Office Of Water
iT ., ...........
,ici*:1 * itii1"v.i's*.1 i
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ACKNOWLEDGEMENTS
This document was prepared by James Montgomery Consulting
Engineers, Pasadena, California, under EPA Contract 68-03-3429.
Arthur Condren was the Project Manager. Charles Vanderlyn was
the EPA Project Officer. Technical direction for the study was
provided by Lam Lim and Randy Revetta of the EPA Office of
Municipal Pollution Control and the members of the Rainfall
Induced Infiltration Study Workgroup. Their time and ;
contributions are gratefully acknowledged.
, NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency and approved for publication. Mention of.trade
names or commercial products does not constitute endorsement or
recommendations for use.
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RAINFALL INDUCED INFILTRATION
INTO SEWER SYSTEMS
REPORT TO CONGRESS
" /
August 1990
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TABLE OF CONTENTS ,
..'"•. •'..." • • •, • ' • • • • . '" . . Page
EXECUTIVE SUMMARY
Study Authorization and Objectives i
Background > ' ' i
. Findings and. Conclusions ' > • ii
Recommendations , , iv
DEFINITION vi?
CHAPTER 1 - INTRODUCTION
Study Authorization and Objectives 1-1
Study Approach . , .1-1
Report Organization , • 1-1
CHAPTER 2 - PROBLEM ASSESSMENT
Background . ' , 2-1
Definition of RII 2-3
Problems Associated with RII 2-4
Possible RII Pathways and Flow Response 2-5
Entry Points of RII into Sanitary Sewer Systems 2-9,
Factors Affecting RII .. 2-10
Case Studies \ 2-14
Summary ' : , 2-27
CHAPTER 3 - CONTROL METHODS
RII Field Investigation Techniques 3-1
Sewer Rehabilitation Methods 3-5
Design Standards and Construction Practices 3-9
RII Control Program Approaches 3-10
Cost Evaluation - 3-12
Institutional and Regulatory Approaches 3-15
Example RII Control Program - EBMUD . 3-17
Summary /.'•-.' ' 3-20
Recommendations 3-21
Appendix A - List of Abbreviations
Appendix B - References-
i ••.,', " "
Appendix C - Case Studies
Appendix D - •
Sewer System Rehabilitation Methods
Appendix E —
Design and Construction Standards
Appendix F - Cost Evaluation
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Executive Summary ,
STUDY AUTHORIZATION AND OBJECTIVES
This Report to Congress, required by Section 523 of the Federal
Water Quality Act of 1987 (Public Law 100-4), presents the results
of an Environmental Protection Agency (EPA) study of rainfall
induced infiltration (RID into municipal sanitary sewerage
systems. The following are .the objectives of the study:
o Study problems associated with RII. -
-.',' o Study appropriate methods to control RII into municipal
sanitary sewerage systems, including that of the East Bay
Municipal Utility District, California.
o Develop recommendations on, reasonable methods to reduce
'
BACKGROUND
The Clean Water Act (CWA) of 1972 clearly established the intent
of Congress to address problems associated with the entry of
extraneous storm water and ground water ( termed
infiltration/inflow, or I/I) into sanitary sewer systems. The CWA
mandated that all "excessive" I /I , be removed from a sanitary sewer
system as a condition for award of a construction grant for
wastewater treatment facility improvements. "Excessive" flow was
defined as that portion of the total extraneous flow that could be
cost-effectively removed. That is, the cost to eliminate the
excessive flow would be less than the cost to transport it in the
sewer system and provide wastewater treatment. .
Based on the requirements of the CWA, EPA developed guidelines, for
identifying extraneous flow, and specifically for determining what
portion of the extraneous flow was excessive. A key concept in
these guidelines was the distinction between "infiltration" and
"inflow." In general, infiltration was used to describe the long
term seepage of water into sewers through underground defects in
the system. Such seepage was not considered to be directly related
to recent storm events. Inflow was defined as water entering
sewers through direct connections', such, as cooling water from
commercial and industrial buildings, cellar or yard drains, or roof
downspouts connected to sanitary sewers .
In. the years following the enactment of the 1972 law, communities
throughout the country undertook sewer system rehabilitation
programs to remove the flow that had been categorized as excessive.
Flows were reduced in: a number of such systems, while in others the
anticipated flow decreases did not occur. One explanation of why
these programs failed to achieve the expected results is that
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Executive Summary
infiltration (which is generally difficult and expensive to
correct) may have been incorrectly identified as inflow, resulting
in an invalid or substantially overestimated assessment of the cost
effectiveness of correction. Such situations can occur when
extraneous flows enter the sewer system through traditional
infiltration points, but produce a peak flow response similar to
that of inflow. •
In 1987, Congress asked EPA to investigate this problem. We
conducted case studies in 10 cities or sewer districts. These
studies attempted to gather information on: an appropriate
definition of rainfall induced infiltration (RII); the
characteristics of RII; the problems associated with RII; the
pathways and entry points into the sewer system; and the major
factors which influence the occurrence of RII. Data on methods to
control or correct RII were obtained from the 10 case studies and
augmented through a review of the pertinent literature.
FINDINGS AND CONCLUSIONS
The findings and conclusions of the study are grouped into two
sections, corresponding to the first two study objectives: to
assess the problems associated with RII, arid to study methods of
RII control. ,
Problem Assessment
The major findings and conclusions of the study with respect to
the characteristics of, and problems associated with, RII are
listed below:
* ' *
o RII 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.
o Because of its flow characteristics, RII has been
misidentified as inflow in many cases. Consequently,
rehabilitation programs have not achieved the anticipated
reductions in extraneous flows.
o RII appears to represent a significant portion of the flow
to sewage treatment plants during wet weather periods. In
the 10 case studies the peak wet weather flow ranged from
3.5 to 20 times the a.verage dry weather flow. The
contribution from RII was estimated to be between 60-90
percent of the wet weather flows. The remainder is
"traditional" groundwater infiltration and inflow.
o Collection and treatment systems typically do not have
the capacity to handle peak wet 'weather flows. Peak
flows, therefore, can cause backups into buildings,-
ii
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Executive Summary
overflows ;and treatment system bypasses. . Such occurrences
-are a hazard to public health or a violation of the
municipality's discharge permit. . >
o Sewer.trenches 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 defectiye points.
o The shallow portions of a collection system (building
laterals and their connections, sewer mains, manhole
defects and foundation drains) are more vulnerable to RII.
Interceptors, which are typically deeper, do not appear to
•' be a significant, entry point.
o The extent of RlI in a sanitary sewer .system is related
to design, construction, climate, geology and degree of
maintenance. ' ;
RII Control Methods
RII control means the 'implementation of measures to reduce existing
RII flows or limit future RII into a sewer system. RII control can
be accomplished through various means, including physical
rehabilitation of the sewer system, improved design standards and
construction practices, preventive maintenance, and institutional
.and regulatory approaches. The major findings and conclusions of
the study with respect to the various methods and approaches for
RII control are: •:',:'
o Accurate field ,investigations and data .analyses are
, important for developing an effective RII control program.
The first step in developing an effective control program
is to accurately identify and quantify RII in the sewer
system, and to distinguish RII from other I/I components.
The traditional I/I field data collection techniques.
commonly in use can be successfully used for RII
investigation as long as the techniques are properly
applied and the data correctly interpreted. For example,
; flow monitoring sites should not be influenced by severe
pipe constrictions, and hydraulic_ conditions must be
considered in interpreting flow monitoring results.
o Many methods -are available for rehabilitation of sewer
systems to reduce RII. - '
Pipeline rehabilitation methods 'include in-place
techniques,, such as grouting and lining, as well as
replacement by excavation or, trenchless installation
methods. The suitability of different methods for
correcting RII. problems depends upon cost, extent of
111
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Executive Summary
problem, arid site-specific physical conditions, including
the condition of the existing pipes.
Manhole rehabilitation techniques include both interior
and exterior repair methods. Many of these methods are
specifically designed to eliminate RII which seeps into
pavement cracks and enters the sewer system through
manhole frame and chimney defects.
.The traditional approach to determining the cost
effectiveness of sewer system rehabilitation to reduce
extraneous flows evaluates each inflow source or defective
sewer component on an individual basis. This traditional
approach can overestimate the amount of flow reduction
achievable from rehabilitation because it fails to acc.ount
for the migration of water to defects that are left
unrepaired.
A comprehensive program of sewer system rehabilitation
that includes both the public and private portions of the
system can be effective in reducing RII, although
sometimes at considerable cost. If the private portion
is not included, a significant portion of the RII may not
be addressed. Water may also migrate to unrepaired
defects in public portions of the system, thereby reducing
the effectiveness of the rehabilitation effort.
RECOMMENDATIONS
o The specific analysis of RII should be included as part
of overall I/I evaluations. Guidelines should be
developed to ensure the proper application of field
techniques and interpretation of data to identify and
evaluate RII.
o The following considerations should be incorporated into
the development of sewer system rehabilitation programs
and evaluation of the cost effectiveness of
rehabilitation:
- Addressing entire areas of the sewer system versus
repair of individual defects only. .
- Including both the public and private portions of
the sewer system versus only the public portion.
o Long-term control of RII should be ensured through
implementation of an effective preventive maintenance
program that includes:
-^ Periodic flow monitoring in the system to identify
areas with increases in RII levels.
iv
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Executive Summary
- A routine program of cleaning and root removal;
A cyclic program of testing and inspection .of the
, sewers throughout the system to identify the need
for repairs and replacement. '
Sewer design standards should be modified to provide a
cost-effective means to minimize future RII into new or
rehabilitated sewers by controlling the development of
extraneous water in sewer trenches.
Effective sewer construction practices should be followed
by: ' • ' •.'/.• ' . - ; ' '..-'"•-.•.'••
- Rigorous construction inspection.
Effective performance testing for public sewer mains
as well as private laterals. , ..-'•=•
The institutional and regulatory framework governing the
construction and maintenance of house laterals (the
connection between the house or building and the collector
sewer in the street .or other public right-of-way) should
be re-examined. Possible options include:
Shifting responsibility for construction and/or
maintenance of house laterals from the home owners
to the municipality.
-. Municipal programs to help home owners pay for
maintenance and repairs of house laterals.
State or municipal ordinances, with appropriate
enforcement provisions/governing inspection, testing
and repair of house laterals.
- \_ Public education programs to inform citizens of the
importance of excluding extraneous flows from . the
• municipal sanitary sewerage systems.
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DEFINITION
A number of closely related phenomena are discussed
throughout this report. For the convenience of the reader, short
definitions of these phenomena and the acronyms used in the report
are included below. Also included are schematic drawings and
graphs to help the reader visualize these phenomena.
Inf litration
Water other than wastewater that enters a sewer system
(including sewer service connections and foundation drains) from
the ground through such means as defective pipes, pipe joints,
connections, or manholes. Infiltration is typically not
intentional and occurs by seepage through defects in the system.
The contribution of foundation drains is considered as infiltration
due to its rate and duration characteristics even though it is an
intentional contribution to the system. Total infiltration is
composed of Rainfall Induced Infiltration and Ground-Water
Infiltration.
Rainfall Induced Infiltration (RID
RII is a particular form of infiltration which behaves like
and is sometimes confused with storm water inflow. RII generally
occurs during and immediately after rainfall events and it is
believed to be caused by the seepage of percolating rainwater into
defective pipes (in many cases service connections or laterals)
which lie near the ground surface. These circumstances cause a
large portion of the rainfall to enter the system relatively
quickly and the extraneous flow lasts only a short time after the
rainfall episode is over. The combination of these factors causes
RII to be of relatively short duration and high intensity as
compared with typical infiltration which is generally constant in
intensity and of longer duration.
Ground-Water Infiltration (GWI)
GWI results from the movement of ground water in the saturated
zone into the sewerage system through defects in the components of
the sewer system located below the water table. GWI is relatively
constant and is generally not significantly affected by rainfall
events (except, where the ground-water is near the sewer pipe).
Inflow
Water other than wastewater that enters a sewer system
(including sewer service connections) from sources such as roof
leaders, cellar drains, yard drains, drains from springs and swampy
areas, manhole covers,, cross connections between storm sewers and
sanitary sewers, catch basins, cooling towers, storm waters,
surface runoff, street washwaters or drainage. Inflow is generally
easier to locate and eliminate from the system than infiltration
because it enters from specific points that can be identified and
closed off.
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DEFINITION
Storm Water Inflow (SWI)
SWI is generally the result of intentional diversion of storm
water into sanitary sewers. These connections are usually easy to
identify and correct. The pattern that they follow is a prompt
response which mirrors the rainfall event, followed by a quick
decrease as the event stops. An example of SWI is roof downspouts
which are connected to a sanitary sewer line.
Dry Weather Inflow (DWI)
DWI is the result of extraneous contributions to the flow of
the sewer, /which are not caused by rain. Some examples are water
from street washing that enters manholes through the holes in the
covers, cooling water for industrial and commercial applications,
and some car washing activities. ,
• . '! . ' . . . . -
Inf i Itrat ion/inflow if I/I)
This is the combination of all the extraneous contributions
to the sewer system. I/I is equal to RII + GWI + SWI + DWI (see
graph). ,, •
VI1
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a.
s
~1 PRECIPITATION
INFLOW (SWI)
o
INFILTRATION (Rll
RAPID Rll RESPONSE
LESS RAPID Rll RESPONSE
X- •
TOTAL I/I (SWI
Rll + GWI)
TOTAL I/I WITH
RAPID Rll RESPONSE
TOTAL I/I WITH
LESS RAPID Rll RESPONSE
TIME
TYPICAL EXTRANEOUS FLOW HYDROGRAPHS
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SCHEMATIC FOR SEVERAL
TYPES
OF EXTRANEOUS
WATER INTO
SEWERS
Rl
EXTRANEOUS WATER
INFILTRATION
•GWI-
INFLOW
SWI
DWI
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CHAPTER 1
INTRODUCTION
STUDY AUTHORIZATION AND OBJECTIVES
Section 523 of the Federal Water Quality Act of 1987 (PL 100-4)
requires that the U.S. Environmental Protection Agency (EPA)
conduct a study and submit a report to Congress concerning rainfall
induced infiltration (.RID into sanitary sewer systems. The
specific requirements of Section 523 were to:
. - \ '•.'•' ' " ' • • • • :
o Study problems associated with RII.
o Study appropriate methods to control RII into sanitary
, sewer systems, including that of the East Bay Municipal
Utility District (EBMUD), California.
o Develop recommendations on reasonable methods to reduce
RII. ; . . ' ' . ' ' - \ '.''"'
STUDY APPROACH !
An approach was developed to accomplish the goals of the study,, as
follows: ' ' . .'• • • , •',:-" ' / • • ••'.•',.•-.
o Establish a definition of RII. .•_."'.'•
b Identify sewer systems in the United States which
, experience RII, and document the characteristics of and
problems associated with RII in those systems.
b Conduct a literature search of applicable methods for
controlling the entry of RII into sanitary sewer systems.
o Conduct an evaluation of the costs of various approaches
to control RII. .
o Develop recommendations on appropriate methods and
approaches for RII control.
REPORT ORGANIZATION
The report is divided into several chapters and appendices. This
chapter briefly describes the study objectives and approach.
Chapter 2 presents an assessment of the RII problem, including the
definition and characteristics of RII,, a discussion of the problems
associated with RII, and the presentation of ten case studies of
sanitary sewer systems identified as experiencing RII. Chapter 3
discusses methods and approaches for controlling RII. The
1-1
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introduction
appendices contain more detailed descriptions of the case studies,
further information on rehabilitation methods and design standards
for RII control, and a detailed discussion of the RII cost
evaluation conducted for this study.
1-2
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1 CHAPTER 2
PROBLEM ASSESSMENT
This chapter discusses the characteristics of and problems
associated with rainfall induced infiltration (RII) into sanitary
"sewer systems. Included are a definition of RII; a discussion of
the typical problems associated with RII; a description of possible
pathways by which rain can be rapidly transported from the ground
surface to where It enters a sanitary sewer system; a discussion
of the types of defects and connections through which Rll'may enter
a sewer system; an assessment of the key factors which may be
important for explaining the potential for RII occurrence in
specific sewer .systems; and a summary of RII case studies.
BACKGROUND
The entry of extraneous water into sanitary sewer systems has been
recognized for many years as a significant problem in communities
throughout the cpuntry. This ^extraneous water, termed infiltration
and inflow (I/I), consists of groundwater and'storm water which
enter the sewer system through defects in pipes and manholes and
through direct connections to the sewer system. When present in
excessive amounts, I/I can cause wastewater, overflows and bypasses
from manholes and pump stations, bypassing and/or inadequate
processing of wastewater at treatment plants, and flooding of
building basements with wastewater. •
The need to address excessive I/I was dictated in the Federal Water
Pollution Control Act Amendments of 1972 (PL.92-500). Under this
law, Congress mandated that all "excessive" I/I be removed from a
sariitary sewer system before a construction grant for wastewater
treatment facility improvements could be awarded. EPA has
interpreted "Excessive" I/I as that portion of the total I/I which
could be cost-effectively removed, i.e. , the cost for removal would
be less than the cost for transport and treatment of the
"excessive" I/I flows.
, ": • ' ' - ' '
In the years immediately following the enactment of the 1972 law,
the EPA developed guidelines for conducting I/I cost-effectiveness
analyses and sewer system evaluation surveys (SSESs) to. identify
excessive I/I (Appendix B). EPA regulations at 40 CFR Part 35
define, the terms "infiltration" and "inflow" as.follows:
Infiltration. Water other than wastewater that enters a sewer
system (including sewer service connections and foundation
.drains) from the ground through such means as defective pipes,
pipe joints, connections, or manholes. Infiltration does -not
include, and is distinguished from, inflow. .
2-1,
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Problem Assessment
Inflow. Water other than wastewater that enters a sewer
system (including sewer service connections) from such sources
as, but not limited to, roof leaders, cellar drains, yard
drains, area drains, drains from springs and swampy areas,
manhole covers, cross connections between storm sewers and
sanitary sewers, catch basins, cooling towers, storm waters,
surface runoff, street wash waters, or drainage, inflow does
not include, and is distinguished from, infiltration.
In general, the understanding of infiltration was that it entered
the sewer system indirectly via groundwater seepage into
underground sewer defects, whereas inflow was rainfall runoff
entering through direct connections. An exception to this
generalization was later made when directly connected foundation
drains were reclassified as infiltration rather than inflow, thus
recognizing the sustained flow contribution of foundation drains
in areas of high groundwater.
The EPA guidelines described procedures for separating and
quantifying infiltration and inflow by use of flow data.
Specifically, infiltration was calculated as the difference between
total flow and estimated wastewater input on non-rainfall days.
Inflow was calculated as the difference between the total flow
during a large storm event and the total flow on the nearest non-
rainfall day. Thus,, in practice, the term "inflow" came to be
synonymous with short-term, rain-induced I/I. The EPA guidelines
acknowledged that both infiltration and inflow are affected by
rainfall, but that it was not possible to precisely quantify
infiltration and inflow in accordance with their literal
definitions. As a result, it was concluded that the accuracy
levels of the calculated values were adequate for estimating that
portion of the I/I which might be considered excessive.
Subsequently, communities throughout the country conducted I/I
analyses and SSESs using the EPA guidelines, and many undertook
sewer system rehabilitation programs to remove the I/I that had
been categorized as excessive. While I/I flows were reduced in a
number of such systems, in others, the anticipated flow decreases
did not occur. One possible explanation of why these programs
failed is that infiltration may have been incorrectly identified
as inflow. This can happen when water infiltrates into the sewer
system through pipe and manhole defects, but produces a peak flow
response similar to that of inflow from direct connections. Inflow
connections can typically be eliminated at a lower cost (per unit
of flow removed) than can defects in pipes and manholes.
Therefore, if flows due to infiltration are incorrectly identified
as being due to inflow, an invalid or substantially overestimated
assessment of the cost effectiveness of I/I correction may result.
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Problem Assessment
One wastewater .system with extremely high rain induced extraneous
flows is the East Bay Municipal .Utility District (EBMUD) in
California, which includes the City of Oakland and six adjacent"
communities. During large rainfall events, the EBMUD system can
experience flows as high as twenty (20) times the average dry
weather flow. As a result,, peak flows exceed the conveyance
capacity of the sewer system, causing overflows onto city streets
and bypasses of untreated wastewater to San Francisco Bay.
To address these problems, EBMUD and its tributary communities
undertook extensive studies to identify and quantify the.rainfall
induced extraneous flows in their sewer system. The goal of these
studies was to develop a regional plan to eliminate peak flows that
could cost-effectively be reduced, and then-to adequately process
the remaining volume of wet weather wastewater.
The comprehensive I/I study conducted by the EBMUD communities
coneluded that only a small fraction of the high peak flows
occurring during rainfall events could be attributed to direct
inflow. The majority of the rainfall induced flow was .attributed
to infiltration, and was called "rainfall dependent infiltration"
in the EBMUD studies. Thus, EBMUD became the impetus for the study
on rainfall induced infiltration called for under the 1987 Water
Quality Act. . ' >
DEFINITION OF RII
For 1the purpose of this report, we have defined rainfall induced
infiltration,(RII) as follows:,
Rainfall Induced,Infiltration. RII is a particular form of
infiltration which behaves like and is spmetimes confused with
storm water inflow. RII generally occurs during and
immediately after rainfall .events and it is believed to be
caused by the seepage of percolating rainwater into defective
pipes (in many cases service connections or laterals) which
lie near, the ground surface. These circumstances cause a
large portion of the rainfall to enter the system relatively
quickly and the extraneous flow lasts only a short time after
the rainfall episode is over. The combination of these
factors causes RII to be of relatively short duration and high
intensity as compared with typical infiltration which is
generally constant in intensity and of longer duration.
Rainfall induced infiltration can be distinguished from "classical"
infiltration because it results in a peak flow response in sanitary
sewer systems which may be'indistinguishable from that of direct
storm water inflow. For the purposes of the discussion in this
report, the long-term, sustained classical type of infiltration
will be described by the term "groundwater infiltration" (GWI).
"Storm water inflow" (SWI) will be used as the term for direct
2-3
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Problem Assessment
inflow as defined by EPA. Both GWI and RII are forms of
infiltration, as described by the EPA definition, but differ
primarily in their flow response.
The distinctions between SWI, GWI, and RII are illustrated by the
hydrographs in Figure 2-1. As shown in the figure, SWI produces
a rapid, peak flow response to rainfall which recedes quickly after
the rainfall stops. Rainfall may also produce a net increase in
the sustained GWI flow rate, as shown in the figure. RII response
may be as rapid as that of SWI, or may include a delayed response
which lags the peak rainfall intensity by several hours and then
recedes slowly. In most sewer systems, the RII response is likely
a continuum from a rapid peak flow to a more gradual, prolonged
response similar to GWI. Therefore, the separation between the.RII
and GWI portions of the hydrograph may not be well-defined. RII
becomes most significant when the type of flow response is more
like inflow, i.e., it results in a rapid and high peak flow in the
sanitary sewer system.
PROBLEMS ASSOCIATED WITH RII
The problems associated with RII are those due to the high peak
flows which occur during and immediately following rainfall.
Typical RII problems include wastewater overflows and bypasses from
manholes and pump stations in the sewer system, and flooding of
building basements. Wastewater backing up into homes or
overflowing into city streets is a hazard to public health and, in
most cases, is a clear, violation of the discharge requirements of
the sewerage agency. Additionally, wastewater bypassed to drainage
channels may result in water quality degradation in downstream
surface waters. If the flows reaching the wastewater treatment
plant are much higher than the plant's capacity, deliberate
bypassing may be necessary to avoid hydraulically overloading the
plant. At very high plant flows, inadequate wastewater treatment
and inability to meet discharge requirements may result. In all
cases, excessive RII flows result in increased operation and
maintenance costs for transport and treatment.
An ancillary problem associated with RII is that there is the
potential for exfiltration of untreated sewage at these same pipe
and manhole defects. This problem is especially likely to manifest
itself when the sewer pipe is above the water table. In -some
cases, discharged sewage may cause ground-water contamination; in
other cases it might be channelled by sewer trenches to potential
points of direct human exposure.
The peak nature of flows due to RII, and the magnitude of these
flows in some systems, means that wastewater collection, transport,
and treatment facilities must be designed for capacities that
greatly exceed normal peak dry weather flows. Thus, very large
capital expenditures may be required to construct, facilities that
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a.
ui
o
n PRECIPITATION
INFLOW (SWI)
O
o
o
INFILTRATION (Rll,+ GWI)
RAPID Rll RESPONSE
LESS RAPID Rll RESPONSE
TOTAL I/I (SWI •+.- Rll -i- QWI)
TOTAL 1/1 WITH
RAPID Rll RESPONSE
TOTAL I/I WITH
LESS RAPID Rll RESPONSE
TIME
FIGURE 2-1
TYPICAL EXTRANEOUS FLOW HYDROGRAPHS
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, Problem Assessment:
can handle the RII flows. Funding for such construction may be
difficult, if not impossible, to obtain. Similarly, system
capacity that might otherwise be available for future growth must
be used for RII. In systems with severe capacity limitations and
problems due to RII, building moratoriums may be necessary to
restrict further increases in wastewater flows.
' > / ', •-•".••' • • • ,i
The alternative to providing excess system capacity to handle high
RII flows is to reduce RII through sewer system rehabilitation.
However, as will be discussed in more detail later in this report,
achieving substantial RII flow reductions throu'gh rehabilitation
can be very difficult and costly. Part of this problem is due to
the fact that in many areas, a significant portion of RII may
originate on private property (from building laterals and
foundation drains). Many communities have invested considerable
sums of money (both under local programs and with state and federal
funding) in rehabilitation programs that have proven ineffective
in reducing I/I flows. The failure of many of these programs has
been due in part to the failure to properly, identify RII as the
major component of I/I, and to implement an adequate program for
RII control. .'.-.. .-.'';•
As noted previously, RII has been identified as the primary cause
of wet weather problems in the EBMUD wastewater system. During
large storms, overflows occurred at over 175 locations within the
community collection systems and about ten times each year from one
or more of seven shoreline bypass points on the District's major
interceptor sewer along San Francisco Bay. To eliminate these
problems and comply with discharge requirements, EBMUD and its
tributary communities have had to initiate a major program of sewer
system rehabilitation and construction of facilities, to handle wet,
weather f lows,'at a cost of over $600 million. The section on Case
Studies, presented later in this chapter describe the problems
associated with RII in nine other sewer systems throughout the
.country. .,, ;
POSSIBLE RII,PATHWAYS AND FLOW RESPONSE
Storm, water may reach sewer system openings through different
pathways/from the ground surface. The resulting RII flow response
will vary depending upon the type and length of the pathway that
the water follows. Factors.such as the characteristics of the
soils, geology, groundwater, topography, and trench backfill
materials will influence the speed of the flow response. A very,
rapid response would bejexpected in situations in which the RII
pathway is more like a direct channel to the sewer entry point.
A slower response would be expected in cases where the permeable"
backfill material in the sewer trench acts as a drain for the water
in the surrounding soil. '',':
2-5
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Problem Assessment
Some possible pathways scenarios which may help explain how and why
RII occurs are described below. While these pathways present
different conceptual models of RII, they are not necessarily
mutually exclusive. RII in any particular sewer system may result
from a combination of several different scenarios.
Soil Channels
Storm water may reach sewer defects through "channels" in the soil,
as illustrated in Figure 2-2. The channels may be large enough to
be called "holes," or may simply be continuous "macropores" from
the ground surface to the system defect. The channels may be
created by soil fauna such as worms or rodents, or by plant and
tree roots. In clay soils with high shrink/swell capacities,
surface_cracks may open which extend to the sewer trench. With
each rain, the percolating water may gradually enlarge the above
described holes, macropores, or cracks.
It is also likely that soil channels within the pipe trench form
via a similar erosion process by water which exfiltrates from leaky
pipe joints and defects, and then infiltrates back into the system
during low flow periods. Such joint-to-joint channels have been
observed around excavated pipes, and also are evident where grout
injected into a pipe joint reappears at another nearby joint.
Flow response in the sewer system due to water movement through
soil channels would vary depending upon the size of the channels,
the distance the water must travel to a sewer defect, and the
surface characteristics of the ground. In particular, for a rapid
response to occur (i.e., faster than the natural transmission rate
of water through the soil),- the soil channels qr pores would have
to be large enough to overcome capillarity (pore diameters of at
least 3 to 4 mm). The length of the soil channel (distance from
the ground surface to the RII entry point) would also impact the
speed of the RII response, with shorter channels, such as those to
shallower sewers, producing faster response times. Where the
surface characteristics are such that the ground over the channel
forms a natural depression for surface runoff collection, the soil
channels would act like direct inflow connections, conveying
surface water rapidly to defects in the pipe.
Shallow Impermeable Strata
Where a shallow, relatively impermeable soil layer or bedrock
exists, rainfall percolating into the soil may create'a perched
water table, as shown in Figure 2-3, and may be carried rapidly to
sewer trenches as the groundwater level rises in response to
rainfall. RII response under this scenario may vary from rapid
(i.e., similar to SWI) to gradual (i.e., similar to GWI), depending
upon the depth and permeability of the overlying soil, the slope
2-6
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Problem Assessment
of the impermeable strata, and/or the extent to which the sewer
trenches penetrate the impermeable material.
French Drain Effect
In some situations, a sewer trench may act like a French drain, an
underground passage for water constructed of material that is
"looser" (more permeable) than the surrounding soil. This
condition would occur where the sewer'trench bedding and backfill
is composed of granular material (sand and/or gravel). As
illustrated in Figure 2-4, the sewer trench would thus provide a
conduit for water from the surrounding .soil. If the surrounding
soil becomes saturated because of rainfall, the sewer trench may
drain the water, resulting in a rise in the transient water level
in the trench. As the static... water pressure over the pipe
increases, the rate of RII into pipe defects will also increase.
.The RII response, will typically be more gradual than that of SWI
or "rapid" RII from soil channels. The French drain effect in a
sewer trench may be accentuated by other pipe trenches crossing or
intersecting the sewer trench1 , . , . • •
Entry from Ground Surface into Sewer Trench Backfill >
If trench backfill material is more permeable than the surrounding
soil and extends to the ground surface, it may provide an area for
rainwater, on the ground surface to more easily infiltrate the
trench, as illustrated in Figure 2-5. Any network of
interconnected utility trenches can convey the water to the
sanitary sewer trenches, typically the deepest utility, and to
defects in the sewers. The RII flow response under this scenario
would depend upon the runoff characteristics of the surface,
surface topography, adequacy of existing storm drainage facilities,
extent of the underlying trench network, depth of pipes, and, type
of trench backfill materials. Where slopes are steep and trenches
are located in natural depressions (as is common for sewer
.trenches), RII flow response in the system could be rapid. in
other situations, the response time could be more gradual.
A similar phenomenon may occur in cases where the sanitary sewer
pipe parallels or crosses under surface drainage ditches. Storm
water quickly co.llects and fills the ditches and infiltrates
downward to the sewer pipe. In the extreme case, the sewer pipe
may be installed directly under the entire length of a drainage
ditch, resulting in rapid infiltration into the backfilled trench.*
Storm Drain Exfiltration ' -
\ _ - .
Where sanitary sewer mains or laterals parallel or cross under
storm drain trenches, water may exfiltfate from leaky storm sewers
or storm laterals and then infiltrate into the sanitary sewer pipe.
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Problem Assessment:
as shown in Figure 2-6. Channels through the soil will gradually
form between defects (exfiltratiqn points) in the storm drain and
defects (RII entry points) in the sanitary sewer. Since the
stormwater would initially be conveyed very quickly from the
surface to the exfiltration points in a ' storm drain, the RII
response .could be fairly rapid. In the extreme case, the storm
drain or. lateral may be installed in a common trench with the
sanitary sewer pipe and backfilled with permeable material,
resulting in a very short indirect cross-connection between the two
pipes. . .
.Subsurface Seepage
When streets are flooded during rainfall, water can seep into
cracks in the pavement and travel laterally underneath the pavement
to the upper portions of manholes, as shown in Figure 2-7. The
water can enter the manholes through defects, typically between the
manhole frame and chimney. Subsidence of trench backfill
'materials may cause channels to form between the pavement and
street subbase. The street subbase, which is typically highly
permeable material,: could also function as a horizontal lens to
direct the flow of water. Channels between the pavement cracks and
manholes would gradually form through erosion. The RII flow
response would be fairly rapid because the defects are located
close to the ground surface, and horizontal water movement is
prompted by street subbase material or channels. This pathway
appears to be more common where freeze/thaw cycles occur in cold
climates; both the cracks in the pavement and the openings between
the manhole frame and chimney may be caused by such freezing and'
thawing of the ground.
