Investigation . of Pipe Cleaning Methods

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The mission of the Awwa Research Foundation (AwwaRF) is to advance the science of water to improve the quality of life. Funded primarily through annual subscription payments from over 1,000 utilities, consulting finns, and manufacturers in North America and abroad, AwwaRF sponsors research on all aspects of drinking water, including supply and resources, treatment, monitoring and analysis, distribution, management, and health effects.

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Investigation of Pipe Cleaning Methods Prepared by: Dan Ellison, P.E. Boyle Engineering Corporation 5851 Thilfe Street, Suite 201 Ventura, CA 93003

With assistance from: Steven J. Duranceau, P.E. Boyle Engineering Corporation Susan Ancel, P.E., and Gabrielle Deagle EPCOR Water Services and Rod McCoy, P.E. Yarra Valley Water

Sponsored by: Awwa Research Foundation 6666 W. Quincy Avenue Denver, CO 80235-3098

Published by the Awwa Research Foundation and American Water Works Association

DISCLAIMER

This study was funded by the Awwa Research Foundation (AwwaRF). AwwaRF assumes no responsibility for the content of the research study reported in this publication, or for the opinions or statements of fact expressed in the report. The mention of trade names for commercial products does not represent or imply the approval or

endorsement of AwwaRF. This report is presented solely for informational purposes.

Library of Congress Cataloging-in-Publication Data

Ellison. Dan. Investigation of pipe cleaning methods / prepared by Dan Ellison. with assistance from

Steven J. Duranceau ... [et al.]; sponsored by Awwa Research Foundation. p. cm.

Includes bibliographical references. ISBN 1-58321-2604

1. Water-pipes--Cleaning. I. Awwa Research Foundation. ll. Title.

TD491 .E435 2002 628.1'5--dc21

Copyright © 2003 by

Awwa Research Foundation and

American Water Works Association Printed in the U.S.A.

ISBN 1-58321-260-4

2002038275

Printed on recycled paper.

CONTENTS

LIST OF TABLES .................................................................................................................... ix

LIST OF FIGURES .................................................................................................................. xi

FOREWORD ............................................................................................................................ xiii

ACKNOWLEDGMENTS. ..... .......................................................... ........................................ xv

EXECUTIVE SUMMARY ......... ............................................................................................. xvii

CHAPTER 1: THE NECESSITY FOR PIPE CLEANING ..................................................... 1 What Does Pipe Cleaning Accomplish? ....................................................................... 2

Replacement of Poor Quality Water .................................... :............................ 4 Removal of Sediment Deposits......................................................................... 4 Removal of BiofilIns ............................................................. ............................ 5 Removal of Tuberculation and Scale ............ ....................... .............. ............... 8 Cleaning and Lining Rehabilitation .................................................................. 10

Final Considerations for Keeping the Distribution System Clean and Clear ............... 10

CHAPTER 2: GENERAL GUIDE TO PIPE CLEANING ...................................................... 13 Selecting Pipe for Cleaning .......................................................................................... 13

Customer Complaints........................................................................................ 14 Water Quality Data-Collection and Analysis................................................. 15 Water Quality Monitoring Plan ........................................................................ 15 Special Studies ........................... ............................................................ ........... 17 Hydraulic Data .................................................................................................. 17 Line Break and Leak Data ................................................................................ 18 Problem Diagnosis ............................................................................................ 18

What Pipe Cleaning Method Should Be Used? ............................................................ 21 How Do the Costs of the Various Methods Compare? ............ :.................................... 24 What Else Should Be Considered in Selecting a Method? ........................................... 25

Distribution System Master Planning ...................................................... ;........ 25 System Considerations ............... ....................................................................... 25

How Can Dirty Water Be Discharged?........................................................................ 25 Dechlorination. .... ........ ...... ........................................ ....... ................................. 25 Sediment Removal..... ....................................................................................... 27 Flow Diffusion................................ ................................ .................................. 28

How Will Water Delivery Be Affected During Pipe Cleaning? ................................... 28 How Should Results Be Measured?........ ...................................................................... 30

Customer Complaints................. ........................................... ............................ 30 Discharge Turbidity.......................................................................................... 30 "Time to Clear" .......................................... ....................................................... 31 Water Quality and Hydraulic Data ................................................................... 31

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Where Should Results Be Measured?.......................................................................... 31 How Frequently Should Pipe Be Cleaned? ................................................................... 31 Conclusions and Recommendations for Selecting a Cleaning Method ........................ 32

