Operation and Optimisation of Distribution Systems

Practical Guide to the Operation and Optimisation of Distribution Systems

P e t e r M o s s e a n d D a n D e e r e (S e c o n d E d i t i o n)

Second Edition, June 2009

Foreword to the First Edition The provision of water services to communities in developed countries has been the single most important development in improving public health at the population level. It has been much more significant than any other factor, notwithstanding the improvements in medical science over the past 100 years. It is also true that lapses in the operation and maintenance of water and waste water treatment facilities and the associated distribution networks have resulted in illness and deaths in affluent societies. If one looks at significant water quality incidents that occur in developed countries, the problems are usually due to the lack of adequate professionalism on the part of management, regulators and/or operational staff, rather than any basic inadequacy of the infrastructure involved.

People in affluent societies do not expect to die or be made ill from using public water supply systems and this is quite a reasonable expectation. Water quality management is a vital and important role. People with primary responsibilities for water quality management, whether at the “coal face” or at a senior or executive level should appreciate the importance of this function. Complacency, inattention and distraction from the core tasks are dangerous features in water utilities. One often hears comments like “I would like to pay more attention to filter backwashing operations but I just don’t have the time”. Unless one wants to be a central player in a water incident, then we need to ensure that the right priorities are applied.

Water quality guidelines have developed significantly over the past few decades in Australia and elsewhere.

The emphasis in the past has been on compliance with tables of numbers that defined the quality of water that had to be produced for distribution - ultimately to the customer’s tap. In the early days, compliance was more or less optional for many of the water authorities, due to the powerful positions the utilities often held in the government bureaucracy. The strengthening of regulatory systems and the use of operating licenses and stronger legislation has improved matters substantially in this regard. The Australian Drinking Water Guidelines (ADWG) now includes a Water Quality Management Framework that sets out a risk based process of proactively managing water quality from its source through to the customer tap. It involves a thorough understanding of each system and the active management of a number of interventions that ensure that the outcome will always be optimal and safe. Compliance should be automatic. It is a logical and straightforward process, but, in some areas of the system, there can be a lot involved in sorting out the detail.

It is with this area of detail in mind that the authors of this series have decided to produce this excellent set of practical guides that will assist operators with responsibilities for key control points in water operations (eg filtration, distribution). The national water quality guidelines, (ADWG in Australia), regulatory changes, licenses and audits all tend to confront water utilities from the top down. These guides are intended to be helpful at the operational “coal face”.

Collectively, all of these relatively recent additions to the water quality management landscape should help to ensure that there are no adverse public health outcomes from the use of public water supplies in Australia. I commend the authors of this series for their excellent initiative and I trust that the series will be helpful in ensuring that we get the very best level of performance and reliability out of our water treatment facilities.

Professor Don Bursill CEO, Cooperative Research Centre for Water Quality and Treatment (1995-2005) Chair of the Coordinating Committee for Review of the ADWG (1996-2004)

Acknowledgements

The authors wish to thank Greg Ryan of South East Water for critical review of the manuscript and for assisting in preparation of the section on corrosion. Thanks are also extended to Vince Sweet of SA Water and Dharma Dharmabalan of Central Highlands Water for assisting in preparation of the section on the management of chloramination in distribution systems. Thanks also to Jill Busch of Gippsland Water for the chlorine demand test method.

The authors also wish to acknowledge the contribution of all the sponsors who have provided funding for the publication of this book. Particular thanks are due to the Water Industry Operators Association (WIOA) for their commitment to improving the skills of operations staff in the water industry and for coordinating the development of this resource as part of the process. The efforts of WIOA CEO, George Wall, in proof reading the final document and for organising the layout and publication of this book have been invaluable.

Thanks to Aqualift P/L for Figures 4.1 to 4.9 Thanks to Nordical Diving Services for Figures 4.10 to 4.17 PREFACE TO THE SECOND EDITION In preparing the second edition we have included new material that relates to the impact of the distribution system on public health. A number of studies have become available since publication of the first edition that clearly show that management or perhaps mismanagement of the distribution system can have an impact on public health. The old saying that no one has become ill is no longer acceptable. These studies prove it isn’t so. We have also included more photographs and small amounts of new information throughout other parts of the guide.

Peter Mosse and Dan Deere May 2009.

General Introduction This series of Practical Guides to Water Treatment focuses on each of the major steps in the process from catchment to tap, namely 1. Catchment 2. Coagulation and clarification 3. Filtration 4. Distribution 5. Disinfection Each guide provides practical advice regarding the management and operation of each of the critical control points identified by utilities as they implement the Australian Drinking Water Guidelines Framework for the Management of Drinking Water Quality (ADWG 2004), the Safe Drinking Water Act 2003 in Victoria, or a HACCP program.

An underlying objective of each of the guides is that on each and every page operational staff should be able to make mental notes to themselves along the lines of • That’s a good idea • We should be doing that • We can start on that immediately The guides are not about identifying costly solutions but simply identifying ways to get the best out of what is available at any particular time. The aim is to provide suggestions and hints that can be implemented easily, cheaply and immediately in the field.

Finally, the Australian Drinking Water Guidelines are concerned “both with safety from a health point of view and with aesthetic quality of drinking water”. These guides deal with both of these aspects; not just with safety aspects. They are about getting the absolute best out of the system, so as to deliver the absolute best quality drinking water to the consumer.

Chapter 2 is common to all of the guides and provides a general background to the concepts of hazards, risks and control points developed in the Australian Drinking Water Guidelines.

Feedback Requested These guides have been written to help operators perform their jobs effectively and to help operators understand the vitally important roles they fulfil within the water industry. The authors would be pleased to receive any feedback on this guide. Suggestions for further information or areas where additional explanation would have aided understanding can all help to make any future editions stronger and more useful for operators in our industry. Any suggestions can be directed by e-mail to the Water Industry Operators Association (WIOA) at info@wioa.org.au or by post to 22 Wyndham Street, Shepparton, Victoria, 3630.

Contents Foreword Acknowledgements General Introduction Chapter 1 Distribution Systems And Public Health...........................................................7 Chapter 2

Chapter 3

Chapter 4

• • • • • • •

• •

Hazards, Risks and Control Points

Hazards and Drinking Water......................................................................................... 11 Pathogens are the Main Hazards in Drinking Water...................................................... 11 Other Hazards...............................................................................................................14 Control Points................................................................................................................14 Critical Limits and Target Criteria..................................................................................16 Monitoring.....................................................................................................................16 Responsibilities.............................................................................................................17

Distribution System Targets

The Importance of Good Distribution System Operation...............................................18 Operating Criteria and Performance Parameter............................................................18

Distribution System Optimisation

• 1. Know Your System....................................................................................................24 Valves..............................................................................................................24 Mains...............................................................................................................25 Disused System Components..........................................................................25 • 2. Prevent Contamination..............................................................................................26 In Treated Water Storages...............................................................................26 In Distribution Mains.........................................................................................30 Maintain positive pressure at all times..............................................................30 Keep Mains in Good Repair and Above the Levels of Ground Water...............31 Avoid rapid increases in flow............................................................................31 Avoid Water Hammer.......................................................................................32 Install Backflow Prevention Devices.................................................................32 Use Sanitary Maintenance Procedures............................................................33 • 3. Ensure Minimum Detention Times............................................................................33 In Treated Water Storages...............................................................................33 In Distribution Mains.........................................................................................34 • 4. Optimise Disinfection................................................................................................35 • 5. Maintain Disinfectant Residuals................................................................................36 • 6. Balance Chlorine Residuals Across The System.......................................................38 • 7. Install Residual Trim Chlorination..............................................................................40 • 8. Use Materials Compatible With Drinking Water.........................................................41 • 9. Stabilise Water Entering The Distribution System.....................................................41 • 10. Minimise Copper Corrosion.....................................................................................42 • 11. Optimise Chloraminated Distribution Systems.........................................................45 Nitrification.......................................................................................................46 Monitors And Management Of Chloramated Systems......................................46

Chapter 5

• • • •

• • • •

Chapter 6

Chapter 7

• • • • • • • •

• •

• • • • •

Monitoring Distribution Systems

Essential Monitoring Equipment....................................................................................48 More Sophisticated Monitoring Equipment....................................................................49 Monitoring Disinfection..................................................................................................50 Laboratory Testing.........................................................................................................52 E coli................................................................................................................53 Total Coliforms.................................................................................................53 Heterotrophic Plate Counts..............................................................................54 Integrated Analysis........................................................................................................54 Consumers As Water Quality Monitors..........................................................................55 Pattern Analysis............................................................................................................55 Proactive Taste And Odour Surveys..............................................................................56

Maintaining A Clean Distribution System

Flushing........................................................................................................................59 Air Scouring...................................................................................................................59 Swabbing......................................................................................................................60 Which Cleaning Method Is Best?..................................................................................61 How Much Does Cleaning Cost?...................................................................................62 How Often Should The System Be Cleaned?................................................................62 Mains Cleaning, Drought And Wasted Water................................................................64 Keeping Treated Water Storages Clean........................................................................65

Mains Breaks, Mains Replacement And New Mains

Sanitary Operating Procedures.....................................................................................67 New And Replacement Mains.......................................................................................67 Swabbing.........................................................................................................68 Hydrostatic Pressure Testing............................................................................68 Disinfection.......................................................................................................69 Testing..............................................................................................................69 Mains Breaks................................................................................................................69 Disinfecting Mains What To Do With The Discharged Water.......................................................................73 Approved Materials.......................................................................................................74 Work Teams And Management Practices......................................................................74

Chapter 8

Operational Verification Audits.........................................................................76

Chapter 9

Closing Words. .......................................................................................................78

Contents

Appendices Appendix 1 Distribution System Contamination Case Studies • • • • • •

Case Study 1. Central Queensland, Australia, 1999.....................................................79 Case Study 2. Gideon Missouri, 1993...........................................................................80 Case Study 3. Queensland, Australia, 2005..................................................................80 Case Study 4. Pennsylvania, USA, 2005......................................................................81 Case Study 5. Alabama, USA, 1986.............................................................................81 Case Study 6. Oulu, Finland, 1998...............................................................................82

Appendix 2 Optimisation Case Study. ...................................................................................83 Appendix 3 Summary Of Distribution System Hazards, Hazardous Events And Preventive Measures............................................................................................94 Appendix 4 A Simplified Method For The Measurement Of Chlorine Demand......100 References . ..................................................................................................................................102

Chapter 1 – Distribution Systems and Public Health The distribution system represents the final step in the delivery of water from the catchment to the consumer.

