Assessing and Assessing and Understanding Understanding Sewer Pipeline Sewer Pipeline DeteriorationDeteriorationRod Thornhill, PERod Thornhill, PE

White Rock ConsultantsWhite Rock Consultants

Dallas, TexasDallas, Texas

UCT International Conference and ExhibitionTrack III-A

Proactive Renovation and Proactive Renovation and ReplacementReplacement

The pavement Management industry has used a history of condition assessment to justify cost-effective proactive renovation

Sewer FailureSewer Failure

0

20000

40000

60000

80000

100000

120000

140000

1880 1900 1920 1940 1960 1980

Mil

es o

f P

ipe

History of Sewer Pipe Installation

EPA Gap Analysis

Total Approx 520,000 Miles

0102030405060708090

100

1910 1930 1950 1970 1990 2010 2030 2050

Average Age of Sewer PipesA

ge

in Y

ears

EPA Gap Analysis

Pipeline Deterioration Pipeline Deterioration AnalysisAnalysis

A “before” and “after” assessment of a A “before” and “after” assessment of a pipelinepipeline

Provides a quantitative understanding Provides a quantitative understanding of rate of deterioration progressionof rate of deterioration progression

Should also include pipe condition and Should also include pipe condition and other factors such as soils, other factors such as soils, surcharging, groundwater, roots, age, surcharging, groundwater, roots, age, etc.etc.

PACP standards provide the ability to PACP standards provide the ability to share with other utilities nation-wideshare with other utilities nation-wide

Deficiencies in Condition Deficiencies in Condition Assessment to DateAssessment to Date

Majority of sewers in place today Majority of sewers in place today were only first televised years were only first televised years after constructionafter construction

Many of the defects in pipes were Many of the defects in pipes were created during constructioncreated during construction

Up until now, the US had no Up until now, the US had no ability to quantitatively measure ability to quantitatively measure change in pipe conditionchange in pipe condition

Steps to Understanding Steps to Understanding Pipe Condition ChangePipe Condition Change

1.1. Thorough assessment of current condition of Thorough assessment of current condition of pipepipe

2.2. Identification and quantification of factors Identification and quantification of factors affecting each individual pipeaffecting each individual pipe

3.3. Understand era and circumstances of original Understand era and circumstances of original constructionconstruction

4.4. Understand Maintenance and Repair History of Understand Maintenance and Repair History of PipePipe

5.5. Use retro-assessment of previous inspection to Use retro-assessment of previous inspection to detect and evaluate changedetect and evaluate change

6.6. Apply knowledge gained to plan the future of Apply knowledge gained to plan the future of each pipeeach pipe

Step 1 Thorough Step 1 Thorough Assessment/Benchmarking of Assessment/Benchmarking of

Current Condition of PipeCurrent Condition of Pipe Adopt and implement a standard code set Adopt and implement a standard code set

and procedures for logging pipe conditionsand procedures for logging pipe conditions Require use of standard condition Require use of standard condition

assessment by all in-house personnel and assessment by all in-house personnel and outside firms.outside firms.

Develop a software and data management Develop a software and data management strategy that assures the longevity of the strategy that assures the longevity of the condition assessment informationcondition assessment information

Maintain an on-going coding quality control Maintain an on-going coding quality control programprogram

Hydrogen Sulfide AttackHydrogen Sulfide Attack STAGE 1 Inverted Syphon / Force MainUnder 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 2Discharge manhole/gravity sewerSulfides 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 1Gravity sewerUnder 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 levelsSTAGE 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.