Foundation Drains -
Where foundation drains are used to lower the permanent or seasonal
groundwater level from around building foundations, direct
connections of the drains to the sewer system may exist, as
illustrated in Figure 2-8; The foundation drains may contribute
GWI during non-rainfall periods, but flow response may increase
significantly during periods of-,rainfall. The magnitude and speed
of the response would depend on lot slope, direction of surface
drainage in relation to the building, location of downspout
discharges, arid permeability of the backfill materials next to the
basement walls and drains. , •
tee and Molzahn utilized a computer groundwater model to simulate
the flow response in foundation drains from rainfall. .The model
demonstrated that foundation drains could produce a peak flow
response that correlated more to total storm rainfall volume than
to rainfall intensity. Rainfall simulation and wet weather flow
measurements for foundation drains from other studies also
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Problem Assessment
indicated that foundation drains can produce a peak flow response
within one hour of rainfall.
ENTRY POINTS OF RII INTO SANITARY SEWER SYSTEMS
Extraneous water enters a sanitary sewer system through various
types of openings. Infiltration entry points include defects in
pipes and service laterals (cracks> holes, open or offset joints,
defective pipe connections; etc.) and similar defects in. other
structures such as manholes and cleanouts. Foundation drain
connections to sanitary sewer building laterals are also defined
as infiltration entry points. Infiltration entry points are RII
entry points whenever rainfall produces a significant, short-term
increase in the 'flow of .extraneous water. The various types of RII
entry points are illustrated, in Figure 2-9. ,. •
RII should not exist in a water-tight sewer system, i.e., a system
where there are.no openings for extraneous water to enter. No
sewer system, is expected to be completely water-tight; even new
systems today are designed with a minimal allowance for
infiltration. However, .many; systems, both old and new, have
developed numerous defects which allow .excessive amounts of
extraneous water to enter. Typical RII entry points are described
below.,
Pipe Defects '
Sewer systems.installed in this country prior to about 1960 often
have numerous defects. These defects are due to both poor
construction practices and the materials that were used for
construction. The short pipe lengths (two to three feet) Installed
in most older sewers resulted in many joints in the sewers.
Specific problems have resulted because of:
o Low tensile strength of the pipe.
O High porosity of pipe materials.
o Hydrogen sulfide corrosion damage to concrete pipes.
o Cracking around the pipe bells due .to the joint rigidity.
o Deterioration of the joint materials.
Better quality pipe and joint materials have come into widespread
use since the 1960s. These include less porous, higher strength
pipe, which is installed with flexible joints, as well as flexible
pipe materials which come in longer pipe, lengths ,(hence fewer
joints). -Use of low pressure air testing for determining the
acceptability of newly constructed sewers .has accelerated the
transition to use of better pipe materials and has helped improve
the quality of sewer construction. ,.
2-9
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. Problem Assessment
Poor construction practices, both in old and new pipe
installations, have also contributed to pipe defects. These
include:
o Inadequate pipe bedding and poor backfill material
compaction.
o Damage caused during construction of crossing utilities.
o Service lateral "hammer tap" connections.
o Unused, unplugged wye connections installed with the
original sewer main.
In addition, external forces such as traffic loads, ground
movement, and root intrusion also generate defects that become
points of entry for RII.
Service laterals typically suffer from the same types of defects
as sewer mains. However, the problems may be accentuated by the
fact that the laterals are typically shallower, have shorter pipe
lengths, are more subject to root intrusion, and are generally
installed by less experienced contractors and subject to minimal
testing or inspection. Often, laterals are broken into for
cleaning purposes and not properly repaired ,or backfilled. Weak
spots in laterals typically occur under .the curb line, at the bend
or vertical drop down to the sewer main connection, and at the
sewer main connection. Service laterals may comprise more than
half of the total pipe footage in a sewer system, hence may be
significant contributors to RII.
Manhole Defects
Defects in manholes occur in the walls and joints, at the
connections to the sewer pipes, and underneath the manhole frame.
The joint between the manhole frame and chimney (corbel) may also
be an entry point of RII when the frame is displaced or the joint
seal is deteriorated> broken, or improperly installed. As with
sewer pipes, manhole defects may also be created by external forces
such as traffic loads, frost heave, and/or root intrusion.
Foundation Drains
Foundation or footing drains connected to building laterals are
direct entry points for infiltration. Foundation drains are
designed to drain the groundwater from around a building or house
foundation to prevent seepage into the basement. The foundation
drain may discharge by gravity or through a sump pump to the
lateral. In some buildings without foundation drains, water
seeping into the basement may be collected by the basement drain
and similarly discharged to the sanitary sewer lateral.
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Problem Assessment
FACTORS AFFECTING RII
In any particular sewer system, a variety of factors may influence
how RII .occurs and the magnitude and type of RII flow response.
These factors relate to the construction and maintenance of the
sewer system and the natural characteristics of the service area.
Sewer system construction and maintenance affect the number, size,
type, and location.; of openings through which RII can enter the
system and the pathways by which water reaches the RII entry
points. Natural characteristics of the service area primarily
influence the pathways by which the rain water reaches the sewer
system and the characteristics o.f-;the flow response .pattern. Each
of these various factors , is discussed briefly in the following
paragraphs. . .
System Age and Construction
- • . ,- . .'•'•-. ' * -
Age is often an indicator of the type of sewer system construction
and the types, severity, and relative number of defects that can
be expected. As discussed previously, older systems, particularly
those constructed before the 1960's, are often characterized by
widespread defects due to the poor quality of the pipe and joint
materials and methods used at the time of construction. These
systems can be, expected to contribute more RII than comparable
newer systems under similar conditions of rainfall, soils,
groundwater, etc. RII can also be expected to be higher in systems
known to contain common- trench storm drain and sanitary sewer
installations. ;
Construction of houses with foundation drains connected to the
sanitary sewer system was common in many areas during certain time
periods. Relatively greater RII. contributions from' foundation
drains would be_expected in areas developed during these periods
than in areas developed after direct foundation drain connections
we're prohibited. ; ..•','*
Density
The magnitude of RII may be directly related to the amount of pipe
within an area. Areas with denser development have more sewer main
and lateral pipe footage, with a correspondingly greater number of
potential RII points of entry.•' Hence, higher RII rates might be
expected in areas rwith denser .development. , '-...
' n. '•-'.-- - • 'I..'' .- '•'••!
Sewer Depth •
The depth of sewers and laterals may influence the amount rof RII
and the speed in which it enters the sewer system. Where soil
channeling or permeable trench backfill material extending to the
ground surface are the pathways of RII entry into the system,
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Problem Assessment
shallower pipes can be expected to exhibit a more rapid RII
response. ,
Groundwater
In areas with high groundwater, an increase in groundwater level
due to rainfall may increase the submergence of the sewer. The
greater hydrostatic pressure on the pipe may result in
significantly higher rates of groundwater infiltration into the
sewer, which in such cases could realistically be classified as
RII.
Soils and Geology
The characteristics of the soils and geology of a service area will
affect the rates of rainfall infiltration and percolation, and the
occurrence of saturated soil zones. Permeable soils such as sands
can transmit water rapidly; clay soils with large shrink-swell
capacities can develop large channels. Hydraulically restrictive
horizons or bedrock at or above the sewer trench bottom can create
perched water table conditions during rainfall which greatly
enhance water transfer to sewer defects. In soils subject to
differential settlement, such as fills and bay muds, or in areas
subject to earth movement from seismic activity, a greater number
of pipe defects may develop, subsequently increasing the amount of
RII which can enter the system.
Topography .
Both water movement through the soil mantle and sewer flow rates
are affected by topography. Sloped bedrock or impermeable soil
layers will tend to cause perched groundwater to drain to sewer
trenches. Sewers constructed on steep slopes carry flows more
rapidly, resulting in higher peak flows in the system. These
higher peaks may cause surcharging, and overflows downstream in
flatter portions of the system. Sewers and laterals constructed
on steep slopes may be subject to earth movement, causing joint
separation and other damage to the pipes. Topographic factors may
also result in depressions or low areas over sewers, as well as
close proximity of storm drains and drainage channels to sanitary
sewers, a situation which can increase RII due to storm drainage
exfiltration.
Roots
Root intrusion is a major cause of pipe defects in many areas.
Roots enter sewer pipes through very small cracks and openings,
enlarging these defects as root growth continues. Particularly
in residential areas, private service laterals are often subject,
to root intrusion from plants and trees; trees lining the street
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Problem Assessment
may result In root penetration into both laterals and sewer mains.
Root growth may also create channeling effects in the soil.
Rainfall Patterns . '*. ' '
The magnitude and pattern of rainfall impacts''the'volume, of RII and
the type of response. Inmost systems that experience RII, it has
been found that extended periods of rain produce larger volumes and
higher peak RII flows than do isolated, short duration, high
intensity storms. Highly seasonal rainfall patterns (i.e.,
prolonged periods without rain), as occur in the far western
portions of the country, may create conditions that are more
conducive to RII, e.g., creation of soil cracks and channels from
the drying out of the soil during the prolonged dry season.
Cold Weather
Cold climate areas with substantial snowfall during- winter
experience higher RII flows when rainfall and snowmelt occur
simultaneously. Peak flow patterns may._ also be produced by
snowmelt alone. Frost heave may damage street pavements and
manholes, creating openings for the rainfall and/or snowmelt to
seep underneath the pavement and enter manholes below the ground
surface/• - ... -\ . .''• • • , > '; '••. : -' '. - ••
Maintenance Practices
The number of new sewer defects through which RII may enter a
system can be minimized by an effective preventive maintenance
program. A system that has undergone routine preventive
maintenance throughout its lifetime would be expected to
contribute less RII than a system which lacks such a maintenance
program. In.general, very few sewer systems have been adequately
maintained. '
Typically, private building laterals are the most poorly maintained
components of a sewer system. This situation is compounded by the
fact that laterals are generally of originally poor, construction.
Most laterals have never been inspected,- repaired, or replaced
since original construction. « >
Ordinance Enforcement
Sewer ordinances may provide the institutional means for agencies
to ensure the proper installation and maintenance of the private
portions of their sewer systems. Examples are requirements for
lateral installation by a licensed plumber or contractor,
inspection prior to backfilling/ requiring that connections to the
sewer main be properly constructed and that abandoned or unused
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Problem Assessment:
service laterals be plugged, to prevent entry of extraneous water,
and prohibitions against the direct connection of foundation drains
to the sanitary sewer system. Where ordinances are not strictly
enforced, RII can be expected to be greater due to illegal
connections or major defects in service laterals left undetected
and unrepaired.
CASE STUDIES
Ten case studies were documented for this study, including that of
EBMUD and nine other systems that were selected through a candidate
system search. Candidate systems were identified through contacts
with EPA regional offices, regulatory agencies of each state, and
major consulting engineering firms throughout the country. A list
of approximately 350 possible candidate systems was initially
compiled. After screening of preliminary information, over 65
telephone contacts were made to ascertain the likelihood of RII
occurrence in candidate sewer systems and to determine what
documentation was available. The general characteristics of RII,
as defined under this study, were described, and each contacted
agency was questioned as to the relative magnitude .of .peak wet
weather flows, the .known or likely sources of RII, and the
availability of data from past studies. In general, most of the
agencies contacted responded affirmatively when asked if it
appeared that they had RII in their sanitary sewer systems.
Reports from approximately 40 systems were received. Most
documented I/I analyses and SSESs completed in the late 1970s and
early 1980s under various EPA projects. Therefore, the study
methodologies and analyses employed largely conformed to EPA
guidelines which were, in effect during that period for identifying
"excessive" I/I. The reports received were fairly representative
of I/I studies .completed over the past 15 years. The best
candidates for case studies were considered to be those agencies
which had documented potential pathways and entry points of RII,
or could with reasonable certainty be assumed to have RII because
of high peak flows with little or no known sources of direct
inflow. However, only a very few had specifically addressed or
attempted to quantify RII, or initiated programs designed solely
to control RII.
Based on contacts made and documentation received, nine candidates
for RII case studies were identified, as listed below:
o City of Springfield, Oregon
o Milwaukee Metropolitan Sewerage District, Wisconsin
o Northeast Ohio Regional Sewer District, Ohio
o City of Baton Rouge, Louisiana
o City of Springfield, Missouri
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Problem Assessment
o North and South ShenangO Joint Municipal Authority,
Pennsylvania
o City of Ames, Iqw'a
o. City of Coos Bay, Oregon ;
o City of Tulsa, Oklahoma
Further information was obtained from site"visits to the first four
systems and through written and telephone contacts with the others.
Detailed discussions of these case studies, including EBMUD, are
included in Appendix C. Brief descriptions of the findings of each
with respect to RI-I are presented below and summarized in Table 2-
1. • .• . • • ' •. " • ' • " '' ' ' ' '' -•.'..
East Bay Municipal Utility District, California
The EBMUD wastewater service area is located on the eastern shore
~of San Francisco Bay, and includes seven community wastewater
collection agencies. EBMUD operates the interceptor system and
treatment facilities which transport and treat the wastewater
generated from, the 'seven communities. The collection systems,
which include about 1,500 m;Lles of sewer main, are owned- and
operated by the'individual communities.
The community collection systems, as well as the EBMUD interceptor
and treatment facilities, do not have adequate capacity to handle
peak Flows which occur during wet weather. As a result, overflows
Onto city streets and bypasses tb local watercourses have occurred-
within.the community systems and at seven locations along the EBMUD
Interceptor, ,
Findings documented from field investigations were:
o High peak flows occurred in response to rainfall. The
ratio of peak wet weather flow (PWWF) to average dry
weather flow (ADWF) was estimated to be about 20 to 1 for
a five-year design storm.
o Identified direct inflow (i.e., SWI) accounted for less
than five percent of the total rain induced extraneous
flows. ', . ; .'.'-. -'.-•;
o From smoke testing programs, numerous pipe defects were
detected in building laterals.
o Numerous defects were observed in sewer mains and
laterals through TV inspection programs.
o Very few direct storm drain/sanitary sewer
interconnections were found.. ,Mpst of the potential
2-15
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Problem Assessment
interconnections detected through smoke testing were
found to be indirect (i.e., through pipe defects).
/ • . • . . '
o Laterals exhibited peak flow responses to actual rainfall
and to simulated rainfall tests.
o Most laterals given air or water leakage tests failed
such tests.
The high rain induced flow response, the absence of significant
direct inflow connections to account for any substantial portion
of the peak flows, and the prevalence of defects in sewer mains and
laterals indicated that RII is a significant component of peak wet
weather flows in the EBMUD sanitary sewer system. The key factors
affecting RII entry points appear to be the age and condition of
the sewer system and the relatively high density of sewers and
laterals. The poor condition of the pipes is primarily due to age
and lack of maintenance, but is also affected by physical factors
such as earth movement due to seismic activity. Other factors
which contribute to the very rapid, high peak flows are the shallow
depth of mains and laterals, clay soils, and steep slopes which
characterize the service area.
The EBMUD communities have initiated a 20-year program to eliminate
overflows and reduce RII in the sanitary sewer system. The
recommended program consists of "comprehensive" rehabilitation
(including sewer mains and the entire portion of building laterals)
in approximately one-half of the subbasins in the system, coupled
with construction of relief sewers to transport the excess flows
not removed by rehabilitation. Rehabilitation work conducted
during the initial phases of the program has consisted primarily
of slip-lining and replacement of sewer mains and the portion of
the building laterals within the public right-of way (lower
laterals). One of the EBMUD communities has included the private
(upper) laterals in the public construction project, and other
communities are considering this approach for subsequent projects,
as well as other options for implementing private lateral
rehabilitation. Analyses of the flow reductions achieved through
the initial rehabilitation projects are not yet complete.
City of Springfield, Oregon
Springfield is located in central western Oregon at the confluence
of the McKenzie and Willamette Rivers. The.City's sanitary sewer
system is tributary to a regional wastewater treatment plant (WWTP)
constructed in 1984, which serves the Cities of Eugene and
Springfield. The Springfield sewer system serves a population of
about 40,000 and includes approximately 165 miles of sanitary sewer
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Problem Assessment
mains. Problems in Springfield caused by rain induced flows have
been reported to include system surcharging, overflows, and'
bypassing of partially treated wastewater from the former
Springfield treatment plant (almost continuously during the months
of December and January).
Findings documented from field investigations were:
o High flows occurred in response to rainfall. .The ratio
of PWWF to ADWF was projected to be about 11 to l. .-•
o Identified direct inflow accounted for less than 20>'
percent of the projected rain induced extraneous flow.
o Numerous pipe defects were detected in sewer mains and
building laterals from smoke testing studies.
o TV inspection detected numerous defects in sewer mains.
o Dye flooding tests confirmed that over 90 percent of the
potential storm drain/sanitary sewer connections
identified by smoke testing were through defects in the
sewers rather than direct connections.
The ,high rain induced flow response, the fact that direct inflow
connections accounted for less than 20 .percent of the peak';rain
induced extraneous flows, and the prevalence of defects in sewer
mains and laterals indicated that RII is a significant component
of peak wet weather flows in the Springfield sanitary sewer system.
The key factors affecting RII appear to .'./be the condition^ of the
sewer mains and laterals, groundwater conditions> and the high
seasonal rainfall in the service area.
The City has conducted rehabilitation of the sewer mains and lower
laterals in four areas of the system, utilizing primarily grouting
and replacement. Rehabilitation of private laterals has also been
done in several small special project areas. Analyses of the flow
reductions achieved by these rehabilitation projects are not yet
complete. •
Milwaukee Metropolitan Sewerage District
The Milwaukee Metropolitan Sewerage District serves 28 communities
in the southeastern portion of Wisconsin, the largest of which is
the City of Milwaukee. The total service area includes over 2,800
miles of sewer mains, of which approximately 20 percent are of the
combined storm/sanitary type, mostly located within the City of
Milwaukee. The remaining 80 percent of the District is served by
separate sanitary sewer systems, which were studied under a
comprehensive SSES. Problems caused by , high rain induced
2-17
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Problem Assessment
extraneous flows have included overflows and bypasses from the
interceptor and collection systems, wastewater back-ups into
building basements, and discharges of inadequately treated
wastewater to Lake Michigan.
The field investigations conducted in the separate portion of the
sewer system documented the following:
o High peak -flows occur in the system, of which 76 percent
could be contributed to rain induced I/I (RII + SWI).
The ratio of PWWF to 2^DWF was projected to be about 7.5
to 1.'
o Numerous defects were found in manholes from smoke
testing and physical inspection programs.
o Manhole frame/chimney defects were found to contribute
significant flows based on street flooding studies to
simulate rainfall conditions.
o Numerous direct foundation drain connections were
identified through building inspections.
o Indirect connections between storm drains and sanitary
sewers were found by smoke testing and dye flooding
programs. ''
o Foundation drains and building laterals exhibited peak
flow responses to rainfall and to experimental rainfall
simulation.
o Approximately 60 percent of peak extraneous flow was
attributed to RII, including 40 percent through
foundation drains and 12 percent through manhole
frame/chimney joints.
The high rain induced flow response and the presence of sewer
system defects and foundation drain connections that accounted for
60 percent of peak extraneous flows indicate that RII is a
significant problem in the system. The key factors affecting RII
appear to be the prevalence of foundation drain connections, storm
and sanitary sewer laterals constructed in the same trench in many
areas of the system, high groundwater, and frost heave. Frost
heave, or lifting and distortion of the ground surface due to
subsurface ice formation, is believed to be a major factor in the
formation of manhole frame/chimney defects and the cracks in
concrete pavements that generate pathways to these defects.
2-18
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Problem Assessment,
As a result "of .its SSES, the District has conducted, I/I correction
work, primarily aimed at eliminating direct inflow through manhole
covers and RII from manhole, frame/chimney interfaces. The District
conducted a manhole rehabilitation pilot project to evaluate
different methods-of correcting manhole frame/chimney leakage. Two
of the District communities have successfully implemented
foundation drain disconnection programs. A permanent monitoring
system is being installed for long-term monitoring of I/I flows
throughout the District.
h ' ' ' "
Nortneast Ohio Regional Sewer District
The Northeast Ohio Regional Sewer District includes .41 communities
in the Cleveland* Ohio, metropolitan area. The District is divided
into two major subdistricts: The City of Cleveland, which has a
combined sewer system; and the surrounding communities, which
primarily have separate systems. Most of the separated portions
of the system are contained within two major planning areas, the
Easterly Separate Sewer Area and the Southwest Interceptor Area
which together contain approximately 1,200 miles of sanitary sewers
serving a population of about 500,000, > .
Overflows arid bypasses occur at over 200 locations in the separated
sewer systems, most initiated by rain events of less than 0.2
inches per hour. Pump stations and regulator chambers in the
interceptor system are". used to restrict, flow to the WWTPs.
Basement back-ups are a major problem during wet weather.
Field investigations in the. separate sewer areas documented the
following: . ' . ,
o High flows occurred in the system in response to
rainfall. The ratios of PWWF to ADWF was projected to be
.about 12 to 1 in the Southwest Area and over 20 to 1 in
the Easterly Area. • ' .
o Identified direct inflow accounted for , only 5 to 15
percent of the peak extraneous flow.
o Sanitary - and storm sewers and building laterals were,
constructed in common trenches in over 50 percent of the
separate system. ,
o ; Indirect flow transfer from storm to sanitary sewers was
found to be very rapid, as documented by dye flooding
tests.
These findings indicated that RII is a significant problem in the
sewer system. The most significant factors affecting RII appear
2-19
-------
Problem Assessment
to be ^the poor condition of the sewers and laterals and the
extensive common trench storm/sanitary system. Therefore, storm
drain exfiltration appears to be the primary pathway for Rll into
this system.
RII correction efforts in the District have primarily concentrated
on rehabilitation and flow regulation in the storm sewer system,
with some sanitary sewer rehabilitation. Work . has included
construction of new storm sewers to replace common trench
facilities and provide additional storm drainage capacity;
rehabilitation of common trench storm/sanitary sewer manholes; and
installation o'f vortex regulators to restrict flow into the storm
drain system and thereby reduce the transfer of flow to the
sanitary system.
City of Baton Rouge, Louisiana
The City of Baton Rouge is located in the southeast portion of
Louisiana along the Mississippi River. Its sewer system serves a
population of about 450,000 and includes approximately 1,500 miles
of mains. The system is divided into four major areas, three of
which comprise the original Consolidated Sewer District and the
fourth, the suburban area. Each of the three original Consolidated
Sewer District areas is served by its own WWTP; the suburban area
includes 144 local wastewater treatment facilities. Overflows and
bypasses have occurred throughput the sewer system during high
intensity storm events.
Findings of field investigations were as follows:
o High peak flows occurred in the system in response to
rainfall. The overall ratio of PWWF to ADWF is estimated
to be about 3.5 to 1.
o Numerous defects were detected in sewer mains, manholes,
•and building laterals through smoke testing programs.
o Most potential transfers of water from storm drains to
sanitary sewers were found to be through defects in the
sewers.
o In four special study areas, building lateral defects
were found to account for 32 percent of the potential
peak rain induced extraneous flow, with the remainder
coming from .sewer mains and manholes.
The high rain induced flow response, the absence of direct inflow
connections to account for any substantial portion* of. the peak
flows", and the prevalence of defects in sewer mains and laterals
indicated that RII is a significant component of peak wet weather
flows in the Baton Rouge sanitary sewer system. The key factors
2-20
-------
Problem Assessment
\ - - ' '
affecting RII appear to be the poor condition, of sewers and
laterals, due to both age and lack of system maintenance ;
construction of sewer trenches in drainage ditches; and the shallow
depth of building laterals. '•
The City is implementing a rehabilitation program to correct all
main line defects identified during field testing in the four
special study areas. Rehabilitation techniques will include spot
repair, pipe replacement, slip-lining, and manhole sealing.
City of Springfield, Missouri
Springfield is located in southwestern Missouri. The wastewater
service area is divided into two main drainage basins, each served
by a separate WWTP. The larger of the two basins is the Southwest
area, which includes approximately 80 percent of the City. This
area includes over 500 miles of sanitary sewers, which serve
approximately 160,000 people.
Identified problems due to rainfall induced extraneous flows
include surcharging of and overflows from the collection system,
as well as basement flooding. Overflows occur at approximately
ten sites during any good-sized storm, and at 100 or more locations
during large rainfall events. I/I correction efforts aimed at
eliminating direct inflow and the repairing of isolated problem
sewer reaches did not have a noticeable impact on peak wet weather
flows.
Findings "of limited field investigations included:
o High flows occurred in response to rainfall, with the
ratio of PWWF to ADWF estimated to be about 8 to 1.
Larger, longer duration storms produced higher and more
sustained peak flows than short-duration, thunderstorm-
type events.
o Relatively few direct inflow connections were found
through smoke^testing programs.
o Evidence of infiltration through manhole walls and
inverts was observed during physical inspections.
o Clear water discharges from laterals were observed during
TV inspection work. • >
o Many sewers were installed in the shallow limestone
bedrock, which supports a perched grbundwater table in
much of the area.
The high rain induced flow response and the failure of the inflow
correction program to reduce rain induced extraneous flows
2-21
-------
Problem Assessment
indicated that RII is probably a significant component of peak wet
weather flows in the system. The key factors affecting RII appear
to be the age and poor condition of the sewers and the
hydrogeologic conditions characteristic of the service area, which
are conducive to rapid transport of water to sewer defects.
The City has conducted sewer grouting in the system since 1972,'
primarily concentrated in older areas. A pilot project in a newer
area was also conducted, with sewer main grouting and manhole
sealing. No significant flow reductions were achieved through
these efforts. The City has implemented a long-term correction
program involving routine TV inspection and rehabilitation of sewer
mains on a priority basis, primarily by slip-lining.
North and South Shenango Joint Municipal Authority, Pennsylvania
The North and South Shenango Joint Municipal Authority includes the
Townships of North and South Shenango, which are located along the
shoreline of Pymatuning Reservoir in northwestern Pennsylvania.
The Authority operates a collection system and treatment plant,
which serve a permanent population of about 1,200 and a summer
population of approximately 6,000. The collection system includes
approximately 90 miles of sewer mains and several pump stations.
The sanitary sewer system was •originally constructed in 1978.
Although the contract specifications for the sewer system included
strict criteria for maximum allowable infiltration, wet weather
flows in the system have far exceeded design capacity, resulting
in overflows at the pump stations and hydraulic overloads of the
WWTP. Major wet weather problems have occurred in four areas of
the system that were installed under one construction contract and
with clay pipe made by a different manufacturer than that installed
in other portions of the system. .
Findings of field investigations were:
o High flows occurred in response to rainfall, with
sustained peak ' flows after the end of rainfall. The
estimated ratio of PWWF to ADWF is about 7 to 1.
o High grpundwater exists in much of the area, and a large
portion of the sewer system is submerged.
o Rapid increases in water levels in sewer trenches .from
rainfall occurrences were noted through monitoring water
levels in the trenches.
o The rate of infiltration into individual pipe joints was
found to increase directly with the depth of water over
the pipe.
2^22
-------
Problem Assessment:
o Many sewers were constructed directly under area drainage
' . ditches.; .'"•/' .
o Limited smoke testing detected no significant direct
inflow connections. '
o Very little extraneous flows from building laterals was
observed during TV inspection of sewer mains.
Sewer flow and trench water level responses to rainfall, .as well
as the absence of direct inflow connections confirmed that the high
rain induced extraneous flows in the North and South Shenango sewer
system are due to RII. Entry points of RII appear to be primarily
through defective pipe, joints. The other key factors which affect
RII are the construction of sewer trenches in drainage ditches and
the high groundwater level in the service area.
To correct the RII problem, the Authority is slip-lining all of the
sewer mains and slip-lining or replacing the lower laterals in the
four problem contract areas (the upper laterals are constructed of
PVC pipe and are not believed to contribute RII) . . Limited
rehabilitation work conducted prior to the full-scale
rehabilitation effort indicated that grouting would not be
effective in eliminating infiltration through the pipe joints. A
pilot slip-lining project, however, appeared to achieve virtually
complete elimination of extraneous flows. '
City of Ames, Iowa
Ames is located in central Iowa along the Skunk River. The
collection system, containing approximately 135 miles of sewer
mains, serves a population of approximately 45,000, almost half of
which comprise the Iowa State University campus.\
During-wet weather periods, the WWTP cannot treat all of the peak
flows in the system.. sAn influent .sluice gate must be throttled,
often for as long as several days, to limit flow entering .the
„plant. Several times each year during extremely wet-conditions,
bypassing of raw wastewater occurs both at the plant and at several
points in the collection system. Basement .backups during wet
weatlier also occur as a result of high wet weather flows.
Findings of field investigations were as follows:
o, High peak flows occurred in response .to rainfall. The
ratio of PWWF to ADWF is estimated to be about 6 to l.
o Identified direct inflow accounted for about 40 percent
of the peak extraneous flow.
2-23
-------
Problem Assessment:
o , A survey identified 1,800 direct foundation drain
connections to the sanitary sewer system. Many
additional potential connections, where foundation drains
incorporated valving to divert flow to the sanitary sewer
during freezing conditions, were also identified.
o Foundation drains were found to exhibit peak flow
responses based on a study of the impact of simulated
rainfall on foundation drain sump pump operating times.
o The flow from foundation drains was estimated to account
for about 50 percent of peak extraneous flows in the
system.
The high rain induced flow response, the existence of many directly
connected foundation drains, and documentation of the peak flow
response from foundation drain discharges to rainfall, indicated
that RII is a significant component of peak wet weather flows in
the Ames sanitary sewer system. High groundwater appears to be a
key factor affecting the occurrence of RII, through foundation
drains.
As part of its overall I/I correction program, the City has
implemented a foundation drain disconnection program targeted at
eliminating 768 foundation drain connections over a ten-year
period. The program involves a public information effort and
includes provisions to reimburse a large portion of the homeowners'
disconnections costs. Over 300 disconnections were achieved in the
initial two years of the program on an entirely voluntary basis.
The City anticipates that the program will continue beyond the
required 768 disconnections.
City of Coos Bay, Oregon
Coos Bay is located on the southwest coast of Oregon. The
wastewater system serves a population of about 15,000 and contains
approximately 60 miles of sanitary sewers. The sewer system is
primarily a separate system, although a small portion is believed
• to be partially combined. The City is divided into two main sewer
service areas, each served by a separate WWTP. The major wet
weather flow problems are concentrated in the collection system
which serves the eastern portion of the City and an adjacent
sanitary district. Problems due to high peak wet weather flows
have included bypassing and overflows in the collection system,
as well as bypasses of untreated wastewater and discharge
requirement violations at the WWTP.
The occurrence of RII in the Coos Bay sanitary sewer system is
indicated by the following:
2--2 4
-------
Problem Assessment:
o From the early 1970's through 1982, field investigations
and rehabllitatio^ work to reduce extraneous flows were-
conducted, including disconnection of known, direct inflow
connections (downspouts and cross connections with the
storm drain system) and a sewer main . rehabilitation
program. '
c \ - ' .' . < . .
o Smoke testing conducted after the rehabilitation work
confirmed,that almost all direct inflow connections had
been eliminated from the system.
o High peak wet weather flows still occurred in the system
after completion of the rehabilitation program. The
ratio of PWWF to ADWF was projected to be about 8 to 1.
This evidence indicates that the peak rain induced flows in the
sanitary sewer system appear to be due primarily to RII. The key
factors affecting RII are the poor, condition of the sewers, due in
part to ground settlement in the bay,mud which underlies"much of
the older portions of the system; the shallow depth .of building
laterals; and.the high groundwater which characterizes the service
area. " ., - "••••'. •.->..'•• • ...'•• .-'.-•• ...
. - ' . . '' • ••.-, - • *
In previous years, the city has conducted rehabilitation (primarily
grouting and some replacement) of sewer mains with major problems
identified through TV inspection and- smoke testing. As noted
above, these efforts did not result in any significant reductions
in wet weather flows. However, a program of routine TV inspection
has been initiated to identify specific areas in need of repair
or replacement'.
City of Tulsa, Oklahoma
Tulsa is located in,northeast Oklahoma along the Arkansas River.