The systems consist of extensive networks of interconnected pipes, valves, tanks and reservoirs, most of it underground. The networks typically form the largest component of the water supply system, both in terms of scale and asset value.

Water quality generally deteriorates as it passes through the distribution system. Distribution systems were historically designed primarily for security of supply rather than quality. Pipes and storages tend to be oversized to allow for future growth and development. As a result, detention times are often too long and flows too low to ensure good water quality. Active chemical and biological processes occur during the passage of water through the pipes, leading to changes in the nature of the water. These changes include the growth of biofilms and the release of chemical contaminants from the biofilms and from the pipe materials themselves. Breaches, intentional or accidental, and backflow, allow the introduction of pathogens and contaminant chemicals further compromising the quality of the water.

The most commonly reported problems in distribution systems are of an aesthetic nature such as taste and odour complaints, however there is considerable potential for contamination events to lead to serious health issues.

Craun and Calderon (2001) reported on waterborne disease outbreaks in the USA caused by distribution system deficiencies. For the period 1971 to 1998 over 21,000 cases of illness were reported in 113 outbreaks.

There were 498 hospital visits and 13 deaths. Of the 13 deaths, 7 were attributed to Salmonella, 4 to E coli, one to ethylene glycol contamination and one unidentified cause. Most of the illnesses were caused

by Giardia and bacterial pathogens. Over half of the disease outbreaks involved over 30 illnesses, 10 % over 300 and the largest event caused over 5000 illnesses.

PAUSE FOR A MOMENT and think about your responsibilities. Think about how you would feel if somewhere between 30 and 5000 people became ill in a system or town supply for which you have some responsibility!!

Recent work in Norway (Nygard et al 2007 as reported in Health Stream, December 2007) has shown that repairs and maintenance works in water distribution systems are associated with increased risks of gastroenteritis among residents in the area affected by the work. The study specifically targeted areas of the distribution system affected by low-pressure events that resulted from a section of the water distribution system being closed off, either as part of planned works e.g. replacement of valves or pipes or cleaning; or unplanned reactive maintenance. Not surprisingly, illness rates were higher in households with higher average daily water intake. Most episodes of illness were of short duration, typically 2 days but up to 14 days. Of the seven waterworks in the study, only one of the seven routinely chlorinated after repair work.

Most flushed, however it is interesting to note that flushing while commonly carried out (87%) was not always carried out…and guess what; the researchers found a decrease in risk of illness where hyperchlorination and flushing was carried out after the repair work.

The important thing to realise about the Norwegian work is that none of these illnesses would have been identified as being due to the water or as a waterborne disease outbreak. But we, the industry caused them.

The old adage that no one has become sick cannot be used anymore as a reason for not doing everything possible to ensure safe water is returned to the consumer after interventions in the distribution system.

So how many utilities adequately manage maintenance work in the distribution system. In an unofficial survey of work practices in Australian water utilities in 2007, the utilities were asked to indicate whether

Chapter 1 – Distribution Systems and Public Health they provided disinfection for new mains and for burst mains. The results are summarised anonymously in Table 1.1.

Table 1.1. Results of a survey of Australian work practices relating to the distribution system.

Utility Disinfection of new mains Disinfection after mains repairs A Yes No B Yes Yes C Yes No D Yes Yes E Not Mandatory Not Mandatory F Yes Substantial breaks only G Yes No H No No I Yes No J Yes Yes K No No How many people might be adversely affected by those utilities with inadequate work practices? How many people may become ill unnecessarily?

Craun and Calderon (2001) report estimates that only 10% to 30% of outbreaks are reported and that outbreaks are more likely to be recognized in large systems rather than small systems, or systems with large population turnovers such as holiday resorts. This supports the findings of the Norwegian studies.

Figure 1.1, based on data from Craun and Calderon (2001), shows the breakdown of the causes of water borne disease outbreaks resulting from distribution system deficiencies.

Figure 1.1. The causes of water borne illness related to the distribution system.

By far the major cause of distribution system based waterborne disease is from cross connection and backflow.

Chapter 1 – Distribution Systems and Public Health Ford (1998) provides an example of an abattoir in a country town in Victoria where a pump was used to transfer blood and stomach contents to a waste treatment plant. To prime the pump a garden hose had been permanently connected to the pump casing. When the pump started there was sufficient pressure to pump contaminated liquid via the hose back into the town water supply. In another case reported by Ford (1998), microbiological samples taken at a cheese factory tap returned large numbers of faecal coliforms. A cross connection was found between a bore in the factory yard and the water supply. Maintenance staff had set up a system to enable tankers to be washed down using either high-pressure water from the bore or the town supply. The isolating valve had been left open allowing bore water to enter the factory water supply.

Unfortunately the factory septic tank and effluent disposal field were only about 20 metres from the bore!

In a quite unbelievable, recent (2007) contamination event in Nokia, Finland, up to half the 30,000 residents may have been exposed to contaminated water as a result of a cross connection that allowed approximately 450 kL of filtered sewage effluent to enter the drinking water system (Health Stream December 2007). A valve that separated drinking water from water used to clean the Sewage Treatment Plant (STP) was opened during repair work. A pressure differential allowed the sewage effluent to enter the drinking water supply system. The cross connection was only discovered when illness started to be reported 2 days after the valve was left open. At least 250 people required medical care. The number ill is likely to be much higher. The most likely cause was contamination of the water with the bacteria Campylobacter and Salmonella.

Craun and Calderon 2001 report two cases where concentrated fluoride solutions were siphoned into the distribution system. One of these was due to a faulty dosing pump check valve, the other due to a low pressure event caused by a mains break. Fluoride concentrations varied from 40 mg/L to 220 mg/L. In another case, boiler-conditioning fluids back flowed into a system causing nitrite poisoning. In 1995 at a high school in Wisconsin, 148 people became ill due to a virus. The likely cause was backflow from a flooded school football oval via submerged hoses.

In a recent irony, a cross connection was discovered at a newly constructed administration building belonging to Melbourne Water Corporation (Health Stream March 2007). The building is located at one of Melbourne’s major STPs. A number of buildings are supplied with Class C recycled water for flushing toilets. The most likely cause is that a contract plumber created a cross connection that resulted in the recycled water being supplied from a kitchen tap via a water cooler. Approximately 25 people were exposed with around 14 reporting gastrointestinal illness. This event raises awareness of a growing risk; that of recycled water/drinking water cross connections. At the 2007 Pipes Wagga conference Smith (2007) showed many photographs of brand new recycled water/drinking water connections including service connections to incorrect mains and crossover connections in distribution pipes and through meter boxes.

In 2008 in England, routine monitoring of water treated at the Pitsford WTP for Cryptosporidium (a regulatory requirement in the UK) detected the pathogen (Healthstream December 2008). A boil water notice was issued for over 250,000 people for a period of 10 days. 22 cases of cryptosporidiosis were reported. Cryptosporidium had not been detected in the raw water. Investigation of the WTP revealed some openings into one of the water storage tanks. When the tanks were drained, a single fresh rabbit carcass was found. The Drinking Water Inspectorate was critical of the procedures in place for checking of the integrity of the storages. The formal risk management plan required checking of storages, however, clearly these were not actually being carried out.

The event highlighted another important issue. Prior to this event it was thought that Cryptosporidium from rabbits did not infect humans. It now appears that rabbits may have to be considered as a source of human infectious oocysts.

Chapter 1 – Distribution Systems and Public Health Some additional case study examples are provided in Appendix 1.

The importance of water treatment has been increasingly recognised over the past 20 years and a significant effort has been made to improve treatment. Waterborne disease outbreaks such as Milwaukee in 1993 where 400,000 people became ill have really emphasised the importance of treatment. Programs such as the Partnership for Safe Water in the USA and to a small extent the Water Treatment Alliance in Australia have helped to reduce the incidence of waterborne disease resulting from treatment deficiencies. However while the total number of known incidences has decreased, there has been a marked increase in the percentage due to the distribution system. This is shown clearly in Figure 1.2.

Figure 1.2 Percentage of waterborne disease outbreaks due to water treatment and distribution system deficiencies. (Modified from data presented at : http://epa.gov/SAFEWATER/disinfection/tcr/pdfs/presentations/meeting_ presentation_tcr-revisions_publichealthperspective.pdf)

The stage is set! Distribution systems must be optimised and operated well to ensure that water quality is maintained or improved. Failure to adequately protect water quality in distribution systems has led to many water contamination events, illness and some deaths. The threat is real and requires due diligence on the part of operators and operational managers.

This manual focuses on methods to maintain the highest quality of water possible as it passes through the distribution system and focuses on both health and aesthetic attributes of the water. This is consistent with the Australian Drinking Water Guidelines (ADWG 2004) that clearly recognises both health and aesthetic requirements. The challenge is to keep the aesthetics in focus whilst never diverting attention from the health requirements.

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Chapter 2 – Hazards, Risks and Control Points The latest edition of the Australian Drinking Water Guidelines (ADWG 2004) includes a new section entitled “Framework for the Management of Drinking Water Quality.” The Framework is based on the recognition that the best way to protect public health and ensure high quality drinking water is to use a preventative management approach that covers all steps in the production of drinking water from catchment to tap.

