to retrofit existing and construct new sewer/sewerage
systems in urban settings?
Proposed Research
1. Conduct a worldwide search of the literature (including grey literature), WERF,
AWWARF, EU, and other international organizations covering advanced sewerage-
system design and technology and from that effort, develop a refined research,
development and demonstration strategy for NRMRL.
2. Develop and demonstrate innovative integrated sewerage system designs for new urban
areas, retrofitting existing urban areas, retrofitting existing CSS, and upstream additions
to existing CSS. This project will result in a series of design/guidance manuals for
engineers involved with municipal/utility sewerage system upgrading, planning, and
design. The initial report will be on innovative integrated sewerage system designs for
new and existing urban areas. This report will be the outcome from a comprehensive
evaluation and assessment of the current state-of-the-art-technology on innovative
approaches for integrating the collection and treatment of dry weather and wet weather
flows to achieve optimal water quality protection in the most cost-efficient manner. The
initial phase will be to develop a comprehensive inventory of approaches being applied
around the world, including approaches for newly developing areas and approaches that
consider retrofitting and upstream/upland control techniques for existing systems. Case
57
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studies of the existing applications will be documented. The advanced design strategy
shall include but not be limited to:
(1) larger diameter sewers, upland impoundment and flow attenuated via soil
infiltration and redirecting runoff, and intermittent mid-stream basins all for the
purposes of adding storage capacity and/or reducing flow of/to the system;
(2) steeper sloped sewers with and without more effective bottom cross-sections
to reduce/eliminate antecedent dry-weather flow (DWF) pollutant and solids
deposition and resulting concentrated storm flushes;
(3) sewer grit/sediment traps and automatic sediment cleaning to reduce and
eliminate blockages and high-pollutant load storm-flush events;
(4) upland best management practices (BMP) and low-impact development (LID)
to reduce down stream flow and pollutant loads;
(5) sacrificial flood zones to protect down streamed (high-population
density/commercial) areas to reduce pollution, drainage channel size, and flood
impact;
(6) beneficial use of stormwater for non-potable purposes to reduce water supply
demand, pollution/flood impacts;
(7) real-time control to optimize routing and storage capacity to reduce system
costs for stormflow control/treatment;
(8) higher WWTP capacity to include treatment of stormflow and not just
treatment of peak DWF;
(9) larger interceptors to be in concert with higher WWTP capacity;
(10) higher WWTP hydraulic loading during stormflow events, and
(11) alternative high-rate WWTP treatment methods.
3. Develop and demonstrate methods for stormwater non-potable beneficial use as a means
of reducing potable and wastewater infrastructure, municipal water demand, and
stormwater pollution, erosion/sedimentation. These stormwater non-potable uses shall
include but not be limited to: lawn irrigation, firefighting, greywater, washwater,
industrial process and cooling tower, subsurface recharge, and dual-pipe non-potable
water supply.
4. Develop and demonstrate planning and design guidance documents on innovative
sanitary sewer technologies including vacuum sewers, low-pressure sewers (LPS), and
small diameter gravity sewers. The initial report will be the outcome from a
comprehensive assessment of the state-of-the-technology of innovative sanitary sewer
approaches. The final report will be the result of actual demonstrated technologies.
5. Develop a guidance documents for blackwater/greywater separation systems based on an
assessment of the state-of-the-technology and an actual demonstration.
6. Assess and develop a guidance document for waste/source separation technology
including the separation of urine on-site and its conversion to fertilizer.
7. Demonstrate an innovative municipal waste management system utilizing advanced
sewer designs and waste separation technologies to result in a design guidance report.
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Environment and Technology. December 1993.
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Inc. Three Lakes, WI.
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Advanced Concepts - Drinking Water Distribution Systems
Background
Deteriorating water infrastructure, increasing populations, limited water resources, and more
stringent water quality requirements pose technical and financial challenges for water utilities.