CHAP'fER 3: FI...USHIN"G ....................................................................................................... 35 What Flushing Method Should Be Used? ..................................................................... 35

Conventional Flushing .. ........... ... ... ............. ......... ....... .... ... .................... ........... 35 Unidirectional Flushing .................................................................................... 36 Continuous or Automated Dead-end Flushing ................................................. 38

How Do the Costs of Unidirectional Flushing and Conventional Flushing Compare? ........................................................................................... 39

What Results Are Achieved by Flushing? .................................................................... 40 Reductions in Customer Complaints/lncreases in Customer Satisfaction ........ 40 Measured Improvements in Water Quality ....................................................... 43 Biofilm RemovallPublic Health Benefits of Flushing ...................................... 46 Effect of Flushing on Disinfectant Level.... ..... .... ...... ........ ............ ............ ....... 49 The Hydraulic Benefits of Flushing.................................................................. 49

How Often Should Mains Be Flushed? ........................................................................ 50 Where to Get Started......................................................................................... 52 Reactive Flushing Triggers ............................................................................... 53

What Velocities Are Needed for Effective Flushing? .................................................. 53 Conclusions About Flushing Velocities............................................................ 55 Why High Velocities in Large Pipe May Not Be As Important ....................... 56

What Lengths of Pipe Should Be Flushed? .................................................................. 56 What Else Should Be Considered in Flushing? ............................................................ 56

Public Notices and Other Stakeholder Contact................................................. 56 Customer Service Impacts .. ...... ...... .... .... ..... ... .... .......... ..... ...... ......... ..... ........... 57 Dechlorination of Discharge ............................................................................. 57 Disposal of Dirty Water .............................................................. ,. .... ..... ........... 57 Valve-position Verification and Documentation .............................................. 57 System Inventory and Assessment........ ...... ..... ............ ....... ......... .... .............. ... 57 Planning of Flushing Runs...... ......... ..... ...... ... ......... ... .... ..... ... ... ..... ....... ............ 57 Contingency Planning ....................................................................................... 58 Crew Training ................................................................................................... 58

CHAPTER 4: AIR SCOURING ............................................................................................... 59 Won't the Water Hammer Hurt the Pipe?.................................................................... 60 What Is Needed for Air Scouring?............................................................................... 60 What Results Can Be Expected From Air Scouring? ................................................... 62 Will Air Scouring Damage the Lining? ........................................................................ 63 What Length of Pipe Can Be Scoured? ........................................................................ 64 What Pipes are Candidates for Air Scouring? ...... ... ... ....... ................ ..... ............. ... ...... 64 How Does Air Scouring Affect Customer Service? ..................................................... 69 What Else Needs to Be Considered in Planning an Air Scouring Project? .................. 69

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CHAPTER 5: SWABBING AND PIGGING ........................................................................... 71 Where Can Swabbing or Pigging Be Used? ................................................................. 71 What Applications Are Suited for Pigging and Swabbing?......................................... 73 What Results Are Achieved by Swabbing? .................................................................. 74 Which Is Most Effective-Swabbing or Air Scouring? ............................................... 76 What Results Are Achieved by Pigging? ................................................... :................. 78 How Does the Cost of SwabbinglPigging Compare With Other Techniques? ............ 78 How Is the Discharge Handled? ................................................................................... 82 What Other Types of Pigs Are Available? ................................................................... 82 What Else Needs to Be Considered When Swabbing or Pigging? ............................... 84

CHAPTER 6: OTHER PIPE CLEANING TECHNIQUES ..................................................... 87 The History of Chemical Cleaning .... ....... .... ...... ......... ..... ..... ......... ............. ....... .......... 87 How Chemical Cleaning is Performed ......................................................................... 88

Scale Analysis ................. .................................................................................. 88 The Chemical Cleaning Process. ......... ...... ..... ........ ... .... ..... ............. ....... .......... 88 The Cleaning Fluid ........................................................................... :............... 89

Using Jetting to Clean Potable Water Pipes ................................................................. 91 Using Balling to Clean Potable Water Pipes ................................................................ 92 Should the Pipe Be Cleaned to Bare Metal? ................................................................. 93 What Else Needs to Be Considered When Using These Methods?............................. 93

CHAPTER 7: IN SITU CLEANING AND LINING TECHNIQUES ..................................... 95 The Need to Do Something........................................................................................... 95 Why Use "Trenchless" Methods? ................................................................................. 96 What Methods Can Be Used for Pipeline Renewal? .................................................... 97