This new approach is quite different to the old approach that relied to a large extent on monitoring the final water using more and more tests with lower and lower limits. Often samples were only taken once per fortnight, or worse, once per month. The major problem with this approach was that if unsatisfactory water had been allowed into the distribution system, it was much too late to do anything constructive by the time the test results came back. In addition, by sampling so infrequently, one really couldn’t be sure what happened in between samples. The new Framework recommends thoroughly monitoring the individual steps. By ensuring that each step is operating correctly, the high quality of the final product can be assured at all times.

Water utilities now have an opportunity to establish an appropriate priority for the entire process of water treatment from catchment to tap, and, by fully adopting and implementing the 12 elements of the Framework, they can develop an excellent supporting management system: one that truly focuses on activities in the field.

Hazards and Drinking Water One of the major aims in supplying water for drinking purposes is to reduce hazards to public health.

A hazard may be thought of as any potential danger to consumers. Hazards associated with the delivery of water include: • Microbiological pathogens e.g. bacteria, viruses and protozoa • Chemical contaminants e.g. aluminium, heavy metals or pesticides • Turbidity and Natural Organic Matter (NOM). While not a direct threat to human health, both turbidity and NOM have been shown to be associated with an increased risk of microbial contamination of water.

A hazardous event is anything that introduces hazards to, or fails to remove hazards from the water supply.

A good example is a mains power failure to a chlorination site leading to a loss of chlorination.

The best way to manage an identified hazard is to remove the hazard. If this cannot be done, then the best option is to control the hazard by reducing the likelihood of the hazard or hazardous event happening, or by reducing the consequences if the hazard or event does occur.

The best way to manage a hazardous event is to anticipate what might go wrong and to develop a failsafe system. For example, at a disinfection site, an uninterrupted power supply (UPS) or standby generator could ensure power supply and maintain disinfection during a mains power failure.

Pathogens are the Main Hazards in Drinking Water The public is generally most concerned about chemicals in water. But in fact the big outbreaks of waterborne disease have arisen due to microbial pathogens. So why have pathogens generally been more of a problem than chemicals? Table 2.1 provides some clues.

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Chapter 2 – Hazards, Risks and Control Points Table 2.1. Comparison of pathogens and chemicals as risk factors for waterborne disease.

Risk Factor

Pathogens

Chemicals

Time to effect

As little as a few minutes of pathogens getting into the treated water can lead to a waterborne disease outbreak and their impact is immediate, and will be evident within days of contamination.

In most cases, chemicals in water don’t cause significant harm unless consumed for many years.

Detection

Pathogens are difficult to detect using existing monitoring techniques, and testing takes time. The results normally don’t come back until after people have drunk the water.

Chemicals are generally easier to detect, with a wider range of on-line instrumentation available, and because in most cases the effect is longer term, it’s possible to respond before harm is done.

Harmful levels

Even swallowing one pathogenic organism can make someone ill, so very low numbers in water can have an effect. Low levels can occur without any other signs. Pathogens don’t smell, taste or have colour.

Often chemicals can be detected through taste, odour or appearance once harmful levels are reached. The generally low levels in water require long exposure to cause illness.

Source

Pathogens come from natural sources.

These sources are very difficult to control. Grazing animals and wildlife can carry pathogens to water. Septic tank run off can contaminate raw water supplies.

Harmful chemicals generally arise from human activities. Their use is controlled to prevent discharge to water.

Design

Pathogens have evolved to be transmitted via food, water, air and direct contact from person to person or animal to person.

Most chemicals are not designed to cause harm in water. So most chemicals are not particularly harmful to humans at levels found in water. They are not able to cross infect from one person to another.

There are hundreds of waterborne pathogens. Each has a slightly different combination of sources, treatment sensitivity and effect on health. But there are simple rules that can be used to understand and manage these risks. The way to simplify this is as follows: • First understand that there are three main groups of pathogens • Then get to know the most problematic pathogen in each group • Finally, understand how to manage the risks from the most problematic organisms.

The idea is that if the more problematic organisms are under control, risks from the hundreds of other waterborne pathogens should also be largely under control.

The three major groups of pathogens of concern are listed below along with the most problematic reference pathogens from a water supply perspective:

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Chapter 2 – Hazards, Risks and Control Points • Enteric (intestinal) bacteria Campylobacter, pathogenic E. coli O157 and Salmonella • Enteric protozoan parasites Cryptosporidium and Giardia • Enteric viruses Enterovirus, Rotavirus, Adenovirus and Hepatitis A virus The protozoan amoebae Naegleria has also been associated with water borne amoebic meningitis. It is generally only a problem in warmer waters above 18oC. Some of the important features of the outbreaks caused by pathogens can be readily explained by understanding the key features of the main pathogen groups. A summary of these features is given in Table 2.2.

Table 2.2. Key features of pathogens commonly causing waterborne disease in humans.

Feature

Bacteria

Protozoa

Viruses

Is sewage a common source?

Yes

Yes

Yes

Is stock manure a common source?

Yes

Yes

No

Are bird droppings a common source?

Yes (Particularly Campylobacter)

No

No

Are wildlife faeces a common source?

Possible source of Salmonella

Possibly

No

What are the principal source controls?

Control all sources of faeces including birds and vermin

Control all sources of manure and sewage

Control sources of human sewage

Is media filtration an effective control?

Yes

Yes

Limited

Is primary disinfection using chlorination an effective control?

Yes

No

Yes

Is maintaining a residual of chlorine in the distribution system an effective control?

Limited (kills pathogens in droppings in water tanks but overwhelmed by large contamination events)

No

No (usually not enough to kill pathogens from sewer ingresses)

Are alternative disinfection techniques such as UV or ozone effective controls?

Yes

Yes

Yes

Is microfiltration an effective control?

Yes

Yes

Limited

Is reverse osmosis an effective control?

Yes

Yes

Yes

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Chapter 2 – Hazards, Risks and Control Points

Other Hazards Having established that the major risks to public health are from pathogens, it is however important to note that risks can also arise from chemicals (particularly over the long term) and algal contaminants in water.

There are three major areas of chemical contamination that have caused waterborne incidents.

• The use of contaminated source water, particularly with arsenic • The introduction of excess or incorrect water treatment chemicals • The backflow of hazardous substances into water distribution systems.

In large surface water catchments with limited industrial or agricultural development, risks to health from chemicals are likely to be rare. Where there is considerable industrial or agricultural activity, chemical contamination, while rare, is possible. Arsenic in water is rare in Australia but does occur. For example in Victoria and Western Australia there are a number of small supplies where the source water is drawn from rock strata with naturally occurring arsenic or close to old mine sites.

Contamination from incorrect chemical dosing and backflow is much more common even in large cities with several documented cases within the last 10 years or so.

Waterborne incidents associated with algae have been quite rare, however as the drought in Australia continues, many storages have needed to be taken off line due to algal contamination and some towns are being supplied from alternative sources by tanker. Problems arising from algae present in source water include: • Toxins may be introduced to the water by cyanobacteria (blue green algae) • Taste and odour chemicals can be introduced to the water by algae and cyanobacteria • Taste and odour chemicals can also be introduced to water from bacteria and fungi in soil near reservoirs.

These possible sources of contamination need to be considered and managed appropriately when they occur. Their occurrence needs to be anticipated and preventive strategies put in place.

Experience has shown that problems with algae can arise sporadically from time to time, often without warning, and the problem can then abate just as quickly. In practice, the management of risks from algae involves case-by-case assessment, based on proactive source water management and the reactive treatment responses. For example, different toxins may require the use of different types of activated carbon, and some may be treatable by other means such as ozone or chlorine. There are also a number of National and Statewide response protocols for the management of algal blooms.

Control Points Within a water supply system from catchment to tap there are several control points. A control point can be considered to be a step in a process where, if the operators do their job well, the chances of increasing the quality and consistency of the final water is increased. Alternatively, if a poor job is done at the control point then there is a greater probability that the final water quality will be poorer.

Figure 2.1 represents a generalised water supply system subjected to complete conventional water treatment. The general diagram can be applied to almost any water supply system with the possible addition or subtraction of a few process steps.

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Chapter 2 – Hazards, Risks and Control Points Figure 2.1. A generalised water supply system

The most important control points in a water supply system are • • • • • • •

Catchment Chemicals introduced to the water Coagulation and flocculation Clarification Filtration Disinfection Distribution.

Clearly where the step is absent it cannot be a control point for that system.

With respect to the distribution system control point the most important day to day functions are: • • • • • • • • • • • •

Selecting the best quality raw water at the entry point into the system in the first place Selecting the best quality materials for construction of the system Establishing and maintaining a closed system with no open storages or tanks Keeping hydraulic residence times to a minimum particularly in warm weather Maintaining a disinfectant residual particularly in warm weather Excluding vermin from water storages Ensuring where possible that positive pressure is maintained at all times in the system Maintaining the system to detect, repair and replace degraded or damaged assets Keeping the system clean Employing hygienic maintenance practices Preventing backflow and ingress into the system Designing any extensions to the system with due consideration to water quality.

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Chapter 2 – Hazards, Risks and Control Points

Critical Limits and Target Criteria To be a control point, there must be something that can be measured or observed to allow the operator to know if the process step is “in control” “heading out of control” or “out of control”. By setting numerical limits, the operator can make this assessment and take whatever action is necessary to maintain control at the control point.

The ADWG 2004 put it this way; “A control point has several operational requirements including • Operational parameters that can be measured and for which critical limits can be set to define the operational effectiveness of the activity (e.g. chlorine residuals for disinfection) • Operational parameters that can be monitored frequently enough to reveal any failures in a timely manner (on line and continuous monitoring is preferable) • Procedures for corrective action that can be implemented in response to deviation from critical limits.”

Two different target levels are often set.

1. Target criteria. The target criteria represent the day to day operational limits. Any deviation of performance from the target should be regarded as a trend towards loss of control of the process and should result in appropriate actions being taken to resolve the problem and restore control. How to retain the process within the target limits would normally be described in well written operational procedures.

2. Critical limit. This is the level that must not be exceeded. Deviation from a critical limit indicates loss of control of the process and should be regarded as representing a potentially unacceptable health risk. If by exceeding the limit, public health might be impacted then the health regulator should be notified. Where there is uncertainty concerning that health risk, then this should be identified and an appropriate response agreed with the health department in advance of the event occurring e.g. a short term failure of chlorination.

