United States
Environmental Protection
Agency
Office of
Research and Development
Cincinnati, OH 45268
EPA/625/6-91/030
October 1991
Technology Transfer
&EPA Handbook
Sewer System
Infrastructure Analysis and
Rehabilitation
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EPA/625/6-91/030
October 1991
Handbook
Sewer System Infrastructure
Analysis and Rehabilitation
U.S. Environmental Protection Agency
Office of Research and Development
Center for. Environmental Research Information
Cincinnati, OH 45268
Printed on Recycled Paper
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Notice
This document has been reviewed in accordance with the U.S. Environmental protection Agency's peer and
administrative review policies and approved for publication. Mention of trade names orcommercial products does not
constitute endorsement or recommendation for use.
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Contents
Chapter Page
.1 INTRODUCTION 1
1.1 Purpose and Intended Audience 1
1.1.1 Definition of Sewer System Infrastructure 1
1.1.2 Importance of Maintaining Infrastructure System Integrity 1
1.1.3 Existing Source Documents 4
1.2 The Need for a Sewer System Infrastructure Handbook 4
1.2.1 Changing Requirements 4
1.2.2 Comprehensive Analytical Procedures 5
1.3 User's Guide 5
1.4 References 5
2 REGULATORY REQUIREMENTS .....7,
2.1 Historical Background 7
2.2 Summary of Applicable U.S. EPA and State Regulations 7
2.3 Description of the Relative Roles of the U.S. EPA, State Agencies,
and Local Agencies ...8
2.4 Certification Requirements 8
2.4.1 Historical Perspective 8
2.4.2 Current Situation 8
2.5 References 11
3 PRELIMINARY ANALYSIS OF SEWER SYSTEMS 13
3.1 Introduction 13
3.2 Historical Reasons for Sewer System Analysis and Evaluation 13
3.2.1 Regulatory Requirements 13
3.2.2 Structural Failure 13
3.2.3 Capacity Limitations 13
3.2.4 Citizens'Complaints 14
3.3 Financial Reasons for Evaluation of Sewer Infrastructure Needs , 14
3.3.1 Need to Enlarge Service Area 14
3.3.2 Budgetary Planning Needs 14
3.3.3 Financial Planning 14
3.3.4 Benefits Versus Cost of Sewer System Evaluation 15
3.4 Methodology for Preliminary Sewer System Analysis 15
3.4.1 Sources of Information and Preliminary Methods of Analysis 15
3.4.2 Monitoring and Equipment Needs for Preliminary Analysis 19
3.5 Infiltration and Inflow Analysis 19
in
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Contents (continued)
Chapter Page
\.
3.5.1 Introduction ..19
3.5.2 Preliminary Information Needed 20
3.5.3 Rainfall Information 252
3.5.4 Topographic and Geologic Information 23
3.5.5 Groundwater Information 24
3.5.6 Baseline Sewer Flows 24
3.5.7 Analysis of Infiltration and Inflow 27
3.6 Exfiftration and Its Impacts 32
3.6.1 Introduction 32
3.6.2 Summary of Information on Impacts '. 32
3.6.3 Consideration in I/I Analysis 32
3.6.4 Present and Future Environmental Impacts 32
3.6.5 Exfittration Tests and Methods 32
3.7 References ....35
4 SEWER SYSTEM EVALUATION 39
4.1 Introduction 39
4.2 Planning the Survey and Use of Sub-System Approach 40
4.3 Physical Survey 40
4.3.1 Aboveground Inspection 40
4.3.2 Flow Monitoring 40
4.3.3 Flow Measurement 40
4.3.4 Manhole and Sewer Inspection ', 4(3
4.3.5 Rainfall Simulation 4(5
4.3.6 Smoke Testing 46
4.3.7 Dyed Water Testing 4(5
4.3.8 Water Flooding Test 4(5
4.4 Cleaning ; 47
4.5 Internal Inspection 47
4.5.1 Television Inspection ; 47
4.5.2 Photographic Inspection •. 47
4.5.3 Physical Inspection 47
4.6 Cost-Effectiveness Analysis 47
4.7 Case Study Example and Detailed Method of Analysis 50
4.8 References , 56
5 CORROSION ANALYSIS AND CONTROL ; 59
5.1 Introduction and Background 59
5.2 Types and Mechanisms of Corrosion 59
5.2.1 Common Types of Pipe Corrosion 59
5.2.2 Other Types of Corrosion 59
5.3 Conducting a Corrosion Survey 59
5.3.1 Factors Affecting Corrosion ; 59
5.3.2 Identifying Likely Locations for Corrosion 60
5.3.3 Performing Visual Inspections 60
, 5.3.4 Collecting Data 60
IV
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Contents (continued)
Chapter Page
5.3.5 Predicting Sulfide Corrosion ,.. 60
5.4 Rehabilitating Corroded Sewers 60
5.5 Controlling Corrosion 60
5.5.1 Sulfide Corrosion Control 60
5.5.2 Control of Other Forms of Corrosion 62
5.6 References 63
6 SEWER SYSTEM REHABILITATION 65
6.1 Introduction 65
6.2 Excavation and Replacement 65
6.2.1 Description..... , , 65
6.2.2 Procedures and Equipment 65
6.2.3 Costs 66
6.3 Chemical Grouting 66
6.3.1 Description 66
6.3.2 Costs 63
6.4 Insertion 63
6.4.1 Description 63
6.4.2 Procedures and Equipment 65
6.4.3 Costs 72
6.5 Cured-ln-Place Pipe Inversion Lining 73
6.5.1 Description 73
6.5.2 Procedures and Equipment 74
6.5.3 Costs .74
6.6 Fold and Formed 74
6.6.1 U-Liner •. 76
6.6.2 NuPipe 76
6.7 Specialty Concrete 77
6.7.1 Description 77
6.7.2 Procedures and Equipment 77
6.7.3 Costs .' 79
6.8 Liners 79
6.8.1 Description 79
6.8.2 Procedures and Equipment 80
6.8.3 Costs 82
6.9 Coatings 82
6.9.1 Description 82
6.9.2 Procedures and Equipment 82
6.9.3 Costs 83
6.10 All Techniques for Manholes 83
6.10.1 Description of Materials, Equipment and Products 83
6.10.2 Description of Procedures 83
6.10.3 Costs 85
6.11 Service Lateral Techniques : 85
6.11.1 Description , 85
6.11.2 Procedures and Equipment 85
6.11.3 Costs •. ..85
6.12 Miscellaneous Costs 86
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Contents (continued)
Chapter Page
6.12.1 Rehabilitation 86
6.12.2 Costs for Preliminary and I/I Analysis with SSES 86
6.13 Matrix of Problems and Applicable Corrective Measures 86
6.14 References 87
GLOSSARY i 89
VI
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Tables
Number Page
1-1 Construction Grants Funding Spending for Category IIIA 2
1-2 Construction Grants Funding Spending for Category IIIB 3
1-3 Summary of Handbook Contents 6
2-1 State Agency Regulations for Sewer System Improvements 9
3-1 Major Infrastructure Financing Mechanisms Advantages and Disadvantages 16
4-1 Sewer System Testing and Inspection Methods '. 39
4-4 Cost Summary for SSES and Sewer Rehabilitation 51
4-3 Qualification of I/I Through the Subarea System
Approach for the Washington Suburban Sanitary Commission , 55
4-4 Cost Effective Analysis for I/I Reduction for the „
Washington Suburban Sanitary Commission..; 55
4-5 Cost Effective Analysis by Point Source for I/I Reduction for the
Washington Suburban Sanitary Commission 55
5-1 Common Sewer Corrosion Problems and Applicable Rehabilitation Methods 61
5-2 Guidelines to Select Pipe Materials to Resist Corrosion 63
6-1 Rehabilitation Costs for Excavation and Replacement 66
6-2 Rehabilitation Costs for Grouting 69
6-3 Advantages and Disadvantages of Sliplining 69
6-4 Rehabilitation Costs for Sliplining with HPDE and Polybutylene Pipe 72
6-5 Rehabilitation Costs for Sliplining with PE Pipe 72
6-6 Rehabilitation Costs for Sliplining with Reinforced Thermosetting Resin 72
6-7 Miscellaneous Rehabilitation Costs for Sliplining 73
6-8 Advantages and Disadvantages of Cured-ln-Place Lining : 73
6-9 Rehabilitation Costs for Cured-ln-Place Inversion Lining 74
6-10 Advantages and Disadvantages of Specialty Concretes 79
6-11 Costs for Rehabilitation Using Specialty Concretes 80
6-12 Advantages and Disadvantages of Liners..... 81
6-13 Rehabilitation Costs for Lining with Cement Mortar and Shotcrete 82
6-14 Rehabilitation Costs for Lining with Anchors 82
6-15 Advantages and Disadvantages of Coatings 83
6-16 Costs for Rehabilitation Using Coatings , 83
6-17 Advantages and Disadvantages of Manhole and Sump Rehabilitation Methods 84
6-18 Rehabilitation Costs-Manhole Techniques : 85
6-19 Service Lateral Rehabilitation Costs 86
6-20 Miscellaneous Additional Rehabilitation Costs 86
6-21 Sewer System Evaluation Survey Costs 86
6-22 Sewer Pipe Problems with Applicable Rehabilitation Methods 87
VII
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Figures
Number Page
3-1 Approach to Conducting Sewer System Evaluation 17
3-2 I/I Analysis Major Activity Flow Chart 21
3-3 Static Groundwater Gauge Installation Elevation 25
3-4 Groundwater Gauge Installation Detail 26
3-5 Effects of Groundwater on Migration 29
3-6 Typical Entry Points of Rainfall Induced Infiltration 31
3-7 Determination of Total Yearly I/I 33
3-8 Determination of Total Yearly Infiltration 34
4-1 Sewer System Evaluation Flow Diagram , 41
4-2 Typical Manhole Defects 44
4-3 Quick Method of Inspecting Sewer Lines 45
4-4 Preparatory Cleaning 48
4-5 Internal Color TV Inspection 49
4-6 Cost-Effectiveness Analysis Curve for Infiltration ! 53
4-7 Cost-Effectiveness Analysis Curve for Inflow 54
6-1 Grouting Equipment and Procedures 67
6-2 Insertion Methods 71
6-3 Installation of Cured-ln-Place Inversion Lining (Insituform) 75
6-4 U-Liner Installation method ; 77
6-5 NuPipe Installation Method , 78
6-6 Detail of Liners with Anchors : 81
Vill
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Acknowledgments
The preparation and review of this Handbook was undertaken by many individuals. Contract administration was
provided by the U.S. Environmental Protection Agency's (EPA) Center for Environmental Research Information
(CERI).
Authors:
John M. Smith, Robert P. G. Bowker, and Hemang J. Shah - J. M. Smith & Associates, PSC, Consulting Engineers,
Cincinnati, Ohio
Peer Reviewers:
Philip M. Hannan - Washington Suburban Sanitary Commission, Hyattsville, Maryland
Roy C. Fedotoff - Metcalf & Eddy, Santa Clara, California
James F. Kreissl - U.S. EPA-RREL, Cincinnati, Ohio
Lam K. Lim - U.S. EPA, Washington, DC
Charles Pycha - U.S. EPA Region 5, Chicago, Illinois
Sarah C. White - Municipality of Metropolitan Seattle, Seattle, Washington
Peer Reviewers:
Andrew T. Cronberg - Department of Sanitary Sewers, Tampa, Florida
Henry N. Gregory - Public Utilities Department, Houston, Texas
Technical Direction/Coordination:
Denis J. Lussier - U.S. EPA-CERI, Cincinnati, Ohio
IX
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CHAPTER 1
Introduction
Many of our nation's sewer systems date back over 100
years to the 19th century, when brick sewers where
common.1 These and other more recent sewer systems
can be expected to ultimately fail in time, but because
they are placed underground, signs of accelerated
deterioration and capacity limitations are not readily
apparent until there is a major failure. Sewer pipe failures
start with cracking, lateral deflection, crown sag and off-
set joints, as well as by deteriorated mortar and exposed
reinforcing caused by hydrogen sulfide (H2S) corrosion.
Most of what the community sees is the inevitable result
of prolonged neglect, such as cracked pavement,
collapsed streets, backed-up sewers, streams and
groundwater contamination or local flooding.1 Proper
sewer evaluation and maintenance schedules would
help communities identify the condition of their sewer
system's infrastructure, and timely rehabilitation could
save the community large expenditures required to
replace the deteriorated sewers, and extend the sewer
use life. Tables 1-1 and 1-2 indicate the amount of
money spent for sewer system major rehabilitation
projects by U.S. EPA under the construction grants
program.2 In addition to the construction grants program,
municipalities and utilities have utilized State Revolving
Funds, Community Development Block Grant and other
funding options to fund Infrastructure needs. Adequate
sewer system Infrastructure evaluation and rehabilitation
is of prime importance as the first step in this effort.
1.1 Purpose and Intended Audience
This Handbook provides guidance on the evaluation and
rehabilitation of existing sewers. It presents information
on typical problems, procedures and methods for
rehabilitation, case study information, budgetary costs,
advantages and disadvantages of rehabilitation
techniques, and application of these techniques and
materials/equipment used in rehabilitation. It also guides
the reader in understanding the importance of, and ways
for, conducting the sewer system evaluation and
identifying the rehabilitation procedure that best suits a
particular problem. By necessity, information contained
in this Handbook for conducting a sewer system
evaluation is general and not site-specific. The intent is
to present sufficient information to enable engineers and
public decision makers to plan and conduct sewer system
evaluation and rehabilitation under circumstances which
might be encountered when dealing with a specific sewer
system. Because a variety of circumstances are
encountered in sewer systems, all of the methodology
presented in this Handbook will not apply to each project.
It is emphasized that the reader should apply only those
portions of the methodology that are relevant to the
specific project under study.
1.1.1 Definition of Sewer System Infrastructure
Sewer system infrastructure conveys wastewater used
by individuals and by commercial and industrial
establishments to wastewater treatment facilities,
ultimately to be returned to the natural environment.
These systems protect public health and the environment
and encourage economic development.3
1.1.2 Importance of Maintaining Infrastructure
System Integrity
The primary importance of sewer system evaluation and
rehabilitation is to maintain the structural integrity of the
sewer system for dependable transfer of wastewater
from the source to the treatment facility.4 Since the
passage of Public Law 92-500 in 1972, more emphasis
has been placed on sewer rehabilitation to reduce the
hydraulic loads placed on the treatment plants from
excessive infiltration/inflow (I/I). When the integrity of a
sewer system is allowed to deteriorate, extraneous water
from I/I sources enterthe sewers. These flows reduce the
capability of sewer systems and treatment facilities to
transport and treat domestic and industrial wastewaters.
As a result, wastewater treatment processes are upset
and poorly treated wastewater is discharged to the
environment.
Infiltration occurs when existing sewer lines undergo
material and joint degradation and deterioration, as well
as when new sewer lines are poorly designed and
constructed. Inflow normally occurs when rainfall enters
the sewer system through direct connections such as roof
leaders, catch basins, manholes, and other direct cross
connections. The elimination of I/I by sewer system
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rehabilitation can often substantially reduce the cost of
wastewater collection and treatment. However, a logical
and systematic evaluation of the sewer system is
necessary to determine the cost-effectiveness of any
sewersystem rehabilitation program designedto eliminate
exfiltration, infiltration and inflow.
The reduction of I/I can result in a significant reduction in
hydraulic loading at collection and treatment facilities
during periods of wet weather, thus lowering capital and
O&M costs and prolonging the lifetime-capacity of the
treatment facility.3 Pipeline rehabilitation techniques can
restorecapacity and structural reliability for30-70 percent
of the sewer replacement costs.
1.1.3 Existing Source Documents
There have been a number of reports published that
provide information on sewer system infrastructure
evaluation and rehabilitation. A description of these
materials is provided in order, starting from the oldest
dated publication:
• Handbook for Sewer System Evaluation and
Rehabilitation*^^ document was prepared to provide
the general guidance and technical information on the
methodology necessary for an effective investigation
and correction of I/I conditions in a sewer system. The
handbook describes the methods for conducting I/I
analysis, sewer system evaluation surveys, sewer
system rehabilitation and budgetary cost estimating
techniques for the rehabilitation methodologies
mentioned. The handbook does not contain regulatory
requirements to indicate the applicable U.S. EPA
regulations on existing, new or upgraded systems.
• Sewer System Evaluation, Rehabilitation and New
Construction: A Manual of Practice.5 This document
was prepared to assist the reader in the detailed
investigation of Sewer System Evaluation and Sewer
Analysis. It emphasized sewer system evaluation,
sewer rehabilitation and the design of new systems to
minimize I/I. Sewer cleaning equipment and methods
of sewer inspection are discussed in detail. Factors
which govern the cost of conducting rehabilitation work
and an analysis of factors to be considered for each
rehabilitation method are described. The MOP does
not provide detailed information on the regulatory
requirements.
• Existing Sewer Evaluation and Rehabilitation.3 This
manual provides guidelines for the evaluation and
rehabilitation of sanitary sewers. It describes the
purpose and scope of sanitary sewer rehabilitation and
also provides detailed information to the user
implementing a sewer rehabilitation program. Major
emphasis of the manual is on the reduction of I/I, while
less emphasis is placed on maintaining the structural
integrity of the sanitary sewer. The manual describes
the various methods and materials used for sewer
system rehabilitation.
• Recommended Specifications for Sewer Collection
System Rehabilitation. Fifth Edition. August 1987. The
National Association of Sewer SJervice Companies
(NASSCO) has published recommended specifications
for sewer collection system rehabilitation. The book is
intended to assist engineers and municipal officials in
properly specifying materials, methods, equipment
and procedures for sewer rehabilitation projects.
Specifications are provided for the following
rehabilitation procedures: sewer line cleaning, sewer
flow control, TV inspection, sev/er pipe joint testing,
sewer pipe joint sealing, sewer manhole sealing, sewer
manhole rehabilitation, sewer manhole lining, sliplining
of sewers, and cured-in-place pipe installations. The
document also contains sections on measurement of
payments, contract responsibilities and definitions.
These reports summarize and provide information and
procedures that were applicable at the time of publication
on various elements of a comprehensive sewer system
analysis. There was not, however until now, a single
source document that can be referred to by a reader to
obtain comprehensive information on state-of-the-art
sewer system rehabilitation techniques and
methodologies.
1.2 The Need for a Sewer System
Infrastructure Handbook
1.2,1 Changing Requirements
This handbook has been prepared to address the need
forconsolidating, updating and expanding the information
presently available from various sources and to refine
some of the previous data analysis methodologies.
The Handbook for Sewer System Evaluation and
Rehabilitation* took into account the regulations in effect
at that time and also the available technological
procedures to reduce I/I. Federal regulations pertaining
to I/I were subsequently revised and simplified in 1981
and 1982.
I
Studies conducted by U.S. EPA in 1980 concluded that
I/I removal rates were substantially less than expected
for those rehabilitation methods due to migration of
infiltration from rehabilitated areas to non-rehabilitated
areas.
Currently, new materials of construction and new
techniques and approaches for sewer rehabilitation have
been developed and shown to be cost-effective in sewer
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system rehabilitation. These new techniques are
described in Chapter 6 of this handbook.
1.2.2 Comprehensive Analytical Procedures
Unique investigative and analytical techniques have
been developed that should be utilized to obtain reliable
flow reduction estimates of rehabilitation effectiveness,
and selection of rehabilitation methods. Measurements
and separate identification of rainfall induced infiltration
(Rll) is carried out by new methods of evaluating and
analyzing flow and rainfall data. New techniques such as
the analysis and understanding of infiltration migration
phenomenon and improved cost-effectiveness analysis
procedures have been implemented by many consulting
engineersto more realistically project I/I reduction. These
new techniques are described in later sections of this
handbook. Studies conducted by the U.S. EPA found
that infiltration sources removed by rehabilitation will
migrate under certain conditions to unrehabilitated
locations.6'7 As a result, the cost-effectiveness analyses
were made applicable for an entire subarea rather than
the more conventional individual source approach.
With the availability of new materials of construction such
as polyethylene, PVC and other plastic and durable
materials described in Chapter 6, coupled with new
techniques fortrenchless pipe installation, sewer system
rehabilitation has become more cost-effective and easy
to implement. Consulting engineers, municipalities and
utilities have started to understand and take into account
the total water balance of a sewer system, based on
infiltration, inflow, Rll, exfiltration and migration. New
data and procedures have led to a more realistic
understanding of the limitations and accuracy of methods
now employed.
1.3 User's Guide
This document contains six chapters that provide the
reader with a condensed summary of pertinent I/I and
SSES evaluation and rehabilitation methodologies. It
differs from previous documents in that more emphasis
is placed on state-of-the art technology rather than on
prescribed regulatory requirements.
Table 1 -3 presents a brief description of each of the six
chapters of this handbook along with a user profile for
each chapter.
1.4 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. Brown and Caldwell. Utility Infrastructure
Rehabilitation. NTIS No. PB86-N14642, Department
of Housing and Urban Development, Washington,
DC, 1984.
2. Grants Information and Control System, Sewer
System Major Rehabilitation Projects, U.S. EPA,
Construction Grants Federal Budget Spending.
3. Existing Sewer System Evaluation and Rehabilitation.
ASCE Manuals and Reports on Engineering Practice
No. 62, WPCF Manual of Practice FD-6. American
Society of Civil Engineers, Water Pollution Control
Federation, 1983.
4. Handbook for Sewer System Evaluation and
Rehabilitation. EPA/430/9-75/021, Municipal
Construction Division, Office of Water Program
Operations, Environmental Protection Agency,
Washington, DC, 1975.
5. American Public Works Association. SewerSystem
Evaluation Rehabilitation and New Construction: A
Manual of Practice. EPA/600/2-77/017d, NTIS No.
PB-279248. U.S. Environmental Protection Agency,
Municipal Environmental Research Laboratory, Office
of Research and Development, Cincinnati, Ohio,
December 1977.
6. RJN Environmental Associates, Inc. National
Alternative Methodology for Sewer System
Evaluation, Wellington Suburban Sanitary
Commission, 1988.
7. National Water Well Association, RJN Environmental
Associates, Inc., and Washington Suburban Sanitary
Commission. Impact of Groundwater Migration on
Rehabilitation of Sanitary Sewers. 1984.
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Tab!* 1>3.
Summary of Handbook Contents
Chapter
Description
User Profile
1. Introduction
2. Regulatory Requirements
Requirements
3. Preliminary Analysis of Sewer Systems
4. Sewer System Evaluation
Describes purpose, intended audience,
definition of infrastructure, describes
source documents, and importance of
sewer system infrastructure evaluation.
Provides summary of past U.S. EPA
regulations relative to roles of state
and federal agencies; provides matrix
of state regulations and approval
requirements for sewer system improvements
Describes historical and financial
reasons for evaluation of sewer
infrastructure needs, outlines a
simplified preliminary sewer system
and I/I analysis evaluation methodology
including sources of information and
required resources, presents flow
diagram of a sewer system evaluation
plan, summarizes the basic elements of
infiltration inflow analysis, including
the impact of exfiltration and migration
Describes new techniques and sub-system
approach to the traditional sewer
system evaluation, includes planning
the survey, the physical survey,
cleaning, inspection and presentation
of separate infiltration and inflow data,
cost effective analysis, references
other source documents for specific
details and proven technological approaches
All readers
Regulatory personnel
City officials
Consulting engineers
Public works directors
City planners
City planners
City officials
Public works directors
Sewer system study planners
Consulting engineers
Su|3ervisors and staff
conducting a sewer
evaluation
City sewer
Public works directors
Public works officials
Consulting engineers
City managers
Su|>ervisorsandstaff planning
and conducting sewer
evsJuations
City sewer maintenance staff
5. Corrosion Analysis and Control
6. Sewer System Rehabilitation
Describes the types and mechanisms of
sewer corrosion, the importance of
corrosion to the integrity of the sewer
system, describes how to plan and conduct
a sewer system corrosion survey,
corrosion inspections techniques,
analytical data required, provides
methods of rehabilitating corroded
sewers; methods for predicting
corrosion and methods of conducting
corrosion surveys
Provides the latest information on
state-of-the-art sewer rehabilitation
techniques including a) excavation
and replacement, b) chemical grouting,
c) insertion lining, d) inversion
lining, e) specialty lining,
f) liners, g) coalings and h) building
sewers; includes detailed cost
estimates for each technique
along with case histories of successful
projects.
City planners
City Officials
Consulting engineers
City engineers
City sewer maintenance
start
Supervisors and staff
conducting a sewer
system evaluation
Public works directors
City managers
Public works officials
Consulting engineers
City engineering staff
Supervisors and staff
planning and conducting
rehabilitation projects
Contractors
Sub-contractors
Inspectors
-------
CHAPTER 2
Regulatory Requirements
2.1 Historical Background
The Water Pollution Control Act Amendments (Public
Law 92-500, October 18, 1972), require that the U.S.
EPA construction grant applicants investigate the
condition of their sewer systems. The grant cannot be
approved unless it is docu mented that each sewer system
discharging into such treatment works is not subject to
"excessive infiltration and inflow." This requirement was
implemented in the Rules and Regulations for Sewer
Evaluation and Rehabilitation (40CFR35.927). In addition,
I/I analysisandSewerSystem Evaluation Surveys(SSES)
were required to be conducted on a routine basis to
document I/I, and also to indicate the most cost effective
method of rehabilitation required to correct the sewer
pipe and manhole structure damage.1
The I/I analysis should document the non-existence or
possible existence of excessive I/I in each sewer system
tributary to the treatment works. The analysis should
identify the presence and type of I/I that exists in the
sewer system including estimated flow rates. The following
information should be evaluated and included:
• Estimated flow data at the treatment facility, all
significant overflows and bypasses, and, if necessary,
flows at key points within the sewer system
• Relationship of existing population and industrial
contribution to flows in the sewer system
• Geographical and geological conditions which may
affect the present and future flow rates or correction
costs for the I/I
• A discussion of age, length, type, materials of
construction and known physical conditions of the
sewer system
The SSES should include a systematic examination of
the sewer system to determine the specific locations,
estimated f tow rates, method of rehabilitation and cost of
rehabilitation versus the cost of transportation and
treatment for each defined sou rce of infiltration and each
defined source of inflow.1 The resultsof the SSES should
be summarized in a report that should include:2
• A justification for each sewer section cleaned and
internally inspected
• A proposed rehabilitation program forthe sewer system
to eliminate all defined excessive I/I
2.2 Summary of Applicable U .S. EPA and
State Regulations
The following is a Summary of Federal and State
Regulations and Guidelines for I/I analysis and SSES
applicable under the U.S. EPA construction grant
program.1'3
The grant applicant must determine the I/I conditions in
the sewer system by analyzing the preceding year's flow
records from existing treatment plant and pump stations.
For smaller systems where flow records may not be
available, the grant applicant shall obtain flow data by
conducting flow monitoring at asingle point atthetreatment
plant during high groundwater periods and also during
rainstorms. If there is a likelihood of excessive I/I in a
portion of the collection system, it is desirable to monitor
that portion separately. No further I/I analysis will be
necessary if domestic wastewater plus non-excessive
infiltration does not exceed 120 gallons per capita perdav
(gpcd) during periods of high groundwater. The total daily
flow during a storm should not exceed 275 gpcd. and
there should be no operational problems, such as
surcharges, bypasses or poor treatment performance
resulting from hydraulic overloading of the treatment
works during storm events. The flow rate of 120 gpcd for
infiltration analysis contains two flow components: 80
gpcd of domestic base f lowand 40 gpcd of non-excessive
infiltration. This is a national average based on the results
of a needs su rvey of 270 Standard Metropolitan Statistical
Area Cities. Where the flow rate (domestic base flow and
infiltration based on the highest 7 to 14 day average)
does not significantly exceed 120 gpcd (in the range of
130 gpcd) the city may proceed with the treatment works
design without further analysis. When infiltration
significantly exceeds 120 gpcd, further evaluation of the
sewer system must be performed to determine the
possibility of excessive I/I through a cost effectiveness
-------
analysis. Following the I/I study, a SSES must be
performed. The result of the SSES will allow the city to
formulate sewer rehabilitation program to eliminate the
portion of the I/I that is excessive and size the treatment
plant accordingly.
With the elimination of the U.S. EPA construction grants
program in October of 1990, all Federal regulations for M
I analysis and SSES underthis program will no longer be
applicable. Individual states nowhavetheirownguidelines
and regulations to follow. A survey of state regulatory
officials indicates that many states however still follow
Ten States Standards2 and past U.S. EPA standards
such as CG853 I/I and SSES guidance documents (See
Table 2-1). State agencies evaluate general plans and
feasibility studies submitted by an applicant for any
treatment plant modification application. If the general
plan and feasibility study submitted by the applicant show
flow variations during wet weather conditions, the State
Agency investigates the cause and may request the
applicant to conduct a SSES and I/I analysis. They may
further request information on the cost effectiveness of
rehabilitation versus building a new plant.
2.3 Description of the Relative Roles of
the U.S. EPA, State Agencies, and
Local Agencies
The U.S. EPA has been very involved in sewer system
evaluation and rehabilitation projects since 1973 as a
result of the construction grant program. Under this
program, the U.S. EPA provided grants to municipalities
for I/I analyses, for SSES if excessive flow was found,
and for rehabilitation if excessive I/I was found. With the
completion of the construction grants program in 1990,
the U.S. EPA will play a smaller role in this effort, while
the roles of the state and local agencies will become
larger.
Table 2-1 outlines the regulations which currently (April
1991) apply to sewer expansion and rehabilitation in
each state.4 As the table shows, requirements vary from
state to state. Within the states, requirements depend
upon the source of funding for the project.
2.4 Certification Requirements
2.4.1 Historical Perspective
Section 204 of the 1981 Amendments to the Clean Water
Act requires that U.S. EPA grant applicants must, after
one year's of operation, certify to the U.S. EPA that the
project meets design specifications and effluent
limitations, including I/I reduction projections. The purpose
of the certification requirementsisto ensure that effective
sewer rehabilitation projects were carried out through the
grant assistance programs. On May 12,1982, U.S. EPA
promulgated regulations which clarified and implemented
the 1981 requirements. These regulations can be found
in 40CFR35. The definition of municipal treatment works
was expanded to include interceptor and collector seweirs.
Furthermore, I/I analysis and SSES work were included
in the treatment works performance certification
requirements. The grantee is required to certify
performance after one year, as stated in the 1981
regulations. In addition, the grantee must prepare a
corrective action report for projects not meeting
performance requirements, establish a schedule for
corrections, and determine a new certification date.