In Situ Cement-Mortar Lining ............................................................ :::........... 97 Epoxy and Other Plastic Linings ..... ........ ......... ..... .... ........... ........ .... ...... .... ...... 98 Structural Liners and Trenchless Replacement....... ............. ............. ......... ....... 98 Proprietary Structural Liners............................................................................. 101

Can Pipe Be Lined Through Bends and Valves?......................................................... 102 What About Service Connections? ............................................................................... 102 How Can Customers Be Kept "In Water"? ................................................................... 103 How Is Pipe Cleaned in Preparation for Relining? ....................................................... 103 How To Choose a Rehabilitation Method .................................................................... 104 How To Start a Pipeline Renewal Project... .................................................................. 106

Drawings ........................................................................................................... 106 Specifications ............ , ..... ............. ...... .... ..... ........ ........ ........ ..................... ......... 106 Construction Management and Inspection........ ............. ...... .......... ......... ....... ... 107

APPENDIX A: SURVEY OF WATER UTILITIES................................................................ 109

APPENDIX B: CITY OF EDMONTON'S 2001-2002 FLUSHING OPTIMIZATION STUDy ......................................................................................................................... 125

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APPENDIX C: FLOW RATES FOR VARIOUS VELOCITIES AND SIZES OF PIPE........ 133

APPENDIX D: FLUSlflNG STANDARD OPERATING PROCEDURE ...................... :....... 135

REFERENCES ......................................................................................................................... 137

ABBREVIATIONS .................................................................................................................. 141

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TABLES

ES.I Summary of case studies reviewed in this report....................................................... xix

1.1 Pipe cleaning results .................................................................................................. 3

1.2 Considerations in keeping the distribution system clean and clear.... ... .... ......... .... ... 11

2.1 Distribution system water quality parameters for pipe cleaning programs ............... 16

2.2 Factors to be considered in developing a water quality monitoring plan .................. 17

2.3 Typical labor, equipment, water use, and productivity for pipe cleaning methods.... 24

2.4 System considerations in the selection of a pipe cleaning method ... :........................ 26

2.5 Recommended initial flushing schedule .................................................................... 32

3.1 Guide to selection of flushing processes.................................................................... 39

3.2 Methods for measuring flushing results ..................................................................... 41

3.3 Case study results, LADWP Focused Flushing Program .......................................... 44

3.4 Case study: Cincinnati Water Works, water quality monitoring program (unidirectional flushing pilot studies) ........................................................................ 46

3.5 Case study: Cincinnati Water Works, pilot flushing program.................................... 48

3.6 Case study: City of Edmonton, 2000 flushing program results for unidirectional flushing groups 3156 and 4627........................................................... 51

3.7 Case study: City of Edmonton, total water quality complaints for unidirectional flushing groups 3156 and 4627........................................................... 52

3.8 Examples of reactive flushing trigger points.............................................................. 53

4.1 Compressor sizing guidelines for air scouring..... ............... ......... .............................. 61

4.2 Case study-Bluffton, air scouring results ................................................................ 63

4.3 Comparison of unidirectional flushing, air scouring, and swabbing-Yarra Valley Water, Australia ..................................................................................... 66

4.4 Case study-Severn Trent Water, selection of pipe cleaning methods...................... 67

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4.5 Considerations in planning air scouring projects ...................................................... . 68

5.1 Approximate pressures and flows required for pigging of water mains ................... . 72

5.2 Frequent applications for swabs and pigs by water utilities ..................................... . 74

5.3 SWC case study (1990-1992), swabbing discharge water characterizations ........... . 76

5.4 Case study-Wilga and Myall Streets, comparison of air scouring and swabbing effectiveness .............................................................................................. . 77

5 5 P· li .. tudi . Ipe ne pIggIng case s es .................................................................................... . 79

5.6 Specialized pigs with applications in the water industry .......................................... . 84

5.7 Considerations in performing swabbing and pigging ............................................... . 85

6.1 Analysis of various pipe scales (ppm) ...................................................................... . 89

6.2 Case study: Cheyenne chemical cleaning, average before and after values ............. . 90

6.3 Considerations in performing chemical cleaning, jetting, or balling ........................ . 94

7.1 Comparison of pipeline renewal methods.. .... ... .... ... ... ..... ... .... .......... .... ...... ..... .......... 105

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FIGURES

1.1 Tuberculated cast-iron pipe ....................................................................................... . 2