Total service area population is approximately 400,000, and the
collection system includes over 1,400 miles of sewer mains. The
City has conducted field investigations and rehabilitation of the
sewer system since 1982, both as part of overall facilities
planning efforts to reduce sanitary sewer surcharging and overflows
during rainfall. • ,
Field investigations documented that: , , .
o High peak flows occurred in response to rainfall. The
ratio of PWWF to. ADWF is estimated to be about 3.5 to 1.
o Numerous defects were found in sewer mains, manholes, and
service laterals from smoke testing programs.
o Defects were observed in sewer mains through TV
. inspection efforts. , - ,
2-25
-------
Problem Assessment.
o Direct inflow connections detected through smoke testing
accounted for 30 percent of the estimated extraneous
flows. RII accounted for the remaining 70 percent.
o Of the potential flow contribution from RII entry points
detected during smoke . testing, about 45 percent Was
estimated to be from service laterals, 35 percent from
sewer mains, and 20 percent from manholes.
o The estimated flow contributions from direct inflow
connections and sewer system defects identified through
smoke testing could not account for all of the rain
induced extraneous flows.
The high rain induced flows, the fact that' direct inflow
connections accounted for less than 30 percent of the peak
extraneous flows, and the prevalence of defects in sewer mains,
manholes, and service laterals indicated that RII is a significant
component of peak wet weather flows in the Tulsa sanitary sewer
system. The key factors affecting the occurrence of RII appear to
be the poor condition of the sewers system, shallow depth of
laterals, granular trench backfill, and the shallow limestone
bedrock that characterizes the service area.
Rehabilitation was performed as part of the City's SSES. The
rehabilitation work consisted primarily of slip-lining, inversion
lining, pipe replacement, manhole sealing, and spot repairs of the
public portions of the system (mains, manholes, and lower
laterals), as well as disconnection of direct inflow sources. In
general, only those specific defects detected through the SSES
field work and determined to be-cost-effective f,or correction were
addressed. Voluntary repair of leaking private laterals and
cleanouts was encouraged through a public relations program. For
eight subbasins in which rehabilitation was performed, the initial
reductions in peak wet weather flows were reported to average
approximately 50 percent.
SUMMARY
o RII is a form of infiltration into sanitary sewer systems
characterized by a significant, short-term increase in
flow in direct response to rainfall.
o RII enters the sewer system from the ground through
defective pipes and manholes and through foundation
drains. RII entry points are similar to those of
"classical" infiltration, or groundwater infiltration
(GWI).
2-26
-------
Problem Assessment
The RII flow response may be indistinguishable from that
of direct storm water inflow (SWI) if it is very rapid
and short-termed:
The RII flow response is likely a continuum from a very
gradually changing flow, similar to GWI, to a rapid peak,
similar to: SWI.
The traditional methodology for analysis of I/I' has
- resulted in RII being incorrectly identified as inflow in
many sewer systems* , .
Peak wet weather flows due to RII can cause overflows and
bypasses in sanitary sewer, systems and at wastewater
treatment plants, as well as backups of wastewater into
building basements. Peak wet weather flows include base
wastewater flow plus GWI plus rain induced infiltration
and inflow. ;
*• " • - -
To handle RII flows, sewer pipelines and pump stations
and wastewater treatment plants must be designed with
considerable additional capacity to convey and treat
relatively infrequent, but large peak flows.
Estimated RII ranged from over 50 to nearly iOO percent
of total peak rain induced extraneous flow for the ten
case studies documented in this investigation. Rain
induced extraneous flow includes only ra'infall
- infiltration and inflow.
- Possible pathways of storm water flow from the ground
surface to the sanitary sewers may include:
- Soil channels from the ground surface to sewer
defects. «
Exfiltration out'of leaky storm drains through the
soil to defects-in sanitary sewer pipes.
- Seepage through pavement cracks with horizontal
movement along the street subbase -to the upper
portions of sanitary sewer system manholes^
- Percolation into permeable trench backfill materials
and along pipe trenches to defects in sewer pipes.
RII was found to enter sanitary sewers through pipe
defects in sewer mains and building laterals, manhole
, defects, and foundation drains directly connected to
service laterals. .
2-27
-------
Problem Assessment
o Several factors were found to be significant in the
formation of RII entry points.
Age of the sewer system.
- Type of pipe and joint materials.
- Construction practices.
- Lack of proper maintenance.
- Freeze/thaw conditions.
- Earth movement.
Root intrusion. .
Lack of ordinance enforcement prohibiting foundation
drain connections.
o Defective building laterals and foundation .drain
connections on private property can contribute
significant RII' flows, and even the majority of RII in
some systems.
o Different types of RII entry points appear to predominate
in various geographical areas of the U.S.
In areas where foundation drains are common, such as the
midwest, foundation drain connections can .contribute a
major portion of the RII. Where sewer mains and laterals
are relatively shallow, such as in the western and
southern portions of the .U.S. , pipe defects may be the
predominant RII entry points.
o For the systems reviewed in this study, the projected
overall system peak wet weather flow (PWWF) to average
dry weather flow (ADWF) values ranged from about 3.5 to
over 20.
However, projected peak flows are not necessarily
directly comparable because they are based on design
storm criteria specific to each system and also because
they typically include at least some component of SWI and
GWI.
o It is likely that RII can occur to some extent in any
sewer system and can be a significant component of wet
weather flows.
While the sample of RII case studies evaluated was not
large enough to conclusively determine the national
significance of the RII problem, sewer system and
environmental factors which appear to influence the
occurrence of RII can be found in systems throughout the
country.
2-28
-------
Problem Assessment
Problems associated with defective sewer pipes are not
limited to RII-. Exfiltration of untreated sewage through
these defective pipes may contaminate ground-water. This
problem is likely to manifest itself when the sewer:pipe
is above the' water table.
2-29
-------
Problem Assessment
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Problem Assessment
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-------
CHAPTER 3
CONTROL METHODS
This chapter discusses different methods and approaches for
controlling rainfall induced infiltration into sanitary sewer
systems. The basis of the discussions was a literature search to
identify sewer system rehabilitation methods currently being
practiced both in the U.S. and in other parts of the world. In
addition, the discussions draw upon information .collected as part
of the RII candidate system search and case study documentation
presented in Chapter 2. A description of an "example" RII control
program, that of EBMUD, is also presented.
"Control" means the implementation of methods to reduce existing
RII flows or limit future RII into a sewer system. RII control can
be accomplished through physical rehabilitation of existing sewers
and application of proper design standards and construction
practices for new sewers. Institutional and regulatory approaches
and preventive maintenance programs are means of facilitating
implementation and ensuring the effectiveness of RII control
programs. The success of an RII control program is dependent not
only on the application of appropriate engineering techniques, but
also on the overall implementation approach used.
Typically, control methods are aimed at correcting the entry points
of extraneous flows into, the sewer system. • physical methods to
rehabilitate sewers are largely applicable to all types of
infiltration (GWI and RII). However, RII control differs from GWI
control in the approaches used to quantify flows and identify entry
points, and the relative importance that is placed on correction
of particular components of the sewer system (e.g., mains versus
laterals). For this reason, this chapter also includes a
discussion on field investigation techniques to quantify and
identify RII, as well as various approaches for implementing RII
control programs.
RII FIELD INVESTIGATION TECHNIQUES
In general, the same traditional methods that have been used for
conventional I/I investigations and SSESs can be used as field
techniques for RII investigation. However, to identify and
quantify RII, it is critical that the field methods be
appropriately applied and the data be properly interpreted. The
field techniques and methods of data interpretation, as they
specifically apply to RII, are discussed below.
'3-1
-------
Control Methods
Flow Monitoring '
Flow monitoring is commonly used to quantify I/I flows in different
portions of a sewer system. To obtain accurate and useful flow
data, no hydraulic constrictions should exist in the vicinity of
the flow monitor, and the sewers upstream and downstream of the
monitoring site should be cleaned prior to monitoring to remove
major root .intrusion and sediment buildup. The monitoring manhole
ideally should have smooth transitions and no .side streams or
changes in flow direction. Collection of useable flow data can be
better assured by appropriate choice of monitoring equipment (e.g.,
depth-velocity meters versus level-only recorders), as well as
suitable monitor location. Surcharging or backwater effects must
be carefully evaluated in interpreting flow monitoring results.
The traditional approach for analyzing wet weather flows is to
subtract the non-rainfall base flow (base sanitary flow plus GWI)
during the period, immediately preceding a storm event from the
total flow during and immediately following the storm. The
difference is, the rainfall induced infiltration and inflow
(RII+SWI). An adjustment can be made to account for the higher
sustained GWI rate at the end of the. storm (see Figure 2-1).
However, it is generally impossible to distinguish SWI from RII on
the basis of this hydrography alone.
One approach to interpreting the (RII+SWI) hydrography is to
separate.it into component parts, each representing a different
response time to rainfall. This type of analysis-can be used to
identify the relative significance of different types of RII by the
relative magnitude of each hydrography component. The most rapid
component (shortest time to peak) will include the SWI portion of
the flow, as , well as some portion of the RII. The slower
components will typically consist of RII only.
If the flow monitoring period is long enough to include different
types of storms (e.g., short, intense storms and extended duration
storms), then a comparison of (RII+SWI) hydrographs may also
indicate the relative significance of RII in the system. In some
systems, it has been found that longer-duration storms and/or those
characterized by considerable antecedent rainfall'produce higher
peaks and larger RII' volumes than comparable isolated, short-
duration storms.
3-2
-------
Control Methods
Flow Isolation
Flow isolation or flow mapping is a technique commonly used to
determine the relative I/I contribution from different "minibasins"
or reaches of sewer within a subsystem. The procedure consists of
taking instantaneous> manual flow measurements at successive
manholes. For RII isolation, flow measurements are taken during
and immediately after rainfall.
Since the objective of RII flow isolation is to determine the peak
RII contribution at different locations in the sewer system, care
must be taken in comparing measurements from different locations
taken at different times during the rainfall. One way to help
overcome this difficulty is to place a continuously recording flow
monitor at a location downstream in the subsystem. The
instantaneous measurements taken within the subsystem at various
times during and after the rainfall are then projected to a peak
flow (assumed to occur at the same time as the peak of the
downstream monitor hydrograph). The projection is based on the
ratio of the monitor flow at the measurement time to the monitor
peak flow, if flow isolation is conducted several hours after the
peak rain period but still while the flows are elevated above
normal levels, the measured flow can reasonably be assumed to
consist primarily of RII because the SWI flow hydrograph should
already have receded.
Flow isolation during rainfall is an effective way to determine the
distribution of RII in the subsystem. This allows rehabilitation
efforts to be concentrated in those minibasins with relatively
higher RII contributions. Equally important, any losses in flow.
between successive manholes indicate exfiltration and therefore,
appropriate corrective measures for the problem should be
considered.
Groundwater Monitoring
Groundwater monitoring is used to determine the elevation of the
groundwater with respect to that of the sewer system and its long-
term or short-term variations. Groundwater monitors placed within
a sewer. trench provide a direct measurement of the hydrostatic
pressure on defects in the sewer pipe. Continuously recording
monitors can be used to determine short-term responses to rainfall,
which can then be correlated with flow measurements in the sewers.
Ground-water monitoring can also be used to monitor the quality of
ground-water when exfiltration is determined to be a serious
problem.
Smoke Testing .
Smoke testing is the traditional field method used to detect direct
inflbw entry points. Under appropriate conditions, it can also
3-3
-------
Control Methods
identify some types of RII entry points. Specificariy, for smoke
testing to be an effective RII investigation technique, the sewer
must be above the groundwater level and the soil must be relatively
dry. Under these conditions, smoke will be transmitted through
channels in the soil and be detected as visible emissions from the
ground over defective sewer pipes, laterals, and manholes, or from
storm drains or catch basins .(in the. case of RII due to
exfiItration from storm drains). ,
In general, detection of RII entry points by smoke testing will be
most successful in cases where most of the defects aire close to the
ground surface (i.e., shallow mains and laterals) and where there
are relatively few direct inflow connections (since these sources
would tend to draw most of the smoke). ,The absence of smoke from
potential RII entry points does not mean that they do not exist;
some pipes may have traps or sags that prevent smoke travel.
However, the defects that do emit smoke are likely to be those with.
the most rapid flow response to rainfall. , ,
Dye Flooding
Dye flooding is generally used to verify direct and indirect
connections between storm drains and sanitary sewers. A storm
1 drain or ditch is flooded with dyed water, arid the sanitary sewer
is observed for appearance of the dye in the flow stream., The flow
rate and concentration of the dye gives an indication of whether
the- connection is direct or indirect. TV inspection of the
sanitary sewer concurrent with dye flooding provides, direct
evidence of specific locations where RII enters the sewer. If the
storm sewer is completely flooded (surcharged) during the dye
flooding, the rate of flow into the sanitary sewer (or into
'• individual defects) may approximate the peak RII flow during a
.large storm.
Street Flooding .
Street flooding can be used to; identify and quantify RII flows into
such entry points as manhole frame/chimney defectSi Surface water
is prevented from entering the manhole by placement of an inner
tube in the frame opening, which still permits visual observation
of the flow entering from the ground, below the frame. The ..leakage
rate through the manhole frame/chimney defect is measured or
estimated based on observation. Leakage rate under this
"simulated" rainfall condition is assumed to approximate the RII
flow. , .
Rainfall Simulation
Rainfall simulation consists of applying water to an area of
suspected RII and observing or measuring the resulting flow.
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Control Methods
Rainfall simulation is typically used on a limited basis to
estimate flows from foundation drain connections or defective
building laterals. The results of rainfall simulation provide
evidence as to the potential magnitude and speed of the flow
response to rainfall from these system components. Note that RII
flows during actual rainfall events can also be .observed or
measured in a similar manner.
Manhole and TV Inspection
Physical inspection of manholes and internal television inspection
of sewers are used to identify defects in sewer pipes and manholes
which can be potential entry points for extraneous flows. Material
deposits and stains, often indiceitors of infiltration, can also be
observed. If conducted during rsiinfall, manhole and TV inspection
can identify specific entry points of RII. TV inspection as a RII
detection technique is limited because many sewers become
surcharged during rainfall conditions, thereby preventing
observation of RII entry to the system. Also, an apparently good
sewer (no observed defects) does not necessarily mean that RII
entry points do not exist. Quite often, infiltration occurs below
the wastewater flow line or at joints in the sewer pipe that cannot
be seen by the camera.
TV inspection is relatively expensive and generally should be used
only after a specific sewer reach has been identified through flow
isolation or dye flooding as contributing significant RII flows.
Its use for inspection of building laterals provides the same type
of information, but lateral TV inspection generally requires
special "mini-cameras" which can crawl or be pushed up the lateral.
Lateral TV inspection is also limited by the availability of access
points (cleanouts).
Building Inspection
Physical inspection of building basements is used to identify
direct foundation drain connections to the sanitary sewer system.
Floor drains are inspected for evidence of a connection with the
foundation drain (via a Palmer valve or drain tile receiver). Sump
pump discharge points are also determined during building
inspections.
SEWER REHABILITATION METHODS
Rehabilitation refers to physical repairs or modifications to
sanitary sewer system components which can reduce the amount of RII
entering the system. Sewer rehabilitation as a RII control method
is generally aimed at eliminating RII entry points, specifically,
pipe and manhole defects and foundation drain connections. The
selection of an appropriate rehabilitation technique to repair any
specific sewer pipe, lateral, or manhole is a design decision that
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ControlMethods
must be based on/existing structural conditioiy, type of defects,
site constraints, and cost considerations. All of the
rehabilitation methods described in this section are applicable for
RII control; the "best" method for any particular situation will
depend upon the factors listed above.
The effectiveness of sewer rehabilitation in reducing RII depends
not only on the proper selection and application of rehabilitation
technique, but also,.and primarily, on the overall rehabilitation
program approach. As discussed later in this chapter,
rehabilitation programs which address only isolated, large defects
or only the public portion of the'sewer system may be ineffective
in reducing RII. Area-wide rehabilitation, including private as
well as public .facilities, is generally necessary to achieve
significant RII reductions.
Sewer rehabilitation methods range from complete replacement- or
construction of new facilities to repairs of individual defects
that can be accomplished in place. In general, the costs for
complete replacement are significant, .especially when based on not
only the cost of construction but also the indirect costs resulting
from construction. These indirect costs have been a driving force
for the development of less expensive, less physically disruptive
techniques for in-place; rehabilitation. The following paragraphs
•briefly review the various techniques available for sewer system
rehabilitation to reduce RII. More detailed descriptions and
discussions of these methods are included" in Appendix D.
Pipeline Rehabilitation
Rehabilitation methods for sewer pipelines include conventional and
trenchless replacement, grouting, arid several different lining
techniques. The rehabilitation techniques listed below are not
' all-inclusive; other techniques are currently being developed.
The; focus in pipeline rehabilitation today is on in-place
techniques such as lining and trenchless replacement. These
methods minimize the impact on traffic, other utilities, and
surface improvements. One of the main shortcomings of the in-place
techniques is making a leak-free connection between the main and
lateral without excavating. Because these connections are .often
responsible for significant leakage, the effectiveness of the seal
at this joint may be essential to RII reduction. ,
Many of the techniques originally developed for sewer mains have
been modified for lateral rehabilitation. However, since laterals
are typically short (less than 75 feet) , may have many-bends or
offsets, and often lack useable points of access, their
rehabilitation by in-place techniques is generally less cost
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Control Methods
effective than for mains. Access to laterals, both for testing
and rehabilitation, is .also an institutional problem, primarily
because the installation and maintenance of laterals are usually
the legal responsibilities of the property owner.
The following techniques are applicable for rehabilitation of sewer
pipelines:
Conventional Replacement. Convemtional replacement can be used as
a method for rehabilitation of a complete manhole-to-manhole pipe
reach, as well as for repair of individual defects. The
replacement of an entire reach using modern pipe materials provides
an essentially leak-free pipe. Excavation and repair of isolated,
joint-to-joint pipe sections (point repairs) may often be required
in conjunction with other sewer rehabilitation techniques such as
grouting or lining. Lateral to main connections• also generally
require excavation for restoration of a leak-free joint.
Trenchless Replacement. Tunneling and moling are methods of
trenchless installation of new pipe. Variations of some of these
techniques, such as that commonly referred to as "pipe bursting,"
can be used to replace a pipe along its existing alignment,
including installation of a larger diameter pipe. Flexible,
jointless pipe, such as'polyethylene, is an effective replacement
material for RII control. Moling is often attractive for laterals
to minimize surface impacts and allow the existing lateral to
remain in service until the new service is installed. Also, new
construction using these techniques does not require granular
backfill, thereby minimizing the potential for transfer of
extraneous water into and along the sewer trench.
Grouting. Grouting is used to seal joints, small holes, and radial
cracks in otherwise sound pipe. Pipes in poor structural condition
or with numerous defective lateral connections generally cannot be
effectively repaired by grouting. Grouting requires no excavation
where manhole entry is available. The long-term effectiveness of
grouting depends upon the type of grout used, the moisture
conditions around the pipe, and proper application and quality
control. Periodic testing after the initial grouting may -be
required, not only to re-test the seal on the grouted joints, but
also to correct new leaks in previously ungrouted joints arid
cracks.
Slip-lining. Slip-lining consists of inserting a new liner pipe
inside an existing sewer pipe or lateral. The liner pipe,
typically high-density polyethylene, can be fused into long, joint-
free (and therefore, leak-free) sections prior to insertion.
Grouting must be used to seal the annular space between the liner
and existing pipe at manholes, and may be used to seal the annular
space for the entire length of the pipe reach. Some newer slip-
lining methods utilize short, threaded liner .pieces, helically
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Control Methods
->''". . '. \ ' - ' ' . , • ' *
wound strips, and expandable liners to facilitate the insertion
'process. When a sewer main is slip-lined, each lateral connection
must be excavated and reconnected to the slip-lined pipe. If the
laterals are also slip-lined, the lateral and main sewer liners can
be fused together to make, a leak-free joint.
Cured-ail-Place Lining. Cured-in-place lining utilizes a thermal-
setting, resin-coated flexible fabric liner. The ;liner is
typically inserted in the pipe by inversion. Once inserted inside
the pipe, the = liner is hardened by circulation of hot water -or
steam. The liner conforms to the internal shape df the existing
outer pipe and provides a smooth, joint-free lining. Although a
remote cutting device,is available to reconnect laterals to the
lined pipe, remote cutting does; not provide any means of sealing
these joints. Therefore, if the lateral connections are subject
to leakage, they must be excavated for repair as in slip-lining.
Cured-in-place lining requires less surface excavation than does
conventional slip-lining, but is generally more expensive.
Manhole Rehabilitation
Specific manhole rehabilitation techniques are designed to correct
manhole frame/chimney defects as well as to eliminate RII entering
through the walls and base. The Milwaukee Metropolitan Sewerage
District has pioneered the development and testing of several new.
repair techniques .as part of its manhole rehabilitation pilot
program. Rehabilitation methods for manholes include both interior
and exterior :techniques. Interior repairs are generally less
expensive and time consuming> but are frequently less effective.
Interior Repair Methods. Interior repair methods, although
typically less effective for RIl control, remain attractive in many
cases due t6 the low cost, and ease of undertaking. These
techniques make possible the sealing of all manhole "joints,
including the lower ones, which are often subject to the largest
hydrostatic forces. Interior repair techniques utilize:
o Elastomeric sealants. . /
,, . ,. o ;Chemical grouts. ,
o Internal boots.
Exterior Repair Methods. Exterior repairs are often more effective
than internal repair methods, but require excavation., Since it is
difficult to gain access to1 all manhole joints, external repairs
generally focus on the joints close to the ground surface,
including the manhole frame/chimney connection. Exterior repair
methods ; ,
utilize: . - • •
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Control Methods
o Elastomeric sealants.
o Elastomeric sheeting,.
o Rubber sleeves.
o Two-piece frames.
Foundation Drain Disconnection
Methods for foundation drain disconnection are relatively
straightforward and depend primarily on the configuration of the
existing connection. The disconnection involves:
o Directing the foundation drainage discharge to a sump.
o Installation of a sump pump.
o Construction of a discharge line to the outside of the
building or to a storm drain.
o Plugging the existing connection to the sanitary lateral.
If the sump and/or sump pump already exists, then the disconnection
may simply involve redirecting the discharge to an appropriate
point. If the discharge is to go to a storm sewer, connection to
an existing storm lateral or construction of a separate storm
lateral to connect into the storm sewer may also be required.
DESIGN STANDARDS AND CONSTRUCTION PRACTICES
Effective design standards and construction practices can ensure
minimization of the potential for RII in new sewer mains, manholes,
and building laterals. Such standards and practices are also
important for existing sewer system rehabilitation. This section
presents the key concepts for design and construction as they apply
to RII control. More detailed discussion of these issues are-
presented in Appendix E.
Modifications of sewer design standards provide a means of
controlling future RII in sewer systems by preventing potential
development of defects and minimizing the potential for the
migration of extraneous water to any sewer defects which may
develop. Such modifications include:
o Restricting the flow of water in granular backfill.
o Reduction of utility trench backfill interconnections.
o Control of migration of fine soil or backfill material
particles.
o Reduction in the number of pipe joints.
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Control Methods
o Incorporation of pipe system flexibility to reduce
settlement stresses. .
. ,'•.'-'• ' . . 5
. o Improved sealing of pipe connections at manholes.
o Provision for tight, but flexible, lateral connections.
o Provisions for access for testing, inspection, and repair
of laterals. .
Implementation of effective sewer construction practices ensures
that design standards are properly addressed. This is accomplished
by regular construction inspection and adequate performance
testing, both for public sewer mains and manholes and private
building laterals. Leakage tests (air pressure or water) must
include stringent standards that assure an acceptable infiltration
rate over the life of the sewer. Tests that allow for relatively
large leaks from individual joints, even though the: over all leakage
in the pipe reach does not appear to be excessive, may not be
acceptable, ,
RII CONTROL PROGRAM APPROACHES
Various approaches have been taken to control infiltration and
inflow into sanitary sewer systems, but few have specifically
addressed RII alone. Typical control programs have consisted of
physical rehabilitation of, portions of the existing sewer system
in an attempt to immediately reduce the, magnitude of extraneous
flows. Rehabilitation projects may have included some private
facilities (building laterals or foundation drains), but typically
have only addressed the public portion of the system. Long-term
control programs have sometimes been initiated either in lieu of
or in conjunction with immediate large-scale rehabilitation
efforts. . ;
The most controversial aspect 6f control programs is the question
of how to deal with problems on private property. In recent years,
many communities have realized that private property sources often
contribute the majority of extraneous flows to the sewer system.
Therefore, significant flow reductions can only be achieved if
sources on private property are also addressed by the control
program. However, rehabilitation on private property entails
institutional, financial, and construction problems that are often
perceived to be prohibitive. ,- .
/This section discusses various approaches to RII control. In. this
context, approaches imply various options for developing an overall
control program, as opposed to selecting specific rehabilitation
techniques or design standards. The latter two involve primarily
engineering judgements. Selection of an appropriate and effective
overall approach to RII control involves both engineering and
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Control Methods
institutional decisions. Institutional and regulatory approaches
discussed later in this chapter, are means of facilitating
implementation of Rll control programs.
Rehabilitation Program Approaches
In developing a rehabilitation program that will effectively
achieve reductions in RII peak flows, it is essential to correctly
identify the areas of the system and the types of entry points that
must be corrected. The first step in any rehabilitation program
should be to eliminate obvious sources of direct inflow. The
reasons for this approach are:
o Direct inflow sources can be detected easily by smoke
testing and are generally cost effective to remove.
o Once inflow sources are removed, Rll can be quantified
from flow monitoring (otherwise it is not possible to
separate the SWI and RII portions of the rain induced I/I
hydrograph), and those areas of the system which
contribute significant RII flows can be readily
identified.
Once the areas to be addressed in the RII control program are
established, a proper approach for identifying the particular sewer
system components to be rehabilitated must be developed.
Approaches to rehabilitation programs may differ in the following
basic ways:
o Addressing entire areas of the sewer system versus repair
. of individual defects only.
o Including both the private and public portions of the
sewer system versus only the public portion.
Rehabilitation programs that have only addressed individual large
defects or only problems on public property have often failed to
achieve projected Rll reductions. One of the reasons is that
migration of RII to unrepaired defects can occur when only some RII
entry points are eliminated. Furthermore, building lateral defects
and/or foundation drain connections on private property may
represent a significant portion of the RII in many systems.
Therefore, the effectiveness of a rehabilitation program in
reducing Rll is dependent not only on the repair techniques used
but also on the extent of the rehabilitation effort.
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Control Methods
Long-term RII Control Approaches
Although a rehabilitation program may be effective in immediately
reducing RII levels in a sewer system, it will not necessarily
guarantee that those RII levels are maintained. Long-term control
requires that RII be prevented from increasing in unrehabilitated
areas of .the system, as well as from entering from newly
constructed sewers. Long-term RII control can be implemented
through: '..•'. , :
o Effective preventive maintenance programs. .
,_ o Implementation of appropriate design standards and
construction practices.;
An effective preventive maintenance program should include:
o Periodic flow!monitoring in the system to identify areas
with increases in RII levels.
o A routine program-of cleaning and root removal.
o A cyclic program of testing and inspection of the sewers
throughout the system to identify the heed for repairs
replacement. ;
In systems where defective building laterals or foundation drains
represent a significant portion of the RII, the program should also
include private facilities.
COST EVALUATION , '
Costs for sewer system rehabilitation to reduce RII must be
compared to. those for transport and treatment of RII flows to
evaluate the cost effectiveness of various RII reduction options.
The "traditional" approach to performing I/I cost-effectiveness
analyses, as described in the EPA Handbook for Sewer System
Evaluation and Rehabi1itation f is based upon determining the flow
contribution and correction cost for each individual I/I source in
the sewer system identified through field inspection and testing.
The I/I sources are then ranked in order of least cost per unit ;of
I/I flow removed. The cumulative flow reduction and corresponding
correction cost for successive elimination of the individual I/I
sources in order of least unit cost ranking are calculated. The
cumulative correction cost is then plotted against cumulative I/I
removed, along with the corresponding (decreasing) cost for
transport and treatment (see Figure 3-1). The low point of the
total cost curve represents the cost-effective level of I/I
reduction for the system. Those individual sources which rank
above this level are considered to be cost effective to correct.
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CO
O
o
i
09
U)
TOTAL COST
TRANSPORT &
TREATMENT COST
MINIMUM TOTAL
COST
REHABILITATION
COST
COST EFFECTIVE I/I REMOVAL
I/I REMOVED
FIGURE 3-1
TRADITIONAL COST-EFFECTIVENESS CURVE
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Control Methods
As noted previously, in sewer systems where the primary entry
points of RII are defects in sewer pipes and laterals and where
such defects are generally widespread, migration of RII to
unrepaired, defects may occur when only some points of RII entry
have been eliminated. Additional defects may become active as the
water seeks new entry-points to the sewers. This migration factor
has resulted in the failure of the traditional cost-effectiveness
analysis approach to accurately predict the amount of extraneous
flow reduction achievable through implementation of many correction
programs^originally calculated to be cost effective.
For this study, a cost evaluation was conducted to analyze the
relative cost effectiveness of different rehabilitation approaches.
Cost-effectivenss analyses were conducted for different "model"
sewer systems, which were defined in terms of their age and general
physical condition, magnitude and distribution of RII, and density
of building laterals. The models were developed to evaluate sewer
systems where the primary entry points of RII are defects in sewer
mains and laterals, as opposed to systems in which the primary RII
entry is through manhole framed/chimney defects, foundation drains,
or other entry points not generally classified as pipe defects.
The purpose of the model system cost evaluation was to identify how
the cost-effectiveness of RII correction was affected by the
characteristics of the sewer system and by the type of
rehabilitation approach selected. The rehabilitation approaches
,evaluated included:, .
o Isolated repair (spot repair of individual defects or
specific pipe reaches).
/ . " •
o. Rehabilitation of public sewer mains only.
o -• Rehabilitation of sewer mains, plus lower laterals (the
portion within the public right-of-way). .
o Rehabilitation of sewer mains plus entire, building
laterals.
The cost analysis was designed to overcome the;major limitation of
the traditional cost-effectiveness methodology, that of
overestimating rehabilitation effectiveness by ignoring the effects
of flow migration. Two key'assumptions were made:
o Rehabilitation was assumed to be conducted throughout
contiguous areas within sewer subsystems, rather than only
addressing individual RII entry points. To address a
significant portion (at least 50 percent) of* the RII in
' . a subsystem, an area that included at least 30 percent or
more of the "worst" sewers in the subsystem would require
rehabilitation. .The RII distribution within any
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Control Methods
particular subsystem could be assumed to fall within a
generalized envelope, as shown in Figure 3-2.
o The assumed Rll reductions (removable percentages of RID
assigned to various rehabilitation approaches were based
on recognized limitations of "incomplete" system
rehabilitation due to flow migration effects. Thus, large
reductions (greater than 50 percent) were considered
achievable only if the rehabilitation program included
both the mains and laterals.'
A detailed description of the assumptions and procedures used for
the model system cost evaluation is presented in Appendix F.
The general results of the model system cost evaluation indicated
that RII correction would probably not generally be cost effective
in a "typical" old sewer system (sewers in generally poor condition
and defects widespread) because of the high cost and need for
extensive rehabilitation. However, under certain conditions (for
example, a newer system with very high RII flows but low lateral
density), RII could be cost effective if the mains and entire
laterals were rehabilitated.
However, since the cost, evaluation was applied to fictitious sewer
systems and involved a number of assumptions regarding sewer system
conditions and existing transport and treatment capacities, it was
not intended to develop costs for RII control that could be applied
to all sewer systems or draw definitive conclusions about the cost-
effectiveness of RII correction in any specific sewer system. As
noted previously, the types of RII correction programs addressed
in the cost analysis are primarily aimed at correcting sewer system
defects (RII entry points) using commonly applied techniques.
Therefore, the cost evaluation did not consider the potential for
RII reduction through improved design.and construction standards,
new or less costly techniques, or through as yet undiscovered
methods that might be developed to intercept or divert water away
from the pathways through which it reaches' the sewers.
The cost effectiveness of RII correction is highly dependent on the
capacity of existing downstream transport and treatment facilities
and on the costs to provide any additionally required transport and
treatment facilities. In a system where pipeline construction
might be required in congested areas or under adverse soil or
groundwater conditions, transport costs would be higher and RII
correction could be more cost effective. Similarly, if treatment
plant site constraints make overall plant expansion or construction
of flow equalization facilities prohibitively expensive, the cost
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100 r
LU
20 40 60 80
PERCENT OF SEWERS IN SUBSYSTEM
100
FIGURE 3-2
HYPOTHETICAL Rll DISTRIBUTION
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Control Methods
effectiveness of RII correction would also be higher. In the EBMUD
system, for example, the high costs to transport,and treat the peak
RII flows have made RII correction cost effective in about 50
percent of the system. This is despite the fact that EBMUD is an
old system with a relatively high lateral density.