Corrective Actions Target criteria are always more stringent than the critical limits. By setting target criteria that are more stringent than critical limits, corrective actions can be taken before the water quality becomes out of specification or an unacceptable health risk occurs (i.e. exceeding the critical limit)

Monitoring The testing and observations that are made to determine whether the process is achieving the limits defined for that control point is process monitoring.

Process monitoring describes the tests and observations taken at a particular control point to determine the compliance or non compliance with the limits defined for that particular point.

By verifying that all the control points in a process are within the recommended range, it ensures that the final product will be within the specified limits. Testing of the final product quality is verification monitoring

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Chapter 2 – Hazards, Risks and Control Points and simply verifies that the total system is working. Quality control should not rely on verification monitoring alone. Process monitoring of control points allows the operator to detect problems before they can have an impact on final water quality.

Operators and management should work together to firstly set target criteria and critical limits, and then to establish appropriate monitoring frequencies for all the tests. Ideally, this will allow the identification of any trends that indicate a drift away from satisfactory operation. The frequency of monitoring needs to be set based on the rate of change for the control measure. There is no point in having a control point and testing once per month if the parameter being measured can vary significantly from day to day!

Responsibilities Water utilities have a responsibility to • produce safe drinking water at all times • produce the best quality water possible from the existing system.

Operators have a responsibility to ensure that • their actions do not compromise the production of safe drinking water at any time • they actively provide feedback to management when they become aware of shortcomings in the treatment sequence that may contribute to the production of unsafe drinking water • they are alert to changes in the system that they operate within • they act to produce water that is aesthetically pleasing.

So, how can operators fulfil these responsibilities?

By ensuring that each step in the process from catchment to tap is optimised and monitored effectively.

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Chapter 3 – Distribution System Targets The Importance of Good Distribution System Operation Chapter 1 provides a background to the role of the distribution system in the maintenance of public health.

Mismanagement of the distribution system can cause illness and even death. The American Water Works Association reports the Centres for Disease Control and Prevention as stating that 32% of waterborne disease outbreaks are caused by microbial pathogens in the water distribution system. The threat is real and requires due diligence on the part of operators and operational managers. Distribution systems must therefore be optimised and operated to ensure that the safety of water is maintained and the quality of water is maintained or improved as it passes through the distribution system. Simple, practical target criteria and critical limits can be set for the distribution system and appropriate monitoring undertaken to check that operations are within specification.

This manual focuses on methods to maintain the highest quality of water possible as it passes through the distribution system and focuses on both health and aesthetic attributes of the water. This is consistent with the Australian Drinking Water Guidelines (ADWG 2004) that clearly recognises both health and aesthetic requirements. The challenge is to keep the aesthetics in focus whilst never diverting attention from the health requirements.

With an appropriate awareness of what can be done, there is considerable scope to improve the operation of distribution systems throughout Australia.

Regardless of the impact of treatment and distribution, water will retain some of the characteristics of the raw water. Typically these include hardness and subtle differences in taste and odour that simply reflect the nature of the catchment and storage conditions. These differences are usually noticed when someone moves from one town or city to another. Such differences from supply to supply cannot easily be controlled, nor is it generally desirable unless the characteristics cause general consumer dissatisfaction. Such acceptable characteristics of the raw water are not considered here.

Operating Criteria and Performance Parameters The concept of multiple barriers can be applied to the distribution system itself. The most important barriers for day to day operations are • For service reservoirs Preventing contamination from human, bird and animal faeces Maintaining disinfectant residuals Securing against human entry and malicious contamination.

• For mains Maintaining system pressure Maintaining flows Preventing backflow Removing cross connections Maintaining disinfectant residuals.

Tables 3.1 and 3.2 provide some useful limits for the management of both health related and aesthetic problems associated with distribution systems. The limits in the table are not meant to be prescriptive but rather provide an indication of the sorts of parameters that can be measured and controlled. Each utility should consider their own requirements, however the targets in the table will assist the majority of utilities to manage their systems well and largely optimise the quality of water supplied to consumers.

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Chapter 3 – Distribution System Targets Once decided by the utility, these target criteria and critical limits should be documented, for example in the operations manuals for the distribution system. Distribution system operators should have copies of these operating criteria readily available and should be trained, regularly assessed and certified as being competent to operate the system to meet the targets.

Table 3.1. Some target criteria and critical limits for distribution system management.

Critical Parameter Target Comment Limits Free chlorine residual at the outlet of closed reservoirs (mg/L)

0.3-0.6

<0.2 and >5

The lower target and critical limit are to help protect health by inactivating bacteria and possibly viruses.

The higher target is to help protect against excessive chlorinous taste and odour.

Note however that water with these levels of chlorine will be noticeable to many consumers.

The upper critical limit is the ADWG health limit.

Free chlorine residual at the end of the distribution system (mg/L)

0.2-0.6

<0.1 and >5

Provides some ongoing protection from microbes and helps control biofilms.

Maintenance of a residual is more important in warmer waters.

The lower target and critical limit are to help protect health and aesthetic water quality and protect assets by controlling biofilms. The higher target is to help protect against excessive chlorinous taste and odour. Note however that water with these levels of chlorine will be noticeable to many consumers.

The upper critical limit is the ADWG health limit.

E. coli (orgs/100mL)

0

1

As per ADWG. Indicates recent faecal contamination and requires immediate action.

Total THMs (ug/L)

<100

250

Long term exposure to high levels of THMs may cause cancer.

Critical limit is ADWG health limit for individual THMs or total THM concentration.

Chloroacetic Acids (ug/L)

<60

100 (150)

Long term exposure to high levels of HAA may cause cancer.

Critical limits are ADWG health limits, 100 ug/L for chloroacetic acid, 150 ug/L for di and trichloroacetic acids.

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Chapter 3 – Distribution System Targets

Parameter

Target

Dissolved Organic Carbon (mg/L)

<2

Heterotrophic Plate Counts (22oC) (cfu/mL)

<100

Critical Limits

Comment Low DOC water does not support biofilm growth and reduces disinfectant demand

500

Indicates cleanliness of the system.

HPC 22oC results in higher counts than HPC 37oC providing better data for managing water quality.

The USEPA specifies 500 as the 95%ile.

Free Chlorine: Total Chlorine ratio

> 0.9

0.8

Measure of chlorine demand and chlorine decay. Indicates cleanliness of system and increasing this value helps reduce taste and odour complaints and may reduce dosing costs.

Turbidity (NTU)

<1 (For a filtered water system)

5

May indicate compromised disinfection and shielding of microbes from disinfectant.

Critical limit is ADWG aesthetic limit. At 5 NTU consumers will notice dirty water.

Note that for water leaving a WTP, turbidity from individual filters should be < 0.1 NTU. Recent studies showed that water with a turbidity > 0.2 NTU had an unacceptable risk to consumers of exposure to pathogens.

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Copper (mg/L)

1

2

Target is ADWG aesthetic limit.

Critical limit is ADWG health limit.

USEPA has health based first draw copper limit of 1.3 mg/L.

Colour (PtCo)

<5

15

Critical limit is ADWG aesthetic limit. (see also DOC above)

Acid soluble Al (mg/L)

<0.1

0.2

To reduce dirty water.

Limits as per ADWG.

Fe (mg/L)

<0.05

0.3

To reduce dirty water.

Target limit is based on experience in Australia as being necessary to control dirty water complaints due to Fe. Critical limit is ADWG aesthetic limit.

Chapter 3 – Distribution System Targets Parameter

Target

Critical Limits

Mn (mg/L)

<0.01

0.1

To reduce dirty water.

Target limit is based on experience in Australia as being necessary to control dirty water complaints due to Mn. Critical limit is ADWG aesthetic limit.

pH

7-8

6.5-8.5

As per ADWG. High pH hinders chlorine disinfection.

Lower pH promotes corrosion.

Alkalinity

> 60

May help minimise corrosion

Langelier index

> -1.5

May help minimise corrosion

Pressure (m)

14-30

<12 and >90

Comment

The lower target and critical limit are to help provide sufficient pressure to prevent backflow into the distribution system and should be measured at points in each pressure zone with the lowest probable pressure during peak demand periods.

The higher target and critical limit are to help reduce the number of bursts and amount of water lost. The pressure should be measured at points in each pressure zone with the highest probable pressure during minimum demand periods.

The American Water Works Association (AWWA) recommends that pressures should be kept above 30 psi (~20m) and below 100 psi (~68m) during normal operations.

Flows (m/sec)

>0.4

Achieved once per day helps prevent particles settling out in the system. May be difficult to obtain in Australian systems.

Hydraulic modelling can be useful to understand the extent of the problem and identify possible improvements.

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Chapter 3 – Distribution System Targets Table 3.2. Some additional target criteria and critical limits for distribution systems operating with chloramine residuals.

Parameter

Target

Critical Limits

Comment

Monochloramine (mg/L)

1.5 – 2.5

3

Critical limit is ADWG health limit.

0.90

In a well balanced system the monochloramine should be approximately 90% to 95% of the total chlorine value.

A value <90% indicates that the ammonia is being under dosed. Lower levels of monochloramine means there will be higher levels of the other undesirable chloramine compounds.

9.0

Chloramine disinfection is more efficient at slightly higher pH levels. A pH reduction in a system can indicate nitrification has occurred. This is likely to be accompanied by rapid increase in total chlorine residual and a decrease in monochloramine.

>0.5

It is desirable to keep the free ammonia levels to a minimum. Failure to do so can lead to greater risk of nitrification.

The critical limit is the ADWG aesthetic limit.

Monochloramine:Total Chlorine ratio (measured after the dosing station)

pH (measured after the dosing station and well into the system)

> 0.95

8 – 8.5

Free ammonia (mg/L) (measured after the dosing station)

0.05– 0.2

Nitrate (mg/L) (measured after the dosing station and well into the system)

No increase after chloramine dosing

Nitrite (mg/L) (measured after the dosing station and well into the system)

0

Nitrifiers

No increase

An increase in nitrate levels after dosing is a good indicator that nitrification may be occurring.