However, these circumstances also provide an impetus for re-assessing traditional drinking water
conveyance system designs and practices for the purpose of identifying and selecting more
effective and efficient approaches for meeting current and future water quantity, quality, and cost
goals.
Another impetus for re-assessing and modifying traditional approaches is the increasing
availability of innovative technology that may enable, at a price, more extensive and intensive
monitoring, assessment, and control of water quality, hydraulic, and structural aspects of water
distribution systems. Examples of innovative technology areas include materials, sensors,
communications, computing, modeling, and geographic information systems.
State of the Technology
Advanced concepts for operating distribution systems fall into two broad categories: dual
systems and innovation to maintain/improve water quality in traditional distribution systems.
• The dual systems approach involves splitting the distribution system into two systems -
one for potable water use only, and the other for firefighting and other non-potable uses.
This approach is most amenable to new systems.
• Maintaining/improving water quality in traditional distribution systems does not
eliminate the problems posed by combined drinking water and fire fighting systems, but
it seeks to minimize them by a combination of design, monitoring, modeling, and control
activities.
Dual Systems
Water distribution systems supply water for fire fighting, non-potable uses (e.g., toilet flushing,
landscape watering), and potable uses (e.g., drinking, bathing, cooking). Although there are
economies of scale from serving all of these needs with one distribution system, there are also
adverse effects on drinking water quality, and on the volumes of water that need to be treated to
potable water standards. The quantity and pressure requirements for fire fighting dictate much
larger pipe diameters and storage tanks than are required to meet potable water uses. "Current
practice, together with the need for larger elevated storage tanks for fire protection, results in
extremely excessive residence time between treatment facilities and the consumer, which has
been shown to be the leading cause of water quality degradation in distribution systems" (Okun,
2005). This causes residence times in current distribution systems to be much longer and more
favorable for biological growth and water quality deterioration in the distribution system.
Deteriorating water quality requires more aggressive disinfection, which can cause an increase in
disinfection byproducts, which have been linked to adverse health effects.
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Dual water systems have been introduced to conserve water through beneficial re-use of
wastewaters for non-potable uses. "Today in the U.S., some 2000 water utilities, large and
small, operate dual systems" (Okun, 2005). However, even in these systems the drinking water
distribution system is still designed to meet fire flow requirements, so the long-residence-time
issue is not resolved. In fact, if the total flow through the drinking water system declines due to
elimination of non-potable usage, then residence time will increase. "A dual system where the
possibility of having drinking water distribution systems being relieved of fire protection has
only appeared in a few places in the U.S. One is a 1997 paper [Okun, 1997]. Another is a 2002
joint publication of the AWWA Research Foundation, and the Netherland's KIWA; Impacts of
Fire Flow on Distribution Systems" (AwwaRF and KIWA, 2002). Okun recommends that all
future new dual systems be designed and constructed to not only conserve water, but also to
substantially improve drinking water quality. He recommends that fire fighting water needs be
met with nonpotable water that is distributed separately from drinking water. Separating fire
flow from drinking water will enable the water distribution pipes and tanks to be designed,
constructed and operated in a manner more conducive to maintaining water quality during
distribution. For example, tanks and pipes could be smaller and flow rates higher, which would
reduce residence times, biofilm growth, sedimentation, and water quality deterioration.
Distribution needs can be met by 2-in. pipes, as opposed to 6-in or 8-in. pipes required to meet
fire flow requirements. Also, if stainless steel were used for the distribution pipes, then longer
pipe lengths (e.g., 60-ft, compared to 18-ft) and welded joints could be used, which would reduce
the number of joints, corrosion, intrusion potential, and leakage. Stainless steel may not require
cement liners, which can promote biofilm growth. In a drinking-water-only system there should
be substantially reduced costs from pipe installation, treatment, pumping, corrosion control,
leakage, and maintenance. The use of much smaller pipes, higher flow rates, less biofilm,
corrosion, and less sedimentation would also reduce both the frequency and the volume of water
used for flushing. One dual water system that separates drinking water and fire protection has
been adopted for a new suburb in Sydney, Australia. The cost savings and water quality
improvements for drinking water need to be compared on a case-by-case basis to the technical
and economic effects arising from integrating the fire fighting and non-potable water systems.
