Assessing and Understanding Sewer Pipeline Deterioration

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Assessing and Understanding Sewer Pipeline
Deterioration
UCT International Conference and
Exhibition Track III-A

• Rod Thornhill, PE
• White Rock Consultants
• Dallas, Texas

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Proactive Renovation and Replacement
The pavement Management industry has used a
history of condition assessment to justify
cost-effective proactive renovation
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Sewer Failure
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History of Sewer Pipe Installation
Miles of Pipe
Total Approx 520,000 Miles
EPA Gap Analysis
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Average Age of Sewer Pipes
Age in Years
EPA Gap Analysis
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Pipeline Deterioration Analysis

• A before and after assessment of a pipeline
• Provides a quantitative understanding of rate of
  deterioration progression
• Should also include pipe condition and other
  factors such as soils, surcharging, groundwater,
  roots, age, etc.
• PACP standards provide the ability to share with
  other utilities nation-wide

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Deficiencies in Condition Assessment to Date

• Majority of sewers in place today were only first
  televised years after construction
• Many of the defects in pipes were created during
  construction
• Up until now, the US had no ability to
  quantitatively measure change in pipe condition

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Steps to Understanding Pipe Condition Change

1. Thorough assessment of current condition of pipe
2. Identification and quantification of factors
   affecting each individual pipe
3. Understand era and circumstances of original
   construction
4. Understand Maintenance and Repair History of Pipe
5. Use retro-assessment of previous inspection to
   detect and evaluate change
6. Apply knowledge gained to plan the future of each
   pipe

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Step 1 Thorough Assessment/Benchmarking of
Current Condition of Pipe

• Adopt and implement a standard code set and
  procedures for logging pipe conditions
• Require use of standard condition assessment by
  all in-house personnel and outside firms.
• Develop a software and data management strategy
  that assures the longevity of the condition
  assessment information
• Maintain an on-going coding quality control
  program

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Hydrogen Sulfide Attack
STAGE 1 Inverted Syphon / Force Main Under
anaerobic (septic) conditions, sulfate present in
the wastewater is converted to sulfides within
the slime layer inside the pipe. Force mains
generally flow full with little aeration
therefore likely points for sulfide production.
Dissolved oxygen levels must be near zero in
order for sulfide production to occur.
STAGE 2 Discharge manhole/gravity sewer Sulfides
in the wastewater are released by turbulent
conditions at discharge point into the sewer
atmosphere and form hydrogen sulfide gas
(H2S).The H2S condenses on the pipe surfaces and
is converted by bacteria into a weak sulfuric
acid. The sulfuric acid attacks concrete and
metal surfaces.
STAGE 1 Gravity sewer Under anaerobic (septic)
conditions sulfate present in the wastewater is
converted into sulfides within the slime layer.
Sewers with laminar flow therefore little
aeration are most susceptible to low dissolved
oxygen levels STAGE 2 Turbulence releases
dissolved sulfides into the sewer atmosphere in
the form of hydrogen sulfide (H2S). The H2S then
condenses on sewer surfaces in the form of
sulfuric acid. The sulfuric acid attacks cement
based materials and metals.
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PACP Concrete Pipe/H2S Damage Descriptors

• Roughness increased (SRI)
• Aggregate visible (SAV)
• Aggregate projecting (SAP)
• Aggregate missing (SAM)
• Reinforcement Visible (SRV)
• Reinforcement Projecting (SRP)
• Reinforcement Corroded (SRC)
• Missing Wall (SMW)

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PACP Reinforcement Projecting (SRP)
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Step 2 Identification and Quantification of
Factors Affecting Each Individual Pipe

• Root Growth
• Characteristics and extent
• Surcharging
• frequency and depth
• Presence of groundwater or mineral encrustation
• Maintenance and repair history of pipe segment

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Root Induced Deterioration

• Roots intrude through existing pipe defects
• Root growth expands existing pipe defects and
  creates new defects
• Root growth can result in blockages and overflows
• Surcharging caused by root growth will accelerate
  structural deterioration

Deterioration Mechanisms
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50 Years of Root Growth
Aug 2006
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Step 3 Understand Era and Circumstances of
Original Construction