ADWG health limit is 50 mg/L.

0.2

Indicates that nitrification may be occurring.

ADWG health limit is 3 mg/L.

Any increase after dosing indicates that nitrification is occurring.

Note: Chloramination is considered further in Chapter 3.

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Chapter 4 – Distribution System Optimisation

An ancient distribution system, the Roman Aqueduct

While this manual focuses on the distribution system it is important to realise that to provide high quality drinking water to consumers at all times, all steps in the process from catchment to tap must be optimised and monitored.

Ideally, water entering a distribution system would be biologically stable with very low DOC, have a very low chlorine demand, be low in disinfection by-product precursors, have a reasonable buffering capacity with near neutral pH and no objectionable taste or odour. In practice however in Australia, the situation is rarely even close to this ideal. Water is commonly sourced from rivers, creeks and reservoirs in heavily impacted catchments. Water entering the distribution system is often biologically unstable with ample organic material to feed and maintain extensive biofilms. It is often quite high in chlorine demand and disinfection by-product precursors since removal of natural organic material is rarely undertaken at Water Treatment Plants (WTPs). Australian waters are also often very soft with poor buffering capacity leading to increases in pH as water passes through the distribution system. Algal metabolites and toxins, and high levels of iron and manganese can impart significant taste and odour to the water.

So how should we manage this less than ideal situation?

Every effort should be made to reduce organic matter, nutrients and particulates in source waters by careful management of the catchment. The remaining contaminants then need to be managed at the WTP by the operation of appropriate treatment steps , e.g. activated carbon for removal of algal toxins and potassium permanganate for iron and manganese removal. The distribution system then needs to be managed to prevent deterioration of the water quality after it leaves the WTP. The following sections detail the steps recommended to optimise the operation of the distribution system to deliver the highest possible water quality to the consumer at all times.

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Chapter 4 – Distribution System Optimisation

1. Know Your System Before the operation of a distribution system can be improved, it is essential to know where everything is and where the water is going.

• Accurate diagrams are required to record where pumps, tanks and reservoirs are actually located • Accurate diagrams are required to record where the valves, high risk backflow prevention devices, pressure reduction valves (PRVs) and hydrants are actually located • Accurate records are required to show whether the valves should be open or closed, what position they are actually in and the direction of opening of the valve (clockwise or counter clockwise opening) • Pressure zones and independent systems should be clearly recorded and regularly updated.

These diagrams and records are usually part of a Geographical Information System (GIS), however in the absence of such a system, detailed street maps from street directories can be used very effectively.

From a public health perspective, the most important thing to know is which water goes where. If this is known then any contaminated water can be easily isolated and scoured out and only those consumers affected need to be notified.

Well calibrated hydraulic models can assist in gaining an understanding of where water travels and how long it takes. They can also be used in the event of a water quality incident to model where the flow has gone and therefore help in planning an effective flushing program to manage the event. In the absence of hydraulic models it may be possible to use more direct methods. For example a short pulse of water with a high chlorine dose can be followed through the distribution system by taking many chlorine residual measurements throughout the system and watching for the pulse to come through. The results will provide information on how water flows through the system and where and when it goes. Some water utilities have used fluoride to carry out a similar practical mapping exercise.

Knowledge of the system needs to be collected and recorded and responses planned prior to any event.

It is too late once contamination has occurred to start asking where the water has gone and which valves need to be operated to restrict further contamination of the system.

Valves Valves are important tools for directing flows, minimising disruption during water system repair and maintenance and managing water quality incidents or emergencies.

Important valves that need to be kept shut, or open, to protect particular customers should be identified by placing clearly visible tags on the valves. This means that whenever anyone tries to operate that valve, they’ll get a reminder. For example, a valve that might shut off a hospital water supply could be tagged to help prevent accidental operation.

Often, valves get left open when ideally they should be closed or vice versa! In addition to having a process for leaving valves in the correct position after work is completed, it is valuable to have a valve checking and exercising program. Ideally the program will cover all valves in the system over time. In large systems this can be difficult to do, however in such systems priority should be given to key valves that separate different pressure zones, and other valves in place for water quality management reasons. Actually exercising the valves verifies their operation and provides confidence that should the valves be needed in an emergency, they will function.

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Chapter 4 – Distribution System Optimisation Some embarrassing incidents have arisen where valves could not be located because they’d been sheeted over and burst water mains couldn’t be turned off, or shut-offs were bigger than they needed to be. Marking valves clearly (Figure 4.1), and regularly checking their operation and renewing the marking to keep them clear, is an important part of water quality management. Keep clear records of any valve checking process.

Figure 4.1. A clearly marked valve

Mains Details of the lengths, diameters, construction materials and the age of all mains should be recorded. This information is useful to calculate residence times in mains at particular flows and also to assess whether the construction material or age may be having an impact on water quality. Again this would usually be recorded as part of a GIS system, however in the absence of such a system, detailed street maps from street directories can be used very effectively.

Disused System Components Many distribution systems reflect the development of the system over time. If parts of the distribution system are no longer used, their continued connection to the parts of the system that are in use can present a hazard. At some point, a valve may be opened or might fail leading to very stagnant, or even contaminated water, entering the distribution system. Disused components such as old reservoirs or mains should be permanently disconnected. This is best achieved by removing a section of pipe and blanking both of the remaining ends.

Many systems originated before the introduction of treated water. As a result, many raw water/treated water connections can still be present. All remaining old connections between the raw water system and the distribution system should be identified and removed permanently from the system by removing a section of pipe and blanking both ends. The connections must not be maintained “just in case”. Utilities need to actively search old records and talk to retired operators to identify where these connections might be and then follow them up, isolate them and update their records accordingly. Untreated water must not be allowed to enter the system under any circumstances.

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Chapter 4 – Distribution System Optimisation

2. Prevent Contamination In Treated Water Storages Treated water storages are an important part of the distribution system. The way in which they are operated has a big impact on the quality of water finally delivered to the consumer. Treated water storages should be kept closed at all times. Every effort must be made to prevent faecal contamination of the water in the treated water storages. Such contamination has been known to cause waterborne disease outbreaks, including cryptosporidiosis and deaths from Salmonella.

Birds, frogs, reptiles, rodents and marsupials can all be carriers of pathogenic bacteria. Storages should be lined and covered. Vermin must be excluded by the use of vermin-proof vents and ensuring that all small openings are closed off. Figures 4.2 to 4.5 clearly show evidence of birds and vermin having gained access to treated water storages.

Figure 4.2. A nest inside a treated water storage is clear evidence that birds can enter a storage.

Figure 4.3. Skeletal remains in a treated water storage of a fox

Figure 4.4. The remains of a possum

Figure 4.5 shows examples of access points to storages.

Figure 4.5. Examples of poor coverings and clear evidence of sites where vermin could gain access.

Rainfall runoff, and wind blown debris must not be allowed to enter the storage. Figure 4.6 shows an example of a treated water storage where surface run off can easily enter the storage.

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Chapter 4 – Distribution System Optimisation Figure 4.6. A hole in a central roof gutter on a treated water storage allows rainfall runoff to easily enter the storage. Leaf debris accumulated in gutters allow water to back up and overflow under the corrugated iron covering .

Cracks and holes should be repaired as soon as they are detected. Raised hatches should be installed to prevent run off entering the storage. Figures 4.7 and 4.8 show examples of poorly designed hatches that do not prevent run off entering the storage.

Figure 4.7. Example of hatches that do not prevent run off from the roof entering a storage

Overhanging tree branches or any other structures that provide bird roosting sites should also be removed.

Figures 4.8 and 4.9 shows the base of a telemetry aerial and clear evidence of bird faecal material on and near the hatches. This faecal material could easily be washed into the storages at these sites.

Figure 4.8. Telemetry aerial and water storage hatch covered in bird faeces.

Figure 4.9. Base of a telemetry aerial with a large bird “dropping” adjacent to a water storage hatch.

The surfaces of floating covers should be kept free of weeds and algal growth and every effort should be made to prevent pooling of water on the surface of these. Figures 4.10 and 4.11 show weeds growing on the surface of floating covers.

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Chapter 4 – Distribution System Optimisation Figure 4.10. Weeds growing on a floating cover.

Figure 4.11. Weeds growing on a floating cover.

Floating covers and membrane liners (Figure 4.12) have been widely used in the industry to convert open reservoirs and basins into covered storages, thereby removing a potential site of recontamination. There is now a lot of evidence, largely obtained from diving teams cleaning these converted storages, that the integrity of both the covers and liners can become compromised. Figures 4.13 to 4.17 show a large range of tears and penetrations through covers and liners. This means that such covers and liners may not be a complete barrier to recontamination. In the light of such observations, individual water utilities need to consider whether such covers provide the necessary barriers for the operation of their distribution systems.

Figure 4.12. A floating cover being assembled

Figure 4.13. Roots penetrating a floating cover

Figure 4.15. A cut in a floating cover

Figure 4.16. A fault in a floating cover Figure 4.17. A tear in a floating cover

Figure 4.14. A tear in a liner

Floating covers have also been associated with the growth of bacterial populations under the cover. A number of Australian utilities have experienced increased numbers of opportunistic pathogens such as Pseudomonas bacteria in reservoirs after floating covers have been constructed. These organisms tend to be associated with low rates of flow and increased water temperatures both of which may occur under floating covers. The problem can be minimised by ensuring a disinfectant residual is maintained in the reservoir and that flow through the reservoir is maximised. There may be a need to introduce baffles inside the storage to encourage flow and prevent the formation of dead pockets of water.

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Chapter 4 – Distribution System Optimisation Entry of humans to the site should be strictly controlled. Human entry points allow malicious contamination of water in reservoirs. Such contamination has been known to cause waterborne disease outbreaks, including from Giardia deposited via human faeces.