Innovative Improvement of Water Quality in Traditional Systems
Successful management of a water distribution system requires balancing multiple factors, some
of them competitive, in order to meet quantity, quality, pressure, and reliability goals at an
acceptable cost. Most existing distribution systems address drinking water, fire fighting, and
non-potable uses, so over-sized pipes and tanks, and the potential for excess residence times,
excess treatment, and sedimentation are unavoidable facets of the system that have to be
addressed in order to maintain or improve water quality. There are also other undesirable water
quality conditions, unrelated to fire protection, that have to be managed. Table 1 lists some of the
factors and their potential effects on the cited goals.
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Table 1. Distribution System Trade-offs
System Feature
Fire flow requirements
Fire pressure requirements
Disinfection
Anti-corrosion lining
Anti-corrosion additives
Measure/model/control
flow
Measure/model/control
water quality
Measure/model/control
structural integrity
Satellite/point of
entry/point of use
treatment
Storage: tanks - size,
distance from plant
Storage: in-ground
Active storage mgt.
Passive storage mgt.
Quantity
+
2
+
+
Quality
i
-/+4
-/+5
+
+
+
+
+
9
9
•
+
-
Pressure
+
+
+
Reliability
-
+
+
+
+
9
Cost
3
-
6
-
-
-
9
+
-
+
+ = the system feature has a positive effect on the element in the header
- = the system feature has an adverse negative effect on the element in the header
? = direction and magnitude of change is unclear
1 = water quantity requirements for fire flow dictate larger pipes and therefore longer
residence times; longer residence times increase biotic and abiotic reactions, in pipe wall
and bulk water, which reduces disinfectant residual, allowing re-growth of pathogens
2 = high pressure increases leakage
3 = increased leakage wastes the investment in treatment and pumping the lost water
4 = disinfection of pathogens is a positive; disinfection byproducts a negative
5 = linings can promote biofilm growth; linings reduce corrosion/tuberculation
6 = Zn-containing additives reduce corrosion, but may affect disposal cost of wastewater
treatment residuals
Innovative technologies and procedures can potentially help determine and maintain the desired
range of system performance. Relevant technologies include:
• pressure, flow, water quality, corrosion, and structural integrity monitoring that is more
intensive, extensive, rapid, accurate, and economical
• predictive models for pipe and tank hydraulics and water quality
• predictive models for contaminant formation, depletion, and migration
• predictive models for structural deterioration and failure
• cost models
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• communications and control systems integrated to measurement and modeling systems
that enable necessary and timely decisions and adjustments of flow rates, flow paths,
pressure, disinfectant, corrosion control, and inspection and maintenance activities
• storage tank design or operation modifications to reduce residence time
• point of entry or point of use treatment
Technologies in the above categories already exist, but further improvement, evaluation, or
verification is needed to support user community decisions on their use. For example, the
development and integration of distribution system computer models, graphical user interfaces,
and geographic information systems has greatly improved and simplified the process of
distribution system modeling. "Modeling water distribution systems with computers is a
proved, effective, and reliable technology for simulating and analyzing system behavior under a
wide range of hydraulic conditions." (Ysusi, 1999). There are a wide range of distribution
system models available. However, further improvements are needed for hydraulic models for:
multiple sources of supply with variable water quality, pipe wall/water column interactions,
disinfection byproducts (DBF) kinetics over time and space, transient low pressures, intrusion
flow and quality, dead end spatial and temporal demands, and cost modeling.
This research will be closely coordinated with other research organizations that have completed,
ongoing, or planned projects on topics in this area.
Research Questions
1. How can distribution systems be designed, constructed, and operated to achieve a better
balance between water quantity and quality requirements, fire protection, and cost?