These certification requirements apply to all Step 3
grants awarded on or after May 12,1982.5
As a basis for the grantee's certification that SSES
performance specifications are being met, a six to twelve
month post-rehabilitation monitoring program is
recommended. This program will generally include one
or more flow monitoring stations, grou ndwater and rainfall
measurements, and other measurements as required to
quantify I/I reduction in the rehabilitated areas.5
It is the grantee's responsibility to certify that the SSES
design and performance standards for I/I reduction have
or have not been met. If it is found that these standards
have not been met, the grantee must identify specific
causes and must rectify the situation at otherthan federal
expense.5
2.4.2 Current Situation
With the completion of the construction grants program,
it is uncertain whetherthe states will require a certification
program similarto the one required forthe federal grants.
However, ft is a good practice for cities to continue this
policy to ensure program effectiveness.
8
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Table 2-1 State Agency Regulations for Sewer System Improvements
Regulations to be followed for SSES and I/I
analysis (CG 85,10 States) or for expansion
or rehabilitation of existing sanitary
sewers or lift stations:
Required before
applying to expand
or upgrade a
treatment plant:
STATE
AK
AL
AR
AZ
CA
CO
CT
DE
FL
GA
HI
IA
ID
IL
IN
KS
KY
LA
MA
MD
ME
Ml
MN
MO
MS
MT
NC
ND
NE
NH
NJ
NM
NV
NY
OH
OK
OR
PA
CG85
(a)
(a)
(a)
no
(a)
(a)
(d)
(a)
(a)
(I)
yes
(a)
yes
(a).
yes
(d)
(?)
no
no
(a)
(d)
(a)
(d)
(a)
no
(a,d)
no
(d)
yes
(d)
(d)
(a)
no
yes
(a)
(a)
no
(c,d)
10 States
Standards
yes
(a)
(b,c)
no
no
no
no
yes
yes
(b,l)
(c)
(I)
yes
no
yes
(d)
yes
no
no
no
no
yes
yes
no
yes
yes
no
yes
yes
no
no
no
yes
yes
(D
no
no
no
State
Review
yes
(a)
yes
yes
(a)
no
yes
(a)
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
State
Approval
yes
(a)
yes
yes
(a)
(b)
yes
yes
yes
yes
yes
yes
(c)
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
(i)
yes
yes
yes
yes
yes
yes
Permit to
Install
yes
no
no
no
no
(b)
no
yes
yes
no
no
yes
no
yes
yes
yes
yes
yes
(i)
yes
no
yes
yes
yes
no
no
yes
no
(b)
no
yes
no
no
(c)
yes
yes
no
yes
Other
no
no
(e)
(g)
no
no
(e)
(h)
no
no
(g)
(g)
no
-------
Table 2-1, continued.
Which regulations must be followed for SSES
and I/I analysis (CG 85,10 States) or for
expansion or rehabilitation of existing
sanitary sewers or lift stations?
What is required
before applying to
expand or upgrade
a treatment plant?
STATE
Rl
SO
SD
TN
TX
UT
VA
VT
WA
Wl
WV
WY
CG85
yes
(c,d)
no
no
yes
(a)
no
yes
(d)
no
(c,d)
(a)
10 States
Standards
no
yes
(d)
d)
no
(a)
no
yes
no
no
yes
no
State
Review
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
yes
State
Approval
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
yes
Permit to
Install
'no
yes
no
no
no
no
yes
yes
no
no
yes
yes
Other
(e)
(g)
no
(g)
no
no
(g)
(e,g)
(g)
(g)
no
(g)
SSES
yes
no
(a)
: (f)
(i)
no
no
yes
no
ttl)
(f)
no
I/I
Analysis
yes
yes
(a)
(a)
yes
no
yes
yes
yes
(g)
yes
yes
(a) for projects funded by EPA grants, the State Revolving Fund,
or similar programs
(b) for expansion or rehabilitation of lift stations.
(c) for expansion or rehabilitation of sewers.
(d) for SSES and I/I analysis.
(e) other published texts, manuals or guidelines.
(f) decision to perform SSES is based on results of I/I analysis.
(g) state regulations or standards.
(h) for expansion.
(I) sometimes.
(|) for state funded projects.
(k) permit to discharge required for expansion of sewers.
(I) as a guideline.
10
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2.5 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. American Public Works Association. Sewer System
Evaluation, Rehabilitation and New Construction: A
Manual of Practice. EPA/600/2-77/017d, NTIS No.
PB-279248. U.S. Environmental Protection Agency,
Municipal Environmental Research Laboratory, Office
of Research and Development, Cincinnati, Ohio,
December 1977.
2. Recommended Standards for Sewage Works,
Policies for the Review and Approval of Plans and
Specifications for Sewage Collection and Treatment,
1978 Edition; A Report of the Committee of the Great
LakesUpper Mississippi River Board of State Sanitary
Engineers. (Ten-States Standards)
3. Construction Grants 1985. EPA/430/9-84/004, Office
of Water, U.S. Environmental Protection Agency,
1984.
4. State Agencies Responses to Questionnaires sent
by J.M. Smith & Associates, August, 1990.
5. Code of Federal Regulations, Title 40 (40CFR35).
Office of the Federal Register, National Archives and
Records Service, General Services Administration,
May 12,1982.
Additional Reading
Handbook for Sewer System Evaluation and
Rehabilitation. EPA/430/9-75/021, Office of Water
Program Operations, U.S. Environmental Protection
Agency, 1975.
Analysis of Acceptable Ranges for Infiltration and Inflow
Reduction in Sewer System Rehabilitation Projects. J.M.
Smith and Associates, EPA, Contract #68-01-6737,1984.
Handbook of Procedures, Transmitted Memorandum
89-1, Office of Water, U.S. Environmental Protection
Agency, 1989.
11
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-------
CHAPTERS
Preliminary Analysis of Sewer Systems
3.1 Introduction
This chapter presents information on how to conduct a
preliminary sewer system analysis to determine quickly
and easily if there are serious infiltration/inflow (I/I)
problems, evaluate the extent of these problems, and
select the approach for fu rther analysis and investigation.
Before implementing a thorough I/I analysis and Sewer
System Evaluation Survey (SSES), a preliminary analysis
of the sewer system should be conducted to quickly
establish the degree of I/I inthesystem. For systems that
have not been evaluated, the following occurrences
indicate the need for a preliminary sewer system analysis:
• Greater than anticipated flows measured at the
wastewater treatment plant
• Flooded basements during periods of intensive rainfall
• Lift station overflows
• Sewer system overflows or by-passes
• Excessive power costs for pumping stations
• Overtaxing of lift station facilities, often resulting in
frequent electric motor replacements
• Hydraulic overloading of treatment plant facilities
• Excessive costs of wastewater treatment including
meter charges levied by sanitary .districts or other
jurisdictional authorities
• Aesthetic and water quality problems associated with
by-passing of raw wastewater
• Surcharging of manholes resulting in a loss of pipe
overburden through defective pipe joints and eventual
settlement or collapse
• Odor complaints
• Structural failure
• Corrosion
3.2 Historical Reasons for Sewer System
Analysis and Evaluation
Historically, the evaluation of sewer systems has occurred
because of regulatory requirements to receive Federal
funding; capacity limitations; structural failure; and indirect
evidence of excessive I/I in theoverall system. I/I problems
are often abated by the construction of relief sewers,
larger lift stations and treatment plants, and by the use of
wastewater bypasses throughout the system. This last
approach, however, often results in untreated wastewater
flows being discharged into rivers, streams, lakes and
open ditches which is no longer acceptable as a solution.
An effective sewer system evaluation and rehabilitation
plan will be required for effective protection of the
infrastructure in nearly all cases regardless of the initial
reasons for the evaluation.
3.2.1 Regulatory Requirements
Regulations promulgated as a result of Public Law 92-
500 require that any engineer or public official concerned
with thedesign of improvements to existing sewersystem
infrastructure componentsorwastewatertreatment plants
become familiar with and follow certain procedures to
insure that excessive I/I was not present in order to
become eligible for U.S. EPA grant funding.
Although many changes in the regulations have since
been made, the underlying importance of preserving
sewer system capacity and structural integrity remains.
As shown in Table 2-1, many state regulatory officials still
follow a rigorous state review and approval process for
improvements to sewer system infrastructure
components.
3.2.2 Structural Failure
Wastewater collection system structural failures often
occur due to H2S crown corrosion, natural ageing, and
factors such as defective design, excessive overburden,
soil settlement, and earthquakes. The historical method
forrepairing structural problems in sewer systems was to
excavate and replace the pipe. With the advent of new
technologies, described herein, rehabilitation of
wastewater collection lines has became more cost
effective and can often be accomplished without extensive
excavation and replacement.
3.2.3 Capacity Limitations
With the natural increase in population and industrial
growth within a city, the capacity of the wastewater pipes
often become insufficient. Sewer collection lines and
13
-------
treatment plants become inadequate to handle the
increase in sanitary flows. Without the correction of
excessive I/I, existing sewer lines, are unable to carry the
increased flows, thus prohibiting expansion and growth
within the existing tributary area.
3.2.4 Citizens' Complaints
Citizens' complaints are often reported during periods of
extensive rainfall because sewers surcharge and cause
local, area, and residential flooding. When such
phenomena occur on a regular basis, a preliminary
analysis of the sewer system is necessary because
these complaints indicate that the sewer lines exhibit
excessive amounts of I/I during periods of rainfall.
3.3 Financial Reasons for Evaluation of
Sewer Infrastructure Needs
3.3.1 Need to Enlarge Service Area
Traditional planning of sewer systems has included
allowances for growth and expansion within specific
drainage basins or within specific geographical or political
subdivisions of communities. As existing systems continue
to expand, however, the demands on the existing sewer
infrastructure continue to grow and the capacity and
condition of existing interceptor sewers, lift stations, and
appurtenant structures must be continually evaluated.
[Hiring these planning activities, it often becomes apparent
that existing facilities have experienced deterioration and
require rehabilitation or replacement to remain serviceable
and to accommodate the flow of expanding service
areas.
Evaluation of many existing systems as a part of federally-
funded I/I and SSES investigations has often shown that
severedeterforation has occurred, thuscreating additional
financial pressures for future sewer system planning and
expansion. Since sewer systems are designed for service
lifetimes of 30-50 years or more and the plan ning of these
systems do not normally include replacement financing,
future expansion and development planning must take
into account the cost of this replacement. The continued
expansion of existing collection systems normally
continues until the capacity of the critical components of
existing collection and treatment systems are reached.
Because of the high cost of increasing interceptor and
collection system capacity especially in fully developed
areas, it is important that I/I be minimized and that the
necessary investment be made over the lifetime of
existing facilitiesto preserve their condition and capacity.
It is forthis reason that the major federal funding sources
forsewer construction have emphasized the importance
of I/I control and protection of systems from major
deterioration due to corrosion.
At any given point in time within a sewered community,
there is a continuing need to recognise the: 1) value of the
existing sewer infrastructure; 2) condition of the system;
3) rateof deterioration;^ cost of mitigation of deterioration;
5) estimated remaining service lifetime; and 6) ultimate
system capacity. A realistic evaluation of the above
factors is a crucial element of sound public works
management and a fundamental requirement for effective
financial planning of sewer system infrastructure
improvements.
3.3.2 Budgetary Planning Needs
Sewer system budgetary planning normally includes the
following major cost categories:
• Legal and administrative ',
• Long term and short term debt
• Short term capital financing
• Operations and maintenance labor
• Operations materials and utilities
• Contingency or reserve funds
These budgets are often prepared on an annual or bi-
annual basis and are presented to city council or other
governing bodies for approval. Whether wholly or partly
financed by sewer or sewer and water revenue bonds,
some elements of the sewer systein budgets compete
with other municipal infrastructure needs.
Evaluation of the age and condition of existing sewer
systems allows inclusion of the total system needs into
the sewer system operations budget. A well planned
sewer system survey will provide information such as:
• Sewer line manhole (other structure) replacement
needs and costs
• Lift station equipment needs
• Extent of corrosion of lift station equipment and
structures, force mains and down stream receiving
sewers
• Immediate and longer term rehabilitation needs
• Long and short term maintenance needs
Although all needs cannot be met by annual operating
budgets, the budgeting and expenditure of funds annually
for repair, maintenance rehabilitation and replacement of
critical sewer system components in many cases can
eliminate or reduce the need for major capital expenses
at a later date. For example, early identification of
deterioration due to corrosion may save over 60 percent
of the cost of eventual repair or replacement.
3.3.3 Financial Planning
Financial planning to satisfy infrastructure needs includes
the consideration of both the short- and long-term
14
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budgetary needs as described in Section 3.3.2, as well as
thegrowth needs as described in Section3.3.1. Effective
planning must recognize not only the importance of an
accurate and realistic assessment of needs, but also
knowledge of the alternative financing mechanism that
are available. These elements should be considered
over a planning period of 15-25 years. It should be
recognized that even though the estimated lifetime of
major portions of the sewer system infrastructure is 30-
50 years, it is necessary to assess the capital improvement
needs of existing systems on a routine basis at least
every 5-10 years. Sewer system needs shou Id be forecast
forl 0-25 years and should include short term rehabilitation
needs and longer term capital improvements needs.
A major element of financial planning includes the analysis
of a wide variety of financing mechanisms available to
municipalities, as well as a clear understanding of the
required financial resources.
Table 3-1 outlines the advantages and disadvantages of
the more common infrastructure financing mechanisms.
3.3.4 Benefits Versus Cost of Sewer System
Evaluation
Since the early 1970's, over 90 percent of sewer system
evaluations were performed in response to Federal
Grant funding requirements as now defined by
40CFR35.2120.
The experience gained during the past 15 years with
sewer system evaluation efforts (either I/I or SSES) has
proved extremely valuable in identifying the need for
precise information regarding the condition of the nation's
sewer system infrastructure. Equally important has been
the development and refinement of a wide range of cost
effective sewer evaluation and rehabilitation techniques.
These include: 1) improved sewer system monitoring,
analysis and inspection techniques; 2) testing and grouting
techniques; 3) slip-lining technology; 4) cured in-place
linings; 5) fold and fomed; 6) specialty concrete products
and grouting techniques; 7) new coatings; 8) new service
lateral techniques; 9) new liners; and 10) new manhole
rehabilitation techniques.
Another major finding of sewer system evaluations has
been the realization of the extent, impact, and monetary
significance of corrosion on existing sewer systems. This
alone prompted U.S. EPA to undertake a series of
investigations and to publish a design manual in 1985 on
sewer system odor and corrosion control techniques.1
Further concerns over the impact of sewer system
corrosion led the U.S. Congress to require U.S. EPA to
undertake additional studies and to submit a report to
Congress on the costs and impacts of corrosion on the
sewer system infrastructure and the effects of rainfall
induced infiltration (Rll) on sewer systems.2'3
Although the costs and benefits of sewer system
evaluation have not been explicitly defined on a national
basis in the United States, some level of routine sewer
system evaluation is cost effective for all of the nation's
sewer systems. Experience over the past 15 years has
shown that rehabilitation cost are significantly less than
replacement costs in most instances. As shown in Chapter
6, rehabilitation costs are 20-25 percent of replacement
cost for specialty concrete, cement mortar, and epoxy
coatings; 60-80 percent of replacement costsforgrouting;
and 55-85 percent of replacement costs for sliplining and
inversion lining. Comprehensive sewer system surveys
including cleaning and inspection are 5-7 percent of
sewer replacement costs. Given the fact that
comprehensive sewer system evaluation plus
rehabilitation costs are 25-92 percent of sewer
replacement costs, sewer system evaluation and
rehabilitation is extremely cost effective in maintaining
the capital asset value of this infrastructure system.
This cost advantage is in addition to the benefit of
maintaining existing flows and future capacities due to
reduction of infiltration and inflow. The highest benefit/
cost ratios are found in areas where the sewer corrosion
potential is the highest.
Deterioration rates in systems due to corrosion have
been shown to decrease sewer life times from the normal
30-50 years to as low as 2-4 years in extreme cases and
9-14 years in moderate cases.
3.4
3.4.1
Methodology for Preliminary Sewer
System Analysis
Sources of Information and Preliminary
Methods of Analysis
The extent of the preliminary sewer system analysis
depends on the size of the system and the amount of
information available. A diagram outlining the major
steps to be taken in a preliminary survey is presented in
Figure 3-1. Each of these steps are discussed below.
A preliminary sewer system survey is normally conducted
by municipal personnel and their consultants. The first
step in the procedure is to assemble the survey team.
The team usually consists of the city's consultants,
representatives from the city or municipal administration
departments, central engineering staff, sewer and
wastewater superintendent, and key sewer system
operating and maintenance personnel. Other staff that
have pertinent knowledge and experience with the major
sewer system components should be assigned. It is
15
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Table 3-1.
Advantages and Disadvantages of Major Infrastructure Financing Mechanisms
Advantages
Disadvantages
General fund appropriation
Genera) obligation bonds
Revenue bonds
State gas tax
Other dedicated taxes
State revolving funds
Administrative: appropriations reflect
current legislative priorities
Equity: ail taxpayers contribute
to capital projects
Fiscal: no debt incurred, so projects
cost less during periods of inflation
Equity: capital costs shared by current and
future users
Fiscal: bonds can raise large amounts of
capital; general obligation bonds usually
carry lowest available interest rates
Administrative: do not require voter approval
and are not subject to legislative limits
Equity: debt service paid by users fees,
rather than from general revenues
Administrative: established structure allows
tax increase without additional administrative
expense
Equity: revenues are usually earmarked for
transportation, so users pay
Fiscal: revenues relatively high compared to
other user taxes
Administrative: voters prefer dedicated taxes
Fiscal: provides relatively reliable funding
source not subject to annual budgeting
Administrative: promote greater State
independence in project selection
Fiscal: debt service requirements provide
incentives for charging full cost for services;
loans'Can leverage other sources of funds;
loan repayments provide capital for new loans
Administrative: infrastructure must
compels with other spending
priorities each year; cannot plan long-
term project around uncertain funding
Equity: no direct link between
beneficiary and who pays, and current
generation pays for capital projects
that benefit future generations.
Administrative: States often impose
debt ceilings and requires voter
approval
Fiscal: adds to lax burden,
especially If interest rates are high
Administrative: require increased
reporting and restricted by Tax
Reform Act limitations
Fiscal: usually demand higher
interest rates them general obligation bond
Administrative: revenue fluctuates with
use of gas
Equity: fiscal burdens are not evenly
distributed between urban and rural
areas
Fiscal: revenue does not rise with
inflation or reflect differences
Administrative: reduces districts
ability to meet changing needs
Fiscal: major economic downturns
can reduce revenues significantly
Administrative: States bear
increased administrative and financial
responsibility
Equity: poor districts cannot afford
loans
Fiscal: repaying loans will mean
increases in use charges or taxes
Source-Office of Technology Assessment 1990
16
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Figure 3-1.
Approach to conducting sewer system evaluation.
Assemble Survey Team
Collect and Review Available Data
co
CO
£
a.
Analyze Available Data
and Develop Survey
Establish System and
Sub-System Boundaries
Non-Problem
Areas
Prioritize Sub-System Problems
and Eliminate Non-Problem Areas
Conduct Further Investigation
of Problem Sub-Areas
Effects of Exfiltration
and Migration
B
W
>»
03
Eliminate Non-Problem Segments
of Problem Areas
Conduct SSES Investigation
and Corrosion Survey
Conduct Cost-Effective Analysis
of All Problems
0)
CC
Develop Final Rehabilitation Plan
Establish Planning Time Frames,
Specific Work Scopes and Budgets
Mappjng Information
Previous I/I, SSES Studies
O&M Records, Inspection Reports,
Construction Reports
Geologic, Topographic,
Hydrologic Information
Flow records from Treatment
Plants. Lift Stations,
Bypasses, Overflows
Odor Complaints, Odor
Surveys, Corrosion Data
Rainfall Records,
Ground/rater Monitoring
Implement Plan, Procure Equipment and
Services, Award Contracts
17
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important that all staff assigned be able to commit the
necessary time for proper planning and implementation
of the survey. The major purposes for conducting a
preliminary sewer system survey are to identify, localize
and prioritize those areas of the sewer system sub-areas
with the greatest potential problems, and to identify the
preliminary scope of the subsequent investigations. A
preliminary survey is a forerunnerto the traditional I/I and
SSES procedures. The major sources of information
used in the preliminary survey are outlined below:
• As-built sewer maps
• Sewer system operation and maintenance (O&M)
records
1 • Existing geographical, geological, climatological and
topographical records
• Existing city or municipal planning documents
• Existing treatment plant performance records
• Sewer system monitoring records such as treatment
plant flow records, lift station flow records, overflows
and by-passes
• Interview information from public officials and
supervisory sewer system O&M staff
• Historical sewer system and treatment plant flow and
performance information
• Rainfall and groundwater data
• Water use records
• Population and user history
• Industrial survey information
The more important of the above data sources are:
available sewer maps, information from previous l/l'and
SSES studies, along with system and sub-flow monitoring
information. The preliminary information also includes
the normal data sources used for I/I analysis including
flow monitoring, rainfall, groundwaterlevels, and anecdotal
evidence of exfiltration.
The proper assignment of data collection responsibilities
toindividualsthat haveaccesstothe required information,
and the organization of responsibilities by the survey
team leader is a major factor in the success and efficiency
of the preliminary survey.
The goal of this preliminary survey, however, is to utilize
the available data to make the best judgments possible
regarding the condition of the existing sewer system and
to define the specific problems within the system and
sub-system areas. The final plan resulting from the
analysis of available data should, as a minimum, provide
the following information:
• Clear delineation of all sub-areas, and location of
monitoring points
• Clear understanding and preliminary ranking of the
problems within each sub-area. This may include the
relative severity of infiltration and inflow, suspected
sources of each, identification of major areas of
corrosion, the impact of lift stationson surf idegeneration
and corrosion, evidence of structural failures, sewer
blockages or other damage to the sewer system
infrastructure
• Identification of all non-problem sewer sub-areas
• Identification of sewer system monitoring and data
needs for all priority problems in each sub-area selected
for study
• Schedule for establishing system monitoring
requirements. For example monitoring for inflow would
be conducted during high-groundwater conditions while
monitoring for corrosion or exfiltration would be
conducted during low-flow, dry weather conditions.
An estimate of resources needed to conduct the
investigation of the sub-systems should include:
• Permanent or temporary sampling and flow
measurement equipment
• Sewer cleaning and inspection equipment
• Sulfide and corrosion measurement and monitoring
equipment
• Groundwater monitoring needs
• Rainfall simulation equipment
The resource estimate should include a summary of all
activitiesto be conducted by municipal employees and all
activities to be completed by contract services. A summary
work scope, budget and schedule should be prepared for
all service contracts.
The preliminary survey differs from the initial stages of an
I/I analysisorSSES investigation in the following respects:
• The scope of the preliminary sewer system survey is
broader than I/I or SSES and includes surveys of
physical damage to the sewer system infrastructure,
capacity limitations, effects of corrosion and sewer
system deterioration rates, and excessive I/I, including
those areas that would possibly be affected by
groundwater migration and exfiltration.
• The preliminary survey establishesthe problem priorities
for the entire system and sub-systems and defines the
overall work scope of subsequent investigations
• The preliminary survey defines the costs, objectives,
and time frames for implementing all investigations
necessary for a complete infrastructure analysis.
18
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3.4.2 Monitoring and Equipment Needs for
Preliminary Analysis
The monitoring and equipment needs for a preliminary
sewer system survey depend on the size of system or
sub-systems under investigation and the schedule for
conducting the survey. Sub-systems may vary in size
from af ew tenths of a square mile to several square miles
and may include up to 20 or more separate monitoring
stations. The preliminary survey includes flow monitoring
at critical junctions, limited physical surveys, preliminary
corrosion surveys and information to correlate flows with
rainfall and groundwater information.
Although equipment needs vary depending on the size of
the sub-system, typical equipment needs for a single
sub-system investigation are:
2-3 fully automatic recording flow meters
1-2 velocity meters
1-2 depth sensors
2-3 20- to 76-cm (8-30-in) weirs
1 metal detector
pH ORP meters
Recording DO meters
Smoke bombs, and a gasoline driven blower (1,500-
3,000 cfm)
Camera and film
Sand bags and plugs, 20-76 cm (8-30 in)
60-90 m (200-300 ft) of fire hose and fluorescent dye
1-2 tipping bucket rain gauges
2 proportional samplers and sample containers
Device for measuring corrosion such as a sonic caliper
1 extendable penetration rod
4-6 sulfide test kits
Miscellaneous sewer and manhole sampling and access
equipment including ladders, lights, buckets, sample
containers, rope, tapes, hand tools, and safety
equipment
Of the above equipment, selection of the appropriate flow
measuring devices (flow meter or weirs) and the
equipment for the preliminary corrosion survey is the
most important. The above list does not include
preparatory sewer cleaning or TV inspection equipment
since the preliminary survey does not extend to that level
of detail.
3.5 Infiltration and Inflow Analysis
3.5.7 Introduction
Infiltration is that volume of water that enters sewers
and building sewer connections from the soil through
foundation drains, defective joints, broken or cracked
pipes, faulty connections, etc.4
Inflow is that volume of water that is discharged into
existing sewer lines from such sources as roof leaders,
cellar and yard area drains, commercial and industrial
discharges, drains from springs and swampy areas, etc.4
I/I is the major deterrent to the successful performance
of a wastewater conveyance or treatment system.5
Excessive I/I in a sanitary sewersystemcan hydraulically
overload sewer lines and wastewater treatment plants,
resulting in surcharging, basement backups, sewer
bypasses, and reduced treatment efficiency.6 It also
adversely affects the urban environment and the quality
of the water resources. Some detrimental effects of I/I
are: utilization of sewer facility capacity that could be
reserved for present sanitaiy waslewater flows and
future urban growth; need for construction of relief sewer
facilities before originally scheduled dates; surcharging
and backflooding of sewers into streets and private
properties; bypassing of raw wastewater at various points
or diversion into storm drains or nearby watercourses;
surcharging of pump stations resulting in excessive wear
on equipment, high power costs, bypassing of flows to
adjacent waterways, diversion of flow away from
secondary or tertiary treatment stages, or bypassing of
volumes of untreated wastewater into receiving waters;
and increases in the incidence and duration of stormwater
overflows at combined sewer regulators.7 Proper analysis
of I/I is thus required to demonstrate possibly excessive
or nonexcessive flows in a sewer collection system and
to identify sources for later correction.
Correction of infiltration in existing sewer systems involves:
• Evaluation and interpretation of wastewater flow
conditions to determine the presence and extent of
excessive extraneous water
• The location and measurement of such infiltration
flows
• The elimination of these flows by various repair and
replacement methods; and
• A diligent, continuous maintenance and monitoring
program.
Correction of inflow involves:
• Discovery of locations of inflow, determination of their
legitimacy, assignment of the responsibility for
correction of such conditions
• Establishment of inflow control policies where none
have been in effect; and
• Institution of corrective policies and measures backed
by monitoring and enforcement procedures.
Control of I/I in all existing and new sewer systems is an
essential part of sewer system management. A sewer
19
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system cannot be rehabilitated and then be expected to
never develop additional points of I/I. Proper preventive
maintenance programs must be established to monitor
and control excessive I/I as an integral part of the
rehabilitation program.
The procedures involved in conducting an I/I analysis
should be listed as an orderly sequence of tasks. Step-
by-step actions should be designed to explore the scope
and details of the problem.6This exploration will ascertain
the need and the techniques required for the subsequent
evaluation of causes, effects and corrective actions.
Information must be gathered for making separate cost
estimates fortransportation and treatment of the infiltration
and inflow components versus elimination through
corrective action. Figure 3-2 provides the sequence of
events that shou Id be considered to properly analyze and
reduce I/I. If this initial analysis indicates that the I/I is
excessive, the next phase should be the SSES, which
should determine the specific locations of inflow, flow
rates, and rehabilitation costs for each I/I source. In
general, the main goals of an I/I analysis report are to:
• Identify which sewer systems have reliable data
available to conclusively demonstrate nonexcessiveor
excessive I/I.
• Generate sufficient flow data and characteristics of the
sewer system to enable a sound engineering decision
to be made regarding excessive and nonexcessive
flow.
• Obtain realistic cost estimates for rehabilitation of
sewers that contain excessive I/I and compare these
costs to thecost of transporting and treating extraneous
water.
• Enable the engineer, in the event of excessive I/I, to
detail the work tasks for the new evaluation i.e., the
SSES.
I/I analysis thus provides the fundamental evaluation and
indication of the existence of excessive flows in sewer
lines.
3.5.2 Preliminary Information Needed
Priorto conducting an I/I analysis, all pertinent information
and data should be collected on the specific wastewater
treatment and collection system under investigation.
This preliminary information should be enough to allow
the investigator to make a judgement of nonexcessive or
possibly excessive I/I.6'7
3.5.2.1 Interviews
Much of the basic data required for the I/I analysis can be
obtained from local sources by carefully planned and
executed interview programs. It is generally found that
the people who are most familiar with the sewer system
are public officials {both present and retired) and local
residents who will know from experience where many
defects may be located, where hidden interconnections
exist, what the history of performance has been, and
what the community's planning and growth needs have
been and will be. They know both permitted and non-
permitted points of flow into sewers as well as the
applicable regulations for plumbing and sewer
connections.
Results from well-conducted interviews may save the
engineer considerable field work and also give a clear
overview of the problems to be faced. The results from
the interviews may be utilized along with other findings to
make a proper judgement as to the seriousness of the I/
I problem in the study area, the major problem areas in
the system, the percentage of the I/I which can possibly
be removed, and the areas which may require further
investigation. A specific interview pattern and form is
used by many consultants and municipal officials; this
form includes a broad spectrum of subjects, such as:
• Sanitary sewer system
• Storm sewer system
• Existing and historical sewer maintenance program
• Problem areas in and around the sewer system
• Geological and geographical conditions in the sewered
area
• Population and water consumption data
• Legal and jurisdictional aspects of the sewer system.
A thorough interview form is included in the Handbookof
Sewer System Evaluation and Rehabilitation.4 This
interview form should be used as a guide and should be
adapted and/or modified to the system under study.
The purpose, nature and significance of the study should
be explained to the individuals being interviewed to avoid
any misunderstandings and to obtain full cooperation.
Good public relations should be practiced at all times.
Before an interview, maps of the study area should be
studied by the interviewer to become familiar with the
area. This will enable the interviewer to mark important
information on the maps to supplement the description
recorded in the interview forms.
Summary information from the interview should be plotted
on the map for easy identification. Discrepancies among
interviewees and/or between the interview results and
existing records should be evaluated. Some spot checking
should be performed to substantiate the interview results.
From the analysis of the collected information, a plan of
action can be made to gather more data needed for the
completion of the I/I analysis.