An important point needs to made about old sewer systems with
respect to assessing the cost effectiveness of rehabilitation.
Many old systems have experienced significant structural
deterioration. Good infrastructure management dictates
rehabilitation, if only for the purpose of maintaining the
structural integrity and proper functioning of the system. If it
is recognized that life-cycle replacement and rehabilitation are
integral parts of sewer system management, then the cost
effectiveness of system rehabilitation can be assessed in terms of
the benefits of both structural maintenance and RII reduction. In
these cases, sewer system rehabilitation may be cost effective for
reasons other than for RII reduction alone.
INSTITUTIONAL AND REGULATORY APPROACHES
Institutional and regulatory approaches can help facilitate
implementation of rehabilitation programs and long-term RII control
programs. These types of measures are particularly suited for RII
control on private property.
Rehabilitation Programs
Institutional and regulatory measures that can be used in
conjunction with rehabilitation programs include:
o Public agency ownership of laterals and/or responsibility
for lateral construction.
o Financing programs (for public and/or private facilities).
o Enforcement (for private property rehabilitation).
o Public information programs.
Rehabilitation of both the public and private portions of a sewer
system as part of a single, integrated construction project has
distinct advantages in terms of lower cost, better quality control,
and minimizing disruption to the community. One option available
to an agency that is contemplating rehabilitation of sewers and
laterals is taking over temporary ownership of the laterals during
construction and assuming responsibility for maintenance of
laterals for a ori'e or two year warranty period after
rehabilitation. These steps would allow the agency to perform any
needed testing and rehabilitation without repeated contact with the
property' owner. After the agreed upon time period, the
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, Control Methods
1 • ' '
responsibility for the- lateral would automatically revert, to.the
property owner. The length of the time period selected should
allow for completion of all necessary work and include a warranty
period to ensure that the work has been properly undertaken.
Rehabilitation programs are expensive and may present considerable
strain on the financial resources of both the public agency and the
individual property owners. Financing options for public agencies
include pay-as-you-go financing from general sewer use revenues,
revenue bonds (repaid out of user fees),, assessment district
financing/and combinations thereof. Financing assistance may also
be offered to individual property owners in the form of low-
interest loans; local assessment district financing; or reduced
costs through agency assistance in design of private property
improvements, preparation of bid documents, and construction
inspection.
Strict enforcement of requirements for private property repairs is
another option. Municipalities with foundation drain connections
to the sanitary sewer system have, in some cases, instituted
inspection programs with mandatory removal of connected drains.
Local ordinances have^been passed for not disconnecting the drains,
with penalties ranging from warnings to fines to forcejd
disconnection. Similar regulatory methods can be used for
enforcing building lateral rehabilitation. Such enforcement would
require an ordinance that requires a building owner to maintain a:
properly operating lateral that does not contribute excessive non-
wastewater flows to the sewer system, or require that the lateral
be capable qf. passing a standard leakage test.
The success'of an overall RII control program may greatly depend
upon how well-informed the general public is regarding the need and
requirements for the program. An effective public education
program can potentially elicit substantial voluntary participation
from individual property owners. For example, in Ames, Iowa, a
public information program, combined with limited financial.
assistance, was successful in implementing necessary foundation
drain disconnections on a voluntary basis.
Long—term Programs ,
Since new sewer facilities are often constructed by the /private
sector rather than a public agency> regulations provide a means of
enforcing desired design standards and construction practices to
minimize future RII. Preventive maintenance programs, particularly
for private facilities, can be facilitated through regulations with
requirements for testing, inspection, and repair of sewer system
components found to be contributing RII.
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Control Methods
SiSi?^ P??"la.rity in *any Parts
ent an lal^i^^^ViSIC^.P"**^
^^^^
cycle, integrating 4e testing re^fremen/to^ refsonai*e time
minimizes both the administrftivf^urden on Iht S&le °f Pr°Perty
financial im agenc and
nsrvurden on h
financial impact on the property owner. agency and the
ac
may be needed to effectively cleaS lLS?> and at the st«cture
Consequently, some communities re™'i~S£eCt' 7 test each lateral.
In some localities wherTa curb ci^™ fleanouts at both locations.
will not maintain the lower SSrtionS?^d°fS.nOt exist' the a9ency
installs one. . in ^ otheT muSicioa?!?! £** t****?1 unless the «««
inspection is required S5SSSX -t • t^ iateral testing or
inspection procesHf they SSSSt b^ f7o,S StalTled as part of ^
country where cleanouts T outSde of Sf * JPtF** areas of the
practical because of weather c««rfr lateral
or inspection. ay be necessary to complete testing
EXAMPLE RII CONTROL PROGRAM - EBMDD
mt^^iS1!?^ Pr°.gram' that °f tte
2 ^ystemTut^^^^^
c^ S the
y^
the field i-tffa^1^^
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Control Methods ,
the SSESs. While the fundamental concept of cost effectiveness was
consistent with basic EPA requirements, a very detailed and
rigorous approach was developed to quantify and identify I/I
• components and analyze the costs for I/I correction.
Field Investigations
The EBMUD sewer system consists of about 1,500 miles of sewer
mains. The initial field effort involved focussing the study on
those areas with the most significant I/I flows and therefore the
greatest potential for cost-effective I/I correction. This was
accomplished through a "gross" monitoring program, in which over
300 flow monitors, each with a tributary area containing an average
of about 20,000 feet of sewer mains, were used to record sewer"
flows over a two-month period during the rainy season. For each
monitor, storm flow data was "decomposed" into base flow and rain-
induced I/I components. A method was developed to quantify the
rain-induced I/I as a percentage of rainfall volume and describe
the shape of the hydrograph with mathematical parameters. These
parameters were then used to develop a "projected" hydrograph for
each area of the sewer system for an established five-year design
storm. This procedure enabled comparison of the rain-induced I/I
flows from all areas of the sewer system on the basis of a common
rainfall event.
Based on the results of the gross monitoring program, specific
areas (subbasins) of the sewer system with the greatest potential
for cost-effective I/I reduction were identified for further field
work. The field work included smoke testing, dye flooding, manhole
inspection, and flow isolation. Based on the results of flow
isolation, specific sewer reaches within each subbasin were
identified for TV inspection. As described in Chapter 2, the smoke
testing results indicated that there were very few direct inflow
sources in the system, and that laterals were a major potential
contributor of RII. other special field studies on laterals (TV
inspection, leakage testing, rainfall simulation, and flow
measurement during rainfall) were conducted to verify this
hypothesis. TV inspection of sewer mains indicated that the sewers
in the system were in generally very poor structural condition,
with numerous cracks, offset joints, and other defects that serve
as entry points for Rli;
Cost-Effectiveness Analysis
The data obtained from flow monitoring and field testing and
inspection were used to conduct a detailed analysis of the qost-
fffectxveness of sewer system rehabilitation to reduce I/I.
Although -the analysis addressed all components of I/I (SWI, Rli,
and GWI) , the primary emphasis was on reduction of peak flows by
controlling Rli entry into the system.
-------
Control Methods
Rehabilitation Program
*
second year of iroiementi?f«« « Program is currently in its
°-
pa« ,.
e<"**ril f
maintenance reasons ra?Lt £^e
-------
Control Methods
Long-term RII control
the EBMUD SSES
odeo - e EBMDD SSES
SUMMARY
and «„ .
rehabilitation
.in-
sPe=if lcally
0
to apply to later ' 3re ™°re costly and
-------
Control Methods
can be effective iti T reducih
ae;irMstisdam?nsiBar2dec?sttruction
rehabilitated sewers by ^" in° new or
. «»~«*
through I/I oorreotionecauet faii t?"n «*i«»
migration of RII to unrepaired LleoU. a°°ount for *»»
nf
transport and treatment f aoiime's aS th»eS ,°l .existin9
to construct additional capacity?' "lative costs
be necessary
enforcement, f inancina a ™HI " ?rder to Pr°vida for
property rehaMuiation. P «*°rfflation for private
RECOMMENDATIONS
«=
Physical conditios
ef ec^f
-------
Control Methods
o The following considerations should be incorporated into
.....the development of sewer system rehabilitation programs
and . evaluation of the .cost effectiveness of
rehabilitation:
Addressing entire areas of the sewer system versus
repair of individual defects only.
- Including both the public and private portions Of the
sewer system versus only the public portion.
o Long-term RII control should be ensured through
implementation of an effective preventive maintenance
program that includes:
- Periodic flow monitoring in the system to identify
areas with increases in RII levels.
- A routine program of cleaning and root removal.
- A 'cyclic program of testing and inspection of the
sewers throughout the system to identify the need for
repairs and replacement.
o Sewer design standards should be modified to include the
following considerations:
Restricting the flow of water in granular backfill.
Reduction of utility trench backfill
interconnections.
Control of migration of . fine soil or. backfill
material particles.
- Reduction in the number of pipe joints.
- Incorporation of pipe system flexibility to reduce
settlement stresses.
- Improved sealing of pipe connections at manholes.
- Provision for tight, but flexible, lateral
connections.
- Provision for access for testing, inspection, and
repair of laterals.
D Effective sewer construction practices should be followed
to ensure that design standards are met by:
3-22
-------
Cont ro 1 • Methods"
- " Regular construction inspection.
- Adequate performance testing for public sewer mains
as well as private laterals.
The institutional and regulatory framework governing the
construction and maintenance of house laterals (the
connection between the house or building and the collector
sewer in the street or other public right-of-way) should
be re-examined. Possible options include:
Shifting responsibility for construction and/or
maintenance of house laterals from the home owners to
the municipality.
\ , • .
- Municipal programs to help home owners pay for
maintenance and repairs of house laterals.
- State or municipal ordinances, with appropriate
enforcement provisions, governing inspection, testing
and repair of house laterals.
- Public education programs to inform citizens of the
importance of excluding extraneous flows from the
municipal sanitary sewerage systems.
The development of new, improved, and potentially less
costly sewer rehabilitation techniques, particularly for
laterals, should be encouraged.
The collection and publication of data documenting the
effectiveness of different rehabilitation methods and
approaches to controlling RII should be encouraged.
3-23
-------
APPENDIX A
LIST OF ABBREVIATIONS
ABS Acrylonitrile butadiene styrene pipe
AC Asbestos cement pipe
ADWF Average dry weather flow
BWF Base wastewater flow -
BOD Biochemical oxygen demand
C-E Ratio Cost-effectiveness ratio
CMP Corrugated metal pipe
CSO Combined sewer overflow
EBMUD . East Bay Municipal Utility District
EPA U.S. Environmental Protection Agency
gpcd Gallons per capita per day
gpd Gallons per day
gpm Gallons per minute
GWI Groundwater infiltration
I/I Infiltration/inflow
mgd Million gallons per day
rag/I Milligrams per liter
MMSD Milwaukee Metropolitan Sewerage District
NEORSD Northeast Ohio Regional Sewer District
NPDES National PoUutant Discharge Elimination System
O&M Operation and Maintenance
PVC Polyvinyl chloride pipe
PWWF Peak wet weather flow
RDI/I
RII
RII/I
Rainfall dependent infiltration/inflow (same as RII/I)
Rainfall induced infiltration
Rainfall induced infiltration/inflow
-------
SSES Sewer system evaluation survey
SWI Storm water inflow
TSS Total suspended solids
VCP Vitrified clay pipe
WWTP Wastewater treatment plant
-------
APPENDIX B
REFERENCES
CHAPTER 2
Lee, David M., arid Molzahn, Robert E., "Foundation Drain Inflow Characterization in a
Rehabilitated Sanitary Sewer System."
Undated,
United States Environmental Protection Agency. "Handbook for Sewer System Evaluation
and Rehabilitation." MCD-19. December 1975.
East Bay Municipal Utility District, California
' • ', ' "~v- ' . , . • . ...'"--
CDM/Jordan/Montgomery. "East Bay Infiltration/Mlow Study, Berkeley Sewer System
Evaluation Survey Report." November 1985.
CDM/Jordan/Montgomery, CH2M HnJL/WLA, The Eastshore Consultants. "East Bay
Infiltration/Inflow Study, Manual for Cost-Effectiveness Analysis." July 1981, revised
December 1985. ,
CH2M-HTJLL. "East Bay Infiltration/Inflow Study, Oakland North Sewer System Evaluation
Survey." January 1986. ; •,-..'"
East Bay Infiltration/Inflow Correction Program. "Final Environmental Impact Report."
April 1986... .
Geotechnical Consultants, Inc. "Ground Water Infiltration Into Sanitary Sewers, Cities of
Albany, Berkeley, Emeryville, and South Oakland,California."April 1982.
'; . "Supplemental Geotechnical Investigation, East Bay Infiltration/Inflow Study, Cities of
Albany, Berkeley, Emeryville, and Oakland, California." April 1984.
The Eastshore Consultants (Black & Veatch, Brown «& Caldwell, Waste & Water
International). "Building Lateral Testing and Rehabilitation Pilot Project." East Bay I/I
Study. October 1984. .
Springfield, Oregon
Black, Edward. "City of Springfield, Oregon, Infiltration/Inflow Analysis." July 1976.
B-l
-------
References
CH2M-HH1. "City of Springfield Sewer System Evaluation Survey, Phase I Report." July
1978.
. "Springfield, Oregon, Sewer System Evaluation Survey Summary Report." December
1980.
Rehabco Pipe Services, Inc. " I/I Control Plan For The City of Springfield." July 1986.
Milwaukee Metropolitan Sewerage District, Wisconsin
Milwaukee Pollution Control Abatement Program, Program Management Office
(CH2M-Hill/Donohue & Associates, Inc./Howard Needles
Tammen & Bergendoff/Graef, Anhalt, Schloemer & Associates, Inc./ Polytech Inc./J.C
Zimmerman Engineering Corp./Klug & Smith Co.) "Milwaukee Metropolitan Sewerage
District, Sewer System Evaluation Survey, Executive Summary." August 1981.
. "Milwaukee Metropolitan Sewerage District, Sewer System Evaluation Survey,
General Report, Volume I." August 1981.
. "Milwaukee Metropolitan Sewerage District, Sewer System Evaluation Survey, General
Report, Volume H" August 1981.
. "Milwaukee Metropolitan Sewerage District, Private Property Infiltration/Inflow Pilot
Project." August 1981.
. "Milwaukee Metropolitan Sewerage District, Manhole Rehabilitation Pilot Project."
April 1982.
Milwaukee Metropolitan Sewerage District, Operations Division. "System Monitoring
Report." August 1986.
. "System Monitoring Annual Report, Appendix." August 1986.
Northeast Ohio Regional Sewer District, Ohio
t j '',•,•
CH2M-HELL. "Easterly Separate Sewer Segment Wastewater Facilities Plan, Volume 2
Infiltration and Inflow Analysis." 1978.
Dalton, Dalton, Newport. "Northeast Ohio Regional Sewer District, Easterly Separate
Sewer Area, Sewer System Evaluation Survey Summary Report." October 1983.
B-2
-------
References
. 'The Northeast Ohio Regional Sewer District Heights/Hilltop Interceptor Sewer
System Update, Summary Report, SSES ERRATA," November 1986.
.'. "The Northeast Ohio Regional Sewer District Heights/Hilltop Interceptor Sewer
System Update Summary Report." November 1986.
Dalton, Dalton, Newport/Frank A. Thomas & Associates, Inc. "Northeast Ohio Regional
Sewer District, Easterly Separate Sewer Area, Sewer System Evaluation Appendices,
Volume 1." June 1983^
_. "Northeast Ohio Regional Sewer District, Easterly Separate Sewer Area, Sewer System
Evaluation Appendices, Volume 3." June 1983.
Dalton, Dalton, Newport/Havens and Emerson, Inc. "Northeast Ohio Regional Sewer;
District, Easterly Separate Sewer Area Advanced Facilities Planning Report." September
' 1983. ' ' • ' . ' '-;-•" " • •" • .../';-' •'-•.'• -."' ; ;' . ..,' '.
__. "Northeast Ohio Regional Sewer District, Easterly Separate Sewer Area, Supplemental
Facilities Planning Report." September 1983.
Dalton, Dalton, Newport/Snell Environmental Group. "Northeast Ohio Regional Sewer
District, Easterly Separate Sewer Area, City of Cleveland Heights Sewer System
Evaluation." June 1983.
. "Northeast Ohio Regional Sewer District, Easterly Separate Sewer Area, City of
Shaker Heights Sewer System Evaluation." June 1983.
_. "Northeast Ohio Regional Sewer District, Easterly Separate Sewer Area, City of
University Heights Sewer System Evaluation." June 1983.
John David Jones & Associates, Inc. "Northeast Ohio Regional Sewer District, Southwest
Interceptor Area Sewer System Evaluation Survey Summary Report." February 1984.
John David Jones & Associates, Inc./Howard Needles Tarnmen & Bergendoff. "Northeast
Ohio Regional Sewer District, Southwest Interceptor Area Sewer System Evaluation Survey
Final Report For Columbia Township, Olmsted Falls, Township, Strongsville." February
1984. ''.'•• .
B-3
-------
References
_ . "Northeast Ohio Regional Sewer District, Southwest Interceptor Area Sewer System
Evaluation Survey Appendices, Volume I, II, and
Strongsvffle." February 1984.
Baton Rouge, Louisiana
Albert Switzer & Associates, Inc; and Naylor Industries, Inc. "Sewer System Evaluation
Survey, Parish of East Baton Rouge, Louisiana, Consolidated Sewer District, North
System." July 1979.
, A ' ^^^ ' ' , '
_ . "Sewer System Evaluation Survey, Parish of East Baton Rouge, Louisiana,
Consolidated Sewer District, South System, Volume I." July 1979.
Barnard & Thomas Engineering, Inc. "Minor Rehabilitation During Sewer System
Evaluation Survey, Central Treatment Service Area, East Baton Rouge Parish, Louisiana,
Final Report." September 1986.
Camp Dresser & McKee Inc. "Population and Flow Projection, City of Baton Rouge,
Parish of East Baton Rouge, Wastewater System Improvement Program." November 1987.
_ . "Inventory of Existing Facilities, City of Baton Rouge, Parish of East Baton Rouge,
Wastewater System Improvement Program."
December 1987.
Springfield, Missouri
Consoer, Townsend and Associates. "City of Springfield, Missouri, Southwest Wastewater
Collection and Treatment System Infiltration/Inflow Analysis." June 1974.
City of Springfield, Missouri. "Sewer System Evaluation Survey." 1980.
North and South Shenango Joint Municipal Authority, Pennsylvania
L. Robert Kimball & Associates. "Sewerage System Evaluation Report for North & South
Shenango Joint Municipal Authority." 1984.
i
_. "North & South Shenango Joint Municipal Authority Flow Monitoring Report."
October 1987.
Ames, Iowa
B-4
-------
References
Rieke Carroll Muller Associates, Inc. "Report on Infiltration/Inflow Analysis, City of Ames,
Iowa." December 1975.
. "Sewer Systeation Survey Report For City of Ames, Iowa," May 1979.
__. "Appendix to Sewer System Evaluation Survey Report For City of Ames, Iowa." May
1979. >
Coos Bay, Oregon ,
Brown & Caldwell "Citos Bay, Wastewater Collection and Treatment Facilities Plan
Supplement." February 1987.
H.G.E., Inc. "Cops Bay Wastewater System Facilities Plan, Draft." 1985.
Tulsa, Oklahoma
Max Holloway Engineering Co., Brutpn Knowles & Love, Inc., Black <& Veatch.
"Wastewater Facilities Plan For Southslope Drainage
Basin City of Tulsa, Oklahoma, Volume III, Infiltration/Inflow Analysis." August 1987.
CH2M-Hill,s Mausur-Daubert-Williams, Kellog, Gutierrez-Smouse-Wilmut. "Executive
Summary Northside 201 Facilities Plan, City of Tulsa, Oklahoma." July 1982.
.'. "Northside 201 Facilities Plan, City of Tulsa, Oklahoma." July 1982.
Gutierrez-Smouse-Wilmut, Mansur-Daubert-Williams, Kellog, CH2M-HH1. "Northside
Infiltration and Inflow Analysis, City of Tulsa, Oklahoma," July 1982.
Gutierrez-Smouse-Wilmut, CH2M-Hffl Inc. "Sewer System Evaluation Survey For The
Northside Facilities Planning Area, Phase I, City of Tulsa, Oklahoma." October 1986.
. "Sewer System Evaluation Surside Facilities Planning Area, Phase II, City of Tulsa,
Oklahoma." October 1986.
CHAPTERS
American Public works Association. '^Control of Infiltration and Inflow into Sewer Systems."
December 1970.
B-5
-------
References
American Society of Civil Engineers and Water Pollution Control Association. "Existing
Sewer Evaluation & Rehabilitation." 1983.
Anon. "Sealing of Sewers in Unstable Soils." American City & County, Vol. 96, No. 3.
March 1981.
Anon. "Polyethylene Pipe Tackles Difficult Sewer Repair Job." Water & Sewage Works,
Vol. 123, No. 2. February 1976.
Anon. "A Sewer System Analysis as Performed for the City of Bellaire, Texas." Texas
Innovation Group, College Station. March 1979.
Anon. "Ground Water Infiltration and Internal Sealing of Sanitary Sewers, Montgomery."
Montgomery County Sanitary Dept, Dayton, Ohio. June 1972.
Backman, Hans. "Infiltration/Inflow in Separate Sewer Systems." Chalmers University of
Technology, Dept. of Sanitary Engineering,
Goteborg, Sweden. 1985.
Brown and Caldwell. "Utility Infrastructure, Rehabilitation." U.S. Department of Housing
and Urban Development. November 1984.
Carter, William C. "The Development and Implementation of a Progressive Rehabilitation
Program for the Removal of Private Sector Infiltration/Inflow." Water Pollution Control
Federation, 60th Annual Conference, Philadelphia, Pennsylvania October 8, 1987.
Carter, William C; Nogaj, Richard J.; Hollenbeck, Alan J. "Cost Effectiveness and Sewer
Rehabilitation." Public Works, Vol. 117, No. 10. October 1986.
CDM/Jordan/Montgomery, "East Bay Infiltration/Inflow Study, Policy Considerations for
Lateral Testing and Rehabilitation for the City of Oakland." July 1987.
Cox, G.C. "Making Use of the Hole - New Techniques for Sewer Renovation." Restoration
of Sewerage Systems, Proceedings of an International Conference organized by the
Institution of Civil Engineers, held in London on 22-24 June 1981. Thomas Telford Ltd,
London. 1982.
Driver, F.T., and Olson, M.R. "Demonstration of Sewer Relining by the Insituform Process,
Northbrook, IL." August 1983.
B-6
-------
References
Emery, J.A. "New Techniques in Non-Many Entry Sewer Renovation." International
Conference on the Planning, Construction, Maintenance & Operation of Sewerage
Systems, Reading, England, 12-14; September, 1984. ,
Evans, Jack, and Spence, Marlene. "Evolution of Jointing Vitrified Clay Pipe." Proceedings
of the International Conference on Advances in Underground Pipeline Engineering,
Madison, WJ,,August 27-29, 1985. . .
Fiddes, D. "Sewerage Rehabilitation Strategy for the United Kingdom." International
Conference on the Planning, Construction, Maintenance & Operation of Sewerage
Systems, Reading, England, 12-14 September, 1984. .
Foster, William. S., and Sullivan, Richard H. "Sewer Infiltration and Inflow Product and
Equipment Guide." American Public Works
Association, Chicago, HI.
Gill, S.M. "Developments in Grouting Technology for Sewer Renovation." International
Conference on the Planning, Construction, Maintenance & Operation of Sewerage
Systems, Reading, England, 12-14 September, 1984.
Goodman, W.J.P., and Hope, P.S. "Inspection and Renovation of Sewers: State of the Art
in Sydney." International Conference on the Planning, Construction, Maintenance &
Operation of Sewerage Systems, Reading, England, 12-14 September, 1984.
Hollenbeck, Alan J. "Designing for Removal of Sanitary Sewer Cross Connections."
Water/Engineering and Management, Vol. 131, No. 4. April 1984.
Holmes, Kenneth T.; Black, Edward; and Brown, Dan E. "Infiltration/Inflow Analysis:
Finding the Source." American City & County, Vol. 97, No. 2 February 1982.
Jacques, W.B. "Stopping Water with Chemical Grout" Civil Engineering, Vol. 51, No. 12.
December 1981.
Jones, M.A. "Small Diameter Pipe Maintenance and Renovation." International
Conference on the Planning, Construction, Maintenance & Operation of Sewerage
Systems, Reading, England 12-14 September, 1984.
Jones, Maurice B. "Sewer Renovation." Tunnels and Tunnelling, Vol. 19, No. 10. October
1987.
B-7
-------
References
Mayer, John K.; Macdonald, Frank W.; and Steimle, Stephen E. "Sewer Bedding and
Infiltration, Gulf Coast Area." Tulane University,
New Orleans, La. May 1972.
Morgan, Thomas R. "Private Source Inflow Removal." Journal of the New England Water
Pollution Control Association, Vol. 19, No. 2.
November 1985.
Munro, L, and Holmes, M.J. "City's Experience of Thin-Shell Sewer Lining." Restoration
of Sewerage Systems, Proceedings of an .
International Conference organized by the Institution of Civil Engineers, held in London
on 22-24 June 1981. Thomas Telford Ltd, London. 1982.
Murray, J.B. "Infiltration Rates for Separate Sewage Collection Systems." Gutteridge
Haskins & Davey, Melbourne, Aust., Water Science and Technology, Vol. 19, No. 3-4,
1987, Water Pollution Research and Control, Part 2, Proceedings of the Thirteenth Biennial
Conference of the International Association of Water Pollution Research and Control, Rio
de Janeiro, Brazil, August 17-22, 1986.
Olson, M.R. "Insituform and Other Sewer Rehabilitation Techniques." November 1985.
Paulson, Richard L; Wylie, F. Samuel; Anderson, David S.; and Miles, Frank. "Attacking
Private Infiltrationflnflow Sources." Public Works, Vol. 115, No. 2. February 1984.
Pefl, Kelly M., and Diehl, Douglas S. "Reducing Sewer Infiltration/Inflow." Civil
Engineering, Vol, 45, No. 12. December 1979.
Penner, I.L. "Grouting Provides Economical and Effective Maintenance in Kansas." Water
& Sewage Works, Vol. 125, No. 3. March 1978.
Peters, D.C. "Social Costs for Sewer Rehabilitation.' International Conference on the
Planning, Construction, Maintenance & Operation of Sewerage Systems, Reading, England,
12-14 September, 1984.
. "Development of a Policy for Sewer Rehabilitation." Restoration of Sewerage Systems,
Proceedings of an International Conference organized by the Institution of Civil Engineers,
held in London on 22-24 June 1981. Thomas Telford Ltd, London. 1982.
Quellette, Herve, and Schrock, B. Jay. "Rehabilitation of Sanitary Sewer Pipelines."
American Society of Civil Engineers, Transportation Engineering Journal, Vol. 107, No.
4 July 1981.
B-8
-------
References
Read, G.F. "Sewer Dereliction and Renovation - An Industrial City's View;" Restoration
of Sewerage Systems, Proceedings of an International Conference organized by the
Institution of Civil Engineers, held in London on 22-24 June 1981. Thomas Telford Ltd,
London. 1982. .
Reed, K, and Rumsey, P.B. "Renovation Development Trails." International Conference
on the Planning, Construction, Maintenance & Operation of Sewerage Systems, Reading,
England, 12-14 September, 1984.
Schrock, B. Jay. "Pipeline Rehabilitation Techniques." International Conference on the
Planning, Construction, Maintenance & Operation of Sewerage Systems, Reading, England,
12-14 September, 1984. -.
. "Solutions in the Pipeline." Civil Engineering, Vol. 55, No, 9. September 1984.
St. Onge, H. "Relming: The Feasibility of Inserting Pipe into Existing Sewers:" Canadian
Water Resources Journal, Vol. 9, No. 3. November 1984.
Steketee, C.H., and Heinecke, Thomas L. "Key to Effective HI Control." Public Works, Vol.
115, No. 6 June 1984.,
Sullivan, Richard H., and Thompson, William B. "Assessment of Sewer Sealants." American
Public Works Association, Chicago, II. May 1982. ,
United States Environmental Protection Agency. "Construction Costs for Municipal
Wastewater Treatment Plants: 1973-1977." MCD-37. January 1978.
__. "Construction Costs for Municipal Wastewater Treatment Plants: 1973-1978." FDR-11.
April 1980.
''.'•' ' • \ ' - ''•''•:' '
, "Handbook for Sewer System Evaluation and Rehabilitation." MCD-19. December
1975. • • • , ;
1 \ • ' < i -' ,
Watson, T.J. "Trenchless construction for underground services." Construction Industry
Research and Information Association,
Technical Note 127. Undated.
B-9
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APPENDIX C
CASE STUDIES
This appendix contains detailed descriptions of the RII case
studies summarized in Chapter 2. The case studies are:
o East Bay Municipal Utility District, California
o City of Springfield, Oregon
o Milwaukee Metropolitan Sewerage District, Wisconsin
o Northeast Ohio Regional Sewer District, Ohio
o City of Baton Rouge, Louisiana
o City of Springfield, Missouri
o North and South Shenango Joint Municipal Authority,
Pennsylvania
o City of Ames, Iowa
o City of Coos Bay, Oregon
o City of Tulsa, Oklahoma
EAST BAY MUNICIPAL UTILITY DISTRICT, CALIFORNIA
The EBMUD wastewater service area is located in northern California
on the eastern shore • of San Francisco Bay. It includes seven
community wastewater collection agencies. EBMUD operates the
interceptor system and treatment facilities which transport and
treat the wastewater generated from these seven communities. The
collection systems, which include about 1,500 miles of sewer main,
are owned and operated by the individual communities. Although the
original sewers installed prior to 1938 were constructed as
combined storm drainage and sanitary sewage facilities, the systems
are now entirely separate sanitary systems.
The community collection systems, as well as the EBMUD interceptor
and treatment facilities, do not have adequate capacity to handle
the peak flows which occur during wet weather. As a result,
overflows onto city streets and bypasses to local watercourses and
to San Francisco Bay occur at numerous locations within the
community systems and at seven locations along the EBMUD
interceptor. Peak wet weather flow rates^ may exceed twenty times
the average dry weather flow in the system.
C-l
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Case Studies
In, 1980, the wet weather problems in the EBMUD service area led to
the initiation of the East Bay Infiltration/Inflow Study to address
the problems within the community collection systems. Concurrent
with this East Bay I/1 Study, EBMUD conducted a . wet weather
facilities plan for its interceptor and treatment facilities. The
;East Bay I/I Study included extensive flow monitoring and SSES
field work within the community collection systems. One of the
major conclusions of the study was that the major portion of the
peak wet weather flows in the EBMUD system are due to infiltration
of storm water into defective pipes and manholes. This RII
appeared to exhibit similar flow characteristics as direct storm
water inflow, with very rapid, high peak flows occurring in direct
response to rain storms. A major source of the RII is believed to
be defective building laterals.
System Description .
\ -.... ' -] :
The EBMUD wastewater service area is located on the east shore of
San Francisco Bay, extending eastward to the steep hills that form
the eastern and northern boundaries of the area. Most of the
developed portion of the service area,is located on an alluvial
plain, at an average elevation of 75 feet and a width of from one
to three miles, which rises gently from the Bay shoreline eastward
to the foot of the hills. Predominantly newer development is
located in the hill areas, which rise to an average crest of 1,200
feet* ' •• '- ^ '••".'''..."'".' ..•."!,. • • :
Rainfall. The average annual rainfall, as measured at the Oakland
Airport located on the shoreline of the Bay, is about 18.7 inches,
with 90 percent of the rain falling during the period November
through April. Winter storms move through the area from west to
east, generally depositing a greater amount of precipitation in the
higher elevations of the study area. (Hence, the actual average
rainfall in the study area is higher than the Oakland Airport
data.) During the winter season, storms may occur one after another
during extended rainy periods, or dry periods of up to several
weeks without any rain may occur. •
Soils. The soils within the study area range from loose sediments,
such as bay muds in the marshy tida^l flats, to sedimentary rocks
in the hillsides. The tidal flats, consisting of clays and silty
clays, extend along the perimeter of the Bay. At higher elevations,
soils were formed along flood plains, river-mouth fans, and low
terraces, and include silty clays, clays; silty clay loams, clay
loams, and sandy clay loams. Much of the soils in the EBMUD service
area haveva high shrink-swell potential and low percolation rates.
