EPA 430/9-75-021
HANDBOOK
FOR
SEWER SYSTEM EVALUATION
AND REHABILITATION
DECEMBER 1975
TECHNICAL REPORT
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF WATER PROGRAM OPERATIONS
WASHINGTON, D.C. 20460
MCD-19
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HANDBOOK
FOR
SEWER SYSTEM EVALUATION
AND REHABILITATION
Municipal Construction Division
Office of Water Program Operations
Environmental Protection Agency
Washington, D. C. 20460
December 1975
MOD-19
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HANDBOOK
FOR
SEWER SYSTEM EVALUATION
AND REHABILITATION
Municipal Construction Division
Office of Water Program Operations
Environmental Protection Agency
Washington, D. C. 20460
December 1975
MCD-19
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Foreword
The extraneous flow associated with infiltration-inflow
(I/I) has long been recognized as a major factor in treatment
facility performance. The impact on stream pollution has been so
great that the subject of I/I must be fully addressed in any
realistic water pollution control program. For this reason, the
Federal Water Pollution Control Act Amendments of 1972 requires
that after July 1, 1973 all grant applicants must identify and
correct excessive I/I for each sewer collection system discharg-
ing into treatment works proposed for grant assistance. The
requirement was implemented in the Construction Grant Regulat-
ions, Section 40 CFR 35.927, and in the Guidance for Sewer System
Evaluation published in March 1974.
This handbook is not a design manual. It is primarily a
supplement to the Guidance for Sewer System Evaluation and
accordingly, it contains technical information and describes the
methodology necessary for an effective investigation and correction
of I/I conditions in a sewer system. Also included is a set of
cost curves showing the correlation between the cost for each
phase of sewer system evaluation work and variables such as sewer
length, population, and magnitude of I/I. Additionally, the
handbook contains a special chapter entitled "User's Guide". It
is emphasized that this chapter should be carefully read before
using the manual.
The handbook does not contain any regulatory materials or
mandatory requirements. To the contrary, it is designed to
provide a wide range of information on conditions found in all
the various types of sewer systems. For this reason, it is
essential that the user of the handbook select only those tech-
niques applicable to a particular system in order to generate the
necessary information. Brevity and simplicity are encouraged.
It is the intention of the Environmental Protection Agency
to revise and update this handbook as new and improved techniques
are developed through experience. All users are encouraged to
submit any pertinent information to the Director, Municipal
Construction Division (WH 547), Office of Water Program Operations,
U.S. Environmental Protection Agency, Washington, DC 20460.
Andrew W. ^Breidenbach
Assistant Administrator
Water and Hazardous Materials
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NOTICE
THIS REPORT HAS BEEN REVIEWED BY
EPA, AND APPROVED FOR PUBLICATION.
APPROVAL DOES NOT SIGNIFY THAT THE
CONTENTS NECESSARILY REFLECT THE
VIEWS AND POLICIES OF THE ENVIRON-
MENTAL PROTECTION AGENCY, NOR DOES
MENTION OF TRADE NAMES OR COMMERCIAL
PRODUCTS CONSTITUTE ENDORSEMENT OR
RECOMMENDATION FOR USE.
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ABSTRACT
Guidance has been provided to assist in the preparation and
review of Infiltration/Inflow Analyses and Sewer System Evaluation
Surveys. In addition, information is given on the techniques
of sewer rehabilitation and the costs related to Evaluation
Survey and Rehabilitation.
The handbook contains chapters on: (1) methodology for
conducting I/I Analysis, (2) methodology for conducting
Sewer System Evaluation Survey, (3) information on current
state-of-the-art techniques for sewer rehabilitation and
(*0 costs associated with conducting Sewer System Evaluation
Survey and rehabilitation.
The chapters on methodology explain in detail each of the
specific tasks that may be required in conducting I/I Analysis
and Sewer System Evaluation Survey. The methodology presented
is proven current state-of-the-art techniques. Other techniques
not presented may be applicable and their use is encouraged.
The sewer rehabilitation techniques presented have been obtained
from specialists in the particular field and are provided
for Information purposes only.
To assist in proper use of this handbook, a chapter on User
Guide is prepared (Chapter 2). THE READER SHOULD READ THAT
CHAPTER BEFORE GOING THROUGH OTHER CHAPTERS.
ii
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TABLE OF CONTENTS
CHAPTER PAGE PAGE
Title Page i
Abstract H
Table of Contents ill
List of Tables v
List of Figures vii
1 Introduction 1-1
1.1 Introduction 1-1
1.2 Purpose 1-6
1.3 Format 1-6
1.4 Overview 1-7
1.5 Implementation 1-9
2 User's Guide 2-1
2.1 Introduction 2-1
2.2 I/I Analysis 2-1
2.3 Sewer System Evaluation Survey 2-2
2.4 Sewer System Rehabilitation 2-2
2.5 Costs 2-2
3 Infiltration/Inflow Analysis 3-1
3.1 Introduction 3-1
3.2 Background Information 3-2
3.3 Determination of Infiltration/Inflow 3-58
3.4 Cost-Effectiveness Analysis 3-71
3-5 Establishment of Excessive or Non- 3-8?
excessive Infiltration/Inflow
3.6 Sewer System Evaluation Survey Program 3-93
Recommendation
4 Sewer System Evaluation Survey 4-1
4.1 Introduction 4-1
4.2 Physical Survey 4-2
4.3 Rainfall Simulation 4-10
4.4 Preparatory Cleaning 4-19
4.5 Internal Inspection 4-24
4.6 Survey Report 4-32
ill
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CHAPTER
APPENDIX
TABLE OF CONTENTS (Continued)
PAGE
Sewer System Rehabilitation 5-1
5.1 Introduction 5-1
5.2 Excavation/Replacement 5-4
5.3 Chemical Grouting 5-4
5.4 Pipe Lining With Polyethylene Pipe 5-13
5-5 Pipe Lining With Fiberglass Reinforced 5-19
Polyester Mortar Pipe
5.6 Pipe Lining With Cement Mortar and 5-21
Epoxy Mortar
Costs for Sewer System Evaluation Survey and 6-1
Rehabilitation
6.1 Introduction 6-1
6.2 Sewer System Evaluation Survey Costs 6-1
6.3 Rehabilitation Costs 6-31
A. References A-l
B. State Certification B-l
C. Glossary of Terms C-l
D. Metric Conversion Table D-l
Iv
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LIST OF TABLES
NO. PAGE
2-1 Check List for Conducting Infiltration/ 2-4
Inflow Analysis
2-2 Check List for Conducting Sewer System 2-5
Evaluation Survey
3-1 Infiltration/Inflow Analysis - 3-6
Interview Form
3-2 Properties of Commonly Used Tracer Dyes 3-18
3-3 Typical Data Sheets for the Inventory 3-22
of Existing Sewer System
3-4 Safety Equipment for Manhole and Sewer 3-56
Inspection
3-5 Work Sheet for Quantity Take-off and 3-78
Cost Estimation - Sewer System
Evaluation Survey
3-6- Work Sheet for Quantity Take-off and 3-79
Cost Estimation - Sewer System
Rehabilitation
3-7 Determination of Priority for Evaluation
Survey - An Example 3-90
3-8 Determination of Costs - An Example 3-90
4-1 Typical Data Sheet for Manhole 4-7
Inspection
4-2 Typical Data Sheet for Sewer 4-8
Inspection
4-3 Characteristics of Sewer Cleaning 4-22
Equipment
4-4 Typical Television Inspection Log 4-28
Sheet
5-1 Infiltration/Inflow Sources and 5-2
Correction Methods
5-2 Typical Compositions of Acrylamide Gel 5-8
Grouting Mixes
6-1 Costs for Sewer System Evaluation Survey 6-2
6-2 Physical Survey Cost Criteria 6-3
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LIST OF TABLES (Continued)
NO. PAGE
6-3 Rainfall Simulation Cost Criteria 6-4
6-4 Sewer Cleaning Cost Criteria 6-5
6-5 Internal Inspection Cost Criteria 6-6
6-6 Sewer Replacement Cost Criteria 6-34
6-7 Pipe Lining Cost Criteria 6-36
6-8 Sewer Line Grouting Cost Criteria 6-38
6-9 Miscellaneous Rehabilitation Costs 6-39
vi
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LIST OP FIGURES
NO. PAGE
3-1 Typical Groundwater Gauge Installation 3-30
in Manhole
3-2 Typical Groundwater Gauge Installation 3-31
in Soil
3-3 Temperature Correction Curves for Dyes 3-46
3-4 Floating Bowl Solution Feeder 3-48
3-5 Floating Platform Solution Feeder 3-49
3-6 Determination of Total Yearly 3-63
Infiltration/Inflow
3-7 Determination of Total Yearly 3-65
Infiltration
3-8 Determination of Peak Inflow 3-67
3-9 Cost-Effectiveness Analysis - Possibly 3-84
Excessive Infiltration/Inflow (Method 2)
3-10 Cost-Effectiveness Analysis - Non- 3-85
excessive Infiltration/Inflow (Method 2)
3-11 Cost-Effectiveness Analysis - Possibly 3-88
Excessive Infiltration/Inflow (Method 3)
3-12 Cost-Effectiveness Analysis - Non- 3-89
excessive Infiltration/Inflow (Method 3)
3-13 Determination of Optimal Design Flow - 3-92
An Example
4-1 Typical Arrangement for Television 4-26
Inspection of Sewer Lines
4-2 Laboratory Test for Estimating 4-30
Infiltration/Inflow Rates
4-3 Cost Curves for Cost-Effectiveness 4-37
Analysis in Evaluation Survey
5-1 Effect of Catalyst Concentration and 5-7
Temperature on Acrylamide Gel Set
Time
5-2 Typical Arrangement for Chemical 5-10
Grouting with Acrylamide Gel
5-3 Remote Connection of House Service 5-18
Line Through Sewer Pipe
vii
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LIST OF FIGURES (Continued)
NO. PAGE
5-4 Remote Connection of House Service 5-18
Line Through New Drilled Hole
6-1 Total Evaluation Survey Cost vs. Sewer 6-7
Length
6-2 Total Evaluation Survey Cost vs. Peak 6-8
Infiltration/Inflow
6-3 Total Evaluation Survey Cost vs. Sewered 6-9
Population
6-4 Total Evaluation Survey Cost vs. Sewage Plow 6-10
6-5 Physical Survey Cost vs. Sewer Length 6-11
6-6 Physical Survey Cost vs. Peak Infiltration/ 6-12
Inflow
6-7 Physical Survey Cost vs. Sewered Population 6-13
6-8 Physical Survey Cost vs. Sewage Plow 6-14
6-9 Rainfall Simulation Cost vs. Sewer Length 6-15
6-10 Rainfall Simulation Cost vs. Peak 6-16
Infiltration/Inflow
6-11 Rainfall Simulation Cost vs. Sewered 6-17
Population
6-12 Rainfall Simulation Cost vs. Sewage Plow 6-18
6-13 Preparatory Cleaning Cost vs. Sewer Length 6-19
6-14 Preparatory Cleaning Cost vs. Peak 6-20
Infiltration/Inflow
6-15 Preparatory Cleaning Cost vs. Sewered 6-21
Population
6-16 Preparatory Cleaning Cost vs. Sewage Plow 6-22
6-17 Internal Inspection Cost vs. Sewer Length 6-23
6-18 Internal Inspection Cost vs. Peak 6-24
Infiltration/Inflow
6-19 Internal Inspection Cost vs. Sewered 6-25
Population
6-20 Internal Inspection Cost vs. Sewage Flow 6-26
viii
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LIST OF FIGURES (Continued)
NO. PAGE
6-21 Report Cost vs. Sewer Length 6-2?
6-22 Report Cost vs. Peak Infiltration/Inflow 6-28
6-23 Report Cost vs. Sewered Population 6-29
6-24 Report Cost vs. Sewage Plow 6-30
6-25 Sewer Replacement Cost vs. Pipe Size 6-32
6-26 Pipe Lining (Polyethylene) Cost vs. Pipe 6-35
Size
6-27 Grouting Cost vs. Number of Pipe Joints 6-37
Grouted
ix
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CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
The Water Pollution Control Act Amendments, Public Law
92-500, dated October 18, 1972 requires construction grant
applicants to investigate the condition of their sewer systems.
Title II, Section 201 (g) (3) of the Law states, "The Administra-
tor shall not approve any grant after July 1, 1973, for treatment
works under this section unless the applicant shows to the
satisfaction of the Administrator that each sewer collection
system discharging into such treatment works is not subject
to excessive infiltration".
Title II, Section 201 (g) (M of the Law states, "The
Administrator is authorized to make grants to applicants for
treatment works grants under this section for such sewer
system evaluation studies as may be necessary to carry out
the requirements of paragraph (3) of this subsection. Such
grants shall be made in accordance with rules and regulations
promulgated by the Administrator. Initial rules and regula-
tions shall be promulgated under this paragraph not later
than 120 days after the date of enactment of the Federal Water
Pollution Control Act Amendments of 1972".
The final Construction Grant Regulations pertaining to the afore-
mentioned were published in the Federal Register dated
February 11, 1974. The following sections in the Construction
Grant Regulations pertain to Sewer System Evaluation and
Rehabilitation.
1 35.927 Sewer System Evaluation and Rehabilitation.
(a) All applicants for grant assistance awarded after
July 1, 1973, must demonstrate to the satisfaction
of the Regional Administrator that each sewer
system discharging into the treatment works project
for which grant application is made is not or will
not be subject to excessive infiltration/inflow.
The determination whether excessive infiltration/
inflow exists, may take into account, in addition
to flow and related data, other significant factors
such as cost-effectiveness (including the cost of
substantial treatment works construction delay,
...), public health emergencies, the effects of
plant bypassing or overloading, or relevant economic
or environmental factors.
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(b) The determination whether or not excessive
infiltration/inflow exists will generally be
accomplished through a sewer system evaluation
consisting of (1) certification by the State
agency, as appropriate; and, when necessary (2)
an infiltration/inflow analysis; and, if appro-
priate, C3) a sewer system evaluation survey
followed by rehabilitation of the sewer system
to eliminate an excessive infiltration/inflow
defined in the sewer system evaluation. Infor-
mation submitted to the Regional Administrator
for such determination should be the minimum
necessary to enable a judgment to be made.
Cc) Guidelines on sewer system evaluation published
by the Administrator provide further advisory
information.
35.927-1 Infiltration/Inflow Analysis.
(a) The infiltration/inflow analysis shall demonstrate
the nonexistence or possible existence of excessive
infiltration/inflow in each sewer system tributary
to the treatment works. The analysis should
identify the presence, flow rate, and type of
infiltration/inflow conditions, which exist in the
sewer systems. Information to be obtained and
evaluated in the analysis should include, to the
extent appropriate, the following:
(1) Estimated flow data at the treatment facility,
all significant overflows and bypasses, and,
if necessary, flows at key points within the
sewer system.
(2) Relationship of existing population and
industrial contribution to flows in the sewer
system.
(3) Geographical and geological conditions which
may affect the present and future flow rates
or correction costs for the infiltration/inflow,
(4) A discussion of age, length, type, materials
of construction and known physical condition
of the sewer system.
(.b) For determination of the possible existence of
excessive infiltration/inflow, the analysis shall
include an estimate of the cost of eliminating
the infiltration/inflow conditions. These costs
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shall be compared with estimated total costs
for transportation and treatment of the infiltra-
tion/inflow. Cost-effectiveness Analysis Guide-
lines (...), which contain advisory information,
should be consulted with respect to this deter-
mination.
(c) If the infiltration/inflow analysis demonstrates
the existence or possible existence of excessive
infiltration/inflow, a detailed plan for a sewer
system evaluation survey shall be included in the
analysis. The plan shall outline the tasks to be
performed in the survey and their estimated costs.
35.927-2 Sewer System Evaluation Survey.
(a) The sewer system evaluation survey shall consist
of a systematic examination of the sewer systems
to determine the specific location, estimated flow
rate, method of rehabilitation and cost of re-
habilitation versus cost of transportation and
treatment for each defined source of infiltration/
inflow.
(b) The results of the sewer system evaluation survey
shall be summarized in a report. In addition, the
report shall include:
CD A justification for each sewer section cleaned
and internally Inspected.
(2) A proposed rehabilitation program for the
sewer systems to eliminate all defined ex-
cessive infiltration/inflow.
35.927-3 Rehabilitation.
(a) The scope of each treatment works project defined
within the Facilities Plan as being required for
implementation of the Plan, and for which Federal
assistance will be requested, shall define (1) any
necessary new treatment works construction, and
(2) any rehabilitation work determined by the
sewer system evaluation to be necessary for the
elimination of excessive infiltration/inflow.
However, rehabilitation which should be a part
of the applicant's normal operation and maintenance
responsibilities shall not be included within the
scope of a Step 3 treatment works project.
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(b) Grant assistance for a Step 3 project segment
consisting of rehabilitation work may be awarded
concurrently with Step 2 work for the design of
the new treatment works construction.
| 35-927-4 Sewer Use Ordinance.
Each applicant for grant assistance for a Step 2, Step 3> or
combination Steps 2 and 3 project shall demonstrate to the
satisfaction of the Regional Administrator that a sewer use
ordinance or other legally binding requirement will be en-
acted and enforced in each jurisdiction served by the treat-
ment works project before the completion of construction.
The ordinance shall prohibit any new connections from inflow
sources into the sanitary sewer portions of the sewer system
and shall ensure that new sewers and connections to the
sewer system are properly designed and constructed.
§ 35.927-5 Project Procedures.
(a) State certification. The State agency may (but
need not)certify that excessive infiltration/
Inflow does or does not exist. The Regional
Administrator will determine that excessive infil-
tration/inflow does not exist on the basis of State
certification, if he finds that the State had
adequately established the basis for its certifica-
tion through submission of only the minimum infor-
mation necessary to enable a Judgment to be made.
Such information could include a preliminary review
by the applicant or State, for example, of such
parameters as per capita design flow, ratio of
flow to design flow, flow records or flow estimates,
bypasses or overflows, or summary analysis of
hydrological, geographical, and geological conditions,
but this review would not usually be equivalent to
a complete infiltration/Inflow analysis. State
certification must be on a project-by-project
basis. If the Regional Administrator determines
on the basis of State certification that the treat-
ment works is or may be subject to excessive
infiltration/inflow, no Step 2 or Step 3 grant
assistance may be awarded except as provided in
paragraph (c) of this section.
(b) Fre-award sewer system evaluation. Generally,
except as otherwise provided In paragraph (c) of
this section, an adequate sewer system evaluation,
consisting of a sewer system analysis, and, If
required, an evaluation survey, is an essential
element of Step 1 facilities planning and is a
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prerequisite to the award of Step 2 or 3 grant
assistance. If the Regional Administrator
determines through State Certification or an
infiltration/inflow analysis that excessive
infiltration/inflow does not exist, Step 2 or 3
grant assistance may be awarded. If on the basis
of State certification or the infiltration/inflow
analysis, the Regional Administrator determines
that possible excessive infiltration/inflow exists,
an adequate sewer system evaluation survey and,
if required, a rehabilitation program must be
furnished, except as set forth in paragraph (c)
of this section before grant assistance for Step 2
or 3 can be awarded. A Step 1 grant may be awarded
for the completion of this segment of Step 1 work,
and, upon completion of Step 1, grant assistance
for a Step 2 or 3 project (for which priority has
been determined pursuant to § 35-915) may be
awarded.
(c) Exception. In the event it is determined by the
Regional Administrator that the treatment works
would be regarded (in the absence of an acceptable
program of correction) as being subject to excessive
or possible excessive infiltration/inflow, grant
assistance may be awarded provided that the applicant
establishes to the satisfaction of the Regional
Administrator that the treatment works project for
which grant application is made will not be sig-
nificantly changed by any subsequent rehabilitation
program or will be a component part of any rehabili-
tated system: Provided, That the applicant agrees
to complete the sewer system evaluation and any
resulting rehabilitation on an implementation
schedule the State accepts (subject to approval by
the Regional Administrator), which schedule shall
be inserted as a special condition in the grant
agreement. Compliance with this schedule shall be
accomplished pursuant to s 35-935-16 and g 30.30^ of
this chapter.
Cd) Municipalities may submit the infiltration/inflow
analysis and when appropriate the sewer system
evaluation survey, through the State agency, to the
Regional Administrator for his review at any time
prior to application for a treatment works grant.
Based on such a review, the Regional Administrator
shall provide the municipality with a written
response indicating either his concurrence or
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nonconcurrence. The Regional Administrator
must concur with the sewer system evaluation
survey plan before the work is performed for the
survey to be an allowable cost.
Draft Guidance for Sewer System Evaluation was circulated
on April 27, 1973 and the final Guidance was published in
March 197^ by the Environmental Protection Agency.
1.2 PURPOSE
The intent of this Handbook is to present a systematic approach
for conducting the evaluations and provide a source of information
to assist the applicants in fulfilling the requirements under
the Act. An effort has been made to convey the current state-
of-the-art in conducting (1) Infiltration/Inflow Analyses,
(2) Sewer System Evaluation Surveys, and (3) Rehabilitation.
Methodology.
The contents of this Handbook are not intended to be specific
requirements that each grant applicant must adhere to, for
site-specific conditions may preclude the utilization of
the state-of-the-art presented hereinafter. The fulfillment
of 'the requirements under the Act will be based on sound
engineering practices and this handbook may be another tool
utilized to achieve the desired intent of the Act. In many
instances the methodology and specific examples presented
will be suited for a sewer system; and for many others, modifica-
tions will be appropriate.
1.3 FORMAT
Chapters 3} ^ and 5 of the handbook addresses the methodology
in accomplishing (1) Infiltration/Inflow Analyses, (2) Sewer
System Evaluation Surveys, and (3) Rehabilitation. (Each
specific task is preceded by an overview explaining the purpose
and expected information to be generated and then the current
methodology is presented.) The methodology consists of an
array of techniques that are currently utilized to accomplish
the specific tasks. The specific techniques that pertain
to the applicant's project may be utilized or other modes
of accomplishing the task may be employed.
Chapter 6 of the handbook addresses the cost information
which may be utilized in cost-effective analyses. The cost
for conducting the Sewer System Evaluation Survey and the
resulting rehabilitation are presented. These costs can be
used to develop the specific costs for the applicant's project.
Again, other cost criteria may be employed for particular
circumstances that are not of a general nature. Cost informa-
tion must be modified, where necessary, to suit local conditions.
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The Appendix of the handbook contains a description of State
Certification and a glossary of terms used in this handbook.
1.4 OVERVIEW
"Extraneous water from infiltration/inflow sources reduces
the capability of sewer systems and treatment facilities
to transport and treat domestic and industrial wastewaters.
Infiltration occurs when existing sewer lines undergo
material and joint degradation and deterioration as well as
when new sewer lines are poorly designed and constructed.
Inflow normally occurs when rainfall enters the sewer
system through direct connections such as roof leaders
and catch basins. The elimination of infiltration/inflow
by sewer system rehabilitation can often substantially
reduce the cost of wastewater collection and treatment.
However, a logical and systematic evaluation of the sewer
system is necessary to determine the cost-effectiveness of
any sewer system rehabilitation to eliminate infiltration/
inflow.
The Federal Water Pollution Control Act Amendments of 1972
require that after July 1, 1973» all applicants for treat-
ment works grants must demonstrate that each sewer system
discharging into the treatment works is not subject to
excessive infiltration/inflow. The requirement was imple-
mented in the Rules and Regulations for Sewer System
Evaluation and Rehabilitation, 40 CPR 35-927-
This document is intended to provide engineers, municipalities,
and regulatory agencies with guidance on sewer system
evaluation."
The three aforementioned paragraphs constituted the
Introduction of the March 197? Guidance for Sewer System
Evaluations and also provide a suitable introduction for the
Overview of this Handbook.
The U.S. Congress, U.S. Environmental Protection Agency and
those involved in the wastewater field recognize the economic
significance of extraneous water in sewer systems. Public
Law 92-500, the Rules and Regulations for Sewer System Evaluation
and Rehabilitation, the March 1974 Guidance for Sewer System
Evaluations and this handbook have all been developed with
the expressed intent of optimizing the expenditure of funds
allocated by Congress for municipal pollution abatement facilities
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The U.S. Environmental Protection Agency has taken the approach
that sewer systems tributary to treatment works for which
an EPA construction grant will be used, should be investigated
sufficient to determine the infiltration/inflow conditions.
Those systems that contain excessive infiltration/inflow
will be eligible for construction grant assistance for rehabili-
tation of the sewer system to eliminate these flows. The
Construction Grant Regulations specifically state that, "Rehabil-
itation which should be a part of the applicant's normal
operation and maintenance responsibilities shall not be included
within the scope of a Step 3 treatment works project."
Thus it is not the intent of the Sewer System Evaluation
Program to rehabilitate all sewer systems nationwide that
are or will be involved in the Construction Grants Program
but rather to ensure that infiltration/inflow is addressed
and reasonableness is utilized when evaluating those sewer
lines which will ultimately be rehabilitated.
This program can be successfully implemented by the following:
Flexible Interpretation of the Rules and Regulations
and Guidance - A good communicative relationship
between the Regulatory Agencies, the grant applicant
and those providing services for the applicant can
result in a workable solution for the most complex
situation. This handbook should point out some of
the solutions but others will have to be devised for
specific problems that are encountered.
Documentation of pertinent data in the Infiltration/
Inflow Analysis Reports and Sewer System Evaluation
Survey Reports - Sound engineering practice has
always dictated that Infiltration/Inflow should be
investigated to some degree in sewer systems that
are to be expanded or upgraded. The documentation of
this type investigative work may have been limited in
the past. It is good practice to document this
information in the Analysis or Survey Reports.
This handbook will demonstrate techniques to accom-
plish specific tasks which may or may not be a
component part of Analysis or Survey Reports. Other
techniques specific to an applicant's need may be
utilized.
Development and/or continuation of operation and
maintenance programs for the applicant's sewer system -
Many municipalities have extensive 0 & M programs
and the continuation of these programs will have a
greater beneficial Impact on the sewer system and
treatment facility than the selective rehabilita-
tion that may be funded under Public Law 92-500
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due to excessive extraneous water. Many other
Municipalities have limited or no 0 & M programs
and they are advised to take cognizance of the
derived benefits of a good program. The resulting
selective rehabilitation that is funded under Public
Law 92-500 will not solve sewer problems that were
marginally nonexcessive or that may deteriorate
before the life of the treatment works is attained.
This handbook does not present criteria for 0 & M
programs but the data generated from conducting
Infiltration/Inflow Analyses and Sewer System Evalua-
tion Surveys form a sound basis for developing such
programs.
1.5 IMPLEMENTATION
The implementation of Sewer System Evaluation and Rehabilita-
tion is documented in the February 11, 197^, Construction Grant
Regulations, sections 35-927 through 35-927-5- The reader is
advised to review these important paragraphs which have been
presented in Section 1.1 of this Chapter.
These aforementioned Rules and Regulations have a considera-
ble degree of flexibility which should permit a realistic
solution to the more complex situations. It is imperative
that U.S. EPA and State Regulatory Agency personnel, grant
applicants and those providing services for grant applicants
be thoroughly familiar with these Rules and Regulations. The
Grant applicant and his consultant should meet with EPA and
the respective State regulatory personnel to discuss the
specific project and the scope of work.
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CHAPTER 2
USER'S GUIDE
2 .1 INTRODUCTION
The data contained in this Handbook for conducting Sewer
System Evaluations are voluminous and in specific detail.
The intent of this Handbook is to present sufficient information
which will enable engineers and reviewers to prepare and/or
review Sewer System Evaluations on the vast array of circumstances
that are encountered in various sewer systems. Because of
the varying circumstances that are encountered in sewer systems
all of the methodology presented hereinafter will not apply
to each project.
This User's Guide is presented to emphasize that only specific
portions of the methodology that applies to the project under
study should be utilized.
2.2 INFILTRATION/INFLOW ANALYSIS
The intent of the Infiltration/Inflow (I/I) Analysis (see
Chapter 3) is to establish possibly excessive or nonexcessive
I/I in an expedient and thorough manner. In order to accom-
plish this, an I/I Analysis should contain:
Background Information
Determination of I/I
Establishment of Possibly Excessive or Nonexcessive I/I
The engineer should always make a first attempt to conduct an
I/I Analysis by utilizing all pertinent existing data. If this
cannot be accomplished, then minimum data must be generated
which will permit the engineer to complete the I/I Analysis.
A check list is presented which may be utilized by the
engineer to determine the components of an I/I Analysis which
are pertinent to the project under study. It is essential
that only the components which will allow successful completion
of the I/I Analysis be considered.
The check list contains a listing of functions and correspond-
ing subheading and page numbers. In addition, a rating of
importance for each function is listed. The following is a
general description of the rating system employed:
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Rating No. 1 - This indicates an essential function
which should be considered for every I/I Analysis.
An attempt should be made to perform the function
by utilizing existing data. The use of minimum data
is encouraged.
Rating No. 2 - This indicates a function which may/
or may not be required to complete the I/I Analysis.
It is a function which provides supporting data for a
No. 1 function. An attempt should be made to perform
the I/I Analysis without these functions; but if it
is considered necessary, the use of minimum data is
encouraged.
2.3 SEWER SYSTEM EVALUATION SURVEY
The Sewer System Evaluation Survey (see Chapter 4) is a
systematic examination of the sewer system to locate all
infiltration and inflow sources which were previously deter-
mined to be possibly excessive, determine the flow rate from
each source and estimate the costs required for the rehabili-
tation of the system. Chapter 4 presents the methodology
for conducting Sewer System Evaluation Surveys. A particular
project may require any number of the functions presented.
A check list is presented which may be utilized by the engineer
to determine the components of a Sewer System Evaluation Survey
which are pertinent to the project under study. The check list
contains a listing of functions and corresponding subheading
and page numbers. In addition, a blank space is provided for
a check mark or comment.
2.4 SEWER SYSTEM REHABILITATION
The Sewer System Rehabilitation Chapter (see Chapter 5) of
this handbook describes the various rehabilitation techniques
that are commonly utilized for sewer systems. The information
presented in that Chapter is for information purposes only.
The engineer is encouraged to read this Chapter in order
to become familiar with specific rehabilitation techniques.
2.5 COSTS
Costs for conducting Sewer System Evaluation Surveys and
Rehabilitation are presented in Chapter 6. The cost infor-
mation presented should be used in the cost-effectiveness
analysis of the I/I Analysis. The costs should be refined
for a particular study when used in the cost-effectiveness
analysis of the Sewer System Evaluation Survey.
2-2
-------
The engineers preparing Sewer System Evaluations and the
Regulatory personnel reviewing the projects should read and
understand the sources and intent of the costs presented
in Chapter 6. In order to effectively use the costs, the
following items should be understood:
Tables 6-1 and 6-9 and Figures 6-25 to 6-27 show
the costs for conducting Sewer System Evaluation
Surveys and Rehabilitation. These costs can be
used in the I/I Analysis after they have been
adjusted for the particular sewer system under
study by analyzing the cost criteria presented in
Tables 6-2 to 6-8.
The aforementioned cost tables and figures can only
be utilized in the Sewer System Evaluation Survey
Phase after incorporating the cost criteria for the
specific rehabilitation required in the system under
study,
Figures 6-1 to 6-24 display the costs for conducting
Sewer System Evaluation Surveys and should only be
used in a preliminary manner, i.e., by Regulatory
personnel when establishing an order of magnitude in
determining the reasonableness of costs presented in
I/I Analysis report.
2-3
-------
TABLE 2-1
CHECK LIST FOR CONDUCTING
INFILTRATION/INFLOW ANALYSIS
Function
BACKGROUND INFORMATION
Interview
Sewer Map Analysis
Inventory of Existing Sewer
System
Geographic and Geological Data
Wastewater Flow Data
Flow Measurement
Physical Condition of Sewer
DETERMINATION OF INFILTRATION/
INFLOW
General Consideration
Determination of I/I Using
Wastewater Flow Data
Determination of I/I by
Direct Flow Measurement
Adjustment of Flow Data
COST-EFFECTIVENESS ANALYSIS
Cost Estimate
Analysis Procedures
Subheading No.
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.3
3.3-1
3.3.2
3.3.3
3.3.4
3.4
3.4.2
3.4.3
Page No.
3-3
3-3
3-16
3-21
3-25
3-34
3-35
3-56
3-59
3-59
3-61
3-70
3-72
3-73
3-74
3-85
Rating
1
2
2
2
2
1
2
2
1
2
1
2
2
2
2
2
ESTABLISHMENT OF POSSIBLY
EXCESSIVE OR NONEXCESSIVE I/I 3.5
SEWER SYSTEM EVALUATION SURVEY
PROGRAM RECOMMENDATION 3.6
Program Recommendation 3.6.1
Cost Estimates 3.6.2
Project Schedule 3.6.3
3-89
3-90
3-91
3-94
3-94
2
2
2
2-4
-------
TABLE 2-2
CHECK LIST FOR CONDUCTING
SEWER SYSTEM EVALUATION SURVEY
Function
PHYSICAL SURVEY
General
Aboveground Inspection
Flow Monitoring
Manhole and Sewer Inspection
Report
RAINFALL SIMULATION
General
Smoke Testing
Dyed Water Testing
Water Flood Test
PREPARATORY CLEANING
General
Equipment
Selection of Cleaning Equipment
INTERNAL INSPECTION
General
Inspection Techniques
SURVEY REPORT
General
Data Analysis
Cost-Effectiveness Analysis
Recommendation for Sewer
System Rehabilitation
Subheading; No
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.4
4.4.1
4.4.2
4.4.3
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.2
4.6.3
4.6.4
Page No.