2. How can measuring, sensing, modeling, and system control be improved and effectively
integrated to improve water quality and system efficiency?
Proposed Research
1 Dual Systems
a. Retrospective Assessments of Dual Systems for Potable and Non-potable
Uses - This project will document the efficiency and performance of in-service
dual systems. Factors considered will include reliability, energy, water quality,
efficiency, water conservation, performance, cost, and applicability.
b Prospective Assessments of Dual Systems for Potable and Non-potable Uses -
Criteria will be developed for determining potential applicability, benefits
(including water quality improvements) and costs of dual systems (with a potable-
water-only component) for new systems. Consider reliability, energy, water
quality, efficiency, water conservation, performance, and cost, etc. In cooperation
with others (e.g., Watereuse Association), candidate, representative systems will
be identified and evaluated against the criteria. If the results are positive, promote
the use of this type of system where applicable, especially those receiving
substantial federal funding. This project will also be conducted in close
collaboration with the Water Science and Technology Board of the National
Research Council, which recently completed a report on health impacts of
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distribution systems. Pending results of the first project, follow up products may
include the following:
i. A guide for estimating benefits-costs of dual systems
ii. A national estimate of the benefits and costs of installing dual systems
iii. An assessment of benefits and costs of installing dual systems in Border
2012 projects. Border 2012 is a US-Mexico border area environmental
program). http://epa.gov/border2012/pdf/2012_english.pdf
iv. An assessment of the benefits and costs of dual systems for addressing
persistent water quality problems.
2 Evaluate/Improve distribution system models - Evaluate and improve hydraulic
models' ability to handle: multiple sources of supply with variable water quality; pipe
wall/water column interactions; DBF kinetics over time and space; transient low
pressures; intrusion flow and quality; dead end spatial and temporal demands; and, cost
modeling. This project will also evaluate performance, cost, and benefits of innovative
options for incorporating real-time data collection into daily treatment plant operation
and distribution system operation (e.g., change flow routes, change tank operation) to
improve water quality in the distribution system.
3. Evaluate/Improve innovative distribution system designs - This project will evaluate
benefits and cost of non-dual system design options that can improve drinking water
quality. Candidate improvements include: improved network design; storage volume
(in-ground, tanks); tank location/operation (e.g., near treatment plant; strategically placed
throughout system; a few large tanks vs. many smaller tanks; in/out configuration;
drawdown strategy); real-time monitoring (e.g., multiple strategic monitoring locations;
advanced management of water quality, flow, and integrity; interfacing distribution
system operation with the treatment plant). The research program will primarily address
distribution , but some treatment options may be addressed in later years of the research
program, such as: decentralized/on-site hybrid systems; advanced treatment strategically
placed; and in-distribution-system treatment (e.g., package plants, POU, POE).
4. Pressure management for new systems - Pressure management is one of the most
effective new approaches to leakage control. It may provide the added advantage of
reducing main breaks. This project will identify and evaluate new infrastructure options
with adequate controls (e.g., district metering, pressure controls) for monitoring and
maintaining efficiency. Potential water quality, energy, cost, and other effects will be
evaluated. The basis for fire flow/pressure requirements for drinking water systems will
be assessed to determine whether pressure can reduced, since many methods and local
ordinances and building codes that may be overly conservative can drive pressure
requirements. An assessment will be made as to whether significant changes are justified
and how they would affect water quality, quantity, and cost.
5 Adaptive water and wastewater engineering analysis and guidelines for sustainable
development - This project will develop and evaluate engineering and management
adaptation methods and techniques for sustainable water and wastewater infrastructure
operations under the new global change environments. Project focus will be storm
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water/wastewater collection and conveyance design and operations, water treatment, and
distribution on a region-by-region basis and in watershed scales.
