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Assessing and Understanding Sewer Pipeline Deterioration Rod Thornhill, PE White Rock Consultants Dallas, Texas UCT International Conference and Exhibition.

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Presentation on theme: "Assessing and Understanding Sewer Pipeline Deterioration Rod Thornhill, PE White Rock Consultants Dallas, Texas UCT International Conference and Exhibition."— Presentation transcript:

1 Assessing and Understanding Sewer Pipeline Deterioration Rod Thornhill, PE White Rock Consultants Dallas, Texas UCT International Conference and Exhibition Track III-A

2 Proactive Renovation and Replacement The pavement Management industry has used a history of condition assessment to justify cost- effective proactive renovation

3 Sewer Failure

4 Miles of Pipe History of Sewer Pipe Installation EPA Gap Analysis Total Approx 520,000 Miles

5 Average Age of Sewer Pipes Age in Years EPA Gap Analysis

6 Pipeline Deterioration Analysis A “before” and “after” assessment of a pipeline A “before” and “after” assessment of a pipeline Provides a quantitative understanding of rate of deterioration progression 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. 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 PACP standards provide the ability to share with other utilities nation-wide

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

8 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

9 Step 1 Thorough Assessment/Benchmarking of Current Condition of Pipe Adopt and implement a standard code set and procedures for logging pipe conditions 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. 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 Develop a software and data management strategy that assures the longevity of the condition assessment information Maintain an on-going coding quality control program Maintain an on-going coding quality control program

10 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.

11 PACP Concrete 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)

12 PACP Reinforcement Projecting (SRP)

13 Step 2 Identification and Quantification of Factors Affecting Each Individual Pipe Root Growth Root Growth Characteristics and extent Characteristics and extent Surcharging Surcharging frequency and depth frequency and depth Presence of groundwater or mineral encrustation Presence of groundwater or mineral encrustation Maintenance and repair history of pipe segment Maintenance and repair history of pipe segment

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

15 50 Years of Root Growth Aug 2006

16 Step 3 Understand Era and Circumstances of Original Construction Many, perhaps most of defects in sewers today were created during construction Many, perhaps most of defects in sewers today were created during construction Most sewers were not first internally inspected until decades after construction Most sewers were not first internally inspected until decades after construction The need for watertight joints was not established until the late 1950s. 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 History of sewers is not only interesting, it is essential to the development of a pipeline condition management discipline

17 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 it’s features, apart from those concerned with treatment of sewerage” First sentence of Introduction First sentence of Introduction

18 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 Discussion of early cement pipe

19 Draining for Profit and Draining For Health Col. 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 Quote on title page of book, referring to William Gisborne, Minister of Public Works, New Zealand

20 Pipe Failure Likely Created During Construction

21 Step 4 Understand Maintenance and Repair History of Pipe Requirement and frequency for cleaning, if any Requirement and frequency for cleaning, if any Root treatment frequency Root treatment frequency Grease accumulation Grease accumulation Point repair or partial replacement history Point repair or partial replacement history Service requests Service requests Backups or SSOs Backups or SSOs Pending work orders Pending work orders Third party damage Third party damage

22 Step 5 Use Retro-Assessment of Previous Inspections to Detect and Evaluate Change Very inexpensive compared to obtaining new data Very inexpensive compared to obtaining new data Audio and Video often of excellent quality Audio and Video often of excellent quality Can add up quickly to a considerable portion of the system 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” Provides immediate ability to assess rate of change by comparing “old” data to “new”

23 Step 6 Use Knowledge Gained to Plan the Future of Each Pipe Which defects probably are construction-related Which defects probably are construction-related Does pipe need to be cleaned Does pipe need to be cleaned What impact does roots and root control have What impact does roots and root control have Aggravating existing defects Aggravating existing defects Creating new defects Creating new defects Is the Pipe Material deteriorating (i.e. H2S) and at what rate Is the Pipe Material deteriorating (i.e. H2S) and at what rate When is the next inspection needed When is the next inspection needed

24 Process of Pipeline Condition Management

25 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

26 Continual Improvement Criticality Process of Pipeline Condition Management Condition Assessment Deterioration Mechanisms Proactive Decision Matrix

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

28 Major Components of Pipeline Condition Management (Cont’d) 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 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) A long term, big picture approach (Continual Improvement)

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

30 A Sample Critical Sewer Matrix Traffic Vehicles/Day Depth of Sewer 10 feet or less Depth of Sewer Greater than 10 ft Good SoilBad SoilGood SoilBad Soil <10,000 10,000 to 15,000 15,000 to 20,000 >20,000 Most Critical 5-10% of System B Critical 10-15% of System C All Other Sewers Criticality

31 Life Cycle of Sewer Line $Costs$Costs RATINGRATING Replacement Costs Structural Grade Renew/Replace Time = 0

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


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