• Many, perhaps most of defects in sewers today
  were created during construction
• Most sewers were not first internally inspected
  until decades after construction
• The need for watertight joints was not
  established until the late 1950s.
• History of sewers is not only interesting, it is
  essential to the development of a pipeline
  condition management discipline

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Excerpts from Metcalf and Eddy Design of Sewers
Volume I, 1914

• American sewerage practice is noteworthy among
  the branches of engineering for the prepondering
  influence of experience rather than experiment
  upon the development of many of its features,
  apart from those concerned with treatment of
  sewerage
• First sentence of Introduction

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Excerpts from Metcalf and Eddy Design of Sewers
Volume I, 1914

• The amount of capital required to put up a small
  plant for making cement tile and pipe is so
  moderate that a large number of these little
  works have been built. Owing mainly to lack of
  skill, working capital, or both, much inferior
  pipe has been produced in these small plants, and
  this poor product has prejudiced many engineers
  against all cement pipe
• Discussion of early cement pipe

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Draining for Profit and Draining For HealthCol.
George E. Waring 1867

• Every reported case of failure in drainage which
  we have investigated, has resolved itself into
  ignorance, blundering, bad management, or bad
  execution Gisborne
• Quote on title page of book, referring to William
  Gisborne, Minister of Public Works, New Zealand

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Pipe Failure Likely Created During Construction
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Step 4 Understand Maintenance and Repair
History of Pipe

• Requirement and frequency for cleaning, if any
• Root treatment frequency
• Grease accumulation
• Point repair or partial replacement history
• Service requests
• Backups or SSOs
• Pending work orders
• Third party damage

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Step 5 Use Retro-Assessment of Previous
Inspections to Detect and Evaluate Change

• Very inexpensive compared to obtaining new data
• Audio and Video often of excellent quality
• Can add up quickly to a considerable portion of
  the system
• Provides immediate ability to assess rate of
  change by comparing old data to new

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Step 6 Use Knowledge Gained to Plan the Future
of Each Pipe

• Which defects probably are construction-related
• Does pipe need to be cleaned
• What impact does roots and root control have
• Aggravating existing defects
• Creating new defects
• Is the Pipe Material deteriorating (i.e. H2S) and
  at what rate
• When is the next inspection needed

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Process of Pipeline Condition Management
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Fundamentals of Sewer Pipeline Condition
Management
Definition An approach that uses continual
condition assessment, preventive maintenance, and
renewal to provide an acceptable level of service
for all pipelines, in perpetuity
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Process of Pipeline Condition Management
Proactive Decision Matrix
Criticality
Continual Improvement
Deterioration Mechanisms
Condition Assessment
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Major Components of Pipeline Condition Management

• Recognition that some pipelines are more
  important than others (Criticality, Consequence
  of Failure)
• Comprehensive condition assessment, data
  collection, and data dissemination (PACP)
• Documentation and understanding factors that
  influence the rate of sewer pipeline condition
  decline (Deterioration Mechanisms)

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Major Components of Pipeline Condition Management
(Contd)

• A work process that continually utilizes new data
  to assign maintenance activities and intervals,
  replacement priorities, management reports, and
  geographical display of information (Proactive
  Decision Matrix)
• A long term, big picture approach (Continual
  Improvement)

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What are Critical Sewers?

• Sewer where the costs associated with the failure
  of the sewer likely to be high.
• Fall into three broad bands
• construction costs associated with repair
• traffic delay costs
• strategically important (trunk sewers)

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Sample Critical Sewer Matrix
Most Critical 5-10 of System
Critical 10-15 of System
A
B
C
All Other Sewers
Traffic Vehicles/Day Depth of Sewer 10 feet or less Depth of Sewer 10 feet or less Depth of Sewer Greater than 10 ft Depth of Sewer Greater than 10 ft
Good Soil Bad Soil Good Soil Bad Soil
lt10,000
10,000 to 15,000
15,000 to 20,000
gt20,000
Criticality
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Life Cycle of Sewer Line
R A T I N G
Costs
Replacement Costs
1
2
Renew/Replace
3
4
Structural Grade
5
Time 0
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Summary

• Temporal, time-sensitive approach needed to
  better understand deterioration mechanisms and
  rates of deterioration
• Standards for describing and documenting
  structural and OM conditions essential for
  industry
• Historical documents have a wealth of information
  
• Think long term, big picture