Under prolonged dry periods, as occur during the summer months, the
soils are subject to shrinking and cracking.
C-2
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Case Studies
Hydrogeology. Numerous small streams discharging to the Bay drain
the basins formed by the Oakland-Berkeley hills. These streams,
together with the intervening ridges, form the topographic features
that describe tributary areas (basins) of the wastewater collection
systems. Groundwater levels in the study area range from less than
five feet below the ground surface in locations near the Bay
shoreline to greater than 10 feet below the surface in the hill
areas. However, some higher groundwater levels may be found in
localized portions of the higher topographic areas due to in-filled
stream channels or soil variations in the Hayward fault zone, which
forms a north-south band through the foothills. Groundwater levels
in the study area generally vary on a seasonal basis, with the
lowest levels occurring in early fall after the long dry season,
and the highest levels in the spring at the end of the rainy
season.
Sewer System. The first sewers in the EBMUD area were constructed
in the 1880's. The original sewers were six- and eight-inch
diameter clay pipes which served as a. combined storm/sanitary
system and generally discharged the flow to the nearest drainage
channel. Most of the early trunk sewers were enlarged and extended
during the 1920's and 1930's, with downstream discharges near the
Bay shoreline. In 1951, the EBMUD interceptor system was
constructed along the Bay shoreline to intercept the east-west
community trunk sewers and convey the flow to the new treatment
plant.
The major portions of the existing EBMUD community sewer systems
were constructed in the first part of this century, and consist
primarily of vitrified clay pipe (VCP) with short, two- or
three-foot pipe sections and rigid, cement mortar joints. Most of
the early sewers were laid with bedding and backfill composed of
the native soil materials. Soil logs from groundwater monitoring
wells drilled adjacent to sewer pipes for the East Bay I/I Study
show that the boundary between the trench fill and the native soils
beneath the trench is generally indistinguishable. Most of the
sewer system was constructed piecemeal by individual developers
with little, if any, construction inspection or quality control
provided by the cities. In addition, maintenance of the sewer
system over the years has been minimal, other than that required
for emergency situations such as blockages or street collapse.
Because the sloping topography of the area facilitates gravity flow
from east to west, and because most building laterals are shallow
(homes generally do not have basements), most of the sewers, are
relatively shallow (typically four to six feet deep), with deeper
pipes being necessary only for the larger downstream trunk sewers
nearer the interceptor. The sloping topography also means that
C-3
-------
Case Studies
travel times through the sewer system are short, and upstream peak
flows cumulate rapidly and reach the downstream end of sewer
drainage basins in a relatively short period of time (typically,
within one to two hours or less).
The study area is characterized primarily by urban, single-family
residential development on small lots. Therefore, the density of
building laterals is relatively high, with an average of 22
laterals per 1,000 feet of sewer main. Many of the original
laterals were not connected to the factory-installed wye fittings
in the sewer main, but were inserted through holes (taps) broken
or chipped into the pipe. In, these cases, some reaches may have as
many inactive and unplugged factory wyes as active lateral
connections. The upper portions of building laterals on private
property are generally very shallow (less than three feet deep),
with a change\in vertical alignment typically occurring at the curb
line where the pipe angles down toward the main sewer in the
-street- '• • •''•'';'. - -.'..-'. :. .. "..-•;'•"
( . ' ' ' ' . , ' - •
RII Documentation. The condition of the EBMUD sewer systems has
been documented by the field work conducted as part of the East Bay
I/I Study. The field work included smoke testing, dye flooding,
physical inspection of manholes, internal television inspection of
sewer mains, and lateral testing and inspection.
Smoke testing was conducted in over 50 percent of the EBMUD system.
The majority of the smoke returns were from defective building
laterals. Direct storm water inflow connections accounted for
relatively few of the observed defects.
Dye flooding was conducted to verify suspected storm drain/sanitary
sewer cross connections detected during smoke testing or potential
"indirect1.1 connections where storm drains crossed over or closely
paralleled sanitary sewers. In most of the dye flooding tests, the
sanitary sewer was concurrently TV inspected in order to observe
the exact location and relative quantity of dye transfer. With only
a very few exceptions, most of the instances of flow transfer from
;the storm to the sanitary sewers were found to be cases of indirect
transfer via exfiltration of water out of the storm drain and
infiltration into the sanitary sewer through cracks and defective
joints. , ,--'"••./
Manhole inspection was conducted for about 20 percent of the
structures in the system. In general, the inspections indicated
that most manholes were in good structural condition with
relatively little evidence of infiltration. Based on these
inspections, it was concluded that manholes were not a significant
source of RII in the EBMUD system.
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TV inspection was conducted for about 10 percent of the total sewer
main footage in the service area, based on I/I flow contribution
as determined through flow monitoring and flow isolation. Numerous
defects in the system were identified through TV inspection,
including structural problems, cracks, offset joints, root
intrusion, and defective lateral connections. The TV inspection
results were used to document the condition of the pipes in the
system and determine appropriate rehabilitation methods, but were
not used to attempt to quantify the I/I contribution from
individual sources.
Lateral Testing and Inspection. Lateral field work conducted as
part of the East Bay I/I Study included air and exfiltration
testing, rainfall simulation, flow measurement during rainfall, TV
inspection, and visual inspection of exposed laterals. Most of this
work was done as part of special pilot projects.
The lateral field studies generally included samples ranging from
10 to 200 laterals. While these samples represent a small fraction
of the total 175,000 laterals in the EBMUD service area, the areas
were selected to be representative of typical conditions in the
area. Lateral inspections revealed that offset joints and root
intrusion occur in most laterals, and other defects such as cracks
(particularly near the bells of the pipes) and misalignment are
common. A limited program in which eleven lower laterals (portion
within the public right-of-way) were excavated and exposed using
"archeological" methods showed that in 90 percent of the laterals,
the original mortar in the joints had deteriorated. Most laterals
failed air and exfiltration tests, and the ones that passed were
generally newer pipes or atypical (e.g. cast iron rather than VCP
construction). A comparison of smoke testing records with the
results of other lateral testing and inspection methods indicated
that only about one-third of defective laterals were detected by
3 smoke testing.
I/I Flow Characteristics. The East Bay I/I Study included extensive
flow monitoring within the community sewer systems. Fifty-six
"long-term" flow monitors were installed for a period of two to
three years, and wet weather flow monitoring was conducted in over
300 locations in the system for periods of approximately two to
three months during the rainy season.
The analysis of flow data for the study was based on separating the
total wet weather flow into its component parts of base wastewater
flow (BWF), groundwater infiltration (GWI), and rainfall-dependent
I/I (RDI/I). The RDI/I was assumed to represent a combination of
direct stormwater inflow (SWI) and rainfall-dependent or rainfall
induced infiltration (RDI or RII); however, it was recognized that
the SWI and RII components could not necessarily be distinguished
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by simple flow hydrograph ^decomposition. The combination of BWF
plus GWI was determined based on the flow during a nohrrainfall
period near the time of the storm event being analyzed. Subtraction
of BWF + GWI from the total storm flow hydrograph yielded the RDI/I
for-the rainfall event, as shown in Figure C-i. The RDI/I volume
.was then expressed in terms;of a percentage of the total rainfall
volume for the storm. This percentage, the ratio of the RDI/I
volume to the total rainfall volume, was termed the "R value" or
"total R" for the storm event. R values ranged from near zero in
some subbasins to over 50 percent in others, depending on soil
saturation (antecedent rainfall) and other factors;
Plots of rainfall volume versus RDI/I volume for all storm events
were developed for each of the 56 long-term monitors. It was found
that the plotted points fit within an "envelope" (see Figure C-2),
with the storms representing early season or dry soil conditions
(low R values) falling near the lower boundary of the envelope, and
the storms representing saturated soil conditions (high R values)
falling near the upper boundary. The dry soil R values were
generally in the range of 2 to 6 percent. The saturated soil R
values typically ranged from 10 to 35 percent for the long-term
monitoring sites.The interpretation of the RDI/I envelope lower
boundary condition is that it represents predominantly SWI
contributions, since the percentage of runoff from impervious
surfaces that collect surface drainage is more or less independent
of antecendent rainfall conditions. The remaining RDI/I volume, and
possibly also a portion of the RDI/I volume represented by the
lower envelope boundary, is suspected of being contributed from
infiltration sources such as defects in sewer mains and laterals,
including indirect transfer from storm drains to sanitary sewers.
,' •, ' j '"'''. "• ;
The interpretation of the upper envelope boundary is that it
represents maximum RDI/I contribution under saturated soil
conditions. Under such Conditions, the capacity of the soil mantle
to absorb and transmit water would be limited, and more water would
.be transmitted through soil channels and through the more permeable
pipe trenches to sewer defects. In some cases, the saturated soil
condition appeared to be better represented by a curvilinear upper
boundary, indicating a reduction in R for larger storms because of
the limitation in the amount of water that can reach the defects
in the pipes once the soil has become saturated, as well as the
inlet hydraulic capacity of the defects themselves. The average R
value for the study area under saturated soil conditions (for the
selected design rainfall event) was found to be approximately 18
percent. If the R value under dry soil conditions (average of
about 4 percent) is assumed to be the maximum SWI, then this means
that three-quarters or more of the total RDI/I volume under
saturated soil conditions is due to infiltration of ^stormwater into
the system, or RII.
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24
12
24
EBMUD I/I STUDY
TYPICAL DECOMPOSED HYDROGRAPH
FIGURE C-1
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lit
Q
X
10
20 30
PRECIPITATION VOLUME
50
| - RAINFALL-DEPENDENT INFILTRATION (R||)
' ALTERNATE CURVILINEAR UPPER BOUNDARY
EBMUO I/I STUDY
TYPICAL BASIN RDI/I ENVELOPE
FIGURE C-2
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To more precisely define the magnitude and shape of the design
storm hydrograph for use in modeling of the sewer system, the RDI/I
hydrograph for each subbasin was separated into three component R
values (Rl, R2, and R3) which summed to the total maximum
(saturated soil) R for the subbasin, as illustrated in Figure C-3.
In general, the Rl component represented the most rapid response,
with a time to peak of from one to two hours after the start of
rain. The Rl component could therefore be assumed to represent SWI
and a portion of RII, presumably from shallow infiltration sources.
Rl was the dominant component in determining the magnitude of the
peak storm flows.
To estimate the magnitude of SWI independently of the flow
monitoring data, smoke testing data were used to identify specific
SWI sources and develop quantitative estimates of the SWI
contribution from those sources. The SWI contributions from all
sources in each subbasin were then summed and compared to the
design storm Rl volume for the subbasin. In almost all cases, the
calculated SWI volume as a percentage of the Rl volume was less
than 10 percent, and in most cases was less than 5 percent.
While the calculated SWI is probably an underestimate of the actual
SWI volume because not all SWI sources may have been included, the
estimated numbers did indicate that SWI appears to be only a small
part of the peak (Rl) component of RDI/I. Therefore, it was
concluded that the major portion of the peak RDI/I flow in the
EBMUD system is due to infiltration (RII), rather than inflow, into
the sewers. Based on the high number of defective laterals detected
during smoke testing, as well as the results of the lateral testing
and inspection work, it was surmised that the peak RII flow is
largely due to the rapid infiltration of stormwater into shallow,
defective laterals. The magnitude of this RII flow can in great
part be explained by the overall poor condition, as well as the
high density of the laterals in the system.
Several of the field studies that were conducted on laterals as
part of the East Bay I/I Study appear to confirm the rapid flow
response in laterals to rainfall events. These studies included
actual flow measurement of laterals which discharged directly to
manholes. During relatively low intensity storms (on the order of
0.1 inches per hour rainfall), approximately two-thirds of the
laterals sampled contributed an average peak flow of 750 to 800 gpd
per lateral. Some individual laterals contributed as high as 5,000
gpd peak flows. (Smoke testing records were used to verify that no
direct SWI connections existed for these laterals.) When projected
to a higher intensity design storm, the average pe.ak flow
contribution from laterals could be greater than 3,000 gpd per
lateral. In most laterals contributing RII, the peak RII flow
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occurred within an hour of the peak rainfall intensity. Several
laterals overlain by relatively impermeable surfaces also exhibited
high peak flbw responses, possibly indicating that infiltration can
apparently move in a horizontal direction, as well as downward
through the soil.
Rainfall simulation testing also confirmed the rapid flow response
of laterals to rainfall. In this program, 230 laterals were tested
by application of simulated rainfall (at a measured rate) in a
six-foot wide spray zone over the upper portion of the lateral
(portion upstream of the sidewalk) . The resulting flow from the
lateral was then measured from .the sewer main using a weir/packer
assembly attached to a TV camera. The flow hydrographs indicated
a rapid response to the rainfall simulation, with the peak flow
generally occurring within one to two hours after the start of the
simulated rainfall. In a few laterals, the simulated rainfall
application rate was increased after several hours of testing, and
the flow response was an almost immediate increase in the measured
infiltration rate. This response appears to indicate that
infiltration rates are related to rainfall rates, and for a given
lateral, an increase in rainfall intensity will cause an increase
in infiltration.
The factors which impact RII flows in the EBMUD system include the
physical characteristics of the service area> including clay soils,
seasonal rainfall pattern, and sloping topography (which influences
sewer depths and flow travel times), as well as the physical
condition and characteristics of the sewer system. The age and
original poor construction, type of pipe material (VCjP with short
pipe lengths and deteriorated cement mortar joints), lack of
maintenance, relatively shallow depth (particularly of laterals),
high density of sewers and laterals, occurence of root intrusion
from landscaping, and pipe damage and joint separation caused by
earth movement and seismic activity are all factors „ which have
resulted in a large number of defects in the system through which
infiltration can enter. The flow data collected as part of the East
Bay I/1 Study document ,the high peak RII flows which occur in the
system.
/ i , , ' .
RII Control Program
The analysis conducted for the East Bay I/I Study found that
rehabilitation was cost effective for approximately one-half of the
subbasins. The recommended I/I correction program consists of
"comprehensive rehabilitation," i.e., including the sewer mains and
the entire portion of the service laterals. Because of the high
cost and size of the construction effort, the rehabilitation
program will be implemented over a period of 20 years.
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SYNTHETIC HYOROGRAPH
- ACTUAL ROI/I HYOROGRAPH
R, COMPONENT
COMPONENT
R3COMPONENT
12
24
12
. !
24
i
24
:ESMUO t/l STUDY
TYPICAL SYNTHETIC HYDROGRAPH
FIGURE C-3
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To date, the cities have completed design and construction of the
first two years of projects. Most of the rehabilitation work has
consisted of slip-lining and replacement, with some grouting. In
most of the cities, only the sewer mains and the portion of the
lower laterals within the ,public right-of-way have been
constructed, and two-way cleanouts have been installed on the
laterals at the property line. Private lateral rehabilitation will
be addressed at a later date. However, one of the seven tributary
agencies, the Stege Sanitary District, elected to construct and
finance the rehabilitation work on private property in one
subbasin.
In addition to the 20-year I/I correction program, it was
recommended that the communities implement long-term I/I management
programs. These programs would provide for routine testing,
inspection, and maintenance of the sewer system and a cyclic
replacement program for sewers that have outlived their useful
• lives. • .... . '''..-,.' .-'•-. ','•-.
CITY OF SPRINGFIELD, OREGON
The City of Springfield is located in central western Oregon at the
confluence of the McKenzie and Willamette Rivers. The City's
sanitary sewer system is tributary to a regional wastewater
treatment plant serving the Cities of Eugene and Springfield. The
City of Springfield system serves a population of about 40,000 and
includes approximately 165 miles of sanitary sewer mains.
In the late 1970's a regional wastewater management study was
conducted for the Eugene/Springfield area to identify appropriate
means for expanding and upgrading the existing wastewater
facilities. At that time, Eugene and Springfield were served by
separate wastewater treatment plants. Problems in Springfield
included surcharging and overflows in the sewer system and.
bypassing of partially treated wastewater from the Springfield
treatment plant during wet weather periods (almost continuously
during December and January). The recommended project included
construction of a regional treatment plant (completed and in
operation since 1984). As part of the facilities planning phase of
that project, Springfield conducted an I/I Analysis, which
determined that I/I was rtexcessive", and subsequently completed a
SSES in 1980. The SSES determined that only 20 percent of the
design peak storm induced flow could be attributed to direct inflow
sources and indirect transfer from storm drains to sanitary sewers.
Therefore it was concluded that 80 percent of the peak storm
induced flow was due to "storm induced infiltration" through
defective sewers, service laterals, and manholes.
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System Description
Most of the service area is relatively flat, with a typical
100-foot east to west variation in elevation. As most of the City
is located in a river floodplain, the soils are primarily alluvial
deposits, ranging from gravelly silt-loams to silty clay-loams. The
climate is typical of the west coast of the U.S., with about 80
percent of the total rainfall falling during the period November
through April. Average annual rainfall is approximately 45 inches.
The groundwater table is typically 10 to 20 feet below the ground
surface during the summer, with about a seven foot annual
fluctuation. The groundwater is highest during the winter rainy
season, and very near the surface in the western portion of the
City near the river confluence.
The sewer system was originally constructed in the central portion
of the City between 1910 and 1940, with expansion of the system
into the eastern and northern portions taking place since 1940. The
older sewers are VCP or concrete with cement mortar or
asphalt-poured joints. Many of the older service laterals were
constructed of Orangeburg pipe, although many of these have
presumably since been replaced. Newer construction since 1960 has
been primarily concrete pipe with rubber gasket joints. The depth
of sewer mains ranges from 5 to 11 feet, with an average depth of
8 to 9 feet. Groundwater monitoring conducted during the SSES
indicates that a large portion of the sewer mains are below
groundwater during the winter. There are approximately 13,000
service connections in the system, for an average lateral density
of 15 per 1,000 feet of main.
'• ' ' / ,
RII Documentation
During the SSES, dry and wet weather flow monitoring was conducted
at 54 sites throughout the sewer system. For each monitored area,
the average dry weather flow, peak non-rainfall infiltration rate
and peak storm induced I/I rate were determined from the flow data.
For the measured storms, peak to average flow ratios ranged from
about 1.5 to 15. The peak storm-induced flow was projected to a
five-year design storm condition based on the ratio of measured
(two-hour) rainfall to design rainfall intensity. For the total
system, the ratio of design PWWF to ADWF was approximately 11 to
1.
The field investigations conducted as part of the SSES identified
numerous defects and I/I sources in the system. Smoke testing was
conducted for over 90 percent of the sewers. A large proportion of
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the smoke emissions were observed along the ground above sewer
mains and laterals and near manholes. Other smoke emissions were
from manhole frames and lids, cleanouts, and storm drainage sources
(catch basins, storm sewer manholes, area and roof drains).
To verify whether storm drainage sources were direct or indirect
connections and to quantify the flow contribution from these
sources, dye flooding was conducted for all smoke emissions from
catch basins, storm sewers, and area drains. The results of the
dye flooding indicated that over 90 percent of these sources were
cases of indirect flow transfer between storm and sanitary sewer
facilities; only five direct connections were found. Physical
reconnaissance was conducted for all other specific smoke emission
sites, such as cleanouts, which appeared to be potential sources
of direct inflow. In addition, all manholes in the system were
inspected to identify potential inflow sources through holes in
manhole covers. ..
Television inspection was used to identify specific defects in
sewers where infiltration during dye flooding was identified. TV
inspection or review of past TV inspection records was also
conducted for those sewers where smoke was observed along the
ground surface over the pipe.
For all direct inflow sources, estimates of maximum flow rate were
made using the rational formula, based on the surface area and
drainage characteristics of each source and the design rainfall
intensity. Flow estimates based on dye transfer rate were made for
indirect connections between storm drains and sanitary sewers. "The
calculated total peak flow from these sources was 13 mgd, or 20
percent of the projected peak storm induced I/I flow of 65 mgd.
Since a portion of the 13 mgd is due to indirect transfer from
storm to sanitary sewers, it can be concluded that over 80 percent
of the peak storm induced I/I appears to be due to RII.
A site visit was made to Springfield during the course of this
study, and City staff were interviewed regarding RII problems in
the sewer system. With respect to the condition of the sewers,
staff identified service laterals as potentially significant
contributors of extraneous flows. Specific problem areas are the
connections between the private and public portion of the lateral,
between the lateral and the main, and at the manhole. Other
potential causes of RII include inactive, unplugged lateral taps
and, root intrusion. Because many of the older mains are located in
backyard alleys, unauthorized and uninspected hookups and repairs
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are frequently made. High flows are also experienced in newer
areas built during the mid-1970's development "boom," when
construction inspection may have been inadequate because of
insufficient City staffing.
* ...
Some the primary factors affecting RII in Springfield, in addition
to the condition of the, sewers, appear to be the high groundwater
and amount and pattern of rainfall. During storms, groundwater in
the trench line has been known to wash out portions of streets and
create small "geysers" up through the asphalt. The flow response
to rainfall is rapid, and generally decreases rapidly after the end
of rain. This rapid rise and recession appear to be independent of
the groundwater infiltration rate immediately prior to the storm.
Larger flows occur during prolonged rainfall periods than from
isolated rain events.
RII Control Program
As a result of the SSES and further cost-effectiveness evaluations,
the City received a construction grant for sewer rehabilitation in
four basins, representing approximately five percent of the total
system. (The official grantee is the Metropolitan Wastewater
Management Commission, the regional wastewater agency for the
Cities of Eugene and Springfield.) The area is an older part of the
City, with most of the original sewers over 40 years in age and
constructed predominantly of concrete pipe with cement mortar
joints. This rehabilitation project (called the "C74" project) was
based on a design philosophy of "complete basin" rehabilitation
(all of the sewers, including service laterals) and was projected
to result in a 65 percent I/I flow reduction. The first phase,
consisting of replacement or grouting of the mains and service
laterals within the public right-of-way, was completed in 1987;
preliminary flow monitoring results indicate that an approximate
50 percent flow reduction has been attained.
In addition to the grant project, several small pilot projects have
been completed, including two in the C74 area and two in newer
areas of the City. The C74 pilot projects involved rehabilitation
of private service laterals where the main had already been
replaced or, grouted. The other two projects were done under a
turnkey-type contract in which the contract bid was based on
achieving 65 percent flow reduction with a price incentive for
greater reductions. Analysis of the flow reductions achieved in
these pilot areas are not conclusive because of the lack of rain
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during the 1987/88 season. However, preliminary results of the two
projects in the newer areas indicate 90 percent and over 50 percent
flow reductions, respectively, based on total storm flow volume
calculations.
The City is currently re-assessing its approach to addressing I/I
and developing a long-term I/1 control plan. In general, City staff
feel that sewer system rehabilitation, particularly in older areas,
is not cost effective. The City is lopking at other options,
including off- line storage for peak flows and concentrating
rehabilitation efforts in newer areas, where they believe it may
be possible to reduce I/I at a lower unit cost.
Impact of Peak Flows on WWTP Operation
The Eugene-Springfield regional WWTP is relatively new, and was
designed to incorporate considerable flexibility for handling flow
variations due to wet weather and future growth. Design ADWF is 49
mgd; maximum design flow is approximately 180 mgd. At flows above
175 to 185 mgd, raw wastewater bypasses at the pump stations and
WWTP would be activated. Current ADWF to the WWTP is 22 mgd. During
a recent storm period, a peak flow of 143 mgd (95 mgd daily flow)
was reached. The flow from Springfield alone, however, cannot be
reliably isolated because of the location and type of flow metering
devices that were installed in the interceptor system.
Effluent requirements for discharge to the Willamette River are
30/30,mg/1 BOD and suspended solids in winter and 10/10 in summer.
The WWTP is an activated sludge plant, which is run as a contact
stabilization process in winter and modified plug flow in summer.
During peak flow periods, effluent quality is maintained, first by
putting on line additional primary and secondary clarifiers, and
then by bypassing a portion of the primary effluent around the
secondary treatment process. Bypassing is generally'required for
only a few hours to one- half day. The flow to the secondary
process can be controlled by pre- selecting the flow level at which
bypassing will start. The disinfected combined primary and
secondary effluent generally does not exceed 20 mg/1 susupended
solids.
In addition to the capital cost for excess capacity, the major cost
associated with treating peak wet weather flows is the increased
labor required for clean-up of the additional clarifier units which
must be put into service during the peak flow periods but are' no
longer needed after the flows recede. Increased energy costs
associated with peak flows are fairly minimal,, since the bypassing
,6f the secondary process means that significant increases in
aeration are not required. Because there is a "trade-off" between
maintaining effluent quality and reducing clean-up requirements,
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there is a certain amount of guess work involved in deciding when
to put additional clarifiers on line during peak flow periods.
Other wet weather impacts at the WWTP include problems caused by
large quantities of grit which are washed out of the sewer system
. during the first large storm of the season, sometimes causing
damage to equipment and plugged lines (the grit chamber is located
downstream of the comminutor). Also during wet weather periods,
solids washout may occur, resulting in decreased gas production in
the digesters. Foreign materials washed out of the sewer system
(oils, grease, etc.) also may inhibit bacterial action.
MILWAUKEE METROPOLITAN SEWERAGE DISTRICT, WISCONSIN
The Milwaukee Metropolitan Sewerage District (MMSD) serves 28
communities in the southeastern portion of Wisconsin. The largest
of the communities is the City of Milwaukee. MMSD operates a
294-mile interceptor system and two treatment plants; the
collection systems are owned and operated by the individual
communities. The total MMSD service area includes over 2,800 miles
of sewer mains, of which approximately 20 percent are combined
storm/sanitary sewers, mostly located within the City of Milwaukee.
In the late 1970»s MMSD initiated the Milwaukee Water Pollution
Abatement Program to address the problems caused by inadequacies
in the wastewater collection, transport, and treatment systems.
These problems included overflows and bypassess from the
interceptor and collection systems, sewage back-ups into building
basements, and discharges of inadequately treated wastewater to
Lake Michigan. The Water Pollution Abatement Program included major
projects to upgrade the interceptor system and treatment plants,
projects to address problems in the combined sewer service area,
as well as a comprehensive SSES for the separate sanitary sewer
portion of the service area. The SSES was completed in 1981.
Although the Milwaukee SSES identified direct inflow as a
significant portion of peak wet weather flows, and much of the
subsequent rehabilitation effort was concentrated on removing those
types of sources, the study did include documentation and extensive
field investigation of sources which the study termed "indirect
inflow." These sources included leakage through manhole
frame/chimney defects, as well sis sources on private property,
primarily foundation drains. The estimates of source flow
contributions developed for the SSES indicate that more than 50
percent of the maximum hour I/I flow is due to these types of RII
sources.
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System Description
The MMSD service area is relatively flat. In general, the, area
drains west to east and north to south toward the Milwaukee River
and Lake Michigan. Soils are typically clay, with more sandy soils
in the western portion of the service area. Many of the soils are
of glacial origin, resulting in seams of more permeable material
throughout the soil mantle. The groundwater level is typically
about six feet below the surface, and increases to about three feet
in the spring.
The Milwaukee area receives approximately 31 inches of
precipitation (water equivalent) annually. Rainfall occurs
throughout the year, although it is lowest in the coldest months
of January and February when most precipitation occurs as snowfall.
In early spring, conditions of rain, showmelt, and high groundwater
occur simultaneously, resulting in the highest I/I flows. Freezing
temperatures in the winter result in frost heave damage to streets
and manholes.
The original sewers in the separate sanitary sewer system were
constructed in the 1920's, with more recent construction in the
outlying communities. The average depth of sewer mains is 15 to 20
feet? service laterals are typically 6 to 10 feet deep. A
considerable portion of the system is therefore below the
groundwater table. In the older portions of the service area,
individual buildings are served by both storm and sanitary
laterals, which have commonly been constructed in the same trench.
RII Documentation
Flow monitoring was conducted at several hundred locations during
the SSES. Infiltration was /identified as the early morning flow
rate, and "inflow" was calculated as the difference between total
storm flow and non-rainfall flow (base flow plus infiltration).
Both infiltration and inflow were projected to a maximum condition
using adjustment factors based on historical data from 34 permanent
monitoring sites in the system. These factors were determined for
diff erent, areas of the system by relating the measured infiltration
and peak hour inflow during the monitoring period at the various
permanent monitoring sites to the infiltration and peak hour inflow
for selected maximum historical infiltration and inflow events. For
the total system, the ratio of design PWWF to ADWF is approximately
7.5 to 1. Of the projected total peak hour flow of 1,155 mgd, 878
mgd or 76 percent is "inflow," i.e., rainfall induced I/I.
Extensive field investigations were conducted as part of the SSES
to identify specific sources of I/I and quantify the flow
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contribution from each source. Physical inspections were conducted
for all manholes in the SSES area, and included lamping of the
inlet and outlet sewers from the manhole. The manhole inspections
identified vented covers, misaligned and unsealed frames, manholes
subject to ponding, and manholes and sewers with evidence of
infiltration (leaks, deposits, roots). Building inspections were
done to identify I/I sources on private property, including
downspouts, roof drains, area drains, foundation drains, and sump
pumps. Inspections were attempted at all residential and small
commercial buildings; approximately 60 percent of the 165,000
attempted inspections were completed.
Smoke testing was conducted for all of the SSES area. Dye flooding
was conducted in approximately 35 percent of the area. All storm
sewers and drainage ditches which paralleled or crossed over
sanitary sewers or laterals were included. Dye flooding identified
both direct and indirect storm/sewer connections. Street flooding
was conducted for about 10 percent of the manholes in the system
in order to identify and quantify I/I which enters manholes through
frame/chimney defects. TV inspection was conducted for about 13
percent of the system on those sewers identified as inflow or
infiltration sources through dye flooding (medium to heavy
transfer) or sewer lamping. In addition, two pilot projects were
developed for in-depth investigation of I/I sources from manholes
and from private property (laterals and foundation drains).
The private property I/I study found that flows from foundation
drains and defective laterals were responsive to rainfall, with the
maximum flows occurring during rain events when the groundwater was
high. Indirect flow transfer from foundation drains and storm
sewers and ditches was identified as a significant source of I/I
in defective laterals. TV inspection of the laterals (primarily
pre-1960 VCP with mortar joints) indicated that two-thirds of the
joints were defective. The direction of surface drainage and
location of downspout discharges were other factors cited as
influencing lateral and foundation drain flows.
The major sources of I/I identified through the SSES were manholes
(97 percent with vented covers and 59 percent with misaligned
frames) and foundation drains. Distinction was made between inflow
and infiltration sources, and between direct and indirect inflow
sources. Indirect inflow (RII) sources include manhole
frame/chimney leakage and manhole, sewer, and lateral defects
detected through rainfall simulation (smoke testing and dye
flooding), including indirect flow transfer from storm sewers.
Manhole frame/chimney leakage occurs when surface runoff seeps into
cracks and joints in concrete streets and enters manholes with
unsealed or misaligned frames. This phenomenon is caused by
freezing and thawing, which create gaps between the frame and
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chimney and in the street pavement. In some manholes which have
been excavated for repair, large voids or channels have been found
around the manhole frame, created by water infiltrating to the
defects. ; .,„''• ' .•;-.". . -• ~ .'_...' ' • ' .
Estimates of flow contribution were "developed for each type of I/I
source. For direct inflow sources, the rational method was used.
For indirect inflow, flow estimates were based oh flow rates
measured during dye flooding and street flooding. The total maximum
hour I/'I calculated in this manner is approximately 800 mgd, of
which 32 percent is attributable to direct inflow sources, 40
percent to foundation drains, 12 percent to manhole frame/chimney
leakage, and 15 percent to infiltration through laterals, sewer
mains, and manholes, a portion of which was identified through
rainfall simulation and therefore can be considered to be RII.
Approximately 60 percent of the peak I/I flow appears to be due to
"''' ''
A site visit was made to Milwaukee during the course of this study,
and District and community staff were interviewed regarding RII
problems in ,the sewer system. Staff indicate that RII from
laterals may have been underestimated in the SSES. .Dye flooding
work during the SSES identified considerable flow transfer from
storm drains crossing over laterals. In particular, the common
trench storm and sanitary laterals that are typical in the older
portions of , the service area are potential sources of indirect flow
transfer. Some of these types of sources were demonstrated as weak
smoke emissions from roof leaders that were presumably properly
connected to a storm lateral, which was then exf iltrating to the
sanitary lateral.