20
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Figure 3-2.
I/I analysis major activity flow chart.
Assemble I/I Survey Team
Collect and Analyze Available Data
on Sewer System
Conduct Interviews
Define System Components
• Define Sub-Basins
• Locate Critical Segments
• Conduct Sewer and Topographic Map Analysis
• Identify Overflow Points
• Locate Critical Monitoring Points
- Identify Surcharge Lines and Points, If Present
I
C Tiduct Short-Term Flow Monitoring
• Select Monitoring Points
• Select Monitoring Techniques
• Select Monitoring Schedules
• Monitor Flow
• Record and Analyze Flow Monitoring Results
• Develop Baseline Flows .
Perform System Hydraulic Analysis
- Inflow/Rainfall Correlation and Distribution Studies
- Infiltration Effects
- Exfiltration Effects
- Migration Effects
- Rainfall Induced Infiltration
- Groundwater Effects
- Capacity Analysis
- Surcharge Predictions
• Model Development and Flow Distribution Analysis
- Future Flow Impact Analysis
Sewer Maps
As-Built Sewer IE-cords
Past Studies, Engineering Reports
Sewer Maintenance reco
Lift Station and Plant Flow Records
Sewer Overflow Records
Conduct Rainfall Simulation and
Inspection Studies as Required
Select Design Rainfall Events
Field Surveys
Smoke Testing
Rainfall Monitoring
Dyed Water Flooding
Nighttime Flow Measurements
Pipe and Manhole Inspections
Groundwater Monitoring
Perform Preliminary Cost-Effective Analysis
• I/I vs. Rule-of-Thumb Excessive vs. Non-excessive I/I
• Sub-Basin Analysis of I/I
• Indentification of SSES Study Areas
• Identification of Major Overflow Locations
• Identification of Surcharged Points/Segments
21
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The patterned interview involves the first look at the
extraneous water problem in the community. A
professional who is experienced in the area of I/I should
interview everyone who is or has been connected with
the sewer system. Subsequent analysis of the data will
answer questions and give the analyst a feel for the
overall problem. The general objective of the interview is
to focus on the more important problem areas. The
questions should cover a broad spectrum of subjects,
ranging from technical matters to municipal performance
capabilities as well as questions regarding the socio-
economic profile of the city. A well-planned interview also
helps the municipality to think about its problems -In an
orderly fashion and to recognize alternate methods for
solution.
3.5.2.2 Mapping and Map Analysis
a. Mapping
• All sewer lines and appurtenant structures should be
recorded on authenticated maps. As-built drawings
should be available for all new sewer systems and
some of the older sewers.
b. Updating or preparation of maps
• Augmentation of existing maps with details of new
construction and revisions
• Preparation of new maps from as-built records,
additional underground surveys and other data
• Sewer maps, as a minimum, should be drawn to scale
and should indicate sewer sizes, slopes, direction of
flow, manhole locations, as well as other major sewer
system elements, e.g., pumping stations, treatment
plants, bypasses, pointsof overflow, force mains, force
main discharge points, etc.
In sewer systems where sewer maps are available, it
may be advisable to verify some of the critical points in
the field before total acceptance. Sewer maps should
also be updated to include new sewer extensions, sewer
line changes, buried manholes, and any other pertinent
data.7
In systems where maps are not available or are
incomplete, they must be developed before the study can
continue.
A street map is generally useful for the preparation of a
sewer map. In cases where street maps are not available,
a schematic layout of the sewer system may be suitable,
oramap may be developed. Sewer location and direction
of flow can also be determined by dye tracers, floats,
smoke, metal detectors and interviews with people having
considerable knowledge of the sewer system.
c. Map Analysis?
Map analysis normally includes the following elements:
• Establishment of rational major sub-basins based on
system layout, drainage areas, main sewers and
tributary lines, system configuration and other local
factors and system conditions
• Determination of sub-sections when and where they
are required to cover a more detailed study of conditions
in specific parts of any sub-basins
• Preparation of sewer system flow diagrams and flow
sheets
• Selection of key junction manholes for monitoring and
gaging flows in each sub-basin which will reflect I/I
conditions in constituent parts of the sewer system
Based on the sewer maps, the following information
pertinent to I/I can be indicated and overlaid on the sewer
maps:
• Topography of the study area
• Soil and hydrogeologic formations
• Groundwater mapping
• Sewer age, type, and size
• Known or potential problem areas such as areas
subject to flooding during rainfalls, surcharged sewers,
overflowing manholes, overloaded pumping stations,
houses with sewer backup problems, obvious inflow
sources, existing and historical swampy areas, etc.
This information, along with the sewer maps, may enable
one to gain valuable information into the I/I problems of
the area such as:7
• Storm sewers crossing, parallel to, or in the same
trenches as the sanitary sewers are likely I/I sources
• Sewersconstructednearrivers, streams, ditch sections,
ponding areas and swamps may present serious I/I
problems due to groundwater seepage or direct
drainage.
• Sewers constructed in unsuitable soils that may be
subjected to settling resulting in open joints and/or
cracked piping
• Older sewers or ones of particular materials, joints or
construction practices may present greater potential
for I/I. Manholes with perforated covers may present
serious inflow problems in low lying street areas.
• Sewers constructed above seasonal high groundwater
level should present few infiltration problems.
3.5.3 Rainfall Information
22
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3.5.3.1 Sources of Information and Methods of
Analysis
The measurement of precipitation as a part of sewer
system evaluation is undertaken to correlate rainfall with
flow metering data. Several items are generally of interest:
rainfall intensity, total volume per event, and duration of
the event. These data can be obtained from tipping
buckets or continuous weighing rain gauges. Charts that
record rainfall for several events and a totalizer that
provides a check against recorded data is useful. Snow
melting devicesforcolder climates are also available with
the precipitation measuring devices. Less sophisticated
devices such as graduated cylinders may also be
appropriate to provide crude, supplemental information
in some cases.
Prfortotheimplementationofaprecip'rtation measurement
program, other less site-specific data should be obtained
and evaluated. Sources of precipitation data are the
National Oceanic and Atmospheric Association (NOAA),
airports, state weather observers, electronic media
weather observers, other public works and research
agencies and private citizens. NOAA has an extensive
nationwide network of recording rain gauges. Those
gauges with hourly rainfall data are summarized by state
in a monthly publication entitled Hourly Precipitation
Data. Another useful publication containing daily
precipitation quantities from NOAA stations is
Climatobgical Data, which is also published monthly for
each state.
Rainfall causes inflow and can also cause infiltration by
the following mechanisms:6
* Rainfall and/or surface run-off may be carried directly
through the cracks in a clay soil surrounding shallow
sewer lines and manholes and leak through the
deteriorated manhole walls and sewers to cause an
infiltration problem.
• During and immediately after heavy rainfall, the
rainwater reaches the groundwater by percolating
through overlying soils and causes an increase in
groundwater level. The amount and rate of piezometric
head increase isafunction of the soil type and structure.
This increases the potential hydraulic head. If the level
is above the sewer pipes it increases the driving force,
which can cause the water to enter the pipes through
defective joints, etc.
• In locations where the sewer pipes are cut in u nderly ing
bedrock, the rainwater, after percolating through the
overlying soils, will likely flow in the same trench and
thereby cause an increased infiltration problem in the
sewers.
• During heavy rainfalls, anotherphenomenon may occur
in the soil and increase the infiltration rate in the
sewers. This is the case when a large ground surface
is covered by impounded rainwater: as this large
blanket of impounded water percolates through the
soils underneath, it leaves little chance for the air in the
soil to escape. Because of this, the air is subjected to
increased pressure. The pressure is transmitted to the
groundwater above the sewer pipe and may cause an
increased infiltration rate through defective pipe joints,
etc.3
3.5.4 Topographic and Geologic Information
3.5.4.1 Sources of Information and Method of
Analysis
Soil conditions in the sewer system study area often
affect the I/I problems. Sewers constructed on unsuitable
soils may be subjected to settling, expansion, or
contraction resulting in open joints or cracked pipes. Soil
chracteristics that affect I/I response are:4
• Permeability, among other soil characteristics, affects
the rate of movement of groundwater through the soil
matrix adjacent to sewers and sewer trench backfill
materials.
• Backfill and bedding materials immediately surrounding
the sewer affect the structural integrity of sewers.
Granular sewer bedding materials are quite porous
and often act as a secondary conduit that transmits
groundwater along the sewer line thus providing
additional opportunities for infiltration at downstream
locations.
• Impermeable soils such as clays that are used as
backfill above the granular bedding layer reduce the
vertical penetration of surface waters entering the
sewer envelope.
Information on soil distribution and soil characteristics in
an area can be obtained from the following sources:7
• Soil Conservation Service. U.S. Department of
Agriculture. The Soil Conservation Service has
published many soil maps with descriptions of soil
characteristics. They have offices in most counties
throughout the country.
• Boring logs in sewer construction contract documents.
Boring logs contained in the sewerconstruction contract
document provide certain details about the soils along
the sewer construction route.
• State Agricultural Extension Service. Data on soil
types and soil characteristics may have been collected
by the State Agricultural Extension Service.
• Local Construction Companies or Contractors. Local
construction companies or contractors, particularly
well drilling firms, should have some information about
the area's soils.
23
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• Field Investigation. For locations where no soil
information is available or existing information is
contradictory or indicative of serious problems, a field
soil study may be needed. The study may include the
test borings at key points and interpretation of the
collected soil samples. For complex and unusual cases,
the soil samples should be interpreted by a soil scientist.
Assistance may be available from the Soil Conservation
Service, Agricultural Extension Service representatives,
consulting soil scientists or agronomists.
3.5.5 Ground Water Information
3.5.5.1 Sources of Information and Methods of
Analysis
Information is required to determine the variations in the
groundwater level. Most of the infiltration phenomena in
sewers are groundwater related. Determination of
infiltration in the sewer system should be based on a
comparison of the wastewater flow data collected in the
high groundwater periods with data collected in the low
groundwater periods. Sewer line inspections should be
conducted during highgroundwaterperiods. Groundwater
monitoring should be conducted if no data are available.
The level and, in certain cases the chemical
characterization of the groundwater affect the degree of
infiltration in the sewers. General groundwater information
can be obtained from a number of sources:47
• State Water Resource Agencies
• U.S. Geological Survey
• Local or County Water Conservation Districts
• Groundwater users, including municipalities, water
companies and individuals
• Local construction companies or contractors
Two types of groundwater level measurement gauges
are commonly used for sewer evaluation studies: the
manhole gauge and the piezometer. The manhole gauge
shown in Figure 3-3 is used to determine groundwater
levels adjacent to manholes. These gauges are
inexpensive and fairly easy to install; however, they do
clog easily from mineral deposits. The piezometer shown
in Figure 3-4 is generally installed in a hole excavated by
a powered flight auger. Piezometers are more permanent
and are far less prone to clogging. They are also more
expensive, but with proper maintenance should last for
years and provide higher quality data than manhole
gauges
Installation sites for groundwater gauges should be
away from underground utilities and streets to prevent
damage from street maintenance equipment.
Groundwater levels can be recorded on a periodic basis.
A plot of groundwater levels versus time is helpful in
interpreting meter data and determining levels of
infiltration. The recorded data obtained from groundwater
gauges should be reviewed and screened carefu lly before
beingused. Pumping waterfrom nearby wellsmay cause
atemporary drawdown of the groundwater surface at the
monitoring stations, which may give biased groundwater
levels. Groundwater levels should be measured during
periods of the day when groundwater pumping in the
study area is at a minimum.
3.5.6 Baseline Sewer Flows
3.5.6.1 Population and Flow Projection Methods
Population and flow data are essential for the
determination of I/I. They determine the theoretical (or
base) wastewater production rate in the study area. The
theoretical wastewater production represents the total
quantity of wastewater including domestic, commercial,
and industrial wastewaterflows, but excluding all infiltration
and inflow. Flow rates are expressed as gal/capita/day
(gpcd).
Monitoring of flows at treatment plants, lift stations, and
properly located junction manholes is essential. Flow
monitoring should be carried out at different times of the
day as necessary to permit differentiation between normal
expected sanitary flows and I/I volumes. Treatment plant
and lift station flow records should be evaluated and
necessary information should be gathered to produce an
adequate I/I analysis. The baseline sewerf low monitoring
tasks should include the following:4
• Verify flows from plant records, pumping or lift station
charts or log sheets, or from previous sewer monitoring
at the same or nearby locations involved in the current
analytical procedure.
• Gauge flows at key junctions, manholes, pumping
stations and overflow points during hours of minimal
flow to determine the presence and amounts of
infiltration volumes in various subsections of the sewer
network.
• Determine daily and hourly flow variations in a limited
number of locations for the purpose of monitoring the
effect of rainfall on the flow characteristics in various
sub-systems and to ascertain the quantity of infiltration
and inflow and to differentiate between the two
components.
The population data should be gathered only for the
periods in which records for water consumption,
wastewater flow, groundwater and rainfall are all available.
Both the total population and the sewered population
should be known for the determination of I/I. In areas
where there are seasonal fluctuations in populations, a
detailed breakdown of the population according to season
24
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Figure 5-3. Static groundwater gauge installation elevation.
Known Elevation
Install Gauge As Near As
Possible to the Top of the
Lowest Pipe in the Manhole
Groundwater
Gauge Reading
25
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Figure 3-4.
Groundwater gauge installation detail.
Threaded Cover
(to extend above
ground surface)
Concrete Seal
Steel Casing
PVC Casing
Opening to Allow
Entering of Groundwater
Filter-Cloth Wrapping
Over Slotted Section
Cap
26
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or month should be provided. Population records are
availablefromthe U.S. Census Bureau, local government
offices and sanitary districts. Such data may also be
reported in previous engineering study reports. If no data
are available, a physical survey to include census, house
count, and aerial maps may have to be performed to
determine the population.6-7 Preference should be given
to wastewaterf low records. All water use does not end up
in the sewer. Water consumption (metered) is also
measured on a cumulative basis (e.g., 100 cu ft/mo).
3.5.6.2 Water Use and Wastewater Generation
Estimates
The water consumption data to be obtained should
coincide with the available records for wastewater flow,
groundwater and rainfall. Metered water data available
for all'users in the study area should be collected and
used for the estimation of the wastewater production
rate. Waterconsumption recordscan usually be obtained
from local water departments, private water companies,
industrial plants and individual well users. Water
consumption estimatescan be made based on population
and an inventory of the residential, commercial and
industrial establishments in the study area using typical
water use rates. Water production records can also be
used where water consumption data are not available. If
water production data are used, allowances for
consumptive use should be made so baseline wastewater
flows are not overstated.
Wastewaterflow recordscovering the entire sewersystem
over a period of 1-2 years should be used for I/I analysis.
These records should include and representgroundwater
and rainfall conditions in the study area. For larger sewer
systems, flow records may have to be gathered from
more than one treatment plant, pump station or flow
measuring station in the system. Flow records for
overflows, bypasses and emergency pumping should be
gathered for the I/I analysis. Wastewater flow records
can be obtained from wastewater treatment plants,
sanitary districts or sewer departments in local
governments.
The water consumption and wastewater flow records
should be checked for accuracy before being used. The
accuracy can be determined by checking the accuracy of
the instruments used for recording and totalizing the
flows.
3.5.7 Analysis of Infiltration and Inflow
3.5.7.1 Purpose of Analysis
Properanalysis of the data to determine I/I flow rates into
the sewer system is essential for accurate estimation of
the effectiveness of sewer rehabilitation. Discrepancies
between estimated and actual I/I reductions are likely if
improper I/I analysis occurs. Establishing the quantities
of I/I entering a collection system is: far from being an
exact science. I/I analysis should consider various
inaccuracies of flow measurement in sewer systems.
The procedures for interpreting I/I data should recognize
the impact of rainfall events, groundwater levels,
antecedent soil and weather conditions and monitoring
schedules on the overallcomponenl flows.
Baseline wastewater flow data are normally collected
during dry-weather conditions. Groundwater infiltration
should be measured during high groundwater since it will
be significantly impacted bygroundwaterlevelsthroughout
the sewer systems. Inflow and Rll component flow
information are strongly related to the characteristics of
the rainfall events occurring during the monitoring period.
As discussed in Section 3.5.7.3, Rll flows are strongly
rainfall dependent even though they do not enter the
sewer system directly.
In many cases it is not possible to clearly distinguish
inflow, groundwater infiltration and Rll. The sum of these
components however can be estimated by subtracting
the baseline flow from the total flow. These numbers can
be used and compared to the accepted rules of thu mb of
450 Lpcd (120 gpcd) of domestic plus non-excessive I/I
flow and the storm flow of 1,000 Lpcd (275 gpcd). The
cost-effective analysis for infiltration and inflow requires
that these two components be separated. The cost of
transportation and treatment requires that peak flows be
determined. A proper cost-effective analysis generally
requires that the following flows be determined:
Peak infiltration
Peak inflow
Peak I/I
Total yearly infiltration
Total yearly inflow
Total yearly I/I
3.5.7.2 Groundwater Migration
It is believed that much of the infiltration removed by
rehabilitation of a source "migrates" to other sources that
were either inactive or less active before rehabilitation.
This phenomenon, known as migration, has led to
disappointing results in typical rehabilitation programs,
which have demonstrated a disparity between anticipated
and actual reduction of infiltration.8
Sanitary sewer rehabilitation has seldom resulted in the
infiltration reduction projected by sewer system surveys.
Studies performed at two sites in the Washington
Suburban Sanitary Commission (WSSC) sought to
determine whether the assumed removable infiltration
27
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migrates to sources which were inactive or less active
before rehabilitation.8 To investigate the impact of
migration on rehabilitation, 43 groundwater wells were
installed in two study areas with a recording flow meter at
each site. Well level readings, nighttime flow, isolation
measurements, and local rainfall data were obtained.
After all sewersystem defects were inventoried, selective
rehabilitation consisting of line and manhole grouting,
excavation and repair of sewer segments and grouting of
service connections was conducted. Rehabilitation was
implemented in two phases in each study area with
groundwater and infiltration response measured before,
during, and after each phase of rehabilitation. Migration
of grou ndwater infiltration to previously inactive locations
was documented at both study sites. This migration
effect was accompanied by a corresponding increase in
groundwater level at one of the two study sites. Based on
an analysis of the data, it was observed that migration
effects travelled as much as 60 m (200 ft) to reach
unrehabil'rtated sources. Results of this study indicate
that the traditional point source method of I/I analysis is
only about half as accurate as it would be if migration
were properly integrated.
Migration of groundwater infiltration to previously inactive
sources can be documented by a corresponding increase
in groundwater level at the study sites. One documented
occurrence of groundwater level increasing after
rehabilitation is illustrated in Figure 3-5. In this figure,
Well 03 was located away from the sewertrench and Well
E was located on the trench.8
One factor that affects migration phenomena is soil
permeability. An important characteristicof existing SSES
methodology is the reliance on individual line section
nighttime isolation and measurement to identify sewer
reaches subject to excessive infiltration. This fragmented
approach provides an opportunity for migration since this
process identifies conditions at one point in time,
eliminating potentially defective elements of the system
from further study. To effectively account for migration,
the flow monitoring procedure must be revised to expand
the data on an individual line segment basis. This will
involve initially monitoring sub-areas with extended
duration metering.9
Migration of infiltration from rehabilitated tounrehabilitated
sources was observed and documented under work
carried out by the WSSC. The extent of migration was
primarily dependent on the number and location of
rehabilitated sources in addition to differences in
permeability between trench material and surrounding
soil. Results of the study by WSSC indicate that
rehabilitation should be clustered in areas conducive to
migration to achieve net flow reductions. If rehabilitation
is not generally concentrated then flow removed from
one source would essentially migrate to nearby
unrehabilitated sources. General conclusions applied to
the WSSC study on migration were:8
• Migration is probably not significant for a sewer system
constructed substantially below the groundwater level
since increases in in-trench groundwater as a result of
rehabilitation would probably result in only a minor
increase in head compared to the existing head on the
sewer system. Interceptors that run along the banks of
creeks and rivers are typical of sewer lines below
groundwater levels.
• Sewers located in highly granular areas would not be
subject to significant migration because groundwater
movement would not be restricted by low permeability,
thereby allowing exfiltration from the trench.
• Topographically flat areas would be less subject to
migration since the lack of steep gradients would result
in some outward dissipation rather than exclusive in-
trench movement.
• Sewers in soils of lowpermeability are highly conducive
to migration. Despite backfill consolidated during
construction the sewer trench would be considerably
morepermeablethanthe surrounding soil since sewers
are normally supported by granular material such as
gravel and sand.
In a comprehensive rehabilitation program, it would be
desirableto eliminate sources located on private property,
especially house services. Here rehabilitation tends to be
more expensive on the basis of unit flow rates. Private
sector rehabilitation has political implications when part
or all of the rehabilitation is paid by the property owners.
3.5.7.3 Rainfall Induced Infiltration (Rll)
Rainfall Induced Infiltration (Rll) is a form of infiltration
that behaves.somewhat similar to and is sometimes
confused with storm water inflow. Rll generally occurs
during or immediately after rainfall events. It is caused by
the seepage of percolating rainwater into manhole, pipe,
and lateral defects that lie near or are readily reached
from the ground surface. Foundation drains are a special
case which has been classified as both inflow and
infiltration by regulatory authorities. The quick rainfall
response of Rll causes a more rapid build-up of flow in
sewers than normal I/I flows thus creating a greater
potential for sewer surcharging and overflow.
An ancillary problem associated with Rll as with any
infiltration problem is that there is the potential for
exfiltration of untreated wastewater at these same pipe
and manhole defects. In some cases, discharged
wastewater may cause groundwater contamination; in
28
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Rgure 3-5.
Effects of groundwater on migration.
t
I *
"S *J .
•e
0)
o>
c =
i S
o
-------
other cases it might be channelled by sewer trenches to
potential points of direct human exposure. Data based on
a study conducted by the U.S. EPA indicates the following
conclusions and findings regarding the impact of Rll:3
• Rll is a type of infiltration since it enters the sewer
system through defects. However, its flow
characteristics resemble those of inflow i.e., there is a
rapid increase in flow which mirrors the rainfall event
followed by a decrease as the rain stops.
• Becauseofitsflowcharacteristics, Rllhasoccasionally
been misidentified as inflow in many cases.
Consequently, rehabilitation programs aimed at inflow
sources have not achieved the anticipated reduction in
extraneous flows in these cases.
• Rll appearsto represent a significant portion of the flow
to some wastewatertreatment plants during wet weather
periods. InthelOcase studies conducted by U.S. EPA,
the peak wet weather flows were 3.5-20 times the dry
weather flow. The contribution from Rll was estimated
to be between 60-90 percent of the wet weather flows,
the remainder being groundwater infiltration and inflow.
• Collection and treatment systems often do not have the
capacity to handle peak wet weather flows. Peak flows,
therefore, can cause wastewaterbackupsintobuildings,
overflows and treatment system bypasses. Such
occurrences are a hazard to public health and a
violation of the municipality's discharge permit.
• Sewer trenches can act as collectors of rainfall
percolating into the soil. The trenches channel the
water, thus providing multiple opportunities for the
water to seep into the collection system at defective
points.
• The shallow portions of a collection system, e.g. building
laterals, manhole defects, etc. are more vulnerable to
Rll. Interceptors sewers, which are typically deeper, do
not appearto be a significant entry point for Rll, but are
more likely sources of groundwater infiltration, which
normally minimizes peak to average flow ratios.
• The extent of Rll problems in sanitary sewer systems
is related to the age and condition of the sewers,
material of construction, pipe, lateral and manhole
defects, climate, geology, groundwater levels, and
depth of sewers.
Figure 3-6 presents the typical entry points of Rll.
3.5.7.4 Method of Analysis
The following techniques can be used to estimate the
total infiltration in a sewer system:
a. Water Use Evaluation
This method uses the water supply records for the
purpose of estimating the amount of domestic wastewater
discharged to the sanitary sewer system. Monthly water
use records are obtained. As an estimate, the percentage
of the water that would reach the sanitary sewer would
range from 70 percent in summerto 90 percent in winter.
Given these facts, the rates at which domestic, industrial
and commercial wastewater should flow into the sanitary
sewers can be determined. These calculated flow rates
can be subtracted from the total flow measured at the
wastewatertreatment plant to obtain an estimate of the
infiltration entering the sewer system. Factors that should
be considered when using this method for infiltration
analysis are:
• Confirmation of the consumptive use mentioned above
• The amount of unaccounted water supplied through
the system through wells, springs, or reservoirs that
would not be accurately measured due to faulty or
inaccurate meters or lack of metering. Unaccounted
for water also includes illegal taps and unmetered
withdrawals from fire fighting lines, street flushing fire
lines, or hydrants.
• For areas supplied with a secondary water system, the
water balance must include this source.
b. BOD Evaluation
The mass BOD loading from domestic and industrial
sources are used in this method. The method assumes
that the average BOD of domestic waste without infiltration
is 200 mg/L Monthly treatment plant flow records are
used to determine total flow and average actual BOD
daily loading. The industrial flow and BOD loading must
also be estimated in order to use this method.
First, the total BOD loadtothetreatment plant iscalculated
in mass/d from the plant influent flow and actual influent
BOD. Next the industrial flow and BOD load is estimated
and subtracted from the total plant load. The normal
domestic flow is calculated by knowing the domestic
BOD load and using an influent BOD concentration of
200 mg/L. The infiltration isthen calculated by subtracting
the calculated domestic flow plus the estimated industrial
flow from the actual plant flow. The procedure can be
completed on a daily, monthly or annual basis. The
accuracy of the procedure depends on the accuracy of
estimating industrial flow and BOD load. It should be
applied to the total system rather than to sub-systems
because of limitations due to unequal distribution of
domestic and industrial flows in smaller sub-systems.
c. Maximum-Minimum Daily Flow Comparison
This method assumes that infiltration will be constant
throughout the day if there is no precipitation. Industrial
flows are also assumed to be constant throughout the
day, so the daily flow variations measured are strictly
attributed to the domestic flow contribution. Treatment
plant influent data can be evaluated to obtain the domestic
30
-------
Figure 3-6.
Typical entry points of rainfall induced Infiltration.
Si
31
-------
flow rate. The domestic flow rate and the industrial flow
rate are subtracted from the total flow rate, which gives
the resultant quantity as the rate of infiltration. This
procedure can be carried out using monthly averages to
obtain the estimated infiltration for the entire year.
d. Determination of Total Yearly I/I
The following procedure is used to estimate the yearly I/
I in the sewer system:
• Obtain the average daily, weekly, and monthly
wastewater flow data from treatment plants for the time
period of interest. A minimum of one year of data
should be used.
• Obtain and/or calculate the theoretical wastewater
production rates; also the rainfall and groundwater
levels throughout the sewer system area should be
noted throughout the study period.
• Plot the rainfall duration and intensity along with
groundwater levels.
• For each storm, plot the average wastewaterf lows and
the theoretical wastewater production rateasafunction
of time, as shown in Figure 3-7.
• The area in the plot which is between the theoretical
wastewater production rate and the recorded
wastewater flow rate represents an estimate of the
yearly I/I.
An estimate of yearly infiltration can be estimated as
follows:
• Select several months of data from the total yearly I/I
plot (Figure 3-7) and plot rainfall duration and intensity,
total recorded wastewater flow and theoretical
wastewater production rate.
• Draw a line through the lower limit of the recorded
wastewater flow as shown in Figure 3-8.
• The distance between this line and the theoretical
wastewater production provides an estimate of the
infiltration.
Total yearly inflow can be estimated by the following
procedure:
• The total yearly inflow can be obtained by subtracting
the total yearly infiltration from the total yearly I/I. The
total yearly inflow obtained may contain some amou nts
of infiltration which is induced by rainfall and is known
as Rll.
3.6 Exfiltration and Its Impacts
3.6.1 Introduction
Exfiltration is a relatively new topic in the sewer system
rehabilitation field. Exfiltration occurs when deteriorated
or poorly designed or constructed sewer lines allow
wastewaterto escape from the sewer into the surrounding
soil. An exfiltration study was initiated by the U.S. EPA
because it was not known what effect exfiltration from
sewers had on the groundwater in the area. It was
believed that industrial and domestic wastes flowing in
the sewers could be escaping into the nearby soil and
possibly percolating to the grou ndwater and contaminating
it. Results of the Evaluation of Groundwater Impacts of
Sewer Exfiltration^0 summarizes the activities and findings
of this study. The U.S. EPA study showed that it was
impossible to correlate infiltration with exfiltration.
Previously exfiltration has been used to estimate
infiltration. This practice appears to have limited
applicability unless a special case can be demonstrated
where such a correlation does exists.
3.6.2 Summary of Information on Impacts
The U.S. EPA study showed that substantial exfiltration
does exist in locations where the groundwater level is
sometimes or always below the sewer. In fact, in the two
field studies which were performed, exfiltration rates
were found to be greater than infiltration ratesin locations
where fluctuating groundwater levels allowed for both
infiltration and exfiltration.
As a part of the U.S. EPA exfiltration study, the
groundwater was sampled and analyzed in areas where
sewer exfiltration existed. The results of the groundwater
analyses were inconclusive. Tests performed in one area
indicated that exfiltration was not contaminating the local
groundwater. Tests in a second area showed slightly
higher levels of several contaminants but the study could
not prove that these contaminants were a result of
exfiltration.
3.6.3 Consideration in I/I Analysis
It is important that the possible effects of exfiltration be
considered in an I/I analysis. Ignoring exfiltration could
lead to the calculation of inaccurate infiltration rates.
3.6.4 Present and Future Environmental Impacts
Even though the results of the exfiltration study were
inconclusive, the environmental impacts of exfiltration
are potentially significant. If exfiltration of wastewater is
contaminating groundwater, it could have a serious
impact on the environment. More research is required
before the environmental impact of exfiltration can be
determined, but the potential for contamination of
groundwater is greatest in coarse soils above unconfined
aquifers.
3.6.5 Exfiltration Tests and Methods
Exfiltration tests have historically been used as an indirect
method of estimating infiltration potential for both old and
32
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Figure 3-7.
Determination of total yearly infiltration/Inflow.
•a
cc
I
2
corded Wastewater Flow
lljlljjjljj. .
Theoretical Wastewater Production Rate
Time
j
1 Year
33
-------
Figure 3-8. Determination of total yearly infiltration.
Recorded Wastewater Flow
Non-Rainfall Day
Wastewater Flow
Theoretical Wastewater Production Rate
•Maximum Infiltration
1 Month
Time
34
-------
new sewer systems. It is most commonly applied io new
sewers and is normally a part of new sewer construction
specifications. Accurate exfiltration tests requires a
knowledge of ground water levels, adequate pre-soak
times and maintenance of adequate head differentials on
the system.