Storages should be surrounded with security fencing and access gates kept locked at all times (Figure 4.18). Entrance hatches and access ladders should also be locked. In high risk areas, telemetered intruder detection systems should be considered.

Figure 4.18. A security fence and gate in place around a treated water storage

Treated water storages should be inspected regularly to ensure that all the preventive measures described above are in place. Figure 4.19 shows an example of a security fence that is not secure with clear evidence of entry to the site. The site is presumably not inspected or the failure of the fence ignored.

Figure 4.19. A water storage tank with a breach in the security fence and clear evidence of entry to the site.

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Chapter 4 – Distribution System Optimisation In Distribution Mains Distribution mains form extensive networks and provide many opportunities for contamination. The risk of contamination can be reduced by • • • •

Maintaining positive pressure at all times Keeping mains in good repair and above the level of ground water Installing backflow prevention devices Using sanitary maintenance procedures.

Maintain Positive Pressures at all Times Studies have shown that it is possible to have short periods of extremely low pressure and even negative pressure in mains at some times. Clearly if the pressure in the main is lower than the water surrounding the pipe and if the pipe has leaks or poor joints, water may be sucked back into the pipe. In a similar way backflow from service connections may occur. Contamination from these sources may be prevented by maintaining adequate positive pressure at all times.

High and low areas present problems for the management of pressure. Low points will tend to experience higher pressures and therefore be more likely to experience leaks and mains bursts leading to loss of valuable water and further increasing the risk of contamination of the water in the system during the repair process. If pressure is reduced to prevent this, the pressure in high points may decrease and allow entry of contaminated ground water in those high areas.

A balancing act is required!

Pressure should be kept between approximately 14m and 30m with critical limits of <12m and >90m (see Table 3.1). The higher limit is set to limit leakage from pipes and mains breaks due to high pressure. The lower pressure limit is necessary to limit ingress of contaminated ground water, prevent backflow and to ensure sufficient pressure for fire fighting and domestic sprinkler systems.

To get a suitable balance, pressures should first be set to prevent backflow or ingress in high areas of the distribution system. System pressure is generally determined by storage levels, pumping rates and the presence of PRVs. The storage level(s) or pumping rate that provide water to the high areas of the distribution at the minimum pressure needed should be determined. This can be done using hydraulic models or trial and error. Once this is set, pressures can be measured in the low areas of the system. If these exceed the maximum operating pressure, PRVs need to be installed to reduce the pressure in lower areas. (The PRVs need to be set so that pressure does not drop too much in distant areas.)

While it may not be possible to achieve all these objectives easily, the operation of most systems could be improved by implementing as many as possible.

PRVs may form part of the solution to maintaining positive pressures at all times, however they may also be part of the problem of recontamination. Where multiple PRVs are present with staggered operating pressures, it is likely that one of the valves will operate infrequently thereby allowing water to stagnate in the region near the valve. The low free chlorine residuals that occur in stagnant areas allow the proliferation of bacteria that can seed the system when the valve does open. The bacteria can then colonise the biofilms and flourish, particularly if chlorine residuals are low. To control this problem it is important to ensure that any unused PRVs are removed and that the remaining PRVs are operated regularly either by normal operation of the system or if necessary, manual operation of the valves during periods of low flow.

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Chapter 4 – Distribution System Optimisation Another possible source of contamination, particularly during periods of low pressure, is from fire plugs.

Such plugs may allow contaminated water to get into the mains. Faulty seals can arise due to improper reseating of the fire plug following hydrant use or through failure of the closure springs. Apart from microbial contamination of the water, tainting of the water with petrol and oil products may result from failed fire plugs.

To help prevent this problem, fire plugs should not be installed in areas of low pressure or in low points or depressions where surface water may accumulate. Fire plugs should be regularly inspected and cleaned.

Each utility needs to consider these recommendations and the applicability to their systems, however wherever there is risk of contamination of the water within the system with pathogens, appropriate steps must be taken to protect the consumer.

Keep Mains in Good Repair and Above the Level of Ground Water While it is almost impossible to have a completely leak free distribution system, every effort should be made to repair all leaks and faulty joints. Every leak repaired is one less possible contamination site. For this reason utilities need to ensure they have an active leak detection and repair program. Such a program is also of paramount importance to ensure water losses are minimised. One of the unfortunate consequences of extended drought is that as the ground dries out more pipes are damaged and the potential for leaks increases.

If there is a significant likelihood that ground water could enter a main, for example in swampy ground or under creek beds, consideration should be given to replacing the main with a continuous impermeable pipe or raising the main above ground in those areas.

On line conductivity monitoring could also be installed to detect ingress of ground water.

In newly designed systems the mains should be above the level of the ground water at all times.

Avoid Rapid Increases in Flow Rapid increases in flow can cause a significant lowering of pressure with the associated risks to water quality described above. Such rapid increases in flow may be caused by • Periods of rapid pumping • Opening of a large number of downstream valves for example during a major mains flushing exercise • A major mains break • A major fire fighting event.

Clark (2000) describes an outbreak of waterborne disease in the small city of Gideon, Missouri in 1993. The event highlights the role of increased flows, low pressure zones and poor tank management in a disease outbreak that affected 44% of the 1104 residents. A number of visitors to the town who drank the water were also infected. A sequential flushing program involving all 50 of the towns hydrants was initiated in an attempt to control a taste and odour problem. The increased flow caused previously full tanks that never adequately turned over to empty. The increased flow stirred up the sediments in the tank and allowed a previously stagnant surface layer to travel into the distribution system. On inspection, one of the tanks was found to have a rusted cover with several holes in it. Large numbers of pigeons were found roosting on the roof of the tank. Feathers were observed floating in the water. Investigating authorities identified the following contributing factors

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Chapter 4 – Distribution System Optimisation • Extensive flushing lowered pressure in the system below the critical 20 psi limit • The increased flow of water during the flushing caused two tanks to turnover and to scour sediments from the bottom of the tank • Tanks with deteriorated covers • A possible source of faecal contamination.

During high flows, such as those generated during fire fighting or flushing programs, pressures may drop significantly below normal. If there is a possibility that pressures may become too low, suitable preventive measures should be implemented such as increasing the chlorine residual or in worst case scenarios issuing a boiled water alert. The AWWA recommends an absolute minimum pressure of 20 psi (14m). If pressure drops below this it is not uncommon for American utilities to issue a boiled water alert (Chase 2000).

Every effort should be made to prevent rapid changes in flow. If this is inevitable during emergency events or extremely high demands during very hot weather, steps must be taken to prevent the impact of any resultant contamination. Increasing chlorine residuals and the issuing of a boiled water alert may be necessary.

Avoid Water Hammer Valves should be operated to avoid water hammer. When a valve is closed rapidly, upstream higher pressure water slams up against the closed valve and then sets up waves moving back away from the valve. These waves are associated with increases and decreases of pressure. Similarly water downstream of the valve continues to flow away from the valve creating very low or even negative pressures. These changes in pressure and flow increase the risk of damaging the pipes and also creating conditions that favour ingress of ground water and possible contaminants into the pipe.

Install Backflow Prevention Devices Backflow of water into a distribution system can occur wherever there is a connection between the distribution system and a non potable source of water. Most commonly this occurs during periods of low or even negative pressure in the distribution system such as might occur during fire fighting operations, or during a mains burst or even in high areas during summer. Backflow can also occur where a higher pressure system is connected to the distribution system such as may occur with a boiler feed pump. If water is able to flow back from its point of use, into the distribution system, then there is a very high risk that it will carry with it bacteria and other microbial organisms. Consider the impact on water quality of backflow from a hobby farm horse trough, or an old raw water cross connection. Ford (1998) provides an example of an abattoir in a country town where a pump was used to transfer blood and stomach contents to a treatment plant. To prime the pump a garden hose had been permanently connected to the pump casing. When the pump started the pressure was sufficient to pump contaminated liquid via the hose back into the town water supply.

Backflow has been known to cause water contamination incidents, including deaths (See Appendix 1 Case Study 4 and 5). It is therefore important to prevent backflow wherever backflow is possible. For this reason backflow prevention devices need to be installed between the water supply and hazardous facilities.

Figure 4.20 shows a backflow prevention device at the entry to an industrial estate. These devices should be installed in accordance with the Plumbing Code AS/NZS 3500:2003. The code requires a backflow prevention device appropriate to the level of risk.

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Chapter 4 – Distribution System Optimisation Figure 4.20. A backflow prevention device at the entry to an industrial estate.

In a practical sense, a program of installing backflow prevention across a system should target areas of known low flows and pressures or areas of high risk e.g. industrial estates.

Although it may not be practical to completely eliminate the risk of backflow in large systems, the higher risk facilities should only be connected to the water supply via testable high hazard backflow prevention devices that are registered and tested annually as required by AS3500. In low hazard locations single check valves may be sufficient to prevent low hazard backflow.

Once installed it is risky to assume that backflow prevention devices will always continue to work as designed. For this reason an active program to inspect and test backflow devices needs to be established, and appropriate records kept to ensure that all devices are checked regularly. The interval of checking should be based on the risks associated with failure of the device.

While it is perhaps a little unclear who is legally responsible for a backflow contamination incident, the consumer expects to receive safe drinking water at all times. It is therefore appropriate that the water utility takes whatever steps are necessary to ensure that a backflow contamination incident does not occur by taking all necessary steps to ensure that backflow cannot occur.

Use Sanitary Maintenance Procedures Waterborne disease outbreaks have arisen from sewage contamination getting into water mains during repairs to burst mains or during the installation of new mains. During routine maintenance operations it is important to ensure that all water main repairs and water main extensions are carried out in such a way as to prevent contamination of the water in the pipe. This is particularly important where water mains run close to sewer mains or where the water main is below the ground water level. Details of sanitary maintenance procedures are provided in Chapter 7.

3. Ensure Minimum Detention Times In Treated Water Storages Once contamination is controlled, aesthetic water quality can be optimised by reducing residence times in storages and minimising areas of dead water.