2.1 Pipe cleaning program framework ............................................................................ . 14

2.2 Diagnostic chart for water delivery problems ........................................................... . 19

2.3 General guidelines to pipe cleaning methods ........................................................... . 22

2.4 Bypass piping ........................................................................................................... .. 29

2.5 Decision guide for selecting pipe cleaning methods ................................................ .. 33

3.1 Flushing in Edmonton .............................................................................................. .. 36

3.2 Conventional versus unidirectional flushing ............................................................. . 37

3.3 Valve operations in Edmonton .................................................................................. . 38

3.4 Volume of w~ter flushed versus complaints .............................................................. . 43

3.5 Monitoring turbidity .................................................................................................. . 45

3.6 Baseline and postflushing water quality measurements, Cincinnati unidirectional flushing pilot program .............................................................. :;: ....... . 47

4.1 Air scouring concept ................................................................................................. . 59

4.2 Air scouring rig ......................................................................................................... . 60

4.3 Baffle box .................................................................................................................. . 62

5.1 Pipe cleaning pigs ..................................................................................................... . 72

5.2 Pig launcher and pig ................................................................................................... . 73

5.3 Receiving a 30-in. swab ........................................................................................... .. 74

5.4 Pig exiting a fire hydrant .......................................................................................... .. 83

5.5 Discharging to a lined roll-off bin ............................................................................ .. 83

6 1 P· . tt' . IpeJe lng ................................................................................................................ . 91

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6.2 Sewer and storm cleaning ball................................................................................... 92

7.1 Cement-mortar lining (before and after) .............................................................. :.... 97

7.2 High-density polyethylene slip lining ......................................................................... 99

7.3 Deformed and banded high-density polyethylene pipe ready for tight-fit insertion ............................................................................................................... ". .... 100

7.4 Pipe bursting..... .......... ......... .......... ......... .............. ..... ......... .... ........ ........... ................ 101

7.5 Drag scraper .:............................................................................................................. 104

7.6 Rack-feed boring machine ......................................................................................... 104

A.l Results of utility survey ............................................................................................. 110

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FOREWORD

The Awwa Research Foundation is a nonprofit corporation that is dedicated to the implementation of a research effort to help utilities respond to regulatory requirements and traditional high-priority concerns of the industry. The research agenda is developed through a process of consultation with subscribers and drinking water professionals. Under the umbrella of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested project based upon current and future needs, applicability, and past work; the recommendations are forwarded to the Board of Trustees for final selection. The foundation also sponsors research projects through an unsolicited proposal process; the Collaborative Research, Research Applications, and Tailored Collaboration programs; and various efforts with organizations such as · the U.S. Environmental Protection Agency, the U.S. Bureau of Reclamation, and the Association of California Water Agencies.

This publication is a result of one of these sponsored studies, and it is hoped that its findings will be applied in communities throughout the world. The following report serves not only as a means of communicating the results of the water industry's centralized research program but also as a tool to enlist the further support of the nonmember utilities and individuals.

Projects are managed closely from their inception to the final report by the foundation's staff and large cadre of volunteers who willingly contribute their time and expertise. The foundation serves a planning and management function and awards contracts to other institutions such as water utilities, universities, and engineering firms. The funding for this research effort comes primarily from the Subscription Program, through which water utilities subscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufacturers subscribe based on their annual billings. The program offers a cost-effective and fair method for funding research in the public interest.

A broad spectrum of water supply iSsues is addressed by the foundation's research agenda: resources, treatment and operations, distribution and storage, water quality and analysis, toxicology, economics, and management. The ultimate purpose of the coordinated effort is to assist water suppliers to provide the highest possible quality of water economically and reliably. The true benefits are realized when the results are implemented at the utility level. The foundation's trustees are pleased to offer this publication as a contribution toward that end.

The internal condition of the water distribution pipelines significantly affects the performance of water utilities in several ways. Tuberculation, scale, and biofilm impede the flow of water, reducing the available supply, increasing energy costs, and sometimes seriously hampering our ability to fight fires. Sediment in pipelines causes water discoloration and, along with tuberculation and scale, provides an environment favorable to the growth of bacteria and degradation of water qUality. Customer satisfaction is adversely affected by the appearance, taste, and odor of water delivered through "dirty pipe." Yet, despite the importance of pipe cleanliness, the subject is not well understood by utilities. Utilities may be uncertain about when, where, and how to clean the pipes, and what benefits are derived. This report seeks to answer these questions, by bringing together the knowledge and experience of many sources, enabling utilities to make better-informed decisions.