Prior to the initiation of an exfiltration test, the level of
groundwater adjacent to each section undergoing the
testing must be measured and recorded. The exfiltration
test works on the basis that a certain pressure will force
water out of the line into the soil surrounding the pipe. The
following is an outline of an exfiltration test procedure:
• Clean the pipe section from manhole to manhole for
each reach of sewer being tested (applies to old
sewers).
• Seal the upstream pipe inlet of the upstream manhole
and the upstream pipe of the downstream manhole
with plugs to ensure tight seals against water leakage.
Since the exfiltration test can take several hours, the
need fortemporary wastewaterbypassing around the
test section should be anticipated.
The exfiltration test is based on the loss of water from the
section of sewer being tested and thus requires a method
of establishing a specific pressure head on the system.
The upstream manhole is often used as a reservoir for
maintaining the pressure head. A standpipe may be used
in stead oftheupstreammanholeforprovidingthe pressure
head on the system.
• Afterproperty sealing and isolating the test section, the
sewer and manhole or standpipe must be filled with
water. The upstream manhole or stand pipe is used to
introducetestwaterintothe system and for maintaining
an adequate pressure head. The test head should be
60 cm (2 ft) above the pipe crown at the highest point
or 60 cm (2 ft) above the groundwater level.
• Water shou Id be allowed to stand in the test section for
a period long enough to allow water absorption in the
pipe. This time should be as much as 6 hours for
concrete pipe depending upon the degree of saturation
prior to testing. After the absorption period, the pipe,
upstream manhole, or stand pipe is refilled and the test
begun. This step is not necessary for vitrified clay or
plastic pipe.
* Determination of the actual exfiltration is based upon
the method used for providing pressure head on the
system, either by standpipe orthe upstream manhole.
• Use of the standpipe requires that a constant water
level be maintained in the standpipe to maintain the
specified pressure head on the sewer section under
test. Therefore, the volume of water added to the
standpipe over the one hour test period is the actual
exfiltration rate from the section under test.
• When using the manhole, the exfiltration rate will be
determined by measuring the difference of the final
water elevation and the initial water elevation and
converting this to actual gallons lost through the pipe in
a one hour period.
• If the pipe being tested does not meet the permissible
loss, the section of sewer is considered unacceptable.
Another exfiltration test should not be conducted until
thegroundwaterconditionssurroundingthe pipe return
to a condition similar to those existing at the beginning
of the test period. The groundwater elevation should be
determined prior to initiation of the second test.
A less commonly used exfiltration testt is the continuous
flow monitoring technique. Continuous flow monitoring
should be performed in a 300-m (1,000-ft) section of
sewer or greater which contains nothing that could
interfere with the test results. The groundwater level
must be below the sewer to ensure that no infiltration
occurs and there must be no laterals or cross connections.
Certain characteristics of the test section must be constant
forthe entire section: the size, type and age of sewer pipe
and the type of soil surrounding the pipe. The flow rates
at the beginning and end of the test section are
continuously measured and the difference between the
two is the amount of exfiltration. In the exfiltration study,
the flow measurements were made using a weir and
differential pressure sensing bubbler flow meter and
flows were measured and recorded for at least 48 hours.5
Other types of flow measurement schemes would also
work, based on the same physical principles.
If a 300-m (1,000-ft) section of sev/er that meets the
above criteria cannot be found, a shorter sewer or one
which contains a few disturbances may be used. The
effect of the disturbances would need to be measured
and analyzed, however, and would introduce significant
errors into the calculation of the exfiltration.
3.7 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. Odor and Corrosion Control in Sanitary Sewerage
System and Treatment Plants. IE PA/625/1-85/018,
EPA, Cincinnati, Ohio, 1985.
35
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2. Report to Congress: Hydrogen Sulfide Corrosion in
WastewaterCollectionandTreatmentSystems.EPfiJ
430/09-91/009. U.S. Environmental Protection
Agency, Washington, D.C.
3. Rainfall Induced Infiltration into Sewer Systems,
Report to Congress, 1990.
4. Handbook for Sewer System Evaluation and
Rehabilitation. EPA/430/9-75-021, Office of Water
Program Operations, U.S. Environmental Protection
Agency, Washington, D.C., 1975.
5. Technology and Design Deficiencies at Publicly
Owned Treatment Works, Water Environment and
Technology, December 1989.
6. American Public Works Association. Sewer System
Evaluation, Rehabilitation and New Construction: A
Manual of Practice. EPA/600/2-77/017d, NTIS No.
PB-279248. U.S. Environmental Protection Agency,
Municipal Environmental Research Laboratory, Office
of Research and Development, Cincinnati, Ohio,
December 1977.
7. Existing Sewer System Evaluation and Rehabilitation.
ASCE Manuals and Reports on Engineering Practice
No. 62, WPCF Manual of Practice FD-6. American
Society of Civil Engineers, Water Pollution Control
Federation, 1983.
8. National Water Well Association, R JN Environmental
Associates, Inc., and Washington Suburban Sanitary
Commission. Impact of Groundwater Migration on
Rehabilitation of Sanitary Sewers. 1984.
9. Montgomery County Sanitary Department. Ground
Water Infiltration and Internal Sealing of Sanitary
Sewers. Water Pollution Control Research Series,
U.S. Environmental Protection Agency, 1972.
10. Engineering-Science. Results of the Evaluation of
Groundwater Impacts of Sewer Exfiltration. Study
conducted under contract no. 68-03-3431,
Performance Assurance Branch, Municipal Facilities
Division, Office of Water, U.S. Environmental
Protection Agency, 1989.
Additional Reading
American Public Works Association. Control of Infiltration
and Inflow into Sewer Systems. 11022 EFF12/70, Water
Quality Office, Environmental Protection Agency and
Thirty-nine Local Governmental Jurisdictions, 1970.
American Public Works Association. Excerpts from
Control of Infiltration and Inflow into Sewer Systems and
Prevention and Correction of Excessive Infiltration and
Inflow into Sewer Systems. EPA/670/9-74-004, Water
Quality Office, Environmental Protection Agency & Thirty-
nine Local Governmental Jurisdictions, 1971.
American Public Works Association. Prevention and
Correction of Excessive Infiltration and Inflow into Sewer
Systems. NTIS No. PB-203208, Manual of Practice,
Water Quality Office, Environmental Protection Agency
& Thirty-nine Local Governmental Jurisdictions, 1971.
Bodner, R. L. and R.E. Nelson. Measuring Effectiveness
of Infiltration/Inflow Removal. Public Works 113:50-52,
October 1982.
Carter, W. C., A.J. Hollenbeck, and R.J. Nogaj. Cost
Effectiveness and Sewer Rehabilitation. Public Works
117:64-67, October 1986.
Connelly, Conklin, Phipps & Buzzell, Inc. Evaluation of
Infiltration/Inflow Program Final Report. EPA-68-01 -4913,
Off ice of Water Program Operations, U.S. Environmental
Protection Agency, 1980.
Construction Grants 1985. EPA/430/9-84-004, Office of
Water, U.S. Environmental Protection Agency, 1984.
Darnell, P.E. Conducting Sewer System Evaluations for
Small Systems. Water & Sewage Works 123:68-71,
November 1976.
Debevoise, N.T. and R.B. Fernandez. Recent
Observations and New Developments in the Calibration
of Open ChannelWastewaterMonitors.J\NPCF5B-A185-
1191, November 1984.
Deciding to Rehabilitate, Repair, or Replace. Water
Engineering & Management 132:50-53, May 1985.
Driver, F.T. Manhole I/I Stopped with Special Repairs.
Water Engineering & Management 130:31 -32, April 1983.
Experts Discuss Private Sector Infiltration/Inflow. Water
Engineering & Management 130-32-34, September 1983.
Fernandez, R. B. Sewer Rehab Using a New Subarea
Method. Water Engineering & Management 133:28-30,
February 1986.
Goss, R., R. Stalnaker, and R. Thornhill. Inflow Reduction
Eliminated Need for New Interceptor. Water Engineering
& Management 136:52-55, September 1989.
36
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Gray, W. R. and R.J. Nogaj. Sanitary Sewer Bypass
Reduction Program. Water Engineering & Management
137-36-40, May 1990.
Heinecke, T.L. and C.H. Steketee. The Key to Effective
I/I Control. Public Works 115:88-92,106-107, June 1984.
Hollenbeck, A.J. Designing for Removal of Sanitary
Sewer Cross Connections. Water Engineering &
Management 131:29-31, April 1984.
Hollenbeck, A.J. and G.D. Lambert. New Approach
Achieves Inflow Reduction in Sanitary Sewers. Public
Works 118:119-121, September 1987.
Hollenbeck, A.J. and R.J. Nogaj. Inflow Distribution in
Wastewater Collection Systems. Water Engineering &
Management 129:30-33, January 1983.
Hollenbeck, A.J. and R.J. Nogaj. One Technique for
Estimating Inflow with Surcharge Conditions. JWPCF
53:491-496, April 1981.
Infiltration Inflow Collection System Management:
Challenge of the 80's. I/I Evaluation and Control Division,
Department of Maintenancelind Operations, Washington
Suburban Sanitary Commission, Hyattsville, MD, 1982.
J.M. Smith & Assoc. Analysis of Acceptable Ranges for
Infiltration and Inflow Reduction in Sewer System
Rehabilitation Projects. Study conducted under contract
EPA 68-01-6737, Performance Assurance Branch,
Municipal Facilities Division, Off ice of Municipal Pollution
Control, U.S. Environmental Protection Agency,
Washington, D.C.
Johnson, W.D., S.R. Maney, and G. McCluskey. Open
Cut Sewer Construction Across Railroad Tracks Saves
Money. Public Works 120:73, June 1989.
Mayer, J.K., F.W. MacDonald and S.E. Steimle. Sewer
Bedding and Infiltration, Gulf Coast Area. 11022 DEI 057
72, Office of Research and Monitoring, Environmental
Protection Agency, 1972.
Montgomery CountySanitary Department. Determination
of Ground Water Infiltration and Internal Sealing of
Sanitary Sewers. Water Quality Office, Environmental
Protection Agency, 1971.
Nelson, R.E. New Ways to Fix Leaky Sewers. American
Crty & County Magazine 95:39-42, September 1980.
Nogaj, R.J. I/IRehab Success Comes With Understanding
System Behavior. Water/Engineering & Management
131:36-38, February 1984.
Owens, R. A U.S. Testforlnsituform;or, Howto Rebuild
a Pipe from Within. American City & County Magazine,
September 1980.
RJN Environmental Associates, Inc., Consulting
Engineers. Making Effective Use of Existing Collection
Capacity. Water/Engineering & Management 132:38-
40, September 1985.
RJN Environmental Associates, Inc., Consulting
Engineers. National Alterative Methodology for Sewer
System Evaluation. Washington Suburban Sanitary
Commission, 1988.
Three Cost Effective I/I Programs. Public Works, January
1983.
Wilson & Company. Implementation of a Comprehensive
Infrastructure Assessment Program, Case Study:
Pittsburgh, Kansas. Department of Public Works, City of
Pittsburgh, Kansas.
Sewerage Rehabilitation Manual. Water Research Center,
Blagrove, Swindon, Wilshire, 1983.
37
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CHAPTER 4
Sewer System Evaluation
4.1 Introduction
The SewerSystem Evaluation Su rvey (SSES) is the third
phase of an overall sewer system evaluation (See Figure
3-1). The purpose of the SSES is to quantify the amount
of infiltration/inflow (I/I) and rainfall induced infiltration
(Rll) that can be reduced and the cost of such reduction
on a source-by-source and sub-system basis. The SSES
confirms and refines the overall findings of the I/I analysis.
The SSES employsTVinspection, rainfall simulation and
othertechniques to identify specific sources as required
to develop the detailed cost-effectiveness analysis for I/
I.
The findings of the SSES should be sufficiently specific
to describe the corrective actions that need to be taken
along with the amount of infiltration, Rll, and inflow that
will beeliminated from each majorsource, sewer segment
and sub-basin . The SSES must separately define the
cost effectiveness of infiltration removal and inflow
removal.
Where corrosion is present, the extent of corrosion
mitigation expected due to I/I rehabilitation should be
noted. Specific corrosion potential shou Id also be defined
and recommendations made to reduce this potential to
acceptable levels. The procedure for conducting a
corrosion survey as a part of an SSES is presented in
Chapter 5.
The following tasks are usually included in the SSES:1"3
• Survey Planning and Cost Estimating
• Physical Survey
• Rainfall Simulation
• Preparatory Cleaning
• Internal Inspection
• Preparation of Survey Report and Cost Effective
Analysis
Table 4-1.
Method
Sewer System Testing and Inspection Methods
Application
Smoke testing
Rainfall simulation (dye
flooding and tracing)
Building plumbing
inspection
Manhole inspection
Flow isolation
TV inspection
Lateral testing
Most common routine source detection
method to identify inflow and Rll sources.
Source detection after previous lining or
replacement.
Used after smoke testing to confirm
suspected storm drainage connections,
' and other inflow and Rll connections.
As needed after smoke testing to confirm
suspected inflow sources, such as roof
leaders and foundation drains.
Primary source detection to evaluate I/I
sources and structural condition.
Inspection performed along with other
investigation procedures.
Follow-up source detection after sealing;
used to verify migration, identify I/I.
Used where flow monitoring indicates
high infiltration in large areas.
Used where smoke testing indicates
potentially major infiltration sources.
Primary internal inspection technique for
SSES, degree of inspection areas for
pipes as determined by I/I analysis.
Routine inspection for pipes rehabilitated
by sealing if interim detection does not
reveal I/I sources
Used after grouting and sealing techniques.
Used to verify smoke testing, flow
isolation or when temporary flow
monitoring indicates excessive I/I.
Used where smoke testing
indicates major defects
Used where building inspection indicates
major defects.
39
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Table 4-1 describes the most commonly used sewer
system testing and inspection methods.
4.2 Planning the Survey and Use of Sub-
System Approach
The SSES must be planned and executed to produce
accurate estimates of flow reduction and estimated
costs. An overall block diagram for the conduct of a
preliminary sewer system evaluation plan was presented
in Figure 3-1. Figure 3-2 presented the sequence of steps
for conducting an I/I analysis. Figure 4-1 presents a
diagram of the methodology to be followed in the conduct
of an SSES. The following sections of this chapter
presents the detailed procedure for an SSES.
The physical survey is performed to isolate the problem
areas and to determine the general physical conditions of
the sewer sections selected for future study. Rainfall
simulation is conducted to locate the rainfall-associated
I/I sources in the sewer lines.
Preparatory cleaning of the sewers is necessary prior to
internal inspection. Internal inspection locates the I/I
sources, the flow rate from each source and the structural
defects in the pipe. Finally, the survey report summarizes
the results obtained during the survey and presents a
cost-effectiveness analysis of the I/I sources which can
be economically corrected.
4.3 Physical Survey
The physical survey of the sewer collection system is
performed to isolate the obvious problem areas, to
determine the general condition of the sewer sections
selected forfurther study. The following tasks are normally
included in the physical survey:2'3
4.3.1 Aboveground Inspection
This should include the investigation of the general
conditions of the study area such as topography, streets,
alleys, access to manholes, etc. Potential problem areas,
such as waterways, river crossings, natural ponding
areas, should also be located. Key manholes are identified
for additional flow measurements and groundwater
monitoring. Manholeaccessproblems.suchaseasement,
access, buried structures, traffic interferences, should
be noted. The accuracy and completeness of sanitary
sewer maps should be verified. The proximity of storm
and sanitary sewers, inflow sources, such as roof
downspouts, yard and area drains, creeks, low or
inundated manhole covers and frames, and foundation
drains, etc. are all indications that rainfall simulation tests
in the form of smoke testing and/or dyed water testing
should be planned. A program for uncovering manholes,
improving and raising frames to above grade should be
planned.
4.3.2 Flow Monitoring
This should include determining and isolating areas
where I/I exists. During the I/I analysis, flow monitoring
work would have already been performed in a few
selected manholes. The additional flow monitoring work
performed during the physical survey is actually a
continued effort to further reduce the number of areas to
be investigated. Flow monitoring should be conducted
during the highest groundwater conditions to identify
maximum infiltration flow. Monitoring for inflow should be
conducted during storm events under wet weather
conditions. Dry weather and wet weatherflows should be
monitored for comparison. To minimize the effects of
normal wastewater flows, the flow monitoring should be
conducted during the early morning hours. Sub-system
and plant flow monitoring should be conducted on a 24-
hr/d basis.
4.3.3 Flow Measurement
Flow in sanitary sewer systems consists of base flows,
infiltration and inflow. Separation and quantification of
these components is the prime objective of flow
monitoring. Flow measurement in sewer systems is
undertakentodefinevariationsof certain flow components
with time or to define peak and/or minimum flow
conditions. Sewers should be cleaned thoroughly before
velocity measurements are undertaken.
Many techniques are used for the measurement of flows
in sanitary sewers. The equipment and techniques
selected will depend upon the resources available, the
degree of precision required, and the physical conditions
within the sewers.
a. Manual Methods
This is the most widely used technique for measurement
of instantaneous or short term flow. Generally, the
equipment is portable and flows can be determined
immediately using published curves, nomographs or
tables.
Weirs
The weir is a common device for measu ring low wastewater
flows because of its ease of installation and low cost.
Flow measurements through weirs are obtained by
recording the head (water level) above the weircrest and
determining flow rates by calculations, nomographs or
tables. Advantages and disadvantages of weirs are:
Advantages
• Low costs
Disadvantages
• Fairly high head loss
40
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FlflUM 4-1.
Sower system evaluation flow diagram.
Assemble SSES Team
Review I/I Report
and Results Study
Develop Specific SSES Study Plan
• Develop Project Study Scope, Budget, and Schedule
• Identify Sub-Basins and Analyze to Minimize Migration Effects
- Develop Physical Survey and Inspection Plan Budget
• Develop Cleaning Plan and Budget
- Develop Physical Survey Plan and Budget
• Select Internal Inspection Methodology
• Identify Need for Rainfall Simulation and Additional Flow Monitoring
Conduct Physical Survey
- Conduct Aboveground Inspections
- Verify Adequacy of I/I Monitoring
- Select Flow Monitoring Equipment
- Conduct Manhole Inspect'ons
- Conduct Rainfall Simulation, If Required
- Conduct Row Monitoring Studies
Conduct Sewer
Cleaning Program
Conduct Internal Inspection
- TV Inspection
- Photographic Inspection
- Physical Inspection (Large Sewer)
Conduct Cost-Effectiveness Analysis of I/I
by Sub-Systems and for Total Study Area
- Develop Costs for Infiltration as a Function of Infiltration Removed
- Array Costs and Develop Cumulative Cost vs. Infiltration Removed Curve
- Develop Cost for Transportation and Treatment
• Develop Total Cumulative Rehabilitation, Transport, and Treatment Costs and Choose Optimum Point
- Develop Costs for Inflow as a Function of Inflow Removed
- Array Costs and Develop Cumulative Cost vs. Inflow Removed Curve
- Develop Cost for Transport and Treatment
- Develop Total Cumulative Rehabilitation Plus Transport and Treatment Cost and Choose Optimum Point
Summarize All Recommended
Rehabilitation Activities
41
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Easy to install
Easy to obtain flow by
standard equations,
nomographs, etc.
Direct flow reading
Many designs available
for flexibility
Generally accurate
Must be periodically
cleaned; must be suitable
for channels carrying
excessive solids
Accuracy affected by
excessive flows and
debris
May be difficult to make
accurate manual
measurements in
sewers because of
limited access
Cannot be used in
sewers flowing full
Additional information on the measurements of flow
through weirs is provided in the report Existing Sewer
System Evaluation and Rehabilitation.3
Flurries
Flumes operate on the Venturi principal. In flumes, the
constriction of the throat causes the flow to have a critical
depth. This is followed by a hydraulic jump if the slope
allows subcritical (low velocity) flow. There are several
types of open channel flumes, including the Parshall,
Palmer-Bowles, H-FlumeandTrapezoidalconfigu rations.
Flumes are capable of providing results accurate to
within 3-5 percent. Advantages and disadvantages of
flow measurements by flumes are as follows:
Disadvantages
• High cost
• May be difficult to install
Advantages
• Self-cleaning to a
certain degree
• Relatively low head loss
• Accuracy less affected by
approach velocity than it
is with weirs
• Data easily converted to
flow using tables or
nomographs
Manual Depth Measurement
An instantaneous flow measurement in sewers can be
obtained by the following formula: Q=AV, where Q is the
volumetric flow rate, V is the mean velocity of flow, and
A is the cross-sectional area of the pipe. The mean
velocity of flow must be measured or obtained theoretically
through the Kutter's formula:
V=1.486R2/3S1/2/N
Where,
N = Mannings Coefficient
R = Hydraulic Radius, ft
S = Slope, ft/ft
Staff gauges marked to the nearest 3 mm (1/8-in) are
used to measure depth. In manholes that are relatively
clean and accessible, the staff gauge may be inserted
into the invert of the manhole channel and the depth of
flow measured. The depth of sediment in the pipe should
be noted and the depth of flow corrected accordingly.
Advantages and disadvantages of this technique are as
follows:
Advantages Disadvantages
• Inexpensive • Instantaneous result
that may not be
representative
• Determination of mean
velocity is critical
• Cannot be used in
surcharged sewers
• Low degree of accuracy
Timed Volume
This method is used to determine flow rates from leaking
manhole walls, wetwell walls and accessible point sources
of inflow. The method involves the use of a vessel of
known volu me; the time to fill this vessel is measured with
a stop watch or a watch. Equipment required for flow
measurement by thistechnique includes plasticcontainers
or 208-L (55-gal) drums, depending on the amount of
flow. A stop watch or a watch with a sweep second hand
is suitable for measuring time. Advantages and
disadvantages to this method are:
Rapid results
Ease of operation
Advantages
• Accurate
Inexpensive
No specific expertise
required
Disadvantages
• Generally cannot be used
for flow in any but the
smallest sewer pipes
• Not adequate for high
velocity flows
Dye-Dilution Method
This technique is a simple, potentially accurate, and
quick method for the determination of flows in sanitary
sewers. The method is based on measuring the
concentration of dye in a waste stream into which has
been added aknown concentration of dye, then calculating
the flow. Flows can be measured under partial or full flow
conditions without entering manholes. This method is
employed to obtain instantaneous flow rates but with
added equipment it can be used to monitor flow on a
continuous basis. Advantages and disadvantages to this
method are:
42
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Advantages
• No entering of manholes
Saves time and provides
instantaneous flow data
on many sewer sections
Independent of sewer
sfte.dimensions, velocity
and surcharging
Disadvantages
• Samples must be
analyzed as soon as
possible (most dyes
decay in sunlight).
• Temperature correction
may be required
• Instrumentation is
expensive
• Dye is expensive
• Need at least 100
sewer diameters for dye
mixing before sampling.
Three watersolublefluorescenttracerdyes are extensively
used: Rhodamine B, Rhodamine WT, and Fluorescein.
For accurate flow measurements in sewers, a dye which
has a low sorptive tendency with the solids in the
wastewater should always be used. The fluorescence of
the Rhodamine dyes is not suitable outside of the pH of
5-10. Since the fluorescence of the dye is also affected
by temperature, a correction factor should be applied to
the measured concentrations if the temperature of the
sample is different than the room temperature.
Commercial solution feeders are available forfeeding the
dye at a constant rate to the manhole. Collection of the
samples at the downstream manholes can be achieved
by lowering a container with a rope attached to the
sampler. To minimize the loss of dye due to absorption,
the sample container should be made of high quality
glass or other similar material. The samples should be
allowed to stand to reach room temperature and to settle
the suspended solids before measurements are taken
b. Automatic Flow Measurement
Automatic flowmeters can continuously monitor flows
with a minimum of labor. Data collected can be displayed,
recorded on charts, sorted on magnetic tapes or solid
stale memory, or even transmitted from the field to the
office by telephone or radio. These meters save
considerable time and effort compared to manually
recorded flow data, but proper installation, calibration,
and maintenance require individuals with a basic
knowledge of hydraulics and proper maintenance
procedures for the meter in use. Following are the
capabilities of various automatic meters:
Depth Measurement
Depth recorders are used to measure liquid levels in a
pipe, head over a weir, depth in a flume, or other
applications. Commonly used equipment for recording
liquid depths includes probes, bubbler, pressu re sensors,
floats, ultrasonic devices and capacitance/electronic
probes.
Velocity Measurements
Automatic flow monitors that use velocity measurements
can provide accurate data even under highly fluctuating
liquid levels. Velocity may be automatically recorded
using ultrasonic doppler methods, magnetic methods,
mechanical current meters, or other methods. In most
cases the depth of flow is recorded along with the velocity
in order to utilize the flow equation Q = AV.
Electromagnetic/Doppler meters
Velocity measurements by these methods are usually
taken by connecting the probe to the outside of the pipe
to be monitored. This is generally used for pipes flowing
full and having sufficient suspended solids to be
transmitted back to the receiver. The advantage to this
type of flow measurement is the ability to record flows in
closed pipes without obstructing the fluid flows.
Orifice/Nozzle/and Venturi meters
These types of flow meters are used for measuring flows
in completely full pipes. The basic concept is to form a
constriction in the flow so that the velocity increases and
the pressure decreases. The constriction provides an
opportunity for solids to accumulate,,
4.3.4 Manhole and Sewer Inspection
This task is required to determine the actual condition of
the sewer system. Inspection should include descending
and examining conditions of manholes and lamping of
sewer lines to ascertain sub-system I/I conditions. Each
manhole should be numbered and its physical condition
noted in log sheets and standardized field forms. Safety
precautions should be taken at all times before entering
the manholes and proper NIOSH-OSHA procedures and
references should be consulted. Sewer inspection should
be carried out and identified on the manholes numbered.
An inventory of the length, size, type, depth and the
general conditions of the sewer pipes provides a basis for
the estimation of the amount of work required for the
preparatory cleaning and internal inspection. Depth of
flow in sewers provides a rough indication'of the capacity
of the sewer pipe and whether or not I/I is present in the
sewer section. Temperature can also be used as an
indicator for the detection of extraneous water entering
the sewer section being investigated since temperature
nearthe point of entry for extraneous waters will be lower
than the average temperature in the sewer lines, if the
extraneous source represents a significant portion of the
total flow. AH the observations made during the manhole
and sewer pipe inspection should be recorded in field log
sheets and correlated with the sewer maps. Figure 4-2
indicates the typical defects found during manhole
43
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Figure 4-2.
Typical manhole defects.
Broken/Cracked Cover
Broken/Cracked Frame
Deteriorated Frame Seal
Deteriorated Frame Adjustment
Defective Cone (Corbel)
Defective Wall
Steps
Deteriorated Trough (Invert)
Deteriorated Pipe Seal
Deteriorated Bench
44
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Quick mathod of Inspecting sawar HIM*.
Magnified Night Scope
Adjustable Polished
Stool Mirror
Remote Halogen Light
45
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inspection and Figure 4-3 indicates a quick method of
inspecting sewer lines without entering the manholes.
4.3.5 Rainfall Simulation
This task involves the identification of the sections of
sewers that exhibit I/I conditions during rainfall events.
Rainfall simulation does not have to be performed in
every SSES. A careful study of the sewer maps and
review of the I/I analysis report, smoke test results and
the physical survey results indicate whether rainfall
simulation is required.
4.3.6 Smoke Testing
This is an inexpensive and quick method of detecting
inflow sources in sewer systems. Many inflow sources
such as roof leaders, cellar, yard, and area drains;
foundation drains; abandoned building sewers; faulty
connections; illegal connections; sewer cross
connections, structural damages and leaking joints can
be identified by smoke testing under ideal conditions.
Key steps for smoke testing are:
• Conduct smoke tests in selected sanitary lines
(adequate notification r^st be made before smoke
testing is done. This requires notification to residents,
the local fire department, public meetings, etc.)
• Record, both in written and photographic form, all
sources from which smoke emissions are noted.
• Visually inspect manholes suspected of having direct
inflow connections into sanitary sewers.
• Identify direct inflow connections to sanitary sewers.
• Identify interconnections between sanitary and storm
systems as evidenced by smoke emissions during the
smoke test.
Smoke testing should not be conducted on sewer lines
which contain sags, or are flowing full. Smoke testing
cannot detect structural damage, or leaking joints in
buried sewers and service connections when the soils
surrounding and above the pipes are saturated, frozen or
snow covered. Smoke testing should not be performed
on windy days when the smoke coming out of the ground
may be blown away so quickly as to escape visual
detection. The following equipment is usually required to
conduct smoke testing:
• Smoke bombs
• Air blowers
• Camera and film
• Sand bags and/or plugs
• Two-way radios
The smoke bombs used should be non-toxic, odorless
and non-staining. An air blower is used to force the
smoke into the sewer pipes. The camera is used to take
pictures of the smoke coming out of the ground, catch
basins, pipes and other sources during the test. Sand
bags and/or plugs are used to block the sewer sections
to prevent the smoke from escaping through the manholes
and adjacent sewer pipes. It is important to coordinate
with the fire department to prevent false alarm if for some
reason the smoke would enter a house and would trigger
a false alarm.
4.3.7 Dyed Water Testing
Dyed-water testing is used primarily to detect infiltration
and Rll sources in storm sewer sections, stream sections,
and ditch sections. It can also be used to verify the results
of smoke testing. This method of testing is more expensive
and time consuming than smoke testing and requires
large quantities of water.
Fluorescent dyes are used for this testing technique. The
dyes should be safe to handle, biodegradable and inert
to the soil and debris in sewers. Further information on
the common types of dyes can be obtained from Reference
5.
The procedure for dyed water testing includes:
• Plug and flood with dyed water any storm sewer
sections which are parallel to or cross sanitary sewers
and house service lines which have shown evidence of
smoke when nearby sections have been smoketested.
• Where applicable, flood catch basins, ditches and
ponding areas in close proximity to sanitary sewers
with dyed water.
• The presence of dye or absence in adjacent downstream
manhole indicates the infiltration potential.
• The response time of the appearance of the dye and in
some cases the visual increase in flow provides
additional insight into the infiltration or Rll pathway.
• Analyze findings and recommend appropriate sewer
sections for cleaning and internal inspection.
4.3.8 Water Flooding Test
This test is similar to dyed water testing, except that no
dyes are used. With accurate flow measurement, pipe
imperfections can be detected with this technique. The
water flooding tests can be conducted by the following
methods:
• Sprinkler test - Inflow and/or Rll under unpaved areas,
particularly in service connections during wet weather
conditions, can be determined by the sprinkler test.
