Assessing and Understanding Sewer Pipeline Deterioration

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

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

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

6. 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

7. 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

8. Steps to Understanding Pipe Condition Change • Thorough assessment of current condition of pipe • Identification and quantification of factors affecting each individual pipe • Understand era and circumstances of original construction • Understand Maintenance and Repair History of Pipe • Use retro-assessment of previous inspection to detect and evaluate change • 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 • 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

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

12. PACP Reinforcement Projecting (SRP)

13. 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

14. 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

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 • 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

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

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

19. 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

20. Pipe Failure Likely Created During Construction

21. 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

22. 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”

23. 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

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

27. 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)

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 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. • Fall into three broad bands • construction costs associated with repair • traffic delay costs • strategically important (trunk sewers)

30. Sample Critical Sewer Matrix Most Critical 5-10% of System Critical 10-15% of System A B C All Other Sewers Criticality

31. 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

32. Summary • 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 • Historical documents have a wealth of information • Think long term, big picture