4-2
4-2
4-3
4-3
4-4
4-10
4-10
4-10
4-12
4-15
4-18
4-20
4-20
4-20
4-24
4-24
4-24
4-25
4-32
4-32
4-33
4-35
4-37
2-5
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CHAPTER 3
INFILTRATION/INFLOW ANALYSIS
3.1 INTRODUCTION
An Infiltration/Inflow (I/I) Analysis is an engineering
analysis demonstrating possibly excessive or nonexcessive
infiltration/inflow in a sewer system or portions thereof.
The principal purpose of the Infiltration/Inflow Analysis
is to establish this expediently and yet thoroughly.
Generally, the I/I Analysis will be incorporated in the
Project Facilities Planning Report or area wide waste manage-
ment plans. There will be instances, however, when the I/I
Analysis Reports will be separate documents. For example,
Analysis Reports that are prepared on projects begun prior
to PL 92-500 will generally be separate documents. Also,
some planning documents will be voluminous; therefore, the I/I
Analysis portion will be a separate document merely for con-
venience.
The I/I Analysis Reports will generally be in one of two
forms:
Sewer systems that have reliable data available which
will conclusively demonstrate nonexcessive or possibly
excessive I/I, the data may be briefly summarized. The
engineer preparing the report should display sufficient
flow data and specific characteristics of the sewer
system to enable a review engineer to properly assess
the system and concur with the report. A cost-
effectiveness analysis may or may not be needed to
establish the existence or nonexistence of excessive
I/I.
Sewer systems that have limited data (including flow
and sewer characteristics) available will generally
require a more structured analysis report than the
aforementioned circumstance. This report generally
will include a cost-effectiveness analysis. The degree
of investigative work required for this type of analysis
will obviously depend on the specific sewer system.
The main goals of this investigative work will be the
following:
3-1
-------
(1) To generate sufficient flow data and characteristics
of the sewer system that will enable a sound
engineering decision to be made on possibly
excessive or nonexcessive I/I.
(2) To obtain realistic cost estimates for rehabilita-
tion of sewers that may contain possibly excessive
I/I and for the transport and treatment of ex-
traneous water.
(.3) Items (1) and (2) should enable the engineer, in
the event of possibly excessive I/I, to scope in
detail the work tasks for the next investigative
Phase, the Sewer System Evaluation Survey,
The following subheadings are the most commonly utilized
components of an I/I Analysis Report. The presentation of
these components or subheadings does not imply that they
must be included in every I/I Analysis. Quite the contrary
is true and only those subheadings that need be utilized
to generate the desired data should be considered. In addition,
other techniques that the engineer may have developed or
generally utilizes, and which may not be displayed here,
are encouraged. It should be kept in mind that this handbook
shows some of the techniques utilized by engineers and municipal-
ities to accomplish specific tasks. There are other techniques
available and others that will be developed that may be as
effective or more effective for a specific sewer system than
those presented hereinafter.
The I/I Analysis report should not reiterate the data that
would normally be presented in the Facilities Planning report
but merely display the pertinent minimum data necessary to
make a sound Judgment of nonexcessive or possibly excessive
infiltration/inflow.
The methodology presented hereinafter, unless otherwise noted,
is applicable to both combined and separate systems.
3.2 BACKGROUND INFORMATION
The first step in conducting an Infiltration/Inflow Analysis
is to obtain all the pertinent information and data on the
specific wastewater collection system and treatment works
under investigation. Much of this Information and data will
normally be collected by the engineer as the first step in
conducting Facilities Planning; thus, duplication of effort
should be avoided.
3-2
-------
The investigator should screen all the background information
and only utilize minimum information necessary to make a
judgment of nonexcessive or possibly excessive infiltration/
inflow. The first attempt at making this determination should
follow the analysis of all the background information or
data. If a reliable judgment cannot be made after this, addi-
tional work, such as flow measuring at key manholes in subsystems
or pumping station flow monitoring, may be required.
3.2.1 Interview
Interviews may be one of the first steps in the study of
infiltration/inflow in a sewer system. The purpose of con-
ducting an interview is to gather as much information as
possible from the people who are familiar with the system.
Results from well performed interviews may save the engineer
considerable field work and also give him a clear overview
of some or all of the problems at the onset and provide him
with guidance as the study progresses. In the final analysis,
the results from"*the Interviews may also be utilized, along
with other findings, to make a proper judgment as to the
seriousness of the infiltration/inflow problems in the study
area, the major problem areas in the system, the percentage
of the infiltration/inflow which can possibly be removed
and the areas which may deserve further investigation. A
spin-off effect of the interview is that it may help the
municipality recognize its problems and develop a program
to eliminate and/or prevent them.
3.2.1.a. Person to Perform the Interview
Because of their Importance, interviews should be well planned
and should be undertaken by an experienced person. In some
instances, discussions with municipal engineers, public works
directors and treatment plant and sewer superintendents should
be conducted by experienced engineers. In other instances,
such as discussions with plant operators and sewer line laborers,
it may be advantageous to have an experienced technician to
conduct the study.
3.2.1.b. Persons to be Interviewed
The persons who might be interviewed are those who know the
sewer system and its related problems, and are familiar with
the general conditions of the study area. They may include
the following:
3-3
-------
Sewer maintenance personnel
Sewage treatment plant operators
Municipal engineers
Municipal Officials
Sewer Commissioners
Consulting engineers
Local contractors
Home owners
Industry representatives
Sewer maintenance personnel and treatment plant operators
possess the first-hand knowledge of the sewer system and the
sewage treatment facilities and are often the major information
sources. Questions to ask this group of people could include
the structure of the existing sewer system, the sewer maintenance
program, the sewer construction practices and the observed prob-
lems in the sewer system and the sewered areas. Much of the
same information could often be obtained from knowledgeable
municipal sanitary engineers.
When necessary, both the retired and the present personnel may
be interviewed. In many older systems, where adequate sewer
ordinances were not previously available, changes of sewers,
additions of cross connections between sanitary sewers and
storm sewers, direct drainage of impounding areas to the
sanitary sewer, etc. were often made without proper authorization
and records are sometimes unavailable. Information of this
sort can often be obtained from retired sewer maintenance
personnel, retired treatment plant operators, or retired
municipal engineers.
Local construction contractors may provide information on the
soil and groundwater conditions in the study area, and the
practice of installing roof leaders, cellar, yard, area and
foundation drains, during the construction of local homes
and public buildings.
Home owners may indicate areas that flood during heavy rain-
falls, homes with sewage backup problems and other obvious
problems related to the sewer system.
-------
The major industrial plants in the area could be contacted
to gather the information on their water usage, wastewater
discharge practices, plant operation schedule, etc. which would
be useful for the estimation of normal sewage flows and for
the planning of the flow monitoring schedules to be needed later.
The Municipal Officials, the City Engineers or the Sewer
Commissioners may provide information on the jurisdictional
and legal aspects of the sewer system and help solve problems
in the areas where more than one municipality is involved.
Questions such as the content and effectiveness of the sewer
ordinances and the solutions to the problems of inflow sources
on private properties, could be discussed with the responsible
officials in the local government. The consulting engineers
retained in the past by the municipality to provide planning
or design work on the sewerage system in the study area may
also have a general knowledge of the sewer system and its
related problems and may also be contacted.
The number of persons to interview depends on the complete-
ness of the information obtainable from the people already
interviewed. The interviews can be conducted either individually
or collectively.
3.2.1.C Content of the Interview
The interview should cover a broad spectrum of subjects
including but not limited to the following:
The sanitary sewer system
The storm sewer system
The existing sewer maintenance program (including
cleaning, inspection and rehabilitation)
The problem areas in the sewer system
The geological and geographical conditions in the
sewered areas
The population and water consumption data
The industrial wastewater flows
The legal and jurisdictional aspects of the sewer system
A typical interview form is presented in Table 3-1. This form
is merely a guide and each engineer should develop a form
specific to the system under study.
3-5
-------
TABLE 3-1 INFILTRATION/INFLOW ANALYSIS
INTERVIEW FORM
(Note: This form is intended as a general guide only. Engineers
should develop their own forms for specific systems under study).
Project: Project No.
Interview Date:
Interviewee: Name
Title
Organization
Address
Length of affiliation with the organization or
living in this area years.
Interviewer:
I. SEWER SYSTEM
A. Type of System: Separated ; Combined
Partially combined with about
of the system being combined.
B. General Comments about the Sewer System:
C. Inventory of Sewer System:
1. Sanitary Sewer System (or combined system)
a. Availability of Sewer maps, construction plans
and contract documentsj
b. Age of sewersj
c. Sizes of sewers:
3-6
-------
TABLE 3-1 (Continued)
d. Total length of gravity sewers:
e. Total length of force mains:
f. Number and locations of treatment facilities:
g. Type of treatment process in the treatment
facilities:
h. Number and locations of pumping stations
i. Number and locations of overflow points:
J. Number and locations of bypassing points
k. Number and locations of river crossings:
2. Storm Sewers
a. Indicate areas where cross connections between
sanitary sewers and storm sewers exist:
b. Indicate locations where sanitary sewers and
storm sewers are constructed in same trenches
or in close proximity:
D. Sewer System Maintenance Program
1. Maintenance Schedule:
2. Work normally performed:
3-7
-------
TABLE 3-1 (Continued)
3. Equipment available:
4. Personnel available:
5. Availability of maintenance records^
6. Indicate areas where sewers require frequent
cleaning:
7. Types of deposits encountered:
8. Cleaning methods used:
9. Sections of sewers T V inspected:
10. Indicate sections of pipes that have been repaired
and dates of repairing:
11. Methods and materials used for repairing:
12. Difficulties involved during maintenance:
E. Sewer Construction
1. General comments on the workmanship of sewer con-
struction for this system
2. Sewers
a. Sewer materials:
b. Joint types:
c. Pipe depths:
d. Bedding materials:
e. Packing materials:
3. Manholes
a. Manhole construction materials:
b. Types of manhole covers installed:
3-8
-------
TABLE 3-1 (Continued)
Indicate locations where sewer lines change
in direction and grade without installing
manholes:
d. Indicate locations of cleanouts in sewer lines:
e. The average distance between manholes is: ft
House service connections
a. General comments on construction methods used:
b. Sizes and materials of pipes installed:
c. Indicate known areas where roof drains, areaway
drains and foundation drains and cellar sump
pumps are discharged to sanitary sewers:
d. Indicate areas where open joints and/or Joint
defects exist:
P. Observed Problem Areas
1. Sewers
a. Indicate locations where the following pipe
defects or problems were observed:
(1) Cracks:
(2) Collapse:
(3) Offset joints:
(4) Misalignment (horizontal or vertical):
3-9
-------
TABLE 3-1 (Continued)
(5) Root penetration:
(6) Heavy deposition:
(7) Vandalism:
(8) Other Observations:
Indicate sections of sewers which surcharge and
state possible causes and consequences:
(1) Location:
(2) Causes:
(3) Consequences:
Indicate areas where emergency manhole pumpings
were required during heavy rainfalls and state
the dates, the rate of pumping and the intensi-
ties and durations of rainfall causing the over-
flows :
(l) Location:
(2) Dates:
(3) Pumping rates:
(4) Rainfall intensity:
(5) Rainfall duration:
Indicate locations where basement backups due to
sewer surcharge were reported:
e. Indicate locations where direct Inflows of
surface drainage waters to the sanitary sewers
were observed:
3-10
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TABLE 3-1 (Continued)
f. Indicate locations where water mains were report-
edly broken:
g. Indicate sections of storm sewers which were
found broken and are adjacent to sanitary sewers
2. Manholes
Indicate locations where the following manhole
defects or problems were observed:
a. Cracks:
b. Leaking:
(1) Location:
(2) Dates:
(3) Weather:
(4) Magnitudes:
c. Depressed manholes:
d. Located in low-lying areas:
e. Receiving surface runoffs:_
f. Perforated or broken covers:
g. Covers missing:
h. Heavy deposition:
i. Inaccessible manholes:
j. Other Observations: _______
3. Overflows and Bypasses
a. Indicate locations where dry weather overflows
occur and estimate magnitudes of overflows:
(1) Locations:
(2) Magnitude;
3-11
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TABLE 3-1 (Continued)
Indicate locations, dates and magnitude of wet
weather overflows and state the corresponding
intensities and durations of rainfalls:
(1) Location:
(2) Date:
(3) Magnitude:
Rainfall intensity and duration:
Indicate locations and magnitudes of bypasses
and methods of activation:
Cl) Location:
(2) Magnitude:
(3) Method of activation:
Indicate locations where overflows from catch
basins in storm sewers occurred:
II. BACKGROUND INFORMATION ABOUT SEWERED AREAS
A. Geological and Geographical Information
1. Indicate types of soils in different areas:
2. Locate areas which were swampy, lowland areas prior
to filling for development:
3. Locate potential problem areas such as waterways,
creek crossings, and natural ponding areas:
3-12
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TABLE 3-1 (Continued)
Indicate groundwater levels in different sewered
areas during:
a. Dry season:
b. Wet season:
5- Indicate water level fluctuations in the streams:
6. Indicate sewered areas that were flooded previously:
a. Location:
b. Date:
c. Rainfall intensity and duration:
Indicate locations of wells that can be used as
groundwater gaging points:
B. Population
1. Present population:
2. Sewered population:
3. Locate the following areas:
a. Most densely populated:
b. Least densely populated:
c. Trailer parks:
d. Commercial areas:
e. Industrial areas:
Water Consumption
1. Total water consumption rate:
2. Per capita water consumption rate:
3« Industrial water sources and consumption rates
a . Sources:
b. Consumption rates:
3-13
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TABLE 3-1 (Continued)
D. Legal Aspects
1. Availability of a sewer ordinancej
E. Industrial
1. Industrial plant operation schedule:
2. Industrial water sources:
3. Industrial water consumption rate:
Industrial wastewater discharge rate and schedule
3-14
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Before the interview, maps of the study area, if available,
should be studied to get familiarized with the area. During
the interview, important information could also be marked
on the maps to supplement the descriptions recorded in the
interview form.
Before an interview, the purpose, nature and significance of
the study should be explained to the persons being interviewed
to avoid any misunderstanding and to obtain full cooperation.
Good public relations should be practiced at all times.
Pertinent existing records, such as treatment plant records,
sewer maps, sewer maintenance records, including information
of previous cleaning, TV Inspection and rehabilitation,
sewer system construction, contract documents, water consump-
tion records, sewer ordinance, discharge permit information,
etc., should be collected during the Interviews to facilitate
further study.
3.2.1.d. Treatment of the Interview Results
After the interviews, tables could be constructed to summarize
the* findings, and problem areas could be plotted on the maps
for easy identification. Discrepancies among interviewees
and/or between the interview results and the existing records
should be evaluated. Some spot checking should be made to
substantiate the interview results. From an analysis of
the collected information, a plan of action can now be made
to gather more needed data for the completion of the infiltration/
inflow analysis.
3.2.2 Sewer Map Analysis
Maps of the existing sanitary and storm sewer systems may be
necessary in order to conduct an I/I Analysis particularly
when the flow data are limited and flow monitoring at key
manholes is desirable. In systems where sewer maps are avail-
able, it may be advisable to verify some of the critical points
in the field before total acceptance. Sewer maps should also
be updated to include new sewer extensions, sewer line changes,
buried manholes, and any other pertinent data.
In systems where sewer maps are not available or incomplete,
efforts should be made to produce adequate maps for the study.
(The methods and equipment used for sewer mapping are discussed
in the following subsection.) Generally, the costs for sewer map
preparations suitable for Infiltration/Inflow Analyses and
Evaluation Surveys are fundable costs, to the extent necessary
for the study.
3-15
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All available information need not be included in the sewer
maps for an analysis report . The following basic items are
generally required:
All sanitary and combined sewers;
Size of sewers and direction of flows;
Locations of treatment facilities, pumping
stations, flow measurement manholes, over-
flow and bypass points and river crossings;
Storm sewers in the vicinity of sanitary
sewers and those crossing or constructed in
the same trenches as the sanitary sewers.
All manholes and their inverts need not be shown for an analysis
report. In some instances, results from interviews or pre-
liminary analysis may indicate that no infiltration/inflow
problems exist in certain areas of the system; sewer layouts for
such areas are not required if not available.
The scale of sewer maps may vary depending on the size of the
system. In general, a scale of 1 inch = 400 feet (or, 1/4,800)
is satisfactory. For larger areas, the sewer system may have to
be broken down into several smaller systems, and a separate map
may be prepared for each smaller system. However, a system flow
diagram should be prepared to show the inter-relationships among
all the systems.
3.2.2.a Map Preparation
A street map is generally useful for the preparation of a
sewer map. In cases where street maps are not available,
a schematic layout of the sewer system may be suitable, or
an aerial photograph of the area may be taken and a map developed.
After the map is prepared, the existing sewers should then
be laid out on it.
Sewer location and direction of flow can be identified by a
number of methods. The following methods are common:
Dye tracer
Floats
Smoke
Metal detectors
Interview
3-16
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These methods can be used to develop a complete sewer map, to
complete a partially completed sewer map, or to check the exist-
ing sewer map for accuracy. The selection of a particular method
or a combination of several methods for a given job will depend
on the field situation and should be judged individually.
3.2.2.a (1) Dye Tracer - The dye tracer method involves
the addition of a water-soluble dye to a manhole and determining
the paths of flow by observing the dye at the downstream
manholes and outlets. A sewer map can be developed by plotting
all the flow paths determined in this manner.
Several types of dyes are available for sewer tracing, including
fluorescein, Rhodamine, Rhodamine W, Rhodamine WT, methyl
orange, nigrosine, etc. The characteristics of some of these
dyes are shown in Table 3-2. Proper selection of a suitable
dye and the respective feed concentration suitable for visible
or instrument observation after dilution in the sewers is
essential for successful application.
Powdered dyes are usually dissolved in water to make concen-
trated solutions for easy handling. The solution concentration
and the quantity to apply depend on the magnitude of sewage flow.
3.2.2.a (2) Floats - Floats, such as wood chips, cork floats,
stoppered bottles, oranges, etc., can also be used to determine
the flow path in a sewer. However, in heavily deposited
or obstructed sewers, this method may not be feasible. The
floats should be specially marked to distinguish them from
similar objects in the sewage.
3.2.2.a (3) Smoke - Smoke produced from a smoke bomb in
a manhole and blown by an air blower will show up in adjacent
manholes if the sewer is not flowing full or if there are
no water traps in the sewer section being investigated.
One added advantage of this tracing technique is that, in
certain cases some infiltration/inflow sources may also be
detected.
3.2.2.a (4) Metal Detectors - Commercially available metal
detectors can be used to locate buried metal sewers and manholes
with metal covers. Because of possible interferences from
other underground utility pipes, the detectors should be
used by an experienced operator.
3-17
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TABLE 3-2
PROPERTIES OF COMMONLY USED TRACER DYES* [12]
Dye color, formula
and common name
Basic Violet 10
C28H31N2°3C1
Rhodamine B
Acid Red 52
C27H29N2°4S2Na
Acid Yellow 73
C20H12°5
Fluorescein
Manufacturer's
brand name
Rhodamine B
Extra
Rhodamine B
Rhodamine
BA
Rhodamine
WT
Sulpho 2
Rhodamine B
Fluoro Brilliant
PinkJ
Fluorescein
Available
forms
Powder
40 percent
solution
(by wt.)
40 percent
solution
30 percent
solution
(by wt.)
20 percent
solution
Powder
Powder
Specific
Gravity
of Solutions
1.12
1.03
1.03
1.19
Remarks
Strong points: Very high
detectibility, moderate
cost.
Weak points: Fair
diffusivity, moderate
sorptive tendency,
moderate rate of
photochemical decay,
high acidity of
solutions given.
Strong points: High
detectibility, low
sorptive tendency, good
diffusivity, low
acidity.
Weak points: High cost,
heavy .
Strong points: Fairly
high detectibility, low
sorptive tendency,
good diffusivity, low
decay rate, fairly
stable at pH extremes.
Weak points: high cost
Strong points: Inexpensive,
low sorptive tendency,
low temperature effect.
Weak points: Very high
photochemical decay
rates; high potential
interference by
background .
*Note: Before using, the health effects of these dyes should be carefully considered.
Dyes with carcinogenic potentials should be avoided.
Product of E. I. DuPont de Nemours Co., Wilmington, Del.
I
Product of General Aniline and Film Corp., New York, N.Y.
Product of Keystone Aniline and Chemical Co., Chicago, 111.
3-18
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3.2.2.a (5) Interview - Interviewing people having a first-
hand knowledge of the sewer system is also one way to construct
a sewer map. Usually, the personnel in the local sewer main-
tenance department have a better knowledge of the sewer system
than anybody else and should be contacted first. To avoid
possible error, some limited field work should be done using
the aforementioned techniques to substantiate the interview
results.
3.2.2.b Map Study
Once the sewer map is prepared, it can be used as a valuable
tool during the study. The following information pertinent to
infiltration/inflow can be indicated or overlayed on the
sewer maps:
Topography of the study area
Soil formation
Groundwater distribution
Sewer age
Known or potential problem areas such as areas
subject to floodings during heavy rainfalls,
surcharged sewers, overflowing manholes, over-
loaded pumping stations, houses with sewer
back-up problems, obvious inflow sources,
existing and historical swampy areas, etc.
A careful inspection of the sewer maps with this added information,
adequately keyed, may enable one to gain valuable insights into
the infiltration/inflow problems of the area. For example:
(1) Storm sewers crossing, parallel to, or in the same
trenches as the sanitary sewers may be potential
infiltration and inflow sources: i.e. storm water may
exfiltrate from the storm sewers and infiltrate through
defective joints, etc. to the adjacent sanitary sewers;
some relief cross-connections between these two types of
sewers may have been made in the past to allow the
storm sewers to overflow to the sanitary sewers.
(2) Sewers constructed near rivers, streams, ditch sections
ponding areas and swamps may present serious infiltration/
inflow problems due to groundwater seepage or direct
drainage.
(3) Sewers constructed in poor soils may be subjected to
settlement resulting in open joints and/or pipe
cracking.
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(4) Low-lying areas may be subjected to flooding during
heavy rainfalls. Manholes with perforated covers in
such areas may present serious inflow problems.
(5) Older sewers may present more structural defects.
Sewers with oakum-bituminous, oakum-mortar or cement-
mortar joints may present more serious infiltration
problems than sewers with gasket joints.
(6) Sewers constructed above seasonal groundwater level
may present little infiltration problems.
(7) Serious infiltration/inflow problems may exist in
areas where there are one or more of the following
conditions:
(a) Sewers being surcharged
(.b) Manholes overflowing
(c) Pumping stations overloaded
(d) Houses having sewage back-up problems
Based on this analysis, an engineering Judgment can be made as to
(1) What the degree of the problems might be in different
areas; and
(2) If more detailed investigation should be made,
where to concentrate the efforts.
3.2.3 Inventory of Existing Sewer System
An inventory of the existing sewer system will enable both the
investigator and the reader to have a general understanding
of the nature of the system. The following items may be sum-
marized and included in the report:
Type of sewer system, i.e., separate or combined
system or combination;
Age of sewers;
Sizes and lengths of sewer pipes;
Pipe materials;
Types of joints and joint materials;
3-20
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Numbers of manholes and catch basins;
Maximum, minimum and average depth of sewers;
Bedding and backfill materials;
Construction techniques;
Types and numbers of overflows and bypasses;
Physical conditions of the sewers.
This information could be obtained from reviewing the sewer
maps, as-built sewer construction plans and specifications, etc.
Some information is also obtainable from interviews. Typical
data sheets for recording the above information (except the
last item) are shown in Table 3-3
3.2.3.a Type of Sewer System
The type of the sewer system should be known because the nature
of the infiltration/inflow problem of a separate sanitary sewer
system may be different from that of a combined sewer system.
In a separate sanitary system, both the infiltration and the
inflow problems should be investigated, while in a combined
system, generally only the infiltration problem needs to
be stressed. Combined sewers are usually designed to remove
the rainfall-induced flows in an area as well as the wastewater
discharges from various sources. By definition, most of
the inflow problems are rainfall-related and should not have
any impact on the combined system. However, inflow sources
not directly related to rainfall, such as industrial cooling
water discharges, drains from springs and swampy areas, etc.,
should be identified and studied in a combined system as
well as in a separate system.
The requirements for handling overflows in separate sewer systems
are also different from those in combined sewer systems. Over-
flows and bypassing should be eliminated from separate sanitary
systems, but not necessarily from combined systems. Overflows
or bypasses from combined sewers may or may not need some
degree of treatment before discharging to the receiving waters
or land disposal, depending on the requirements in the National
Pollution Discharge Elimination System (NPDES) permit. This
will affect the treatment costs in the final cost-effectiveness
analysis.
3-21
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TABLE 3-3
TYPICAL DATA SHEETS FOR THE INVENTORY OF
EXISTING SEWER SYSTEM
I. SANITARY GRAVITY SEWERS OR COMBINED SEWERS
JointNo.Sewer""~
Size Length* Pipe Type & of Depth, Bedding Backfill
Pipe Age In. Ft Materials Material MH's Ft Material Material
Sub-
Total
II, SANITARY FORCE MAIN
Pipe Size, Length,
Age In. In. Material
Sub-
Total
III. OVERFLOWS
Frequency Over- Probable Dis-
No. Location Description of Over- flow Causes of charge
flows Rate, Overflow Point
Tjmes/yr gpm
IV. BYPASSES
FrequencyBypassConditionDis-~
No. Location Description of Flow Flow Required charge
Bypass, Rate, for By- point
Times/yr gpm passing
3-22
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TABLE 3-3 (Continued)
V. PUMPING STATIONS
No. Location Type of Pump Rate, Average Daily Flow, gpd
Pumps gpm Low High
Groundwater Groundwater
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3.2.3-b Age of Sewers
The age of a sewer system may partially reflect Its general
conditions and the degree of the potential infiltration/inflow
problems. Buried sewers are constantly subjected to different
adverse environmental conditions and deteriorate with time.
Sewers constructed in poor soils may settle and create offset
joints or cracks. Sewer pipes and pipe joints may be attacked
by the chemicals in the groundwater, such as sulfates and
organic acids. Metal sewers may be electrolytically corroded
by the stray currents in the groundwater. Sewer joints may
be penetrated by plant roots. Increased surface loadings may
cause crushing or cracks in gradually deteriorated sewers.
Such factors render the older sewers more vulnerable to
infiltration than the newer ones . In addition, one can ex-
pect to find more cross-connections between sanitary sewers
and storm sewers and more direct inflow sources in older
sewer systems than in relatively new systems because most older
systems were constructed when there were no adequate sewer
ordinances, and without thorough inspection.
3.2.3c Other Appurtenances
Bypasses and overflows should be identified and observed
in the field. The specific construction of the overflows and
bypasses should be determined and the operation of each should be
understood. Information regarding the activation of overflows
and bypasses should be established either from past observations
or throughout the I/I Analysis and/or Evaluation Survey.
Pumping stations should be identified and design and opera-
tional characteristics of these should be documented.
3.2.4 Geographic and Geological Data
A general knowledge of the geographic and geological condi-
tions of the sewered area may enable the engineer to better
understand the infiltration/inflow problems in the area.
Provided with sufficient data, the engineer can pinpoint
some potential problem areas and plan possible corrective
actions. As will be discussed in Chapter 5, for sewer rehabili-
tation work, the type of the soils and the groundwater conditions
around the sewers also dictate the type of the chemical grout
to be used.
3.2.4.a. Topography
3.2.4.a_(l) Importance of Topographic Data - The topography
of an area reveals the extent and direction of surface drainage,
the locations of low-lying areas and the areas where sewers
are close to or crossing rivers, streams and/or swampy areas.
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Low-lying areas are subjected to possible floodings during
heavy rainfalls and the extent of the surface drainage determines
the seriousness of the flooding problem. In such areas,
a considerable amount of surface runoff may enter the sewer
system through exposed open joints, perforated sewer manhole
covers, structurally defective manholes, abandoned house
connections, etc. Prolonged rainfall may also saturate the'
soils and increase the possibility of rainfall-related infiltra-
tion through deteriorated pipes, pipe joints and/or manhole
walls. Sewers constructed in the vicinity of or crossing
rivers, streams or swampy areas may have a higher possibility
of being surrounded by saturated soils than those constructed
in the other areas and may present a greater infiltration/inflow
problem than the sewers lying in areas farther away from
the water sources.
3.2.4.a (2) Data Collection and Presentation - Topographic
maps and aerial photographs may both provide sufficient informa-
tion for topographic study. Topographic maps are generally
available from the U.S. Geological Survey. Aerial photographs
can be obtained from: (1) U.S. Department of Agriculture,
Commodity Stabilization Program, (2) Local or County Planning
Departments, (3) U.S. Corps of Engineers Offices, and (4)
Private Photogrammetry and Mapping companies.
The topographic maps should be studied and analyzed by the
engineer to locate areas of potential infiltration/inflow
problems. The important findings from this study may be
shown and discussed in the analysis report.
3.2.4.b Rainfall
3.2.4.13 (1) Importance of Rainfall Data - Both infiltration and
inflow are affected by rainfall. By definition, the amount of
inflow to a sewer system is, mostly, directly related to rainfall,
The direct relationships between rainfall and infiltration, on
the other hand, are not so apparent. While most of the infiltra-
tion phenomena are caused by the seepage of the groundwater
through defective pipes, pipe joints, connections, or manhole
walls, rainfall during a high groundwater period indeed
aggravates the infiltration problem. On the one hand, rainfall
and/or the surface run-off may seek the cracks in the soil sur-
rounding the manholes and leak through the deteriorated manhole
walls to cause an infiltration problem. On the other hand, dur-
ing a heavy rainfall, the rainwater may reach the groundwater
by percolating through some highly permeable soils and cause a
general increase of the groundwater level. This increases the
total hydraulic head above the sewer pipes and causes more water
to enter the pipes through defected joints, etc. In locations
where the sewer pipes cut the underlain bedrock, the rain-
water, after percolating through the overlying soils, may flow
over the rock surface to the areas of lower elevations, generally
in the sewer trench, and there cause an increased infiltration
problem in the sewers.
3-25
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During heavy rainfalls, another phenomenon may occur in the
soil and increase the infiltration rate in the sewers. This
is the case when a large ground surface is covered by impounded
rainwater; as this large blanket of impounded water percolates
through the soils underneath, it leaves little chance for
the air in the soil to escape. Because of this, the air
is subjected to increasing pressure. The pressure is trans-
mitted to the groundwater above the sewer pipe and causes
an increase in infiltration rate through defective pipe Joints,
etc.
Therefore, rainfall data are very important for the infiltration/
inflow study. For adequate infiltration/inflow analysis,
the following rainfall data are generally needed:
Average annual rainfall;
Daily rainfall for the wettest season in the
most recent year;
Hourly rainfall for some typical raining days.
3.2.4.b (2) Data Collection - Rainfall data are usually ob-
tainable from the following sources:
National Weather Services, local offices;
Climatological data published by the National
Weather Service;
Airports;
Universities;
Military installations; and
Sewage treatment plants.
When this information is not available or additional data are
required, rainfall gauges may be installed at selected locations
in the study area and the data gathered over some reasonable
length of time. These data should then be compared with data
from nearby sources.
3.2.4.C Soil
3.2.4.0. (1) Importance of Soil Data - Soil conditions in an
area affect the magnitude of the infiltration/inflow problem
in the sewer system in two ways, i.e.:
3-26
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(a) The permeability of the soil determines the rate of
movement of the groundwater through the soil and the
subsequent effects on the sewers.
(b) The nature of the backfill and bedding materials
surrounding the sewers affects the structural integrity
of the sewers. All other conditions being equal,
sewers constructed in permeable soils receive more
infiltration than those constructed in less permeable
soils. Relatively impermeable soils, such as clay,
may also seal off pipe openings and reduce the
quantities of infiltration that would otherwise
enter these openings.
Sewers constructed on poor soils may be subjected to settlement,
resulting in open joints or cracking of pipe. Unequal settle-
ments of manholes and sewers in soils may result in open
connections through broken pipes or joints. Elastic soils such
as clay may subject the pipes to expansion and contraction,
resulting in loose joints and/or broken pipes.
Thus a study of the soil conditions in the sewered area may be
necessary to the understanding of some observed infiltration
problems. It may also assist the engineer to locate areas
where there are potential infiltration problems.
In .the selection of chemical grouts for the sealing of sewer
pipes and joints during sewer rehabilitation, the type of the
soil surrounding the pipe is also one of the deciding factors.
3.2.4.C (2) data Collection and Presentation - The information
on soil distribution and soil characteristics in an area can be
obtained from the following sources:
Soil Conservation Service, U.S. Department of
Agriculture;
Boring logs in sewer construction contract documents;
State Agriculture Extension Service;
Local construction companies or contractors;
Field investigation.
The Soil Conservation Service has published many soil maps
with descriptions of soil characteristics to a depth of 5
feet. It has offices in most counties across the country.
Boring logs contained in the sewer construction contract
3-27
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documents provide detailed information about the soils along
the sewer construction route. The State Agriculture Extension
Service may have collected data on the soil types and soil
characteristics in the study area. Local construction companies
and contractors may also have some information about the
area's soil. For locations where no soil information; is
available, some field soil study may be needed. The study
may include the conducting of test borings at key points
and the interpretation of the collected soil samples. For
complex and unusual cases, the soil samples should be interpreted
by the soil scientists in the Soil Conservation Service,
Agricultural Extension Service representatives, consulting
soil scientists or agronomists.