Edmund G. Archuleta, P.E. Chair, Board of Trustees Awwa Research Foundation

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James F. Manwaring, P.E. Executive Director Awwa Research Foundation

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ACKNOWLEDGMENTS

The authors of this report acknowledge the contributions made by the various researchers and authors whose works are the references for this report. Special thanks are due the following people who each gave time and effort directly to this project:

Awwa Research Foundation (AwwaRF) Project Manager: Stephanie Morales, Denver, Colo.

AwwaRF Project Advisory Committee:

Michael Grahek, Los Angeles Department of Water and Power, Los Angeles, Calif. Dammika Vitanage, Sydney Water Company, Sydney, Australia William Kirkpatrick, East Bay Municipal Utility District, Oakland, Calif. Ray Sterling, Louisiana Tech University, Ruston, La.

Technical Editors:

Steven J. Duranceau, Boyle Engineering Corporation, Orlando, Fla. Susan Ancel and Gabrielle Deagle, EPCOR Water Services, Edmonton, Alta. Rod McCoy, Yarra Valley Water, Melbourne, Australia

Other Participants:

Gunter (Fritz) Redlin, Boyle Engineering Corporation, Fresno, Calif. Ed Davis, city of Bluffton, Ind. Faye Cossins and Gardell Smith, Cincinnati Waterworks, Cincinnati, Ohio Brian Kellsey, EPCOR Water Services, Edmonton, Alta. Howard Schumacher, EPCOR Water Services, Edmonton, Alta. Stan Goodreau, Flow-Line Services, Downey, Calif. Ken Morgan, KCM Consulting, Denver, Colo. Jim Farmerie, HERe Products, Inc., Wexford, Pa. Steve Carl, HERC Products, Inc., Phoenix, Ariz. Rupam Barthakur and Martin Kane, Severn Trent Water, Birmingham, U.K. Henry Topf, Severn Trent Pipeline Services, Greencastle, Ind. John Miller, Los Angeles Department of Water and Power, Los Angeles, Calif. Spencer Cubage, Pipeline Pigging Products, Houston, Texas Koby Cohen, Southern California Water Company, Carson, Calif. Will Ridgely, Washington Suburban Sanitation Commission, Laurel, Md. Asoka Jayaratne, Yarra Valley Water, Melbourne, Australia Francis Pamminger, Yarra Valley Water, Melbourne, Australia

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EXECUTIVESUNrndARY

A well-planned, well-executed pipe cleaning program provides many benefits. Cleaning removes sediment and biofilm from pipes, thereby reducing the risk of water discoloration, taste and odor problems, coliform regrowth, and regulatory noncompliance. Pipe cleaning can also remove scale and tuberculation, dramatically improving hydraulic capacity, increasing fire flows in particular, while reducing pumping costs. Yet despite these benefits, many utilities clean pipes only occasionally-usually in response to customer complaints, or to address specific water quality problems. Uncertainties about how, when, and where to clean pipes have contributed to this oversight. The purpose of this report is to give utility managers the guidance needed to make informed decisions.

Nearly all distribution pipes need cleaning eventually. Sediments accumulate, biofilms grow, scale develops, and water quality deteriorates in processes that promote one another. As this occurs, customer complaints increase, hydraulic capacities decrease, and the risks of coliform and other water quality problems rise. In most systems, the greatest single source of problems is the unlined iron pipe inventory. Its corrosion products are the largest source of sediment, and its tubercles are the greatest impediment to effective cleaning. Biofilm thrives in these pipes, protected by the sediment and scale.

Common pipe cleaning techniques include conventional flushing, unidirectional flushing, air scouring, swabbing, pigging, and drag scraping and rack-feed boring. Less common techniques include chemical cleaning, jetting, and ball cleaning. The effectiveness of these methods varies considerably, as does the cost.

Flushing, the oldest and least expensive technique, is practiced by virtually all water utilities. It is used frequently to replace poor quality water, to raise disinfectant residuals, and to respond to customer complaints. When performed unidirectionally, flushing can be fairly effective in removing sediment and biofilm. A program of regular flushing thus reduces the risks of water discoloration, taste and odor problems, and coliform regrowth. Unidirectional flushing also uses less water than conventional flushing. Unfortunately, flushing is often not effective in cleaning pipes with tuberculation, scale, or other adherent materials--or pipes with large diameters.