6. Optimized water distribution systems - The objective of this research is to develop a
generally agreed to, practical, reasonably achievable, definition of "optimized" water
distribution system. This effort will require bringing diverse perspectives into common
perspective and desired level of service considerations and cost considerations. This
topic was supported at the workshop, but due to other ongoing activities by AwwaRF,
Pennsylvania DEP, and US EPA, it will be re-visited later in the program to determine
whether additional basic or applications research is necessary. The ongoing research will
be monitored for collaboration or follow-up opportunities. The relevant ongoing research
is AwwaRF's RFP 4109 (Criteria for Optimized Distribution Systems), which has as its
objective to "define and develop a continuous improvement program based on
optimization principles for water distribution system operation. In particular a self-
assessment approach needs to be developed that defines critical components and
objectives of optimized distribution system operations, and then also defines metrics
measuring the degree of optimization...." AwwaRF RFP 4109 builds on previous
projects/reports, including Development of Water Quality Optimization Plans (2005).
Since 2005, US EPA's Technical Support Center (TSC) of the Office of Ground Water
and Drinking Water has been working on the development of a distribution system (DS)
optimization program, and the Pennsylvania Department of Environmental Protection
(PADEP) began an initiative to develop a distribution system optimization program in
2006. Also, as part of the Center for Distribution Systems Optimization, the University
of Cincinnati is conducting research on distribution system optimization, with a particular
emphasis on factors affecting disinfection byproduct formation.
References
Water Science and Technology Board, Division on Earth and Life Studies, National Research
Council of the National Academies. 2006. Drinking Water Distribution Systems:
Assessing and Reducing Risks. The National Academies Press. Washington, DC. 392 pp.
; http://books.nap.edu/catalog.php?record_id=l 1728
Ysusi, Mark A. 1999. System Design: An Overview. In: Water Distribution Systems
Handbook. Ed., Larry W. Mays. McGraw-Hill. New York, NY.
Okun, Daniel A. 2005. Dual Water Systems Can Save Drinking Water While Improving its
Quality. Environmental Engineer. December.
Okun, Daniel A. 1997. Distributing Reclaimed Water Through Dual Systems." Journal
AWWA. November, pp. 52-64. pp. 10-12 & 20-22.
AwwaRF and KIWA. 2002. Impacts of Fire Flow on Distribution System Water Quality,
Design, and Operation, Chapter 6, pp. 133-144.
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Innovative Treatment Technologies for Wastewater and Water Reuse
Background
With the passage of the Clean Water Act in 1972, the National Pollutant Discharge Elimination
System (NPDES) Program was established to control the release of deleterious pollutants from
discrete point sources into our nation's waterways. As it applies to municipal wastewater
treatment plants, also referred to as Publicly Owned Treatment Works (POTWs), the NPDES
program establishes both technology-based and water quality based treatment requirements to be
achieved. Technology-based requirements for POTWs have been established in the "secondary
treatment standards" which reflect the proper performance of typical biological treatment plants.
These standards establish POTW performance levels for the discharge of 5-day biochemical
oxygen demand (BODS) and total suspended solids (TSS) of 30 mg/1. In some cases, secondary
treatment standards are not sufficient to support the attainment of state water quality standards in
the receiving water. In these situations, water quality-based treatment requirements must be
established for a POTW. These more stringent treatment requirements may result in tighter
controls on BODS and TSS. In many cases, water quality-based treatment requirements for
POTWs address additional pollutants, including nutrients (nitrogen and phosphorus) and metals.
The majority of POTWs in the U.S. were constructed during the 1970s and 1980s, when the
Federal Construction Grant Program was subsidizing a major proportion of the construction
costs. As these treatment plants begin to reach the end of their design lives and as their effluent
quality requirements are becoming more restrictive, the need to rehabilitate or upgrade treatment
will expand and innovative treatment technologies will be in demand.
In addition to addressing aging wastewater treatment challenges, the demand for more cost-
effective municipal wastewater treatment technologies is being driven by many other factors.
There is a growing challenge to more effectively manage and treat peak wet weather flows at
wastewater treatment plants, especially focusing on the effectiveness of pathogen reduction.