PACP ConcretePACP Concrete Pipe/H2S Damage Descriptors Pipe/H2S Damage Descriptors

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

PACP ReinforcementPACP Reinforcement Projecting (SRP) Projecting (SRP)

Step 2 Identification and Step 2 Identification and Quantification of Factors Quantification of Factors Affecting Each Individual Affecting Each Individual

PipePipe Root GrowthRoot Growth

Characteristics and extentCharacteristics and extent SurchargingSurcharging

frequency and depthfrequency and depth Presence of groundwater or mineral Presence of groundwater or mineral

encrustationencrustation Maintenance and repair history of Maintenance and repair history of

pipe segmentpipe segment

Root Induced DeteriorationRoot Induced Deterioration Roots intrude Roots intrude

through existing pipe through existing pipe defectsdefects

Root growth expands Root growth expands existing pipe defects existing pipe defects and creates new and creates new defectsdefects

Root growth can Root growth can result in blockages result in blockages and overflowsand overflows

Surcharging caused Surcharging caused by root growth will by root growth will accelerate structural accelerate structural deteriorationdeterioration Deterioration

Mechanisms

50 Years of Root Growth50 Years of Root Growth

Aug 2006

Step 3 Understand Era and Step 3 Understand Era and Circumstances of Original Circumstances of Original

ConstructionConstruction Many, perhaps most of defects in sewers Many, perhaps most of defects in sewers

today were created during constructiontoday were created during construction Most sewers were not first internally Most sewers were not first internally

inspected until decades after constructioninspected until decades after construction The need for watertight joints was not The need for watertight joints was not

established until the late 1950s.established until the late 1950s. History of sewers is not only interesting, History of sewers is not only interesting,

it is essential to the development of a it is essential to the development of a pipeline condition management disciplinepipeline condition management discipline

Excerpts from Metcalf and Excerpts from Metcalf and Eddy Design of Sewers Eddy Design of Sewers

Volume I, 1914Volume I, 1914““American sewerage practice is American sewerage practice is

noteworthy among the branches of noteworthy among the branches of engineering for the prepondering engineering for the prepondering influence of experience rather than influence of experience rather than experiment upon the development experiment upon the development of many of it’s features, apart from of many of it’s features, apart from those concerned with treatment of those concerned with treatment of sewerage”sewerage”

First sentence of IntroductionFirst sentence of Introduction

Excerpts from Metcalf and Excerpts from Metcalf and Eddy Design of Sewers Eddy Design of Sewers

Volume I, 1914Volume I, 1914““The amount of capital required to put up a The amount of capital required to put up a

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

Discussion of early cement pipeDiscussion of early cement pipe

Draining for Profit andDraining for Profit and Draining For Health Draining For Health

Col. George E. Waring 1867Col. George E. Waring 1867

““Every reported case of failure in Every reported case of failure in drainage which we have investigated, drainage which we have investigated, has resolved itself into ignorance, has resolved itself into ignorance, blundering, bad management, or bad blundering, bad management, or bad execution”execution” Gisborne Gisborne

Quote on title page of book, referring to Quote on title page of book, referring to William Gisborne, Minister of Public William Gisborne, Minister of Public Works, New ZealandWorks, New Zealand

Pipe Failure Likely Pipe Failure Likely Created During Created During ConstructionConstruction

Step 4 Understand Step 4 Understand MaintenanceMaintenance

and Repair History of Pipe and Repair History of Pipe Requirement and frequency for cleaning, if Requirement and frequency for cleaning, if

anyany Root treatment frequencyRoot treatment frequency Grease accumulationGrease accumulation Point repair or partial replacement historyPoint repair or partial replacement history Service requestsService requests Backups or SSOsBackups or SSOs Pending work ordersPending work orders Third party damageThird party damage

Step 5 Use Retro-Step 5 Use Retro-Assessment of Previous Assessment of Previous

Inspections to Detect and Inspections to Detect and Evaluate ChangeEvaluate Change

Very inexpensive compared to obtaining Very inexpensive compared to obtaining new datanew data

Audio and Video often of excellent qualityAudio and Video often of excellent quality Can add up quickly to a considerable Can add up quickly to a considerable

portion of the systemportion of the system Provides immediate ability to assess rate of Provides immediate ability to assess rate of

change by comparing “old” data to “new”change by comparing “old” data to “new”