Shorter residence times reduce particle settling, reduce disinfection by-product formation, help maintain chlorine residuals, maximise the free to combined chlorine ratio and help reduce biofilm formation.

Acommon problem is the tendency to “keep storages full just in case” This approach often results in long

33

Chapter 4 – Distribution System Optimisation detentionstimes and loss of chlorine residuals and deterioration of water quality. Residence times in storages can be reduced by running them with lower volumes of water and taking reservoirs offline when they are not required. However before changing levels in a storage, it is important to check that the altered level will not cause an overall reduction in the pressure in the distribution system that might result in ground water ingress or backflow. While reducing levels is important to minimise water age it is important to keep levels high enough to maintain good positive system pressure. The final operating level is a balance between minimising low pressures in the distribution system and minimising detention times.

Poorly mixed water in treated water storages can lead to the formation of areas of stagnant water that contribute to an overall deterioration in the quality of water delivered to the consumer. These stagnant areas can be minimised by • Adding mechanical mixers to storages • Offsetting the inlet and outlet to create some mixing within the storage. Offsetting may be achieved in both a vertical and horizontal plane • Having separate inlet and outlet lines rather than combined inlet outlets • Installing baffle systems • Regular cleaning of storages.

Because of the nature of changing demand at different times of the year, storage levels need to be varied seasonally to minimise detention time at all times. Storages should not be run full all year round simply because they are there and of a certain size. Utilities need to decide on a minimum security of supply, perhaps 24hrs and set the upper and lower levels according to the demand from that particular storage.

The actual levels selected will require balancing of minimised detention times and minimum acceptable pressures and storage volumes (security of supply). Hydraulic modelling is very useful in helping to determine a suitable outcome for these competing demands.

Divers can be used to clean storages and to install simple baffle systems to encourage flow through the entire storage.

In Distribution Mains To achieve the highest possible water quality, the ideal distribution system would be sized and operated so as to minimise hydraulic residence times. Typically however distribution systems are sized for fire flows and peak demands and possibly future extension of the system.

Within the constraints of the “as built” system, residence times should be reduced, dead pockets minimised and flow velocities maximised. These modifications help to reduce particle settling, reduce disinfection byproduct formation, maintain disinfectant residual, maximise free to combined chlorine ratio and reduce biofilm formation. Examples of practical solutions to reduce hydraulic residence times and maximise flow velocities in distribution lines include • • • •

Reducing the diameter of the pipe towards the end of the dead end Lining of pipes with smaller diameter linings (slip lining) to reduce the diameter of the pipe Installing automatic flushing devices Using intelligent valving to create unidirectional flows and reduce residence times as much as possible. Well calibrated hydraulic models can help to determine this • Scheduled flushing of dead ends.

Most established distribution systems cannot easily be changed. A system with numerous dead ends for example is very difficult to change once constructed, but can be retrofitted with slip-lined pipes to reduce the actual internal diameter. Where new systems are being constructed, or old systems extended, it is 34

Chapter 4 – Distribution System Optimisation important to explain to developers and network planners that dead ends should be minimised through intelligent system design to stop this problem growing.

4. Optimise Disinfection The following paragraphs relate principally to primary disinfection but are included here to help ensure that water that has entered the distribution system has been adequately disinfected. Primary disinfection would normally occur at the WTP. Disinfectants kill microbes, though the extent to which they do this varies. The effectiveness of a disinfectant at killing microbes depends on the concentration of the disinfectant, the time that the microbes are exposed to the disinfectant and the temperature and pH of the water.

For a given temperature, the concentration/time relationship is referred to as the Ct. The Ct value therefore defines the effectiveness of disinfection. The guide provided by the World Health Organisation (WHO) over many years for chlorine has been 0.5 mg/L for 30 minutes giving a Ct of 15 mg.min/L. The WHO recommendation can be taken as a starting point, however individual utilities should consider their own individual circumstances and establish what level of disinfection is appropriate in their circumstances.

The final target Ct should be based on catchment and other risk assessments along with microbiological monitoring data from the 30 minute contact point and elsewhere throughout the distribution system.

Ct requirements for different disinfectants can be found in most textbooks on disinfection. The Australian Drinking Water Guidelines contain one such table that is reproduced in part here for convenience (Table 4.1).

Table 4.1. Summary of Ct value ranges for 99% (Log 2) inactivation of various micro-organisms by disinfectants at 5oC (Source Australian Drinking Water Guidelines 2004)

Microorganism

Free chlorine pH 6-7

Preformed chloramine pH 8-9

Chlorine dioxide pH 6-7

Ozone pH 6-7

E coli

0.034-0.05

95-180

0.4-0.75

0.02

Polio

1.1-2.5

768-3740

0.2-6.7

0.1-0.2

Rotavirus

0.01-0.05

3806-6470

0.2-2.2

0.006-0.6

Phage f2

0.08-0.18

-

-

-

Giardia intestinalis cysts

47->150

-

-

0.5-0.6

Giardia muris cysts

30-630

-

7.2-18.5

1.8-2.0

To ensure the production of safe drinking water, all drinking water needs to be adequately disinfected. To achieve this, all the water to be disinfected must be exposed to the disinfectant for the necessary time at all times, including during peak flows, prior to the water entering the distribution system. This requires, in the first instance, that the water is thoroughly mixed with the disinfectant. Mixing can be achieved using purpose built in line mixers or alternatively by injecting upstream of a 90o bend or a flow meter. If this is not possible then the injection point should be moved as far back along the pipe as possible. Mixing will ultimately occur in a pipe. Where only short pipe lengths are available prior to the water entering a contact or other tank,

35

Chapter 4 – Distribution System Optimisation static in line mixers or in line mechanical mixers should be installed to ensure adequate mixing (See Murray and Mosse 2008). Once mixed, all the dosed water must then be held in “contact” for the necessary time to achieve the Ct. This requires a carefully designed contact tank or sufficient pipe length before the first customer offtake. Short circuiting of the contact tank must not be allowed to occur. A good contact structure requires purpose built baffles to ensure that the water flows as a unit through the tank. Basins or tanks with a single inlet pipe and a single outlet pipe are prone to short circuiting and represent the worst alternative.

Baffles can be retrofitted to an existing basin or tank by use of divers and careful placement of flexible walls.

Figure 4.21 shows an example of a baffle arrangement for a tank that provides excellent contact.

Figure 4.21. Example of baffle arrangements to produce excellent contact during disinfection.

Inlets can also be modified to provide better mixing and prevent stagnation. Figure 4.22 shows an example of a directional nozzle fitted to an inlet Figure 4.22. An example of a directional nozzle fitted at the bottom of a treated water storage to provide mixing and minimise stagnant areas.

Utilities should keep a formal record of Ct achieved on a daily basis. In particular the minimum Ct should be recorded and regularly reviewed to ensure the primary disinfection requirements have been met.

Additional guidance on the operation of chlorine and chloramine disinfection systems is provided in Mosse, Braden and Hourigan (2009).

5. Maintain Disinfectant Residuals Disinfectant residuals are typically provided by either chlorine or chloramine. Even if UV light or ozone is used as the primary disinfectant, it is usually still necessary to provide a residual in the distribution system particularly in warmer conditions. In systems with stable water (very low DOC, and not generally found in Australia) or in short systems, or where temperatures are very low, it may be possible to operate the system without a chlorine residual. In such situations it is necessary to demonstrate microbial compliance

36

Chapter 4 – Distribution System Optimisation by frequent and regular monitoring. Where this is not demonstrated, a residual needs to be maintained.

Longer systems and warmer conditions definitely require maintenance of a residual.

Disinfectant residuals decrease as water passes through the distribution system. This decrease is referred to as disinfectant demand and is due the disinfectant being consumed by • • • • •

Biofilms Sediments Post floc Organic and nitrogenous matter Rusting cast iron fittings.

The amount of disinfectant chemical that needs to be dosed depends on • The length of the pipes from the last disinfection site to the consumers tap • The disinfectant demand in the water • The disinfectant demand exerted by the pipes themselves. This is determined by how clean the pipes are; in particular the extent of biofilms and corroded fittings. The more biofilm and corrosion, the greater the disinfectant demand.

Biofilms play an important part in the operation and management of distributions systems. A biofilm is a “slime” layer made up of living, dead and inorganic material lining a pipe or other surface continually immersed in water. Biofilms contain bacteria, fungi and other organisms glued together in a gelatinous material. The biofilm provides a home to disease causing microbes, protects microbes from disinfectants, consumes chlorine and generally contributes to deterioration of water quality as the water passes through the system.

A suitable starting point for the maintenance of a residual using chlorine is to aim for 0.2 mg/L free chlorine at the far reaches of the distribution system. This can be modified based on monitoring data for microbial compliance and the extent of biofilm formation and cleanliness of the system. The primary chlorine dose can be slowly changed (usually increased) and the levels of free chlorine throughout the distribution system measured. Once a level of 0.2 mg/L is achieved consistently at the ends of the distribution system, the primary dose can be set at the level used at the time. If this primary dose is such that consumers near the dosing point experience unacceptable taste and odour then the primary dose needs to be reduced and secondary dosing sites established throughout the distribution system to achieve the objective of 0.2 mg/L at the ends of the distribution system.

For oxidant disinfectants (chlorine, chloramine, ozone) it is also useful to measure DOC coming out of the WTP to provide some idea of how much disinfectant demand is present. For chlorine based systems, to establish how much chlorine will be used up it is possible to compare free and total chlorine at the primary dosing point and at points along the system. The rate of decrease of % free chlorine provides information on distribution system cleanliness. A rapid decline in the free chlorine residual with an associated rapid increase in total chlorine suggests the area needs cleaning. (see Table 3.1 for target objectives and critical limits).