RII Control Program
The I/I correction work resulting from the SSES consisted primarily
of eliminating direct inflow through manhole covers and indirect
inflow (RII) through manhole f tame/chimney interfaces. The program
also included the correction of illegal clear water connections to
the sanitary sewer from private property (other than foundation
drains) , some sewer main grouting, correction of connected catch
basin leads, and bulkhead repairs. The District conducted a manhole
rehabilitation pilot project to evaluate different methods of
correcting manhole frame/chimney leakage. (A more ..detailed
discussion of these manhole frame/chimney rehabilitation methods
is presented in Appendix D.)
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5?h £c J?*e serv^ce lateral rehabilitation that was recommended in
the SSES was done due to legal ramifications. Two of the
™r$7tii^S ^YV^ssfully addressed foundation drain sources.
The Villages of Brown Deer and Menomonee Falls have enforced the
disconnection of the foundation drains identified in the SSES and
have instituted ordinances requiring inspection and disconnection
£,,««? sanitary sewer connections (foundation drains, sump
vSSXo turasp°utsi: The Brown Deer ordinance requires conformancS
before the property can be sold. The Menomonee Falls ordinance
empowers the plumbing inspector to enter a property Son
identification, to ascertain the quantity, quality; and condition
?f S™?^*11* clear:wate? discharges-, and provides the lu?horl?y
to require disconnection within six months of Written notification
of violation of the ordinance. Brown Deer has taken further steps
T™ S*!??' .Ille9al connections in buildings that were not
inspected during the SSES.
«™ comnuilitie3 ±n the District «ave prevailed upon property
owners to correct illegally connected sump pumps and area and roof
drains, at least for those properties inspected during the SSES.
All communities have also adopted ordinances that prohibit clear
water connections to the sanitary sewer system. However, only the
two communities identified above have gone beyond the
SSES-recommended private property rehabilitation program to address
illegal connections on properties not inspected during the SSES and
foundation drain connections that existed prior to adoption of the
ordinance.
orr iS4-in ^ Process of implementing a long-term control
SSS^ I m??y?-JP. levels throu9h01* the system and track the
impact of rehabilitation work. Permanent monitors with telemetry
are installed at approximately 50 locations, and further phases of
the program will include 100 to 150 monitoring sites for smaller
areas within the communities. The data collected from the
long-term monitoring program will be used to identify specific
areas which continue to have particularly high I/I flows so that
correction work can be planned.
Impact of Peak Flows on WWTP Operation
~ao °S?raJ:es two major wastewater treatment plants: Jones
Island and South Shore. Both plants discharge to Lake Michigan. The
Jones Island plant service area includes the combined sewer portion
of the system, as well as portions of the separate sewer system.
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The District's interceptor system includes 20 diversion structures
(with 15 more planned),. which are used to control the flow during
wet weather periods. Nine of these diversion chambers are
automatically controlled based on the monitored hydraulic grade
line at key points in the system, as well as monitored
precipitation. Because of the size of the District, precipitation
and flow trends must be monitored closely and are used to trigger
the activation of flow diversions. The interceptor diversions are
used to divert flows from Jones Island to the South Shore WWTP
during peak flow periods. .
The Jones Island WWTP is currently undergoing expansion to increase
maximum day capacity from 200 mgd to 330 mgd. The design maximum
hourly flow is 390 mgd, of which 330 mgd receives full treatment
and 60 mgd is in-line flow receiving only disinfection and
dechlorination. Current average flows during low rainfall months
are in the range of 115 to 135 mgd. Prior to the current expansion,
the plant was limited by secondary clarifier capacity. Flow was
taken until secondary clarifier blankets were in danger of spilling
into the effluent. When high secondary clarifier blankets were
observed, a portion of the flow was bypassed to prevent solids
carry-'over into the effluent. All bypassed flows received primary
treatment and were chlorinated and dechlorinated before discharge.
The current operating strategy for high wet weather flows includes
diverting flow to the South Shore WWTP and controlling the influent
flow through two (low- and high-level) siphon gates at the entrance
to the plant. Throttling of these gates backs up the flow into the
collection system. The objective of system operation during high
flows is to maintain the sludge blanket in the secondary clarifiers
and avoid spilling solids into the effluent. Standard procedures
and criteria for wet weather operation have been developed and are
followed during periods of high wastewater flows. After the plant
expansion is completed, return sludge capacity rather than
clarifier capacity could become the limiting factor in handling
high flows during bulking sludge conditions.
The South Shore WWTP has an average flow of 80 to 90 mgd, but may
experience peak flows in excess of 450 mgd. A typical "good-sized"
storm will produce flows of 300 to 350 mgd. There is a significant
lag time in the sewer system, with normal dry weather peak flows
reaching the plant eight hours after the time of peak system flow.
During wet weather, the flow through the plant is increased to
avoid back-ups , in the collection system. This is done by
increasing the grit channel velocity by opening 1Uie butterfly
valves. Primary clarif iers that may have been out of service for
maintenance or repair are put back on line. Flow through the plant
is limited by secondary clarifier capacity, which is normally 240
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caPacity through the secondary process by §6
NORTHEAST OHIO REGIONAL SEWER DISTRICT; OHIO
™™ °!£0 Re9ional Sewer District (NEORSD) includes 41
SS3XS tS *? .cl*veland, Ohio, metropolitan area. NEoHo is
divided into two ma} or subdistricts : The city of Cleveland which
has a combined sewer system; and the surrounding communities; which
have primarily separate systems . NEORSD operates an interceptor
system and five treatment plants; the collection Systems arfow^ed
individual communities. Most of the separSSd
™*S °?ntained W±thin two ma3°r Planningareas?
Separate Sewer Area (ESSA) and the Southwest
(TA)' f °f which SS*S '• ^ere ccn-pl^to ills
me,S? seParate sewers in the District are located
rt?°gethe5' «» ESSA a^ SWIA contain approximately
°f sanitary sewers serving a population of about
500,000
Overflows and bypasses occur at over 200 locations in the senarate
sewer system, most activated by rain events of 1m San 0.1 incheS
ar ued to
Basenent back~ups are a
System Description
g^aP L°f the area ra™?es from flat to fairly steep, the
elevations located on a glaciated plateau in the
^?"*100 °f *?» Di-^i<* in the ESSA. Numerous SreamS
River t£d iSL p4rea^ ^th draina^ generally toward the Cuyahoga
S ^.SS ^t ^' S°lls consist Primarily of moraine deposits
S™3£?- it and gravel* The Predominant soil association S
characterized by very slow permeability (less than 0.2 iri/hrJ and
a seasonally high groundwater table from November through 5une Se
groundwater level is typically six to ten feet below the surface?
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however> high bedrock exists in some areas, with perched
groundwater at 12 to 30 inches below the surface. Rainfall occurs
year round and averages 35 to 40 inches, depending on location.
Both localized and area-wide storms can occur in the system.
Construction of the original separate sanitary systems began around
1915, with a majority of the sewers constructed during the first
part ?f tne century. Most of the sewers are clay, with mortar or
bituminous joints in the older pipes and compression-type joints
used since 1965. Most older manholes are brick, with concrete
manholes being constructed since 1970.
Service laterals are also predominantly clay pipe, and are
typically constructed in the same trench as.storm laterals. Almost
all buildings in the service area have storm laterals to convey
roof and foundation drainage to the storm sewer system. Direct
foundation drain connections to the sanitary system are not common,
since storm laterals are generally deep enough to collect
foundation drainage without the need for sump pumps.
The oldest.sanitary sewers, constructed prior to about 1930, were
installed in common trenches with storm sewers; Over 50 percent of
the separate system (80 percent of the ESSA) consists of common
trench sewers. There are two basic types of common trench
construction: dual system (side-rby-side) and over-under. In the
dual system, the storm sewer was typically laid next to and about
one foot higher than the sanitary sewer. This was generally done
by digging a single wide trench and refilling the bottom of the
trench on one side to form a bench for the storm sewer. The entire
trench was filled with granular backfill; porous slag material was
often used as bedding and fill material between the storm and
sanitary sewers. The two sewers were generally accessed by separate
manholes; where common manholes existed, they were separated by
either partial or full-height walls. However, the sewers are so
close together that the storm pipe walls are usually visible in the
sanitary sewer manholes.
In the over-under sewers, the storm drain is laid on top of the
sanitary sewer,, often with less than one foot clearance between the
top of the sanitary pipe and the bottom of the storm sewer. In many
cases the fill material between the two pipes has eroded, which
causes settlement of the storm sewer and structural damage
(springline cracks and potential crushing) to the underlying
sanitary pipe. The over-under sewer manholes were generally
constructed with a steel or cast iron plate separating the access
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plates have
RII Documentation
o ?°?in0r*n£-WaS conducted at 85 long-term monitoring sites and
SS V^Vh(^~term Sites' Flow data were analyzed tl determine
base infiltration and peak (rain-induced) I/I. Rain induced I/I
fi£^JSre ^°JeCtf-,d t0 a design storm Condition based on rainfall
SJSS^ ity* These flow Projections resulted in ratios of ADWF to
IS?? °Lreon20 t0 V* the ESSA and Approximately 12 to l in thS
SWIA. Over 90 percent of the PWWF is due to rain induced I/I.
investigations conducted during the SSES's included smoke
dye floodin9' and TV inspection. Smoke testing was
ln. approximately 30 percent of the system. In many cases,
ftnfl n ^ ^f0If0n trench storm and sanitary sewers wer4
found to leak so badly that the smoke could not reach inflow
connections, such as drains on private property. Also it was
often difficult to distinguish between direct and ^indirect
?SS Sn! °n private Property (e.g., roof downspouts) because of
iS J?6 ^^.^ common trench storm and sanitary sewer laterals.
Dye flooding indicated -that the flow transfer between the storm and
WSS rapid- In ov®r-under systems, the peak flow
sewer was reached within 10 minutes; in
sePafate trench sewers, within 20 to 30 minutes.
™ insP.ec.tlon of the sewers indicated that most of the
leaks were. from 3oints and service connections.
o°f i direct inflow, based on smoke testing and dye
fi™ account for 5 to 15 percent of the peak wet weather
flow. It was concluded that the remaining rainfall induced flow was
fto™0^^ ^^tion, primarily due to exf iltration fromTeS?
storm drains and storm laterals into sanitary sewers and laterals.
Ll^Sf^ Tf %?ade t0- ? ORSD during the course of ***** ,
and District staff were interviewed regarding Rll problems in the
sewer system, staff identified potential Rll sources in soviet
n?^011^17^6 connection to the main, including hammer
S S* S? *^e steePer grade and often vertical drop of the
main connection; traffic loads; and the greater
portion of the laterals wLn the
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RII Control Program
The primary emphasis of the District's program is construction of
new interceptor sewers. Each community within the District is
responsible for. its own rehabilitation program. With few
exceptions, the rehabilitation work is addressing only the public
portion of the sewer system. Since cross leakage between storm and
sanitary sewers, particularly with common trench construction, is
the major source of I/1, correction efforts are concentrated on
rehabilitation and flow regulation in the storm sewer system, as
well as sanitary sewer rehabilitation. Work includes separation of
common trench sewers by construction of new storm sewers, addition
of storm sewer capacity, and rehabilitation of common trench
storm/sanitary sewer manholes (constructing walls in manholes
between side-by-side sewers, sealing plates in over-under sewers).
Vortex regulators are being used in many communities to restrict
the flow into the storm drain system. The impetus for these types
of solutions is to eliminate basement flooding. Essentially, the
vortex regulators restrict storm flows from entering the storm
sewers, causing temporary flooding on the streets. This reduces the
load on the storm drain system and thus reduces overflows and
indirect flow transfer to the sanitary system.
The District is coordinating several pilot rehabilitation projects
in various communities. Each community is responsible for the
rehabilitation work, and pre- and post-rehabilitation flow
monitoring is conducted by the District. Each of the pilot areas
includes approximately 2,500 feet of pipe and 100 laterals. The
evaluation of the results of the pilot projects! has not yet been
completed*
Impact of Peak Flows on WWTP Operation
The District operates three major wastewater treatment plants,
called Easterly, Westerly, and Southerly, based on their respective
locations within the District service area. The Westerly and
Easterly plants discharge to Lake Erie. The Southerly plant
discharges to the Cuyahoga River. All of the plants receive some
amount of combined sewer discharges. The majority of the combined
sewer flows go to the Westerly plant, which includes a CSO
treatment facility. The Easterly plant, which serves a portion of
the combined sewer area, as well as the ESSA with..a large
proportion of common trench construction, has a wet weather
capacity of 330 mgd. Flows in excess of that amount are bypassed
to Lake Erie.
The Southerly plant has undergone a recent expansion to provide up
to 400 mgd of two-stage secondary capacity (plus filtration), with
an additional 335 mgd of primary only treatment capacity for peak
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CITY OF BATON ROUGE, LOUISIANA
is6 ?^L°« B5ton*ou*e' Parish of East Baton Rouge (Baton
sssss:
plant that discharges to the Mississippi
has 144 local wa^ewater tre^mSS
streams that flow to either the
In the late 1970 's an extensive SSES program was conducted in the
area served by the three main treatment plants / The result! of tha?
1^ X/X 1S "e^ssive..Pin tL collection Astern!
es<.occur tharoughout the collection systei
! St0rm eVents that a^e common in the area?
large number of direct connections between the
ogl SSES i«nrS at-^at .time' Errors found ^ SJ
1987^8 i»f«l/«?? ^ t0 Yerifl°ation field work performed in
o! th2 -nJfJ? Pilot areas in the collection system. The results
defS£sP in ?hegr™^ndlCatt ^ the ~J«ity of I/I sources are
DotentLi ^^ *• sewers'. not direct connections. Only sixteen
potential direct connections have been found in the uilot ar-^*!
during the additional, field work. The City^stSf believl that a
System Description
Most of the service area is relatively flat, averaging 45 feet
easTinlo tSZ^ ¥** V 2* S-Urface ^alnagi-ln thl alea fllws
east into the Comit or Amite Rivers, where as most of the sewatre
Sver Is mosT^^ treatme*t and discharge l^tlS'ittSlSSl
ciayf with a low permeability. Bedrock is several thousand feet
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below the ground surface. The groundwater is usually below the
sewers except in those areas immediately adjacent to the
Mississippi, Amite, and Comite Rivers.
The climate is typical of states around the Gulf of Mexico, with
about 54 inches of rainfall per year occurring throughout the year.
Average monthly rainfall is 3 to 5 inches, and storm events range
from high intensity short duration thunderstorms to more protracted
rainfall from hurricanes and other tropical storms. Peak
intensities of greater than one inch per hour are fairly common for
storms in the area.
The sewer system was originally constructed in 1890 with clay pipe.
Sewers constructed up to 1960 were constructed with clay pipe and
cement mortar or asphalt poured joints. Beginning around 1960
concrete pipes were installed for a major portion of the collection
system for all pipe sizes including service laterals. Approximately
80 percent of the new sewers constructed in recent years.have been
installed in backyard and cross country easements and drainage
corridors.
Joint construction , in the 1960's shifted to rubber gaskets. In
recent years, PVC has been used extensively in smaller sewers
because of its ease of installation. Creek crossings and canal
crossings are made with cast or ductile iron pipe. Sewer mains are
typically placed on the opposite side of the street from the storm
sewer with pipe crossings at intersections and catch basins. The
depth of the sewers ranges from 4 to 20 feet, at which point a pump
station is normally constructed. Service laterals range in depth
from the .ground surface to about three feet at the curb. Service
lateral are constructed with a six-inch pipe from the main to the
curb line and a four- or six-inch upper lateral from the curb to
the .building. There are approximately 105,000 service connections
in the system, for an average lateral density of 13 per 1,000 feet
of main.
RII Documentation
During the earlier SSES work flow monitors were placed at key pump
stations and bypasses throughout the CSD area. The flow monitoring
and subsequent field work indicated what was believed to be inflow
resulting from direct cross connections to storm sewers,- drainage
crossings, and manhole leakage. The PWWF (hour) to ADWF (day)
ratio ranged from 4 to 8 depending on the District. The peak flows
were projected to a 6-inch, 24-hour duration storm.
Follow-up investigations of the early SSES work "'showed many
inconsistencies between the data and the results presented, so new .
field work was performed in four pilot areas in the CSD service
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Case Studies
area, containing 93,000 feet of sewers. The majority of the field
work conducted in the pilot areas was smoke testing since it proved
52*22. m°? ®JfeCt:LVe durin9 the earlier SSES work for finding
22£?i in I 5*wers- The results of the smoke testing in
S2JSJ lar showed. * dramatic increase in the number of Snoke
testing returns than had been detected during the earlier SSES
IS?' +."2* tPpr°Ximately 16 Potential cross connections. The
estimated potential peak day I/I flow from each pilot area was 2 .3
to 2.8 times the estimate of the earlier SSES work.
o™* 6,°R, *ef??*s we.re looted during the pilot program
compared to 157 in th. earlier SSES for the same areas tested. The
greater than two times increase in the I/I flow estimates for the
pilot areas may be attributable to the differences in field
procedures and that the 1988 field work was conducted during
*°^ht condlti°ns. Drought conditions provided the maximum dryness
. Se S?I:L' allowing more smoke to reach the surface from defects
in the pipes.
Each smoke return was classified by type and location of defect,
and amount of smoke observed. Based on the three observations, th4
defect was then assigned an estimated I/I flow value that was used
to calculate the estimated peak flow for each pilot area. The data
was summarized to show the percent of leaks detected and percent
for*ributed by main line, service line (laterals) , and
manhole leaks. For three of the four pilot areas, the estimated I/I
°,WfL m •the sewer mains and laterals were 85 percent or greater
and the fourth area had 63 percent from the mains and laterals. The
estimated I/I from the laterals ranged from 9 percent to 58 percent
with an average value of 32 percent. Based on the information from
3?16*.? areas, the main lines contribute the majority of the I/I
to the collection systems, with the laterals also contributing a
SS?J?S?"^ Portion of the I/I. The majority of the defects found
during the pilot program appear to be from Rll with only 16 defects
suspected of being direct connections. The earlier SSES work
apparently included both direct connections and indirect flow
transfers in the inflow estimates.
Television and manhole inspection of the sewers during the earlier
SSES work concluded that the mains were generally in good
structural condition except at the joints. The pipe joints in many
cases were offset or open, and lateral connections to the mains
were often cracked, protruding, or otherwise improperly' sealed.
To date no television inspections have been performed on the
laterals to determine structural condition.
A site visit was made to Baton Rouge during the course of this
study, and City staff and consultants were interviewed regarding
RII problems in the sewer system. With respect to the condition of
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Case Studies
the sewers, those present identified mains and laterals as being
the primary sources of RII in the collection system. Specific
problems are connections between the lateral and the main,
connections at manholes, and location of sewer lines either in
easements or alongside drainage ditches. Roots are a common problem
in the Baton Rouge area, particularly in easement areas. The roots
expand the size of a defect once the root has made an entrance into
the sewer. Based on the types and locations of smoke returns, it
would appear that soil channels to the sewer .defects may be the
primary RII pathway. The French drain effect of the backfill in the
trench was felt to be of minor significance except in local areas
where the predominant soils are clay.
The smoke testing in the pilot areas found many cave-ins above and
next to sewer mains ranging in size from 6-inches to over
24-inches. Defects of this size adjacent to drainage ditches or
along curbs and gutters allow large amounts of RII into the
collection system. The City currently has no routine maintenance
program other than responding to emergency problems. The current
backlog of over 600 defects and cave-ins means that only the worst
defects can be addressed. City staff felt that a good maintenance
program would greatly aid the reduction of .RII in the system.
RII Control Program
As a result of the early SSES and subsequent cost effectiveness
analysis, limited rehabilitation work was performed but no
reduction in I/I flows were noted. The current pilot program is
currently in the design phase to rehabilitate all the main line
defects identified during the field testing program. At this time,
City staff projects that a 40 percent reduction in I/I will be
achieved using this type of rehabilitation approach. The City is
also looking into expanding the current rehabilitation program to
include work on the service laterals.
Rehabilitation techniques used in the past in the CSD area have
consisted of most of the currently available techniques including,
slip-lining, inversion lining and pipe replacement. Rehabilitation
techniques being considered for the pilot program include point
repairs, pipe replacement, slip-lining, and manhole sealing.
Results from the pilot program are anticipated to be available
within a year. .
The City has re-assessed its approach to I/I and feels that a long-
term solution is required to properly achieve long-lasting results.
The early SSES work performed by the city was copducted in a
compressed time frame and the results could not be* verified or
repeated. As part of the City's overall plan, all wastewater from
the suburban areas will be treated and disposed of at either the
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t« £f a™?t ^stewater treatment plants to eliminate discharges
to the Amite River Basin. Also one of the goals of the I/I
am ^ elimination of at least 40 knSwnbypasi
Impact of Peak Flow on WWTP Operations
^^^y-,^erate-,S-, three main wastewater treatment plants and has
another 144 smaller wastewater treatment facilities within its
jurisdiction. The three main plants discharge to the Mississippi
S" S smaller plants discharge to stream and sloughs in the
River Basin. The three main WWTP's are the North CSD, central
S°Uth CSD Plants' the smaller wastewater treatment
™ a/e referred to as the "suburban plants". A brief
discussion of the operation of the three main plants follows.
?«rth^C?D*WWTP- The North CSD Plant was Decently rehabilitated and
upgraded from primary to secondary treatment with a design process
capacity of 8 mgd and a hydraulic capacity of 23 mgd. To date all
wet weather flows that reach the plant can be trelted. The plant
nas been designed to allow bypassing of peak flows in excess of the
23 mgd peak capacity. Some bypasses exist upstream in the
occodH- - t0 bypass plant flows has
occurred. The pro} ected design (year 2010) peak hour wet weather
flow to the plant is about 47 mgd.
Thf ?inal effluent limits for the North CSD plant are 30 mg/1 BOD
and 30 mg/1 TSS. The plant has just come on line recently after
being upgraded from primary treatment only. The new process at
this plant uses trickling filters to achieve secondary standards.
A£WFC«? ?«VDTv, f °r ,the. P-lant is about 6 *9d- The Stal PWWF to
ADWF ratio for this plant is projected to be 7.
The major cost associated with treating the wet weather flows is
increased labor required to operate the plant under peak flow
S?« ?• i°nSl P°Wer costs do not increase significantly since the
final discharge is a gravity outfall. Chlorination use is also
increased and therefore is more expensive than during dry weather
flow operations.
Central CSD WWTP. The Central CSD plant was constructed in i960 and
upgraded to secondary treatment in 1978. The secondary portion of
the plant has a process capacity of 20 mgd, and the' overall
hydraulic capacity of the primary section of the plant is 40 mgd.
Current operation of the plant during wet weather is to process
SS^?«L 2° -"?* 23 **d through the secondary system with the
remainder of the flow receiving only primary treatment. The
influent flow meter to the plant peaks at 40 mgd, but City staff
are certain that higher flows have come through the system. Peak
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projected flows for the Central region are approximately 55 mgd,
and bypasses do occur in the collection system. Current ADWF at the
plant is 15 mgd. The ratio of PWWF to ADWF for the plant is
approximately 2.7.
Discharge parameters for the plant are the same as those for the
.North CSD plant. Even during wet weather the seven day averages for
both BOD and TSS have been met without difficulty. The !basic
secondary process flow train is a high purity oxygen activated
sludge system with secondary clarification. Secondary effluent BOD
during peak flow is sometimes high due to solids loss over the
weirs at the clarifiers.
The costs associated with operating the treatment plant during wet
weather consists of increased labor and power costs. Final effluent
is pumped to the Mississippi River for discharge. Higher flows
increase chemical costs particularly for oxygen and chlorine.
South CSD WWTP. The South CSD treatment plant was constructed in
1962 as a primary plant and is currently being upgraded to a
secondary process. The secondary process will consist of trickling
filters to bring the final effluent into compliance with discharge
requirements. Discharge requirements are the same as those for the
North CSD plant. The ADWF for the plant is currently about 14.5
mgd; the PWWF to ADWF ratio is approximately 3.5. The current
capacity of the plant is 16 mgd, and the plant can handle up to 30
mgd peak flows. The 30 mgd peak flow limit is caused by the
limitations of the effluent pumps.
Three major bypasses exist upstream of the treatment plant, so true
peak flows in the collection system never reach the plant. Other
than the effluent pumps, the hydraulic capacity is estimated at
greater than 50 mgd. When the suburban area connects to the CSD
system the majority of the flow that went to the many small plants
will go to the South CSD plant. This connection is scheduled to
take place by 1994.
The costs associated with operating the treatment plant during wet
weather flows are labor and power with some additional cost for
chlorine. With the secondary treatment plant on line, the costs
should not increase significantly for wet weather flows, since the
plant, will have trickling filters for the secondary process.
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CITY OF SPRINGFIEIJD, MISSOURI
S ? Springfield is located in southwestern Missouri. The
wastewater service area is divided into two main drainaae bas
JfV6^ by a seParate WWTP- The larger of the twogSasiS
the Southwest area, which includes approximately 80 percent of
' 1
ovmle
plople. sanitary sewers serving approximately 160,000
5i??lef? due to I/Z include surcharging and overflows in the
collection system and basement flooding. Overflows occur a?
approximately ten sites during any good-siled stlrm and a? ?So '£
SrL^^n%lUrin? large rai"f^l events. Durln^the period ?957
SSrSS r/-?3-' ^f C±ty conducteI—SI
*
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Although the perennial groundwater table is at least 25 feet deep,
about 30 percent of the area is characterized by a perched water
table which rests atop the bedrock or impermeable fragipan. Sink
holes and crevices in the limestone create underground passageways
for water. Average annual rainfall is approximately 41 inches, with
May and June being the peak rainfall months. The area experiences
both localized thunderstorm-type events, as well as more general,
longer duration storms.
The original sewer system was constructed during the period 1894
to 1911. Roughly half of the sewer system is constructed of older
type VCP with mortar joints and brick manholes. The remaining half
of the system has been constructed over the past 30 years with
newer, improved joint materials and precast concrete manholes.
Service laterals are generally of similar construction as the
mains. The sewer mains are typically six to eight feet deep;
therefore, a substantial portion of the sewer trenches extend into
the bedrock. Only a small portion of the City is served by a storm
sewer system. Surface drainage is generally carried by overland
flow along street gutters, ditches, and natural drainage channels.
Roughly 20 percent of the buildings in the City have basements and
foundation drains.
/ • • _ . . , '.'•-,•--,.
RII Documentation
I/I flows within the sewer system were documented through flow
monitoring during the SSES, which was completed by City staff in
1980. Ten areas of the system were selected for monitoring, based
on known I/I problems. For the measured storms, maximum daily wet
weather to average dry Weather flow ratios for the individual
monitored subareas ranged from about 5 to 20.
The field investigations conducted during the SSES included smoke
testing, dye flooding, and manhole inspection. The smoke testing
and dye flooding identified relatively few sources, primarily
because direct inflow connections (roof and yard drains) had been
identified and corrected under previous programs. Some indirect
connections between storm and sanitary sewers were located and
corrected, and some smoke returns were observed from sewer mains.
It was generally felt that the soil may not have been sufficiently
dry to detect r pipe defects in mains and laterals. The manhole
inspection work primarily identified sources of infiltration
through manhole walls and inverts. Television inspection conducted
since 1966 throughout the system with the City's own equipment
identified lateral taps and laterals with clear water discharges
(from lateral defects or foundation drain connections.) as specific
sources of infiltration. •
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Although specific flow estimates based on source detection work
were not developed as part of the SSES, the I/I Salylis did
vSSX ?°^;nt^Y the total flow Contributions from dTreSTnflow
versus infiltration sources. Estimates of direct inflow were
5?Se? °n the observation of rain-induced I/I flo^s fo?
thunderstorm-type events during relatively dry soil
^Vh*St 12?MMI °f St0rms' it: was observed that a
*X£ PSak fl°W was reached in direct response to
It ws »«SLS he peak receded quickly after the rainfall stopped.
It was assumed that this response was due primarily to direct
~fi°W11SOl";CeS' and a relationship between inflow volume and
SS??li rf.^.^s^yeloped. This relationship was then used to
quantify the direct inflow portion of the- flow for a large,
5aS ?n»«?Sf Ja:L.nsto,rm filing under saturated soil conditions . It
oS J! ^? at direct mflow could account for approximately 40 mgd
of the 84-mgd peak flow. However, the flow was sustained at nearly
raLSf?ik i*ya'J* infiltration alone for several hours aftJr the
™v ~ -,£ ad stopped and direct inflow subsided. This sustained
peak could not be accounted for as storage in the system. Rather,
it was theorized that during the initial peak storm period the
its peak flow rate dniy after
also analyzed the flow trends in the system
^ing,.the P^ious 13 years. It was found that both I/I as a
percentage of total flow and as a percentage of rainfall had
increased steadily over that period. The increlsed severity of I/I
*a J^ribU*ed,,t0 b0th dete*ioration of the existing sewer system,
a»™?i v,aS .inadre/(^ate quality of construction of new sewers. On aA
a^?i,-bafXS' T/\ Was cal.culated to be about 15 percent of total
precipitation and approximately 25 to 30 percent of effective
precipitation (total precipitation minus evaporation) .
Factor affecting Rll in Springfield may include inadequate storm
drainage and the hydrogeologic characteristics of the area. Because
.
WhiGh exists in many Potions of the
• Slnk?°ieS and crevic«s characteristic of the
bedrock' storm water can easily and rapidly
Ai-ho -r and lateral trenches and foundation drains.
Although most buildings do not have foundation drains, a single
RII Control Program
The City has conducted sewer grouting since 1972, particularly in
older areas of the system, with little success in reduSig peak wS
weather flows. As part of the SSES, a pilot rehabilitation pro jlct
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was conducted in a newer area of the City (sewers constructed after
1968) which experienced very high flows during rainfall periods.
During a three-day heavy storm period prior to rehabilitation, the
total flow volume was nearly seven times the normal dry weather
flow. Manholes in the rehabilitation area were inspected during
this storm period, and those that exhibited significant
infiltration were subsequently sealed. The sewer main joints were
air tested and grouted if neqessary; however, most of the joints
were found to be tight. During TV inspection, it was noted that
many laterals were discharging clear water flows; however, no
lateral rehabilitation was conducted as part of the project. The
results of the pilot project indicated that although the
infiltration through the rehabilitated manholes had been reduced
or eliminated, the rehabilitation efforts had had negligible effect
on the flows from the overall area.
Since the SSES, the city has allocated approximately 10 percent of
its annual sewer budget for rehabilitation work, primarily
slip-lining of isolated problem sewer reaches. Ongoing TV
inspection is used to prioritize areas for rehabilitation. City
staff believe that grouting has been ineffective in reducing RII,
primarily because of migration of the RII to other sewer defects
and to laterals. In general, they feel that sewer system
rehabilitation is not cost- effective on a large scale basis.
Impact of Peak Flows on WWTP Operation
The existing Springfield Southwest WWTP is an advanced secondary
treatment facility with nitrification, effluent filtration, and
ozone disinfection with discharge to Wilson Creek. Effluent
discharge limits are 10/10 mg/1 BOD and suspended solids and 2 mg/1
ammonia. The plant utilizes equalization basins during peak flow
periods. Under high flow conditions, however, the plant sometimes
experiences problems meeting the suspended solids and ammonia
discharge limits. Currently, the equalization basins have limited
capacity during extreme flow events. The State of Missouri is
considering amending the City's discharge requirements to allow
discharge from the equalization basins after some settling, to be
dependent on stream flow and stream water quality.
NORTH AND SOUTH SHENANGO JOINT MUNICIPAL AUTHORITY,
PENNSYLVANIA
The North and South Shenango Joint Municipal Authority includes the
Townships of North and South Shenango, located along the shoreline
of Pymatuning Reservoir in northwestern Pennsylvania. The
Authority operates a collection system and treatment- plant which
serve a permanent population of about 1,200 and a summer population
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^^
System Description
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Because of the high groundwater and the fact that North and South
Shenango are largely resort communities, few of the houses have
basements. Therefore, many of the laterals are as shallow as three
to four feet below the surface. Storm drainage in the communities
is by ditch system.,Many of the sewer mains are located directly
under ditches or gutters along the side of the roadways.
RII Documentation
' • '" ,"•-•- . ,- ' 4- t '' '
Field work in the collection system was included in a Sewerage
System Evaluation conducted in connection with the litigation over
the pipeline construction. The field work included flow monitoring,
flow isolation, groundwater monitoring, and limited smoke testing.