Air scouring is similar to unidirectional flushing, except that air is introduced to the fluid column, which results in a high-velocity, very turbulent flow. Air scouring is useful where system pressures are too low or pipelines are too large for effective flushing. Air scouring is also used to remove soft scale, biofilm, or other adherent materials. For these applications. it is generally more effective than flushing. However, the costs of air scouring are typically at least twice those of unidirectional flushing.

More aggressive techniques such as swabbing and abrasive pigging work to varying degrees in removing heavy sediment, biofilm, adherent material, tuberculation, and even very hard scale. Swabs and pigs are cylindrical or bullet-shaped tools that are forced through pipelines using water pressure. Compared to air scouring, swabbing can be considerably more effective in removing sediment and biofilm. Harder, more abrasive pigs are used to remove tuberculation and hard scale, thereby improving capacities, raising pressures, and reducing pumping costs. In water distribution systems, pigs and swabs can be important tools for reducing the risk of water quality deterioration. The cost of pigging and swabbing is considerably higher than that of simple flushing, particularly if launching and receiving ports must be constructed.

xvii

Chemical cleaning, jetting, and ball cleaning are techniques developed for other industries that have found some use within the water utility community, but applications of these methods in potable water pipelines have been limited. With these methods come concerns about damage to pipes, linings, and appurtenances, along with the potential for system contamination.

Very aggressive cleaning can exacerbate problems by exposing bare metal, leading to increased corrosion, water discoloration, and chlorine depletion. Cleaning and lining rehabilitation-a time-proven technique that can produce a like-new pipeline-solves this problem. Before most in situ lining, pipes are cleaned mechanically, using either rack-feed boring or drag scraping. For traditional cement-mortar or epoxy lining, a device is then pulled through the pipe that sprays the coating on the pipe wall. In recent years, numerous new pipe rehabilitation techniques have been developed, many of which are capable of restoring or increasing the strength of the pipe. These methods may be useful as part of an overall infrastructure renewal program. Although the cost of cleaning and lining rehabilitation can be as little as 25% of the cost of replacement, it is 10 to 100 times that of flushing. However, unlike flushing, the process should never need repeating.

This report presents criteria, flow charts, and tables to assist in selecting pipes to be cleaned and the cleaning methods to employ. Because the quality of the water, the condition of the infrastructure, and the hydraulic characteristics of the system all affect pipe cleanliness, the analyses are not always clear-cut. Ideally, physical data (pressure, flows, turbidity, heterotrophic plate count [HPC], pH, and disinfectant residual) should be gathered at regular intervals from key locations throughout the distribution system, reflecting the water quality and hydraulic conditions within the mains. This infonnation is needed to diagnose problems, select cleaning methods, and evaluate program effectiveness.

Through a detailed survey of more than 100 utilities, this study documents the current state of pipe cleaning practices. By reviewing current research and case studies from leading utilities, the report also documents the state of the science. These case studies, briefly described in Table ES.l, demonstrate the results that can be achieved by various methods.

The report also outlines what is needed to implement the various pipe cleaning methods, including the necessary equipment and labor, and the amount of water that will be expended. A key consideration is how to properly contain and dispose of the water and sediment resulting from pipe cleaning. The impacts on customer service are also important. Bypass piping is usually needed to supply customers where invasive cleaning processes are employed. The cost of cleaning can be heavily influenced by these and other site-specific considerations. .

Tuberculated, sediment-laden pipelines are common to utilities around the world, but the associated risks and liabilities should not be taken lightly. The various pipe cleaning techniques offer ways to maintain the infrastructure, extend service lives, and improve water quality at the tap. These tools should be used in coordination with other system initiatives, including watershed protection, filtration, treatment, disinfection, and infrastructure renewal.

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Table ES.l Summary of case studies reviewed in this report

Los Angeles Department of Water and Power, Calif.

Cincinnati Water Works, Ohio

Yarra Valley Water, Australia

City of Edmonton, Canada

Severn Trent Water, U.K.

A focused flushing program resulted in 40% fewer complaints system-wide.

In zones where the flushing took place, complaints dropped as much as 95%.

Unidirectional flushing of cast-iron pipes resulted in a 90% reduction in HPC bacteria.

Turbidity, color, and iron dropped by 40% to 55%.

Air scouring and unidirectional flushing are used to regularly remove natural sediments from the system.

Customer complaints have been reduced up to 50% with unidirectional flushing and up to 70% with air scouring.