The soil distribution and characteristics in the study area
may be presented in the report. The significance of the effects
of the soils on the integrity of the sewers and on the
infiltration/inflow problems in the study area may also be
discussed.
3.2.*Kd Groundwater
3.2.4.d (1) Importance of Groundwater Information - By defini-
tion, most of the infiltration phenomena in sewers are ground-
water-related. In areas where the groundwater level is lower
than the sewer installation, infiltration may occur only during
heavy storms. Both the level and the chemical characteristics
of the groundwater affect the degree of infiltration in the
sewers. Sewers in contact with groundwater may be attacked by
the chemicals in the groundwater, such as sulfates and organic
acids. Metal sewers may also be electrolytically corroded in the
presence of groundwater. Once the openings in the sewers have
occurred, under favorable soil conditions, the degree of infil-
tration is directly related to the level of the groundwater
above the sewers.
Because of the influence of the groundwater on infiltration,
the determination of infiltration in the sewer system should
be based on a comparison of the sewage flow data collected
in the high groundwater seasons versus those collected in
the low groundwater seasons. To obtain realistic infiltration
flow data in the Sewer System Evaluation Survey, the sewer
line inspection should also be conducted during high groundwater
seasons. Thus, accurate groundwater information of the study
area is essential to the Infiltration/Inflow Analysis and
the Sewer System Evaluation Survey. Groundwater monitoring
will be needed if no data are available.
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3«2.4.d (2) Data Collection and Presentation - General ground-
water information may be obtainable from a number of sources
such as:
State Water Resources agencies;
U.S. Geological Survey;
Local or county water conservation districts;
Groundwater users, including municipalities,
water companies and individuals;
Local construction companies or contractors.
To obtain more detailed groundwater information in the study
area, field groundwater monitoring may have to be conducted.
This can be accomplished by one or a combination of the fol-
lowing setups:
Installation of groundwater gauges in sewer
manholes at the crown of the pipe;
Installation of groundwater gauges adjacent
to the sewer pipes;
Observation of the water levels in existing
water wells;
Observation of the water levels in specially
dug water wells.
In a typical groundwater gauge installation in a manhole (Figure
3-1), the gauge is installed by inserting a pipe through
the wall of the manhole at an elevation near the top of the
lowest sewer and attaching a visible plastic viewing tube with
calibrated scale to this pipe. The space between the pipe and
the hole in the wall should be properly sealed to prevent leakage.
The groundwater elevation outside the manhole is observed at the
plastic pipe inside the manhole. Figure 3-2 shows a typical setup
for a groundwater monitor in a specially dug or drilled water
well. This installation would generally be made adjacent to the
sewer pipe. The groundwater level can be determined by insert-
ing a stick into the well casing and measuring the length of the
unwetted portion of the stick after retrieval.
After the gauges or monitors are installed, they should be
inspected regularly to obtain needed information. Continuous
recording devices can also be installed if necessary. To deter-
mine seasonal groundwater variations, the monitoring may have
to be extended to an entire year.
3-29
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3-30
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Cover
Ground Surface
' Diam, Augered Hole
Groundwoter Surface
Diam. PI/C Casing
-Cloth Wrapping to Exclude
Silty Material
Open Slots to Allow
Entrance of Grounawater
Figure J-2, Typical Grouncwater Gauge Installation in Soil
(Courtesy of Dufresne-Henry Engineering Corp.)
3-31
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The recorded data should always be reviewed and screened care-
fully before being used. Pumping water from nearby wells may
cause a temporary draw down of the groundwater surface at the
monitoring stations. Under such conditions, the recorded water
levels do not represent the highest possible groundwater levels
in the area under normal conditions. For infiltration studies,
the highest groundwater levels are of major concern. Therefore,
whenever possible, the groundwater levels should be recorded
during the periods of a day when groundwater pumping in the
study area is at a minimum.
Clogging of the gauging pipes or monitors by silt, clay or
other minerals in the groundwater may also cause erroneous
results. The gauges or monitors should be frequently checked
to detect and correct any possible cloggings.
In the analysis report, the groundwater elevations should be
presented along with the dates of measurements and monitor
locations. The determination of infiltration and inflow should
be made with proper considerations of the groundwater conditions
in the study area.
3.2.5 Population, Water Consumption and Wastewater Flow Data
3 . 2. 5 . a Intrqduction
The population, water consumption and wastewater flow data
are essential for the determination of infiltration and
inflow. From population and water consumption data, the
theoretical (or base) wastewater production rate in the study
area can be determined. This production rate represents the
quantity of wastewater normally expected in the sewer system,
including domestic, commercial and industrial wastewater
flows, but excluding all infiltration and inflow. Once the
theoretical wastewater production rate is derived, the infil-
tration and inflow can be calculated by comparing it with the
actual wastewater flow data. Wastewater flows over and above
the theoretical wastewater production rate, correlated with
weather and groundwater conditions, are considered as the
infiltration/inflow. (Detailed procedures for the determina-
tion of infiltration and inflow are presented in Section 3.3.)
However, if the infiltration/inflow in a system can be
determined by direct flow measurement, then the data for
population and water consumption may not be the controlling
factors in the I/I determination.
3.2.5.b Population
The population data need to be gathered only for the period
in which records for water consumption, wastewater flow,
groundwater and rainfall are all available. If these records
were not available in the past and need to be generated
during the study period, the population for the same period
should then be known.
3-32
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For the determination of infiltration and inflow, both the
total population and the population serviced by the sewers
(.the sewered population) need to be known. In areas where
there are seasonal fluctuations of populations, a detailed
breakdown of the population according to season or month
should be provided.
The population records are usually available in the U.S. Census
Bureau, local government offices and sanitary districts. They
may also be contained in previous engineering study reports. If
no data are available, a house-to-house count may have to be done
to determine the population.
3.2.5.c Water Consumption
The water consumption data should be obtained for the year(s)
for which records for wastewater flow, groundwater and
rainfall are all available. If these records are not available
and need to be generated during the study period, the water
consumption data for the current year or the immediate previous
year should be obtained.
If'metered water use data are available for all users in the
study area, they should be collected and used for the estimation
of wastewater production rate.
In communities where metered water use records are not available,
the water supply data from all supply sources should be collected
Along with these, the portion of water consumption which is not
expected to enter the sewer system, such as system losses,
irrigation use, etc., should be estimated.
Water consumption records are usually obtainable from local
water departments, private water companies, industrial plants
and individual well users.
If no records are available, estimations can be made based on
population and an inventory of the residential, commercial and
industrial establishments in the study area using some typical
water use rates.
3.2.5.d Wastewater Flow
Whenever possible, uninterrupted wastewater flow records
covering a period of 1 to 2 years of the most recent years
should be obtained for infiltration and Inflow determination.
Records which cover a period (or periods) shorter than this
may also be sufficient if the period (or periods) includes all
representative groundwater and rainfall conditions in the study
area.
3-33
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The flow records should cover the wastewater flows in the
entire sewer system under study. In large sewer systems,
flow records may have to be gathered from more than one
treatment plant, pumping station or flow measurement station
in the system. In addition, flow records for overflows,
bypasses and emergency pumping should also be gathered, if
available. Wastewater flow records, if available, can
normally be obtained from sewage treatment plants, sanitary
districts or sewer departments in local governments.
All records should be checked for accuracy before being
used. The accuracy of the records can be determined by
checking the accuracy of the instruments used for recording
and totalizing the flows.
If no wastewater flow records are available, a flow measure-
ment program should be initiated.
3.2.6 Plow Measurement
3.2.6.a Introduction
In the Infiltration/Inflow Analysis, flow measurements may
be required for various reasons:
(1) For sewer systems which have sufficient existing
flow data for the determination of infiltration/
inflow, flow measurements may be needed for the
following purposes:
(a) To check the accuracy of the existing flow
records;
(b) To determine the infiltration/inflow in sub-
divided areas (the subsystems) to facilitate
the determination of whether there is possibly
excessive infiltration/inflow, through a cost-
effectiveness analysis or other approaches; and
(c) To determine the infiltration/inflow in sub-
divided areas so that subareas with no
infiltration/inflow problems can be eliminated
from further study and the planning of a Sewer
System Evaluation Survey program can be accom-
plished.
(2) For systems which have no existing flow records
or where data are insufficient or inaccurate, flow
measurements are always needed for infiltration/
inflow determinations and also for the aforementioned
purposes.
3-34
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Flows which need to be determined may include:
Total wastewater flows, including domestic,
commercial and industrial wastewaters and
infiltration/inflow;
Industrial wastewater flows;
Bypasses;
Overflows;
Emergency pumpings; and
Infiltration/inflow.
Along with flow measurements, groundwater and/or rainfall
gaugings may also have to be performed in some instances.
Depending on the availability and adequacy of the existing
flow data and the conditions in the sewer system and study
area, either instantaneous flow measurement or continuous
flow monitoring may have to be conducted.
3.2.6.b Planning of Flow Measurements
3.2.6.b (1) General - To obtain sufficient flow data for
the analysis in as short a period of time as possible, proper
planning cannot be overemphasized. The time suitable for
flow measurement is generally limited because peak infiltra-
tion occurs only during high groundwater periods and peak
inflow normally occurs only during heavy rainfall seasons.
If high groundwater periods or heavy rainfall seasons are
missed, the investigation may have to be postponed and the
facilities planning may be delayed.
3.2.6.b (2) Timing of Flow Measurement - For accurate
determination of infiltration/inflow, it is desirable to
obtain continuous flow data over a period of an entire year;
but, in most cases, extending the measurements to such a long
period of time is not warranted. For adequate infiltration/
inflow analysis, flow data for the periods covering high
groundwater and rainfall conditions are usually all that are
needed.
For the determination of peak infiltration, flows should be
measured during the highest groundwater period of a year,
To determine the peak inflow, flow data for the heavy
rainfall periods should be obtained. To determine the
total yearly infiltration/inflow, flows may also have to be
measured during other typical groundwater conditions.
3-35
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Continuous flow measurements are desirable. However, if
the infiltration is to be directly measured, instantaneous
flow measurement would be sufficient because the groundwater
level is normally relatively stable over periods of several
days. For direct inflow measurements, the flows should be
monitored continuously throughout each rainfall period.
If infiltration is to be measured directly, the measurement
should be performed in nonrainfall days, preferably at least
24 hours after a rainfall to minimize the direct influence
of rainfall. To minimize the interferences caused by domestic,
commercial and industrial flows, flow measurements should
be performed during early morning hours, approximately from
midnight to 6 a.m. To avoid possible errors caused by waste-
water discharges during flow measurement, repeated flow
measurements should be conducted in three consecutive non-
rainfall days for each typical groundwater condition.
Consideration must'be given to Industries that operate 24
hours per day, the living habits of the community and flow
lag time in the pipes.
To minimize the interferences caused by domestic, commercial
and industrial flows, direct inflow measurements should be
performed during rainfall in the early morning hours.
To avoid surge flows, all pumpings in the sewer system
should be temporarily stopped during flow measurement if
instantaneous flow measurements are taken.
3.2.6.b (3) Division of Subsystems - For the determination
of infiltration/inflow, flow measurement can normally be
conducted at a single station to which the flow in the
entire sewer system discharges, such as a sewage treatment
plant or a pumping station.
However, in many sewer systems, there may be more than one
treatment plant or pumping station, and they may not be inter-
connected. Under such circumstances, flow measurements have
to be conducted in all plants or pumping stations.
To facilitate the cost-effectiveness analysis and to formulate
a Sewer System Evaluation Survey program, a sewer system
may be divided into a number of subsystems and the flows
in each subsystem measured separately. The number of subsystems
will vary from system to system, depending on the size, configu-
ration and nature of the system and the complexity of the
infiltration/inflow problems in the system. One or a combination
of the following criteria can be used to divide the sewer
system:
3-36
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(a) Drainage Area - Sewer systems can be divided into
subsystems according to the flow conditions in the
sewers. A sewer map may reveal that the sewers
are generally constructed in several major groups.
The flows in the sewers of an area may converge to
a single major point before reaching the next group
of sewers downstream. The converging point can be
a manhole or a pumping station. Under such conditions,
it may be convenient to consider the sewers within
the area upstream from the converging manhole or
pumping station as a subsystem and measure the flows
in this manhole or pumping station.
In systems that contain several treatment
plants, the sewers contributing the flows to each
plant can also be considered as a subsystem. The
flow records in each plant can be used for infil-
tration/inflow determination. Additional flows, if
needed, may also be measured at the treatment plants.
(b) Age or Type of Sewers - The sewers in a sewer
system may have been constructed in different years.
The degree of pipe deterioration varies in accordance
with the age, the pipe and joint materials and the
construction method used. Sewers constructed in
different years may present different infiltration/
inflow problems. To isolate the individual problem
areas, sewer systems may also be divided into sub-
systems according to the age of the sewers and
type of pipe.
(c) Groundwater and Soil Conditions - In a large study
area, groundwater levels may vary in different regions.
Some of the sewers may be constantly submerged in the
groundwater; some may never be submerged; some others
may be subjected to seasonal submergence; and in
coastal areas, the sewers may be affected by a ground-
water which fluctuates with the tide. Different
groundwater conditions cause different types and
degrees of infiltration/inflow problems in the sewers.
Therefore, in some sewer systems, the subsystems can
also be divided according to the groundwater con-
ditions in the different regions of the study area.
Similarly, the soil conditions in the different
regions of a study area may also vary widely and
cause varied types and degrees of infiltration/
inflow problems in the sewers. Subsystems may
also be divided according to the soil conditions
in the study area.
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(d) Problem Areas - If, through interviews or other
means, some major infiltration/inflow problem
areas are suspected, these areas may also be
singled out for detailed flow measurements and
cost-effectiveness analysis.
3.2.6.b (.4) Selection of Key Manholes - Before flow measurements
are undertaken, the manholes used for measurements should
be carefully selected. Manholes selected for flow measurement
should be accessible and safe, suitable for installing flow
measurement devices and in key locations, Careful selection
of flow measurement manholes will save field work and provide
sufficient essential flow information for further analysis.
Initially, the flow measurement manholes should be selected
on the basis of an analysis of the sewer maps and the subsystems
divided previously. Sufficient manholes should be chosen to
adequately isolate the flows in each subsystem. It is not
necessary to select one manhole for each subsystem, Similarly,
more than one manhole may have to be selected in one subsystem
to more precisely define the flows in some problem areas.
After the manholes are selected and before actual flow measure-
ments are conducted it is advisable to locate the manholes
in the field. This is important, especially when early
morning flow measurements are planned. To make the Job easy,
personnel from the local sewer maintenance crew can be asked to
help locate the manholes and provide background information about
the manholes. In case a predetermined manhole cannot be found
in the field due to various reasons, another key manhole should
be selected and field-located.
When the flow measurement manholes are located, they should be
opened and checked for accessibility and suitability for install-
ing flow measurement devices. Items to check include:
Safety precautions before entering the manhole;
Size of the manhole opening and the inside
diameter;
Depth of the manhole;
Workability inside the manhole;
Stability of the manhole structure;
Condition of manhole steps;
3-38
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Plow condition in the manhole;
Amount of debris accumulation;
Any additional pipe connections unrecorded
in the sewer maps;
Suitable location for installing flow
measurement devices; and
Traffic conditions during flow measure-
ment periods.
A constantly surcharged manhole may not be suitable for flow
measurement. All manholes found to be unsuitable for flow
measurement should be replaced with other suitable manholes.
3.2.6.b (5) Other Measurements - Besides wastewater flow
and infiltration/inflow measurements, other measurements
which may have to be conducted are:
Groundwater levels,
Rainfall,
Industrial wastewater flows,
Bypasses,
Overflows, and
Emergency pumpings.
Plow measurements for the determination of infiltration
should be accompanied by a measurement of the groundwater
levels in the study area. Plow measurement for the deter-
mination of inflow should be accompanied by a measurement of
the rainfall. When flows are continuously monitored, both
groundwater and rainfall should be gauged simultaneously.
The groundwater and rainfall information can be obtained
either from existing gauging stations or through new setups.
Industrial wastewater flows may have to be measured for the
determination of infiltration/inflow. If the infiltration
and/or inflow are to be directly measured during the early
morning hours, the wastewater flows from the night shifts
of the industrial plants should be determined and deducted
from the measured flows to derive the actual infiltration
and/or inflow.
3-39
-------
The flows from all bypasses, overflows and emergency pumpings
which occur during flow measurement periods should be deter-
mined and added to the measured wastewater flow or infiltra-
tion/inflow so that true peak infiltration/inflow can be
derived.
3.2. 6.c Flow Measurement Techniques
When flow data must be generated, the flow measurements
become a critical component of the I/I Analysis and/or
Sewer System Evaluation Survey. It is necessary to use a
sound approach and good flow measurement techniques to
ensure reasonable results. The obtained results do not
necessarily have to be as accurate as flow data obtained
from a continuous flow monitor at the treatment plant.
These measured flows will, however, be used in determining
possibly excessive or nonexcessive I/I and thus some degree
of accuracy should be employed.
To determine I/I, flow measurements may be taken at several
locations. These locations will depend on the sewer system
being investigated, the flow data that are available and the
flow data that must be obtained. Plow measurements may be
obtained at the following:
Treatment plant influent,
Treatment plant effluent,
Pumping stations,
Key manholes,
Inflow sources that directly enter catch basins or
manholes,
Infiltration sources that directly enter manholes,
Industrial waste sources, and
Overflows and bypasses.
Other locations and sources of I/I may be measured in a
particular sewer system. There are a variety of methods
and equipment available for flow measurement in sewers.
The selection of the proper method or equipment will depend
on the cost, source to be measured, accessibility, manpower
availability, degree of precision and type of data required.
In the following subsections, a few of the most commonly
used methods and equipment will be presented. The general
format which will be employed will be as follows:
3-^0
-------
Description of the method,
Equipment available,
Installation instructions, and
Advantages and disadvantages.
3.2.6.C (1) Depth Measurement (Manual) -
Method - This method involves obtaining an instan-
taneous depth of flow measurement in sewer pipes.
In addition, a mean velocity of flow must be obtained
in order to utilize the flow formula, Q = AV. The
mean velocity may be obtained theoretically by use
of the Kutter formula or the more simplified Manning
equation, v _ 1.486 -2/3 cl/2. The velocity may also
V R s
be determined by actual measurement with a velocity
meter or by time-distance measurements using dye or
floating objects.
Equipment - Staff gauges marked to the nearest 0.01 ft
or 1/8-Inch would be suitable for depth measurements.
Installation - In manholes that are relatively clean
and accessible, the staff gauge may be inserted into
the invert of the manhole channel and the depth of
flow measured. The depth of sediment in the pipe
should be noted and the depth of flow corrected
accordingly.
Some manholes may not be accessible. In these
instances, depth of flow may be obtained by utilizing
a stadia rod. An initial reading may be taken by
placing the rod on the manhole channel invert and
noting a reading on the rod with respect to a
reference such as the manhole frame. A second
reading can then be taken by raising the rod to the
channel water surface and obtain a reading from the
same reference. The difference in the two read-
ings will be the depth of flow.
Advantages -
(1) Inexpensive
(2) Rapid results
(3) Ease of operation
Disadvantages -
(1) Instantaneous result that may not be representative
3-41
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(2) Determination of mean velocity is critical
(3) Cannot be used in surcharged sewers
(4) Low degree of accuracy
3.2.6.C (2) Depth Measurement (Instrument) -
Method - This method Involves obtaining continuous
depth-of-flow measurements in sewer pipes by various
depth measuring and recording devices. In order to
determine flow, the mean velocity must be established
as described in the preceding section.
Equipment -
(.1) Float-operated device which rides on the
surface of liquid and transmits a signal to a
receiver which records the relative depth or
percentage of flow.
(.2) Pressure-differential depth or percentage-of-
flow recorders which bubble air at a regulated
rate through a tube which is secured to the
invert of the sewer pipe or channel. The depth
of flow above the bubble tube will cause a back
pressure and thus the differential pressure can
produce a signal which will be proportional to
the depth of flow.
(3) Sensing devices which continuously travel up and
down and sense the water surface.
(4) Ultrasonic sensing devices which utilize high
frequency sound to sense the water surface.
(5) A low pressure transducer installed in the invert
of the sewer pipe which measures height (pressure)
of flow and transmits a signal proportional to the
depth of flow.
Installation - Generally, the devices are installed
in manholes and the floats or sensing devices are
placed in or near the liquid. The specific Instal-
lation of the various types of devices should be in
accordance with the manufacturer's recommendations.
Advantages -
(.1) Provides continuous recording
(2) Provides a record of results
(3) Generally accurate
3-42
-------
Disadvantages -
(1) Relatively high capital cost
(2) Routine maintenance required
(3) Danger of theft and/or vandalism
(4) Danger of exposure to adverse conditions
3.2.6.c (3) Weirs and Flumes
Method - This method involves the observation or
recording of depth of flow over a specific weir or
through a flume. Weir or flume formulas or tables
are utilized to determine the flow.
Equipment - For flow measurements in sewer pipes,
various V-notch weirs can be utilized. Commonly
used V-notch weirs are 22-1/2°, 30°, 45°, 60° and
90°. In addition, rectangular and trapezoidal weirs
may be used. Portable flumes are also available.
Installation - When installing weirs and flumes, it is
important to ensure that a good seal is made between
the device and the pipe or,channel. Sponge rubber or
sand bags may be used for sealing purposes. The weirs
and flumes should also be installed level.
Advantages -
(1) Low costs
(2) Direct flow reading
(3) Many designs available for flexibility
(4) Generally accurate
Disadvantages -
(1) Must be installed in the sewer or channel
(2) Cannot be used for sewers flowing full or surcharged
(3) Weirs not recommended for fast flowing sewers
(4) Instantaneous result
3.2.6.C (4) Timed Volume -
Method - This method is used to determine flow rates
from leaking manhole walls, wet well walls and
accessible point sources of inflow. The method
involves the use of a vessel of known volume; the
time to fill this vessel is measured with a stop
watch or watch.
3-43
-------
Equipment - One-, two- or five-gallon plastic pails
are suitable for measurement of small streams.
Larger vessels such as 55-gallon drums may be used
but are cumbersome to handle. A stop watch or a
watch with a sweep second hand is suitable for
monitoring time.
Installation - The equipment used for this method of
flow determination is generally portable and no
specific installation is required. When making
the flow determination, the entire stream should
be measured and the measurement repeated to ensure
accuracy.
Advantages -
(1) Accurate
(2) Inexpensive
(3) No specific expertise required
Disadvantages -
(1) Generally cannot be used for flow in sewer pipes
(2) Not adequate for high-velocity flows
3.2.6.C (.5) Pumping Rates -
Method - This method of flow measurement uses pump
design curves and the pumping time. In addition,
some pump stations have flow recorders which
facilitate the gathering of flow data. For ejector
stations, the number of times the system ejects may
be counted; and coupling this with the volume per
discharge, one can determine the flow.
Advantages -
(1) Extra flow-measuring equipment not generally
necessary
3.2.6.C (6) Dye-Dilution Method -
Method - The dye-dilution method is a simple and
quick method for the determination of the flows in
the sewers. The flow measurement can be conducted
above ground; no manhole-entering is necessary.
Using this method, flows can be measured even if
the sewers are running full or surcharged. The
method is normally used to measure the instantaneous
flow rates in sewers. However, with some added
equipment, continuous flow monitoring is also
possible.
-------
Basically, the method involves the following procedure:
(.1) Feed a fluorescent dye at a constant rate to an
upstream manhole.
(2) Collect the water samples from the sewers in
the downstream manholes.
(3) Measure the dye concentrations in the collected
samples with a fluorometer.
(4) Calculate the rate of sewage flow in each sewer
section using the following formula:
Qf = QI £l (3-D
Cf
where:
= the flow rate in the sewer;
= the dye concentration in the sewage
collected at the downstream manhole;
QJ_ = the dye feed rate;
C-^ = the dye concentration in the feed tank,
Materials - Three types of fluorescent dyes have been
used extensively as water tracers: Rhodamine B,
Rhodamine WT, and Pluoresceln (Table 3-2). For
accurate flow measurements in sewers, a dye which
has low sorptive tendency with the solids in the
sewage should always be used. The fluorescence of
the rhodamine dyes is not stable outside of the pH
range of 5-10. Most dyes undergo photochemical decay
in the sunlight. Therefore, the samples should be
stored in the dark and analyzed as soon as possible
after collection. The fluorescence of the dyes is
also affected by temperature. During sample analysis,
if the temperature of the sample is different than
the room temperature, a correction factor should be
applied to the measured concentrations. (The
temperature correction curve for Rhodamine B and
Rhodamine WT are shown in Figure 3-3. The temper-
ature effect of Pluorescein is small and, normally,
need not be corrected.)
Installation - Although commercial solution feeders
are available, a simple homemade constant-head
solution feeder is usually sufficient for feeding
-------
Rhodamine B
Rhodamine WT
0.9 ~
0.8
0.7
0.6
Example:
Dial reading 51 J.
Sample temperature 62°
Base temperature 72°
Temperature difference . . . +10°
Correction factor 0.86
Corrected dial reading = 0.86x5l=*W
-30 -25 -20 -15 -10 -5 0 +5 +10 +15 +20 +25 +30
TEMPERATURE DIFFERENCE (BASE TEMPERATURE MINUS SAMPLE TEMPERATURE), IN °F
Figure 3-3. Te/nperofure-correcf ion curve for Rhodamine B and Rhodamine WT
Dyes [2]
-------
the dye at a constant rate to the manholes. Figures
3-4 and 3-5 show two solution feeders which can be
assembled easily in the laboratory. In each of these
feeders, the feeding rate can be changed by adjust-
ing the head between the water surface in the tank
and the opening of the inflow tube or orifice.
For collecting the samples at the downstream man-
holes, there is no need to enter the manhole. A
container with a rope attached can be dropped down
into the manhole to collect the sample. This would
minimize the need for elaborate safety equipment.
However, if the flows are small, it would still be
more convenient to collect the samples by physically
descending into the manholes. To minimize the loss of
dye due to adsorption, the sample container should be
made of high-quality glass, whenever possible. Plastic
containers can also be used but ordinary soft-glass
containers should be avoided. The samples should be
allowed to stand to reach room temperature and to
settle the suspended solids before being taken for
measurement.
There are two fundamental types of fluorometers:
(1) fluorescence spectrometers, or spectrofluoro-
meters, and (2) filter fluorometers, or fluorimeters.
The filter fluorometer is usually sufficient for an I/I
study. Each fluorometer should be individually cali-
brated with standard dye solutions of known concen-
trations. A calibration curve should be obtained
for each dye used. In the suitable concentration
range, the calibration curve should show a linear
relationship between the fluorometer readings and the
dye concentrations. To avoid possible interferences
by the solids or chemicals in the tap water, distilled
water should be used to prepare the standard dye
solutions.
The concentration, flow rate and quantity of the dye
solution to be used should be determined before the
flow measurement. To make such determinations,
the total length of sewers to be studied and the
approximate flow rate and flow velocity in the down-
stream sewer section should be estimated. The
following example illustrates the calculation pro-
cedure:
-------
TUBE
»
RUBBER
" or 6
FLEX IB
OR RUB
*
WATER LEVEL -1
IN BOWL I
rxXsZ1"^
^x^-MTU r~srv^-
rTf* M^
L JL -Ji ,, . ^}\ s<*
L^
STOPPER ~~~^
mm dia. )
LE PLASTIC /
BER TUBE 11
f
i
^ TUBE (1/8" or
1
I
i_
HEAD
I '
_(^fc£J£
^ ICx^x^rvT
^^
'^ L
-
^-TUBE (1/8"
- GUIDE STRING
3mm dia.)
WATER LEVEL
IN TANK
BOWL
BALLAST
or 3mm dia. )
FLOATING
BOWL (SEE
DETAIL ABOVE]
FLEXIBLE
RUBBER OR
PLASTIC HOSE
- GUIDE STRING
CONTAINER
Figure 3-4. Floating Bowl So lull on Feeder [3]
3-^8
-------
Flush Drain
ij
IT
PLAN VIEW
Vent
Guide
Rubber stopper
Liquid Level
Brass Tube
Bind rubber tube
and brass tube
with copper wire
Wooden Float
Orifice(Sized to
prevent siphoning)
Brass tube
cast in wal1
Shut-off Valve
Plastic Tubing
ELEVATION SECTION
Figure 3-5. Floating Platform Solution Feeder [4]
3-^9
-------
Example:
Given: Dye to be used - Rhodamine WT, 20% solution,
specific gravity 1.19- Total length of sewer
to be studied - 40 manholes at 250-foot inter-
vals, or 40 x 250 = 10,000 ft. Plow in the
last sewer section downstream equals approxi-
mately 100 gallons/min.
Desired : The concentration, flow rate and quantity
of the dye solution required and the amount of
the 20$ dye solution required.
Solution: From the fluorometer calibration curve
find the optimum dye concentration which can be
detected, e.g. 50 parts per billion (ppb).
A constant-head solution feeder is constructed
which can adjust the flow rate between 0-50 ml/
mln. Use a flow rate of 20 ml/rain or 0.0053
gallon/min Cgpm) .
Rearrange Eq. C3-1) to give
ci °r (3-2>
Where :
Qf = 100 gpm;
Cf = 50 ppb;
Q± = 0.0053 gpm
Therefore,
c . 100 Spm - x 50 ppb
°i ~ 0.0053 gpm vv
= 9.4 x 105 ppb
= 940 ppm; say 1,000 ppm
Assume a flow velocity of 2 ft/sec in the sewer,
For 10,000 feet of sewer, the total flow time
would be:
10i°0.0 ft = 5000 sec = 83 min
2 ft/sec
3-50
-------
At a flow rate of 0.0053 gpm, the total dye
solution required would be:
0.0053 gallon/min x 83 min =0.44 gallon
Therefore, about 0.5 gallon of a 1000-ppm dye
solution should be used for this part of the
sewer system. The dye should be applied con-
tinuously at a constant rate of 20 ml/min
until all the samples are collected from the
downstream manholes. To insure that a suffi-
cient quantity of dye solution is available,
when feeding, approximately 1 gallon should be
prepared.
To prepare 1.0 gallon of 1000-ppm dye solution
from a 20% Rhodamine WT solution (Sp gr 1.19)
the amount of the latter required can be cal-
culated as follows:
20% solution = 2 x 10^ ppm solution.
The amount of the 20% solution required
to prepare 1.0 gallon of 1000-ppm solution
_ 1.0 gallon x 1000 ppm
2 x io5 ppm x 1.19 CSp gr)
= 4.2 x 10-3 gallon
The specific gravity of the solution should be
taken into account because in the diluted dye
solution the specific gravity is close to one,
which is different from that of the concentrated
solution.
For continuous flow monitoring, a fluorometer equipped
with a flow-through door should be used. The samples
are withdrawn from the sewer with a pump and fed to
the fluorometer, where the dye concentrations are
measured and recorded automatically on a strip-chart
recorder. The pump is powered either by commercial-
line power or by a gasoline driven generator. If the
generator is used, a constant-voltage transformer is
normally installed between the fluorometer and the
generator supply to smooth out variations in generator
output which might affect fluorometer readout. How-
ever, because of relatively high cost and possible
interferences by the solids and the air bubbles in the
samples, this technique is not normally recommended
for continuous flow monitoring.
3-51
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Advantages -
(1) Accurate
(2) Saves time and provides flow data on many sewer
sections
Disadvantages -
(1) Manpower involved
(2) Maintenance cost
(3) Expensive instrumentation cost
3.2.6.d Safety Measures
Entering manholes imposes a potential safety hazard which may
be far more serious than many people think. The following facts
should be realized:
(1) Poisonous and explosive gases, such as hydrogen
sulfide, carbon dioxide, ammonia and methane, may
accumulate in the manholes. Overexposure to these
gases can kill a person. Flame or sparks can cause
an explosion.
(2) The structure of a manhole may not be sound: the
wall bricks may fall off; the steps may be corroded.
(3) Objects can fall through the manhole opening onto
one's head; sharp objects such as broken glass, razor
blades, etc., may cut one's hands and feet; a sudden
increase in sewage flow in a large sewer may drown
and sweep a person away; one can accidentally fall
in a manhole due to various reasons.
(4) An open manhole without a guard and safety markers
around it is dangerous to both the traffic above and
the person working in the manhole.
To avoid any accident, proper safety precautions should always
be observed when entering a manhole even for only a short period
of time. Safety procedures should be developed in accordance
with the Occupational Safety and Health Act (OSHA) and the Water
Pollution Control Federation (WPCF) Manual of Practice No. 1.
Before undertaking a manhole investigation project, the project
engineer should review and summarize for his subordinates
detailed information on safety procedures.
3-52
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3«2.6.d (1) General Safety Precautions - The proper procedures
and general safety precautions of entering a manhole for
flow measurements or sewer inspection are summarized as follows:
(a) Always organize and plan the work before entering a
manhole. Avoid prolonged stays in manholes.
(b) Prior to starting the work, all persons expecting
to work in the manholes and the sewers should obtain
typhoid and tetanus innoculations .
(c) Never enter a manhole without someone attending topside
(d) Before opening a manhole, always place markers or
traffic cones around it to caution the pedestrians and
motorists. An open manhole should always be attended
by a guard and have safety markers around it.
(e) Never smoke in or around a manhole.
(f) Use proper tools to open the manhole covers. Avoid
hurting back, feet and fellow workers. The generally
used tool is a manhole hook or crowbar.