Irrigation sprinkler pipes with spray nozzles are used to
simulate rainfall conditions, and the rate of application
of the waterandthetotalwaterdistributed are monitored.
• Exfiltration test - The exfiftration test is used to check
the sewer lines and manholes for possible leakage.
46
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The procedures involved in the exfiltration test are
covered in Chapter 3.
4.4 Cleaning
Internal inspection of lines suspected of having I/I sources
and any flow velocity measurement requires clean pipes.
Debris in sewer inverts, grease accumulation and heavy
root infestations notonly obstruct visual orvideo inspection
but they also may hide or mask actual infiltration sources.
Preparatory cleaning is an essential first step in any
meaningful internal examination procedure. Thecleaning
procedure should clean the sludge, mud, sand, gravel,
rocks, bricks, grease and roots from the sewer pipes,
manholes and pumping station wet wells to be inspected.
The pipe walls should be clean .enough for the camera
used in the inspection to discover structural defects,
misalignment and I/I sources. The .following steps are
required for cleaning:
• Clean all sewer lines by appropriate means and with
proper equipment immediately prior to internal
inspection or velocity measurement.
• Determine, if possible, allobstructionsorotherphysical
alignment, joint or connection conditions which could
interfere with or prevent the insertion and movement of
inspection equipment.
The equipment required for cleaning includes:2'3
• Rodding machines, bucket machines, high-velocity
water machines and other hydraulically propelled
devices
• Debris removal equipment, such as vacuum machines
and trash pumps
• Debris transport vehicles
• A proper debris disposal site
Forpropercleaning, factorsto be considered are: access
and condition of manholes, depth of sewer, size of pipe,
depth and type of solid materials to be removed, degree
of root intrusion, amount of flow, structural integrity of
pipe, availability of hydrant water and the degree of
cleanliness required. Figure 4-4 indicates some
techniques involved in preparatory cleaning. Direct
observation and camera are the usual forms of internal
inspection equipment used for sewer lines. Direct
observation is used for large lines that can be walked or
crawled, while cameras are used on small-diameter
sewers.
4.5 internal Inspection
Internal inspection involves the following tasks:3-4
• Set up TV camera or other equipment in the sewer lines
under investigation.
• Plug and flood all storm sewers in close proximity to
sanitary sewers under inspection, if recommended by
rainfall simulation findings.
• Internally inspect, designate footage, and note all
structural defects and all leaks in terms of location and
flow rates.
• If services are found to be running, verify whether the
flow is caused by infiltration or actual water usage.
• Record findings on log sheets and support with video
tapes.
Internal inspections can be accomplished in the following
ways:3-4
4.5.1 TV Inspection
The TV inspection technique utilizes a closed-circuit TV
camera to observe the conditions in the sewer lines. The
TV cameras used are specially designed to detect the
sewer conditions.
The camera is mounted in a casing and is pulled through
the sewer with cables. Recently self propelled cameras
have been used, but the disadvantage of this type of
camera is required service and recovery if they fail or get
stuck in the middle of the pipe run. The results are shown
on the TV monitor and documentation can be made by a
videotape or by photographs of the monitor. A light
source isprovidedby the camera for illumination purposes.
4.5.2 Photographic Inspection
This technique utilizes a camera to take a series of color
photographs along the inside of sewer lines. This
technique is best for analyzing the structural conditions
of the sewers. A camera is pulled through the sewer line
being inspected. Pictures are taken at equidistant intervals
or at some predetermined problem sections.
4.5.3 Physical Inspection
This technique involves the direct inspection of larger
sewers not in service. Before inspectiion, the safety of the
person entering the line should be carefully considered
and the sewer section thoroughly ventilated to remove
H2S and other harmful gases that might be present.
Proper NIOSH-OSHA safety practices and procedures
should be followed to properly carry out physical
inspections.
Figure 4-5 shows the technique involved in TV inspection.
4.6 Cost Effectiveness Analysis
47
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Figure 4-4.
Preparatory cleaning.
48
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Figure 4-5. Internal color TV Inspection.
49
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Based on the results and findings of the SSES, a detailed
evaluation and analysis should be carried out to determine
the most cost-effective means of correcting or alleviating
excessive I/I conditions found in the system.
Cost-effectiveness analysis for SSES is similar to the
cost-effectiveness analyses for I/I. However, the SSES
cost-effectiveness analysis provides a detailed and
thorough analysis of the sewer system including the flow
rates from each source, and the best method for
rehabilitation of each source. For an effective cost
analysis, the cost of correction for infiltration, inflow, Rll
and groundwater migration must be considered. Existing
SSES methodologies rely on individual line segment
nighttime isolation and measurements to identify
excessive infiltration.
Subarea SSES analysis including migration effects is an
Improved approach to the traditional point source
approach for evaluating sewer systems. (See Section
4.7 for a description of the subarea approach to
rehabilitation). Row adjustments for infiltration should be
carried out before the cost-effectiveness analysis is
conducted.2
Costs for the evaluation survey should be based on the
total actual expenditure for the survey. Costs for
rehabilitation should be based on the actual physical
conditions discovered. The costs for transportation and
treatment of wastewater shouId then be developed for at
least four typical flow conditions so that a cost curve can
be drawn to indicate the general cost pattern.3
Acost summary similarto that shown in Table 4-2 can be
prepared to summarize the overall cost of a sewer
system evaluation and rehabilitation program. The
presentation of the costs for Infiltration and Inflow must
beseparatelydevetoped.Thegeneralproceduresoutlined
below should be followed to develop both Infiltration and
Inflow costs in a format forthe cost effectiveness analysis
curve preparation:
• Determine the total correction cost for each Infiltration
and Inflow source and calculate the cost required for
eliminating each unit of flow.
• Arrange the costs in a descending order with lower
costs ahead of the higher costs.
• Arrange the costs in groups and determine the total
correction cost for each group. Add costs for engineering
services, administrative costs, contingency costs,
interest during construction, etc. to derive the total
required cost to eliminate the I/I from all sources within
each group.
• Calculate the total accumulative cost (Curve B of
Rgures 4-6 and 4-7) against the total accumulative
infiltration and inflow separately to be reduced and
draw a curve passing through all data points. Plot a
curve showing the relationship between the cost of
transportation and treatment and the total infiltration
and inflow (separate) to be reduced (Curve A). Derive
a composite cost curve (Curve C) by adding the costs
of each of the two derived curves' (curves A and B). •
Locatethe minimumcost point on the composite curve,
and draw a straight line passing this point and parallel
to the cost axis. The line intercepts the cost curve for
infiltration and rehabilitation (Figure 4-6) and inflow
rehabilitation (Figure 4-7) at a point which represents
the optimal point for sewer rehabilitation. The flow
figure corresponding to these points on each curve
represents the infiltration or inflow which can be cost-
effectively removed from the sewer system, and the
cost figure corresponding to this represents the total
cost which will be needed for the corrective actions.
4.7 Case Study Example and Detailed
Method of Analysis
This section outlines a detailed method of analysis for
SSES taking into account migration and rainfall-induced-
infiltration. This detailed analysis was performed by the
WSSC to develop a new approach to sewer system
evaluation and rehabilitation known as the System
Approach to evaluate Subarea Rehabilitation (SASR).4
The subarea approach represents a large area (6,000-
30,000 lineal m [20,000-100,000 lineal ft] of sewer)
undergoing a sewer system evaluation survey as opposed
to the traditional method of evaluating smaller segments
and single sources. Field activities incorporated in this
study included the following:
Rainfall Monitoring - Monitoring was conducted by four
continuous recording gauges to measure precipitation to
1/100th of an inch versus time, to allow for correlation of
inflow to rainfall intensity.
Continuous Flow Monitoring - This was performed at
each subarea outlet utilizing flow meters to record depth
and velocity.
Internal Night-Time Flow Measurements - Flow
measurements conducted within each subarea to identify
mini-systems subject to infiltration.
Manhole and Visual Pipe Inspections - Inspection for
each manhole began at the surface by identifying potential
for ponding and concluded with evaluation of the condition
of the bench and trough, and lamping of connecting
pipes.
50
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Table 4-2. Cost Summary for SSES and Sewer Rehabilitation1
Est. Quantity Estimated Cost
Description Quantity Unit $/Unit Total
SEWER SYSTEM EVALUATION SURVEY
1. PHYSICAL SURVEY
Above Ground Inspection manhour
Flow Monitoring manhour
Manhole and sewer inspection ft(m)
Subtotal
2. RAINFALL SIMULATION
Smoke Testing ft (m)
Dyed Water Testing ft(m)
Water Flooding Tests ft (m)
Subtotal
3. PHYSICAL SURVEY REPORT manhour
4. PREPARATORY CLEANING . ft(m)
5. INTERNAL INSPECTION ft(m)
6. ENGINEERING manhour
7. OTHERS
TOTAL SSES COSTS
SEWER SYSTEM REHABILITATION
• CORRECTION FOR INFILTRATION
1. SEWER EXCAVATE AND REPLACE ft(m)
2. CHEMICAL GROUTING ft (m) Lump
3. SLIPLINING OR INSERTION ft(m)
4. CURED-IN-PLACE INVERSION LINING ft(m)
5. SPECIALTY CONCRETE ft (m) or Lump
6. LINERS ft (m) or Lump
7. COATINGS ft (m) or Lump
8. MANHOLE WET WELL REPLACEMENT Lump
9. MANHOLE WET WELL REPAIR Lump
10. FAULTY TAPS REPAIR Lump
11. HOUSE SERVICE PIPE REPLACEMENT ft (m) or Lump
12. HOUSE SERVICE PIPE REPAIR ft (m) or Lump
• CORRECTION FOR INFLOW
1. LOW LYING MANHOLE RAISING Lump
2. MANHOLE COVER REPLACEMENT Lump
3. CROSS CONNECTION PLUGGING Lump
4. ROOF LEADER DRAIN DISCONNECTION Lump
5. FOUNDATION DRAIN DISCONNECTION Lump
6. CELLAR DRAIN DISCONNECTION Lump
7. YARD DRAIN DISCONNECTION Lump
8. AREA DRAIN DISCONNECTION Lump
9. COOLING WATER DISCHARGE
DISCONNECTION Lump
10. DRAINS FROM SPRINGS AND SWAMPY
AREAS TO BE PLUGGED Lump
BOTHERS
1. ENGINEERING SERVICES Lump or Manhours
2. LEGAL AND ADMINISTRATIVE SERVICES Lump
3. CONTINGENCY Percent
4. INTEREST DURING CONSTRUCTION Percent
5. SALVAGE VALUE Lump
TOTAL REHABILITATION COST
51
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Figure 4-C.
Cost-effectiveness analysis curve for Inflltralon.
i Composite Cost Curve
Infiltration Reduction
(Curve C)
Cost Curve for Transportation
and Treatment of Infiltration
(Curve A)
Optimal Cost/Bnefit Level for
Infiltration Sewer Rehabilitation
(Curve C)
Cost Curve for
Infiltration Rehabilitation
(Curve B)
Infiltration Reduced, gpd
52
-------
Rgura 4-7.
Cost-«H»ctIven«ss analysis curve for Inflow.
Composite Cost Curve
Inflow Reduction
(Curve C)
Cost Curve for Transportation
and Treatment of Inflow
(Curve A)
UJ
S
Optimal Cost/Bnefit Level for
Inflow Sewer Rehabilitation
(Curve C)
Cost Curve for
Inflow Rehabilitation
(Curve B)
Inflow Reduced, gpd
53
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Smoke Testing - Performed with an intensive technique
requiring isolation of each segment by blocking flow and
injecting smoke using blowers, one on each of two
adjacent manholes.
Dyed Water Flooding - Inflow sources identified during
smoke testing were quantified by the dyed water flooding
technique.
TV Inspection - As a result of nighttime flow
measurements, certain sewers were identified for TV
inspection.
Building Inspections - This consisted primarily of
determining inflow connections to the service laterals,
such as storm and combination sump pumps, and external
drains such as areaway and roof drains.
The total of the assigned flows from all of the identified
inflow sources was then compared to and balanced with
the measured flow of each subarea at a 1 -yr storm event.
Inflow at a 1 year storm event was determined by linear
regression of moderate storms, when the system was
not in a' hydraulscally restricted or surcharged state.
Infiltration sources were quantified and monitored at the
outlet flow meters. Quantification of inflow and infiltration
obtained during the subarea evaluation is presented in
Table 4-3.
A cost-effectiveness analysis'for the WSSC example
was performed on a subarea basis incorporating the
effects of migration, capital cost of treatment, O&M cost
fortreatment, cost of relief lines, and cost of rehabilitation.
As a result of the analysis, clustered rehabilitation was
recommended by subarea. This type of rehabilitation
minimizes the migration effect. Also, the effectiveness of
rehabilitation can be measured more rapidly because
flow reduction is concentrated instead of dispersed over
a wide area. I/I rehabilitation was then recommended for
the entire subarea
A summary of the cost effective analysis for the subarea
is presented in Table 4-4. Anticipated flow reductions
after implementation of the recommended rehabilitation
provides the estimated unit construction cost ($/gpd).
Finally, a comparison of point-source rehabilitation with
the sub-system approach was performed for each method
and is presented in Table 4-5.
The point-source analysis initially resulted in a unit
rehabilitation cost of $0.25/L/cl ($0.95/gpd), but by
incorporating the effect of migration, less infiltration
would actually be removed, thus resulting in an actual
54
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Table 4-3. Quantificationof 1/IThroughtheSubareaSystem
Approach for the Washington Suburban
Sanitary Commission4 (Reprinted with
Permission from Water Engineering and
Management
Table 4-4. Cost-Effective Analysis for I/I Reduction for the
Washington Suburban Sanitary Commission4
(Reprinted with Permission from Water
Engineering and Management}
Source
INFLOW
Public Sector Inflow
Manhole Defects
Cover/rim leaks, ponding(1)
Frame seals
Corbels and broken frames
Cross connections
Subtotal
Private Sector Inflow
Downspouts
Area-wide drains
Foundation drain connection
Flow {mgd) Percent of Total
(
0.020 0.8
0.261 10.1
0.078 3.0
0.026 1.0
0.385 14.9
0.288 11.2
0.539 20.9
0.011 0.4
Suspect foundation drain connection 0.773 30.0
Defective lateral dean outs
Suspect defective service laterals
Storm sump pump connection
Subtotal
Total
0.009 0.3
0.364 14.0
0.212 fiJ2
2.196 85.1
2.581 100.0
SUMMARY OF RECOMMENDED PLAN
INFILTRATION
Manhole Defects
Cracked/defective walls
Defective pipe seals
Bench/trough leaks
Pipe Defects
Groutable defective joints/pipes
Non-groutable defective pipes
and groutable service connection
Infiltration in line segments and
manholes not inspected
Total
0.039
0.024
0.004
0.387
0.34
0.137
0.932
4.2
2.6
0.4
41.5
36.6
JfLZ
100.0
Estimated
Rehabilitation Item Quantity
Inflow
Manhole cover/frame replacement
Manhole frame seals/raising
Manholes corbel
Cross-connection
Subtotal
Infiltration
Manhole walls, pipe seals, bench/trough
Relining/replacement
Line grouting
Pipe replacement
Connection grouting, lateral repair
Subtotal
38
121
16
1
22
20
27
7
25
Estimated
Construction
Cost, $(1986)
17.710
96,800
9,900
4.000
127.800
14,996
386.015
20,082
35.000
45.000
501.091
Total
ESTIMATED FLOW REDUCTION
Source Type
Estimated
Flow Reduction,
mgd (1986)
628,891
Estimated
Construction Cost,
$/gpd (1986)
Inflow
Infiltration
0.385
0.297
$0.33
$1.69
Table 4-5. Cost-Effective Analysis by Point Source for I/I
Reduction for the Washington Suburban
Sanitary Commission4 (Reprinted with
Permission from Water Engineering and
Management)
Approach
Removable
Infiltration, mgd
Rehabilitation Costs
Total $ $/gpd
Point Source Approach
Assumed without migration 0.164 $156,000 0.95
Estimated, with migration 0.081 $156,000 1.93
Sub System Approach 0.143 $238,000 1.66
55
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unit rehabilitation cost of $0.51/L/d ($1.93/gpd). I/I cost
effective analysis utilizing the subarea approach,was
found to be $0.44/L/d ($1.66/gpd).4
4.8 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. Handbook for Sewer System Evaluation and
Rehabilitation. EPA/430/9-75-021, Office of Water
Program Operations, U.S. Environmental Protection
Agency, Washington, D.C., 1975.
2. American Public Works Association. Sewer System
Evaluation, Rehabilitation and New Construction: A
Manual of Practice. EPA/600/2-77/017d, NTIS No.
PB-279248. U.S. Environmental Protection Agency,
Municpal Environmental Research Laboratory, Office
of Research and Development, Cincinnati, Ohio,
1977.
3. Existing Sewer System Evaluation and Rehabilitation.
ASCEManualsand Reportson Engineering Practice
62, WPCF Manual of Practice FD-6, American Society
of Civil Engineer, Water Pollution Control Federation,
1983.
4. Fernandez, R.B. Sewer Rehab Using a NewSubarea
Method. Water/Engineering & Management 133-28-
30, February 1986.
5. Odor and Corrosion Control in Sanitary Sewerage
System and Treatment Plants. EPA/625/1-85/018,
U.S. Environmental Protection Agency, Cincinnati,
Ohio, 1985.
6. American Consulting Services, Inc. Sewer System
Evaluation for Infiltration/Inflow. Technology Transfer
Program, U.S. Environmental Protection Agency.
Additional Reading
American Public Works Association. Control of Infiltration
and Inflow into Sewer Systems. 11022 EFF12/70, Water
Quality Office, Environmental ProUjction Agency and
Thirty-nine Local Governmental Jurisdictions, 1970.
American Public Works Association. Excerpts from
Control of Infiltration and Inflow into Sewer Systems and
Prevention and Correction of Excessive Infiltration and
Inflow into Sewer Systems. EPA/S70/9-74-004, Water
Quality Office, Environmental Protection Agency & Thirty-
nine Local Governmental Jurisdictions, 1971.
American Public Works Association. Prevention and
Correction of Excessive Infiltration and Inflow into Sewer
Systems. NTIS No. PB-203208, Manual of Practice,
Water Quality Office, Environmental Protection Agency
& Thirty-nine Local Governmental Jurisdictions, 1971.
Braam, G.A. and R.J. Nogaj. Selection of Optimum
Storm Frequency for Sewer Studies. JWPCF 54:1401-
1407, October 1982.
Carter, W.C., A.J. Hollenbeck, and R.J. Nogaj. Cost
Effectiveness and Sewer Rehabilitation. Public Works
117:64-67, October 1986.
Connelly, Conklin, Phipps & Buzzell, Inc. Evaluation of
Infiltration/Inflow Program Final Report. EPA-68-01 -4913,
Officeof Water Program Operations, U.S. Environmental
Protection Agency, 1980.
Construction Grants 1985. EPA/430/9-84-004, Office of
Water, U.S. Environmental Protection Agency, 1984.
Cronberg,A.T.,J.P.Morriss,andT.Price. Determination
of Pipe Loss Due to Hydrogen Sulfide Attack on Concrete
Pipes.
Darnell, P.E. Conducting Sewer System Evaluations for
Small Systems. Water & Sewage Worksxi23:67\8-71,
November 1976.
Deciding to Rehabilitate, Repair, or Replace. Water/
Engineering & Management 132:50-53, May 1985.
Driver, F.T. Manhole I/I Stopped with Special Repairs.
Water/Engineering & Management 130-31 -32, April 1983.
Edward H. Richardson Associates, Inc. Evaluation of
Trenchless Sewer Construction at South Bethany Beach,
Delaware. EPA/600/2-78/022, NTIS No. PB-278776.
U.S. Environmental Protection Agency, Municipal
56
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Environmental Research Laboratory, Off ice of Research
and Development, Cincinnati, Ohio, 1978.
Evaluating Utility System Conditions. Water/Engineering
& Management 132:43-49, May 1985.
Gray, W.R. and R.J. Nogaj. Sanitary Sewer Bypass
Reduction Program. Water/Engineering & Management
137:36-40, May 1990.,
Gutierrez, A.F. and J.H. Rowell. Five Years of Sewer
System Evaluation. Journal of the Environmental
Engineering Division, December 1979.
Heinecke, T.L. and C.H. Steketee. The Key to Effective
I/I Control. Public Works 115:88-92,106-107, June 1984.
Hersch, P. Philadelphia Formulates a Comprehensive
Main Rehab Program. Water/Engineering & Management
132:61-66, May 1985.
Hollenbeck, A.J. Designing for Removal of Sanitary
Sewer Cross Connections. Water/Engineering &
Management 131:29-31, April 1984.
Hollenbeck, A.J. and M.J. Jankovfc. Smoke Testing: It's
Not Always as Easy as It Seems. American City and
County Magazine, February 1982.
Hollenbeck, A.J. and G.D. Lambert. New Approach
Achieves Inflow Reduction in Sanitary Sewers. Public
Works 118(9):119-121, September 1987.
Hollenbeck, A.J. and R.J. Nogaj. Inflow Distribution in
Wastewater Collection Systems. Water/Engineering &
Management 129:30-33, January 1983.
Hollenbeck, A.J. and R.J. Nogaj. One Technique for
Estimating Inflow with Surcharge Conditions. JWPCF
53:491-496, April 1981.
Infiltration Inflow Collection System Management:
Challenge of the 80's. I/I Evaluation and Control Division,
Department of Maintenance and Operations, Washington
Suburban Sanitary Commission, Hyattsville, MD, 1982.
Infrastructure in the Commonwealth. Department of Local
Government, Frankfort, KY, 1989.
J.M. Smith & Assoc. Analysis of Acceptable Ranges for
Infiltration and Inflow Reduction in Sewer System
Rehabilitation Projects. Study conducted under contract
EPA 68-01-6737, Performance Assurance 'Branch,
Municipal Facilities Division, Off ice of Municipal Pollution
Control, U.S. Environmental Protection Agency,
Washington, D.C.
Johnson, W.D., S.R. Maney, and G. McCluskey. Open
Cut Sewer Construction Across Railroad Tracks Saves
Money. Public Works 120:73, June 1989.
Lipman, S.G. Metropolitan District Commission, I/I
Experience. Presented at Technology Transfer Seminar
on New Concepts in I/I Evaluation and Sewer System
Rehabilitation, U.S. Environmental Protection Agency,
Cincinnati, Ohio, March 1984.
Mayer, J.K., F.W. Macdonald and S.E. Steimle. Sewer
Bedding and Infiltration, Gulf Coast Area. 11022 DEI 05/
72, Office of Research and Monitoring, Environmental
Protection Agency, 1972.
Milwaukee Metropolitan Sewerage District Cost-
Effectiveness Analysis.
Montgomery County Sanitary Department. Determination
of Ground Water Infiltration and Internal Sealing of
Sanitary Sewers. Water Quality Office, Environmental
Protection Agency, 1971.
Montgomery County Sanitary Department. Ground Water
Infiltration and Internal Sealing of Sanitary Sewers. Water
Pollution Control Research Series, U.S. Environmental
Protection Agency, 1972.
National Water Well Association, RJN Environmental
Associates, Inc., and Washington Suburban Sanitary
Commission. Impact of Groundwater Migration on
Rehabilitation of Sanitary Sewers, 1984.
Nelson, R.E. New Ways to Fix Leaky Sewers. American
City & County Magazine 95:39,40,42, September 1980.
One Way to Handle Lateral Connections. American City
& County Magazine.
RJN Environmental Associates, Inc. Making Effective
Use of Existing Collection Capacity. Water/Engineering
& Management 132:38-40, September 1985.
RJN Environmental Associates, Inc. National Alternative
Methodology for Sewer System Evaluation. Washington
Suburban Sanitary Commission, 1988.
RoyF. Weston, Inc. Analysis ofNonexcessive Infiltration
Rates, Study conducted under EPA Contract No. 68-01 -
6737, Municipal Construction Division, Office of Water
Program Operations, U.S. Environmental Protection
Agency, Washington, D.C., 1983.
57
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Roy F. Weston, Inc. Determination of Excessive/
Nonexcessive Inflow Rates. Study conducted under
EPA Contract No. 68-01-6737, Municipal Construction
Division, Office of Water Program Operations, U.S.
Environmental Protection Agency, Washington, D.C.,
1984.
Wilson & Company. Implementation of a Comprehensive
Infrastructure Assessment Program, Case Study:
Pittsburgh, Kansas. Department of Public Works, C'rty of
Pittsburgh, Kansas.
58
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CHAPTERS
Corrosion Analysis and Control
5.1 Introduction and Background
Structural problems in wastewater collection systems
can sometimes occur as a result of corrosion, and thus
it is important to consider corrosion when designing,
rehabilitating, or analyzing sewer systems. This chapter
discusses the types of sewer corrosion, explains how a
corrosion survey is conducted, and describes methods
for controlling corrosion. Major emphasis is placed on
hydrogen sulf ide (H2S) corrosion, as it isthe most prevalent
form of corrosion in sewer systems.
Internal corrosion in sewer systems is normally related to
the characteristics of the wastes being transported and
is caused by chemical, electrochemical, and biochemical
reactions. External corrosion is primarily caused by
thermal, physical, structural or electrochemical stresses.
5.2 Types and Mechanisms of Corrosion
5.2.7 Common Types of Pipe Corrosion
Internal pipe corrosion in sewer systems is primarily
caused by two mechanisms: 1) direct attack by corrosive
gases released from the wastewater, such as H2S and
SO2; and 2) bacterial oxidation of H2S to sulfuric acid in
the unsubmerged portions of the pipes. H2S and SO2 in
their gaseous forms are directly corrosive to metals. It is
important to note that the presence of H2S raises concerns
for safety, as H2S gas is toxic to humans. H2S represents
an imminent life threat at a concentration of 300 ppm by
volume in air. OSHA recommends a time weighted
average exposure during an 8-hr period of less than 10
ppm by volume.1
Corrosive wastes (e.g. industrial acidic wastes) discharged
to the sewer can cause direct corrosion in submerged
portions of the sewer. Furthermore, certain chemicals
which are, used in wastewater treatment and collection
systems can be corrosive.
5.2.2 Other Types of Corrosion
Electrochemical corrosion may occur due to electrical
currents created between dissimilar metals or when an
electrolytic waste removes one or more metals from an
alloy.2
Hydrogenation occurs when hydrogen ions react with
metal pipes.Thishoweveroccursunderhightemperature,
pressure, stress and anaerobic conditions, and is not
commonly found in sewer systems.
Fatigue corrosion and stress corrosion are similar, as
both are caused by external stresses applied to the pipe
and occur inside of the pipe. Fatigue corrosion occurs
when pipes are exposed to repeated stresses.
Filiform corrosion occurs on metal piping with organic
coatings. It is characterized by filament-like corrosion in
the metal surface originating at pinpoint penetrations of
the surface. It is important to note that corrosion is often
the result of more than one mechanism. For example, if
iron pipe is already experiencing hydrogen sulfide
corrosion, it becomes more brittle and is more prone to
cracking when stress is applied.
Further information on the mechanisms of both internal
and external corrosion may be found in Reference 2.
5.3 Conducting a Corrosion Survey
5.3.1 Factors Affecting Corrosion
As a part of a Sewer System Evaluation Survey (SSES),
sewer systems should be examined for certain
characteristics that encourage corrosion. Corrosion is
more likely to occur when the dissolved oxygen (DO) is
belowO.Smg/L, since theseconditionsfavorthe anaerobic
bacteria that convert sulfate to sulfide. In gravity sewers,
DO levels are likely to decrease when the wastewater
velocity decreases, because the lower velocity: 1)
decreases the scouring of the microbial slime growing on
the submerged pipe walls and invert; 2) promotes solids
deposition; and 3) increases the residence time. In force
mains, inverted siphons, and surcharged sewers,
anaerobic conditions often exist since the pipe is full,
thereby precluding surface aeration by oxygen addition
from the sewer atmosphere.
59
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The depth of flow in sewers, the amount of exposed
surface area, BOD of the waste, and pipe slope also
affectthe DO. Turbulence (which isfound at pipe junctions
and places where the pipe changes direction or slope)
can add oxygen to the water, preventing sulfide
generation. However, if sulfide is present, turbulence has
an overall negative effect as it allows H2S gas to be
released from the wastewater making h available for
corrosion above the water level.
5.3J2 Identifying Likely Locations for Corrosion
The first step In a corrosion survey is to interview people
involved in design, cleaning, inspection, and repair of the
sewer system to identify locations where corrosion may
have been observed. Collection system maps should be
available that include sizes and type of pipes, slopes of
lines, flows, manhole locations, frequency of pumping
operations, and locations of force main discharges and
surcharged sewers. Maintenance records, odorcomplaint
files, and TV inspection logs can also be informative.
Likely field locations to check include:
Locations of low velocities or solids deposits
Force main discharge points
Transition manholes
Sewage lift stations
Areas of high turbulence
Sewers w'rth flat slopes and long detention times
Inverted siphon discharges
Headworks of wastewater treatment plants
Junction chambers and metering stations
5.3.3 Performing Visual Inspections
Avisual inspection of the condition of manholes, metering
stations, wet wells, headworks, and other structures as
apart of the SSES physical survey, is essential to identify
corrosion problems. Areas that are accessible can be
entered and inspected, However, hazardous atmospheres
can exist in such confined spaces, and proper safety
procedures for confined space entry must be strictly
followed.
Items noted in a visual inspection include:
• Condition of ladder rungs, bolts, conduit, and other
metal components
• Presence of protruding concrete aggregate
• Presence of exposed reinforcing steel
• Development of'black coating (copper sulfate) on
copper pipes and electrical contacts
• Loss of concrete from pipe crown or walls
• Soundness of concrete
• Depth of penetration, using screwdriver or a sharp tool
to expose uncorroded material
A quick method of inspecting the general condition of
sewers can be performed with a telescoping rod onto
which are attached a halogen light and adjustable mirror
at one end, and a low-magnification (e.g., 4x) sight scope
at the other end. The rod is inserted into a manhole, and
by slightly tilting the rod and flashing the light beam down
the sewer, its condition can be obser/ed. This procedure
is useful when small-diameter sewers are involved. Also,
because entry into a confined space is not required, there
is little risk of being overcome by potentially harmful
sewer gas.
5.3.4 Collecting Data
Usefuldatawhichcan be collected to assess the presence
of, or the potential for corrosion include the following:1
• Concentration of gaseous H2S in manholes and sewer
atmospheres
• Wastewater pH
• Total and dissolved sulfide in wastewater
• DO and Oxidation Reduction Potential (ORP)
• Surface pH on manhole and sewer walls
• Total and soluble BOD
• Temperature
• Depth of corrosion penetration
One of the most useful "early warning" indicators of
potential H2S corrosion problems is the pH of the pipe
crown or structure wall. This is a simple test using color
sensitive pH paper which is applied to the moist crown of
the pipe. New concrete pipe has a pH of 10-11. After
aging the pH of the crown under non-corrosive conditions
may drop to near neutral. Pipe experiencing severe H2S
corrosion may have a pH of 2 or lower. pH levels below
4 are generally indicative of corrosion problems.