Step 6 Use Knowledge Step 6 Use Knowledge Gained to Plan the Future Gained to Plan the Future

of Each Pipeof Each Pipe Which defects probably are construction-Which defects probably are construction-

relatedrelated Does pipe need to be cleanedDoes pipe need to be cleaned What impact does roots and root control What impact does roots and root control

havehave Aggravating existing defectsAggravating existing defects Creating new defectsCreating new defects

Is the Pipe Material deteriorating (i.e. H2S) Is the Pipe Material deteriorating (i.e. H2S) and at what rateand at what rate

When is the next inspection neededWhen is the next inspection needed

Process of Pipeline Process of Pipeline Condition ManagementCondition Management

Criticality

ConditionAssessment

ContinualImprovement

ProactiveDecisionMatrix

DeteriorationMechanisms

Fundamentals of Sewer Fundamentals of Sewer Pipeline Condition Pipeline Condition

ManagementManagement

Definition: An approach that uses

continual condition assessment,

preventive maintenance, and renewal

to provide an acceptable level of

service for all pipelines, in perpetuity

ContinualImprovement

Criticality

Process of Pipeline Process of Pipeline Condition ManagementCondition Management

ConditionAssessment

DeteriorationMechanisms

ProactiveDecision

Matrix

Major Components of Major Components of Pipeline Condition Pipeline Condition

ManagementManagement Recognition that some pipelines are more Recognition that some pipelines are more

important than others (Criticality, important than others (Criticality, Consequence of Failure)Consequence of Failure)

Comprehensive condition assessment, data Comprehensive condition assessment, data collection, and data dissemination (PACP)collection, and data dissemination (PACP)

Documentation and understanding factors Documentation and understanding factors that influence the rate of sewer pipeline that influence the rate of sewer pipeline condition decline (Deterioration condition decline (Deterioration Mechanisms)Mechanisms)

Major Components of Major Components of Pipeline Condition Pipeline Condition

Management (Cont’d)Management (Cont’d) A work process that continually A work process that continually

utilizes new data to assign utilizes new data to assign maintenance activities and intervals, maintenance activities and intervals, replacement priorities, management replacement priorities, management reports, and geographical display of reports, and geographical display of information (information (Proactive Decision Proactive Decision Matrix)Matrix)

A long term, big picture approach A long term, big picture approach (Continual Improvement)(Continual Improvement)

What are Critical Sewers?What are Critical Sewers?

Sewer where the costs associated with the Sewer where the costs associated with the

failure of the sewer likely to be high.failure of the sewer likely to be high.

Fall into three broad bandsFall into three broad bands

construction costs associated with repairconstruction costs associated with repair

traffic delay coststraffic delay costs

strategically important (trunk sewers)strategically important (trunk sewers)

A

Sample Critical Sewer Sample Critical Sewer MatrixMatrix

TrafficVehicles/Day

Depth of Sewer10 feet or less

Depth of SewerGreater than 10 ft

Good Soil Bad Soil Good Soil Bad Soil

<10,000

10,000 to 15,000

15,000 to 20,000

>20,000

Most Critical5-10% of System B

Critical10-15% of System C All Other Sewers

Criticality

Life Cycle of Sewer LineLife Cycle of Sewer Line

$

Costs

1

5

2

3

4

RATING

Replacement Costs

Structural Grade

Renew/Replace

Time = 0

SummarySummary

Temporal, time-sensitive approach Temporal, time-sensitive approach needed to better understand needed to better understand deterioration mechanisms and rates deterioration mechanisms and rates of deteriorationof deterioration

Standards for describing and Standards for describing and documenting structural and O&M documenting structural and O&M conditions essential for industryconditions essential for industry

Historical documents have a wealth of Historical documents have a wealth of information information

Think long term, big pictureThink long term, big picture