(g) Before entering a manhole, determine if there are any
explosive gases in it using an approved gas analyzer
and, with the same analyzer, determine if there is
sufficient oxygen in the manhole. Never assume that a
manhole is safe because it was safe last time entered.
Never assume that a manhole is safe because there is
no smell of gas. If it is impossible to perform
these tests or if the tests show that the explosive
gas is present or the oxygen content is not sufficient,
the manhole should be thoroughly purged with fresh air
using an air blower and continuously ventilated using
a 600 cubic feet per minute (cfm) air blower.
(h) Personal safety equipment (see Section 3.2.6.d(2))
should always be worn by the persons entering the
manholes. Wear long trousers and heavy duty work
shirts to avoid bruises and scrapes.
(i) Make sure that the manhole's brickwork is sound and
that the steps can carry a person's weight. Watch
out for slippery, broken, or loose steps, benches, etc.
(j) Never leave loose, small tools or other objects near
an open manhole. To avoid being hit in the face or
eyes by dropping objects, do not look up while in
the manhole.
3-53
-------
(k) Do not lift a person out of a manhole by his arm unless
it is an emergency; this may cause a serious shoulder
separation,
(1) Never tie a safety harness rope to a car or truck.
3.2.6.d (2) Personal Safety Equipment - The following is
a list of the safety equipment that should be worn by all
persons working in the sewer manholes at all times unless stated
otherwise. All equipment should be OSHA approved .
(a) Hard Hats - Hard hats should be worn by all persons
working in the manholes. On jobs where heavy
machinery is involved, hard hats should also be
worn while working outside of the -manholes.
(b) Safety Harnesses and Rope - Safety harnesses should
be worn by persons working in manholes. A safety
rope is attached to the harness to allow the person
on top of the manhole to quickly remove an injured
or overcome person from a manhole and to prevent
a person from being swept away by a high flow
in a large manhole or sewer.
(c) Steel-Toed Work Shoes - These shoes are designed
to protect the upper part of the foot from being hurt
by falling objects and to protect the soles from being
penetrated by sharp objects such as broken glass, razor
blades, etc. These shoes are also designed for better
foot support than ordinary shoes, being able to relieve
some of the foot fatigue.
(d) Rubber Gloves - Rubber gloves should be worn by persons
when hand contact with raw sewage or grouting chemicals
is likely.
(e) Orange Safety Vests - These vests should be worn by
persons working in or near any public road so they
will be more visible to motorists.
(f) Goggles - Safety glasses or goggles should be worn by
persons working in areas where chipped debris or
chemicals may cause eye injury.
(g) Gas Ampoules - Gas ampoules are used to detect the
presence of the following gases:
Hydrogen Sulfide
Methane
Carbon dioxide
3-54
-------
Gas ampoules should be put on before descending into
a manhole and should be periodically checked to detect
any overexposure.
3.2.6.d (3) Other Safety Equipment - Other equipment essen-
tial to the safety of the persons working in manholes and
sewers is listed in Table 3-4.
3.2.7 Physical Condition of Sewer System
3.2.1.a General
If cost-effectiveness analysis (Section 3 *0 is to be
used to determine whether the infiltration/inflow in a sewer
system is possibly excessive or nonexcessive, some field work
may also have to be conducted to assess the general physical
conditions of the sewer system.
Normally, due to time limitation, the physical condition
of a sewer system cannot be thoroughly investigated in the
infiltration/inflow analysis. Only the information essential
for the cost-effectiveness analysis needs to be collected.
Some information about the physical condition of the sewer
system may have been obtained from interviews and sewer maintenance
records; however, additional information may have to be collected
through other efforts, such as:
Plow measurement in subsystems (Section 3.2.6),
Physical inspection of key manholes and sewer lines
(Section 4.2.4),
Aboveground inspection (Section 4.2.2), and
Smoke testing or rainfall simulation (Section 4.3).
For the convenience of cost-effectiveness analysis, it may be
necessary to divide a sewer system into a number of subsystems
(Section 3.2.6.b (3)) and consider each subsystem as an in-
dependent unit for the investigation.
Sufficient work should be performed to collect the informa-
tion needed for formation of some sound bases for the
estimation of:
The work required to conduct a Sewer System
Evaluation Survey (Chapter 4);
3-55
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TABLE 3-4
SAFETY EQUIPMENT FOR MANHOLE AND SEWER INSPECT ION [5]
First-aid kit
Self-contained breathing apparatus
Bump caps
MSA wristlets with 25 ft rope
Gas mask (H2S)
Knee boots
Air blower, 3 HP, 1750 CFM
Air hose with air check
Aluminum ladder, 16 ft extension
Drop cord
Safety cones 28 in.
Isolation transformer (1-5 KVA, 50/60 HZ)
Beacon
Fire bottle (C02)
Fire extinguishers
Rain suits
3-56
-------
The portion of sewer lines requiring rehabil-
itation to remove the infiltration/inflow and
the types of rehabilitation needed (Chapter 5);
and
The types and approximate number of inflow
sources which may need correction (Chapter 5).
3.2.7'b Investigation Procedures
As a first step of investigation, flows in the key manholes
of each subsystem should be measured so that the seriousness
of infiltration/inflow problems in each subsystem can be
evaluated. Infiltration and inflow are usually measured
directly during the early morning hours (Section 3.2.6.b
(2)). Subsystems with no apparent infiltration/inflow problems,
as judged by the amounts of infiltration and inflow measured,
can be eliminated from further investigation, and they should
be excluded from the cost-effectiveness analysis.
One method which can be used to Judge the seriousness of
the infiltration problem is to compare the measured infiltra-
tion rates, in unit of gallons per day per inch diameter per
mile with the installed infiltration specification allowance
for the sewer lines under consideration. If the former is
less than the latter, it can be concluded that there is no
excessive infiltration in the sewer lines((Section 3-5).
If, after flow measurement, some subsystems are found to
exhibit infiltration/inflow problems, the investigation can
be continued by conducting a physical inspection of a few
selected key manholes in each of these subsystems. The
purpose of this inspection is to:
Understand the general physical conditions
of the manholes"and sewers;
Determine the types of infiltration/inflow
sources and amount of flow from each source,
if possible; and
Determine the type and degree of deposits
in the manholes and sewers.
To determine the types and general locations of the inflow
sources in each subsystem, some aboveground inspection,
smoke testing and/or rainfall simulation may also have to
be performed.
(Detailed procedures for these investigations are given in
Chapter 4).
3-57
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3.3 DETERMINATION OF INFILTRATION/INFLOW
3.3.1 General Considerations
The determination of infiltration/inflow is one of the most
important tasks in the Infiltration/Inflow Analysis. Without
adequate flow information, it would be difficult to conduct
either a cost-effectiveness analysis, or some other method
of analysis to determine the existence or nonexistence of
excessive infiltration/inflow in a sewer system; and, if
the flow data are incorrect, false conclusions may result.
For the convenience of cost-effectiveness analysis and for
establishing the design flow and criteria, the following
flows are usually individually determined:
Peak Infiltration
Peak Inflow
Peak Infiltration/Inflow
Total Yearly Infiltration
Total Yearly Inflow
Total Yearly Infiltration/Inflow
The peak flow rates affect the sizing of the sewers and the
pumping facilities. They also affect the sizing of the
hydraulic treatment units, including clarifiers, chlorination
units and plant pumping stations. In fact, even the biological
treatment units can be affected by the sewage flow conditions.
Sudden increases in sewage flow due to infiltration/inflow
may wash out the active biomass from the aeration units
and disturb the biological balance, resulting in reduced
treatment efficiencies. Flow increase due to infiltration/
inflow may also reduce the hydraulic detention time in the
aeration units to a value insufficient for adequate biological
reactions to take place. These situations may have to be
remedied by either designing larger aeration units or adding
a flow equalization basin, both of which increase the treatment
costs.
The total annual quantities of infiltration and inflow
should be determined for the estimation of the annual
operation costs for the pumping and treatment facilities.
Using the peak rates of infiltration and inflow for cal-
culations will overestimate the operation costs.
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The infiltration and the inflow should be individually
estimated because the characteristics and sources of these
two types of flows are quite different and their correction
and treatment methods may also differ. By separate deter-
minations, the significance of each type of flow can be
individually recognized. And, in conducting the cost-
effectiveness analysis, more realistic treatment alter-
natives can be formulated.
Often, however, it is not possible to precisely determine
the infiltration and the inflow by their literal definitions.
The infiltration determined from the dry weather high ground-
water flow data may contain some amounts of inflow which are
not related to rainfall. Similarly, the inflow determined
from the wet weather flow data may also contain some amounts
of infiltration which are induced by rainfall. Without in-
depth field investigations, it is almost impossible to
separate the two flows in either of these two cases. The
flows determined in the former case may be more aptly termed
the "dry weather infiltration/inflow"; and the latter, the
"wet weather infiltration/inflow" or the "rainfall associated
infiltration/inflow". For the purpose of determining whether
there is possibly excessive infiltration/inflow, normally these
flows can readily be used for conducting the cost-effectiveness
analysis; in either case, it is not necessary to accurately
determine the individual flows.
When sewage flow data and other pertinent information are
available, normally the infiltration and inflow can be
readily determined without additional flow measurements.
Conversely, if there are no sewage flow data and other pertinent
Information or if the data and information are insufficient
or inaccurate, a flow measurement program should be initiated
to gather sufficient information for infiltration/inflow
determination (Section 3.2).
The information which is normally needed for infiltration and
inflow determinations includes:
Sewage flow data,
Water consumption records,
Rainfall data, and
Groundwater records.
Under appropriate conditions, infiltration/inflow in a sewer
system may also be directly measured.
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3.3-2 Determination of Infiltration/Inflow Using Wastewater
Flow Data
3.3*2.a Introduction
The wastewater flow data to be used for infiltration/inflow
determination may come from either existing flow records or
records of flow measurements conducted during the study
period. The records may be either long term (i.e., one year
or more), or short term. They may be collected from either
one terminal flow measurement station, such as a sewage treat-
ment plant, or several stations in the sewer system. The
basic procedures of determining infiltration/inflow using
all such flow data are similar.
3.3.2.b Determination of Infiltration/Inflow Using Long-Term
Flow Data From One Measurement Station
Basically, the procedure includes the following steps:
(1) Determination of theoretical wastewater production
rate,
(2) Determination of total yearly infiltration/inflow,
(3) Determination of total yearly infiltration,
(4) Determination of total yearly inflow,
(5) Determination of peak infiltration,
(6) Determination o.f peak inflow, and
(7) Determination of peak infiltration/inflow.
3.3.2.b (1) Determination of Theoretical (or Base) Wastewater
Production Rate - The theoretical wastewater production rate
is the rate of wastewater flow which should be expected in a
sewer system if there is no infiltration/inflow. This rate is
usually determined from water consumption data. The frequently
used design average wastewater flow of 100 gallons per capita
per day should not be used for such purpose because the
actual per capita wastewater production rate in an area may
be different from this arbitrarily chosen figure.
For infiltration/inflow determinations, generally, it is
only necessary to derive an annual average theoretical waste-
water production rate. However, in locations where large
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fluctuations of water consumption and wastewater flow rates
occur due to seasonal change in population or other reasons,
seasonal or monthly wastewater production rates may have to
be determined.
The water consumption data used for this determination should
be of the same year, or immediate previous year, as the waste-
water flow data to be used for the determination of infiltration/
Inflow. Data from a different year can also be used if it
can be substantiated that there has been no significant change
in water consumption in the two years. This precaution is
necessary for the derivation of reasonable infiltration/inflow
rates .
If metered water use data are available, the theoretical waste-
water production can be determined by estimating the percentage
of the water which would reach the sewer system. In general,
80 to 90$ of the residential water use would reach the sewers.
Industrial plants may or may not treat and discharge their
wastewaters separately; the amounts of wastewater discharged
to the sewer system under study should be individually determined
If no metered water use data are available, the total water
consumption (or, water production) data can be used. To
determine the theoretical wastewater production from the
water consumption data, one should realize that not all the
water consumed reaches the sewer system. Portions of the
consumed water may be lost through a number of routes, such
as:
Lawn watering,
Irrigation,
Car washing,
Fire fighting, hydrant testing,
Separate treatment and disposal of wastewater by
industries,
Subsurface disposal by septic tank users, and
Leakage from water mains, and service pipes.
These losses should be properly estimated and deducted from
the total water consumption rate to derive the theoretical
wastewater production rate. In general, 60 to 80% of the water
consumption will become sewage.
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The wastewater separately treated and disposed of by industries
and the water lost to fire fighting and septic tank sub-
surface disposal areas can normally be estimated rather
accurately by reviewing related records . The water loss
from pipe leakage may be estimated by comparing pumping and
water meter records.
The water losses to lawn watering, irrigation, car washing,
etc. are usually not easy to determine. However, for most
northern states, the water losses in this category are
usually small during the winter months. Therefore, the annual
average theoretical wastewater production rate may be assumed
to be approximately equal to the average water consumption
rate for the winter months minus the water losses due to
private and industrial wastewater disposals, fire fighting,
pipe leakage, etc., if these losses are found to be significant.
In southern states, the water losses to lawn watering, irrigation,
car washing, etc., may still be significant even in winter
and they still have to be properly estimated and deducted
from the total water consumption rate to derive the theoretical
water production rate.
3.3.2.b (2) Determination of Total Yearly Infiltration/Inflow -
To determine the total yearly infiltration/inflow and the general
nature of the infiltration/inflow problem in a sewer system,
the following procedure is- recommended:
(a) Calculate the average monthly, average weekly,
or daily wastewater flows for the year(s) for which
records have been obtained.
(b) Plot these average flows against time (see Figure 3-6).
(c) Plot the theoretical wastewater production rate,
rainfall and groundwater levels on the same plot.
(d) On this plot, measure the total area above the
theoretical wastewater production curve and below
the wastewater flow curve for each one-year period.
This area would represent the total yearly Infiltra-
tion/inflow. If more than one year's total
infiltration/inflow can be determined, the highest
figure should be used.
(e) On the same plot, measure the total area, if any,
below the theoretical wastewater production curve
and above the wastewater flow curve for each one
year period. This area could represent the total
yearly exfiltratlon in the sewer system. (This
situation is not demonstrated in Figure 3-6).
(f) Compare the curves for wastewater flow, rainfall
and groundwater to reveal their inter-relationships.
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I
I
s
.3
V.
0)
».
I
I
u!
V.
I
i
Recorded Wastewater Flew
Total Infiltration/Inflow
£Theoretical Wastewater Production Rate
I Yr.
Time
Figure 3-6. Determination of Total Yearly InfiItration/Inflow
3-63
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If the plot indicates no exfiltration in the sewer system,
the total yearly infiltration/inflow may also be directly
calculated by subtracting the total yearly theoretical waste-
water production from the total yearly wastewater flow.
3.3.2.b (3) Determination of Total Yearly Infiltration -
The total yearly infiltration can be determined by the
following procedure :
(a) Prom the plot generated by the procedure outlined
in the previous section (Figure 3-6), select
several months with typical wastewater flow con-
ditions, including highest, lowest and average
flow conditions. The months in which exfiltration
is suspected to have occurred should also be
included.
(b) For each of these months, plot the daily wastewater
flow, the theoretical wastewater production rate
and the rainfall data against the time (Figure 3-7).
If groundwater data are available, they can also
be shown in the same plot.
(c) For each month, estimate the lower limit of the
wastewater flow curve corresponding to the flows
for nonrainfall days. Measure the area between
this limit and the theoretical wastewater production
rate. This area would represent the base infiltra-
tion, or exfiltration, for the month (Figure 3-7).
(d) Calculate the average of the base infiltration for
all typical flow months, adjust it with estimated
exfiltration rates, if any, and project it to a
yearly total. The latter would represent the
total yearly Infiltration.
The total yearly infiltration determined in the above manner
may also include some amounts of sustained inflow which
enter the sewers during nonrainfall days, such as cooling
water discharges, drains from springs and swampy areas,
foundation drains, etc. Therefore, the determined flow
could be more properly termed "the total yearly dry weather
infiltration/inflow."
If the sustained inflow can be determined during the study
period, it should be subtracted from the flow derived
through the above procedure to determine the "true" total
yearly infiltration. However, for the cost-effectiveness
portion of the Infiltration/Inflow Analysis, it is generally
not necessary to make this correction.
3.3.2.b (*Q Determination of Total Yearly Inflow - After
the total yearly infiltration/Inflow and total yearly
infiltration have been determined, the total yearly Inflow
may be calculated by subtracting the latter from the former.
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o
H-
c
I
0)
1
i
5
2
Recorded Wastewater Flew
Non-rainfall day
Wastewater Flow
-J\
Total Infiltration
L Theoretical Wastewater
Production Rats
Maximum InfiIt rat ion
Time
I month
Figure 3-7. Determination of Total Yearly Infiltration
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Just as the total yearly infiltration determined in the
previous section, the total yearly inflow determined in
this manner may not be purely inflow in the literal sense.
It may contain some amount of infiltration which is
induced by rainfall, and it could be more properly termed
the "wet weather infiltration/inflow" or "rainfall associated
infiltration/inflow". However, for the cost-effectiveness
portion of the Infiltration/Inflow Analysis, it is generally
not necessary, and may not be possible, to find out what
percentage of the total yearly inflow determined above is
actually rainfall-induced infiltration.
3.3.2.b (5) Determination of Peak Infiltration - Since the
groundwater levels are normally relatively constant over
periods of several days, the peak infiltration can be con-
sidered as the maximum infiltration which occurs during
the maximum groundwater period of a year. Prom the waste-
water flow curves for the months of highest flow conditions,
the peak infiltration can be readily determined (Figure 3-7).
3.3.2.b C6) Determination of Peak Inflow - The following
procedure may be used to determine the peak inflow:
(a) Carefully examine the wastewater flow and rainfall
records to select the days with highest wastewater
flows and heaviest rainfalls.
(b) For each of these days, plot the actual hourly
wastewater flow rates against time. All emergency
pumpings, bypasses and overflows should be Included
in each corresponding hourly wastewater flow curve.
The hourly rainfall data should also be shown in
the same plot (Figure 3-8).
(c) Superimpose on each of the above flow curves a
typical hourly wastewater flow curve for one of
the nearest nonrainfall days (Figure 3-8).
(d) Measure the difference in flow for each hour
between each set of two flow curves described in
Steps b and c and record the maximum difference
for each day.
(e) Compare the maximum flow differences for all the
days considered and select the peak value. This
peak value would represent the peak inflow in the
sewer system.
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i
I
Total Bypasses,
Overflows,
Emergency
Pumping, etc.
- Peak Inflow
Wastewater Flew
of Highest Flow
Wastewater Flew of Nearest
Hon-RainfaU Day
Time
I Day
Figure 3-8. Determination of Peak Inflow
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3.3.2.b (7) Determination of Peak Infiltration/Inflow -
The peak infiltration/inflow can usually be approximated
as the sum of peak Infiltration and peak inflow separately
determined above.
3.3.2.C Determination of Infiltration/Inflow Using Long-Term
Flow Data From Several Flow Measurement Stations
If the wastewater flow data is from several flow measurement
stations in a sewer system, the infiltration/inflow can be
determined separately in each subarea contributing flows to
the flow measurement station, following the procedure des-
cribed in Section 3.3.2.b.
In order to do so, the water consumption data for each sub-
area should be obtained to derive the theoretical wastewater
production rate. If it is not possible to obtain such data,
then the sewered population in each subarea should be
determined. Prom the total water consumption and the total
sewered population in the entire sewer system, the per capita
water consumption rate can be determined. Multiplying this
rate by the sewered population in each subarea, the water
consumption in each can be determined.
If the sewer system handles industrial wastewaters, the
industrial water consumption should be subtracted from the
total water consumption before the aforementioned calculations.
The industrial wastewaters in each subarea should be Individually
determined and added to the theoretical wastewater production
rate derived by using the adjusted water consumption value.
3.3.2.d Determination of Infiltration/Inflow Using Short
Term Flow Data
For the purpose of this discussion, the short term is
defined as a period (or periods) of less than one year.
Wastewater flow data covering a period (or periods) of
shorter than one year may also be used to determine the
infiltration/inflow if the period (or periods) covers all
representative groundwater and rainfall conditions, including
high, low and average conditions, in the study area. The
following are the recommended procedures:
(1) Determine the total infiltration/inflow, total
infiltration and total inflow in each period for
which wastewater flow data has been obtained,
following procedures similar to those outlined
in Section 3.3-2.b (1) through 3-3.2.b
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(2) Calculate the sum of all total infiltration deter-
mined in Step 1 and the sum of total days in the
period or periods. Determine the average daily
infiltration by dividing the total infiltration by
the total sum of days. Determine the total yearly
infiltration by multiplying this final average
daily infiltration by the total number of days in
a year.
(3) Calculate the sum of all total inflow determined
in Step 1 and the sum of all rainfalls which
occurred in the flow measurement periods . Deter-
mine the total yearly inflow by dividing the sum
of total inflows by the sum of all rainfalls which
occurred in the flow measurement periods and mul-
tiplying the result by the average yearly rainfall,
(4) Calculate the total yearly infiltration/inflow
by adding the total yearly infiltration and total
yearly inflow.
(5) Determine the peak infiltration, peak inflow and
peak infiltration/inflow following the same pro-
cedures outlined in Sections 3-3.2.b (5) through
3.3.2.b (7).
3.3.3 Determination of Infiltration/Inflow by Direct Flow
Measurement
1'3'3-a Introduction
The infiltration/inflow in a sewer system can also be
determined by measuring the infiltration and the inflow
directly. Plow measurement requirements and general pro-
cedures have been presented previously (Section 3.2.6).
The procedures for the calculation of yearly total and peak
flows are discussed in the following subsections.
3.3«3.b Determination of Total Yearly Infiltration
(1) List all measured infiltration. (The measurements
should have covered all typical groundwater con-
ditions of a year.) Adjust the flow values
by subtracting from them all wastewater flows
which might have entered the sewers during
flow measurement periods, including domestic,
commercial and industrial flows, and adding to
them all flows which might have left the sewer
system in the same periods, such as overflows,
bypasses, etc.
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(2) Calculate the total infiltration in each typical
groundwater period, assuming that the infiltration
is constant throughout the entire period and
equal to the infiltration rate measured during
the period.
(3) Calculate the sum of all total infiltration
derived. This sum would be the total yearly
infiltration.
(4) If flow measurements were conducted in more than
one station, the total yearly infiltration in
each subsystem should be determined and added
together to obtain the total yearly infiltration
for the entire system.
3.3.3.0 Determination of Total Yearly Inflow
(1) Determine the total inflow during each rainfall
period using the hydrograph on the flow recording
chart. Adjust the flow values by subtracting
from them all wastewater flows which might have
entered the sewers during flow measurement
periods, including domestic, commercial and
industrial flows, and adding to them all flows
which might have left the sewer system in the
same periods, such as overflows, bypasses,
emergency pumpings, etc.
(2) Calculate the sum of all total inflows and the
sum of rainfalls which occurred during all inflow
measurement periods.
(3) Calculate the total yearly inflow by multiplying
the sum of all total inflows derived above by
the average yearly rainfall in the study area
and then dividing it by the sum of rainfalls
which occurred during all inflow measurement
periods.
(4) If flow measurements were conducted in more than
one station, the total yearly inflow in each
subsystem should be determined and added
together to obtain the total yearly infiltra-
tion for the entire system.
3.3.3.d Determination of Total Yearly Infiltration/Inflow
The total yearly infiltration/inflow is the sum of the
total yearly infiltration and total yearly inflow determined
in the previous two subsections.
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3.3.3.e Determination of Peak Infiltration
The peak Infiltration can be approximated as the infiltra-
tion measured during the highest groundwater period of a
year, with proper adjustments for wastewater flows entering
the sewer system and overflows, bypasses, etc. leaving the
system during the flow measurement period.
3*3«3.f Determination of Peak Inflow
The peak inflow can be assumed to be the maximum instantaneous
inflow recorded during flow measurement periods. Adjust-
ments should also be made for all wastewater flows entering
the sewer system and overflows, bypasses, emergency pumpings,
etc., leaving the system during the flow measurement period.
3«3«3.g Determination of Peak Infiltration/Inflow
The peak infiltration/inflow can be approximated as the
sum of peak infiltration and peak inflow determined in
the previous two subsections.
3.3.4 Adjustment for Peak Inflow
The peak inflow determined by the above procedures should be
adjusted for the desired design period or design condition.
The design rainfall frequency normally used for designing storm
sewers in the area under study should be used for such adjust-
ment. The ratio of the design and observed rainfall intensities
is used to adjust the peak inflow.
3.n COST-EFFECTIVENESS ANALYSIS
3.^.1 Introduction
For the purpose of determining whether the infiltration/inflow
in a sewer system is possibly excessive or nonexcessive, a
cost-effectiveness analysis may be conducted. Infiltration/
inflow is defined as being possibly excessive if the total
costs for the correction of infiltration/inflow conditions
are less than the total costs for transportation and treat-
ment of these flows. The cost-effectiveness analysis, however,
is not the only method which may be used; other methods may
also serve the same purpose (Section 3-5)
The basic information which is needed for the cost-effective-
ness analysis includes:
Average and peak wastewater flows (including
domestic, commercial and industrial flows)
for the design year of treatment facilities;
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Peak and total yearly Infiltration and
inflow in the entire sewer system and/or
in the subsystems;
General physical conditions of sewer
system; and
Capacities of existing sewers, pumping
stations and treatment facilities.
The design wastewater flows should be developed on the basis
of population and water consumption projections as well as
infiltration allowances for new sewers, as ordinarily practiced
in the planning of treatment facilities. In addition, the
bypasses and overflows in the sewer system should also be
quantitatively determined.
The peak and total yearly infiltration and inflow may be
determined by one of the methods presented in Section 3.3.
The physical conditions of the sewer system can be in-
vestigated following the procedures discussed in Section
3.2.7-
Information about the capacities of the existing sewers,
pumping stations and treatment facilities is normally avail-
able from other phases of study in facilities planning.
Once the above information has been gathered, the costs
for transportation and treatment of wastewater (including
infiltration/inflow) and for correcting the infiltration/
inflow conditions can be estimated. This is followed by an
analysis of the cost data to determine the existence or
nonexistence of excessive infiltration/inflow. Detailed pro-
cedures for cost estimations and analysis are presented in the
following subsections.
The cost-effectiveness analysis should be conducted in accordance
with the "Cost-Effectiveness Analysis Guidelines" published
in the Federal Register 40 CPR 35. [6]
In the following discussions, the infiltration and Inflow
are considered together for cost-effectiveness analysis;
but, in some cases, engineers may find it more convenient
to conduct separate analyses for infiltration and inflow,
following the same procedures.
3.11.2 Cost Estimation
3. 4. 2. a Introduction
For cost-effectiveness analysis, two types of costs are
developed:
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Costs for correction of infiltration/
inflow conditions; and
Costs for transportation and treatment of
vrastewater (including infiltration/
inflow).
For the convenience of cost comparison, all costs should be
converted to their present worth or average annual equivalent
values. The facility planning period and the most current
interest rate (currently 6 1/8%') should be used for the con-
version. (The interest rate is published in the Federal
Register annually by the Water Resources Council).
3.4.2.b Sources of Cost Information
Cost information for the correction of infiltration/inflow
conditions usually can be obtained from sewer inspection
and rehabilitation companies. (Some cost data are presented
in Chapter 6.)
Cost information for the construction of sewers and sewage
treatment facilities can be obtained from contractors, equip-
ment manufacturers, as-bid construction estimates and
various cost estimation publications.
Operation and maintenance costs can be determined by
estimating the operation and maintenance needs in each type
and size of treatment facility or sewer system and their
associated costs.
3.4.2.C Cost Estimation for Correction of Infiltration/Inflow
Conditions
3.fr.2.e (1) Introduction - For the correction of infiltration/
inflow conditions, two major tasks have to be conducted:
Sewer System Evaluation Survey
Sewer System Rehabilitation
The costs required for conducting both tasks should be estimated
3.4.2.C (2) Costs for Sewer System Evaluation Survey - The
Sewer System Evaluation Survey is needed to locate sources
of infiltration/inflow, quantify the flows from each source
and determine the most cost-effective way of correcting the
infiltration/inflow conditions. The Evaluation Survey can
be accomplished through the following functions:
Physical survey,
Rainfall simulation,
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Preparatory cleaning,
Internal inspection, and
Preparation of report.
(Details of these functions are discussed in Chapter 4.)
Not all of these functions, nor all of the tasks within each
function, need to be included in each Evaluation Survey. Only
those functions judged to be necessary should be included in
the cost estimates.
Before the costs can be derived, the scope of work must be
first estimated. Data collected during the study can be
used to estimate the amount of work needed. The following
are the suggested procedures:
(a) Determine the number of subsystems to b^jlncluded.
If the cost-effectiveness analysis is to be conducted
using Methods 1 and 2 in Section 3.4,3, the entire
sewer system is considered as a single study unit.
If the analysis is to be conducted using Method 3,
the system should be divided into several subsystems
and the infiltration/inflow condition in each sub-
system studied individually.
The subsystems to be included in the cost-effectiveness
analysis are those which are suspected of having
serious infiltration/inflow problems. One of the
methods which can be used to single out these areas
is to determine the infiltration and inflow (through
either direct flow measurements or analysis of
wastewater flow data; see Section 3.3) in each
designated subsystem, and compare the flow rates
with some reasonable criteria.
To determine whether there is an Infiltration
problem in a subsystem, the infiltration rate,
in gallons per day per inch diameter per
mile pipe, can be compared with the infiltration
specification allowance for the pipe when in-
stalled. If the former is greater than the latter,
it can be concluded that there is a possible infil-
tration problem in the subsystem and the subsystem
may be included in the cost-effectiveness analysis
insofar as infiltration is concerned. Some
Regulatory Agencies utilize a rule of thumb
indicating infiltration rates of 1,000 gallons
per day per inch diameter per mile of pipe or
le-ss as nonexcessive.
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To determine whether there is an' inflow problem
in a subsystem, while there is no criterion as
in the infiltration case, the flow rates can
still be used to formulate a judgment. Thus,
for example, if the quantity of inflow is very
small, say a few thousand gallons per day, there
is probably no Inflow problem in the subsystem
at all. The apparent value of inflow may be
caused by the rainwater entering the sewers through
infiltration sources, such as pipe cracks, etc.,
due to the increase in groundwater level during
the rain period, or it may be simply caused by
the flow measurement instrument limitations or
calculation omissions/or assumptions.
If, after a careful analysis, one is confident
that there is no inflow problem in a subsystem,
the subsystem should be excluded from the
cost-effectiveness analysis as far as inflow
is concerned.
All subsystems found to have either infiltration
or inflow problems, or both, should be included
in the analysis. For subsystems with only infil-
tration problems, only the costs for correcting
infiltration conditions should be included in the
cost-effectiveness analysis. Similarly, for sub-
systems with only inflow problems, only the costs
for correcting inflow conditions should be in-
cluded. When both infiltration and inflow are
problems, the costs for correcting both conditions
should be included.
In the subsequent estimation procedures, each
subsystem selected for analysis should be con-
sidered as a separate study unit.
(b) Estimate the amount of work required for Physical
Survey.
The following tasks may have to be conducted in
Physical Survey:
Aboveground inspection,
Plow monitoring, and
Manhole and sewer inspection.
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A plan of action for performing these tasks should
be first prepared. The manpower and equipment
requirements can then be estimated.
All manholes in a system or subsystem may not need
to be entered, as the flow monitoring program may
eliminate some subareas from further investigation.
The total number of manholes that need to be inspected
should be properly estimated. Results from the study
of the physical condition of the sewer system (Section
3.2.7) can be especially helpful for such estimation.
After a number of randomly selected manholes and
sewer lines have been inspected, the general condition
of the sewer system could be estimated by proportional
projection.
(c) Estimate the amount of work required for rainfall
simulation.
Both infiltration and Inflow sources can be located
by rainfall simulation. The simulation can be
accomplished by one or a combination of the follow-
ing techniques:
Smoke testing,
Dyed water testing, and
Water flooding test.
The lengths of pipes and trenches, total number of
houses and other possible inflow sources in a system
or subsystem which need to be investigated by each
rainfall simulation technique should be estimated.
Results from interviews (Section 3.2.1),
map study (Section 3.2.2.b), study of physical
condition and other information obtained during
the study can all be utilized to make the estimate.
(d) Estimate the length of sewer pipes which need to be
cleaned and internally inspected.
Results from the study of the physical condition of
the sewer system (Section 3.2.7) and the exist-
ing sewer system maintenance records should have
provided some information for such estimation.
Not all the sewers in a system or subsystem may need
to be cleaned or inspected, or both.
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(e) Estimate the manhours required for the preparation
of an Evaluation Survey Report.
This can tie done based on experience obtained from
previous jobs of a similar nature. The manhour
requirement would depend on the size of the system
and the magnitude of the infiltration/inflow pro-
blem.
After the scope of work has been established, the unit cost
for conducting each task can be obtained from proper sources
(Section 3.^.2.b), and the total costs can be derived. (See
Table 3-5-)
3.4.2.C (3) Costs for Sewer System Rehabilitation - The
sewer system rehabilitation is needed to remove the infil-
tration/inflow sources from the sewer system. The work
involves the repair and/or replacement of sewers and man-
holes and the disconnection or plugging of inflow sources.