Water quality tests conducted before and after flushing have enabled the city to extend the time intervals between flushings. About one third of the city will now be flushed every 4 years.

Flushing has not been effective in alleviating problems in a predominantly cast-iron area. Pipes there have been scheduled for in situ cleaning and lining rehabilitation.

Cleaning methods are selected based on an analysis of six parameters: water quality, pipe material/lining, dead ends, customer complaints, hydraulic conditions, and system activities.

Swabbing, air scouring, and unidirectional flushing are used to reduce the risks of noncompliance with customer-complaint regulations.

Sydney Water Corporation, Australia Pipe cleaning was used to reduce the frequency of positive coliform tests. In one zone, flushing and swabbing helped achieve significant improvement as components of an integrated water quality improvement strategy.

A side-by-side comparison of swabbing and air scouring demonstrated that swabbing was much more effective in removing sediment and biofilm.

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CHAPTER! THE NECESSITY FOR PIPE CLEANING

The cleanliness of water pipes is an important, but often neglected, part of prudent water utility management. The neglect stems partly from uncertainties about how, when, and where to do cleaning, and what results might be expected. Utility managers have struggled with how much to spend, where to spend it, what methods to use, how often to clean, and how to measure results. As a result, expenditures for cleaning pipes are often difficult to justify. But it is also a mistake to ignore cleaning. The cleanliness of the pipes can, to a large extent, determine the quality of product and services delivered to the customer, and consequently how the customer views the utility (see Figure 1.1).

From the customer's perspective, the cleanliness of a utility's system of piping affects:

• The aesthetic qualities of the water delivered to the tap • The pressure at which the water is delivered

From the utility's perspective, the cleanliness and condition of the pipes affects:

• The healthful properties of the water delivered to the tap • The ability to comply with regulations, particularly regarding colifonns • The cost of water delivery, particularly the pumping cost • The flow that is available to fight fires or meet demand • The longevity of the pipes

For many years, the water community had focused on the quality of water leaving the treatment plant. Concerns about parasites, viruses, bacteria, heavy metals, and carcinogens led to ever more sophisticated analysis and treatment of source waters. In recent years, the focus has shifted to distribution systems, with the realization that pristine water leaving the treatment plant can be far less than pure at the taps of many customers because of changes that occur within the pipes along the way. Compliance with the Total Coliform Rule is often dependent on having a "clean" distribution system. The Lead and Copper Rule is also an expression of this new focus. However, discoloration, taste, and odor problems are also prime concerns to most utilities. The color, taste, and odor of water are direct measures of utility performance in the eyes of most customers.

Water discoloration is a major reason for customer complaints about water quality, and, unfortunately, discoloration occurs in most utilities. Discoloration is commonly caused by the suspension of sediments from (1) piping material corrosion, (2) natural sediments from well water or unfiltered surface water, and (3) oxidation of dissolved iron and manganese. i The discoloration is often considered benign, in that it may not be directly associated with adverse health effects, but it can damage porcelain plumbing fixtures, ruin laundry, and soil a utility's reputation.

Several methods currently exist for cleaning pipes in place. The most common is simple hydrant flushing, which is practiced to some extent by practically all water utilities. Unidirectional flushing refers to a technique that has evolved in recent years, in which valves are closed and

I Water discoloration can also come directly from the corrosion process--<:opper corrosion is a particular example-and from algae, where the water is unfiltered.

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Figure 1.1 Thberculated cast-iron pipe (Photo courtesy of Los Angeles Department of Water and Power)

hydrants opened in a systematic fashion, to scour the pipes with high-velocity water, and confine and expel the turbid water from isolated segments of the system. Other methods include:

• Air scouring. In this method, volumes of air, then water, and then air, are alternately introduced to the pipe through a fire hydrant, creating turbulence that scours film and lifts and transports the sediment.

• Soft swab pigging. In this method, a foam plug is forced through the pipe using water. For small-diameter pipe, often the pig can be introduced and recovered from fire hydrants.

• Poly pigging. The method here is the same, but the construction of the pig is different. Sometimes the pig is simply foam covered by a plastic shell, but for harder scales and more aggressive cleaning, any number of abrasive materials are adhered to or embedded in the exterior of the pig, such as carbide straps, plastic brushes, and wire brushes.

• Chemical cleaning. In this method, an inhibited acid is circulated through a closed system, dissolving mineral scale, biological growth, and corrosion by-products. After several hours of circulation, the pipe is flushed, and passivating inhibitors are circulated to prevent flash corrosion. The pipe is then disinfected, filled with clean water, and placed back in service.