New and emerging contaminants, such as endocrine disrupting compounds (EDCs),
Pharmaceuticals and personal care products, present challenges not only relating to their fate
through a wastewater treatment plant and into the environment, but to their potential capacity to
interfere and inhibit treatment effectiveness. The control of nitrogen and phosphorus is a
growing priority, especially in the basins that drain to the Mississippi River, Great Lakes and the
Chesapeake Bay. There is an ever present demand for wastewater treatment technologies that
are more energy efficient and produce smaller volumes of residuals.
The demands for water around the nation are driving an increasing demand for alternative
sources, especially for non-potable wastewater and stormwater reuse. Depending on the nature
of the wastewater and stormwater source and the intended reuse application, treatment
requirements may exceed tertiary levels and demand the use of advanced filtration and
membrane technologies.
Unlike the NPDES program which regulates point source discharges on a national basis, the
regulation of wastewater and stormwater reuse in the U.S. is controlled at the state level. In late-
2002, 25 states had adopted regulations on the use of reclaimed wastewater, 16 states had
guidelines or design standards, and 9 states had no regulations or guidelines. (EPA, 2004) While
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there are no national regulations that apply to water reuse in the U.S., the EPA, along with the
U.S. Agency for International Development (USAID), published the "2004 Guidelines for Water
Reuse (EPA/625/R-04/108)." These guidelines were published to help utilities and regulatory
agencies determine appropriate levels of treatment for reclaimed municipal wastewater.
State of the Technology
For municipal wastewater treatment, biological treatment processes are the most predominantly
applied technologies. Biological treatment utilizes microorganism populations to degrade
organics and nutrients in the wastewater. As microorganisms consume these compounds, they
are converted to biomass and removed by subsequent processes. Biomass can be either fixed or
suspended and treatment processes can be either aerobic or anaerobic. In addition to these
conventional biological treatment processes, currently practiced municipal wastewater treatment
includes physical and chemical treatment processes. Course screening and preliminary settling
processes typically precede biological treatment. In addition, secondary settling is applied to
remove excess biomass from biological systems. Finally, after secondary clarification, a
disinfection step is utilized to address potential pathogens in the treatment plant effluent.
Typically, chlorine is added to the wastewater and adequate contact times provided to promote
pathogen kills.
There have been many recent advances in biological treatment technologies. In addition to
becoming more cost-effective, especially in terms of energy consumption, many of these
emerging and innovative technologies can be easily retrofitted into aging systems, can result in
treatment systems with smaller "footprints," and can enhance treatment effectiveness, especially
for nutrient removal.(EPA, 2007) Innovative biological treatment technologies emerging over
the past several years include:
• Membrane bioreactors (MBR),
• Mobile bed biofilm reactor technology (MBRT),
• Integrated fixed-film reactor technology (IF AS), and
• Biological aerated filters (BAF).
Recent innovative technology development in the area of physical chemical treatment processes
include membrane filtration, compressible media filters, cloth media filters, fine grit removal and
disinfection processes.(EPA 2007) Some of these technologies include:
• Fine/Advanced grit removal system (AGRS),
• Microfiltration/Microseive,
• Ultrafiltration,
• Nanofiltration, and
• Ultraviolet disinfection.
Treatment technologies for reclaimed wastewater reuse are mostly developed from the physical,
chemical and biological treatment processes applied to municipal wastewater and drinking water.
Most existing regulatory standards for wastewater reuse can be met by applying conventional
treatment practices. However, the treatment effectiveness of these conventional technologies on
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new and emerging contaminants, such as endocrine disruption compounds (EDCs),
Pharmaceuticals and personal care products is uncertain due to limited data and information. As
the demand for high-quality reclaimed wastewater increases, the application of new and
innovative technologies, such as MBRs, microfiltration, ultrafiltration, nanofiltration, and reverse
osmosis will also increase.(Levine and Asano, 2004)
Research Questions
The following key research questions relating to emerging and innovative treatment technologies
for municipal wastewater and water reuse have emerged from input and comments from key
internal and external stakeholders and recent work completed by EPA's Office of Wastewater
Management on innovative and embryonic treatment technologies.(EPA, 2007) These key
research questions reflect critical gaps in our knowledge of the performance of new and
innovative treatment technologies, especially when determining technology performance for the
review and approval of permits and determining the suitability of specific technologies to
address site-specific treatment challenges.