(Details of the rehabilitation techniques are presented in
Chapter 5)
Again, for cost estimation, the required rehabilitation work
should be first estimated. All data obtained during the study
should be synthesized and analyzed to provide a basis for such
estimation. (See Table 3-6.)
3.*4.2.d Cost Estimation for Transportation and Treatment of
Wastewa_t_er
3.4.2.d (1) General Considerations - Cost estimates for
transportation and treatment should be based on some preliminary
designs. For all designs, only the most cost-effective and
technically and environmentally feasible alternatives should
be used. In addition, the following items should be considered:
(a) Bypasses and overflows; In separated sanitary
sewer systems, bypass and overflow may or may not be
allowed depending on the Reliability Class of the
facility and the conditions stated in the NPDES permit.
All such flows in the sewer system should be con-
sidered and included in the derivation of the total
design flows.
In combined sewer systems, the requirements for
the control or treatment of bypass or overflow
are stated in the NPDES permit. If the permit
does not require control or treatment of bypasses
or overflows, the bypasses or overflows attributable
to the combined sewer inflow should not be included
in the total design flows. On the other hand,
if the permit requires control or treatment of
combined sewer bypasses or overflows, these flows
should be included in the total design flows.
3-77
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TABLE 3-5
WORK SHEET FOR QUANTITY TAKE-OFF AND
COST ESTIMATION - SEWER SYSTEM EVALUATION SURVEY
Subsystem No.
Page
Function
1. PHYSICAL SURVEY
Above Ground Inspection
Flow Monitoring
Manhole & Sewer Inspection
Subtotal
2. RAINFALL SIMULATION
Smoke Testing
Dyed Water Testing
Water Flooding Test
Subtotal
3. PHYSICAL SURVEY REPORT
4. PREPARATORY CLEANING
6-inch pipe
8-inch pipe
10 inch pipe
12-inch pipe
15-inch pipe
18-inch pipe
21-inch pipe
24-inch pipe
27-inch pipe
30 inch pipe
36-inch pipe & up
Subtotal
5. INTERNAL INSPECTION
6-inch pipe
8-inch pipe
10-inch pipe
12-inch pipe
15-inch pipe
18-inch pipe
21-inch pipe
24-inch pipe
27-inch j>ipe
30-inch pipe
36-inch pipe & up
Subtotal
6. ENGINEERING SERVICE &
REPORT
Estimated Quantity
Quantity
Unit
Manhour
Manhour
ft (m)
ft (m)
ft (m)
ft (m)
Manhour
ft (m)
ft- (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft fm)
ft (m)
ft (m)
ft Cm)
ft (m)
ft (m)
ft (m)
ft (m)
ft Cm)
ft (m)
ft (m)
ft (m)
ft (m)
Manhour
Estimated Cost
Unit Cost,
$/Unit
Total Costs,
$
TOTAL EVALUATION SURVEY COST
3-78
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TABLE 3-6
WORK SHEET FOR QUANTITY TAKE-OFF AND
COST ESTIMATION - SEWER SYSTEM REHABILITATION
Subsystem No.
Page_
Function
I. CORRECTION OF INFILTRATION
CONDITIONS
Sewer Replacement
6-inch pipe
8-inch pipe
10-inch pipe
12- inch pipe
15-inch pipe
16-inch pipe
21-inch pipe
24- inch pipe
27-inch pipe
30-inch pipe
36-inch pipe
48-inch pipe & up
Subtotal
Pipe Lining
6-inch pipe
8-inch pipe
10- inch pipe
12-inch pipe
15-inch pipe
18-inch pipe
21-inch pipe
24-inch pipe
27-inch pipe
30-inch pipe
36- inch pipe
48-inch pipe & up
Subtotal
Chemical Grouting
6-inch pipe
8-inch pipe
10-inch pipe
12-inch pipe
15-inch pipe
18- inch pipe
21-inch pipe
24-inch pipe
27-inch pipe
30- inch pipe
36-inch pipe
48-inch pipe & up
Estimated Quantity
Quantity
Unit
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft cm)
ft (m)
ft (m;
ft (m)
ft (m;
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft (m)
ft u;
Estimated Cost
Unit Cost,
$/Unit
Subtotal
Total Cost
$
3-79
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TABLE 3-6 (Continued)
WORK SHEET FOR QUANTITY TAKE-OFF AND
COST ESTIMATION - SEWER SYSTEM REHABILITATION
Subsystem No.
Page_
Function
Manhole Wet Well
Replacement
Manhole Wet Well
Repair
Faculty Taps Repair
House Service Pipe
Replacement
House Service Pipe
Repair
Total Cost for Infiltration
Correction
II. CORRECTION OF INFLOW
CONDITIONS
Low-lying Manhole Raising
Manhole Cover Replacement
Cross Connection Plugging
Roof Leader Drain
Di s conne c t ion
Foundation Drain
Disconnection
Cellar Drain
Disconnection
Yard Drain Disconnection
Area Drain Disconnection
Cooling Water Discharge
Disconnection
Drains from Springs and/
or Swampv Areas Plugging
Total Cost for Inflow
Corrections
III. ENGINEERING SERVICES
IV. LEGAL FISCAL AND
ADMINISTRATIVE SERVICES
V. CONTINGENCY
VI. INTEREST DURING
CONSTRUCTION
VII. SALVAGE VALUE
Estimated Quantity
Quantity
Unit
each
each
each
each
each
each
each
each
each
each
each
each
each
each
each
Lump Sum
Lump Sum
Lump Sum
Lump Sum
Lump Sum
TOTAL REHABILITATION COST
Estimated Cost
Unit Cost,
$/Unit
Total Cost
$
-. . ... _
3-80
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(b) Capacities of existing facilities: The capacities
of the existing sewers, pumping units and treat-
ment facilities should be evaluated to determine
whether additional construction of these facilities
will be needed in the design year to handle the
anticipated wastewater flows and the infiltration/
inflow remaining in the system.
Special attention should be directed to the areas
where there are known problems such as manhole
overflow, pipe surcharge, basement sewage backup,
etc. Relief sewers, pipe realignment, holding
ponds, etc., may be considered among other trans-
portation and treatment alternatives to alleviate
these problems.
(c) Design Plows: The flows which are needed for the
design of transportation and treatment facilities
are:
Average and peak normal wastewater flows in
the design year,
Peak infiltration,
Peak inflow, and
Peak infiltration/inflow.
The sum of the peak infiltration, which normally
sustains for a period of days, and the average
normal wastewater flow is used as the design
average flow, and, the sum of peak infiltration/
inflow and peak normal wastewater flow can be used
as the design peak flow for the sizing of sewers,
pumping and treatment facilities. Due to the
instantaneous nature of peak inflow, in many
cases, it may be more economical to build a flow
equalization basin or basins than to design large
transportation and treatment facilities.
The estimation of operation and maintenance costs
for the transportation and treatment facilities
should be based on average;rather than peak,
flows. Thus, the total yearly infiltration and
inflow, along with the average wastewater flows
from domestic, commercial and industrial sources,
should be used for such estimation.
3-81
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(d) Pollutant loadings: The BOD and suspended solids
loadings and other pollutants in the infiltration
and the inflow are usually low. Their impacts
on the secondary treatment processes and the
sludge handling processes may not be significant.
However, direct inflows entering manholes from
perforated manhole covers and defective manhole
structures may contain high pollutant loadings,
characteristic of those in urban runoffs. The
actual pollutant loadings in the infiltration and
the inflow can be determined only by field measure-
ments. Measuring and analyzing the pollutant
loadings as well as flows in the sewer system
under different groundwater and weather conditions
may also reveal the actual loadings contributed
from the infiltration and the inflow.
The treatment requirement for each type of
pollutant is determined by the effluent limitations
set in the NPDES permit(s).
3.4.2.d (2) Cost Estimates - To develop the costs for the
transportation and treatment facilities, the reader is
referred to the "Guidance for Preparing a Facility Plan"
published by EPA in May 1975. £73
Generally, both capital costs and operation and maintenance
costs should be included. The capital costs should include
the following items, when appropriate:
Estimated contract construction costs of all
transportation and treatment facilities,
Costs for engineering services,
Costs for legal and administrative services,
Costs of land,
Startup costs,
Interest during construction, and
Contingency allowances.
In addition, the salvage value and revenue produced, if any,
should also be included.
3-82
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3.^.3 Methods of Analysis
The cost-effectiveness analysis can be conducted using one
of the following methods.
3.4.3.a Method 1
If, after proper study, the amount of infiltration/inflow
removable by corrective action and the required evaluation
and rehabilitation work can be determined, a simple cost
comparison between the cost required to correct the infiltration/
inflow conditions and that required to transport and treat the
remaining flow in the system is sufficient to determine whether
the infiltration/inflow in the system is possibly excessive.
This method normally applies to very small sewer systems or
subsystems where estimations of flow and correction work can
be made with confidence.
3.4.3.b Method 2
The second method consists of estimating the costs required
to remove different percentages of infiltration/inflow from
the system and those required to transport and treat the
remaining flows. From these costs', two cost curves are plotted,
and'a total cost curve can be generated by adding the costs on
the two plotted curves. (See Figures 3-9 and 3-10.) Examine
the total cost curve to locate a minimum cost point. If this
cost is less than the total cost corresponding to 0% infiltration/
inflow reduction, it can be concluded that possibly excessive
infiltration/inflow exists in the system, and the optimum
percentage of infiltration/inflow which should be removed is
the value corresponding to the minimum total cost point. (Figure
3-9.) From this, the infiltration/inflow which should be in-
cluded in the design of treatment facilities can also be deter-
mined.
Conversely, if the total cost corresponding to 0$ infiltration/
Inflow reduction is the minimum cost point on the curve, it
can be concluded that the infiltration/inflow is not excessive.
(Figure 3-10.) All infiltration/inflow should be included in
facility design.
3.4.3.Q Method 3
The third method is more complex. It involves the division
of a system into several subsystems. After proper study, all
subsystems suspected of having infiltration/inflow problems
are selected for the cost-effectiveness analysis. For each
selected subsystem, the following are determined:
3-83
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o
$
v. *-
S'S
M/n/mum
Total Cost
Point
o
Total Cost Curve
Transportation
8 Treatment
Cost Curve
Correction
Cost Curve
/
r
Optimum
I/I to be
too
% Infiltration/Inflow Reduction
Figure 3-9 Cost-Effectiveness Ana lysis-Possibly Excessive
Infiltration/Inflow (Method 2)
3-84
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Total Cost Curve
Minimum Total
Cost Point
Transportation
81 Treatment
Cost Curve
Correction Cost
Curve
% Infiltration/Inflow Reduction
Figure 3-/0 Cost-Effectiveness Analysis-Nonexcessive
Infiltration/Inflow (Method 2)
3-85
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(1) Infiltration/inflow;
(2) Amount of infiltration/Inflow removable by
corrective action;
(3) Corrective cost; and
(4) Transportation and treatment cost.
The procedure for the analysis is shown below. A numerical
example is contained in Tables 3-7 and 3-8 and Figure 3-13.
(a) List, in a table, the titles of all subsystems
and the total peak infiltration/inflow removable
and total cost required for the correction of
infiltration/inflow conditions (the correction cost)
for each subsystem.
(b) For each subsystem, calculate the correction cost
required to remove a unit quantity (say, 1,000
gallons/day) of infiltration/inflow by dividing
the total correction cost by the total infiltration/
inflow.
(c) Assign a priority value to each subsystem accord-
ing to the increasing unit correction costs.
(d) In another table, rearrange the subsystems
according to the ascending priority values assigned
in Step c. List the titles of the subsystems
and the peak infiltration/inflow removable and
correction cost for each subsystem. Also list,
corresponding to each subsystem, the total transporta-
tion and treatment cost which would be needed if
the peak infiltration/inflow in the subsystem and
in all subsystems listed prior to the subsystem
are removed from the total flow in the entire system
(including both normal wastewater flow and peak
infiltration/inflow).
(e) Determine the accumulative peak infiltration/inflow
removable, the peak infiltration/inflow remaining and
the accumulative correction costs .
(f) Calculate, corresponding to each subsystem, the
total flow which would remain in the entire sewer
system if the peak infiltration/inflow in the
subsystem and in all subsystems listed prior to
the subsystem were removed by corrective measures.
3-86
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(g) Determine the sum of the accumulative correction
cost and the total transportation and treatment
costs, corresponding to each subsystem, to derive
the total cost.
(h) Plot the total cost, corresponding to each sub-
system, against the total flow remaining. The
total cost for transporting and treating the
total flow without infiltration/inflow removal
should also be included. Draw a curve passing all
the data points. (Figures 3-11 and 3-12.)
(i) Locate on the cost curve a point corresponding to
the minimum total cost. If the cost corresponding
to this point is less than the cost required to
transport and treat the total flow without infil-
tration/inflow removal, it can be concluded that
possibly excessive infiltration/inflow exists in
the sewer system (Figure 3-11). The flow corres-
ponding to the minimum cost point is the flow which
would remain in the system after an optimal amount
of infiltration/inflow is removed from the system.
Refer to the table discussed in Step d; all sub-
systems with total flow remaining greater than the
flow corresponding to the minimum cost point should
be considered for Sewer System Evaluation Survey
and Rehabilitation to correct the infiltration/
inflow conditions.
If all costs on the cost curve are found to be
greater than the cost required to transport and
treat the total flow without infiltration/inflow
removal, it can be concluded that the infiltration/
inflow in the system is nonexcessive (Figure 3-12).
3.5 ESTABLISHMENT OF POSSIBLY EXCESSIVE OR NONEXCESSIVE
INFILTRATION/INFLOW
To determine whether infiltration/inflow is nonexcessive or
possibly excessive in a sewer system, a cost-effectiveness
analysis is usually conducted (Section 3.H). However,
other methods may also be used, for example:
Example: If the sewers in a system were installed according
to some specifications which limit the maximum infiltration
rate to certain gallons per day per inch diameter per mile
of sewer and the actual infiltration/inflow rate in the
system is found to be less than that limit, then it can be
concluded that the infiltration/inflow in the system is
nonexcessive.
3-8?
-------
I
0)
TOTAL COST TO
TRANSPORT AND
TREAT ALL
INFILTRATION/INFLOW
AND NORMAL WASTE
WATER FLOW _
TOTAL COST CURVE
V MINI MUM TOTAL
\ PROJECT COST
TRANSPORTATION &
TREATMENT COST
CURVE
CORRECTION
COST CURVE
TOTAL FLOW INCLUDING
ALL INFILTRATION/
INFLOW
TOTAL FLOW EXCLUDING
ALL INFILTRATION/INFLOW
j r~ OPTIMAL DESIGN FLOW
Total Flow
Figure 3-11 Cost -Effectiveness Analysis - Possibly
Excessive Infiltration/Inflow (Method 3)
-------
&
2
I
O
5 -a
SS
Uj
TOTAL COST TO TRANSPORT
AND TREAT ALL INFILTRATION/
INFLOW AND NORMAL WASTEWATER
FLOWS = MINIMUM TOTAL
PROJECT COST
TOTAL COST CURVE
CORRECTION COST CURVE
TRANSPORTATION 4
TREATMENT COST CURVE
TOTAL FLOW
INCLUDING
ALL INFILTRATION/
INFLOW = OPTIMAL
DESIGN FLOW
TOTAL FLOW EXCLUDING ALL
INFILTRATION/INFLOW
Total Flow
Figure 3-12 Cost-Effectiveness Analysis-Nonexcessive
Infiltration/Inflow (Method 3)
3-89
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TABLE 3-7
DETERMINATION OF PRIORITY FOR
EVALUATION SURVEY - AN EXAMPLE
Priority
Total Peak for
Total Peak I/I Removable*, Correction Unit Correction Evaluation
Subsystem I/1, mgd mgd Cost. $ Cost, $/lfOOO gpd Survey
I
II
III
IV
V
VI
VII
VIII
0.88
0.44
0.50
0.76
0.90
1.40
0.64
0.36
0.44
0.22
0.25
0.38
0.45
0.70
0.32
0.18
20,000
24,000
180,000
70,000
105,000
152, ,000
49,000
18,000
45
109
720
184
233
217
153
100
1
3
8
5
7
6
4
2
5.88 2.94 618,000
*For the purpose of this example it is assumed that 50% of the I/I can be
removed from each subsystem.
3-90
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TABLE 3-8
DETERMINATION OF COSTS - AN EXAMPLE
Subsystem
Total
Peak I/I
Removable,
mgd
Accumulat ive
Total Peak
I/ I Removable,
mgd
Total
Peak I/I i
Remaining ,
mgd
Total
Flow _
Remaining ,
mgd
Correction
Cost, $
Accumulative
Correction
Cost, $
Transportation
& Treatment
Cost,3 $
Total
Cost,
$
UJ
l
VD
I-1
I
VIII
II
VII
IV
VI
V
III
0.44
0.18
0.22
0.32
0.38
0.70
0.45
0.25
0.44
0.62
0.84
1.16
1.54
2.24
2.69
2.94
5.88
8.88
5,030,000
5,030,000
5.44
5.26
5.04
4.72
4.34
3.64
3.19
2.94
8.44
8.26
8.04
7.72
7.34
6.64
6.19
5.94
20,000
18,000
24,000
49,000
70,000
152,000
105,000
180,000
20,000
38,000
62,000
111,000
181,000
333,000
438,000
618,000
4,961,000
4,940,000
4,900,000
4,860,000
4,830,000
4,700,000
4,630,000
4,600,000
4,981,000
4,978,000
4,962,000
4,971,000
5,011,000
5,033,000
5,068,000
5,218,000
"'"Total peak I/1 in system is 5.88 mgd.
r\
Average wastewater production (3.0 mgd) plus total peak I/I remaining.
Present worth of all costs.
-------
S2
o
5.94
MINIMUM COST POINT
TOTAL COST CURVE
TRANSPORTATION &
TREATMENT COST CURVE
CORRECTION
COST CURVE
)PTIMAL
DESIGN FLOW
mgd
8.88
Flow, mgd
Figure 3-/3 Deferm/nof ion of Opt//no/
Design Flow -An Example
3-92
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If the infiltration rate alone is found to be less than that
limit, then it can be concluded that the infiltration in the
system is nonexcessive. To determine whether-inflow is also
nonexcessive, other methods, such as cost-effectiveness
analysis, may still have to be used.
If the infiltration rate in any subsystem is found to be
less than that limit, it can be concluded that the infiltra-
tion in that particular subsystem is nonexcessive. All sub-
systems which show nonexcessive infiltration should be
eliminated from further infiltration study. If eventually
a cost-effectiveness analysis is to be conducted, the
survey and rehabilitation costs for the sewers in such
subsystems should not be included except for those costs
related to inflow study.
The rationale behind the above determinations is that if
the sewers were installed according to a certain specifica-
tion, the material and workmanship used for the construction
were designed to meet that specification and one should not
expect to obtain a sewer better than that. If more is
expected, the entire system may have to be rehabilitated.
There are instances, however, where sewers were installed with
opened joints to serve as area drains; these sewers could be
rehabilitated to attain a tighter sewer system than when
originally installed.
3.6 SEWER SYSTEM EVALUATION SURVEY PROGRAM RECOMMENDATION
Having established that infiltration/inflow is possibly excessive in
a sewer system, a recommended program that will culminate in
the solution of the problem should be presented. For conduct-
ing a systematic examination of the sewer system to determine
the specific location, flow rate and rehabilitation costs of
the infiltration/inflow problem, the following five phases
of work are usually recommended:
Physical survey
Rainfall simulation
Preparatory cleaning
Internal Inspection
Preparation of report
3-93
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Because of the different nature of the problems in the sewer
systems, the required work may vary among projects. The sequence
of carrying out these five phases of work may also vary among
projects. All five phases of work need not be included in the
program if not necessary. The purpose of the Evaluation Survey
is to continually redefine the problem areas of the sewer
systems. For each phase of work recommended, the following
details should usually be included:
The specific areas to be studied;
The functions to be performed and their
purposes;
The recommended method or methods for perform-
ing each function;
The manpower, materials and equipment and the
time duration required to perform each
function; and
The costs required to complete each phase of
work.
Finally, a project schedule should be set up for the performance
of all the recommended work within the allowable time limit.
3.6.1 Program Recommendation
An outline of all the possible functions which may be included
in each phase of the Sewer System Evaluation Survey is presented
in the following subsections. These functions should be evaluated
with discretion. Only those functions found necessary should
be included in the recommended evaluation survey program.
The method(s) to be recommended for performing each of the
required functions- should be determined by the conditions
of each individual system. (See Chapter 4 for more details,)
3.6.1.a Physical Survey
The purpose of the physical survey is to determine the flow
characteristics, groundwater levels, physical conditions of
the sewer system and the possible infiltration and inflow
sources, and to reduce the study areas for cleaning and internal
inspection. The functions that may be included in the physical
survey are:
Flow monitoring in key manholes to isolate
problem areas;
3-94
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Groundwater monitoring at key manholes or
along routes of problem sewers;
Physical inspection of the manholes and
the sewers;
Searching for possible cross-connections
between storm sewers and sanitary sewers;
Searching for low manholes;
House to house search for possible inflow
sources such as roof leader, cellar, yard
and area drains, foundation drains, sump
pump connections, cooling water discharges,
etc; and
Searching for inflow sources from springs
and swampy areas.
The areas to be surveyed can be initially determined through a
careful study of the data collected during the I/I Analysis.
Areas with no obvious infiltration/inflow problems should not
be recommended for survey. If the' cost-effectiveness analysis
is conducted for each individual subsystem, the subsystems with
nonexcessive infiltration/inflow should also be excluded from
further investigation.
3.6.1.b Rainfall Simulation
The rainfall simulation is used to identify sections of sewer
lines which have infiltration/inflow conditions during periods
of surface runoff. The following conditions can be identified
by rainfall simulation:
Cross-connections between storm sewers and
sanitary sewers, or between catch basins
and sanitary sewers;
Inflow sources, such as streams, open ditches,
ponding areas, etc., which contribute clean
water to the sanitary sewers during dry or wet
weather conditions;
Inflow sources in residential and commercial
areas such as roof leader, cellar, yard and
area drains, foundation drains, cooling water
discharges, etc; and
Low-lying manholes which receive surface
runoffs during storm periods.
3-95
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The locations where rainfall simulation studies are to be
conducted can be preliminarily determined by reviewing the
results from the interviews, map analysis and field observa-
tions. Results from the physical survey may further help
pinpoint these locations.
The rainfall simulation techniques usually applied are:
Smoke testing
Dyed water flooding
Water flooding
3.6.1.c Preparatory Cleaning
The preparatory cleaning is needed to prepare the sewer lines
for unobstructed internal inspection. It is usually recommended
for the sections of the sewer lines which are to be internally
inspected unless studies show that the lines are sufficiently
clean for the inspection technique(s) to be recommended.
Sewers can be cleaned by a number of methods, depending on
the type and degree of deposition and the sizes of the pipes.
The degree of cleaning required can be preliminarily estimated
by reviewing the results from interviews and from observations
in key manholes during flow measurements. Sewers in. municipalities
having good sewer maintenance programs usually require less
cleaning than those in municipalities having poor maintenance
programs.
3.6.1.d Internal Inspection
The internal inspection is performed to determine the specific
location, condition and estimated flow rate of each source of
infiltration/inflow defined in the selected sewer sections.
Inspection by television is usually recommendedj however,
other available methods can also be utilized, if suitable.
Internal inspection should be performed during periods of
maximum groundwater levels. To simulate rainfall conditions,
storm sewer sections, stream sections, ditch sections, and
ponding areas related to infiltration/inflow conditions should
be flooded during the inspection. Alternatively, the inspection
can be conducted during heavy rainfall periods. In some systems,
because of the area where they are located, it is essential to
conduct internal inspection during rains.
3-96
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3.6.1.e Preparation of Report
After the previous four phases of the Sewer System Evaluation
Survey are completed, a report should be prepared to summarize
all the findings. The following information is usually in-
cluded in the report:
A complete documentation of all the informa-
tion gathered during the evaluation survey;
A justification for each sewer section
cleaned and internally inspected;
A cost-effectiveness analysis to determine
the sewer sections which can be cost-
effectively rehabilitated to remove the
infiltration/inflow;
A proposed rehabilitation program to
eliminate all defined excessive infiltra-
tion/inflow.
3.6.2 Cost Estimates
The costs required to accomplish each phase of the work
described above should be estimated. For cost estimation,
the functions to be performed during each phase should be
first listed. Difficulty factors involved and manpower
and equipment required for each function can be evaluated
on the basis of available information. The cost related to
each function should be determined.
3.6.3 Project Schedule
To accomplish all the work required for the Sewer System
Evaluation Survey in an allotted time limit with lowest
possible costs, a realistic project schedule should be estab-
lished. The time limit is determined by the overall schedule
outlined in the facilities plans, which should meet the schedule
stated in the discharge permit issued by the regulatory agencies.
In some instances, however, the required work may only be
realistically achievable by a long-range program. This type 01
situation should be discussed with State and EPA Officials
and a workable solution developed. In order to obtain meaningful
information, the studies should always be conducted unaer
most favorable ground water and weather conditions. The
sequence of carrying out the different phases of the work
is determined by the conditions in the sewer systems and
the availability of manpower and equipment for the specific
Job.
3-97
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CHAPTER 4
SEWER SYSTEM EVALUATION SURVEY
4.1 INTRODUCTION
The Sewer System Evaluation Survey is a systematic examina-
tion of the sewer system to locate all the infiltration and
inflow sources which were previously determined to be possibly
excessive, determine the flow rate from each source and
estimate the costs required for the rehabilitation of the
system. The following tasks are usually included in the
evaluation survey:
Physical Survey
Rainfall Simulation
Preparatory Cleaning
Internal Inspection
Survey Report
The tasks are not necessarily performed in the order in which
they are presented.
The physical survey is performed to isolate the problem
areas and to determine the general physical conditions of the
sewer sections selected for further study. The rainfall
simulation is conducted to locate the rainfall associated
infiltration/inflow sources in the sewer system. Preparatory
cleaning is needed to prepare the sewer lines for internal
inspection, which determines the infiltration/inflow sources,
the flow rate from each source and the structural defects in
the pipes. The survey report summarizes the results obtained
during the survey and presents a cost -effectiveness analysis
which determines the portion of the infiltration/inflow
sources which can be economically corrected.
To perform all these tasks in as short a period of time as
possible, proper planning is essential. The physical survey
is usually performed during the high groundwater period, so
is the internal inspection. However, the physical survey is
normally performed before the internal inspection. In order
to complete both tasks in the same high groundwater season,
the physical survey, rainfall simulation, if required, and
preparatory cleaning should be conducted as rapidly as
possible. To shorten the total study period, the rainfall
simulation can be performed concurrently with the physical
survey, the preparatory cleaning or internal inspection.
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The preparatory cleaning and internal inspection normally
demand much more time than other tasks. However, all sewer
systems do not require internal inspection. Before pro-
ceeding to the preparatory cleaning and internal inspection,
the results from the physical survey should be carefully
analyzed. If the infiltration/inflow sources can be located
and quantified during the physical survey, no internal
inspection will be needed. This may be the case if the
infiltration/inflow sources are located in the manholes or
near both ends of the sewer lines. To minimize both the
time and the cost for the study, all efforts should be made
to eliminate as many sewer sections from internal inspection
as possible.
4.2 PHYSICAL SURVEY
4.2.1 General
The physical survey involves all the tasks which are required
to accomplish the following objectives:
(a) Identify the segments of the sewer system which
may require further study;
(b) Determine the general physical conditions of the
manholes and sewer lines in the selected segments
of the sewer system; and
(c) Compile the background information required for
the planning of the subsequent studies.
The following tasks are normally included in.the physical
survey:
(a) Aboveground inspection,
(b) Plow monitoring, and
(c) Manhole and sewer inspection.
After the completion of a physical survey, a report may be pre-
pared. This report is required by some states. The report
summarizes all the data collected during the survey and provides
Justification for:
(a) The sewer sections recommended for internal inspection.
(b) The degree of cleaning required for each sewer section
recommended for internal inspection.
(c) The location and sewer sections where rainfall simu-
lation should be conducted.
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4.2.2 Aboveground Inspection
The aboveground Inspection is conducted to accomplish the
following objectives:
(a) Investigate the general conditions of the study
area, such as topography, streets, alleys, access
to manholes, etc.;
(b) Locate potential problem areas, such as waterways,
river crossings, natural ponding areas, etc.; and
(c) Select the key manholes for additional flow
measurement and groundwater monitoring.
Conducted by a trained observer, valuable information can be
obtained which would facilitate the planning of other tasks
in the evaluation survey.
However, if sufficient information has been gathered during
the Infiltration/Inflow Analysis, this task may not be necessary.
4.2.3 Flow Monitoring
The purpose of flow monitoring is to locate and isolate the
areas where infiltration/inflow problems exist. Generally,
portions of the system pose no problem; therefore, they will be
eliminated from further study. This task should be accomplished
at the earliest possible stage in order to minimize the survey
costs.
In the analysis phase of the study, the flow monitoring work
has already been performed in a few selected key manholes.
All subsystems which present no infiltration/inflow problems
are eliminated from further study in the evaluation survey.
The additional flow monitoring work performed during the physical
survey is actually a continued effort to further reduce the
number of areas to be investigated.
The flow monitoring is usually conducted in a number of selected
key manholes. The flows should be monitored during the highest
groundwater level period. Both dry weather high groundwater
and wet weather high groundwater flows should be monitored to
determine the magnitude of inflow as well as of infiltra-
tion in each subsystem. To minimize the interferences caused
by the normal wastewater flows, the flow monitoring is usually
conducted during the early morning hours. However, on large
systems early morning flows may be substantial because of
continuous discharges to the sewers and lag time of flow due
to the length of sewers.
4-3
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For detailed information regarding the procedures for select-
Ing key manholes, the methods and equipment used, the
safety measures, and other pertinent considerations, see
Section 3-2.6.
4.2.4 Manhole and Sewer Inspection
4.2.4.a General
The manhole and sewer inspection is a task to determine the
actual physical condition of the sewer system. The data
generated from the inspection would be valuable for the identi-
fication of infiltration/inflow sources. It also provides a
factual base for the establishment of a preparatory cleaning
program for internal inspection and a routine sewer maintenance
program.
The inspection can be started after all the problem areas have
been isolated through a flow monitoring program. It may also
be conducted concurrently with the flow monitoring program to
accelerate the evaluation survey.
All the manholes and sewer lines in the designated problem
areas of the sewer system should be included in the inspec-
tion. Each manhole should be entered. The manhole and the
sewer pipes connected to it should be inspected carefully to
determine the physical conditions, infiltration/inflow sources,
type and degree of deposition and other special problems and
conditions.
4.2.*J.b Time for Inspection
The manhole and sewer inspection is usually performed during
the high groundwater period, for, during this period, the
groundwater-associated infiltration/Inflow sources can be
easily detected. The inspection can be performed during
either dry weather high groundwater or wet weather high
groundwater conditions. But it is more convenient to do it
in the dry weather as the flows in the sewers during dry
weather are lower and the physical conditions of the manhole
and the sewers can be checked more easily. The Inspection
is normally conducted during the daytime, at the hours when
the wastewater flows are low, if possible.
4.2.4.C Preparation
Before the Inspection is started, a complete sewer map of
all the manholes and sewer lines to be Inspected should be
prepared. The manholes should be properly numbered for easy
Identification. The equipment which is needed for manhole and
sewer inspection includes:
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Personal safety equipment
Portable lamps
Hand-held mirrors
Ruler
Thermometer
Other equipment
Manhole entering imposes potential safety and health hazards.
The personal safety equipment should always be carried and
used in the field. The safety equipment required for manhole
entering is presented in Section 3.2.6.d. All the safety
measures discussed in that section should also be followed
closely.
The hand-held mirror and the portable lamp are used to lamp
the sewer lines for easy inspection. The lamp should be
flameless to avoid accidental explosion of the gases in the
sewers. The commonly used flashlights are sufficient for
such purpose.
The ruler is used to measure the dimensions and the water depths
in the sewers and manholes. The thermometer is used to measure
the temperature of the flow in the pipe. Equipment for the
determination of conductivity, sulfate, fluoride or other con-
stituents in sewage may also be needed in some cases.
4.2.4.d Procedure
J|.2.4.d (1) Manhole Inspection - The manhole inspection involves
the observation and recording of the following information in
each manhole:
(a) Manhole identification;
(b) Construction materials and conditions of cover, ring,
corbel work, walls, steps, aprons and troughs;
(c) Manhole depth and opening size;
(d) Number and size of holes, if any, in manhole cover;
(e) Visible infiltration sources and estimated flow
rates;
(f) Evidence of leaks and location;
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(g) Level of high water mark in the manhole;
Oh) Type and depth of debris;
(i) Groundwater level at the manhole, If monitored; and
0j) Special problems and conditions, such as sources of
inflow, overflows, bypasses, manholes located in
natural ponding areas, etc.
A typical data sheet used to record the above information
during manhole inspection is shown in Table 4-1.
For manholes which cannot be inspected because of, say,
inability to locate, inability to open, surcharged, no steps,
etc., the reasons should be recorded.
4. 2.4.d (2) Sewer Inspection - After the inspection of a
manhole is finished, the incoming and outgoing sewer lines
connected to the manhole are inspected in turn. The sewers
are inspected by lamping the line both at the manhole being
inspected and at the manhole down the line. By lamping at
both ends of the pipe, a greater visibility can be achieved.