If it is possible to estimate the amount of concrete lost
from sewers or manholes and their age is known, the rate
of corrosion can be approximated.1 Estimates of the
remaining useful life of a structure (e.g., to exposure of
reinforcing steel) can then be used to prioritize sewer
segments or structures for further action.
5.3.5 Predicting; Sulfide Corrosion
Models have been developed which allow the prediction
of the rate of sulfide accumulation in sewers as well as the
rate of hydrogen sulfide corrosion of concrete pipe. The
predictive equations can be found in References 1 through
4.
5.4 Rehabilitating Corroded Sewers
If it is determined that a sewer is severely corroded and
will require rehabilitation, an appropriate rehabilitation
method must be chosen. Table 5-1 lists common sewer
60
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Table 5-1. Common Sewer Corrosion Problems and
Applicable Rehabilitation Methods
Problem Rehabilitation Method
1. Severe corrosion and poor
structural integrity
2. Severe corrosion; minor
structural reinforcement
needed
3. Corrosion in structurally sound
pipes with diameters 76 cm
(2.5 ft) or greater
4. Corrosion in non-circular pipes
5. Corroded pipes under busy
streets
a. Excavation and replacement
b. Sliplining
c. Some specialty concretes
a. Cured-in-place inversion lining
b. Sliplining
c. Some specialty concretes
d. Fold and formed pipe
a. PVCor other corrosion resistant
liners
b. Sliplining
c. Cured-in-place inversion lining
d. Some specialty concrete
e. Fold and formed pipe
a. Cured-in-place inversion lining
b. Some specialty concretes
a. Cured-in-place inversion lining
b. Fold and formed
c. Sliplining (may be applicable)
problems involving corrosion and provides applicable
rehabilitation methodsforeach. Rehabilitation techniques
are discussed in detail in Chapter 6.
5.5 Controlling Corrosion
5.5.7 Sulfide Corrosion Control
H2S corrosion can be controlled by reducing the levels
of dissolved sulfide in the wastewater. Common control
techniques includeoxygenation, oxidation, precipitation,
and pH elevation.2
If the concentration of DO in the wastewater exceeds
1.0 mg/L, sulfides will not be generated. Therefore,
maintaining a high DO concentration is an effective
method of sulfide corrosion control. Common methods
of H2S control in sewer systems are summarized below.
5.5.1.1 Aeration
Aeration can be a cost effective method for controlling
sulfide generation, but unless air is introduced by passive
means, such as the presence of turbulent conditions in
the system, equipment must be provided to compress
the air and to introduce it into the wastewater. An
advantage of using air injection can be the simplicity of
equipment when compared to other sulfide control
methods.1'3 Often, compressed air is added to the
discharge side ofthewastewater pumps atthe upstream
end of a force main. The major disadvantages of this
approach are: 1) the potential for gas pocket formation
and air binding, and 2) the relatively short duration for
which aerobic conditions can be maintained due to DO
uptake by bacteria.
5.5.1.2 Pure Oxygen
Because pure oxygen is five times more soluble in water
than air, it is possible to achieve higher DO levels in
wastewater by injecting pure oxygen into wastewater
instead of air. As with air injection, use of pure oxygen as
a sulfide control measure is particularly advantageous in
pressurized systems, because dissolution of oxygen is
greater at higher pressures. However, since less oxygen
gas is required than air to achieve the desired DO levels,
the potential for gas pocket generation in force mains is
substantially reduced. Maintaining the DO above 1 mg/
L is usually sufficient to prevent sulfate reduction.
5.5.1.3 Hydrogen Peroxide
When hydrogen peroxide (H2O2) is added to wastewater,
itoxidizesdissolved sulfide. Excess H2O2decomposes to
water and oxygen. Common dosage rates are 1-5 Ib
H2O.,/lb H2S, depending upon the degree of control
desired, wastewater characteristics, sulfide levels and
length of time involved between the injection and sulfide
control point. Equipment used for H2O2 addition is relatively
simple, consisting mainly of a storage vessel and metering
pumps. Materials for storage and feed equipment must
be compatible with H2O2.1'3
5.5.1.4 Potassium Permanganate
Potassium permanganate (KMnO4) is a strong oxidizing
agent which has a reaction similar to that of H2O2. It is
normally supplied in a dry state, and is fed as a 6-percent
solution in water. Therefore, equipment for dissolving
and feeding it must be supplied. Because of its high
costs, it is not commonly used for sulfide control in
wastewater collection systems.
5.5.1.5 Chlorine
Chlorine will oxidize sulfide to sulfate or to elemental
sulfur, depending on pH. It is commonly added at a
dosage rate of 10-15 Ib Cl/lb H2S removed. It may be
added as sodiu m hypochlorite or a chlorine solution using
equipment similar to that installed in wastewater treatment
plants for effluent disinfection.
5.5.1.6 Iron Salts
Iron salts react with sulfide to produce insoluble
precipitates, and are added afterthegeneration of sulfides
has occurred to tie up the dissolved sulfide and prevent
the release of H2S into the sewer atmosphere. Dosages
are usually dependent on initial sulfide levels and the
targeted level of control, but will generally be 4-15 Ib Fe/
Ib H2S. Iron salts may be purchased as dry chemicals and
dissolved in waterforease of injection, but are commonly
61
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purchased as a solution. Ferrous chloride and ferrous
sulfate are often purchased in bulk, usually as a 40-
percent solution, and being acidic in nature, they must be
handled in corrosion-resistant materials. As with other
sulfide control chemicals (such as hydrogen peroxide), a
typical feed system involves feeding the iron solution at
multiple rates in relationto diurnal fluctuations in dissolved
sulfkte and flow rate.1-5
5.5.1.7 Sodium Hydroxide
H2S corrosion may also be controlled by inactivating the
sulfate-reducing bacteria. Sewer systems in LosAngeles,
as well as other cities, have used pH elevation to control
sulfide corrosion. A caustic solution is added as a shock
dosage for 20-30 minutes, raising the pH in the sewer to
12-13. Soon after the high-pH slug has passed, the
sulfate-reducing bacteria will become re-established so
that dosing with caustic must be repeated when sulfide
levels begin to increase. Typically, the caustic will be
added at intervals which vary from several days to two
weeks.1-5
With this approach, caution must be taken to avoid
upsetting the biological treatment system with the slug of
high pH wastewater. The slug may be diluted as it passes
through the sewer system, in which case there is no
problem. If this in not the case, the slug can be diluted by
directing it to spare tankage and slowly adding it to
treatment plant influent.1'5
Although a pH above 8.0 will result in lower levels of
dissolved H2S gas, continuously adding causticto maintain
a high pH is not generally practical.
5.5.1.8 Sodium Nitrate
The addition of sodium nitrate to sulfate-containing
wastewaters will suppress the generation of H2S. This
occursbecause bacteria will preferentially reduce nitrates
before sulfates. Thus, no sulfides will be produced until
the sodium nitrate has all been reduced.1-5
5.5.1.9 Designing to Avoid Corrosion
Sulfide corrosion can be minimized through careful design
of the sewer system. The corrosion resistance of the
, materials used is an important factor. The characteristics
of many typical materials are described in detail in
several references. Other aspects of the design are also
discussed in these references. The most important
considerations when designing for sulfide control are:1
• Minimizing the occurrence offeree mains, siphons and
surcharged sewers
• Designing for velocities which are sufficient to prevent
the accumulation of solids and which provide surface
aeration of the wastewater.
• Prohibiting the direct addition of sulfides from any
source
Further details on each of these sulfide control
recommendations can be found in the Design Manual:
Odor and Corrosion Control in Sanitary Sewerage
Systems and Treatment Plants,3 Sulfide in Wastewater
Collection and Treatment Systems* and Detection,
Control, and Correction of Hydrogen Sulfide Corrosion in
Existing Wastewater Systems.6 These referencse are
also an excellent source of information on designing
sewer systems to avoid corrosion problems.
Design practices can affectthe degree of corrosion found
in a sewer system. If pipes are oversized, wastewater
flow rates will be reduced and organic materials may
accumulate. This condition is favorable forthe production
of sulfide and can lead to corrosion problems. O&M
practices also affect corrosion. Since accumulation of
organicsolidsisfavorableto initiation of sulfidegeneration,
regular cleaning of oversized segments will help prevent
these problems. Prolonged surcharging, or other
conditions which result in full pipes, should be avoided
since lack of air in the pipes can increase sulfide
production. Short periods of surcharging, however, can
be beneficial since the increased flow rates may wash out
accumulated solids.1 Lift station and force main designs
that allow long pipeline detention times increase the
pressure of H2S.
5.5.2 Control of Other Forms of Corrosion
Where industrial wastes contribute to H2S generation,
industries which dischargetothe sewer should be required
to meet some type of pretreatment standards. If the
wastewater in the sewers is found to be significantly
acidic or basic, the pH should be adjusted.
Moisture must be present for most types of corrosion to
occur. Forexample, a moist atmosphere allows corrosive
vapors to condense on pipe walls and on other fixtures in
the sewer system. Ventilation systems have been used
to reduce moisture and corrosion in sewers. Some
general guidelines for these systems can be found in the
Design Manual: Odor and Corrosion Control in Sanitary
Sewerage Systems and Treatment Plants.3
When designing a new system or making replacements
in an old system, materials should be chosen which are
resistant to the types of waste present. Guidelines for
selecting resistant materials are provided in Table 5-2.4
If electrochemical corrosion of iron or steel isthe problem,
cathodic protection may be appropriate. One type of
62
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Table 5-2. Guidelines to Select Pipe Materials to Resist
Corrosion (4)
Various types of pipe material can be specified as part of the overall
design strategy. Eithercorrosion-resistantor co rrosksn-sensitive materials
can be employed, depending on predicted sulfide levels, required service
life, and economic considerations. The designer has the option of simply
specifying an acid-resistant material or specifying an acid-sensitive
material together with other corrosion control strategies, such as:
Providing O2 to water.
Providing chemical control of sulfide generation.
Designing system hydraulics to avoid sulfide generation.
Providing sacrificial concrete cover.
Providing sacrificial metal thickness (steel or ductile iron).
Using concrete modification, such as calcareous aggregate.
Using a protective liner or coating.
The following materials, varying in sensitivity to acid corrosion, are
available for sanitary sewer construction:
• Vitrified Clay Pipe (VCP) is virtually immune to acid attack. In older
VCP lines, cement mortar joints expanded, and sometimes broke the
bells. Other types of gasketed joints now in general use avoid this
problem. However, VCP is brittle, and so needs special installation
practice and care in handling and transport.
• 'Steel pipe is susceptible to direct corrosion by H2SO4, H2S corrosion
of the iron component, and the normal oxidation of iron.
• Cast Iron Pipe (CIP) is also susceptible to H2SO4and H2S, and normal
oxidation corrosion. It generally lasts longer than steel, simply because
a thicker pipe wall is used.
• Reinforced Concrete Pipe (RCP) is susceptible to acid corrosion.
However, despite its vulnerability, concrete represents an important
sewer pipe material, particularly for large trunk sewers. Concrete can
be fortified against attack by using calcareous aggregate, increasing
the cement content, or both, which provides additional alkalinity and
acid neutralizing capacity where severely corrosive conditions are
anticipated, PVC liners can be employed.
• Asbestos Cement Pipe (ACP) is susceptible to acid corrosion. Due to
its higher cement content, it corrodes at a slower rate than granitic
aggregate concrete, although this attribute is offset by a generally
thinner pipe wall.
• Thermoplastic pipes, such as Polyvinyl Chloride (PVC), Polyethylene
• (PE), and Acrylonitrile-Butadiene-Styrene (ABS), are resistant to acid
corrosion, although subject to strain corrosion in the presence of some
materials, such as detergents, organic solvents, and fats and oils.
• Thermoset plastic pipes, such as Reinforced Plastic Mortar (RPM) and
Reinforced Thermosetting Resins (RTR), are resistant to acid attack.
cathodic protection involves impressing an electrical
current on the corroding surface. The metal surface
which is to be protected is electrically connected to the
negative terminal of a current source and a "sacrificial"
anode is connected to the positive terminal. The sacrificial
anode must be in the electrolytic wastewater and must be
constructed of a material which has a higher electrical
potential than the protected material. Cathodic protection
does not always work well, so an experienced corrosion
control engineer should be consulted before such a
system is attempted.1
5.6 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. Odor and Corrosion Control in Sanitary Sewerage
System and Treatment Plants. EPA/625/1-85/018.
U.S. Environmental Protection Agency, Cincinnati,
Ohio, 1985.
2. Report to Congress: Hydrogen Sulfide Corrosion in
Wastewater Collection and Treatment Systems. EPA/
430/9-91/009. U.S. Environmental Protection Agency,
Office of Water, Washington, D.C. in preparation.
3. Odor and Corrosion Control in Sanitary Sewerage
System and Treatment Plants. EPA/625/1-85/018,
EPA, Cincinnati, Ohio, 1985.
4. Sulfide in Wastewater Collection and Treatment
Systems. ASCE Manual and Reports on Engineering
Practice No. 69, ASCE, New York, 1989.
5., Sulfide and Corrosion Prediction and Control.
American Concrete Pipe Association, Vienna, VA.,
1984.
6. Detection, Control, and Correction of Hydrogen
Sulfide Corrosion in Existing Wastewater Systems.
EPA/430/9-91/019. U.S. Environmental Protection
Agency, Office of Water, Washington, DC. 1991.
63
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CHAPTER 6
Sewer System Rehabilitation
6.1 Introduction
Many methods of sewer system rehabilitation are
available. This chapter examines contemporary methods
and provides guidance on the situations where each
method is applicable. A general description of each
rehabilitation technique, and the procedures, equipment,
and cost estimates are discussed in the following sections.
The reader is cautioned in the use of the costs for various
rehabilitation techniques presented herein. Although the
cost information presented is from the best available
sources, there are some major differences in the basis of
these costs since all cost components are not included in
every rehabilitation technique. Some costs have been
extracted from earlier reports and indexed to the present
time while other costs are from recent sources. Some
costs include engineering and some do not. An attempt
was made to present the cost on a consistent basis ($/
length of sewer), but this may be misleading for some
techniques such as chemical grouting since these costs
vary depending on the number of joints grouted.
It should further be recognized that there are some rather
strong geographical differences in cost for some of the
techniques such, as sliplining and cured-in-place inversion
lining. Also the reported cost of some techniques exhibits
a wide cost range for the same size of pipe due to site-
specific factors. The actual cost ranges are reported
where available. Examinationofthecosttables will show,
forexample, that the high side of the reported cost ranges
for some techniques such as sliplining and inversion
lining are higherthan replacement costs. The basis of the
cost for each rehabilitation technique is described at the
bottom of each cost table. All costs have been indexed to
a March 1991 Engineering News Record Construction
Cost Index (ENRCCI=4773).
6.2 Excavation and Replacement
6.2.1 Description
Replacement of deteriorated pipelines was once the
most common rehabilitation practice but is becoming
more limited due to the availability of trenchless
technologies. Excavation and replacement of defective
pipe segments is normally undertaken underthe following
conditions:1
• When the structural integrity of the pipe has deteriorated
severely; forexample, when pieces of pipe are missing,
pipe is crushed or collapsed, or the pipe has large
cracks, especially longitudinal cracks
• When the pipe is significantly misaligned
• When additional pipeline capacity is also needed.
• When trenchless rehabilitation methods that would be
adequate to restore pipeline structural integrity would
produce an unacceptable reduction in service capacity
• For point repair where short lengths of pipeline are too
seriously damaged to be effectively rehabilitated by
any other means
• Where entire reaches of pipeline are too seriously
damaged to be rehabilitated
• Where removal and replacement is less costly than
other rehabilitation methods
The following are the disadvantages of pipeline removal
and replacement as a method of sewer line rehabilitation:
• Removal and replacement is usually more expensive
than other rehabilitation methods.
• Removal and replacement construction causes
considerably greater and longer-lasting traffic and
urban disruption than does rehabilitation.
• Removal and replacement construction involves a
greater threat of damage to, or interruption of, other
utilities than does pipeline rehabilitation.
6.2.2 Procedures and Equipment
Sewer pipe rehabilitation through pipeline replacement
can be carried out in the following two general forms:
• Excavation and replacement where the existing pipeline
is removed and a new pipeline is placed in the same
alignment
• Abandonment and parallel replacement where the
existing pipeline is abandoned in place and replaced by
a newpipeline in either: 1) physically parallel alignment
65
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adjacent to the existing line, or 2) a functionally parallel
alignment along a different route
Pipeline replacement materials include traditional
materials such as reinforced concrete, clay, ductile iron
and a variety of plastics.
Removal of an existing pipeline and replacement with
new pipe involves all of the problems which occur in
construction of new pipelines in new alignments, plus
special problems which are unique to removal and
replacement. The problems unique to removal and
replacement are:
• MaintainingtributaiysystemanaVorserviceflowsduring
construction
• Removal and disposal of old pipes
• Fill up old abandoned pipes with structurally sound
material to prevent potential collapse
• Workingthroughutilitiesoverlyingorcloselyparallelto
the pipe. These special problems usually result in
added construction costs which often do not occur in
new construction along a new pipe alignment.
Problems which occur in both removal and replacement
and in new construction on a new alignment are:
• Disruption of street traffic
• Disruption of access to residential, commercial, and
industrial properties
• Temporary loss of street parking
* Trench shoring in deep construction involving unstable
soil
* Trench dewatering in areas with high groundwater
6.2.3 Costs
The cost of pipeline excavation and replacement is
specific to individual job conditions. Cost factors are:
Old pipe removal and disposal
Manhole removal and replacement
Trench shoring
New pipe materials installation
Service reconnections to sanitary sewer
Street inlet reconnections to storm drains
Upstream flow diversion during construction
Maintenance of local sanitary service
Traffic control systems and scheduling
Pavement restoration
Interference with other utilities
Table 6-1 presents approximate costs forthe excavation
and replacement method of sewer rehabilitation. The
costs in this table are based on costs taken from the
Handbook for Sewer System Evaluation and
Table 6-1. Rehabilitation Costs* for Excavation and
Replacement (EMRCCI-4773)
Pipe
Diameter
(in)
6
8
10
12
14
16
18
20
30
40
48
54
60
72
90
102
Reference 2*
45-70
50-75
55-85
65-95
70-105
75-110
80-120
95-145
135-205
195-240
235-285
240-295
275-340
365-450
465 - 555
530-645
Cost ($/Lf\
' References**
40-55
45-65
50-75
.65-90
70-105
105-155
150-225
190-230
235-285
260-320
325-360
415-510
495 - 605
2.7 m (9 ft) depth assumed.
Costs include site preparation, excavation, backfill, pavement,
pipe materials, removal of existing pipes, pipe installation,
reconnection of one house service connection for every 6 m (20
ft) of pipe installed. Depth of cover over crown of pipe at 2.7 m (9
ft), pipe in moderately wet soil conditions. Cost to remove the
existing pipe is 50 percent of that required to install a new pipe.
Excludes ledge excavation.
3 m (10 ft) depth assumed.
Costs based on minimum project size of 300 m (1,000 LF).
Costs do not include design engineering, construction
management, bypassing of wastewater, reconnection of services
or street drain inlets, trafficcontrol, utility interference, or removal
and replacement of manholes.
Excludes ledge excavation.
Rehabilitation2 and from Utility Infrastructure
Rehabilitation3 and were adjusted to current pricesthrough
the use of the ENRCCI. Costs were also verified by
contacting vendors and contractors.
6.3 Chemical Grouting
6.3.1 Description
Chemical grouting of sewer lines is mainly used to seal
leaking joints and circumferential cracks. Small holes
and radial cracks may also be sealed by chemical
grouting. Chemical grouts can be applied to pipeline
joints, manhole walls, wet wells in pump stations and
other leaking structures using special tools and
techniques.1 One grouting procedure is illustrated in
Figure 6-1. All chemical grouts are applied underpressure
after appropriate cleaning and testing of the joint. Chemical
grouting is used in precast concrete brick, VCP sewers
and other pipe materials to fill voids in backfill outside the
sewer wall. Such backfill voids can reduce lateral support
66
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Figure 6-1. Grouting equipment and procedures.
.Chemical Catalyst and
Air Pressure Feed Lines
Winch
Manhole
Roller
Assembly
Sealing
Packer
TV Camera
67
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of the wall and allow outward movement resulting in the
rapid deterioration of the structural integrity as the arch
of the top of the pipe looses its support. Chemical
grouting adds no external structural properties to the pipe
where joints or circumferential cracking problems are
due to ongoing settlement or shifting of the pipelines. It
is not effective to use chemical grouting to seal longitudinal
cracks or to seal joints where the pipe near the joints is
longitudinally cracked. Grouting is a joint sealing technique
to be used for each joint in a pipeline segment that fails
the initial leakage test. Chemical grouting is normally
undertaken to control groundwater infiltration in non-
pressure pipelines when these are caused by leaking
pipe joints or circumferential cracking of pipe walls.
Chemical grouting is applied internally within a pipe, and
thusdoesnotdamageorinterferewithotherunderground
utilities. It does not require excavation or surface
restoration, such as pavement or sidewalk replacement
and ground cover reseeding.
Chemicalgroutingdoes not improvethe structural strength
of the pipeline and thus should not be considered when
the pipe is severely cracked, crushed or badly broken.
Chemical grouts may also dehydrate and shrink if the
groundwater drops below the pipeline and the moisture
content of the surrounding soil is reduced significantly.
Large joints and cracks may be difficult to seal because
large quantities of grout may be required. Large cracks,
badly offset joints and misaligned pipes may not be
sealable. Offset joints may prevent the inflatable rubber
sleeves of the sealing unit from seating properly against
the walls of the pipe, making it impossible to isolate and
seal the joint.
The most common chemical grouts currently available
are acrylamidegel, acrylic gel, acrylategel, urethanegel,
and polyurethane foam. The use of acrylamide gel as a
grout may possibly be banned by U.S. EPA since it is
suspected that this grout causes health problems for the
application workers. The basic characteristics of foam
and gel grouts are described below.
Gel Grouts are resistant to most chemicals found in
sewer lines but they may produce a gel-soil mixture
which is susceptible to dehydration and shrinkage
cracking. When using gel grouts, the grouting contractor
and/or the grout supplier should be required to submit
data supporting the non-shrink characteristics of the
grout. Acrylamide gel is significantly more toxic than the
acrylate polymer or urethane gel grouts. Urethane gel
uses water as the catalyst. No significant water
contamination of the urethane grout should be permitted
prior to its injection. Gel grouts are not recommended
where there are large voids outside the pipeline joints.
Foam grouts consist of liquid urethane prepolymers
which are catalyzed by waterduring injection. Thefoaming
reaction of the grout and water expandsthe materials into
the joint cavity, thereby sealing the crack. The foam
grouts are capable of expanding 8-12 times their initial
volumes. Foam grouts are usually difficult to apply and
are more expensive than gel grouts,
Before choosing to use grouting for joint rehabilitation,
the pipeline should be inspected for the following:1
« Determine pregrouting cleaning needs and extent of
root intrusions. For effective grouting, the pipeline
must be relatively free of sand, sediment and other
deposits. Cleaning should occur just prior to grouting.
• Identify crushed or broken sections that must be
replaced. Deformed and longitudinally cracked pipe
sections should not be grouted.
Joints and circumferential cracks in small- and medium-
sized pipes (15-107 cm [6-42 in] diameters) can be
remotely tested and grouted using a packer system
monitored by closed-circuit IV.
The service life of the grout is an important consideration.
Acrylamide grout has been used successfully since the
1950's to stabilize soils and help control underground
water movements in tunnels, darns, dikes, pits and
various other underground structures. The urethane
grouts are more recent. Pipe size, joint spacing, and the
percentage of joints requiring sealing are. factors to
consider in determining the cost of chemically sealing a
line. The larger the pipe, the higher the cost because of
increased manpower, equipment and materials. Chemical
grouting requires rerouting of wastewater flow around
the section being grouted until the grout is cured.
6.3.2 Costs
See Table 6-2 for approximate grouting costs. The costs
in this table are based on costs taken from Utility
Infrastructure Rehabilitation3 and were adjusted to current
prices through the use of a cost index. Costs were also
verified by contacting vendors and contractors. Table 6-
2 reflects 100 percent joint grouting with 60-cm (2-ft) pipe
sections. Grouting costs may be significantly lower than
that shown for grouting fewer joints based on leakage
tests or for longer (1 -2 m [3-6 ft]) pipe lengths.
6.4 Insertion
6.4.1 Description
Pipe insertion is used to rehabilitate sewer pipelines by
sliding a flexible liner pipe of slightly smaller diameter into
an existing pipeline and then reconnecting the service
68
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Table 6-2.
Rehabilitation Costs for Grouting
Pipe
Diameter
(in)
6
8
10
12
15
18
21
24
27
30
33
36
39
42
48
54
60
66
72
78
84
90
96
102
108
Grouting
Prep. Cost
($/LF)
1.00
2.00
2.00 •
3.50
6.00
7.50
9.50
12.00
14.50
18.00
21.50
28.00
32.50
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
Dec. 1984
Grouting Cost
($/tF)
18.00
21.00
24.50
28.00
32.00
36.00
61.00
70.00
79.00
83.00
93.00
104.00
110.00
122.00
325.00
365.00
450.00
580.00
645.00
780.00
865.00
1,000.00
1,500.00
1,325.00
1,465.00
Total
($/LF)
19.00
22.00
26.50
31.50
38.00
43.50
70.50
82.00
93.50
101.00
114.50
132.00
142.50
Mar. 1991
Total Costs
($/LF)
20-30
24-36
28-42
32-48
36-54
40-60
68-102
76-95
88-132
96-144
108-162
124-186
132 - 198
Grouting Preparation Costs
Table 6-3. Advantages and Disadvantages of Sliplinlng
Advantages Disadvantages
• Based on minimum project size of 300 m (1,000 LF).
« Root kill includes application of herbicide inside pipe before root
removal and cleaning. -
• Cleaning costs apply to entire pipe reach.
• Costs are at December 1984 cost level (ENRCCI=4144); 1991 costs
based onadjustmentofthe 1984coststoMarch 1991 (ENRCCM773).
Unit Grouting Costs
• Based on minimum project size of 300 m (1,000 LF) and grouting 100
percent of joints.
• Remote testing and grouting packer system monitored by closed
circuit TV.
• Costs are at December 1984 (ENRCCM144); 1991 costs based on
adjustment of the 1984 costs to March 1991 (ENRCCI=4773).
• Does not include grouting preparation costs.
connection to the new liner. This is done by pulling or
pushing new pipe into a deteriorated pipeline. The liner
forms a continuous, watertight length within the existing
pipe after installation.1
Pipe insertion techniques can be used to rehabilitate
sewer, water and other pipe lines that may have severe
structural problems such as extensive cracks, lines in
unstable soil conditions, deteriorated pipes in corrosive
environments, pipes with massive and destructive root
intrusion problems and pipes with relatively flat grades.
Minimal disruption to
traffic and urban activities
(as compared to replacement)
• Minimal disturbances to other
underground utilities; affects
only those in the vicinity of
access pits.
Significantly less costly than
replacement
Quick installation time.
Good protection against acid
corrosion
Does not require bypassing.
Wide range of pipe sizes
(i.e.,3-144in)
Can be used to rehabilitate
pipelines with severe
corrosion.
• Possible reduction in
pipecapacity
Requires excavation
of an access pit.
Less applicable to sewers with
numerous curves or bends, since
multiple pits would be required.
Requires obstruction removal
of internal obstructions prior to
sliplining.
Installation difficulties may be
encountered during
grouting of annular space.
Advantages and disadvantages of sliplining as a method
of rehabilitation can be found in Table 6-3.
The most popular materials used to slipline sewer lines
are polyolefins, fiberglass reinforced polyesters (FRP),
reinforced thermosetting resins (RTR), polyvinyl chloride
(PVC), and ductile iron (cement lined and polyvinyl lined).
Polyethylene (PE) isthe most common polyolefin material
used and is available in low density, medium density and
high density. High-density PE (HOPE) compounds are
best suited for rehabilitation applications as they have
good stiffness, are hard, strong, tough and corrosion
resistant. PE pipe is manufactured as either extruded or
corewall.1 Extruded pipe has smooth inner and outer
surfaces and has structural characteristics that are
determined by wall thickness. Corewall pipe has an
exterior hollow rib which gives structural integrity to the
pipe and minimizes pipe weight. Extruded PE pipe is
manufactured in diameters of 5-122 cm (2-48 in) and
corewall PE pipe 30-366 cm (12-144 in). Two national
specifications ASTM P1248 and ASTM D3550, are
available for design and reference. These standards
apply to extruded PE pipe with circular cross-sections
and diameters of 10-122 cm (4-48 in).
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Polybutytene (PB), another polyolefin, is similarto medium
density PE pipe in stiffness and chemical resistance but
has better continued stress loading characteristics. It
also has good temperature resistance. PB pipe is
manufactured as extruded pipe in diameters of 8-107 cm
(3-42 in).
Centrifugally cast FRP pipe was originally manufactured
in Switzerland in the 1960's and is now being widely used
in U.S. It is a composite of resin made from fiberglass and
sand that is formed within a revolving mold. It is frequently
specified as an acceptable alternative to polyethylene.
FRP pipe has very good chemical and corrosion resistance
and is suitable for use over a pH of 1-10. FRP pipe is
manufactured in standard 6-m (20-ft) lengths and is
available in diameters of 46-244 cm (18-96 in).
RTR pipe is a composite of fibers and resins that are
either spiral wound on a rotating mandrel or composited
on the inside of a rotating drum, similarto FRP pipe. RTR
pipe has good axial and longitudinal strength, enabling it
to be pushed into an existing pipe without buckling.
Friction losses are low due to smooth interior surfaces.
This pipe has high strength and a high modules of
elasticity. It also hasgood corrosion, erosion and abrasion
resistance. Manufactured sizes are lengths of 6-24 m
(20-80 ft) and diameters of 10-360 cm (4-142 in).
Flexible PVC has been used successfully as a sliplining
material. PVC is highly resistant to acid attack and is very
smooth, exhibiting good hydraulics. Grouting of the
annular space is required to give strength to the PVC.