Can emerging and innovative treatment technologies, for both municipal wastewater and
water reuse, be identified, evaluated, verified and demonstrated in field settings to
improve our understanding of their applicability, cost-effectiveness, technical
performance, and reliability?
Can knowledge of the performance and reliability of municipal wastewater treatment
technologies and systems be transferred to the application of these technologies or the
development of new technologies in meeting the water quality requirements for water
reuse?
Can new and innovative treatment technologies and systems be evaluated based on the
performance of full-scale installations to better inform utilities and regulators and provide
reliable, objective technical assessments?
Can established treatment technology and system design, operation and maintenance
practices be updated based on information on the performance, cost-effectiveness, and
reliability of new and innovative technologies?
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Proposed Research
Based upon the key research questions presented above and the known research projects that are
ongoing or recently completed by other stakeholders, the following research, demonstrations and
technology transfer products are proposed. Each proposal indicates the estimate time frame for
the work. While these proposals address the issues in the questions above, modified, alternative
or additional projects may evolve as this plan is implemented.
1. Technology Transfer Product: Nitrogen Control Design Manual - An updated
technology design manual based on the original EPA manual published in 1975 and
updated in 1993 (EPA 625/R-93/010). This manual will reflect innovations in controlling
nitrogen discharges from municipal wastewater treatment plant and present up-to-date
design procedures. This design manual will reflect recent technology assessments
completed by EPA's Office of Wastewater Management. (12-18 months)
2. Technology Transfer Product: Phosphorus Removal Design Manual - An updated
technology design manual based on the original EPA manual published in 1971 and
updated in 1975 and 1987. This manual will reflect innovations in the removal of
phosphorus from municipal wastewater treatment plant discharges and present up-to-date
design procedures. This design manual will reflect recent technology assessments
completed by EPA's Office of Wastewater Management. (12-18 months)
3. Technology Transfer Products: Technology Design Manuals and Handbooks -
Based on the information and data generated from the treatment research,
demonstrations, evaluations, verifications, and assessments conducted under this plan, it
is expected that several technology design manuals and handbooks will be developed.
These manuals and handbooks will provide up-to-date technical guidance on the
application of municipal wastewater treatment technologies and treatment technologies
for water reuse. (24-60 months)
4. Applied Technology Research, Evaluation and Demonstration: Water Reuse
Applications of Wastewater Treatment Technologies - This project will be a multi-
year effort that will include pilot-scale research of treatment technology effectiveness on
conventional and emerging pollutants; pilot-scale fate and transport studies in simulated
water reuse applications; development of monitoring indicators and analytical techniques;
and predictive models for engineering design and evaluations. (48-60 months)
5. Wastewater Treatment Technology Evaluations - These evaluations will address
knowledge gaps on the performance, cost-effectiveness and reliability of new, innovative
technologies emerging into practice. These evaluations will use full-scale installations of
technologies to provide reliable, objective data and information for use in technology
selection by utilities and in permitting programs by state and EPA regional staff. It is
likely that one of the initial technology evaluation projects will be on membrane
bioreactors. (24-60 months)
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References
Levine, Audrey D., and Takashi Asano, Recovering Sustainable Water from Wastewater,
Environmental Science & Technology, June 1, 2004.
U.S. Environmental Protection Agency, 2004 Guidelines for Water Reuse, EPA/625/R-04/108,
August 2004.
U.S. Environmental Protection Agency, Wastewater Treatment and In-Plant Wet Weather
Management, 2007.
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