A mirror is used to deflect the light from the lamp to different
parts of the pipe for close inspection. The following informa-
tion is usually recorded:
(a) Length, size, type and depth of pipe;
(b) Depth and temperature of flow;
Oc) Other parameters in sewage such as conductivity,
sulfate concentration, fluoride concentration, etc.
(d) Root growth in pipe;
(e) Type and depth of deposition in pipe and recommended
cleaning method;
Of) Visible infiltration/inflow sources;
(g) Structural condition of pipe; and
Oh) Special problems and conditions in pipe.
A sketch showing the relative locations of the manholes and
the pipelines should also be included in the data sheet.
Table 4-2 shows a typical data sheet for sewer inspection.
4-6
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TABLE 4-1 TYPICAL DATA SHEET FOR MANHOLE INSPECTION
MH# Location s Drainage Area_
Project:
Client
Project No.
Date
Time
Weather: No rain
A. INVENTORY
a.m.
p.m.
Inspector
rain
snow
Item
Cover
Ring (frame)
Steps
Corbel Work
Walls
Aprons
Troughs
Construction
Material
Condition
Good
Pair
Poor
B. OBSERVATIONS
1. Diameter of manhole opening
2. Holes in cover : number
in.
, size
in.
3. Visible infiltration through joints, cracks, lines, etc.,
height above sewer invert, estimated flow rates
4. Evidence of leaks in manhole, height above sewer invert
5. High water marks in manhole, height above sewer invert,
possible cause
6. Manhole has
7.
8.
does not have
ground water level
gauge ground water level above sewer invert
Debris: No ; yes , type , depth
Special problems, conditions, sources of inflow,
overflows, bypasses.
in,
4-7
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MH#
TABLE 4-2 TYPICAL DATA SHEET FOR SEWER INSPECTION
LocationDrainage Area
Project :
Project
No.
Client:
Date: /
a .m
/ , Time p.m
Inspector
Weather: No rain; rain
snow
Pipe Data
Pipe Sizes, in.
Type of Pipe
Depth from MH
Top to Invert
Depth of Plow,
in.
Temperature of
Plow, °P
Conductivity of
Sewage, mho/cm
Sulfate
Concentration, ppm
Fluoride Concen-
tration, ppm
Root Growth in
Pipe
Type of
Deposition
Depth of
Deposition, in.
3e commended
Cleaning Method
Visible Infiltra-
tion/Inflow Sources
in Pipe
Structural Condi-
tions of Pipe
Special Problems
and Conditions
Incoming Lines
From MH #
Distance
ft
From MH#
Distance
ft
From MH#
Distance
ft
Outgoing lines
To MH#
Distance
Sketch of Manholes and Sewers
4-8
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An inventory of the length, size, type, depth and the general con-
ditions of the sewer pipes would provide a basis for the estima-
tion of the amount of work required for the preparatory cleaning
and internal inspection. It also provides a basis for sewer
rehabilitation work and routine sewer maintenance.
The depth of flow would provide a rough indication about the
capacity and/or structural condition of the sewer pipe and
indicate if infiltration/inflow is present in the sewer section.
For example, a surcharged line under normal conditions may
indicate a deficiency in pipe capacity or the existence of some
infiltration/inflow sources along the pipe.
The flow temperature may also be used as an indicator for the
detection of the extraneous water entering the sewer section
being investigated. Thus, if the measured flow temperature is
much higher or lower than the average sewage temperature measured
in the upstream manholes and there is no discharge from the
service connections at the time of measurement, there are
definitely some infiltration/inflow sources along the sewer
pipe. Similarly, the conductivity, the sulfate concentration
and the fluoride concentration in the sewage may also be used
to detect the infiltration/inflow sources.
The root growth condition and the type and depth of deposition
in the pipe would dictate the selection of the methods for the
root control and for the sewer cleaning before internal inspec-
tion. An experienced sewer Inspector should be able to judge
the condition in the field and recommend the best cleaning method
for each section of pipe. (The commonly used cleaning methods
are presented in Section 4.4.)
All visible infiltration/inflow sources should be recorded.
Each sewer line is actually inspected from two different man-
holes. This provides a chance to detect any infiltration/inflow
sources and/or structural defects which are undetectable from
only one end of the pipe.
The structural condition of the sewer pipe should also be
recorded. All structural defects and other unusual conditions,
such as cave-ins, crushed pipes, cracks, signs of deterioration,
horizontal misalignments (kicked Joints), vertical misalignments
(dropped joints), sags, open Joints, protruding taps, missing
pipes, etc., should also be recorded.
The physical survey is most effectively conducted during
high groundwater periods, thus an additional task which
should be performed is measurement of the groundwater depth.
(See Section 3.2.4.d for details.)
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4.2.5 Report
The main purpose of preparing a report at the end of the
physical survey is to provide a document to justify all the
subsequent work required in the evaluation survey. This report
is required by some states. After finishing all the tasks in
the physical survey, the general conditions in the sewer system
are clear to the investigator. A judgment should be possible
at this stage as to what sections of sewer lines should be
further studied, which lines would need preparatory cleaning
before internal inspection, what are the justifications for the
cleaning and for the inspection, and where and how the rainfall
simulation should be conducted.
The sewer lines located in the subsystems which are found from
the flow monitoring program to have possibly excessive
infiltration/inflow are generally recommended for further
investigation. The lines which need preparatory cleaning are
those which have deposition of any kind which may interfere with
the internal inspection. The degree of cleaning (light clean-
ing or heavy cleaning) and the recommended cleaning equipment
can be determined on the basis of the degree and type of deposi-
tion, and the structural conditions and accessibility of the
sewers to be inspected. The inspection method to be recommended
would depend on type of information required, pipe size and
internal conditions.
The areas where the rainfall simulation should be conducted
are those which show infiltration/inflow conditions during
rainfall periods. The method to be recommended for the simu-
lation would depend on the type of infiltration/inflow source
expected and other conditions in the sewer system and the
study area.
4.3 RAINFALL SIMULATION
4.3.1 General
The rainfall simulation techniques are utilized to identify
sections of sewers which have infiltration/inflow conditions
during rainfall periods. Generally these techniques are only
employed on separate sewer systems since combined systems were
designed to collect some inflow.
The infiltration/inflow sources which can be identified by
the rainfall simulation techniques Include:
(a) Roof leader, cellar, yard and area drains and
foundation drains;
4-10
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(b) Abandoned building sewers, faulty connections and
illegal connections;
Cc) Cross-connections between sanitary sewers and storm
sewers;
(d) Storm sewer sections, stream sections, ditch sections
and ponding areas which may cause infiltration/inflow
in sanitary sewers; and
(e) Structurally damaged sewers and manholes.
Although a convenient tool, rainfall simulation does not have
to be performed in every sewer system evaluation study. A
careful study of the sewer maps and reviews of the Infiltration/
Inflow Analysis report and the physical survey results would
indicate whether rainfall simulation is needed and, if so,
where it should be applied and what techniques should be used.
The following are the situations where rainfall simulation may
be considered:
(a) Storm sewer sections which parallel or cross sanitary
sewer sections (including service connections) and
have crown elevations greater than the invert eleva-
tions of the sanitary se'wers may be potential infil-
tration/inflow sources. If the sanitary sewer sections
which parallel or cross such storm sewer sections show
excessive infiltration/inflow and there are no other
conceivable or detectable infiltration/inflow sources,
the rainfall simulation techniques may be considered.
(b) Stream sections, ditch sections and ponding areas
located near or above sanitary sewer sections may also
be potential infiltration/inflow sources. The rainfall
simulation techniques may also be utilized to identify
such sources for sewer sections which show excessive
infiltration/inflow if no other sources are con-
ceivable or detectable.
(c) Roof leader, cellar, yard and area drains and
foundation drains, abandoned building sewers, faulty
connections and illegal connections which are sus-
pected to exist but cannot be identified by other
means during the physical survey may be detected by
the rainfall simulation techniques.
Besides being an identification tool, rainfall simulation can
also be utilized in conjunction with flow measurements to
quantify the infiltration/inflow from each of the identified
sources.
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The rainfall simulation techniques may be utilized to estimate
the quantity of infiltration/inflow that may reach the sewer
lines under unpaved areas, particularly service lines. However,
although rainfall may be simulated in small areas, it is often
almost impossible to simulate actual wet weather conditions.
Plow measurements performed during actual wet weather conditions
usually provide data which are more meaningful than those
gathered under the simulation rainfall conditions.
Many of the tests are performed on private properties. It is
essential to obtain full cooperation of the property owners.
Before the tests, the owners should be notified and the nature
of the tests should be explained to them.
The rainfall simulation techniques commonly used are:
Smoke testing
Dyed water testing
Water flooding test
In the following sections, details of these techniques are
presented.
*J .3.2 Smoke Testing
^.3.2.a Application and Limitations
Smoke testing is an inexpensive and quick method of detecting
infiltration/inflow sources in sewer systems. The method is
best used to detect inflow sources such as roof leader, cellar,
yard and area drains, foundation drains, abandoned building
sewers, faulty connections, Illegal connections and storm
sewer cross connections. It can also be utilized to detect
the structural damages and leaking Joints in sewer pipes and
the overflow points in the sewer systems.
The method is only a detecting technique and cannot be used
to quantify the flows. To accomplish the latter, one should
measure flows in the sewer sections which are found by the
smoke testing to have infiltration/inflow conditions. The
flow measurements can be performed during the wet weather
conditions or during the simulated rainfall conditions.
If reliable information is to be derived from smoke testing,
the method should not be applied to the sewer lines which
contain water traps or sags. Both of these two pipe conditions
may prevent the smoke from passing through and result in
false conclusions. Similarly, the methods should not be
applied to sewer sections that are flowing full. The method
cannot be utilized to detect the structural damages and leaking
Joints in buried sewers and service connections when the
4-12
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soils surrounding and above the pipes are saturated, frozen
or snow covered. In each case, the smoke will be trapped
and will not come out of the ground even though there are
cracks or leaking joints In the pipes. Rain and snowy days
are not suitable for smoke testing. The test should not
be performed on windy days when the smoke coming out of the
ground may be blown away so quickly as to escape visual detection,
Because of the many unknowns in the sewer systems and the
uncertainties about the soil and groundwater conditions, the
results from smoke testing should be analyzed carefully. The
positive findings during the tests definitely indicate the
existence of the infiltration/inflow sources. The negative
findings, however, may not prove that the problems do not
exist. Whenever the results from the smoke testing are in
doubt, the more positive detection method, i.e., the dyed water
testing, may be tried, or observations conducted during wet
weather.
The method normally does not cause safety or health hazards.
It is usually performed above the ground and no manhole enter-
ing is necessary. However, because of possible confusion re-
sulting from smoke appearing in and around dwellings, the public
should be notified prior to the test and the local fire depart-
ment should also be informed. A typical smoke testing, between
two manholes, usually takes about 10 to 15 minutes. More time
will be needed under unusual sewer and manhole conditions.
4.3.2.b Equipment
The following equipment is usually needed to conduct smoke
testing:
Smoke bombs
Air blower
Camera and film
Sand bags and/or plugs
The smoke bombs are used to generate the smoke required for
the test. The smoke should be nontoxic, odorless and non-
staining. The 3-minute and 5-minute bombs are normally used
although bombs which can last longer or shorter are also
available. The air blower is used to force the smoke into
the sewer pipes. A gasoline-driven blower is most convenient
for this purpose. The air blower should have a minimum capacity
of about 1500 CFM. The camera is used to take the pictures
of the smoke coming out of the ground, catch basins, pipes
and other sources during the test. The photographs are taken
for permanent documentation of the infiltration/inflow sources.
The sand bags and/or plugs are used to block the sewer sections
to prevent the smoke from escaping through the manholes and
adjacent sewer pipes.
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The smoke bomb and the air blower are usually set up above-
ground near the manhole to be tested.
4.3.2.C Procedure
The following procedures are normally followed to perform the
smoke testing:
(1) Preparation for the test
(a) Determine the sewer sections where the smoke
tests are to be performed. Locate the sewer
sections and manholes. Check the manholes for
accessibility and check the flow conditions in
the sewer pipes. Make provisions for flow by-
passing, if necessary.
(b) Determine the time for the tests. Avoid rainy,
snowy and windy days. Schedule the test for
the period when the groundwater levels are
low and the ground is not snow covered.
(c) Notify the residents in the areas where the
tests are to be performed regarding the nature
and time of the test. Also notify the loca,l
fire department.
(2) Test procedure
(a) Usually two manhole sections are tested simultan-
eously. Set up the equipment at the intermediate
manhole of-the sewer sections to be tested. The
smoke is usually introduced into the sanitary sewer
sections, even for the detection of the cross-
connections between storm sewers and sanitary
sewers.
(b) Partially plug the sewer lines at the far ends
with sand bags or plugs. The sand bags or
plugs are attached with ropes to facilitate
lowering and retrieving from above the manhole.
(c) Ignite the smoke bomb and force the smoke into
the sewer section with the blower. The supply
of smoke should be continuous until the area
serviced by the test sections is thoroughly
examined and all problems recorded.
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(d) Observe the appearance of the smoke coming out
of the ground, storm sewer, catch basins,
roof drains, abandoned building sewers, etc.
Record the observations with the camera. Mark
down on the back of the photographs, or on a
log sheet, the dates, locations and situations
of the results.
fr.3.3 Dyed Water Testing
4.3.3.a Application and Limitations
The dyed water testing is usually used to determine whether
the storm sewer sections, stream sections, ditch sections
and/or ponding areas which are located near or above the
sanitary sewer sections are contributing any infiltration/
inflow to the sanitary sewers. The method can also be
utilized to detect the other infiltration/inflow sources
listed in Section 4.3.1. It can be used to check the results
from the smoke testing. Under unfavorable weather, ground-
water, soil, sewer structure and/or flow conditions, the
dyed water testing can be utilized to substitute for the smoke
testing to obtain more reliable Information. Quantification of
the flows is possible when the dyed water testing method is used
to identify the infiltration/inflow sources.
The method, however, is usually more expensive and time-consuming
than the smoke testing technique. It is also limited to locations
where large quantities of water are available for the test. Man-
holes and storm sewers may have to be entered for the test;
therefore always be safety conscious.
4.3.3.b Equipment
The equipment needed for the dyed water testing is limited
to that required to carry the water to the testing site and to
block the sewers or the study areas before the testing.
When fire hydrants are close to the sewer sections to be tested,
a fire hose is all that is needed to deliver the water to the
testing site. On the other hand, when the water source is not
close by, water tankers will be required to deliver the water.
Sand bags or sewer pipe plugs are normally used to block the
sewer sections.
The fluorescent dyes are usually used for the test. Each dye has
a distinct color which is readily detectable by eye. A suit-
able dye should be safe to handle, visible in low concentra-
tions, misclble in water, inert to the soils and the debris
in the sewers and biodegradable. (Typical dyes available for
this purpose are listed in Table 3-2.)
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4.3.3.C Procedures
Depending on the infiltration and inflow sources to be identified,
the procedures for the dyed water testing differ.
4.3.3.G CD Determination of Infiltration/Inflow Conditions
Caused by Storm Sewer Sections - The storm sewer sections
which parallel or cross sanitary sewer sections and have
crown elevations greater than the invert elevations of the
sanitary sewers can be either infiltration sources or inflow
sources. They are inflow sources if there are cross-connections
between the storm sewer sections and sanitary sewers. They
are infiltration sources if the storm water can exfiltrate
from them, percolate through the soil and enter the sanitary
sewers through pipe defects, broken pipes and/or leaking
Joints. The dyed water testing can be used to detect both
of these possibilities. To differentiate between the two,
an analysis of the percolative capacity of soil is necessary
in addition to the determinations of the presence, concentration,
flow rate, and travel time of the dyed water entering the
sanitary sewers. A careful analysis of these factors would
also enable one to locate the sources and quantities of infiltra-
tion/inflow. If the technique is to be used merely to determine
whether cross-connections are existing between the sanitary
sewers and the storm sewers or catch basins, then it is only
necessary to determine the presence and travel time of the
dyed water into the sanitary sewers.
The general procedures for dyed water testing in storm sewer
sections are as follows:
(a) Plug both ends of the storm sewer section to be tested
with sand bags or other materials. Block all the
overflow and bypass points in the sewer section.
Provide bypassing of flow, if necessary.
(b) Pill the storm sewer section with water from fire
hydrants or other nearby water sources. Add dye
to the water.
(c) Monitor the downstream manhole of the sanitary sewer
system for evidence of dyed water. Determine the
time of travel and, if desired, the concentration of the
dyed water.
(d) Measure the flows in the manhole before and during the
dyed water testing. As an alternative, the flows can
be simultaneously measured at both the upstream and
downstream manholes during the test.
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(e) Record the location of storm and sanitary sewer lines
being tested, the time and duration of tests, the
manholes where the flows are monitored and the flow
rates, the observed presence, concentrations and
travel time of the dyed water into the flow monitoring
manholes, and the soil characteristics.
4.3.3.C C2) Determination of Infiltration/Inflow Conditions
Caused by Stream Sections 3 Ditch Sections and Ponding Areas -
To determine whether the stream sections, ditch sections and
ponding areas located near or above sanitary sewer sections
are causing infiltration/inflow conditions in the sanitary
sewers, the procedure similar to that described in the previous
section is recommended. In these cases, the stream sections,
ditch sections and pond areas to be tested should be plugged
or dammed and filled with dyed water to the desired levels.
The presence, concentration and/or travel time of the dyed
water into the sanitary sewers are then monitored in the
downstream manholes. The flow rates can be monitored if
necessary. The percolative capacity of the soil can be deter-
mined to facilitate the estimation of the sources and quantities
of infiltration/inflow.
4.3.3.C (3) Identification of Roof Leader, Cellar, Yard and Area
Drains, Abandoned Building Sewers, Faulty Connections and Illegal
Connections - Most of these inflow sources are located on
private properties. The property owners should be notified
before the tests to identify the aforementioned inflow sources.
To identify the above mentioned inflow sources, dyed water is
poured into the corresponding fixtures and their presence is
checked in the closest downstream manhole in the sanitary sewer
system. The date of the test, the address where the inflow
sources are identified and the type of inflow sources should
all be recorded.
4.3.3.C ... (.4) Identification of Structurally Damaged Manholes -
The dyed water test .can also be used to identify the structurally
damaged manholes which impose potential infiltration/inflow
problems. This is accomplished by flooding the area close to
the suspected manholes with dyed water and observing the presence
of the dyed water at the manhole walls.
4.3.3.C (5) Outflow Dye Test - Besides being a technique for
identifying infiltration/inflow sources, the dyed water testing
method can also be utilized to determine the location and quantity
of water escaping from a sewer system through bypasses, overflows
and cross-connections.
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To accomplish this, the downstream manhole of the sewer section
is first plugged. The sewer section is then surcharged with
dyed water to the desired level. Upon attaining the desired
condition, all suspected areas, such as creeks, ditches, storm
sewers, catch basins and nearby sewer lines, are visually in-
spected for the appearance of the dyed water. Record the
location, time and duration of test, water level, amount of
water used and location of all cross-connections or outflow
sources detected and estimate the loss of flow from each of
these outflow sources.
4.3.4 Water Flooding Test
The water flooding test is similar to the dyed water testing
method except that no dye is used. Because of the lack of a
visible indicator in the water flooding test, the task of
identifying the infiltration/inflow sources becomes more tedious.
Accurate flow measurements are essential to the successful appli-
cation of this technique. With proper flow monitoring, all the
infiltration/inflow sources which can be identified by the dyed
water testing method can also be identified by the water flooding
test .
In addition, the following two types of water flooding tests
can also be performed without the need of the dyed water:
Sprinkler test
Exfiltration test
4. 3. 4. a Sprinkler Test
The sprinkler test is used to determine the quantity of infiltra-
tion being experienced in sewer lines under unpaved areas, par-
ticularly service connections, during wet weather conditions.
The rainfall is simulated by sprinkling the areas above the
sewer lines to be tested with water, using the irrigation
sprinkling pipe with spray nozzles or yard sprinkling hoses.
The rate of application of water and total water distributed
are monitored by installing rainfall gauges in the immediate
area of the test. Flows are periodically measured at the
manholes both upstream and downstream of the test section.
Comparison of these flow readings would determine the quantity
of infiltration (if any) and the time required for the infiltra-
tion to reach the sewer section.
The data to be recorded may include type, size, depth, number
of taps on and location of sewer lines tested as well as
topography, soil type, time and duration of test, rainfall gauge
readings and flow readings versus time.
4-18
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4.3.4.b Exfiltration Test
The exfiltration test is used to check the sewer lines and
manholes for possible leakages. Sewer sections and manholes
which do not show significant exfiltration rates during this
test usually would not display high infiltration rates during
wet weather conditions. The results from exfiltration tests
can also be compared with the infiltration rates determined by
the sprinkler tests in a given area. If a definite relationship
can be established, the exfiltration test can be used to re-
place the more costly sprinkler test in that area.
The procedures involved in the exfiltration test are as
follows:
(1) Isolate the manholes and sewer lines to be tested
by plugging incoming and outgoing lines.
(2) Pill the manholes and sewer lines with water and
allow the water surface to stabilize.
(3) Measure the rate of recession of water in the manhole
and amount of water required to refill the sewer
section.
(4) Record the location, length, depth, type of pipe and
manhole construction, and number of taps in the test
section. Also record the time and duration of the
test, head established, rate of water loss and amount
of water required to refill the test sections.
(5) Calculate the exfiltration rate from the test section.
4.4 PREPARATORY CLEANING
4.4.1 General
After the physical survey and the rainfall simulation, the
general conditions of the sewer system can be determined.
Sewer sections which present obvious potential for excess
infiltration/inflow are selected for internal inspection
to pinpoint the causes, sources and magnitudes of infiltration/
inflow before being recommended for rehabilitation. To
facilitate the internal inspection, the sewers should be
properly cleaned.
The preparatory cleaning should remove all the sludge, mud,
sand, gravel, rocks, bricks, grease and roots from the sewer
pipes, manholes and pumping station wet wells to be inspected.
The cleaning is normally more thorough than that done for routine
4-19
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maintenance. The pipe walls should be clean enough for the
camera used in the inspection to discern structural defects,
misalignment and infiltration/inflow sources. A full-diameter
tool or cleaning device is often needed to assure adequate
cleanliness and clearance.
The cleaning is usually far more time-consuming than the
actual internal inspection. For this reason, it is not advis-
able to have a television camera on site at all times while
the cleaning crews are working. However, for lines which
clog easily, the inspection should be done as soon as possible
after the cleaning is finished to avoid the necessity for
recleaning at a later time.
4.4.2 Equipment
A complete sewer cleaning job involves the following four
tasks:
(a) Dislodging the materials,
(b) Transporting the materials to a point of access,
(c) Removing the materials from the sewer system,
(d) Disposing of the materials.
The equipment required to accomplish these tasks can be
divided into three general categories:
Cleaning equipment,
Debris removal devices,
Debris transporting vehicle.
*J.4. 2. a Cleaning Equipment
The cleaning equipment is used to dislodge the materials
in the pipeline and to transport the materials to the point
of access. Most cleaning equipment cannot be used to remove
the materials from the sewer system but some may also be
used to accomplish this task. There are four basic types
of sewer cleaning equipment:
Rodding machines,
Bucket machines,
High-velocity water machines,
Hydraulically propelled devices.
4-20
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These types of equipment differ in their capacities to handle
the materials in the sewers, applicable pipe size ranges, man-
hole accessibility requirements and methods of operation.
(Table 4-3).
The rodding machines are most effective in dislodging roots
and blockages in sewer lines. The bucket machines are most
suitable for heavy cleaning which involves the removal of
sand, gravel, rocks, bricks and roots. The high-velocity
water machines and the hydraullcally propelled devices can
both be used for light cleaning to remove the sludge, mud,
sand and gravel in the sewers.
4.4.2.b Debris Removal Devices
The debris removal devices are used to remove the materials
from the sewers after the materials are dislodged and
transported to the points of access (manholes) by the clean-
ing equipment. The commonly used debris removal devices are:
Vacuum Machines
Trash Pumps
The bucket machines used for the cleaning can also be used
to remove the debris from the sewers.
4.4.2.C Debris Transporting Vehicle
The debris transporting vehicles, or dump trailers, are
used to transport the debris to a dump site. The vehicles
are sometimes equipped with pumps and settling baffles for
separating the solids from the water.
4.4.3 Selection of Cleaning Equipment
To select proper types of cleaning equipment for the pre-
paratory cleaning of a sewer system, many factors have to
be considered, including:
Access to manholes,
Condition of manholes,
Size of pipe,
Depth of deposition,
Type of solid materials to be removed,
Degree of root intrusion,
4-21
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TABLE 4-3
CHARACTERISTICS OP SEWER CLEANING EQUIPMENT [9]
Equipment
Applicable
Pipe Size
Materials to
be Removed
Advantage
Limitation
Rodding Machines 6"-15"
.t-
i
ru
IV)
Bucket Machines 8"-36"
Best for dislodging
roots and blockages
1,
2,
3
Also for dislodging
and transporting
sludge, mud and grease,
using special tools
and flushing water
May reach 1,000 ft
Easy to stop
Can be used for
threading sewer
1. Best for dislodging, 1
transporting and
removing sand, gravel,
rocks, bricks and
roots 2.
2. Also for dislodging
and transporting 3-
mud and grease
, Can remove large
amounts of heavy
solids and roots
Effective in large
diameter pipes
Can remove materials
from sewer system
Winch machine can be
used with a variety
of tools
1. Require direct
access to down-
stream manhole
2. Require large
quantity of water
for flushing
3. Poor in trans-
porting heavy
solids
4. Do not remove
materials from
sewer.
1. Require complete
access to both
manholes
2. Require threading
of sewer line
3. Time-consuming
for light clean-
ing
4. Heavy tools may
damage pipe
5. Cannot be used in
structurally
damaged pipe,
offset joints,
curved pipe and
pipes with intrud-
ing service con-
nections
-------
TABLE 4-3 (Continued)
High-Velocity
Water Machines
6"-15" or
larger
1. Best for dislodging 1.
and transporting
sludge, mud, sand and
gravel 2.
2. Also for dislodging
and transporting
rocks and grease in 3-
pipes up to 12"
diameter
4.
3. May be used with
special tools to dis-
lodge roots in pipes 5.
up to 12" diameter
4. Good for cleaning
manhole walls and
bench
Manhole access is
not critical
Can be used for
threading sewer
line
Easy to set up and
operate
Past cleaning
method
Low pipe-damage
potential
3,
4,
Require access to
downstream man-
hole
Water must be
available near job
Least effective on
large heavy debris
May damage
deteriorated pipe
5. Do not remove
materials from
sewer
Hydraulically
Propelled
Devices
6"-36"
1. Best for dislodging 1. No equipment access
and transporting
sludge, mud and sand
Also for dislodging
and transporting
gravel, rocks,
bricks and grease
limitations
2. Minimum equipment
requirements
3. Ease of operation
1. Require large
quantity of water
at site
2. May cause base-
ment flooding
3. Not applicable to
blockage result-
ing in surcharge
conditions
4. Do not remove
materials from
sewer
-------
Depth of sewer,
Amount of flow,
Structural integrity of pipe,
Availability of hydrant water,
Degree of cleanliness required.
A review of the general characteristics of the sewer cleaning
equipment (Table 4-3) and the results of the physical survey
will indicate the cleaning equipment which should be used for
each section of sewer recommended for cleaning. Firms experi-
enced in sewer cleaning should be consulted for detailed infor-
mation on operational procedures and other specific features.
4.5 INTERNAL INSPECTION
4.5.1 General
Following the preparatory cleaning, the sewer sections are
internally inspected to determine the location, condition
and estimated flow rate for each source of infiltration/inflow
defined in the sewer sections. During the inspection, all
the infiltration/inflow sources, structural defects, service
connections, abnormal conditions and other pertinent observations
are recorded. The results from the inspection provide a
factual base for the cost-effectiveness analysis to determine
the sewer lines which can be cost-effectively rehabilitated
and for the selection of the most suitable methods for rehabili-
tation. The information documented during the inspection
can also be used to locate the pipelines and problem sections
in the pipes during actual rehabilitation.
Internal inspection is normally conducted during periods of
maximum groundwater levels. However, for sewer lines which
are above the groundwater levels throughout the entire year,
the inspection can be performed any time. During the inspec-
tion, all storm sewer sections, stream sections, ditch sections,
and ponding areas which are found to contribute infiltration/
inflow to the sanitary sewer section should be flooded. The
purpose is to duplicate the worst possible weather and ground-
water conditions in the sewer sections so all the infiltration/
inflow sources will show up during the inspection.
4.5.2 Inspection Techniques
Sewer inspection can be accomplished by any one of the follow-
ing four techniques:
4-24
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Television inspection,
Photographic inspection,
Physical inspection, and
Air test.
The television inspection technique is most commonly used;
however, the photographic, physical inspection and air test
techniques can also be used under special conditions. The
method used for internal inspection should be the best and
most cost-effective method of obtaining the necessary infor-
mation.
4.5. 2. a Television Inspection,
The television inspection technique utilizes a closed-circuit
television camera to observe the conditions in the sewer lines
The results are shown in the television monitor. Documen-
tation can be made with videotape or photographs of the
monitor. The technique can be applied to sewers with sizes
ranging from 8 to 36 inches and with lengths up to 1,000
feet (Figure 4-1).
4.5.2.a (1) Equipment - The cameras used for TV inspection
are specially designed to fit the sewer pipe conditions.
The camera is mounted in a casing and is pulled through the
sewer with cables. A light source is provided along with
the camera for illumination purposes. A TV monitor is used
to show the actual conditions in the sewer as the camera is
pulled along.
4.5.2.a (2) Procedure - During the inspection, the cameras
are stopped at the points where one or more of the following
conditions are observed:
Infiltration/inflow sources;
Service connections;
Structural defects, including broken pipe,
collapsed pipe, cracks, deterioration,
punctures, etc.;
Abnormal Joint conditions, such as horizontal
and vertical misalignments, open joints,
joints not fully seated, etc; and
Unusual conditions, such as root intrusion,
protruding pipes, in-line pipe size changes,
mineral deposits, grease, obstructions, etc.
4-25
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TV Monitor
Winch
CT\
Roller Assent Iy
Manhole -
-TV Camera
Figure 4-1. Typical Arrangement for Television Inspection of
Sewer Lines
-------
All such conditions should be recorded. Photographs of all
questionable conditions should be taken for subsequent review.
The photographs are usually taken from the TV monitor with
Polaroid or 35 MM films. All infiltration/inflow sources
should be quantified while observing through the TV monitor
(see Section 4.5-2.a (3) for detail). If necessary, the
infiltration/inflow sources may also be recorded with videotape
for flow estimation in the laboratory and for later review.
Before taking the photographs or videotape, the TV camera
should be properly positioned so that the optimum view of
the defects, etc., can be obtained. If necessary, the same
problem object can also be viewed from the opposite direction
by pulling the TV camera from the other manhole in the sewer
section. For reference purposes, photographs and videotapes
of typical sewer sections and joints in lines being inspected
should also be taken.
At the connecting points between the.service connections
and the sewer being inspected, the TV camera should be
stopped to check for any flows coming out of the service
connections. Whenever a flow is observed, its source should
be checked out immediately. The building to which the
service connection is connected should be checked first for
any wastewater discharge during the inspection. If no flows
are being discharged from the building, then it can be
assumed that the observed flow is infiltration or Inflow.
If the estimated flow from the service connection is greater
than the total wastewater discharge from the fixtures in the
building, then the infiltration/inflow can be determined by
calculating the difference of these two flows.
The locations of all the conditions recorded should also be
identified by recording the distance from each defect or
point of interest to an established point in each sewer
section. The distance is usually measured from the center
of the starting manhole to the plane of focus of the camera.
Table 4-4 shows a typical television inspection log sheet. In
addition to the columns for recording the footage, observa-
tions and infiltration/inflow rates, the sheet also includes
columns for recording the recommended corrective action and
the photograph number. The recommended corrective action for
each pipe defect or infiltration/inflow source is based on
the conditions of the defect or the type of infiltration/
inflow source. This information is essential for conducting
the cost-effectiveness analysis and for planning the sewer
rehabilitation program. For the convenience of cross-
reference, the photographs should be numbered and the photo-
graph number for each item should be recorded on the log
sheet.
4-2?
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TABLE 4-4
TYPICAL TELEVISION INSPECTION LOG SHEET
AREA
SHEET NO.
PROJECT:
CLIENT :
PROJECT NO:
DATE:
INSPECTOR:
SECTION ON:
FROM MANHOLE #_
PIPE SIZE
TO MANHOLE
IN., PIPE TYPE
PIPE LENGTH
FT TYPE OF JOINTS
REF.
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
FOOTAGE
OBSERVATIONS
INFILTRATION/
INFLOW
gpm
RECOMMENDED
CORRECTION
ACTION
PHOTO
NO.
SPECIAL NOTES
MH I
o
MH //
DIRECTION OF FLOW [
DIRECTION OF MEASUREMENT J_
4-28
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4.5.2.a (3) Estimation of Infiltration/Inflow Rates -
Estimating the flow rates of the infiltration/inflow sources
through a television camera is a difficult task. The accu-
racy of the estimate depends largely on the experience
of the operator in front of the TV monitor or the person
reviewing the videotapes. The experience is usually gained
by observing the infiltration/inflow conditions simulated in
the laboratory and comparing the estimated flows with the
measured flow rates.