6.43 Procedures and Equipment
Prior to sliplining. the sewer should be first thoroughly
cleaned and inspected by closed circuit TV to identify all
obstructions such as displaced joints, crushed pipes and
protruding service laterals. The inspection also should
JocateaHserviceconnectionsthatwillneedto be connected
to the new liner pipe. The pipe must be thoroughly
cleaned. It may at times be necessary to proof test the
existing pipe by pulling a short piece of liner through the
sewer section.
Sliplining is performed by either apush or a pull technique;
both methods are illustrated in Figure 6-2.1 In the pull
method a pulling head is attached to the end of the pipe.
A cable is run from the termination point to the access
point and is connected to the pulling head. The sliplining
pfpe is then pulled through the existing pipe with the cable
by a track mounted winch assembly. Pulling is used for
extruded PE and PB pipe that is heat fused into a
continuous length. The push method can be performed
by ertherabackhoeorajacking machine. Abackhoe can
be used for extruded heat fused PE or PB pipe, Corewall
PE pipe, FRP pipe and RTR pipe. However, the backhoe
is limited to small diameter and/or short length pipe. The
jacking machine is used for larger diameter, sleeve-
coupled or bell spigot jointed pipes (e.g. Corewall PE,
FRP, and RTR) but it is not used for heat fused polyolefin
pipe.
For most insertion projects it is not necessary to eliminate
the entire flow stream within the existing pipe structure.
Actually, some amount of flow can assist positioning of
the liner by providing a lubricant along the liner length as
it movesthroughthe deteriorated pipe structure. Excessive
flows can inhibit the insertion process, however, the
insertion procedure should be timed to take advantage of
cyclic periods of low flows that occur during the operation
of most gravity piping systems. During the insertion
process, often a period of 30 minutes or less, the annular
space between the sliplining pipe and the existing pipe
will probably carry sufficient flow to maintain a safe level
in the operating section of the system being rehabilitated.
Flow can then be diverted into the liner upon final
positioning of the liner. During periods of extensive flow
blockage, the upstream piping system should be
monitored, and provisions for bypassing provided in
order to avoid unexpected flooding and drainage areas.
Once the sliplining pipe has been pulled through the
existing pipe, it is grouted in place. Grouting at manhole
connection is required, but grouting of the entire length of
the pipe is not required if the liner is strong enough to
support loads in the event of collapse of the original pipe.
It must be determined on a site-specific basis whether or
not to grout after evaluating the severity of structural
deterioration and anticipated hydrostatic and structural
loadings. Grouting provides the following advantages:
Provides structural integrity
Increases hydrostatic and structural loading capabilities
Prevents liner from moving
Locks in service connections
Extends the service life of the pipe
Provides increased temperature resistance
Provides support to liner when cleaning
One of the advantages of sliplining to replacing a sewer
line is that it requires minimal excavation which limits
traffic disruption and minimizes interferences with surface
structures, such as retaining walls, landscaping, or
portions of buildings. Sliplining also can be used to avoid
extensive dewatering that is necessary for conventional
open trench construction. Sliplining can be installed in
pipelines having moderate horizontal or vertical deflection
due to the flexible nature of the sliplining pipe.
70
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Figure 6-2. Insertion methods.
"Pull" Insertion Technique
/Winch Assembly
Ramp for
Two-Way Insertion
Min. of 12x
Liner Diameter
Liner Pipe
Remote Manhole
or Access Pit
Existing Pipe Cable Attached
to Guide Cone
Pipe Support Roller
"Push" Insertion Technique
Existing Pipe
Winch Asembly
7*7 /
Guide Cone
Existing Pipe
Remote Manhole
or Access Pit
Minimum of Standard
Pipe Length
Cable Passing Through
Lining Pipe Anchored
to Push Plate
71
-------
Equipment required forthe insertion of the sliplining pipe
are: jointing equipment, pulling or pushing head, winch,
rollers, proofing tool, grout tank and pump. The jointing
equipment is used to join segmented pipe lengths to form
a continuous pipe of desired length. This is done by
aligning the two pipes together, heating the ends and
butting the ends together. The pulling head is used to
facilitate the pulling of the pipe into the sewer. One end
of the pulling head is attached to the pipe to be pulled
while the other end is attached to the pulling cable. The
winch, consisting of a power operator and a pulling cable,
is used to pull the pipe. The rollers are used to grout the
annular space between thepipe and manhole connections
to prevent groundwater migration.
6.4.3 Costs
Tables 6-4 through 6-7 indicate the approximate costs for
sliplining as a method of sewer rehabilitation. The data in
these tables are based on costs taken from the Handbook
for Sewer System Evaluation and Rehabilitation* and
Table 6-5.
Rehab Costs for Sliplining with PE Pipe
Tab!* 6-4. Rehab Costs for Sliplining with HOPE and
Polybutylene Pipe
Pipe
Diameter
4
8
12
16
20
24
28
32
36
40
42
48
55
63
Dec. 1984
ENRCCI-4144
(S/LF)
8-17
12-29
19-38
25-47
30-60
28-75
44-92
58-112
68-132
78-152
85-156
90-196
105-209
123-252
March 1991
ENRCCI=4773
($/LF)
9-20
15-35
25-45
30-55
35-70
35-90
55-110
70-130
80-155
90-180
100-185
105 - 230
125-245
145-295
1984 costs from Reference 3; 1991 costs based on adjusted 1984
costs.
Based on mln. project size of 300 m (1,000 LF).
Polybutylene pipe not available In sizes larger than 122 cm (48 in).
Lower cost ranges may apply to pipelines with good alignment, no
need for spot repair, and no significant groundwater.
Higher cost ranges may apply to pipe with poor alignment, some need
for spot repair and need for groundwater dewatering.
Costs do not Include: preparation of Insertion access pit(s); grouting
or sand fitting of entire liner pipe/existing pipe annual space; bypassing
ofwastowa!er;costs Jordeslgnenglneering, construction management
or design related services.
Pipe
Diameter
(in)
6
8
10
12
14
16
18
22
26
28
32
36
42
48
52
58
68
72
80
88
92
100
Mid 1974
ENRCCI=1993
($/LF)
20
21
23
25
28
32
34
39
45
54
62
72
88
102
110
135
152
174
200
225
250
275
March 1991
ENRCCI=4773
($/LF)
35-60
40-60
45-70
50-75
55-80
60-95
65-80
75-115
90-130
105-155
120-180
155-190
190-230
220 - 275
250-290
290-355
330-400
375-460
430-530
485 - 595
540-660
595-725
1974 costs from Reference 2; 1991 costs based on adjusted 1974
costs.
Costs include site preparation, insertion pit, pipe, materials, pipe
welding, pipe installation, connection of one house service for every 6
m (20 ft) of pipe, pipe sealing at manholes J'.nd mobilization.
Table6-6. Rehab Costs for Sliplining Reinforced
Thermosetting Resin
Pipe
Diameter
(in)
8
12
16
20
24
30
36
42
48
54
60
66
Dec. 1984
ENRCCI=4144
($/LF)
20-26
35-45
45-55
60-70
75-80
85-110
. 110-130
125-150
145-170
165-185
175-220
185-235
March 1991
ENRCCI=4773
($/LF)
25-30
40-55
55-65
70-85
85-90
100-130
130-150
145-175
170-200
190-215
215-255
215-275
Costs based on min. project size of 300 m (1,000 LF).
1984 costs from Reference 3 ; 1991 costs based on adjusted 1984
costs.
Lower costs may apply for existing pipe with poor alignment, some
need for spot repair, and need for groundwater dewatering during
construction.
Costs do not include preparation of insertion access pit, connection of
service to new line, grouting or sand fitting of the entire "liner pipe
existing pipe" annular space, or bypassing of wastewater.
72
-------
Table 6-7.
Service
Connection Size
Miscellaneous Rehab Costs for Sliplining
Dec. 1984
ENRCCI=4144
March 1991
ENRCCI=4773
4 or 6 in @ 4-8 ft depth
4 or 6 in @ 8-12 ft depth
4 or 6 in @ 12-16 ft depth
4 or 6 in @ 16-20 ft depth
Grouting
Access Pit
<1 Oft depth
10-20 ft depth
>20 ft depth
($)
400/each
550/each
750/each
1,000/each
200/cu yd of grout
($)
465/each
640/each
870/each
1,165/each
230/cu yd
1,000/ft depth 1,165/ft depth
800/ft depth 930/ft depth
1,000/ft depth 1,165/ft depth
Costs are for average traffic conditions and include pit sheeting and
shoring in reasonably stable soil where groundwater dewatering is not
necessary.
1983 costs are from Reference 3; 1991 costs based on 1984 adjusted
costs.
from Utility Infrastructure Rehabilitation* and were
adjusted to current prices through the ENRCCI. Costs
were also verified by contacting vendors and contractors.
6.5 Cured-in-Place Pipe Lining
6.5.1 Description
Inversion lining is formed by inserting a resin-impregnated
felt tube into a pipe, which is inverted against the inner
wall of the pipe and allowing it to cure. After the lining
system has been installed and cured, a special cutting
device is used with a closed-circuit TV camera to reopen
service connections, which are located with the camera
before the liner is installed. The pliable nature of the
resin-saturated felt prior to curing allows installation
around curves, filling of cracks, bridging of gaps, and
maneuvering through pipe defects. After installation, the
fabric cures to form a new pipe of slightly smaller diameter,
but of the same shape as the original pipe. The new pipe
has no joints or seams and has a very smooth interior
surface which may actually improve flow capacity despite
the slight decrease in diameter.
Two resin types (polyester and epoxy) are widely used in
this method of pipe rehabilitation. Both these resins are
liquid thermosetting resins, and have excellent resistance
to domestic wast ewater. Chemical resistance tests should
be specified forCIPP forotherthan domestic wastewater
in accordance with ASTM F1216x2. Vinylester resins
may be used where superior corrosion resistance is
required at high temperatures. Epoxy resins are used
where adhesion to the existing pipeline is desired.
Table 6-8. Advantages and Disadvantages of Cured-ln-
Place Unlng
Advantages Disadvantages
Bypass required during
installation
Post-installation remote
camera inspection required
Maximum effluent
temperature 82°C (180°F)
using specially formulated
resins
Applicable to all shapes
Rapid installation
Minimum traffic disruption
Excavation normally not required
In-line lateral reconnections
Improved hydraulics
Bridges gaps and misaligned joints
Special resins are available
to provide acid resistance.
Custom designed wall thickness
to aid in structural strength
Only 50-70 percent of
replacement costs
Adds some structural integrity
Does not interfere with or
damage other utilities
No pavement repairs
Safer than some other rehabilitation methods.
Inversion lining is successful in dealing with a number of
structural problems, particularly in sewers needing minor
structural reinforcement. Caution must beused, however,
in the application of this method to any structural problems
involving major loss of pipe wall. Inversion lining can be
accomplished relatively quickly and without excavation
and thusthis method ofpipeline rehabilitation is particularly
well suited for repairing pipelines located under existing
structures, large trees, or busy streets or highways
where traffic disruption must be minimized. Inversion
lining produces minor reductions in pipe cross-sections.
It is applicable to non-circular pipes and pipes with
irregular cross-sections. This method is also effective in
correcting corrosion problems and can be used for
misaligned pipelines or in pipelines with bends where
realignment or additional access is not required. See
Table 6-8 for a summary of the advantages and
73
-------
disadvantages of sewer rehabilitation by cured-in-place
lining.
There are currently three processes that have been
introduced in the United States that are classified as
cured-in-place: Ins'rtuform, Pattern, and KM Inliner.
6.5.1.1 Insltuform
The Ins'rtuform process was developed in England in the
early seventies. Since its introduction in the United
Statesln 1978, approximately 2,400 linear km (8,000,000
ft) have been installed in a variety of piping applications.
Third party testing has been performed by several
agencies verifying structural properties, design methods,
corrosion resistance and the ability to enhance, flow
capacity. The process has been used on circular and non
circular pipes in diameters of 10-275 cm (4-108 in). The
maximum installation length is approximately 360-750 m
(1,200-2,500 ft) depending on the diameter and wall
thickness. ASTM F-1216-89, as well as other national
and federal specifications, specifically covers the
Ins'rtuform process. The Insrtuform process is installed
throughout the United States by a network of licensed
instaiters. Ins'rtuform tubes are manufactured inthe United
States by Ins'rtuform of North America, Inc.
6.5.1 £ Pattern
PaRem (Pipeline Automatic Lining System) wasdeveloped
in Japan through a joint venture between Tokyo Gas and
a private company, Ashimori Industries, for rehabilitating
natural gas lines. Since being brought to the United
States in 1988, there have been various demonstration
projects and some full-scale municipal sewer projects.
The published size range is 2-100 cm (0.75-40 in);
however, in the United States, 10-60 cm (4-24 in) is
available for gravity flow sanitary sewer work. Although
information is available through the parent company
relevant to physical testing, at this time there appears to
be no third party documentation for the Pattern system.
The specifications covering this process is included in
ASTM F-1216.
6.5.1.3 KM Inliner n
TheKMInlinerprocess was developed in West Germany
by the Kanal Mueller Gruppe in 1985. It has been
marketed in the United States since 1988. The material
is being manufactured in Germany; however, there are
plans to establish a manufacturing facility in the eastern
United States. Diameters of 20-60 cm (8-24 in) can be
reconstructed using this process, and there are indications
that pipes up to 90 cm (36 in) may be available sometime
in the future. The maximum installation length is
approximately 180 m (600 ft). Application for inclusion in
ASTM F-1216 was made in 1990 and is still pending.
There is no third party testing available verifying the
Table 6-8.
RehabCostsforCured-livPlacelnveislon Lining
Pipe
Diameter
(in)
6
10
14
18
21
24
27
30
33
36
42
48
54
60
Dec. 1984
ENRCCI=4144
($/LF)
25-40
49-65
65-105
75-125
85-135
95-165
105-175
115-190
120-215
130-230
140-265
160-300
175-335
185-375
Mar. 1991
ENRCCI=4773
($/LF)
30-45
60-75
75-125
90-145
100-160
110-190
125-205
135 - 220
140-250
155-270
165 - 305
185-350
205-390
215-435
Costs are based on minimum project size of 300 m (1,000 LF).
1984 costs from Reference 3; 1991 costs based on adjusted 1984
costs.
Costs do not include providing temporary water or natural gas service
for the curing process, design construction management, or design
related services.
physical properties or design parameters used for this
process.
6.5.2 Procedures and Equipment
Installation of cured-in-place inversion lining is carried
out by inserting the resin-impregnated fabric tube (turned
inside out) into the existing pipe line and inverting it as it
progresses inside the pipe. It is then cured in place
through the use of heated water or air steam. Prior to the
installation of the liner, the pipeline section must be
cleaned to remove loose debris, roots, protruding service
connections, and excessive solids. The preparation and
installation procedures are illustrated in Figure 6-3.1 The
pipeline segment must be isolated from the system by
bypassing flows during the installation of the inversion
lining. The inversion felt tube liner is usually inserted from
existing manholes. Following curing of the liner, the ends
are cut and sealed and service connections are restored.
6.5.3 Costs
See Table 6-9 for approximatecostsof sewer rehabilitation
by cured-in-place inversion lining. The costs in these
tables are based on costs taken from Utility Infrastructure
Rehabilitation3 and were adjusted to current pricesthrough
the use of a cost index. Costs were also verified by
contacting vendors and contractors.
74
-------
Figure 6-3. Installation of Cured-ln-PIace inversion lining (Insituform).
STEP 1
RESIN
IMPREGNATED
INSITUTUBE©
INVERSION TUBE
I I
MANHOLE
75
-------
6.6 Fold and Formed
This process uses a folded thermoplastic (PE or PVC)
pipe that is pulled into place and is then rounded to
conformtothe internal diameterof the existing pipe. This
method of pipe rehabilitation can be considered as an
improved version of sliplining. Excavation is not required
for installation when there are existing manhole access
points, and lateral reinstatement is accomplished
internally. The finished pipe has no joints and produces
a moderately-tight fit to the existing pipe wall. This
method of pipe rehabilitation is less versatile than cured-
in-place methods in terms of diameter range .and
installation length. Only slight offsets and bends can be
negotiated.
The fotd and formed method of rehabilitation does not
require a long curing process in terms of speed of
installation. This process of rehabilitation has been canied
out in the United States for the last 2-3 years.There are
currently two fold and formed processes commercially
available in the United States: U-Liner and .NuPipe.
Some municipalities have tried them for experimental
and evaluation purposes. Fold and formed method of
pipeline rehabilitation are suitable for pipe diameters of
10-40 cm (4-16 in) with typical lengths of installation of
90-180 linear m (300-600 ft). Fold and formed technology
is currently being developed for 60-cm (24-in) diameter
pipe. Butt-fused U-Liner pipe can be used for lengths up
to the stress-resistant pull force of the material.
6.6.1 U-Liner
The U-Liner technology was developed by Pipe Liners
Inc. of New Orleans with the pipe material being
manufactured in the United States by Quail Pipe
Corporation of Roaring Springs, Texas. The U-Liner
manufacturing process is specified by ASTM as deformed
HPDE. This rehabilitation technology has been
commercially available in the United States since 1988.
High density polyethylene resin conforming to the
requirements of ASTM 1248, Type III, ClassC, Category
5, Grade P34, is used, and it is currently available in SDR
32.5, 26 and 21. The selection of the appropriate wall
thickness will depend on the particular loading conditions
from project to project. U-Liner is extruded as round pipe,
conforming to ASTM D-3350, and then through a
combination of heat and pressure, is deformed into the
"U" shape. It is then wound onto spools ready for
installation. This technology is currently applicable for
pipe sizes of 10-40 cm (4-16 in). Approximately 100
linear km (350,000 ft) of pipe has been installed in the
U.S. by U-Liner Licensees. The U-Liner polyethylene
material has been independently tested for material
strength and physical properties and has been accepted
in the Standard Specifications for Public Works
Construction.6
The installation of U-Liner is basically a three step
process. After cleaning and TV inspection and analysis
to identify defects and to determine the applicability of U-
Liner, the first step includes winching of a pre-engineered
seamless coil of pipe of a precut length into place. The
pipe is pulled off the spool at ambient temperature, fed
through an existing manhole, and is winched through the
existing pipe to the terminal point. Once it is in place,
steam is fed through the inside of the folded pipe,
softening the plastic to allow for the reforming process.
Installation in pipes below the water table may make it
difficult to heat the plastic sufficiently due to groundwater
entering the system which will coo) the plastic.
Temperatures of 110-130°C (235-270°F) are used to
soften the plastic. A diagram depicting the U-Liner
installation procedure is presented in Figure 6-4. After
the plastic has been heated, pressure is used to reround
the pipe. The rerounding of the pipe occurs simultaneously
from end to end and may trap water or air in between the
U-Liner and the host pipe. The pressure required to
reround the pipe will vary, depending on the wall thickness,
between 170 and 240 kPa (25 and 35 psi).
Due to the relatively high coefficient of thermal expansion
of polyethylene combined with the extreme temperature
changes associated with the process, sufficient time
should be allowed for the system to stabilize before
laterals are reinstated and end treatment is finished.
Laterals are recut utilizing a remote-controlled cutter
head, in conjunction with a TV camera.
6.6.2 NuPipe
The NuPipe process was developed in the U.S. and has
been commercially available since 1990. NuPipe is
manufactured from PVC and is extruded in a folded
shape. While it is still pliable, the folded PVC is wound
onto spools. It is currently available in 15-30 cm (6-12 in)
in SDR 35. Third party testing has shown that SDR 35 is
capable of withstanding nearly all loading conditions
experienced in buried pipelines.7 The resin composition
conforms to ASTM 1784, cell class 12454-B or 12454-C
and the installed pipe meets the performance
requirements of ASTM D-3034 which is standard
specification for direct bury PVC pipe. As with
polyethylene, the corrosion resistanceof PVC is excellent.
The installation of NuPipe includes cleaning of existing
host pipe along with a TV inspection to determine the
extent of deterioration and to verily the applicability of
NuPipe. A flexible reinforced liner called the Heat
76
-------
6.6 Fold and Formed
This process uses a folded thermoplastic (PE or PVC)
pipe that is pulled into place and is then rounded to
conform to the internal diameter of the existing pipe. This
method of pipe rehabilitation can be considered as an
improved version of sliplining. Excavation is not required
for installation when there are existing manhole acess
points, and lateral reinstatement is accomplished
internally. The finished pipe has no joints and produces
a moderately-tight fit to the existing pipe wall. This
method of pipe rehabilitation is less versatile than cured-
in-place methods in terms of diameter range and
installation length. Only slight offsets and bends can be
negotiated.
The fold and formed method of rehabilitation does not
require a long curing process in terms of speed of
installation. This process of rehabilitation has been carried
out in the United States for the last 2-3 years. There are
currently two fold and formed processes commercially
available in the United States: U-Liner and NuPipe.
Some municipalities have tried them for experimental
and evaluation purposes. Fold and formed method of
pipeline rehabilitation are suitable for pipe diameters of
10-40 cm (4-16 in) with typical lengths of installation of
90-180 linear m (300-600 ft). Fold and formed technology
is currently being developed for 60-cm (24-in) diameter
pipe. Butt-fused U-Liner pipe can be used for lengths up
to the stress-resistant pull force of the material.
6.6.1 U-Liner
The U-Liner technology was developed by Pipe Liners
Inc. of New Orleans with the pipe material being
manufactured in the United States by Quail Pipe
Corporation of Roaring Springs, Texas. The U-Liner
manufacturing process is specified by ASTM as deformed
HPDE. This rehabilitation technology has been
commercially available in the United States since 1988.
High density polyethylene resin conforming to the
requirements of ASTM 1248, Type III, Class C, Category
5, Grade P34, is used, and it is currently available in SDR
32.5, 26 and 21. The selection of the appropriate wall
thickness will depend on the particular loading conditions
from project to project. U-Liner is extruded as round pipe,
conforming to ASTM D-3350, and then through a
combination of heat and pressure, is deformed into the
"U" shape. It is then wound onto spools ready for
installation. This technology is currently applicable for
pipe sizes of 10-40 cm (4-16 in). Approximately 100
linear krn (350,000 ft) of pipe has been installed in the
U.S. by U-Liner Licensees. The U-Liner polyethylene
material has been independently tested for material
strength and physical properties and has been accepted
in the Standard Specifications for Public Works
Construction.6
The installation of U-Liner is basically a three step
process. After cleaning and TV inspection and analysis
to identify defects and to determine the applicability of U-
Liner, the first step includes winching of a pre-engineered
seamless coil of pipe of a precut length into place. The
pipe is pulled off the spool at ambient temperature, fed
through an existing manhole, and is winched through the
existing pipe to the terminal point. Once it is in place,
steam is fed through the inside of the folded pipe,
softening the plastic to allow for the reforming process.
Temperatures of 110-130°C (235-270°F) are used to
soften the plastic. A diagram depicting the U-Liner
installation procedure is presented in Figure 6-4. After
the plastic has been heated, pressure is used to reround
the pipe. The pressure required to reround the pipe will
vary, depending on the wall thickness, between 170 and
240 kPa (25 and 35 psi).
Due to the relatively high coefficient of thermal expansion
of polyethylene combined with the extreme temperature
changes associated with the process, sufficient time
should be allowed for the system to stabilize before
laterals are reinstated and end treatment is finished.
Laterals are recut utilizing a remotee-controlled ..cutter
head, in conjunction with a TV camera.
6.6.2 NuPipe
The NuPipe process was developed in the U.S. and has
been commercially available since 1990. NuPipe is
manufactured from PVC and is extruded in a folded
shape. While it is still pliable, the folded PVC is wound
onto spools. It is currently available in 15-30,cm (6-12 in)
in SDR 35. Third party testing has shown that SDR 35 is
capable of withstanding nearly all loading conditions
experienced in buried pipelines.7 The resin composition
conforms to ASTM 1784, cell class 12454-B or 12454-C
and the installed pipe meets the performance
requirements of ASTM D-3034 which is standard
specification for direct bury PVC pipe. As with
polyethylene, the corrosion resistance of PVC is excellent.
The installation of NuPipe includes cleaning of existing
host pipe along with a TV inspection to determine the
extent of deterioration and to verify the applicability of
NuPipe. A flexible reinforced liner called the Heat
76
(Revised 4/94)
-------
-------
Figure 6-4.
U-Uner installation method.
Power, Steam/Pressure Generation,
Studio Operating Room
Winch Pulls Pipe
Coil
Steam, Pressure,
Temperature
Instrumentation
Hydraulic Advantage
Gradual Transition
Steam,
Pressure
000 Injector
Lateral recognized
for Remote Cutting
Restored Broken Pipe
End Restrained
Containment Tube (HCT) is inserted into the host pipe.
The HCT provides a closed environment in which the
NuPipe is installed and processed. After the HCT has
been strung through the host pipe. The folded PVC is
heated while on the spool and is pulled through the host
pipe. Heating the plastic reduces the forces required to
pull the pipe in place. Once the folded NuPipe reaches
thetermination point, steam is introduced into the system
both through the interior and around the exterior of the
folded pipe. The use of the HCT also allows for heating
both sides of the plastic to provide complete heat transfer
through the pipe wall which minimizes the effect of
infiltrating water. After the PVC becomes pliable, a
rounding device is introduced into one end of the pipe
which is then propelled through the folded pipe. The
rounding device progressively rounds the NuPipe, moving
standing water out of the way while also expanding the
plastic tightly against the host pipe, creating a mechanical
lock at joints and laterals. Approximately 35-70 kPa (5-10
psi) is needed to propel the rounding device. Cold water
is then injected into the Nu Pipe effectively quenching the
plastic. The installation process is shown in Figure 6-5.
6.6.3 Costs
The costs of U-Liner and NuPipe are not well established
due to the recent entry of these two technologies into the
sewer rehabilitation field. The cost of Fold and Formed
installations vary widely in different geographic regions of
the country depending on availability of materials,
availability and experience of installation contractors,
level of competition, and length and loading condition of
the sewers to be rehabilitated.
Review of limited competetive bid prices received from
Pipe Liners, Inc. for U-Line indicates a price range of $60-
78/LF for 20- to 30-cm (8-12-in) diameter pipe, including
cleaning. Laterial reinstatement costs were reported to
range from $200 to $216/unit. Price information was not
available from NuPipe.
Engineers and municipalities considering Fold and
Formed technologies are encouraged to contact the
manufacturer and local installers of thetechnology and to
review installation costs for recently-installed projects in
their locality.
6.7 Specialty Concrete1
6.7.1 Description
Specialty concretescontaining sulfate resistant additives
such as potassium silicate and calcium aluminate have
shown greater resistance than typical concrete to acidic
attack on sewer pipes and manhole structures.
77
-------
Flflur* 6>5. NuPlpfl Installation method.
78
-------
Table 6-10.
Advantages
Advantages and Disadvantages of Specialty
Concretes
Cement Mortar
• Minimal service interruption
• Improved structural integrity
• Applicable for wide range of
pipe sizes
Shotcrete
• Minimal excavation required
Access is through manholes
• Can restore structural
integrity to a pipe that
would otherwise require
replacement
• Minimum traffic interruptions
• Applicable to all shapes of
man-entry size pipes
Cast Concrete
• Established procedure
• Simple to design
• Applicable to all shapes of
pipes
Excavation required for sharp
ends or curves
Cannot be done in winter if
freezing potential exists
Bypass required
Extensive surface
preparation required
(e.g., chipping, sandblasting)
Access holes required every
150-210 m (500-700 ft)
Concrete shelf life must be
tracked for the project duration
Transportation cost
higher for concrete
May not provide adequate
corrosion resistance
Extensive surface
preparation required
Extended downtime period
of 3-7 days or longer
required for cleaning
Some reduction in
hydraulic capacity
Limited to man-entry
size structures
Concrete shelf life to be
tracked for project duration
Transportation cost high
for concrete
May not provide 'adequate
corrosion resistance.
Cleaning required
Bypass required
Seldom applicable to pipes
less ttian 1.2m (4 ft) in
diameter
Concrete shelf life to be
tracked for project duration
Transportation cost high for
concrete
May not provide adequate
corrosion resistance
Specialty concrete isusedtoreinforce weakened concrete
pipes and structures by applying an acid resistant coating
over the original surface. Specialty concretes are unique
in that their matrix is not formed by a hydration reaction.
Rather, they are the result of the reaction of an acid
reagent with an alkaline solution of a ceramic polymer of
potassium silicate. Portland cement releases calcium
hydroxide during hardening whereas the specialty
cements do not release calcium hydroxide. Specialty
cements can resist attack by many substances including
mineral salts, mild solutions of organic and mineral acids,
sugar solutions, fats and oils. Acid reagents used in some
cases are also effective bactericides.1
Applicability of specialty concrete depends on the degree
of corrosion-related deterioration and the structural
integrity of the sewer. Thin film specialty concrete is
applicable to mildly deteriorated pipes or structure,
whereas an elastic membrane concrete system is
applicable to all cases. After curing, the specialty concrete
bonds firmly to the original surface. The new acid-
resistant layer, if applied and cured properly, extends the
useful life of the structure. Advantages and disadvantages
of specialty concretes are listed in Table 6-10.
6.7.2 Procedures and Equipment
Specialty concretes are available in three types: cement
mortar, shotcrete, and cast concrete. Acid resistant
mortars have been used in industry as linings in tanks or
as mortar bricks. Development of mechanical in-line
application methods (centrifugal and mandrel) has
established mortar lining as a successful and viable
rehabilitation technique for sewer lines, manholes and
other structures.
Mortar lining is applied using a centrifugal lining machine.
The machine has a revolving, mortar-dispensing head
with trowels on the backto smooth the mortar immediately
after application. In smaller diameter pipes a variable
speed winch pulls the lining machine through a supply
hose. Reinforcement can also be added to the mortar
with a reinforcing spiral-wound rod. The reinforcing rod is
inserted into the fresh mortar and a second coat is
applied over it. For man-entry structures the mortar can
be applied manually with a trowel.
Shotcrete, sometimes referred to as gunite, is a low-
moisture, high-density mixture of fine aggregate (particle
size of 19 mm [0.75 in] and smaller), cement and water;
solids to liquid mix ratios are typically 5:1. Well placed
shotcrete has a high modules of elasticity (greater than
4 million psi) and a coefficient of thermal expansion
similar to that of low carbon steel. Bonding with the
original surface is usually stronger than the base material
itself, with better adhesion occurring with the more
deteriorated and irregular existing pipe. Shotcrete is
applied to a minimum thickness of 5 cm (2 in). Shotcrete
is used in man-entry size sewers (81 cm [32 in] or
greater) and manholes. Prior to shotcreting, reinforcing
steel is set into place. The shotcrete lining machine is self
propelled and controlled by a person riding it. Mortar is
supplied to an electrically driven supply cart that conveys
mortar from the access hole to the feeder which is
attached to the lining machine. The dry specialty cement
79
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Table 6-11. Costa for Rehabilitation Using Specialty
Concretes
Repair Cost Repair Cost Cost to
Item Severely Corroded Mildly Corroded Apply to
Concrete ' Concrete New Concrete
Cement with
Polymer Unlng
Cement with add
Proof Concrete
Cement with urethane
Membrane
(5/sqft)
16-18
22-27
22-27
($/sqtt)
9-11
16-19
16-19
($/sqft)
5-6
16-19
16-19
• Mildly Corroded - Loss than 19-mm (3/4-In) loss of concrete. No
reinforcement attack.