The major focus of the field work was to isolate and quantify the
infiltration in the differeht pipeline contract areas, and to
determine the relationships between groundwater level,
infiltration, and precipitation. ,
Groundwater monitors were installed in sewer trenches at 144
locations in the collection system. These monitors were designed
to measure the hydrostatic head over the pipe in the trench. In
addition, shallow wells were drilled at four locations adjacent to
sewer trenches to document the differences in water level between
the trench and the undisturbed soil around the trench.
The groundwater monitoring information was used to develop maps of
groundwater elevation contours at different points in time and to
identify areas where the sewer system was submerged. In general,
the groundwater levels were highest in early spring and decreased.
during the summer. A considerable portion of the sewer system was
found to be submerged during the spring and early summer,
particularly in the western portion of the service area near the
lake. Comparison of the groundwater data in the eastern and western
portions of the system indicated that the east-to-west sewer
trenches appear to drain the groundwater from the undisturbed
natural soil in the eastern portion of the area and transport it
in the trenches toward the western portion of the area via a French
drain effect.
At several of the groundwater monitoring sites, continuous
recorders were used to monitor the response of groundwater level
to precipitation. Data from the recorders showed that water level
in the sewer trench can increase rapidly in response to rainfall.
Increases of three feet (the limit of monitoring) within^ a few
hours of the onset of rainfall were recorded at sites throughout
the system. Water levels seemed to be the most responsive to
rainfall during the winter and early spring, and also'-responded to
the daily thawing and snowmelt which occurred during parts of the
winter- Sewage flows, as measured by flow monitors in the system,
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d Study' . measurements were made of infiltration from
SSSS2 • f r plpe ?oints at six locations in the system. This
procedure involved isolating the joints with a packer assembly and
quantifying the infiltration rate under a range of piezomltric
heads (measured as the differential between the piezometric
pressure in the trench and the inside of the sewer PpfpeT SS
infiltration rate clearly increased as the head differential
increased, with rates ranging from 10 to as high as 2,600 gpd. The
magnitude of the infiltration response varied from location to
location*
i i ?iat y-**1** infiltration rates were observed in sewers
installed in trenches underneath ditch lines. Many of these ditches
have been observed to be flowing with water over one foot deJp
"IS S™ ^?S/^Whl*h,Can easily Percolate into the disturbed soil
S2oPSSfSf t ba1Cliflll1 mat^ial in the underlying trench. It was
S rSSSi^? laterals and lateral connections did not appear to
be contributing significant extraneous flows, based on TV
inspection conducted in conjunction with subsequent rehabilitation
Vr O JTJC • - ' •
Because the sewer system was constructed so recently, it is
unlikely that any significant direct inflow sources exist in the
system. This was confirmed by limited smoke testing that was
?£?d™ =, f °r thS .f t?dll' in Wh±Ch °nly One Potential surface water
S?S ~J ource was detected. Therefore, it can be concluded that the
»iS «£ wf ather f lows in «ie sewer system are due to infiltration,
and the flow increases during rainfall are due primarily to the
increase in infiltration into defective sewer joints as a result
of the increased groundwater level in the sewer trenches.
RII Control Program
As part of the work to evaluate methods to solve the infiltration
problems in the sewer system, some sewer grouting was conducted in
8*1 The gr°Ut aPPeared to seal the joints internally, but
noreduced- » is believed that the- .inherent
H - .
SiSf ^ the ^oint compression rings made grouting ineffective
preventing leakage due to external hydraulic pressure.
A Pilot slip-lining project was performed on 1,400 feet of sewer
86"1' Yith flow monitoring before and' after the
11- W°£ ^ ^esults of the project indicated that
in the slip-lined sewer was completely eliminated
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through the rehabilitation work. As a result of the settlement of
the construction litigation, the Authority is now slip-lining all
of the mains and slip-lining or replacing the lower laterals in the
four problem contract areas. Due to the lack of rain this year,
evaluation of the flow reduction resulting from the rehabilitation
work has not been completed, although early results indicated
substantial reductions in those areas rehabilitated in March 1988,
prior to the drought period.
Impact of Peak Flows on WWTP Operation
The North and South Shenango WWTP is,.an activated .sludge plant,
which was designed for an average flow of 1.2 mgd and a maximum
flow rate of 3.0 mgd. The plant consists of three separate
400,000-gpd contact stabilization units. It was envisioned that
only one unit would be operated in the wintertime, and the
additional units would be put into operation to handle the
increased summertime population. Although the current wintertime
service area population is less than 15 percent of the design
maximum population, this high flows in the system to date have
forced the operation of all three process units, even during the
winter months. Since overflows and bypasses occur in the system
during peak flow conditions, the current testa! peak wet weather
flows cannot be measured, and the entire flow does not reach the.
WWTP.
During high flow periods, the influent is so dilute that it often
meets the discharge limits for the plant effluent. The major
problem, aside from lack of available capacity for future growth,
is that the plant cannot meet the NPDES permit treatment
performance requirements for 85 percent removal of BOD, due to the
extremely dilute influent. The plant has also been flooded out a
few times due to the high flows.
CITY OF AMES, IOWA
The City of Ames, Iowa, is located in central Iowa along the Skunk
River. The collection system and treatment plant serve a population
of approximately 45,000, including the Iowa State University
campus, which comprises almost half of the total population; The
collection system contains approximately 135 miles of sewers.
The City conducted an I/1 Analysis and SSES during the late 1970's
in conjunction with a facilities plan for expansion of the WWTP.
During wet weather .periods, the plant cannot handle the peak flows
in the, system, and the influent sluice gate must be,throttled to
limit the flow entering the plant, often for as long as several
days. Several times each year during extremely wet conditions,
bypassing of raw wastewater occurs both at the plant and at several
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System Description
I situated Primarily on the uplands surrounding the flood
ol ^°HriVerS* The toP°^phy varies from level to s?igh??y
as
The sewer system ranges from new to over 80 years old. Most of the
X25? £0rti°n °f System is Concentrated in two of ten su?sy2tems
About 40 percent of the collection system is over 30 vef?s old*
shallow plastic line to the street curb or yard However it iS
wta dlsoha ^
. - S
winter during freezng
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RII Documentation
The I/I Analysis and SSES field work included flow monitoring,
smoke testing, dye flooding, manhole inspections, flow isolation
and TV inspection. Smoke testing and dye flooding were used to
identify direct inflow sources and sources of indirect flow
transfer from storm drains to sanitary sewers. Manhole inspections
12f" • ea sources of direct inflow through manhole lids. In
addition, a foundation drain study was conducted to provide
documentation of the I/I flow contribution from foundation drains
directly connected to the sanitary sewer-system.
The foundation drain study included a survey to locate foundation
drain connections, and measurements of foundation drain flows
durinig rainfall and rainfall simulation. The survey included over
8,500 buildings and identified over 1,800 foundation drain
connections to the sanitary sewer system. These included about 100
•wet basements11 with no foundation drain, but where water flowing
through cracks in the basement walls enters the sanitary sewer
.through the basement drain. In addition, another 1,600 foundation
drain sump pumps with normal discharge to the ground were found
Many of these have valving capability to divert flow to the the
sanitary sewer during freezing conditions. Presumably, if
homeowners neglect to switch the discharge back to the yard at the
end of winter, a portion of these foundation drains would also
contribute flow to -the sanitary sewer system during peak flow
conditions in the spring.
Running time clocks were installed oh 12 foundation drain sump
pumps over a one and one-half year period. The locations were
selected to provide a representative range of soil and groundwater
conditions, and included locations where the sump pumps ran only
during; extreme wet weather periods, as well as locations where the
foundation drain was active continuously except tinder extreme dry
weather conditions. The data from the sump pump pumping study was
used to project average flow rates for different design conditions.
For the .one-hour maximum flow condition, the average flow
contribution per foundation drain was estimated to be 5.6 gpm.
Rainfall simulation was conducted for seven foundation drain
locations. The testing was designed to simulate a 1 in/hr. rainfall
(estimated two-year recurrence frequency). For two of the sites
in which the lots sloped away from the house, no response was
detected and the testing was discontinued after 30 minutes. (These
foundation drains were normally active during wet weather.) For
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approximately 50 percent of the applied flow rate.
Based on the results of the SSES field work and
SoSST *evel?>?d of the «~ on
sources. Direct inflow was estimated to account for
n -4° Percent of the maximum Sur i/i |?oSf f Sd
foundation drains were estimated -to contribute about 50
The proDected PWWF is estimated to be about six times
SnL^h?^ t f los? in the svstem typically occur during the spring
under high groundwater and saturated soil conditions resulting from
successive rainfall events. The response of foundation drains
Cstaf hav « , - Under «oo
city staff have observed that soil shrinkage may pull the soil awav
°a ?ai1S'<> which.may ^ one facto? in the rapid rale
into foundation drains. The factors tha
The factors that affect
$£* ata£s
- cons truotion- iocati™ ~
RII Control Program
Pfrf-?d since the SSES' «» City has completed much of
.ita?i01? W°rk that was determined to be Sost effective
Sd «fJf Analysis primarily correction of direct inflow slurceJ
and some sewer rehabilitation. About two years ago, the Cit?
initiated a foundation drain disconnection program! targeted at
SJKS*1^!? ?68 found.ation drain connections 9over a ttn-year
SS?2; / fi:091?* includes Provisions to reimburse a l™
portion of the homeowners' disconnection costs. TO date
ai?SnSaSely 3°° *oundation drain connect?^ havl be^A
?i ^ ^" ^Vn entlrely voluntary basis. About half of these are
in aSarwfthe1 ai?aS' rj1* Priority f0^ disconnection being pfaSI
Jh4 A listing storm drain facilities. The City anticipates
that the program will continue beyond the required 768
SfSSTSS?-* N° f°110W-!P flow ^nitoring has been^conducted?
and basLSfL053^^ a decrease in «» "-bir- of complaint
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Impact of Peak Flows on WWTP Operation
The existing WWTP, constructed in 1950, iss a single-stage trickling
filter plant with van design average flow capacity of 2.2 mgd.
Although flows in excess of design capacity have been effectively
handled at the plant, peak flows exceeded about 8 mgd must be
bypassed. Current average flows are approximately 5 to 6 mgd, with
peak hour wet weather flow rates estimated to be over 35 mgd. The
current WWTP expansion will increase design capacity to 12 mgd
average, 20 mgd peak day, and 34 mgd peak hour flow, utilizing a
two-stage trickling filter/solids contact process and equalization
basins to handle flows in excess of 20 mgd.
Generally, the existing plant can achieve 80 percent removal of BOD
and suspended solids* During high flows, plant efficiency drops to
55 to 60 percent. Other problems which have been experienced during
high flows include hydraulic washouts, carryover of solids, and
digester upsets due to fluctuating solids loadings.
CITY OF COOS BAY, OREGON
The City of Coos Bay is located on the southwest coast of Oregon.
The City is divided into two main sewer service areas, each served
by a separate WWTP. The major I/1 problems are concentrated in the
collection system tributary to WWTP No. 1, which serves the eastern
portion of the City and the adjacent Bunker Hill Sanitary District
outside of the city. The Coos Bay wastewater system serves a
population of about 15,000 and contains approximately 78 miles of
sanitary sewers (not including tributary districts). The sewer
system is primarily a separate system, although a small portion is
believed to be partially combined.
Problems due to high peak wet weather flows include bypassing and
overflows in the collection system, as well as raw sewage bypasses
and discharge requirement violations at WWTP No. 1. In 1971, the
City completed a comprehensive sewerage study, which identified
I/I as a major problem in the collection system. From the early
1970«s through 1982, the City conducted source detection and
rehabilitation work to reduce I/I. The program included
disconnection of known direct inflow connections, including
downspouts and cross connections with the storm drain system, as
well as sewer main rehabilitation. However, despite the
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rehabilitation program, the system still experiences high peak wet
weather flows. Since smoke testing has confirmed that almost all
direct inflow connections have been eliminated from the system, it
is believed that the majority of the peak rainfall induced flows
are due to infiltration into sewer main and service lateral
System Description
The City is located on a peninsula surrounded by Coos Bay the
largest estuary in Oregon. The two sections of the city are
situated on the eastern and western sides of the peninsula.
corresponding to the WWTP No. l and WWTP No. 2 service areas
respectively. The topography is characterized by rolling foothills
with elevations varying from sea level to 500 feet. The flatter
SS*8!?**-1?0?^ near the edges of the estuary. Soils are marine
and alluvial deposits, primarily sandy loams with greater amounts
™LS* ^jand clay in the eastern (WWTP No. l) area, including bay
mud in the downtown area near the estuary. A large portion of the
older area of the City is located in a tidal basin and constructed
on dredge spoils (fill) . Average annual rainfall is approximately
62 inches, with 75 percent of the rain falling during the period
November through March. Groundwater elevations near the estuary are
very high and influenced by tidal fluctuations. In other areas, the
groundwater level is typically below the sewers for most of the
year, but increases during the winter rainy season.
T5eJtewef.fystem was originally constructed in the central portion
?L* Jrlty
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RII Documentation
JSrJK ^ P monitoring at 34 locations and wet weather flow
mapping (early morning flow measurements taken at key manholes)
™rnd. as part of a Facilities Plan Supplement completed
d ference Between wet weather and dry weather flows
*^®^"-11**11 dePei»dent flow, and ranged from zero
* * he 34 subbasins- The projected peak rainfall
dependent flow for a five year design storm was calculated,
resulting in a projected PWWF of about 14 mgd and a PWWF to ADWF
ratio of about 8 to 1 . ,
Extensive smoke testing was conducted during the period 1972 to
1975 as part of the sewer system rehabilitation program. Although
the^ primary objective of the smoke testing was to locate direct
inflow sources, many leaking service laterals also exhibited smoke.
TV inspection identified problems in sewer mains due to leaking
Doints and root intrusion. In areas near the estuary, ground
settlement has caused considerable pipe movement, resulting in
cracks, breaks, and offset joints in the sewers and service
laterals .
Based on the previous elimination of all identified direct inflow
connections and the known poor condition of the sewer system, it
can be concluded that the peak wet weather flows in the Coos Bay
system are primarily due to RII.
RII Control Program
In previous years, the City has completed rehabilitation (primarily
grouting and some replacement) of sewer mains with major problems
identified through smoke testing and TV inspection. No work on
service laterals has been conducted. Although the basic approach
to addressing the wet weather flow problem in the system consists
primarily of expansion of the WWTP, the City has instituted a
program of routine TV inspection of the sewers to identify
particular areas in need of repair or replacement.
Impact of Peak Flows on WWTP Operation
The existing Coos Bay WWTP No. i is a conventional activated sludge
treatment facility with a design average flow of 2.66 mgd and a
maximum hydraulic capacity of 5.85 mgd. in addition to raw sewage
bypasses, the biological process is frequently upset by hydraulic
overloading, resulting in solids washouts. A split stream treatment
scheme is practiced, which -provides primary treatment with
disinfection to all plant influent flows and secondary treatment
up to process design limits. This practice has been relatively
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.atF1meeting Affluent discharge limits except during
high flow conditions. Salt water shock loads that upset
??era£10n .ha,Ye al.SO occurred at the plant, believed to be
r,»l ^ infl°W int-° Storm sewers through malfunctioning
g ™ tnd P"*"8*0"* infiltration into the sanitary sewel
• t tre?3"61* Plant is currently being expanded to handle
• e
Jrr?, f rejected five-year storm design peak hour flow of 14 mgd
utilizing a similar split-stream process scheme during peak flow
P^ZTxOdS *
CITY OF TULSA, OKLAHOMA
A^a«CitY r,°f TulSa is located in northeast Oklahoma along the
Arkansas River. The wastewater service area is divided into two
main drainage basins, referred to as the Northside and Southside
?£« «««* The total service area population is approximately
*** collection s
««« aey
sewer m4i *** collection system includes over 1,400 miles of
The City has conducted SSES work in the sewer system since 1982 as
part of overall facilities planning efforts and in order to reduce
surcharging and overflows in the collection system during rainfall
In subbasins determined to have excessive I/I, SSES work has been
followed by rehabilitation. In the Southside basin, SSES work was
completed in 36 of 41 subbasins, and rehabilitation has been
SSS? S® -,fr de^gned for 17 subbasins. In the Northside basin,
SSwf^J- W°^ W3S co?ducted in 12 of 22 subbasins and
SS2S *5 i«2e.xn.8 f"1*351113- Source flow estimates based on the
Northside SSES indicate that over 70 percent of the peak
rain-induced I/I flow is contributed by infiltration sources in
collection sewers, manholes, and service laterals.
System Description
The topography of the .service area ranges from flat to gently
sloping. The area is generally characterized by shallow bedrock
ranging from 20 to 60 inches below the ground surface. The bedrock
consists mainly of limestones, shales, and sandstones, overlain by
moderately to well-drained loamy soils formed from materials
weathered from the bedrock or from alluvial deposits. In the
eastern portion of the service area, the soils are typically tight,
S£ansive ?lay-fV Avera^ annual rainfall is about 39 inches; th4
highest rainfall occurs during the months of April through June and
September and October. Groundwater levels are typically low. Onlv
scattered areas experience high groundwater, typically near the
rivers, and the maximum seasonal groundwater levels are generally
not higher than about six feet below the surface.
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The oldest portions of the sewer system date to the early 1900's.
About one-half of the existing system was constructed before I960,
and the system has continued to expand through the 1980's. The
sewers in the system are predominantly VCP, with some concrete and
plastic pipe. Cast iron or PVC laterals are most common, with VCP,
AC, concrete, arid Orangeburg pipe in the older areas. The,older
pipes in the system utilized tar, jute, or cement mortar joints and
were bedded and backfilled using native soil materials. Newer-
pipes have been installed with,sand bedding, and since 1962 have
utilized molded plastic or rubber gasket joints. Manholes are
predominantly brick and mortar construction, with precast concrete
manholes being installed more recently in some of the newer areas
of the system. In general, the manholes do not have vent holes. The
sewers mains average about ten feet deep and are generally located
above the groundwater. Service laterals are typically two and
one-half to six feet deep. About 90 percent of the sewers are
located in backyard easements or alleyways*
RII Documentation . .
Flow monitoring was conducted at 24 sites in the Northside basin
and 46 sites in the Southside basin to determine dry weather flows
and rainfall induced I/I. In both systems, dry weather
(non-rainfall) infiltration was not found to be excessive, which
is consistent with the low groundwater levels in the service area.
Measured PWWF to ADWF ratios typically ranged from 2 to 5, with a
few subbasins experiencing higher peaks. For the overall Northside
and\Southside systems under projected design storm conditions, the
PWWF to ADWF ratios are about 3.5 to l. The rainfall induced I/I
represents about 70 percent of the peak wet weather flow.
The field investigations conducted as part of the SSES's included
extensive smoke testing, as well as dye flooding, manhole
inspection, and TV inspection. Based on ttye data collected in the
eleven SSES subbasins in the Northside basin, the predominant types
of I/I sources identified were leaks from service laterals, sewer
mains, cleanouts, and under manhole frames. Over half of the
defects were detected as smoke returns observed along the ground
over service laterals and sewer mains. There were very few direct
inflow connections such as roof leaders, area drains, or storm
drain/ sanitary sewer cross connections.
Visual and TV inspections were conducted, to assess the overall
condition of the system. The TV inspection data was used primarily
to determine appropriate rehabilitation methods, and not to
specifically identify or quantify I/I sources.' Common deficiencies
observed during these inspections included offset joints, cracks,
and root intrusion. Lateral taps were also found to be a
significant problem.
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" "
RII Control Program
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based on the SSES tests were notified and requested to make
repairs. An overall 70 to 80 percent compliance was achieved in
many areas. j.cy«=u
Flow monitoring was performed before and after rehabilitation in
order to assess the overall effectiveness in reducing i/i -For
eight Northsiide subbasins in which rehabilitatibn was performed,
the initial reductions in peak wet weather flows ranged from
approximately 30 to 90 percent, with an average of about 50
percent. ^ ««wuu
Impact of Peak Flows on WWTP Operation
The City is served primarily by two major WWTP's, Northside and
Southside. Both are conventional activated sludge plants, each
treating an average dry weather flow of about 30 mgd. At the
Southside WWTP, the peak flow reaching the plant is limited to 50
to 60 mgd by pump station capacity. Flows in excess of this amount
are bypassed to the Arkansas River. The Northside WWTP has limited
equalization storage capacity; however, it is insufficient for
handling peak wet weather flows. All flows which enter the plants
pass through all treatment process units. During very high flows
or prolonged high flow periods, washouts can occur in the secondary
treatment process.
C-47
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APPENDIX D
SEWER SYSTEM REHABILITATION METHODS
This appendix contains discussions on sewer system rehabilitation methods applicable for
control of RII. The appendk is divided into three sections: Pipeline Rehabilitation,
Manhole Rehabilitation, and Foundation Drain Disconnection
PIPELINE REHABILITATION
; '
Rehabilitation methods for sewer pipelines are divided into two categories: (1) replacement
by conventional and trenchless techniques, and (2) rehabilitation by grouting and by lining
techniques, including slip-lining and cured-in-place lining. The methods described in this
section are not all-inclusive; other techniques are currently being developed.
The focus in pipeline rehabilitation today is on in-place techniques such as trenchless pipe
replacement, slip-lining, and cured-in-place lining. These methods minimize the impact at
the surface, for example, minimizing traffic disruption and conflicts with other utilities
One of the main shortcomings of all the in-place techniques is making a leak-free joint at
the main and lateral connection without excavating. Because these connections are often
significant sources of leakage, the effectiveness of the seal at this joint may be essential to
RII reduction.
Many rehabilitation techniques orginally developed for sewer mains have been modified
tor lateral rehabilitation. However, the cost effectiveness of these methods generally
becomes less as the length of the individual rehabilitated pipe decreases. Since laterals are
typically short (less than 75 feet) and may have many bends or offsets, rehabilitatation of
aterak by in-place techniques is generally less cost effective than for mains. Access to
laterals for both testing and rehabilitation also remains a technical and institutional
problem.
Replacement
Replacement is an effective option for RII correction, as well as for repair of structural
deficiencies. Replacement of an entire manhole-to-manhole reach initially provides a new
essentially leak-free pipe. Conventional replacement methods involve excavation and
removal of the existing pipe or excavation of a parallel trench for the new pipe with
abandonment of the existing -. F H
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Sewer System Rehabilitation Methods
pipe in place. Excavation and .replacement of isolated, joint-to- joint pipe sections (point
repairs) may also be used as a means of RII source correction, or in conjunction with other
sewer • • " '.'- .-'-.• •" • ' ..': ... •, . •• ' - • ' •
rehabilitation techniques. Whereas in-place repair techniques
leave the original pipe grade, offsets, and sags unchanged, excavation and replacement
generally correct these types of problems, as well as more severe problems such as sewer
collapses. . Excavation for point repairs are often necessary with other rehabilitation
techniques. For example, severe joint offsets must be excavated and repaired prior to
slip-lining. Lateral to main sewer connections are also frequently excavated for repair.
Some of pipe replacement techniques that do not require excavation are described in the
following paragraphs.
Tunneling. There are a wide variety of construction techniques that can be classified as
tunneling. These techniques include microtunneling and auger boring as well as
conventional tunneling. Tunneling is a means of replacing an existing pipe without
extensive excavation. ,
Microtunneling refers to tunnels which are too small to allow man entry. Microtunneling
techniques are also varied, and many are steerable. In general these techniques allow
installation of pipe up to a maximum of 300 to 400 feet. The minimum pipe size for
today's equipment is about 8 inches. Techniques are available for installation below
groundwater. The technique is generally applicable in silts, clays, sands, and gravels, but
deals poorly with stones or cobbles larger than two inches. The accuracy of the installation
depends in part on the length. Concrete, clay, and fiberglass reinforced plastic pipe have
been installed using this technique. Access requires excavation of a launch pit 12 to 20
feet long. Microtunneling can also be used to replace an existing pipe along its alignment.
The technique has been used extensively in Japan, Germany, France, and Singapore.
Auger boring is used to describe a nonsteerable technique. Accuracy and length of
installation are less than for microtunneling. Pipes as small as six-inch diameter with
lengths up to 400 feet can be installed. Access requires pits at each end, 6 to 15 feet in
length. The pipe installed is generally steel and called a casing. The process or carrier
pipe is slipped inside the larger steel casing. This technique, often referred to as boring
and jacking, has been used,since the 1940's in the United States. Pipe jacking is a
variation of the bore and jack technique where the casing is eliminated and the pipe itself
is jacked. -_
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Sewer System Rehabilitation Methods
Moles. Moling mvolves use of a percussive hammer to create a duct through the soil.
niere are two major variations, impact moling and pipe bursting (also referred to as
SS^hTT n^ Tto§e teClmiqUeS aI1°W ** trencWegss mstaUatoof new
K non-steer
n^ rencess mstaaof new
K ^ y non-steerable' PiPe burstm§ depends on an existing pipe for
Impact moling typically utilizes a percussive hammer driven by air, although hydraulic
versions have been developed. The mole creates a duct through clay, siltsfsands and
gravels. Isolated boulders or cobbles can be broken but often ihrow the moToff te
alignment. Very soft soils do not provide enough support for the weight of the mole; the
mole may drop making reasonable grade control impossible. Normal installations are 100
?™, g bu< mstf at'ons u? to 20° f^t long have been made. Steerable moles exist;
however most moles depend on the initial orientation for their alignment. Pipes between
one- and six-inch have been installed with this technique. The size of the launch pit is
generally determined by the length of the pipe sections installed; the mole itself requires
a launch pit of about six feet in length. This technique is widely used in the United
.Kingdom to install individual services.
Pipe bursting uses an expander in conjunction with a conventional impact mole. The
expander larger than the existing pipe diameter, breaks the pipe and allows a new pipe
£h»n?? 6i °r puushe(lmto the sPace behind the expander. The pipe installed may
SST ™ger than ** e3dS?g Pipe' Pipes up to 18-mch have been installed by this
technique. The maximum length of installation is about 450 feet. Pipe bursting is effective
in existing cast iron, unreinforced concrete, clay, and asbestos cement pipes. New
po yethylene, polypropylene, and clay pipes have been installed by this technique. Butt
welded polyethylene is particularly attractive for rehabilitation for RH control, since it is
C bf™ T? & ?*** ™ ** * length fc ^^d, although a longer launch pit
may be required depending upon the type of pipe installed.
Moles are frequently utilized for laterals, both for new construction and rehabilitation.
^tiltT f U'Cd b0th ^ eXfSting Pipes for ^acement (rehabilitation) and for
installation of a new pipe. Impact moling provides a number of advantages. Parallel
replacement of a lateral can allow the existing lateral to remain in service until the new
seiyice is installed. Also, new construction using impact moling installation does not
requu-e granular backfill, thereby minimizing the potential for inflation into the sewe
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Sewer System Rehabilitation Methods
Rehabilitation
Rehabilitation (as opposed to complete replacement) of an existing pipe can be
accomplished "in-place" by several methods, including grouting slip-lining, and cured-in-
place lining. These methods are discussed below.
Grouting. The least disruptive technique for rehabilitation, grouting, focuses on the sealing
of joints, small holes, and radial cracks in otherwise sound pipe. This technique involves
ho excavation where manhole entry is available. Grouting is performed with a miniature
television camera which locates the pipe joint and defects. Air testing may be used to
determine which joints are leaking and therefore require grouting. After positioning, a
temporary, double-bladder seal isolates the joint and grout is pumped through the joint.
After grouting, the joint is pressure tested to ensure the adequacy of the seal.
A variety of chemical grouts are available. The chemical grouts include acrylamide gel,
acrylate gel, urethane gel, and polyurethane foam. The gels are all capable of penetrating
the pipe joint and filling voids outside the pipe wall. The foam simply forms a gasket in
the pipe joint.
The; longevity of grout sealing may vary. Some of the grout products are susceptible to
shrinkage under alternate wet and dry cycles (such as when the groundwater level varies
above and below the pipe), reducing their sealing effectiveness. Foam grouts are designed
to be unaffected by water conditions, but may be difficult to apply. In all grouting, quality
control during application may have a significant impact on grouting effectiveness.
Therefore, periodic testing after the initial grouting (e.g., every three to five years) may be
required, not only to re-test the seal on grouted joints but also to ensure that new leaks
in previously ungrouted joints and defects are also addressed.
Lateral Grouting. Specific grouting techniques have been devised for lateral rehabilitation.
One technique involves pumping the lateral full of grout under pressure and then cleaning
the excess grout'from the pipe interior. This method of joint sealing has shown limited
success.
A second method known as the "sewer sausage" for grouting laterals has been devised. In
this method, an inflatable plastic sock is inserted into the lateral through the. main sewer
using a special device that is operated by remote control. The device is located inside the
sewer at the lateral, and is controlled by the operator by viewing through a TV camera.
The inflatable plastic sock generally covers the first two to three joints. Grout is injected
under pressure into the annulus created by the sock. After the grout Is set, the plastic
sock is pulled out and moved to the next lateral in the sewer. Although the sewer sausage
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Sewer System Rehabilitation Methods
method has been used for entire laterals, it is most effectively used for sealing the first
joint between the lateral and the main sewer.
In addition to the above techniques, direct joint grouting techniques, as used in larger
diameter sewers can also be utilized for laterals.
Slip-lining. In slip-lining, a liner pipe, slightly smaller in outside diameter than the inside
diameter of the existing pipe, is inserted into the existing sewer. Prior to installation, the
existing pipe must be televised to identify potential obstructions such as severe offset joints
and protruding laterals, and failed pipe sections. These must be corrected by point repair
Televising also serves to identify the locations., of services .which must be connected to the
completed slip-lining. Proofing the pipe by pulling a short piece of liner through the pipe
is recommended. r
The slip-line insertion process involves excavating a small length of existing pipe to provide
an insertion pit The depth and size of the excavation depend on the depth, diameter, and
the flexibility of the pipe liner. The liner, most often high-density polyethylene, is flexible
and can be butt fused into long joint-free sections on the ground surface. The slip-lining
pipe is pulled by a steel cable and is oftentimes assisted by pushing the lining into the
existing pipe. A tapered, pulling head provides gradual size transition and prevents debris
from entering at the leading end. The gradual size transition makes it possible to pass
minor obstructions.
The ends of the liner at the manholes typically are grouted to seal the annular space
between the liner and the outer pipe. Full grouting of the annular space may also be
done. This decision is generally based on cost, the condition of the existing sewer, depth
of cover, the potential for point loads on the pipe, and the amount of groundwater present.
The slip-lining is resistant to attack from acid, such as sulfuric acid commonly formed from
hydrogen sulfide in sanitary sewers. This characteristic makes slip-lining suitable for repair
of sewers with high potential for corrosion.
When a sewer main is slip-lined, each lateral connection must be excavated and
reconnected to the slip-lined pipe. If the lateral is also slip-lined, the lateral and main
sewer liners can be fused together to make a leak-free joint.
Two variations of the conventional slip-lining method are now available, both of which can
be installed from existing manholes and therefore eliminate the need for excavation for
insertion pits. The first method utilizes short, threaded high density polyethylene (HDPE)
pieces. The physical properties of this material are higher than polyvinyl chloride (PVC),
while its resistance to chemicals and effect of temperature on physics] properties are
similar to that of PVC lining. The assembled liner pipe can either be pushed or pulled
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Sewer System Rehabilitation Methods
with the existing pipe by using simple winching equipment. Low density grout is used to
fill the space between the pipe and the lining. The cost of sliplining with short pieces may
be less than other systems because non-skilled labor can be used for installation.
The second non-conventional slip-lining method uses a specially designed PVC strip that
is spun directly into the existing sewer to be rehabilitated. The PVC strip is helically
wound by a machine placed in an existing manhole. The space between the pipe and the
lining is filled with low density grout to stop groundwater from leaking into the annular
space. The PVC lining used in this process has excellent properties as a protective lining
against corrosion and can be designed for any strength requirements.
In another variation of this method, the lining is expanded after insertion into the existing
sewer. This is accomplished by pulling an inflated plug through the liner in the sewer
while/spiral joints slip before the cement is set. With this method, no grouting is required
since the lining touches the pipe. However, a bonding resin is recommended to be used
between the lining and the pipe.
As with conventional slip-lining, there is no dependable remote control method for cutting
the internal connections. The connections must be excavated and exposed, the liner pipe
cut, and a fabricated connector fitted and adhered to the lining with solvent cement. The
entire fitting is then covered with cement mortar.