A simple laboratory simulation technique for testing the estimation
of flows from the infiltration/inflow sources in the sewer
pipes is illustrated in Figure 4-2. A section of sewer pipe
of the same size and type as the sewer to be examined is
used for the test. On this section of pipe, a defect is
created to simulate a certain condition in the actual sewer
line. The pipe is installed in an inclined position in a
water container which has two holes in the opposite walls.
The adjustable rubber ring is tightened around the pipe to
assure watertightness. A television camera is pulled into
the pipe section and focused to give a clear view of the
defect on the pipe wall. Water is added to the water container
to a desired level.. The person being trained may then proceed
to turn on the TV monitor and watch the shape and speed of
the water leaking through the pipe defect very carefully
from the screen. Record the flow with videotape if desired.
Gather the water flowing out of the pipe with a bucket and
record the starting and ending time with a stop watch. Measure
the volume of water gathered and calculate the flow rate.
Correlate the measured flow rate with the shape and flow
speed shown in the TV monitor. Repeat the process for different
water heads, type and size of pipe defects, pipe size and
pipe material to cover as many field pipe conditions as possible.
The videotape recorded during the test can be used for repeated
training of the field TV inspectors.
However, even with the simulation technique, it is often
not possible to accurately determine the infiltration/inflow
rates in the field. Whenever possible, the infiltration/
inflow rate in a sewer section should be measured by plugging
and weiring (or by other flow measurement techniques) during the
low flow hours. After the normal wastewater flows are deducted,
the measured flow rate is compared with the total estimated
infiltration/ inflow rate. If the two are not equal, a
correction should be made to adjust the estimated flow rate.
This can be done by dividing the measured total flow rate by
the estimated total flow rate. The resulting factor is used
to multiply the estimated flow rate from each individual
source to derive the corrected flow rate.
4-29
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Pulling Cable
Water
Water Container
-Adjustable Rubber Ring
Pipe Section
TV Monitor
Defect
Figure 4-2. Laboratory Test for Estimating Infiltration/Inflow
Rates
-------
4.5.3 Photographic Inspection.
The photographic inspection technique uses a camera to take
a series of color photographs along the inside of the sewer
lines. The technique can be applied to sewers with sizes
ranging from 8 to 36 inches.
The technique is best for analyzing the structural con-
ditions of the sewers. The photographs can also be used to
determine the joint conditions and root intrusion problems
in the sewers .
In applying this technique, a camera is pulled through
the sewer line being inspected. Pictures are taken at
equidistant intervals or at some predetermined problem
sections. The distances at which the pictures are taken
are measured from a reference point, usually the center of
the starting manhole.
4.5.4 Physical Inspection
Two physical inspection techniques can be used to inspect
the sewer:
Lamping
Entering (large sewers only)
The lamping inspection technique has been discussed in the
section on Physical Survey (Section 4.2.4). The entering
Inspection technique is a direct method for sewer inspec-
tion. However, this technique Is usually limited to new
construction, large storm sewers and large sewers not in
service. In applying this technique, the safety of the
person entering the line should always be carefully guarded.
Before entering the line, the sewer section should be thorough-
ly ventilated to remove all the harmful gases. Forced ventila-
tion should be provided throughout the inspection period.
The person entering the line should be provided with redundant
lights as well as all the personal safety equipment required
for manhole and sewer inspection (See Section 3.2.6.d.)
4.5.5 Air Test
Specific circumstances may warrant the use of air testing of
sewer joints, In conjunction with television inspection, to
accomplish internal Inspection. This technique may be employed
on projects which have missed the high groundwater period and
economics would justify an air testing program to avoid a costly
delay of the project.
4-31
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The procedure for air testing is described in Chapter 5,
Section 5.3.2.c(l).
4.6 SURVEY REPORT
4.6.1 General
After finishing all the investigative work, a survey report
has to be prepared. A complete survey report usually contains
the following items:
(.a) A description of all the tasks performed, covering:
The purpose of conducting each task,
The methods and equipment used,
The location of the study area and/or the
sections of sewer lines investigated;
(b) A summary of all the results gathered during the
investigation;
Cc) A cost-effectiveness analysis to determine the
portion of sewer sections which can be cost-
effectively rehabilitated and the infiltration/
inflow which is expected to remain in the sewer
system after rehabilitation;
(d) A proposed sewer system rehabilitation program and
its related costs;
Ce) A documentation of all the field data gathered
during the Investigation.
For clarity, the results, conclusions and recommendations
are usually summarized in tabulated forms and illustrated on
maps.
4.6.2 Data Analysis
The initial step in the preparation of a survey report is
a summarization, in tabulated forms, of the results of all
the tasks performed in the evaluation survey. The following
table headings are suggested for each respective task:
(a) Physical Survey
(1) Aboveground inspection: Location; observation
4-32
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(2) Flow monitoring: Location; key manhole number;
sewer lines (size and length); method of
measurement; test condition (dry weather and
wet weather); measured Infiltration (gpd and
gpd/in-mile of sewer); suggestion for further
study.
(.3) Groundwater test: Manhole number; date;
measurement device; groundwater level.
(.4) Manhole Inspection: Location; manhole number;
type of construction; structural condition;
infiltration/inflow sources; estimate flow rate;
remarks; reference page of field report.
(.5) Sewer inspection; Location; sewer section
number (or, manhole numbers); type; length;
size; deposition (type and depth); visible
infiltration/inflow sources; structural con-
dition; special problems; recommended cleaning
method; recommendation for internal inspection;
reference page of field report.
(b) Rainfall Simulation
(1) Smoke testing; Location; test conditions;
observation; conclusions; recommendations.
(2) Dyed water testing; Location; test conditions;
observed infiltration/inflow sources; estimated
flow rate; conclusions; recommendations.
(3) Water flooding test: Location; test conditions;
observed infiltration/inflow sources; estimated
flow rate; conclusions; recommendations.
(c) Preparatory Cleaning
Location; sewer section number (or, manhole numbers);
pipe (size and length); deposition (type and depth);
cleaning method used.
(d) Internal Inspection
Location; sewer section number (or, manhole numbers);
observed leakage (type, location and flow rates);
recommended corrective action; reference page of
field report.
4-33
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A detailed sewer map Is usually included in the report. The
map should show all the manholes, pumping stations, bypasses,
overflows, and sewer lines in the sewer system under study.
For reference purposes, the manholes should be properly
numbered. The size, material and flow direction of each
sewer section should be clearly indicated. The important
information related to the evaluation survey can also be
shown in the sewer map. This information may include:
Special problems observed during aboveground
inspection;
Key manholes for flow monitoring and flow-
monitored sewer lines;
Groundwater monitoring station;
Manholes and sewer lines inspected during
physical survey;
Sewer sections investigated by smoke test-
ing, dyed water testing or water flood
testing;
Sewer sections cleaned and internally
inspected;
Sewer sections Justified for internal
inspection but nonaccessible.
4.6.3 Cost-Effectiveness Analysis
4.6.3.a Introduction
After all the results have been analyzed and summarized, a
cost-effectiveness analysis should be conducted to determine
which portion of the infiltration/inflow conditions in the
sewer system can be cost-effectively corrected. The method-
ology for conducting the cost-effectiveness analysis is
basically similar to that presented in Section 3.4.3.C for the
Infiltration/Inflow Analysis. However, in the Sewer System
Evaluation Survey Phase, the types of infiltration/inflow
sources, the flow rate from each source, the best method for
correcting each source and the costs for the corrections are
all better defined than they were in the Infiltration/Inflow
Analysis Phase. Therefore, somewhat different procedures can
be used.
4-34
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*J.6.3.b Flow Adjustment
Before the cost-effectiveness analysis can be conducted, the
estimated flow from each infiltration/inflow source should
be adjusted. The following are the recommended procedures:
4.6.3.b (1) Plow Adjustment for Peak Infiltration -
(a) Determine the sum of estimated flows from all
infiltration sources.
(b) Compare the total flow with the total peak
infiltration determined in the Infiltration/
Inflow Analysis. If the former is greater than the
latter, no flow adjustment will be needed. If the
reverse is true, calculate the ratio of the latter
over the former and multiply the estimated flow
from each source by this ratio to derive the adjusted
flow, which is then used in the cost-effectiveness
analysis.
*>.6.3.b (2) Flow Adjustment for Peak Inflow - The estimated
peak inflow values should be adjusted for the desired design
period or design condition. The design rainfall frequency
normally used for designing storm sewers should be used for
such adjustment. The ratio of the design and observed rainfall
intensities is used to adjust the peak inflow.
4.6.3.C Cost Estimation
Two types of costs need to be developed:
Costs for the correction of infiltration/inflow
conditions,
Costs for transportation and treatment of waste-
water (including infiltration/inflow).
The cost for the correction of infiltration/inflow conditions
should be developed for each individual infiltration/inflow
source. The cost for both the Evaluation Survey and the
Rehabilitation should be included. (The Cost for the Evalua-
tion Survey has been expended; however, it should be included
in the cost-effectiveness analysis in the Evaluation Survey
Report because (1) it was included in the cost-effectiveness
analysis in the Infiltration/Inflow Analysis Report and (2)
the cost-effectiveness analysis in the Evaluation Survey
is intended to be a refinement of that in the Infiltration/
Inflow Analysis.) The estimated cost of the Evaluation Survey
for each source should be based on the total money actually
expended for Evaluation Survey in the entire sewer system.
Estimated costs for rehabilitation should be based on the
actual physical conditions discovered.
4-35
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The costs for transportation and treatment of wastewater
can be developed following essentially the same procedures
as those presented in Section 3-4.2.d. Costs should be
developed for at least four typical flow conditions so
that a cost curve can be drawn to indicate the general cost
pattern.
4.6.3'd Analysis Procedures
The analysis procedures are as follows:
(1) Determine the total correction cost for each
infiltration/inflow source and calculate the
cost required for eliminating each unit of flow
(the unit cost).
(2) Arrange the infiltration/inflow sources in order,
putting the sources with lower unit costs ahead
of those with higher unit costs.
(3) With the sources arranged in order, break them
into several groups and determine the total
correction cost as well as total infiltration/
inflow to be reduced for each group. Add to the
total correction cost the engineering services
costs; legal, fiscal and administrative costs;
contingency costs; interest during construction;
etc., to derive the total cost required to
eliminate the infiltration/inflow from all sources
within each group.
(4) Arrange the groups in order, putting the groups
with lower total cost ahead of those with higher
total cost, and, calculate the accumulative total
cost and accumulative total infiltration/inflow
to be reduced.
(5) Plot the accumulative total cost against the
accumulative total infiltration/inflow to be
reduced and draw a curve passing all data points.
(Cost Curve for Rehabilitation shown in Figure 4-3).
(.6) On the same graph, plot a curve to show the
relationship between the costs for transportation
and treatment and the total infiltration/inflow to
be reduced (Cost Curve for Transportation and
Treatment shown in Figure 4-3).
(7) Derive a Composite Cost Curve (Figure 4-3) by adding
the costs on the two derived curves.
4-36
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§
1
h
il
Composite Cost Curve
Minimum
olaI Cost
Cost Curve
for Transportation
and Treatment
Optimal Point
for Sewer
Rehabilitation
Cost Curve for Rehabilitation
Infiltration/Inflow Reduced, GPD
Figure 4-3. Cost Curves for Cost-Effectiveness Analysis in Evaluation Survey
14-3?
-------
(8) Locate a minimum cost point on the -Composite Cost
Curve. Draw a straight line passing this point
and parallel to the cost axis. The line intercepts
the Cost Curve for Rehabilitation at a point which
represents the optimal point for sewer rehabilita-
tion. The flow figure corresponding to this
point represents the infiltration/inflow which
can be cost-effectively removed from the sewer
system, and the cost figure corresponding to it
represents the total cost which will^be needed for
the corrective actions (including the money
already expended for Evaluation Survey). Determine
the infiltration/inflow sources which should be
rehabilitated to remove the optimal amount of
infiltration/inflow determined above, starting
from the sources with the lowest correction costs.
4.6.^ Recommendations for Sewer System Rehabilitation
After the cost-effectiveness analysis, the infiltration/
inflow sources which can be most cost-effectively eliminated
are determined. A sewer system rehabilitation program should
then be recommended. For the planning of the rehabilitation
work, a tabulation of all the sewer sections, manholes,
service connections, and inflow sources which can be cost-
effectively rehabilitated or corrected should first be made.
A typical tabulation may include the following information:
(a) Sewer Line Rehabilitation
(1) Method of rehabilitation;
(2) Description of infiltration/inflow sources;
(3) Sewer line or manhole identification;
(4) Sewer length, size, type, depth and type of
cover;
(5) Location of infiltration/inflow sources in
pipe;
(6) Section of pipe to be rehabilitated.
(b) Manhole Rehabilitation
(1) Method of rehabilitation;
(2) Description of infiltration/inflow sources;
4-38
-------
(3) Manhole identification;
(.4) Type and depth of manhole.
(c) Service Connection
(1) Method of rehabilitation;
C2) Description of infiltration/inflow sources;
(3) Address of service connection;
(4) Sewer line to which the service connection is
connected;
(.5) Length of service line;
(6) Type of cover.
(d) Inflow Sources
(1) Method of correction;
(2) Description of inflow source;
(3) Location of inflow source.
Whenever possible, the time schedule for the proposed
rehabilitation work and related costs should also be in-
cluded in the recommendation. For the benefit of a continued
operation and maintenance program, it Is also advisable
to tabulate all the problems in the sewer system observed
during the evaluation survey.
4-39
-------
CHAPTER 5
SEWER SYSTEM REHABILITATION
5.1 INTRODUCTION
The sewer system rehabilitation involves all the work that
is necessary to correct the infiltration/inflow conditions
which were found to be cost-effective to correct in the
Sewer System Evaluation Survey.
The infiltration and inflow sources which are commonly
found in sewer systems are shown in Table 5-1- In the same
table, the possible correction methods for each source
are also shown.
The correction methods for inflow sources are relatively
simple and will not be considered in further detail. The
techniques which are most frequently used for correcting
infiltration sources include [93*.
(a) Excavat i on/Replac ement
(b) Chemical Grouting
(1) Acrylamide gel
(2) Polyurethane foam
(c) Pipe Lining (Slip-lining)
(1) ^Polyethylene pipe
(2) Fiberglass-reinforced polyester mortar pipe
(d) Pipe Lining
(1) Cement mortar
(2) Epoxy mortar
The advantages, limitations, applications and procedures
of these techniques are discussed in the following sections.
Engineers should be aware of any new products which may be
made available in the future. The use of new products is
encouraged If they are proved to be effective.
For applications, only the most effective technique or material
should be used. When several techniques or materials are
equally effective, the one with the minimum overall cost
should be chosen.
5-1
-------
TABLE 5-1
INFILTRATION/INFLOW SOURCES AND CORRECTION METHODS
Sources
Possible Correction Methods
Infiltration Sources
Collapsed pipe
Broken or crushed pipe
Cracked pipe
Deteriorated pipe joints
Leaking off-set Joints
Open joints
Deteriorated mortar joints in
brick pipes
Leaking house service connections
Faulty taps between sewers and
manholes
Faulty taps between service con-
nections and main sewers
Collapsed manhole and wet wells
Deteriorated manhole walls, bases
and troughs
Deteriorated mortar Joints in
brick manholes
Deteriorated wet wells and pumping
station structures
Other sources such as deteriorated
regulators, tide gates, etc.
Replacement; slip-lining
Replacement; slip-lining
Slip-lining; lining with cement
mortar or epoxy mortar;
replacement
Chemical grouting
Slip-lining; chemical grouting;
replacement
Slip-lining; chemical grouting;
replacement
Brick mortar replacement
Chemical grouting; slip-lining;
replacement
Excavation and repair
Excavation and repair
Replacement
Lining with cement mortar or epoxy
mortar; chemical grouting;
cement grouting
Brick mortar replacement
Lining with cement or epoxy
mortar
Repair according to situation
5-2
-------
TABLE 5-1 (Continued)
Sources
Possible Correction Methods
Inflow Sources
Low lying manholes
Perforated manhole covers
Cross connections
Roof leader drains
Foundation drains
Cellar drains
Yard drains
Area drains
Cooling water discharge
Drains from springs and swampy
areas
Manhole raising
Replace with water tight covers
Plugging
Disconnection
Disconnection
Disconnection
Plugging
Plugging
Disconnection
Plugging
5-3
-------
5.2 EXCAVATION/REPLACEMENT
This technique involves the removal of the existing pipes
or manholes from the ground and replacing them with new
ones. If suitable material and construction methods are
utilized, the technique may produce the most effective
rehabilitation results. The cost of this technique,
however, is normally much higher than other rehabilitation
techniques and the time requirement is usually much longer.
The technique is normally considered for application under
one or more of the following conditions E9]:
In locations where pipes or manholes have lost
their structural integrity, such as pipes or
manholes which are collapsed, crushed, broken,
or badly deteriorated and cracked;
In cases where pipe size enlargement, change in
grade and/or line realignment are needed in addi-
tion to pipe deficiency corrections;
In cases where the causes of damages to the
existing pipes or manholes (such as corrosion,
soil movement, increasing traffic load, etc.)
have been identified and it is desirable to pre-
vent the reoccurrence of these damages by replacing
the existing structures with new ones having better
quality and greater strength.
Just as for new sewer construction, this rehabilitation
technique may require the removal of pavement, disruption of
traffic, dewatering, well-pointing, shoring, interference
with utilities and structures, and repavement. In addition,
during the construction period, the sewage flows in the sewer
sections should also be bypassed. All the costs involved in
these tasks should be considered when comparing this technique
with other rehabilitation techniques.
5.3 CHEMICAL GROUTING
5.3.1 Introduction
Chemical grouting is most commonly used to seal leaking
joints in structurally sound sewer pipes. With special
techniques and tools, the method can also be used to seal
leaks in house connections, manhole external drops, man-
holes, wet wells and pumping station structures.
The information described hereinafter was supplied by American
Cyanamid Company and 3M Company. For specific use of these
products, the reader should consult with the manufacturers.
-------
Two chemical grouts have been used extensively: acrylamide
gel and polyurethane foam. Basically, grouting with the
acrylamide gel stops the leaks by internally injecting the
grout to the soils surrounding the leaks to decrease their
permeability. Grouting with the polyurethane foam, on the
other hand, seals the leaks by injecting the grout into
the cracks and letting it solidify to form a barrier.
The acrylamide gel was developed in the early 1950 's by
American Cyanamid Company and was initially used for soil
stabilization. It was not used for sewer rehabilitation
until I960. The polyurethane foam was developed in the
late 1960's and early 1970's by the 3M Company and has been
used for sewer rehabilitation since 1973.
5.3.2 Chemical Grouting With Acrylamide Gel
5.3.2.a Properties of the Acrylamide Gel
The acrylamide gel is commonly known by its trade name,
AM-9. The basic chemical used in the acrylamide gel is a
mixture of two organic monomers, acrylamide and N,N'-methyl-
ene bisacrylamide. The chemical is in the form of a white
powder with a specific weight of about 35 pounds per cubic
foot. A 10-percent (by weight) aqueous solution of this
chemical is usually used for sewer grouting. When the
aqueous solution of this chemical is properly catalyzed,
gelation occurs through a polymerization-crosslinking
reaction.
The catalysts used for the reaction are B-dimethylamino-
propionltrlle and ammonium persulfate. The former is a
caustic solution and is used as an activator for the
reaction. The latter is a strong oxidizing agent used as
an initiator to trigger the reaction.
In field applications, the monomer powder and the activator
are usually dissolved in water in one container and the
initiator is mixed with water in a second container. The
individual solutions are stable for about two weeks. Gel-
ation occurs when these two solutions are mixed together.
The gel time (or "set time" or "induction time") is
primarily affected by the concentrations of the catalysts
and the solution temperature. Generally, the higher the
catalyst concentrations and the temperature, the shorter
the gel time. However, the concentration of the ammonium
persulfate should normally be less than 3-0 percent (by
weight) since at higher concentrations the mix may be too
acidic to gel. Other factors which affect the gel time include
monomer concentration, pH, metal ions, salts, particulate
5-5
-------
matter, hydrogen sulfide and chemical composition of mixing
water. By altering the concentrations of the catalysts,
the gel times can be controlled from 5 to 500 seconds. A
gel time of approximately 20 seconds is commonly chosen in
sewer grouting. Longer gel times are used in structural
waterproofing which needs deeper penetration at lower flow
rates. The effect of catalyst concentration and temperature
on gel time has been documented by American Cyanamid Company
(A typical example is shown in Figure 5-1.) Table 5-2 shows
the compositions of the grouting mixes suggested by the man-
ufacturer for summer and winter applications at ground
temperatures of 60° F and 50° F, respectively.
Before gelation, the grouting mix has a viscosity very
close to that of water. This allows it to penetrate into
small leaks and cracks in pipe walls and to mingle with
outside soil particles. The acrylamide gel formed from the
solution is a translucent, rubbery and elastic material.
Under moist conditions, the gel is resistant to attack by
microorganisms, dilute acids, alkalies, and the ordinary
salts and gases normally found in the ground. When the
gel is formed in a soil matrix, the permeability of the soil
is reduced. The degree of reduction of the permeability
depends upon the extent to which the voids are filled with
the gel. If they are completely filled, the gel-soil mix-
ture is virtually impermeable.
If allowed to dry, the gel will shrink due to dehydration.
In a gel-soil mixture, dehydration may cause shrinkage
cracks which would not be rehealed even if the moisture
content of the mixture is restored later. However, chemical
additives such as ethylene glycol or calcium chloride may be
added to the grout to prevent dehydration.
Before gelation, the acrylamide gel is toxic. Inhalation
of its vapor, contact with skin and swallowing should all
be avoided.
5.3.2.b General Considerations in Applications
The acrylamide gel can be used for sealing pipe joints, but
it cannot be used as a structural repair for broken, crushed
or badly cracked pipes and appurtenant structures.
In soils containing large interstices, such as coral sand,
gravel or rocks, especially in the presence of moving ground-
water, the effectiveness of the gel may be reduced. This
situation may be remedied by one of the following measures:
(1) Judicious use of shorter gel time
5-6
-------
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Temperature
°F
Ammonium Persulfate
Figure 5-1. Effect of Catalyst Concentration and
Temperature on Acrylamide Gel Set
Time
5-7
-------
TABLE 5-2
TYPICAL COMPOSITIONS OP ACRYLAMIDE GEL
GROUTING MIXES [11]
A. SUMMER GROUTING MIX
Ground Temperature: 60° F.
Gel Time: 20 seconds
Composition
AM- 9 tank <
AP tank (
1
fAM-912
DMAPN
, Water
' AP3
, Water
B. WINTER GROUTING
Wt*
10.0
0.8
39.2
3.0
47.0
100.0
MIX
Ibs.
50.0
4.0
196.0
15.0
235.0
500.0
gal.
__
0.56
23.5
MM
28.0
60.0
Ground Temperature: 50° F.
Gel Time: 18 seconds
Composition
(AM-9%
AM-9 tank j DMAPN
I. Water
AP tank ( AP3
1 Water
Wtjf
10.0
1.6
38.4
2.5
47.5
100.0
Ibs.
50.0
8.0
192.0
12.5
237.5
500.0
gal.
1.13
23.0
28.0
5o7o
Mixture of two monomers: acrylamlde and N, N'-methylenebisacrylamide
>
"B-dimethylaminopropionitrile
Ammonium persulfate
5-8
-------
(2) Intermittent grouting
(3) Using higher gel concentration
Before grouting, the pipes should be cleaned. There should
be no obstacles in the pipe to prevent the passage of sealing
packer. The sealing packer can only be used at joints where
the pipe wall on each side of the joint can provide continuous
contact with the packer.
In locations where prolonged dry conditions are expected,
dehydration resisting additives should be used.
5.32.c Applications
5.3.2.C (1) Sewer Grouting - Grouting of sewer pipe joints
is generally accomplished with a sealing packer and a closed
circuit television camera. The sealing packer is used to
apply the chemical grout to the pipe joint. It is usually
made of a hollow metal cylinder which has an inflatable rubber
sleeve on each end of a center band. The television camera
is used to remotely position the packer on the pipe joint and
to inspect the joints before and after the sealing operation.
The sealing packer and television camera are pulled by cables
through a sewer section from manhole to manhole. In addition,
the air testing equipment is sometimes used to determine the
integrity of the joints and to check the effectiveness of the
sealing. The practice of finding the leaking pipe joints
with the air testing equipment followed by immediate chemical
grouting is commonly known as "test and seal".
Figure 5-2 shows a schematic diagram of a sealing packer and
a television camera in place during a grouting operation.
The procedure is as follows:
(a) Clean the pipe.
(b) With the aid of the television camera, position
the sealing packer on the Joint to be grouted.
(c) Pump air to the rubber sleeves of the packer
until they expand and seal against the pipe wall
on both sides of the Joint.
(d) If air testing is to be conducted, it is done
at this time by applying air pressure to the
space created between the two Inflated sleeves.
The joint is usually considered to be adequate
when a pressure equal to or slightly greater than
the maximum expected groundwater static head
pressure can be maintained for a period of several
seconds.
5-9
-------
Manhole
Catalyst
Roller Assembly
Sealing Packer
Chemical
Grout
Catalyst
TV Monitor
fanhole
Roller Assembly
Figure 5-2. Typical Arrangement for Chemical
Grouting with Aery lamide Gel
-------
(e) For the joint which needs sealing, pump the
chemical grout into the space created between the
two inflated sleeves. In this space, the grout
and the initiator solutions are mixed together
and squeezed out through the joint leak into the
surrounding soil. There, the grout displaces the
groundwater and fills the voids between the soil
particles.
(f) After proper gelation time, deflate the packer
and move it to the next joint. To make certain
the sealing is proper, air testing can be con-
ducted. (Before the test, the packer should be
deflated and reinflated to break up the gel inside
the pipe. The packer can also be used to wipe
the pipe before being reinflated.) If the sealing
is unsuccessful, more grout can be pumped through
the joint until a seal is obtained. The gel formed
on the inside of the pipe is very weak and can
be washed away easily by the flowing sewage.
5.3*2.0 (2) Grouting of House Connections and Manhole
External Drops - The acrylamide gel can often be used to
seal the leaks in the house connections and manhole external
drops. However, because of size and/or access limitations,
the sealing packer-television camera technique is normally
not applicable. The frequently used technique for the house
connection is to pump the grout to fill the entire length of
the house connection until the grout exfiltrates through the
various leaks. This technique is also applicable to seal
manhole external drops. Reaming of the house connection
line to remove excess grout may be necessary after the gel
time.
5.3.2.C (3) Grouting of Manholes, Wet Veils and Pumping
Station Structures - To grout manholes, wet wells and
pumping station structures, a special probe-type grout
applicator can be used. The grouting operation is per-
formed by physically entering each of the above structures.
5.3.3 Chemical Grouting with Polyurethane Foam
5.3.3»a Properties of the Urethane Foam
The polyurethane foam grout is normally known as 3M Brand
Elastomeric Sewer Grouting Compound. The grout is a liquid
urethane prepolymer with a specific weight of 9*15 pounds
per gallon and a viscosity of 300-350 centipoises at 70° F
[123.
5-11
-------
When mixed with an equal amount of water, the grout initially
foams and then cures to a tough, flexible cellular rubber.
The first stage of the reaction is referred to as the "foam
time", "induction time" or "cream time" and the second stage
is called "cure time", "set time" or "gel time". Both the
foam time and the cure time are temperature-dependent.
Generally, the higher the temperature, the shorter the
reaction times. An accelerator, which is a water-soluble
amine, is usually added to the mixing water to reduce the
foam and cure times. When a 0.4$ accelerator is added, the
foam time and cure time at 40° P are 45 seconds and 5.5
minutes, respectively, and, at 100° F, they are 15 seconds
and 2.5 minutes, respectively.
The cured grout has a tensile strength of 90 psi and elonga-
tion of 800$. Since the grout contains only about 15* of
the solvent initially, the linear shrinkage upon drying is
only 15*. Cyclic wetting and drying conditions do not sub-
stantially affect the grout. The grout is resistant to most
organic solvents, mild acids and alkalies.
The unreacted polymer solution is toxic and flammable.
Breathing of its vapor and contact with eyes, skin and
clothing should be avoided. The container of this solution
should be kept away from sparks, heat and flame.
5.3.3.b General Considerations in Applications
The polyurethane foam can be used for sealing pipe Joints, but
it cannot be used as a structural repair for broken, crushed
or badly cracked pipes. Before grouting, the pipes should be
cleaned. There should be no obstacles in the pipes to prevent
the passage of sealing packer. The sealing packer can only be
used at Joints where the pipe wall on each side of the Joint
can provide continuous contact with the packer.
The grout can be used in places where prolonged dry conditions
occur. The sealed Joints can accept movement because of high
flexibility of the cured grout.
5.3.3.C Applications
5.3.3.0 (1) Sewer Grouting - For grouting sewers with the
polyurethane foam, procedures similar to those with the
acrylamide gel are followed. A sealing packer, similar to the
one used for the acrylamide gel, is used for injecting the
polyurethane foam. The packer is made of a hollow metal
cylinder with three inflatable sleeves covered by a continuous
outer sleeve. In operation, the packer is positioned on the
Joint to be grouted with the aid of a television camera and
its end sleeves are inflated. The polymer and water are then
5-12
-------
introduced into the space created between the two inflated
sleeves, and the foam time begins. At the end of the foam
time, the center sleeve of the packer is inflated, forcing
the grout into the pipe joint. After the cure time ends,
the sleeves of the packer are deflated and the packer is
moved to the next joint.
To determine the integrity of the joints before and after
the grouting, a water testing system rather than an air
testing system is usually used for the pressure testing.
5.3*3.0 (2) Manhole Grouting - The polyurethane foam can
also be used to grout the leaking joints and cracks in the
manholes. A probe-type applicator is usually used to
inject the grout directly into the leaks. The grouting is
performed by physically entering the manhole.
5.4 PIPE LINING WITH POLYETHYLENE PIPE
5.4.1 Introduction
This sewer rehabilitation technique is commonly called slip-
lining. It involves the pulling of a polyethylene pipe
through a straight section of sewer line to replace the
latter. The following technical advantages are associated
with this method [9]:
For installation, the excavation is less than
that required for complete pipe replacement.
The installed pipe will have low joint leakage
since all joints are butt-fusion welded.
The smooth inner surface of the polyethylene
pipe offers very low resistance to flow.
The polyethylene pipe is corrosion- and abrasion-
resistant .
The pipe is capable of deflection and movement
without breaking.
Because of these advantages, the slip-lining technique may
be considered under one or more of the following sewer con-
ditions :
Extensively cracked pipe, especially if the pipe
is constructed in unstable soil conditions;
5-13
-------
Deteriorating pipe having shallow grade, septic
conditions and corrosive liquids;
Pipe with massive and destructive root intrusion
problems ;
Pipes in locations where the excavation/replace-
ment technique is not applicable .
Installation Equipment
The following equipment is required for the insertion of
the polyethylene pipes into sewers :
Joining equipment (heat fusion rig)
Pulling head (nose cone)
Winch
Rollers
Proofing tool
Grout tank and pump
The joining equipment is used to join the standard poly-
ethylene pipe sections (usually 38 feet in length) above-
ground into a continuous pipe of the desired length. The
joints are made by aligning the pipe sections on the
joining equipment, heating the ends of the pipes and
butting the heated ends together. The formed Joints are
normally stronger than the rest of the pipe and completely
waterproof. The pulling head is utilized to facilitate the
pulling of the pipe into the sewer. One end of the pulling
head is attached to the pipe to be pulled while the other
end is attached to the pulling cable. The winch, consist-
ing of a power operator and a pulling cable, is used to pull
the pipe. The rollers are used to facilitate the movement
of the pipe aboveground during the pull. The proofing tool
is utilized to make certain that the proposed liner can pass
through the sewer without difficulties . The proofing tool
can be fabricated with pulling heads on both ends from a
piece of pipe of the same diameter as the one to be inserted
and of a length equivalent to two sections of the sewer
(normally 8 feet). The grouting tank and pump are used to
grout the annular space between the pipe and manhole connec-
tions to prevent groundwater migration. When greater struc-
tural strength is desired, the annular space in the entire
manhole-to-manhole distance can also be grouted.
5-14
-------
5.4.3 Installation Procedures
(a) Clean and inspect the sewer to determine the
structural conditions, obstructions, offset
joints, intruding service connections, size and
grade. Determine the applicability of the slip-
lining technique to the specific sewer lines
being considered
Evaluation Survey Phase).
(b) Determine the size and wall thickness of the
polyethylene pipe to be inserted. Remove all
obstacles in the sewer, such as deposits, pro-
truding laterals and root intrusion. Pull the
proofing tool through the sewers to make certain
the proposed pipe size is feasible.
(c) Establish the excavation points on the basis of
location of the lines to be slip-lined, pulling
distances and traffic conditions. The locations
of the excavation points should be such as to
minimize traffic disruption. The number of
excavations can be reduced by planning to insert
the pipe in both directions from a single opening.
Normally, a pipe length of 2-3 manhole sections
can be lined from a single excavation.
(d) Excavate to expose the sewer and remove the crown
of the sewer. The access ditch should be long
enough to avoid imposing a bending radius of less
than 35-^0 times the outside diameter of the pipe
liner during insertion. The ditch is sloped
gradually from the ground surface to the top of
the sewer. The width of the ditch should be
sufficient to allow the entry of the workmen.
Sheathing and bracing requirements would depend
on depth and ground conditions.
(e) Join the polyethylene pipe sections to the desired
length at the job site and attach the pulling head
to one end of the joined pipe sections.