• High-pressure water jetting. This method is similar to the technique commonly used to dean sewer pipes. A hose with several radial jets is pulled through the pipe. High­velocity water blasts deposits and films from the pipe surface.

• Mechanical cleaning. Various mechanical methods are used to clean water pipes. Generally these are used in conjunction with lining rehabilitation. The most common methods are power boring and drag scraping.

WHAT DOES PIPE CLEANING ACCOMPLISH?

Simply stated, clean pipes deliver better quality water at higher hydraulic efficiencies. The benefits to the customer and to the water purveyor are manifested in various ways-better taste and aesthetics, more healthful water, fewer regulatory compliance notices, fewer complaints, greater flows, higher pressures, and reduced energy consumption.

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Physical process

Replacement of poor quality water

Removal of sediment deposits

Removal of tuberculation or other scales

Pipeline rehabilitation

Table 1.1 Pipe cleaning results

Primary benefits

• Removes bacteria/contamination in the water • Raises disinfectant residuals by drawing in

fresher water • Minimizes the risks of nitrates and nitrites

resulting from nitrification • Reduces risk of taste and odor problems • Reduces risk of color and appearance

degradation (removes suspended materials)

• Reduces risk of taste and odor problems • Reduces risk of color and appearance

degradation • Improves hydraulic efficiency • Better disinfectant penetration-impedes

growth of biofilms

• Improves taste and odor • Improves color and appearance • Impedes growth of biofilms • Reduces risk of coliform regrowth • Reduces disinfectant demand • Improves hydraulic efficiency

• Improves taste and odor • Improves color and appearance • Impedes growth .of biofilms • Reduces risk of coliform regrowth • Reduces disinfectant demand • Improves hydraulic efficiency (flow,

pressure, energy) • Extends life of pipe

Pipeline cleaning achieves five physical results:

1. Replacement of poor quality water 2. Removal of sediment deposits 3. Removal of biofilm 4. Removal of tuberculation or other types of scale 5. Preparation for pipeline rehabilitation

Table 1.1 summarizes the benefits of these physical results.

Recorrunended methods

• Conventional flushing • Unidirectional flushing

• Unidirectional flushing • Air scouring • Soft swab pigging

• Poly pigging • Chemical cleaning • Jetting • Mechanical drag

scraping

Mechanical or other cleaning, followed by:

• Cement-mortar lining rehabilitation

• Epoxy lining rehabilitation

• Structural lining rehabilitation

The secondary benefits of pipe cleaning should also not be ignored, specifically:

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• Fewer customer complaints • Reduced pumping costs • Greater flow capacity (particularly for fire fighting) • Higher pressures during periods of high demand • Lower risks of water quality problems • Better customer (and political) goodwill • Better compliance with primary and secondary water quality regulations • Possibly reduced disinfectant by-product formation, as a result of less chlorine

demand, lower detention times, and removal of organic material

Replacement of Poor Quality Water

Probably all water utilities have flushed poor quality water from their systems at some point, and this is not a practice that is ever expected to be discontinued. The reasons for this type of flushing are varied but familiar and do not require much discussion here.2 In areas where problems are chronic, particularly in areas where flow velocities are low, flushing is sometimes performed routinely-or even continuously.3 More commonly, such flushing is prompted by customer complaints or water quality measurements. For that reason, "reactive flushing" is a term frequently applied to this process.

Typical objectives for replacing poor quality water include:

• Removing suspended sediment that has entered the system from treatment malfunction

• Removing suspended sediment that has been stirred up by the opening or closing of valves, the use of hydrants, a main break, construction activity, flow reversal, or unusually high demand

• Removing sediment accumulations from dead ends4 or other areas where buildups result in water quality problems and customer complaints

• Eliminating "milky" water (caused by the release of air dissolved in the water) • Mitigating taste and odor problems caused by organic matter • Elevating chlorine levels that have become depleted because of stagnation • Eliminating coliform • Removing free ammonia and nitrite to prevent nitrification • Eliminating other sources of water contamination (treatment failure, backftow, or cross

connection)

Removal of Sediment Deposits

Sediments deposited within pipes can lead to both water quality and flow problems. By impeding the diffusion of disinfectant, sediments can provide an environment that harbors and

2See AWWA 1986. 3 Bleeding a blowoff continuously into a stonn drain is a typical procedure. 4 Note that dead ends also occur at points in the system where valves are closed, such as for pressure zone division.

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