Expandable plastic liners (polyethylene and PVC) are recent developments in lining of
pipe. These liners come in flattened rolls. They are heated slightly as inserted to increase
flexibility. After installation, further heating results in reversion to the original circular
cross section. Handling of manhole and lateral connections is similar to that for other
slip-lining methods. These products have been through limited actual usage.
Cured-In-Place Lining
Cured-in-place lining techniques utilize a thermal-setting, resin-coated, flexible fabric, which
is prepared to match the diameter and the length of the pipe section to be lined. The
material is saturated with resin and kept chilled prior to installation. Once in place the
liner is cured and hardened. The liner conforms to any shape and discontinuities and
provides a smooth, joint-free lining. The liner thickness is a design choice; thicker linings
can be designed to support weakened pipe or support greater hydrostatic loads.
Until recently, only one cured-in-place lining method was available in the U.S. However,
several other methods have been developed and are in use in Europe and Japan. At least
one of these has recently entered the U.S. market All cured-in-place lining methods use
the same basic materials (thermo-setting resins), but differ in the techniques used to insert
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Sewer System Rehabilitation Methods
the liner into the pipe and the method for curing the resin. In most methods, the lining
is inserted into the existing pipe by inversion, although in at least one method the lining
is dipped inside the pipe. Inversion is generally accomplished with water or compressed
air. Different methods may be used for curing the liner; hot water or steam are the most
common, but ultraviolet light is used in one process.
Cured-in-place lining does not require any excavation unless there are major pipe failures
or-severe lateral protrusions into the existing line. The pipe material is resistant to acid
and can be used to repair corroded concrete sewers. Although a remote cutting device
can sometimes be used to reconnect laterals to the lined pipe, the exact location of the
lateral connections may sometimes be difficult to find. If the original lateral connections
are subject to leakage, remote cutting will not provide any means of sealing these joints
In such cases, the lateral connections would have to be excavated and repaired.
MANHOLE REHABILITATION
The magnitude of RII through manhole defects appears to vary widely from system to
system. It is well known that inflow through manhole lids can contribute to peak wet
weather flows, particularly when manholes are located in areas subject to ponding or
flooding. Less well documented is the RH through manhole defects where pavement
defects allow rain to move quickly into base rock materials adjacent to manholes.
Milwaukee Metropolitan Sewerage District (MMSD) studies suggested significant RII flows
can result from manhole defects, specifically, frame and chimney connections. RII may
also enter manholes through the walls and base, particularly in brick manholes with
deteriorated mortar.
Rehabilitation methods for manholes include both interior and exterior techniques. Interior
repair techniques are less expensive and less time consuming than external repairs but are
frequently less effective. MMSD has conducted a pilot testing program on the various
manhole rehabilitation techniques described below, as well as others deemed ineffectual-
they continue to evaluate the effectiveness of the arious techniques.
Interior Repairs
Interior repairs are typically less effective for infiltration control but remain attractive in
many cases due to the low cost and ease of construction. These techniques make possible
the sealing of all manhole joints including the lower ones, which are often subject to the
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Sewer System Rehabilitation Methods
largest hydrostatic forces. Interior repair techniques utilize elastomeric sealant, chemical
grout, or an internal boot.
Sealants. Internally applied sealants are intended to seal leaky joints in the manhole wall
including the manhole frame and chimney joint. The surface must be free of loose
material, gaps filled, and the surfaces must be cleaned to assure a bond for the sealant.
Various products are available to be either troweled or brushed. A potential disadvantage
of elastomers is that hydrostatic pressure can destroy the bond, requiring replacement in
the future.
Grouts. Grouts may be utilized to plug voids behind manhole walls much as they are used
in pipeline rehabilitation. The chemical gels have not functioned well in applications where
alternate wetting and drying occur. A grout that is not subject to this complication could
provide a positive seal since hydrostatic forces would not destroy the sealing capabilities.
Internal Boot An internal boot utilizes a continuous band of elastomeric material forced
against the manhole walls with adjustable expansive metal bands to seal manhole joints.
The boot provides for vertical displacement at the joint but has limited offset capabilities.
The concrete contact surface must be smooth and without ridges which might preclude a
seal.
' ' . . S s
Exterior Repairs
Exterior repairs are often more effective than internal repair methods, but require
excavation. Therefore, external manhole repair methods are more costly more than
internal repairs. It is difficult to gain access to all the manhole joints, consequently repairs
focus on the joints close to the surface. These techniques utilize elastomeric sealant,
elastomeric sheet, rubber sleeves, and two-piece frames.
Elastomeric Sealants. These elastomeric compounds are poured around or troweled on
the manhole joint. The poured versions are available in cold pour and hot pour mixtures
both requiring a form to contain the pour. The cost of both techniques are similiar since
the excavation, backfill, and pavement repair costs are significant percentages of the total
cost. MMSD found the trowellable version to be most attractive.
Elastomeric Sheeting. Elastomeric sheeting can be banded or applied with adhesive to the
outside of the manhole structure. Joints in the sheeting may be thermally welded when
thermoplastic materials are utilized.
Rubber Sleeves. Rubber sleeves similiar to the internal boot are manufactured. These can
be slipped over the manhole chimney. The sleeves are held in place by upper and lower
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Sewer System Rehabilitation Methods
stainless steel band clamps. Some versions are designed to accommodate vertical
movement in between the manhole frame and chimney.
J""™?* STS* Tw°-Piece frames Prov*de another means of achieving vertical
flexibility. The lower section of the frame is securely anchored to the top of the manhole
chimney and will not be displaced by surface movement; therefore, the frame/chimney
joint remains intact. An elastic, water-tight gasket provides flexibility for vertical movement
and a seal against infiltration between the two pieces of the frame. Since the upper
portion of the manhole frame must be supported by the pavement, a two-piece frame is
probably only suitable for application in rigid concrete pavement.
FOUNDATION DRAIN DISCONNECTION
Foundation drains may be a significant RH source in some areas, as shown by the case
studies presented for MMSD and Ames, Iowa. Many cities have ordinances that prohibit
direct connection of foundation drains to sanitary sewers. However, many older
installations still exist. It is also not uncommon for foundation drains to be diverted to
sanitary sewers because of accumulation of ice or water outside the building or in the
street when the discharge is not connected to a storm sewer.
Foundation drains may be connected to sanitary sewer laterals in one of several ways:
o Direct gravity connection to the sanitary lateral.
sanitarfDiamagb into a sump with a pumped discharge to the
Kanitar|Diamagfe into a sump with a gravity discharge to the
o Discharge onto the basement floor and drainage to a basement drain
connected to the sanitary lateral.
Methods for foundation drain disconnection are relatively straightforward. Depending upon
which of the above existing configurations apply, the foundation drain discharge is directed
to a sump (if one does not already exist), and a sump pump and discharge line are
installed (or the existing sump pump discharge is redirected) to the ground surface outside
of the building or to a storm drain. Discharge of the foundation drainage to the storm
drain system would also require connection to an existing storm lateral or construction of
a separate storm lateral to connect into the storm sewer. The connection to the sanitary
sewer lateral must also be plugged. It is important to make sure that sanitary sewage
cannot enter the storm sewer, and that basement floor drains are connected to the sanitarv
sewer. , J
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APPENDIX E
DESIGN AND CONSTRUCTION STANDARDS
This appendix contains a discussion on design and construction for minimising RH into new
sewer constmr.tinn
sewer construction.
DESIGN STANDARDS
Modifications to sewer design standards provide a means to minimi^ future RII in new
construction. Such modifications include: restricting the flow of water in granular backfill,
reducing interconnections between backfills of various utilities, reducing the number of pipe
joints, providing flexibility to reduce settlement stress and breakage, sealing pipe/manhole
connections, and control over lateral installations.
i . ' v " : •-"'-? - '
Restricting Flow of Water in Granular Backfill
Granular backfill in pipe trenches can dewater surrounding soils with resultant increased
settlement potential for the pipe and the ground surface. This results in stress and the
potential for creation of RII entry points in the buried pipeline. Furthermore, the granular
backfill provides a permanent hydraulic conduit (French drain) along the exterior of the
pipeline. This hydraulic conduit can provide the means for large quantities of water to
travel to damaged joints and pipe defects.
This phenomenon can be alleviated by the addition of impermeable trench cut-off walls,
or trench plugs. The trench plugs consist of concrete, grout with cement, or bentonite clay
to create an impermeable dam. The number of trench plugs needed depends upon the
slope of the pipe (and the backfill); trench plugs at more frequent intervals should be
specified for higher slopes. An interval of 50 feet is common for such trench plugs.
If possible, a connection should be provided between the backfill and a point where the
collected water can be discharged. Such connections could be to a storm drain or a creek.
It is ideal to provide these connections at trench plugs at an elevation below the spring line
of the sewer.
In some areas, other methods to reduce the permeability of the granular backfill have been
tried. These include the introduction of impermeable grouts into the granular backfill after
placement, the inclusion of additives such as cement or bentonite clay to granular backfill,
or the specification of a well-graded backfill material. These measures sfcrve to retard the
rate at which water can infiltrate into sewer trenches.
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Design and Construction Standards
Reduction of Utility Backfill Interconnections
A related issue is the common practice of placing granular backfill in areas where utilities
cross. This is done because adequate compaction is difficult to achieve when utility
trenches are in close proximity, either vertically and horizontally. Granular backfill (e.g.
pea gravel) can be compacted to higher levels with less compactive effort. Unfortunately'
this backfill material also provides a pathway for water collected in the shallower utility
trenches to move into the backfill surrounding the sanitary sewer, almost always the
deepest utility. Trench plugs can be installed at these locations to prevent this connection.
Control of Migration of Fines/Piping
Sewers constructed at steep slopes and in areas where groundwater is constantly fluctuating
present the problem of migration of soil fines. This migration can take place along the
pipe and at cross section to the pipe.
Two separate measures should be considered in such situations. Installation of trench
plugs may prevent the fines from being carried away downstream. Installation of a semi-
permeable membrane below and around the backfffl may prevent soil migration in and out
of the trench. These measures will benefit in reducing pipe subsidence and the subsequent
formation of cracks and openings in the pipes., Also, the migration of fine particles away
from the pipe trench will be discouraged, resulting in more resistance to RH movement
within the trench and into the sewer pipes.
Reduction in the Number of Pipe Joints
The use of pipe with fewer pipe joints is advantageous since the joints are potential RH
sources. Old vitrified clay pipe used in the past for sewer mains and service laterals had
joints as close as two feet apart Early joints were mortared and were subject to cracking
and deterioration. New pipe materials, such as polyethylene, PVC, or ABS pipe can
provide almost jointless construction. Fewer joints simplify the determination of the source
of problems indicated by failed performance tests following construction. Fewer joints are
also likely to reduce the number of problems with roots growing into pipe joints.
Flexibility to Reduce Settlement Stresses
Stress points occur at the connections of the main and lateral, the lateral to the house,
manholes, cleanouts, and other structures. Stress points may also occur in trenches where
underlying soil conditions change. The ability to accommodate differential settlement is
important since unless the pipe transfers a part of the overburden soil load to the
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Design and Construction Standards
supporting soil, the pipe must carry the entire load. Flexible connections may be provided
by two joints in close proximity as well as by flexible materials such as rubber couplings.
Flexible connections are important between laterals and sewer mains, since these
connections are often documented as major sources of leakage.
Manhole Connections/Joint Sealing ,' •" '
Sealing pipe connections at manholes is equally as important as providing flexibility.
Manholes generally have greater hydrostatic pressures outside the manhole than within.
Most manholes have no seep ring or water stop around the pipe as it enters the manhole.
Many of the pipes used today, such as PVC and polyethylene, do not bond well to concrete
manholes. Some additional means of sealing the pipe connection to the manhole is
required to prevent infiltration into this joint. Rubber seals have been developed for
small pipes. Tape seals, which are composed of bentonite and butyl rubber mixtures with
adhesive backing, wrap around the pipe to form an expansive seal.
Laterals ,
Laterals are extremely important because they may represent about one-half or more of
the total length of collection system piping. RE in laterals has been shown to be very high
in many areas. This is due in part to lack of design and construction standards for. laterals,
limited degree of construction inspection normally provided, and because laterals typically
receive little or no routine maintenance. Exterior cleanouts allow ready access, fpr testing;
one two-way connection at the street (property line) and one at the building is ideal. To
minimize RII, each lateral connection at the main should be closely inspected, and the
connection should utilize a manufactured sanitary tee, wye, or a saddle. Pipe penetrations
(hammer taps) should be replaced. Flexibility can be provided as described earner.
Cut-off walls or trench plugs in the lateral trench can be an element of construction,,
particularly here grade change or lateral length is great and granular backfill is utilized.
CONSTRUCTION STANDARDS
Construction standards imply conformance to the design intent This conformance is
accomplished by inspection and testing.
Regular Inspection ,,-.'.
Stringent construction standards for sewer lines cannot be realized without adequate
inspection. Major sewer construction should be continually monitored. Although this
would be ideal with laterals, it is impractical to provide more than a periodic inspection
during construction. Many agencies require post-construction television inspection of new
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Design and Construction Standards
lines and lateral This is quite valuable, but is not a substitute for inspection during
construction For example, post inspection viewing does not indicate if adequate
compaction has been performed, if trench plugs have been installed, or if flexible couplings
have been provided. Ordinances requiring strict compliance with standard construction
details may help.
Performance Testing
Stringent standards for leakage testing (air pressure or water) should be set and achieved
Since the results at the time of testing are probably the best the pipe will ever achieve'
stringent test standards are necessary to assure acceptable infiltration over the life of the
Leakage testing rarely imposes limitations on the length of pipe to be tested at one time
Anything shorter than manhole to manhole testing is impractical. However since
permittable leakage is a function of length, longer reaches allow greater losses. Current
standards permit some joints to leak and this is practical to accommodate construction
capabilities. However, one joint may be responsible for 90 percent of the leakage in a test
L6™!?1; -i ^teSt in?UdeS ^ j0intS' ** °ne * the "* badly leaking J'oint> the test
would fail If the test includes 40 joints, and badly leaking joint is included, the test may
pass. Although testing of individual joints would eliminate this problem, it could be costly
and time consuming. • • J
With leakage tests, no pipe lengths greater than single manhole-to-manhole reaches should
be tested at one time. Testing of individual joints is recommended in large diameter
piping, 18-inch and larger, using joint testing equipment.
Criteria for exffltration and air testing for gravity sewers and laterals are presented below
rest criteria should be modified according to the manufacturer's recommendations.
Exffltration Test Criteria. Maximum allowable leakage of 25 gallons in 24 hours per inch-
diameter-mile of sewer is recommended by some manufacturers. The Standard
Specifications of Public Works Construction prepared by the County Sanitation Districts
or Los Angeles County recommend the following formula for maximum allowable
exfiltration.
E= 0.0001 LD (H)w
E = Allowable leakage (gpm)
L = Length of test section (feet)
D = Internal diameter of pipe (inches)
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Design and Construction Standards
H= Differenpe m elevation between water surface and invert at lower end
of pipe (feet)
Air Test Criteria. When testing a new pipe, the common procedure is to maintain air
pressure at 3.5 psig while the temperature stabilizes. The system passes the test if loss of
pressure is 0.5 psig or less in 30 minutes. Failure to hold air pressure is usually indicated
within 15 to 30 seconds.
E-5
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APPENDIX F
COST EVALUATION
This appendix describes the methodology and results of the RII cost evaluation summarized
in Chapter 3.
ANALYSIS METHODOLOGY
The approach utilized for the RII cost evaluation is primarily intended to address sewer
systems, such as the EBMUD system, where the primary sources of RII are defects in'
sewer mains and laterals. It is not intended for systems in which the primary RH sources
are manhole frame/chimney leakage, foundation drains, or other specific types of sources
not generally classified as pipe defects.
The approach also assumes that the primary component of the peak I/I flow is RII. In
particular, it is assumed that base groundwater infiltration (GWI) is not "excessive" (as
defined under current EPA regulations) and that direct storm water inflow (SWI) is
insignificant compared to RH peak flows.
The cost analysis procedure is intended to be applied to a sewer subsystem which is
relatively homogeneous with respect to age, soils, geology, groundwater conditions, sewer
depths, and the general physical condition of the system. A typical application would be
for a monitored area of between 10,000 and 50,000 linear feet of sewer mains. It is
assumed that the RE flows for the subsystem have been previously determined by flow
monitoring or that a reasonable estimate of the RH can be made. As discussed in Chapter
2, the magnitude and pattern of RE flows are a function of many different interacting
factors. Therefore, the RH response cannot necessarily be predicted for any particular
area based solely on the physical characteristics of the area or the sewer system.
The assumptions used in the cost analysis should not be perceived as limiting its
applicability to more "realistic" situations, for example, where GWI is also a significant flow
component The basic concepts and approach can be applied to more complex situations
with appropriate modifications.
/
The RE cost analysis procedure consists of ten basic steps which are described below:
1. Determine Subsystem Peak RO Flow. In the cost evaluation, RII flow is
expressed in terms of a peak flow rate, since the major impact 61 RII in the
sewer system is on the capabilities of facilities to handle peak flows. Typically,
F-l
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•'<.-, Cost Evaluation .
the RII flow will be based on the peak hour (or other suitable short-term) flow
for a specified design storm. The choice of design storm conditions may depend
on regulatory requirements or simply reflect the degree of conservatism that is
desired in sizing facilities.
2. Estimate RII Distribution. In a typical subsystem, the RH will not be evenly
distributed among all pipes in the area. Certain "worse" pipe reaches, or
"mmibasins," may have higher unit RII contributions than others, i.e., contribute
a greater proportion of the RII flow. In the field, the RII distribution can be
determined through flow mapping (flow isolation) or intensive flow monitoring
during rainfall.
Figure F-l presents a generalized RII distribution envelope. Although the
envelope is conceptual in nature, it agrees well with data from several sewer
systems in which infiltration (RII or GWI) distributions have been developed
based on flow isolation data. Based on a general knowledge of the key RII
factors in the subsystem, the envelope can be used to estimate the RII
distribution. Typically, older systems with more widespread defects will exhibit
a more diffuse distribution (lower envelope boundary), while hewer systems might
be characterized by more concentrated distributions (upper envelope boundary).
3. Target the Percentage of the Subsystem for Rehabilitation. This target value
generally represents the point on the RII distribution curve where the curve starts
to 'level off." Above this percentage, the benefits of rehabilitation, in terms of
incremental RII flow removed, begin to decrease. However, the target
percentage of the subsystem should at least be large enough to significantly
impact the RII flow (e.g., the targeted portion of the subsystem should contribute
at least about 50 percent of the RE). For the envelope shown in Figure F-l, the
target rehabilitation percentage for a newer system (concentrated distribution)
might be about 30 percent of the subsystem, and 50 percent for an older system
(more diffuse distribution). In these cases, the amount of the total subsystem RII
contributed by the target percentage of the subsystem would be about 80 percent
of the RH.
4. Select the Method of Rehabilitation. Pipe rehabilitation methods that can be
used for RII control were described in Appendk D. Most commonjy used
methods are grouting and slip-lining. Although in very old, deteriorated systems,
it may be necessary to replace a considerable number of pipes or pipe sections
because of structural problems, the rehabilitation method selected for the RH
cost analysis should'be based on rehabilitation for RII correction only. It can be
F-2
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20 *0 60 80
PERCENT OF SEWERS IN SUBSYSTEM
100
FIGURE F-1
HYPOTHETICAL Rll DISTRIBUTION ENVELOPE
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, . Cost Evaluation
assumed that structural repair or replacement would be required regardless of
RII considerations.
For this cost analysis, the rehabilitation method is assumed to be grouting or
slip-lining. The selection of either method should be based on known conditions
in the sewer system. In general, grouting would be most appropriate in newer
systems in good structural condition, with few root problems, and in which the
groundwater level does not fluctuate below and above the pipes. Sh'p-lining
would be more appropriate for older systems, in areas with extensive root
intrusion, or in areas where grout shrinkage could be a problem due to changing
soil or groundwater conditions.
5. Select Rehabilitation Approach. The rehabilitation approach refers to the extent
of rehabilitation in the project area, specifically, whether the project includes bnty
the publicly owned portion of the system, or also addresses the private, service
laterals. Four rehabilitation approaches are evaluated in this cost analysis:
o Isolated repair.
o Mains only.
• • • " ' " * '
o Mains plus the lower portion of service laterals (to property line).
o Mains plus entire service laterals (to building).
In this context, isolated repair could include spot repairs of specific defects or
manhole-to-manhole rehabilitation of non-contiguous reaches. The selection of
rehabilitation approach may be dictated by financial or institutional constraints
6. Estimate Rehabilitation Effectiveness. The significance of the distinction between
the four rehabilitation approaches described above is in the amount of RH
reduction that can be expected from rehabilitation. In general, the more
comprehensive the program, i.e., the more components of the sewer system that
are included, the greater reduction that will be achieved. Thus, rehabilitation of
the mains plus the lower laterals should achieve a proportionately greater
reduction in RE than rehabilitation of the mains only.
However, because RII will migrate to unrepaired defects, the percentage
reduction in RII cannot be directly related to the amount of Rn originally
contributed by the portion of the system that is rehabilitated. The following
estimated ranges for thb effectiveness of each of the four rehabilitation
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Cost Evaluation
approaches are based largely on engineering judgement, but supported by the
touted data available from sewer rehabilitation projects for which an assessment
of rehabilitation effectiveness has been able to be made.
o Isolated Repair 0 to 10 %
o Mains Only 0 to 20 %
o Mains plus Lower Laterals 30 to 40 %
o Mains plus Entire Laterals 65 to 80 %
The ranges are intended to reflect different types of sewer systems. For example
the lower end of each range might apply to old sewer systems, and the higher
end of the range to newer systems constructed with modern joint materials
For any given system, different assumed reductions might be warranted if such
data is available from previous rehabilitation projects, or if known conditions in
the system would suggest other values. For example, in the sewer system in
North and South Shenango, Pennsylvania, described in Appendix C, a greater
rehabilitation effectiveness would be expected through rehabilitation of the mains
and lower laterals alone because the mains and lower laterals are known to have
defective joints, and the upper portion of the laterals, constructed of different
pipe materials, are believed to be relatively watertight.
The rehabilitation benefit percentages presented above are intended to represent
reductions in the peak RH flow, rather than the total storm volume of RH. Also
the percentages represent average reductions over the period of the cost analysis
(20 years), reflecting the creation of new RH sources due to damage and
deterioration of the system over time. Initial reductions would be expected to
be higher. For example, a rehabilitation program projected to have an average
70 percent reduction over 20 years might be expected to achieve a 90 percent
• reduction immediately after construction.
7. Calculate RH Reduction. The RE reduction is the rehabilitation benefit
percentage (from Step 6) applied to the portion of the total subsystem RII
contributed by the rehabilitated portion of the subsystem (from Step 3).
8. Estimate Rehabilitation Costs. The cost of rehabilitation depends on the amount
of the subsystem included in the rehabilitation program (from Step 3) the
selected rehabilitation method and approach (from'Steps 4 and 5), and'such
physical parameters as depth of the sewers, lateral density, and soil and
groundwater conditions.
F-4
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Cost Evaluation
In the cost-effectiveness analysis, the rehabilitation costs are calculated, on a
present worth basis. Therefore, the useful life of the rehabilitation method must
be considered. For example, slip-lining is a relatively "permanent" type of
rehabilitation method, and might be considered to have a useful life of about 50
years. Grouting, on the other hand, would typically not last as long because of
grout deterioration and development of new RH sources in the previously
grouted pipe reach. Therefore, grouting might be assigned a useful life of 5 to
15 years. The determination of useful life might depend on the type of grout to
be used, the anticipated quality of the work, the relative age and condition of the
sewers, and physical conditions such as groundwater level which may affect the
long-term durability of the grout.
9. Estimate Cost Savings in Transport and Treatment. The cost savings in
transport and treatment is the difference in cost between those facilities required
to handle the entire peak flow without system rehabilitation and those required
after RH reduction (from Step 7). Transport and treatment costs will be highly
dependent on the capacity of existing facilities, as well as the length of trunk
sewers and interceptors downstream of the subsystem. Transport and treatment
costs must generally be estimated based on the overall plan for the total sewer
system, since the incremental cost reductions due to rehabilitation in one single
subsystem may not be significant. Therefore, reasonable assumptions must be
made regarding potential RE reductions in the other subsystems in the system.
\ • ,'•'.'',.. - i \
Although RII correction will reduce the annual operation and maintenance
(O&M) costs of the system as well as the capital costs for construction of
additional system capacity, the magnitude of the O&M cost savings will generally
be very small compared to the capital costs for construction. This is because
system facilities must be constructed to carry the design storm peak REE flow,
whereas peak flows of this magnitude wfll occur relatively infrequently.
Furthermore, the cost for treatment may not be significantly affected by the peak
flows, since treatment schemes wfll typically be designed for flow equalization or
split-stream processing so that costly secondary treatment, for example, is hot
provided to the entire peak flow (i.e., the plant effluent consists of combined
primary and secondary effluent meeting overall plant discharge requirements).
Whether or not O&M costs are significant wfll depend both on the treatment
plant process and the seasonal rainfall pattern of the area. Since RII is not a
sustained flow like GWI and since treatment plants wfll generally not be designed
to process peak hourly flows, the cost to treat the annual volume of RII will
generally not be a significant component of total O&M costs. - -„
F-5
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Cost Evaluation
As with rehabilitation costs, transport and treatment cost savings should be
expressed on a present worth basis.
10. Calculate Cost Effectiveness of KH Control. The cost effectiveness of RII
control is determined by comparing the present worth cost savings in transport
and treatment resulting from RII reduction (from Step 9) to the present worth
cost of rehabilitation (from Step 8). The ratio of transport and treatment cost
savings to rehabilitation cost is termed the "C-E Ratio". A C-E ratio greater than
or equal to 1.0 indicates that RH correction is cost effective.
COST EVALUATION OF MODEL SYSTEMS
The cost analysis approach described in the previous section was applied to different
"model" sewer systems. The purpose of this exercise was to identify how the
cost-effectiveness of RII correction is affected by the characteristics of the sewer system,
the type of rehabilitation approach selected, and other variables in the cost calculation.
Model System Descriptions
To facilitate the cost evaluation of model systems using a computer spreadsheet, four basic
model system descriptions were developed:
o Type A - Relatively old system generally below the groundwater level.
o Type B - Relatively old system generally above the groundwater level.
o Type C - Relatively new system generally below the groundwater level.
o Type D - Relatively new system generally above the groundwater level.
The designations "old" and "new" are not necessarily intended in the literal sense, but are
used to characterize the general construction and condition of the subsystem. Specifically,
each subsystem type is intended to describe a particular RE distribution (see Figure F-
1), as indicated in Table F-l.
Each of these basic system types were evaluated with respect to several variables, as
follows:
o Magnitude of RII flows (as expressed as the ratio of peak RII to average base
sanitary flow, ranging from 5 to 20).
F-6
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Cost Evaluation
b Density of service laterals (ranging from 10 to 40 per 1,000 feet of sewer main).
o Rehabilitation approach (isolated repair, mains only, mains plus lower laterals,
mains plus entire laterals).
o Rehabilitation method (grouting or slip-lining).
The cost evaluation was used to identify the relative sensitivity of the cost effectiveness of
RII correction to each of these model variables.
Model Assumptions
The following assumptions were used in the cost evaluation:
System Size. The analyzed subsystem was assumed to contain 30,000 feet of, sewer main.
The subsystem was assumed to be part of an overall sewer system containing 50 similar
size subsystems, 20 of which were assumed to have similar RII characteristics and therefore
included in the rehabilitation program.
Wastewater Flows before Rehabilitation. Average base wastewater flow (BWF) was
assumed to be 70 gpcd. For the analyzed subsystem, average BWF was calculated based
on the assumed lateral density in the subsystem, assuming three persons per lateral. For
the entire system, average BWF was calculated based on an average of 1,500 persons per
subbasin (average lateral density of 16.7 per 1,000 feet). Peak BWF was assumed to be
1.5 times average BWF for the total system flow to the WWTP, and 2.5 times average
BWF for a trunk sewer serving the analyzed subsystem and four other similar subsystems.
Peak non-rainfall flow was also assumed to include an allowance for "non-excessive"
groundwater infiltration (GWI) of 50 gpcd. The peak RII flow in the analyzed subsystem
and in the 20 similar subsystems was calculated as the RD/BWF ratio times the average
BWF. Peak RII flow in all other subsystems in the system was assumed to be 3 times
average BWF. The total peak flow before rehabilitation was calculated as the sum of the
peak BWF plus GWI allowance plus peak RE.
F-7
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Cost Evaluation
Wastewater Flows after Rehabilitation. An assumed effectiveness of rehabilitation (the
percentage reduction in the peak RII flow in the rehabilitated portion of the subsystem!
Tti8??*^10 CaCh SyStem type based on the rehabffitation approach, as indicated in
lable F-l. The amount of the RII reduction was then calculated based on the percentage
reduction applied to 80 percent of the total subsystem peak RII flow. The same reduction
was assumed to occur in the 20 similar subsystems also being rehabilitated. The total peak
flow after rehabilitation was calculated as the total peak flow before rehabilitation minus
the RH reduction in all rehabilitated subsystems.
Capacity of Existing Facilities. The peak flow capacity of the existing WWTP was
assumedI tobe 25 times average dry weather flow. The peak capacities of the interceptor
to the WWTP (assumed to carry the entire flow from the system) and the trunk sewer
serving the analyzed subsystem (assumed to carry the flow from five similar subsystems}
were assumed to be 4 times average dry weather flow.
Cost Basis. The cost analysis was done on a present worth basis assuming a 20-year
analysis period and 8-7/8 percent discount rate.
Rehabffitation Costs. Unit costs for grouting and slip-lining were developed as shown in
iawe t-i. The unit costs were applied to the pipe footage and number of laterals in the
rehabilitated portion of the subsystem. The present worth rehabilitation cost was
calculated based on a useful life of 50 years for slip-lining (with a salvage value at 20 years
based on straight-line depreciation) and a useful life of 5 or 10 years for grouting (with
equivalent re-grouting required at the indicated interval).
Transport and Treatment Costs. Based on the capacity of existing facilities and the total
peak flows before and after rehabilitation, the additional capacities (for the WWTP
interceptor, and trunk sewer) required before and after rehabilitation were calculated. The
cost for additional WWTP capacity was based on providing flow equalization to handle
peak wet weather flows in excess of peak dry weather capacity. The costs for additional
interceptor
and mink sewer capacity were based on providing parallel gravity sewers. Unit costs for
additional capacity were based on standard cost curves. The length of the interceptor was
assumed to be 30,000 feet (about five miles), and the trunk sewer was assumed to be 5 000
feet (about one mile). '
The costs of facilities to carry these additional capacities were calculated for the before
and after rehabilitation conditions, and the cost savings, or difference between before and
after costs, were determined. The cost savings were expressed in terms of present worth
values, assuming a useful life of 20 years for WWTP facilities and 100 years for new
F-8
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Cost Evaluation
pipelines. The total cost savings for the WWTP, interceptor, and trunk sewer were
distributed equally among all the rehabilitated subsystems (including the analyzed
subsystem) served by each facility.
Cost Effectiveness. The cost effectiveness of RII correction (C-E Ratio) was calculated as
.the ratio of the total cost savings for the analyzed subsystem to the subsystem
rehabilitation cost. , .
Model System Cost Analysis Results
The results of the cost analysis are presented in Table F-2,. Based on the assumptions
described in the previous section, the general results of the analysis are:
o RII correction is not calculated to be cost effective in subsystem types generally
classified as "old."
o RII correction is calculated to be cost effective under certain conditions in
subsystem types generally classified as "new," specifically, if peak RH flows are
high, lateral density is low, and the mains and entire laterals are rehabilitated.
Under certain very liberal assumptions, grouting was found to be cost effective for isolated
repair or mains-only rehabilitation of new systems with relatively high peak RII flows. This
was the case only if the rehabilitation effectiveness indicated in Table F-l could be
achieved even if the lateral connections to the main were not included in the rehabilitation
program and the useful life of grouting was assumed to be at least 10 years. Since lateral
connections are typically significant sources of RII, and since the useful life of grouting
depends on a variety of factors, including quality control during construction, these may hot
be realistic assumptions. In general, assuming a five-year versus a ten-year useful life for
grouting reduces the cost effectiveness of RE correction by 40 to 50 percent.
F-9
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