• Severely Corroded - Greater than 19-mm (3/4-ln) concrete loss. May
require replacement of reinforcement
• Costs Include Installation.
• Costs obtained from Report to Congress: Sulffde Corrosion In
Wastewatar Collection and Treatment Systems1.
and aggregate is mixed with water in a specially designed
spray nozzle. Hydration occurs, and the resulting mixture
is shot into place under pressure. Curing occurs under
moist conditions for the first 24 hours and an additional
six days at a temperature above 4°C (40°F).
Cast concretes are potassium silicate bonded, poured or
cast in place structural concretes. They typically have
half the in-place density or strength value of shotcrete.
Solids to liquid mix ratios are generally 2:1, similar to
cement mortar.
Cast concrete is poured over prefabricated or hand built
interior pipe forms that can be removed and reused
sectkm by section. Reinforcing steel is added between
the original surface and the form, setting within the cured
thickness.
Each of the three application techniques requires prior
cleaning to remove oils, greases, foreign objects, and
loose materials, as well as wastewater bypass during
application and initial curing.
6.7.3 Costs
Table 6-11 provides typical costs for the three types of
specialty concrete.1 The costs in this table were obtained
itomReportto Congress: Sulfide Corrosion in Wastewater
Collection and Treatment Systems'1 and were adjusted to
current pricesthrough the use of acost index. Costs were
also verified by contacting vendors and contractors.
6.8 Liners1
6.8.1 Description
Rehabilitation techniques using liners include the
installation of prefabricated panels or flexible sheets on
the existing structure usually with anchorboltsorconcrete
penetrating nails shot into place. The following materials
of liners are available for rehabilitation purposes1:'
• PVC liners
• PE liners
• Segmented, fiberglass reinforced plastic liners
• Segmented, fiberglass reinforced cement liners
PVC liners are manufactured from acid-resistant, rigid
unplasticized PVC which has excellent resistance to
acids and also is initially conductive to better hydraulics
than concrete. The liner is composed of high molecular
weight vinyl chloride resins combined with chemical-
resistant plasticizers. The completely inert mixture is
extruded under pressure and temperature into a liner
plate with a minimum thickness of 1.6 mm (0.065 in). The
liners are pin-hole free, forming an effective barrier to
gaseous penetration.
PE liners are similar to PVC liners but are made of
polyethylene resins. These liners are tough, rigid, acid-
resistance, smooth and inexpensive.
Fiberglass reinforced plastic liners are manufactured in
a range of wall thicknesses and consist of a composite of
fiberglass and acid-resistant resin. The resins are specified
according to the degree of acid resistance required. The
composite has high mechanical and Impact strength and
good abrasion resistance. These liners can be
manufactured to a wide variety of shapes and are
applicable to sewers over 107 cm (42 in) in diameter.
These liners do not provide any structural support but
they do provide an adequatecorrosive barrier and smooth
lining for structurally sound sewers. These liners have
little absorption and no apparent permeability.
Fiberglass reinforced cement liners consist of cement
and glass fibers. They usually are 9.8 mm (0.385 in) thick
and are in thin panel form. They have high mechanical
and impact strength and good acid and alkaline resistance.
They are also highly resistant to abrasion with negligible
absorption and permeability. These liners are not designed
to support earth loads and should be used only in
structurally sound sewers. The liners can be easily
assembled to fit variations in grades, slopes and cross-
section. The smooth interior surface improves hydraulic
capabilities. These liners can be used in circular, oval,
rectangular and other sewer shapes above 107 cm (42
in) in normal size and can be segmented to fit the
diameter required.
80
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Table 6-12. Advantages and Disadvantages of Liners
Advantages Disadvantages
Material cost inexpensive
Liner materials have very
good acid resistance
No disruptions to traffic
as installation is performed
entirely in-line
Smooth surfaces provide
good hydraulics
Applicable only to man entry
size sewers (i.e., 76 cm [2.5 ft]
or greater)
Susceptible to leakage
due to number of joints
Timely to install. Thus
total project cost may be
uneconomical.
Prolonged bypass required
Surface preparation required
PE can crack in areas of
turbulent flow
Figure 6-6.
Detail of liners with anchors.
Extruded Anchors
9.5-mm High
Concrete Poured in Form
Flexible PVC Membrane
1.5-mm Thick
• O
81
-------
Tablo 6-13.
Advantages and disadvantages of liners as a sewer
rehabilitation technique are listed in Table 6-12.
6.8.2 Procedures and Equipment
Segmented plastic and fiberglass reinforced cement
liners are installed so they overlap at the joints and are
then attached to the concrete surface by anchor bolts or
nails. Space is left between the existing surface and the
linersforgrouting purposes. After athorough line cleaning
and dewatering, the segments are installed in 2.4-m (4-
ft) lengths which overlap at the joints, and the flanges on
the segments may be pre-drilled for filling by screws or
impact nail gun. Joints are coated with an adhesive to
better connect panels and are sealed with an acid
resistant resin. After all the panels are set in place, the
entire section is cement pressure grouted in place to
prevent sagging and deformation. Some liners are
installed in conjunction with the casting of concrete by
placing the liners against the inner surface of the form
prfor to pouring. Anchors become embedded in the
concreteduring curing, thereby securing the liner in place
(see Figure 6-6).1 Alternate installation procedures for
flexible PVC liners or ribbed sheets involve only grouting,
without anchor bolts or impact nails for attachment.
Installation of another type of liner requires an access pit
to fit the special winding machine that joins a male and
female PVC strip. This process is applicable to pipes up
to 76 cm (2.5 ft) in diameter. The latest liner installation
method uses an acid resistant mastic to fasten the sheets
directly to the sewer concrete surface. This technique
does not require grouting but requires thorough cleaning
prior to installation.
Liner failures can occur due to leaking joints that allow
H2S gas or sulfuric acid to penetrate the liner materials
and attack the concrete substrate beneath. Linerfailures
have also been reported in areas of high turbulence
where cracks developed. Cracking has been identified in
PE pipes and thus PE is not recommended in areas of
turbulent flows.
6.8.3 Costs
Table 6-13 gives approximate costs for rehabilitating
sewersbyliningthepipes with cement mortar orshotcrete
and Table 6-14 gives approximate costs for lining with
anchor liners. The costs in these tables are based on
costs taken from Utility Infrastructure Rehabilitation* and
were adjusted to current prices through the use of a cost
index. Costs were also verified by contacting vendors
and contractors.
6.9 Coatings
Rehabilitation Costs for Lining with Cement
Mortar and Shotcrete
Pipe 1984
Diameter ENRCCI=4144
(in)
Cement Mortar Lining
12
24
36
48
60
($/LF)
12-21
13-27
16-34
17-42
22-51
March 1991
ENRCCM773
($/LF)
15-25
15-30
20-40
20-50
25-60
Costs are for cleaning and lining only.
Valve rehab., bypass installation, pavement removal, etc., are not
included.
Costs are base contractor bids.
1983 costs are from Reference 3; 1991 costs based on 1983 costs.
Reinforced Shotorete Unit Costs
48 100-125
54 115-150
60 125-175
66 135-185
72 150-220
84 176-250
96 200 - 285
108 225-315
115-145
135-175
145-205
160-215
175-255
205-290
230-330
260-365
Based on minimum project size of 300 m (1,000 LF).
1983 costs are from Reference 3; 1991 costs based on adjusted 1983
costs.
Costs apply to circular and non-circular pipe.
Lower rates for existing pipe with good pipe alignment, no need for spot
repair, and no significant groundwater.
Higher costs for existing pipe with poor pipe alignment and some need
for groundwater dewatering.
Costs include cleaning of existing line; material, labor and equipment
for reinforced shotcrete placement; bypassing of wastewater;
restoration of up to 20 services; contractor mobilization and
demobilization; bonds and insurance.
Table 6-14.
Rehabilitation Costs for Lining with Anchors
Unit Costs for PVC T-Lock Uners
Item
Black: 4 x 8 ft sheet
White:4x8ft sheet
Anchor liner 4-ft W x 20-ft L
Anchor 25-ft W x 20-tt L
1/16-in thick -48x50 in
3/32-in thick -48x50 in
1/8-in thick -48x50 in
3/16-in thick -48x25 in
April 1989
ENRCCI=4577
($)
60.80/each
60.80/each
1.90/sqft
2.25/sq ft
220/roll
300/roll
400/roll
325/roll
March 1991
ENRCCI=4773
($)
65/each '
65/each
2/sqft
2.35/sq ft
230/roll
320/roll
420/roll • %
340/roll
Prices do not include primer and installation.
Prices do not include any site work.
1991 costs based on adjusted 1989 costs.
82
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Table 6-15. Advantages and Disadvantages of Coatings
Advantages Disadvantages
Table 6-16.
Costs for Rehabilitation Using Coatings
• Economical
No disruption to traffic or
other utilities
Most are fast curing, some
cure in less than one hour
Quick to apply
Can be applied to uneven
surfaces
Applicable only to man-entry
sewers and manholes
Surface imperfections-
pinholes, blowholes
Poor bonding to vertical
or overhead surfaces
Bypass required
Surface preparation
required
Few contractor inexperience
with products
Surface repairs often required
prior to application
St'll a developing technology
6.9.1 Description
Coatings include a myriad c-proprietary materials including
coal tar epoxy, concrete sealers, epoxy, polyester, silicone,
urethane, and vinylester that can be applied by spray
machines or brushed onto a concrete surface. They are
intended to form an acid resistant layer that protects the
substrate concrete from corrosion. Coatings have been
applied to sewer pipes and manholes since the 1960's,
with mixed success. The lack of success is largely due to
the specification of coating materials on the basis of
manufacturer claims without actual field testing1. As a
result of these findings, rehabilitation engineers are
recommending standard field testing of new products
prior to their use. Some of the advantages and
disadvantages involved with the use of coatings are
listed in Table 6-15.
6.9.2 Procedures and Equipment
Application of coatings usually includes the following
procedures:
• bypass of wastewater
• prepare/clean concrete surface
• allow concrete surface to dry
• apply coating by brush or spray (more than one coat is
usually necessary)
• allow coating to cure
• remove bypass.
April 1989
Item ENRCC1=4577
Agatapoxy (Epoxy)
Agatapoxy Gel (Epoxy)
Plasite (Epoxy)
Sancon (Urethane)
($/sqft)
9-19
7
5
9
March 1991
ENRCCW773
, ($/sqft)
9-20
7.50
5.50
9.50
Costs obtained from Report to Congress: Sulfide Corrosion in
Wastewatar Collection and Treatment Systems1.
1991 costs based on adjusted 1989 costs.
Most coatings can be brush or spray applied. Spray
application requires3,000 psi, which isdoublethe pressure
used for conventional airless spraying.
Spraying is excellent for coating uneven surfaces and is
much faster than brush application methods for some
products.
6.9.3 Costs
Approximate costs for various types of coatings are
shown in Table 6-16.
6.10 All Techniques for Manholes
6.10.1 Description of Materials, Equipment and
Products
Sewer manholes require rehabilitation to prevent surface
water inflow and groundwater infiltration, to repair
structural damage and to protect surfaces from damage
by corrosive substances. When rehabilitation methods
will not solve the problems cost-effectively, manhole
replacement should beconsidered. Selection ofaparticular
rehabilitation method should consider the type of
problems, physical characteristics of the structure,
location,condition, age and type of original construction.4
Extent of successful manhole rehabilitation experiences
and cost should also be considered.
Manhole rehabilitation methods are directed at either: (1)
the frame and cover, or (2) the sidewall and base. The
following is a summary of manhole and base rehabilitation
methods.4'5 Advantages and disadvantages for these
rehabilitation methods are presented in Table 6-17.
6.10.2 Description of Procedures
Manhole rehabilitation methods are directed at either: (1)
the frame and cover, or (2) the sidewall and base.
Manhole frame and cover rehabilitation prevents surface
water (storm water runoff) from flowing into the manholes.
83
-------
Tabto 6-17. Advantages and Disadvantages of Manhole and Sump Rehabilitation Methods'18
Method Advantages Disadvantages
FRAME ANO COVER
Stainless steel,
and neoprene washers
or corks In holes
fn covers.
Prefabricated ltd
Insert
Joint sealing tape
Hydraulic cement
Rates frame above
grade
Simple to install
When Installed properly It
prevents surface water, sand and
grit from entering manhole
through or around cover.
Simple tojinstafl
Provides strong waterproof
seal to stop infiltration
Minimizes inflow through
cover and frame.
Restricts natural venting
Requires perfect fit
for success.
Short service life.
Labor-intensive;
freeze thaw cycto may
reduce patch life.
Limited to areas outside of
street right-of-way.
S1DEWALLAND BASE
Epoxy or pdyurethane
coatings on Interior
Infiltration
Chemical grout
Structural liner
Hydraulic cement
Raise frame
SIDEWALL AND BASE
Epoxy or poryurethano
coatings on Interior
walls
Protects interior walls
against corrosion and
Can be very inexpensive
method for stopping
infiltration.
Provides structural
restoration; manholes requires
less disruption of traffic and
utilities than replacement;
longer service life than coatings.
Seals manhole frame in
place. Prevents infiltration
between frame and cone section.
Prevents surface water
inflow through manhole cover.
Protects wall from corrosion
and infiltration on structurally
sound manholes.
Requires structurally
sound and dry manhole surface walls
must be very dean prior
to application; short service life.
Short service life;
cannot predict amount of grout
required to eliminate infiltration.
Complex and easily installation
84
-------
Surface water from storm runoff, etc., can often flow into
the manholes through the holes in the cover lid, through
the annular space around the lid and the framed cover
and under the frame if it is improperly sealed. Manhole
frames and covers can be rehabilitated by the following
techniques:
• By installing stainless steel bolts with caulking
compound and neoprene washers or corks to plug
holes in the cover.
• By installing a prefabricated lid insert between the
frame and the cover. These plastic lids are resistant to
corrosion and damage by su If uric acid or road oils. The
lids come with gas relief and vacuum relief valves to
allow gas escape. They prevent water, sand, and grit
from entering the manhole. The lids are easy to install,
can fit any manhole, and require periodic maintenance
to function properly.
• By installing a resin based joint sealing tape between
metal frame and cover. The sealing tape provides
flexibility to seal imperfectly fitting surfaces and to
move with ground shifting. These sealing tapes can be
used for all types of manholes.
• Cracks and openings on the existing manhole/frame
seals are applied with hydraulic cement and
waterproofing epoxy.
• By raising the manhole frames to minimize flows
through the frame covers.
Manhole sidewall and base rehabilitation is primarily
done to prevent infiltration of groundwater. Casting or
patching can be used to rehabilitate structurally sound
sidewalls. Complete replacement should be carried out
for severely deteriorated manholes and bases. Manhole
steps also deteriorate frequently and they should be
replaced. Manhole sidewall and base rehabilitation can
be carried out by the following procedures:
• By applying epoxy, acrylic or polyurethane based
coatings to the interior wall of the manhole. These
waterproof and corrosion resistant coatings can be
applied to brick, block and precast concrete manholes
and bases. The coatings are applied by towel brush or
sprayer. Prior to coating application, the surfaces of
the manhole walls should be cleaned and all leaks are
plugged using patching or grouting materials.
• By applying chemical grout from interior walls to exterior
walls to stop infiltration through cracks and holes.
• By inserting structural liners inside existing manholes.
These liners are typically fiberglass of the reinforced
polyester mortar type.
6.10.3 Costs
Manhole rehabilitation costs are provided in Table 6-18.
Table 6-18. Rehabilitation Costs - Manhole Techniques
March 1991
Item ENRCCI=4773
($)
540-835/manhole
395-415/manhole
395-430/manhole
645-1,095/manhole
415-645/manhole
4,610 - 13,825/each
1,200-2,395/each
120-1,200/each
240 - 360/each
120-240/each
Chemical grouting*
Seal frames to corbels*
Chemically seal and plaster walls*
Raise manhole to grade*
Replace frame*
Insert structural liner*
Manhole replacement**
Manhole repair**
Raise manhole frame and cover**
Manhole cover replacement**
* Costs based on Reference 3, Dec. 1984(ENRCCI=4144)adjustedto
March 1991 (ENRCCI=4773).
** Costs based on Reference 2, Mid. 1974 (ENRCCM 991) adjusted to
March 1991 (ENRCCM773).
6.11 Service Lateral Techniques
6.11.1 Description
Service laterals are the pipes that connect building
sewers to the public sewer main. The service laterals
usually range in size from 7.5 to 15 cm (3-6 in) and are
often laid at a uniform slope from the building to the
immediate vicinity of the main sewer. They can enter the
sewer at angles of 0-90 degrees from horizontal. For
many years the effect of leaking service connections
were considered insignificant because it was assumed
that most service connections were above the water
table and therefore subject to leakage only during periods
of excessive rainfall or high groundwater levels. Recent
studies indicate that a significant percent of infiltration in
any collection system is the result of service connection
defects such as cracked, broken or open-jointed pipes.
Service connections may also transport water from inflow
sources such as roof drains, cellar and foundation drains,
basement or subcellar sump pumps, and storm water
flows from commercial and industrial properties. In a
national survey carried out by state and local agencies,
it was found that the estimated percentage of total
system infiltration from service laterals ranges from 30 to
as high as high as 95 percent in some cases.
6.11.2 Procedures and Equipment
Following are the procedures and equipment used for
rehabilitating service laterals:
Chemical Grouting: The following chemical grouting
methods are utilized:
85
-------
T«bl»$-18.
Service Lateral Rehabilitation Costs
Table 6-20.
Miscellaneous Additions I Rehabilitation Costs
Method
Unit Cost
Item
Sealing (test and seal by Joint)
SllptWog
Add two way dean out
Air test
Padal or entire lateral
Lateral connection to main
ExfKtraHon test
Partial or entire lateral
TV Inspection
Seal with chemical grout
Lateral connection to main
Remaining lateral
Replacement
Chemical Grouting
($/lateral)
1,980
1,730
450
75
200
75
200
650
590-
2,880
460-1,155
March 1991
ENRCCI=4773
• Costs based on Reference 3, December 1984 (ENRCCU4144)
adjusted to March 1991 (ENRCCI-4773).
Pump Full Method: Chemical grout is injected through
a conventional sealing packer from a sewer main into the
service connection to be grouted. The forced grout
surroundsthe pipe and a seal is formed afterthe gel has
set. Excessive grout is augured from the building sewer
and the sewer is returned to service afterthe sealing has
been accomplished.
Sewer Sausage Method: This method is similar to the
pump full method except that a tube is inverted into the
service connection before sealing to reduce the quantity
of grout to be used and to minimize the amount of
cleaning required afterthe sealing has been completed.
Camera-Packer Method:This method utilizes a miniature
TV camera and a specialized sealing packer which is
pulled out while it is simultaneously repairing faults that
are seen through the TV camera. The equipment is
House service pipe replacement
House service pipe repair
Roof leader drain disconnection
Foundation drain disconnection
Cellar drain disconnection
Area drain disconnection
Cross connection plugging
Drain from springs plugging
($)
•I ,440-2,875 each
480-960 each
120-180 each
720-2,875 each
120-840 each
120-840 each
240 -1,200 each
1,200-5,990
Costs based on Reference 2, Mid. 1974 (ENRCCI-1993) adjusted to
March 1991 (ENRCCI=4773).
Table 6-21. Sewer System Evaluation Survey Costs
March 1991
ENRCCI.4773
($/ft)
Physical Survey Costs 0.35 - 0.60
Rainfall Simulation
Smoke testing 0.35 - 0.75
Dyed water testing 0.60 -1.20
Water flooding 0.60-1.20
Preparatory Cleaning
(Pipe Diameter, in)
6
8
10
12
15
18
21
24
30
36
Internal Inspection
(Pipe Diameter, in)
6
8
10
12
15
18
21
24
30
36
0.75-2.65
0.60-2.15
0.75-3.15
0.85-4.10
0.95-5.05
1.20-5.40
1.70-8.40
1.95-10.20
2.75-13.20
3.50-16.30
1.10-3.00
0.85-2.90
0.75-2.75
0.75 - 2.90
0.75-3.15
0.85-3.35
0.95-3.75
1.20-4.20
1.35-4.80
1.80-5.30
Costs based on Reference 2, Mid. 1974 (ENRCCM 991) adjusted to
March 1991 (ENRCCM773).
86
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Table 6-22. Sewer Pipe Problems with Applicable
Rehabilitation Methods
Problem
Rehabilitation Method
1. Poor structural integrity
2. Significantly misaligned pipe
3. Additional sewer capacity needed
4. Most rehabilitation methods would
reduce sewer capacity to
unacceptable levels
5. Pipe is seriously damaged
6. Excessive infiltration in
non-pressure pipes
7. Leaking pipe joints which are not
badly offset or misaligned
8. Circumferential cracks
9. Small holes
10. Small radial cracks
11. Serious root problems
12. Severe corrosion
13. Damaged pipes under structures,
large trees, or busy streets
14. Problems in non-circular pipes
15. Mildly deteriorated structure
16. Corrosion; structurally sound;
diameters of 76 cm (2.5 ft) or
greater
17. Corrosive or acidic wastes
18. Pipes with misalignment or bends
a. Excavation and
replacement
b. Insertion
c. Some specialty concretes
a. Excavation and
replacement
a. Excavation and
replacement
a. Excavation and
replacement
a. Excavation and
replacement
a. Chemical grouting
sliplining CIPL, etc.
a Chemical grouting, CIPL
a. Chemical grouting
a. Chemical grouting
a. Chemical grouting
a. Sliplining, CIPL
a. Sliplining, CIPL
b. Cured-in-placs inversion
lining, sliplining
a. Cured-in-place inversion
lining, sliplining, coatings
a. Cured-in-place inversion
lining
a. Cured-in-place inversion
lining
a. Uners, CIPL
b. Coatings
a. Sliplining
b. Specialty concretes
c. Uners
d. Coatings
e. Cured-in-place inversion
lining
a. Cured-in-place inversion
lining
87
-------
removed and the service connection returned to service
after the repairs are completed.
inversion Lining: This technique is similarto the sewer
main installation in that it involves the insertion of a resin-
impregnated flexible polyester felt liner into the service
line. No annular space is created between the liner and
the pipe that might result in infiltration migration. No prior
excavations are required to correct slight offsets. An
access point is always needed on the upstream side of.
the service connection line. A variation from the sewer
main installation istheuseofaspecialpressurechamber
to provide the needed pressure to invert the fabric
materialsthroughthe service pipeline. Afterthe completion
of the curing process, the downstream end of the liner is
cut manually or via a remotely controlled cutting device
placed in the sewer main. The upstream end is trimmed
at the access point, restoring the sewer service.
6.11.3 Costs
Costs for rehabilitating service laterals are presented in
Table 6-19.
6.12 Miscellaneous Costs
6.12.1 Rehabilitation
There are miscellaneous rehabilitation costs which were
not covered by the other sections in this chapter. These
costs are based on costs taken from the Handbook for
Sewer System Evaluation and Rehabilitation* and are
presented in Table 6-20.
6.12JZ Costs for Preliminary and I/I Analysis and
SSES
Approximate costs involved in preliminary analyses, I/I
analyses, and SSES's are given in Table 6-21.
6.13 Matrix of Problems and Applicable
Corrective Measures
Table 6-22 lists common problems in sewer pipes with
applicable rehabilitation method(s) for each.
6.14 References
When an NTIS number is cited in a reference, that
reference is available from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
1. Report to Congress: Hydrogen Sulfide Corrosion in
Wastewater Collection and Treatment Systems.EPfiJ
430/9-91/009. U.S. Environmental protection Agency,
Office of Water, Washington, D.C. in preparation.
2. Handbook for Sewer System Evaluation and
Rehabilitation. EPA/430/9-75-021, Office of Water
Program Operations, U.S. Environmental Protection
Agency, Washington, D.C., 1975.
3: Brown and Caldwell. Utility Infrastructure
Rehabilitation. NTIS No. PB86-114642, Department
of Housing and Urban Development, Washington,
D.C., 1984.
4. American Public Works Association. Sewer System
Evaluation, Rehabilitation and New Construction: A
Manual of Practice. EPA/600/2-77/017d, NTIS No.
PB-279248. U.S. Environmental Protection Agency,
Municipal environmental Research Laboratory, Office
of Research and Development, Cincinnati, Ohio,
December 1977.
5. Existing Sewer System Evaluation and Rehabilitation.
ASCE Manuals of Reports on engineering Practice
No. 62, WPCF Manual of Practice FD-6, American
Society of Civil Engineers, Water Pollution Control
Federation, 1983.
6. American Public Works Association and Southern
California Districts Associated General Contractors
of California. Standard Specifications for Public Works
Construction.^ 991.
7. Structural Performance of NuPipe. Prof. Reynold K.
Watkins, Civil and Environmental Engineering, Utah
State University, Logan, Utah.
Additional Reading
Boyer, K.W. and V. Caballero. Rehabilitating Lakeland's
Western Trunk Sewer. Operations Forum: 17-19, July
1990.
Brennan, L.N., A.A. Doyle, R.C. Fedotoff, B.J. Schrock,
and M.P. Weber. Sewer System Rehabilitation Case
Histories. Presented at 58th Annua.l Conference of the
Water Pollution Control Federation, 1985.
Fernandez, R. B. Sewer Rehab Using a New Subarea
Method. Water/Engineering & Management 133:28-30,
February 1986.
Farmer, H. Sewer System Evaluation and Rehabilitation
Cost Estimates. Water & Sewage Works, April 30,1975.
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Farrar, R.R., K.R. Guthrie, and P.M. Hannan. Remote
Chemical Sealing of the Sewer House Lateral. No-Dig
1988, October 1988.
Hannan, P.M. Cured-ln-Place Pipe: An End User
Assessment. ASTM Buried Plastic Pipe Technology,
September 1990.
American Public Works Association. Control of Infiltration
and Inflow into Sewer System. 11022EFF 12/70, U.S.
EPA, Washington, DC, NTIS No. PB-200827 (1970).
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Glossary
U.S. EPA
SRF
CDBG
CG85
PL-92-500
NASSCO
ENRCCI
ASCE
WPCF
Rll
LF
PVC
CFR
SSES
CWA
H2S
O&M
NOAA
WSSC
BOD
S02
DO
NIOSH
OSHA
Service
PE
ASTM
FRP
RTR
T-Lock
Infiltration
Inflow
I/I
United States Environmental Protection Agency
State Revolving Funds
Community Development Block Grant
Construction Grants 1985
Public Law 92-500
National Association of Sewer Service Companies
Engineering News Record Construction Cost Index
American Society of Civil Engineers
Water Pollution Control Federation
Rainfall Induced Infiltration
Linear foot
Polyvinylchloride
Code of Federal Regulations
Sewer System Evaluation Survey
Clean Water Act
Hydrogen Sulfide
Operation and Maintenance
National Oceanic and Atmospheric Association
Washington Suburban Sanitary Commission
Biological Oxygen Demand
Sulfur Dioxide
Dissolved Oxygen
National Institute of Occupational Safety and Health
Occupational Safety and Health Administration
LineSewer pipes that connect building sewers to public sewers
Polyethylene
American Standards for Testing of Materials
Fiberglass Reinforced Polyester
Reinforced Thermosetting Resins
Trade name for Ameron Liners
The water entering a sewer system and service connections from the ground, through such
means as, but not limited to, defective pipes, pipe joints, connections, or manhole walls.
Infiltration does not include, and is distinguished from inflow.
The water discharged into a sewer system, including service connections, from such
sources, as but not limited to, roof leaders, cellar, yard and area drains, foundation drains,
cooling water discharges, drains from springs and swampy areas, manhole covers, cross
connections from storm sewers and combined sewers, catch basins, storm sewers, surface
run-off, street wash waters, or drainage. Inflow does not include, and is distinguished from,
infiltration.
The total quantity of water from both infiltration and inflow without distinguishing the source.
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I/I Analysis
Excessive I/I
Combined Sewer
SSES
Storm Sewer
Sanitary Sewer
Rehabilitation
Preparatory Cleaning
Internal Inspection
Physical Survey
Rainfall Simulation
An engineering and if appropriate, an economic analysis demonstrating possible excessive
or non-excessive I/I.
The quantities of I/I which can be economically eliminated from a sewer system by
rehabilitation, as determined by cost-effectiveness analysis that compares the costs for
correcting the I/I condition with the total cost for transportation and treatment of the I/I.
A sewer intended to serve as a sanitary sewer and a storm sewer, or as an industrial sewer
and storm sewer.
Asystematic examination of the tributary sewer systems or subsections of the tributary sewer
systems that have demonstrated possibly excessive I/I. The examination will determine the
location, flow rate and cost of correction for each definable element of the total I/I problem.
A sewer intended to carry only storm waters, surface run-off, street wash waters, and
drainage.
A sewer intended to carry only sanitary and industrial wastewatere from residences,
commercial buildings, industrial plants and institutions.
Repair workon sewer lines, manhole and other sewer system appu rtenainces that have been
determined to contain excessive I/I. The repair work may involve grouting of sewer pipe joints
or defects, sewer pipe relining, inversion an desliping, sewer pipe replacement and various
repairs or replacement of other sewer system appurtenances.
An activity of the sewer system evaluation survey. This activity involves adequate cleaning
of sewer lines prior to inspection. These sewers were previously identified as potential
sections of excessive I/I.
An activity of thesewer system evaluation survey. This activity involves inspecting sewer
lines that have previously been cleaned. Inspection may be accomplished by physical,
photographic and/or TV methods.
An activity of the sewer system evaluation survey. This activity involves determining specific
flow characteristics, groundwater levels and physical condition of the sewer system that had
previously been determined to certain possibly excessive I/I.
The activity of the sewer system evaluation survey. This activity involves determining the
impact of rainfall and/or run-off on the sewer system. Rainfall simulation may include dyed
water or water flooding of storm sewer sections, ponding areas, stream sections and ditches.
In addition, other techniques such as smoke testing and water sprinkling may be utilized.
* U.8. GOVERNMENT PRINTING OFFIC&1992-648-003/41821
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