(f) Run the pulling cable through the sewer pipe and
connect it to the pulling head. Pull the pipe
liner through the sewer pipe steadily. The annular
clearance between the liner and the pipe is usually
sufficient to permit normal sewage flow during
installation. However, if a high sewage flow is
anticipated, sewer bypasses should be provided
before installation. Once in place, allow the
pipe to reach ground temperature.
(g) Cut in and connect the service connections to the
pipe liner. (See Section 5.4.M for procedures.)
5-15
-------
(h) If pulling has been carried out in both directions
from the same opening, the adjoining pipe ends
should be touching together, wrapped and encased
in concrete. Alternatively, the connections can
be made by using sleeves extending at least one
foot beyond the butted ends and strapped into
position.
(.1) Grout the annular space between the pipe and the
manhole connections. Grouting of the annulus
between the liner and the pipe is usually not
required if the liner is strong enough to with-
stand the anticipated loads in the event of the
collapse of the pipe.
(j) Backfill and compaction of the excavation.
5.**. 4 Methods for Connecting House Service Lines
Three methods have been developed for connecting the house
service lines to the newly inserted polyethylene pipe
liners in sewers [133:
Remote connector
Heat-fusion saddle
Tapping saddle
.4 . 4 . a Remo t e C onne c t or
This method is most suitable for application under the
following conditions:
Access to the house service line is relatively
shallow;
Existing house service line is large enough and
sufficiently straight to permit insertion of a new
4-1/2-inch (outside diameter) polyethylene pipe.
Using this method, the connection can be made with minimum
excavation as follows:
(1) Locate the point where the house service line
leaves the shallow burial and starts dipping down
to connect with the main sewer.
(2) Excavate to expose the service line at this turn-
ing point and break away the shoulder of the turn
in the pipe to create an access opening.
(3) Insert a cutting tool down the line through the
access opening to cut a hole into the new pipe
liner in the main sewer.
5-16
-------
(4) After the cut is completed, insert a piece of
4-1/2-inch polyethylene pipe of appropriate length
down to the main sewer. The connection end of
this pipe is butt-fused with an expandable fitting.
The fitting f-its into the hole previously cut into
the pipe liner and is expanded into place by
using a heating tool. The fitting has also an
integral neoprene gasket which further minimizes
the chance of infiltration at the joint.
(5) Remove the excessive protrusion of the new polyethy-
lene service line into the main sewer with a
trimming tool.
(.6) Connect the upper end of the new service pipe
to the service line leading to the house.
(7) Backfill.
(The complete Installation is illustrated in Figure 5-3)
If the existing house service pipe is too small to permit
insertion of a 4-1/2-inch (O.D.) polyethylene pipe, or if
the pipe route is too tortuous to insert a pipe, the same
method can still be used but with some modifications. In
this case, a 12-inch hole can be drilled from the ground
level to the main sewer line to facilitate the installation
of the remote connector. (The installation is illustrated
in Figure 5-4.)
5.4.4.b Fusion Saddle
This method involves more excavation than the previous
method. The procedure is as follows:
(1) Excavate to the point where the house service
line is connected to the main sewer. Expose
enough space for two workmen.
(2) Break away a portion of the house service pipe
and the old sewer main, and clean the surface
area on the newly Installed polyethylene liner
where the fusion saddle is to be connected.
(.3) Heat both the fusion saddle and the surface of
the polyethylene liner with the heating tool.
When the heating cycle is completed, press the
saddle firmly against the melt patch on the liner.
(4) After solidification, cut a hole through the
outlet of the saddle fitting into the liner.
5-17
-------
GROUND
ECCENTRIC REDUCER ATTACHED
WITH SHRINK SLEEVE
SHRINK SLEEVE
U-l/2" O.D. POLYETHYLENE PIPE
EXISTING 6" PIPE
EXPANDABLE FITTING
INSERTED POLYETHYLENE PIPE
SEWER PIPE
Figure 5-3. Remote Connection of House Service Line
through Sewer Pipe [13]
GROUND SURFACE
HOUSE
EXIST. 6" PIPE
ECCENTRIC REDUCER ATTACHED WITH
SHRINK SLEEVE
4-1/2" O.D. POLYETHYLENE PIPE
SHRINK SLEEVES
DRILLED HOLE - 12" DIA.
INSERTED POLYETHYLENE PIPE
SEWER PIPE
Figure 5-4. Remote Connection of House Service Line
through New Dri I led Hole [13]
5-18
-------
(5) Connect a piece of polyethylene pipe to the out-
let of the fusion saddle using a socket heating
tool.
(6) Connect the new polyethylene service pipe to the
house service pipe leading to the house .
(7) Backfill.
.c Tapping Saddle
This method, as follows, uses a full-encirclement saddle
fitting to make the connection:
(1) Excavate to the point where the house service
line is connected to the main sewer. Expose
enough space for two workmen.
C2) Break away a portion of the house service pipe
and the old sewer main and clean the surface
area on the newly installed polyethylene liner
where the tapping saddle is to be connected.
(3) Drill a hole in the polyethylene liner at the
point of connection.
(4) Fit the saddle to the hole in the polyethylene
liner. Use neoprene gaskets between the under-
side of the saddle and the liner to provide a
tight seal.
(5) Draw the straps around the saddle and the full-
encirclement backing to complete the connection.
C6) Use a cement grout or cement-stabilized sand to
reinforce the connection area to protect against
earth shifting.
(7) Backfill.
5.5 PIPE LINING WITH FIBERGLASS-REINFORCED POLYESTER
MORTAR PIPE
5.5.1 Introduction
Similar to the polyethylene pipe, the fiberglass-reinforced
polyester mortar pipe can also be used to line the exten-
sively cracked sewer pipes with less excavation than the
excavation/replacement technique. This lining method is
usually applied to pipes equal to or greater than 21 inches
in diameter with no service sewers connected [9], Because of
the nature of the pipe material, it is difficult to cut in
and connect the service sewers to this type of pipe. The
pipe can be pulled only in straight sections of sewer lines.
5-19
-------
The fiberglass-reinforced polyester mortar pipe is
corrosion-resistant. The pipe sections are usually 20 feet
in length. They are joined by 0-ring-sealed inverted bell
and spigot joints. The inner surface of the pipe is
smooth. However, because of the inverted bell joints,
some flow reduction is expected after lining.
5.5.2 Installation Procedures
Before installation, the sewer pipe should be internally
inspected and thoroughly cleaned. The liner pipe is in-
serted by excavating over the sewer and pulling or jacking
the pipe upstream against the sewage flow. Sewage flows
are normally uninterrupted during the entire operation.
The specific procedures are as follows:
(a) Clean and inspect the sewer to determine the
structural conditions, obstructions, offset
joints, size and grade. Determine the applica-
bility of this lining technique to the sewer
lines being considered (completed in the Sewer
System Evaluation Survey Phase).
(b) Determine the size and wall thickness of the
polyester pipe to be inserted. Remove all
obstacles in the sewer, such as deposits, root
intrusion, etc. Pull the proofing tool through
the sewers to make certain the proposed pipe size
is feasible.
(c) Establish the excavation points on the basis of
locations of the sewers to be lined, pulling dis-
tances and traffic conditions. The locations of
the excavation points should be such as to
minimize traffic disruption. Pipes are usually
pulled upstream against the sewage flow. There-
fore, the excavation point should be located at
the downstream locations on the sewer lines to
be lined.
(d) Excavate to expose the sewer and remove the crown
of the sewer. The working pit should be long
enough to accommodate the liner sections and the
jacking equipment. If the liner sections are to
be pulled into the pipe, a shorter pit (approxi-
mately 26 feet) would be sufficient. Sheathing
and bracing requirements would depend on depth
and ground conditions.
5-20
-------
(e) Join the liner pipe sections at the job site.
Jack or pull the pipe through the sewer steadily.
The annular clearance between the liner and the
pipe is usually sufficient to permit normal
sewage flow during installation. However, if
unusually high sewage flow is anticipated, sewer
bypasses should be provided before installation.
Cf) Grout the annular space between the liner pipe and
the manhole connections. Grouting of the annular
space between the liner and the pipe is usually not
required if the liner is strong enough to with-
stand the anticipated loads in the event of the
collapse of the pipe.
(g) Backfill and compact the excavation.
5.6 PIPE LINING WITH CEMENT MORTAR AND EPOXY MORTAR
Cement mortar and epoxy mortar can be used to internally
line round concrete or brick pipes which are still structurally
sound. This lining method is generally applied to pipes 24
inches in diameter or larger although it may also be applied
to smaller pipes [93. The cement mortar linings are vulnerable
to chemical attack and should not be used in sewers trans-
mitting corrosive liquids. For corrosive environments, the
epoxy mortar should always be used. The drawback of this
type of lining is that the corrosion caused by hydrogen
sulfide may continue underneath the lining.
The mortars are usually machine-applied to the interior
surface of the sewer pipes. Before application, the pipe
surface should be thoroughly clean, all loose materials
should be removed, the sewage flow should be stopped or by-
passed, and the water standing in the pipe should be removed.
During application, no active infiltration through joints,
pipe walls and service connections is allowed. The pipe
surface should be dried if the epoxy mortar is used; however,
for cement mortar lining, a moist pipe surface is acceptable.
The thickness of the lining is usually 3/16 inch to 3/8 inch
[9].
5-21
-------
CHAPTER 6
COSTS FOR SEWER SYSTEM EVALUATION SURVEY
AND REHABILITATION
6.1 INTRODUCTION
The cost data presented in this chapter provides a general
guidance for engineers performing the cost-effectiveness
analysis in Infiltration/Inflow Analysis. To a limited
extent, the data can also be used for conducting the cost-
effectiveness analysis in Sewer System Evaluation Survey.
The methodology for performing each respective cost-
effectiveness analysis has been described previously (Sections
3.4 and 4.6.3).
The limitations of these cost data must be recognized. The
costs are mainly a compilation of the data from several
reference sources (14, 15, 16, 17) and a number of Infiltration/
Inflow Analysis reports submitted to EPA, and reflect the
average costs prevailing in mid-1974. Individual costs may
vary significantly due to location, site condition, sewer
system condition, weather condition, availability of labor
force, work requirements, and numerous other factors.
Therefore, use of the data presented herein should be
limited to preliminary cost estimates. Engineers are encour-
aged to develop their own cost data from reliable sources to
fit the specific conditions of each project at hand.
6.2 SEWER SYSTEM EVALUATION SURVEY COSTS
Table 6-1 shows the costs required for conducting each phase
of Sewer System Evaluation Survey, except report preparation.
The unit costs presented are the costs required for each foot
of gravity sewer actually included in the evaluation survey.
The range of costs presented for each function reflects the
possible variation of costs for performing the work in
different sewer systems. Factors which may affect the costs
for each phase of study are shown in Tables 6-2 to 6-5.
Figures 6-1 to 6-24 show the cost curves for the Sewer System
Evaluation Survey and for conducting each phase of work in
the Evaluation Survey in terms of the following four
parameters:
Total length of gravity sewer in system
Peak infiltration/inflow
6-1
-------
TABLE 6-1
COSTS FOR SEWER SYSTEM EVALUATION SURVEY
Function
Cost, $/foot of sewer
Physical Survey
Rainfall Simulation
Smoke Testing
Dyed Water Test
Water Flooding
Preparatory Cleaning
6-inch Pipe
8-inch Pipe
10-inch Pipe
12-inch Pipe
15-inch Pipe
18-inch Pipe
21-inch Pipe
24-inch Pipe
30-inch Pipe
36-inch Pipe
Internal Inspection
6-inch Pipe
8-inch Pipe
10-inch Pipe
12-inch Pipe
15-inch Pipe
18-inch Pipe
21-inch Pipe
24-inch Pipe
30-inch Pipe
36-inch Pipe
0.15-0.25
0.15-0.30
0.25-0.50
0.25-0.50
0.30-1.10
0.25-0.90
0.30-1.30
0.35-1-70
0.40-2.10
0.50-2.25
0.70-3.50
0.80-4.25
1.15-5.50
1.45-6.80
0.45-1.25
0.35-1.20
0.30-1.15
0.30-1.20
0.30-1.30
0.35-1.40
0.40-1.55
0.50-1.75
0.55-2.00
0.75-2.20
6-2
-------
TABLE 6-2
PHYSICAL SURVEY COST CRITERIA
Size of study area
Access to manholes
Manhole opening
Manhole size
Manhole depth
Manhole condition
Hazardous gases in manholes
Cleanliness of manholes and sewers
Pipe size
Depth of flow
Flow rate
Weather conditions
Availability and cost of labor
6-3
-------
TABLE 6-3
RAINFALL SIMULATION COST CRITERIA
Access to manholes
Manhole conditions
Hazardous gases in manholes
Cleanliness of manholes and sewers
Pipe size
Depth of flows
Plow rate
Availability of water
Random vs. successive manhole sections
Weather conditions
Availability and cost of labor
6-4
-------
TABLE 6-4
SEWER CLEANING COST CRITERIA
Access to manholes
Manhole conditions
Type of manhole construction
Size of manholes
Depth of sewer
Depth of flow
Depth of deposition
Type of deposition
Pipe size
Structural condition of sewer
Length of manhole section
Intruding building sewers
Requirement for transportation and
disposal of material removed from the sewer
Distance to disposal site
Traffic control requirement
Availability of water
Degree of root intrusion
Random vs. successive manhole section
Weather condition
Mobilization distance
Availability and cost of labor
6-5
-------
TABLE 6-5
INTERNAL INSPECTION COST CRITERIA
Access to manholes
Length of manhole section
Manhole conditions
Hazardous gases in manholes
Depth of sewer
Depth of flow
Plow rate
Pipe size
Pipe cleanliness
Structural condition of sewer
Random vs. successive manhole sections
Flooding conditions
Plugging requirements
Bypass requirements
Terrain
Traffic control requirement
Weather conditions
Documentation requirements
Report requirement
Mobilization distance
Availability and cost of labor
6-6
-------
1,000
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Length of Gravity Sewer, Miles
1,000 2,000
Figure 6-1. Total Evaluation Survey Cost vs Sewer Length
6-7
-------
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Figure 6-2. Total Evaluation Survey Cost vs. Peak Infiltration/Inflow
6-8
-------
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Figure 6-3. Total Evaluation Survey Cost vs. Sewered Population
6-9
-------
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Figure 6-4. Total Evaluation Survey Cost vs. Sewage Flow
6-10
1,000
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6-13
-------
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6-15
-------
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6-16
1,000
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6-17
-------
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to
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6-18
-------
10,000
LO
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10,000
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Figure 6-13. Preparatory Cleaning Cost vs. Sewer Length
6-19
-------
10,000
1,000
100
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Figure 6-14. Preparatory Cleaning Cost vs. Peak Infiltration/Inflow
10,000
I ,000
100
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6-20
-------
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6-21
-------
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10,000
1,000
100
1.0
6-22
-------
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100
10,000
I ,000
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1.0
Peak Infiltration/Inflow, mgd
Figure 6-18. Internal Inspection Cost vs. Peak InfiItralion/In flow
6-24
-------
10,000
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Sewered Population, Thousand Persons
Figure 6-19. Internal Inspection Cost vs. Sewered Population
6-25
-------
o
s
e
10,000
1,000
100
10
1.0
,
r
E£2
C^ C^ ^(f LD (O r^« OO CT)
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100
Sewage Flow, MGD
Figure 6-20. Internal Inspection Cost vs. Sewage Flow
6-26
-------
10,000
3
o
1000
2000
Length of Gravity Sewer. M//es
Figure 6-21. Report Cost vs. Sewer Length
6-27
-------
10,000
1,000
100
10
1.0
8
H
7
B
4
'I
8
9
4
3
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10,000
Peak Infiltration/Inflow, mgd
Figure 6-22. Report Cost ks. Peak Infiltration/Inflow
6-28
1,000
100
10
1.0
-------
10,000 r
y
8
6
e
"
4
3
0
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,000
-
Sewered Population, Thousand Persons
Figure 6-23. Report Cost vs. Sewered Population
6-29
-------
10,000
1 ,000
100
10
1.0
CN *"J ^ IO tD f*~ CQ CTl
C-* rj n in to i
O.I
10
r») ^ lT> CD f" QOCT1
100
Sewage Flow, VGD
Figure 6-24. Report Cost i/s. Sewage Flow
6-30
10,000
1,000
100
10
.0
-------
Total sewered population
Total sewage flow
These cost curves are derived from the cost estimates included
in approximately thirty Infiltration/Inflow Analysis reports
submitted to the ten EPA regional offices for review in 1974-
1975 and represent the average costs one would expect in
conducting the Sewer System Evaluation Survey.
However, because of the specific conditions of each sewer
system, it is highly probable that the costs developed from
other reliable sources for a particular sewer system are
completely off the aforementioned cost curves. Therefore,
these curves should be used only as a general guidance to
determine the reasonableness of the costs generated.
In each figure shown, the solid line is the line of best fit
determined by the least square method for all the data points
plotted. The dashed lines represent the 95% confidence limits
for the mean.
The cost curves shown in Figures 6-1 to 6-4 are the total
evaluation survey costs which include the costs for physical
survey, rainfall simulation, preparatory cleaning, internal
inspection and report preparation. Due to the incompleteness
of the cost data in some reports, the set of cost data used to
derive these curves are not taken from exactly the same
number of reports as those used to derive the curves (Figures
6-5 to 6-24) for each individual phase of work. One may find
that the total evaluation survey costs taken from the cost
curves shown in Figures 6-1 to 6-4, corresponding to each
parameter, do not necessarily equal the sum of the costs
required for the five phases of work, taken from the cost
curves shown in Figures 6-5 to 6-24, corresponding to the
same parameter. This further points out the importance of
using these cost curves with caution and the need for engineers
to develop more accurate costs for each sewer system under
investigation.
6.3 REHABILITATION COSTS
6.3.1 Sewer Replacement Costs^
The cost curve for replacing the existing gravity sewer with
a new pipe of the same size is shown in Figure 6-25. Included
in the costs are the costs for site preparation, excavation,
backfill, pavement, pipe materials, removal of existing pipe,
pipe installation^ reconnection of one house service connec-
tion for every 20 feet of pipe and field inspection. In
6-31
-------
10
30
10
40 50 60 70 80 90 100
Pipe Size, Inches
Figure 6-25. Sewer Replacement Cost vs. Pipe Size
6-32
-------
deriving the cost curve, it was assumed that the depth of
cover over the crown of the pipe is 9 feet, the pipe is laid
in moderately wet soil conditions, the excavations are limited
to earth excavations and the cost required to remove the
existing pipe is 50/5 of that required to install the new pipe.
The cost required for sewage bypassing during construction is
not included.
For preliminary estimations, this curve should be sufficient
in most applications. For more detailed cost estimations,
which may be required in the Sewer System Evaluation Survey,
individual costs should be developed based on the actual
field conditions. Factors which may affect the cost for
sewer replacement are shown in Table 6-6.
6.3-2 Pipe Lining (Polyethylene) Costs
The cost curve for pipe lining with polyethylene pipe is
shown in Figure 6-26. Included in the costs are the costs
for site preparation, insertion pit, pipe materials, pipe
welding, pipe installation, connection of one house service
connection for every 20 feet of pipe, pipe sealing off in
manholes and mobilization. It was assumed that the depth
of cover over the crown of the sewer is 9 feet.
Factors which may affect the pipe lining cost are shown in
Table 6-7- They should be considered in developing more
refined cost data for the studies.
6.3.3 Grouting Costs
The costs for chemical grouting of sewer pipes are shown in
Figure 6-27. The costs are developed based on the following
assumptions [9]:
(a) Length of manhole section: 300 ft
(b) Type of pipe: Vitrified clay
(c) Depth of flow: Less than 2Q% of pipe diameter
(d) Type of joint: Factory made
(e) Joint spacing: 4 feet
(f) Access to manholes: Readily accessible
(g) Manhole opening: 21 inches
(h) Manhole diameter: 4 feet
(i) Manhole condition: Structurally sound with steps
for access
(J) Manhole depths: 6-8 feet
(k) Hazardous gas: None present
(1) Random vs. successive manhole sections: All sections
requiring grouting are successive
(m) Mobilization distance: Within 100 miles
(n) Weather conditions: Mild temperature and no storm
(o) Traffic control: None required
(p) Chemical grout used: Acrylamide gel or urethane foam
6-33
-------
TABLE 6-6
SEWER REPLACEMENT COST CRITERIA
Size of pipe
Depth of pipe
Type of service
Type of pipe
Removal of existing pipe
Number of service connections to be made
Groundwater elevation
Proximity to other utilities
Pipe transportation requirements
Infiltration allowance requirements
Access to site work
Availability of storage area for pipe materials
and equipment
Availability of storage area for excavated materials
Weather conditions
Availability and cost of labor
6-34
-------
5 6 7
60 70 80 90 100
Pipe Size, Inches
Figure 6-26. Pipe Lining (Polyethylene) Cost
. Pipe Size
6-35
-------
TABLE 6-7
PIPE LINING COST CRITERIA
Size of sewer
Length of sewer
Depth of sewer
Grade and direction change of sewer
Depth of flow in sewer
Size of liner pipe
Liner pipe wall thickness required
Annulus grouting requirements
Number of service connections to be made
Type of surface restoration required
Pipe transportation requirements
Type of manhole "seals" required
Extent of sewer cleaning required
Technique to "prove" or preinspect sewer lines
Excavation requirements
Groundwater elevation
Access to site of work
Availability of electrical power for fusing
Availability of storage area for pipe materials
and equipment
Availability of storage area for excavated materials
Mobilization distance
Availability and cost of labor
6-36
-------
4000
10
20
30
70 75
Number of Joints Grouted
Figure 6-27. Grouting Cost vs. Number of Pipe Joints Grouted
6-37
-------
TABLE 6-8
SEWER LINE GROUTING COST CRITERIA
Mobilization distance
Weather condition
Terrain
Type of soil
Access to manholes
Manhole opening
Manhole size
Manhole cleanliness
Manhole depth
Hazardous gases in manhole
Type of pipe
Pipe size
Pipe alignment
Pipe grade
Pipe cleanliness
Depth of flow
Flow rate
Ability to plug
Type of joint
Joint spacing
Offset joints
Intruding service connections
Structurally damaged pipe
Random vs. successive manhole sections
Availability and cost of labor
6-38
-------
TABLE 6-9
MISCELLANEOUS REHABILITATION COSTS
Item
Manhole Replacement
Manhole Repair
Raise Manhole Frame & Cover
Manhole Cover Replacement
House Service Pipe Replacement
House Service Pipe Repair
Roof Leader Drain Disconnection
Foundation Drain Disconnection
Cellar Drain Disconnection
Area Drain Disconnection
Cross Connection Plugging
Drains From Springs Plugging
Unit
each
each
each
each
each
each
each
each
each
each
each
each
Cost, $/Unit
500-1,000
50-500
100-150
50-100
600-1,200
200-400
50-75
300-1,200
50-350
50-350
100-500
500-2,500
6-39
-------
-------
APPENDIX A
REFERENCES
1. "Sewer System Evaluation for Infiltration/Inflow." Prepared
for the United States Environmental Protection Agency
Technology Transfer Program, American Consulting Services,
Inc., Minneapolis, Minnesota.
2. Wilson, J. P., Jr., "Fluorometric Procedures for Dye
Tracing." In "Applications of Hydraulics", Chapter A12,
Book 3) Techniques of Water-Resources Investigations of
the United States Geological Survey, U.S. Government
Printing Office, Washington, D.C. (1968).
3. "Floating Bowl Hypochlorite Solution Feeder." AID-UNC/
IPSED Series Item No. 9, G. V. R. Marais and F. E.
McJunkin (ed.), International Program in Sanitary
Engineering Design (IPSED), University of North Carolina,
Chapel Hill, N.C. (October, 1966).
4. "Floating Platform Hypochlorite Solution Feeder." AID-UNC/
IPSED Series Item No. 7, G.V.R. Marais and F. E. McJunkin
(ed.), International Program in Sanitary Engineering
Design (IPSED), University of North Carolina, Chapel Hill,
N.C. (October, 1966).
5. "Safety Manual." The Penetryn System, Inc., Winter Park,
Florida.
6. "Cost-Effectiveness Analysis Guidelines." Federal Register
40 CFR 35 (February 11, 1974).
7. "Guidance for Preparing a Facility Plan." U.S.
Environmental Protection Agency, Washington, D.C. (Revised -
May 1975).
8. Farmer, H., personal communication (1975).
9. "Preliminary Report for a Manual of Practice." The Sewer
Rehabilitation Subcommittee, Technical Advisory Committee,
American Public Works Association (1975) .
10. "AM-9 Chemical Grout." American Cyanamid Company, Wayne,
New Jersey (1965)
11. "AM-9 Chemical Grout Mix Calculation." American Cyanamid
Company, Wayne, New Jersey.
A-l
-------
12. "3M Brand Elastomeric Sewer Grouting Compound." Specifica-
tion Sheet, 3M Company, Saint Paul, Minnesota.
13. Anonym., "Lateral Connections with Inserted Polyethylene
Piping." Water & Sewage Works, 122, 3, 66-67 (March,
1975).
14. Farmer, H., "Sewer System Evaluation and Rehabilitation
Cost Estimates." Water & Sewage Works. Reference
Number, R8-R9 (April, 1975).
15. "Procedural Guidance for 197^ Survey of Needs for Municipal
Wastewater Treatment Facilities." U.S. Environmental
Protection Agency, Washington, D.C. (May, 197*0.
16. "Building Construction Cost Data." R. S. Means Co., Inc.,
Duxbury, Mass. (197*0 .
17. "Costs of Wastewater Treatment by Land Application."
Office of Water Program Operations, U.S. Environmental
Protection Agency. Technical Bulletin, EPA-^30/9-75-003
(June, 1975).
A-2
-------
APPENDIX B
STATE CERTIFICATION
The U.S. Environmental Protection Agency has granted
authorization to the States to certify if excessive
Infiltration/inflow does or does not exist in a sewer
system tributary to a treatment works. The States have
the prerogative to undertake this authorization if they
desire.
The State certification information is documented in the
Rules and Regulations of 40 CFR 35 Section 35-527-5. This
Section states that "the Regional Administrator will deter-
mine that excessive Infiltration/inflow does not exist, on
the basis of State certification, if he finds that the
State had adequately established the basis for its certifi-
cation through submission of only the minimum information
necessary to enable a judgment to be made. Such information
could include a preliminary review by the applicant or
State, for example of such parameters as per capita design
flow, ratio of flow to design flow, flow records or flow
estimates, bypasses or overflows, or summary analysis of
hydrological, geographical and geological data, but this
review would not usually be equivalent to a complete infil-
tration/Inflow analysis. State certification must be on a
project-by-project basis. If the Regional Administrator
determines on the basis of State certification that the
treatment works is or may be subject to excessive infiltra-
tion/inflow, no Step 2 or Step 3 grant assistance may be
awarded except as provided in paragraph (c) of this section."
Section (c) indicates that the applicant may receive grant
assistance if it is established that the treatment works
will not be significantly changed by subsequent rehabilita-
tion. The grant may be conditioned such that resulting
rehabilitation be performed over some suitable implementation
program.
The State certification program is Intended to hasten the
process of fulfilling the infiltration/inflow requirements
of PL 92-500. Generally, State regulatory personnel are
more familiar with the projects applying for grant assistance
and thus a review of minimal data on a sewer system can
provide sufficient information In which to make a judgment
on excessive or nonexcessive infiltration/inflow.
B-l
-------
State certification is not limited to applicants who provide
minimal information on sewer systems but also applies to
the complete structured infiltration/inflow analysis. In
addition, State certification may be established on both
nonexcessive and possibly excessive infiltration/inflow in
sewer systems. In any event, EPA must issue the final approval
of the infiltration/inflow requirements. As a result, EPA
may provide a cursory or substantial review of the presented
data and/or report. It is expected that in the first years
of the Sewer System Evaluation Program these EPA reviews
of State certified data or reports will be substantial in
view of the fact that all parties involved are developing
experience in this previously neglected area of planning.
As time passes, it is probable that State certification of
projects will receive reduced EPA review.
Currently, those States that are providing certification
of infiltration/inflow data and/or reports do so by review-
ing the data, working closely with those who prepared the
data and then make a judgment on whether possibly excessive
or nonexcessive infiltration/inflow exists. The States then
submit the data and/or report to EPA with a certifying
letter. The certifying letter generally contains statements
which indicate the following when possibly excessive infil-
tration/Inflow exists:
The treatment works for which the grant application
is made will not be changed by any rehabilitation
program and will be a component part of any re-
habilitation program.
The grant applicant has assured that the sewer system
evaluation will be completed.
Any resulting rehabilitation program will be con-
ducted on a schedule consistent with treatment works
construction and satisfactory to the Regional
Administrator.
EPA encourages the States to adopt a certification program.
Cooperation among EPA, the State and the grant applicant
will result in a workable program.
B-2
-------
APPENDIX C
GLOSSARY OP TERMS
1. Combined Sewer
A sewer intended to serve as a sanitary sewer and a storm
sewer, or as an industrial sewer and a storm sewer.
2. Excessive Infiltration/Inflow
The quantities of infiltration/inflow which can be
economically eliminated from a sewer system by rehabilita-
tion, as determined by cost-effectiveness analysis that
compares the costs for correcting the infiltration/inflow
conditions with the total costs for transportation and
treatment of the infiltration/inflow.
3. Infiltration
The water entering a sewer system and service connections
from the ground, through such means as, but not limited
to, defective pipes, pipe joints, connections, or
manhole walls. Infiltration does not include, and is
distinguished from, inflow.
4. Infiltration/Inflow
The total quantity of water from both infiltration and
inflow without distinguishing the source.
5. Infiltration/Inflow Analysis
An engineering and, if appropriate, an economic analysis
demonstrating possibly excessive or nonexcessive
infiltration/inflow.
6. Inflow
The water discharged into a sewer system, including service
connections, from such sources, as but not limited to,
roof leaders, cellar, yard and area drains, foundation
drains, cooling water discharges, drains from springs
and swampy areas, manhole covers, cross connections
from storm sewers and combined sewers, catch basins,
storm waters, surface run-off, street wash waters, or
drainage. Inflow does not include, and is distinguished
from, Infiltration.
C-l
-------
7. Internal Inspection
An activity of the Sewer System Evaluation Survey. This
activity involves inspecting sewer lines that have pre-
viously been cleaned. Inspection may be accomplished by
physical, photographic and/or television methods.
8. Physical Survey
An activity of the Sewer System Evaluation Survey. This
activity involves determining specific flow character-
istics, groundwater levels and physical condition of
the sewer system that had previously been determined to
contain possibly excessive infiltration/inflow.
9. Preparatory Cleaning
An activity of the Sewer System Evaluation Survey. This
activity involves adequate cleaning of sewer lines prior
to inspection. These sewers were previously identified
as potential sections of excessive infiltration/inflow.
10. Rainfall Simulation
An activity of the Sewer System Evaluation Survey. This
activity involves determining the impact of rainfall
and/or runoff on the sewer system. Rainfall Simulation
may include dyed water or water flooding of storm sewer
sections, ponding areas, stream sections and ditches.
In addition, other techniques such as smoke testing and
water sprinkling may be utilized.
11. Rehabilitation
Repair work on sewer lines, manholes and other sewer
system appurtenances that have been determined to contain
excessive infiltration/inflow. The repair work may involve
grouting of sewer pipe joints or defects, sewer pipe re-
lining, sewer pipe replacement and various repairs or
replacement of other sewer system appurtenances.
12. Sanitary Sewer
A sewer intended to carry only sanitary and industrial
wastewaters from residences, commercial buildings,
industrial plants and institutions.
C-2
-------
13 Sewer System Evaluation Survey
A systematic examination of the tributary sewer systems
or subsections of the tributary sewer systems that have
demonstrated possibly excessive infiltration/inflow.
The examination will determine the location, flow rate
and cost of correction for each definable element of the
total infiltration/inflow problem.
1*J. Storm Sewer
A sewer intended to carry only storm waters, surface
run-off, street wash waters, and drainage.
C-3
-------
APPENDIX D
METRIC CONVERSION TABLE
English Unit
Cubic feet per minute
Degree Fahrenheit
Feet
Gallons
Gallons per capita
per day
Gallons per day
Ga liana per day per
inch-nile
Gallons per minute
Inches
Hi lea
Million gallon* per day
Pounds
Pounds per cubic feet
Pounds per gallon
Pound* per square Inch
Abbievlation
cu ft/nin
r
ft
s»i
gpcd
gpd
gpd/ln-mile
gP»
In.
ml
»gd
Ibs
Utt/cu ft
Ibs /gal
P«l
Multiplier
0.0283
0.555 (°P-32)
0.305
0.0038
0.0038
0.0038
0.0009
0.0038
2.54
1.61
0.0038
0.454
16.02
0.12
70.31
Abbreviation
cu a/mln
c
9
Cu Dl
cu n/capita/day
cu m/day
cu B/day /en km.
cu rn/nin
Cl
ka
million cu B/day
kg
kg/cu B
gB/CC
ga/sq cm
Metric Unit
Coble meters per minute
Degree Celsius
Meters
Cubic meter
Cubic secera per capita per dt*y
Cubic Betera per day
Cubic meters per day per
centlmeter-kiloineter
Cubic meters per minute
Centimeters
Kilometers
Million cubic meters per day
Kilograms
Kilograms per cubic meter
Uraoa per cubic centimeter
Grama per square centimeter
} U S GOVERNMENT PRINTING OFFICE 1976-677-876 300 REGION NO 8
D-l
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