Chlorine demand can also be measured in a WTP laboratory. A suitable method for this is included in Appendix 4. By regularly measuring the chlorine demand in the treated water, the primary dose can be better managed to achieve consistent levels of chlorine throughout the system. Measurement of chlorine demand should be a regular part of testing at a WTP. Another important consideration in maintaining chlorine residuals, is the need to maintain a suitable pH. Chlorine in solution exists as either hypochlorous acid, HOCl or hypochlorite ion, OCl-. Hypochlorous acid is the more powerful disinfectant. As the pH decreases the percentage of OCl- decreases and the percentage of HOCl increases. Thus the disinfection power of chlorine is higher at lower pHs. For example the disinfection power of chlorine at pH 7 is over 20 times greater than at pH 9. A pH of 8.5 is often considered the maximum pH for disinfection with chlorine because at this point, less than 10% of the chlorine is in its germicidal form.

37

Chapter 4 – Distribution System Optimisation Clearly, if the pH is too high, the disinfection power of chlorine is low. Cement lined pipes often lead to elevated pH at the far ends of the distribution system. In these cases disinfection efficiency of the remaining chlorine residual is reduced at the ends of the distribution system. Where pH increases due to the presence of cement lined pipes, increased microbial monitoring should be implemented to establish whether the existing disinfectant residual is sufficient. If not, the chlorine residual must be increased until microbial compliance is achieved. Alternatively a change to chloramination could be considered. Higher pH actually improves the effectiveness of chloramine.

Maintenance of chlorine residuals can be further improved by ensuring that storage reservoirs and mains are kept clean. Reservoirs should be cleaned at regular intervals, to remove deposits on walls and on the bottom. This is best done by specialist diving teams with specific training in diving in potable water. The advantage of using diving teams is that the cleaning can occur while the storages are on line. Several companies exist in Australia. Some are listed in the Australian Water Association Directory (AWA 2007).

6. Balance Chlorine Residuals Across The System The big challenge in maintaining chlorine residuals is balancing them across a distribution system.

Consumers further from the last chlorination point will experience water with less chlorine taste and odour.

Those closer will be more aware of chlorine and any variations.

Once again a balancing act is required! The water utility needs to balance the following requirements.

• The initial chlorine dose needs to be high enough to achieve the necessary Ct to ensure that all the water is disinfected.

• At the entry point to the distribution system, the chlorine concentration needs to be low enough that consumers can’t easily detect it by taste and smell, otherwise large numbers of complaints will result.

As a guide, 0.5 mg/L free chlorine at the first consumer tap will generally be acceptable. However be aware that water with this level of chlorine will still be detected by some consumers and may contribute to overall consumer dissatisfaction with the water.

• Chlorine decays quite rapidly in most Australian drinking waters since they are not biologically stabilised. Therefore chlorine residuals must be maintained throughout the system. A target of 0.2 mg/L at the end of the distribution system is usually adequate. Once these levels have been established and stabilised, the free chlorine residual may be reduced. The amount that it can be reduced depends on microbiological monitoring results. Systems can be operated with levels of 0.1 mg/L or even slightly less, however in these situations monitoring must be excellent and go beyond the base requirements of the health department for monitoring.

• Chlorine decay is more rapid in warmer water and in lower quality water, particularly water with a high DOC content. For example, during a warm wet period that may coincide with increased organics in the source water, getting chlorine residuals through the distribution system without booster chlorination might be extremely difficult.

• Excessive amounts of combined chlorine need to be avoided. Combined chlorine generally in the form of dichloramine and trichloramine, even at low levels, can cause taste and odour complaints. As a rule of thumb, it is best to make sure that the free chlorine is at least 90% of the combined chlorine concentration (see Table 3.1).

So how can these often conflicting requirements be managed? The requirement for primary disinfection can never be compromised. If as a result of the necessary disinfectant dose consumers close to the primary disinfection site receive a free chlorine residual that is considered to be too high, the only option is to build a storage or to change the primary disinfectant. Chloramines or chlorine dioxide can be used as an alternative to chlorine where either taste and odour problems or THMs are too high. If a change is contemplated, it is essential to ensure that adequate disinfection occurs prior to the water reaching the first consumer.

38

Chapter 4 – Distribution System Optimisation If as a result of optimising levels at the first consumers tap, the levels at the far ends of the system are < 0.2 mg/L, assuming the system is clean, consideration must be given to installing booster sites in appropriate locations to boost the residual so that the target residual levels are achieved at the far reaches of the system. If however the system is not clean, based on HPC data and the change in free to total chlorine ratio throughout the system, then the system may need to be cleaned and then maintained clean by regular flushing, scouring and swabbing (See Chapter 6 and Figures 6.1 and 6.2). Where there is a significant and persistent chlorine demand with associated high disinfection by products, steps must be taken at the WTP to further reduce the DOC in the water. In the first instance, the application of enhanced coagulation techniques can be tried. Guidance on enhanced coagulation can be found in a USEPA publication on the subject (USEPA 1999). If this fails then ozone/BAC, Nanofiltration, Reverse Osmosis or MIEX systems will need to be installed.

Portable residual trim chlorination units (Figure 4.23) are also available that can be installed relatively quickly at a site. These can be used to balance chlorine residuals, assess the effect of a secondary dosing site in a distribution system or to top up areas with unacceptably low chlorine residuals. The units consist of a sodium hypochlorite storage tank, a dosing pump, a data logger and controller system (Figure 4.24).

The units could be powered by mains electricity, 12 volt car batteries or a petrol generator so they can be deployed almost anywhere. Residual trim dosing has been achieved with samples taken as little as 1 to 2 pipe diameters from the injection point. Whether the chlorine is fully mixed at this close point is not completely clear, but it is sufficient to allow good residual trim control.

Figure 4.23. A portable residual trim chlorination unit

Figure 4.24. Inside a portable residual trim chlorination unit

For small systems or where money is not immediately available a small modification to pipework allows the introduction of a tablet dosing system to a pipe. Figure 4.25 shows the tablet cassette being removed from the flush ground fitting. In treated water storages, floating tablet dispensers can be used effectively (Figure 4.26).

Figure 4.25. An in pipe chlorine tablet dosing system.

Figure 4.26. A floating chlorine tablet dispenser

39

Chapter 4 – Distribution System Optimisation If consumers can receive water from different sources, e.g. from different raw water sources or from different storage basins within a given system, every effort should be made to ensure the disinfection regime is such that the consumer doesn’t know any difference based on chlorine levels. If the raw water sources vary in taste or odour then it is likely that the consumer will notice the difference, however every effort should be made to BALANCE chlorine levels in the supplies to minimise the impact of chlorine awareness. This can be done by careful measurement of chlorine residuals in the distribution system and carefully adjusting the primary doses to achieve the same levels prior to mixing.

Therefore to achieve and maintain constant and balanced chlorine residuals in the optimal range throughout the entire system, a very flexible and responsive disinfection management system needs to be established and maintained. The system needs to be able to respond to daily and even seasonal changes and requires substantial regular monitoring and review of the data. For example, chlorine residuals should be measured at least once a week at a large number of sites across the entire distribution system.

7. Install Residual Trim Chlorination Due to differences in the amount of water used by consumers during a 24 hour period, the time that water is held in storages will vary. For example, in the morning when everyone showers and uses the toilet, demand rises rapidly and detention time decreases. However this demand follows a period of very low demand during the very early morning when chlorine residuals will have decayed in the storages. Thus consumers may experience water in the morning with very low chlorine smell or with a noticeable chlorine smell or taste depending on which water they actually receive. They may even notice it changing. These changes are shown in Figure 4.27 for one site in one street.

Figure 4.27. Changes in free and total chlorine at a site over a 13 hr period show why consumers experience changes in chlorine taste and odour. This data was obtained by manually taking samples every hour.

Although instrumentation is available to obtain this data continuously it is important to realise that if you don’t have the fancy equipment you can still get that all important data.

40

Chapter 4 – Distribution System Optimisation Typically, consumers ask why the water utility increases the chlorine dose in the mornings. In most cases the utility has not done anything to the dose rate. The changes are the result of differential chlorine decay in response to different detention times and temperature.

The best way to manage these fluctuations and therefore increase consumer satisfaction is to install residual trim chlorine dosing systems (see for example Figure 4.23) at the exit point from all major storages and from all secondary or booster disinfection sites. Programmable Logic Controllers (PLCs) allow the entry of a set point, say 0.4 mg/L free chlorine. The system then measures the free residual in the water entering the site and leaving the site and supplies just enough chlorine to make sure the water leaving the system has reached the required set point. In this way, variations in chlorine levels at particular sites within the distribution systems can be levelled out. These systems work particularly well and can be made to work in small booster sites where the samples of both inflow and outflow water must be obtained close to the dosing site. Figures 4.28 and 4.29 show chlorine residuals at a site before and after the installation of the residual trim control.

Figure 4.28. Free chlorine residual at a site before the installation of residual trim control.

Figure 4.29. Free chlorine residual at the same site after installation of residual trim control.

8. Use Materials Compatible With Drinking Water To help maintain water quality in the distribution systems they should be constructed from pipes and fittings that are stable to the ambient water chemistry and that do not release anything into the water. Only materials that comply with AS/NZS 4020:2005 Testing of Products for Use in Contact with Drinking Water should be used.

9. Stabilise Water Entering The Distribution System Water found on the East Coast of Australia, and in Tasmania, is typically low in alkalinity and hardness.

Such water can leach calcium and hydroxide ions from cement linings in pipes and concrete in reservoirs.

Operational problems commonly experienced with water of this type include • high pH values (up to 10.5 or 11) at the ends of the distribution system due to the dissolving of concrete and cement linings within the system • reduced disinfection efficiency at these elevated pHs.

41

Chapter 4 – Distribution System Optimisation These problems can lead to a reduced service life for pipes and fittings thereby increasing operational costs. Note that this is not always the case however and that investigation should be undertaken to confirm what is occurring in your supply system. For example, in Melbourne, there are cement lined pipes over 35 years old that are leaching sufficient calcium and hydroxide to give noticeable pH changes, but with no significant loss of pipe lining material.

A number of indices can be calculated and used to estimate the potential aggressiveness or corrosivity of treated waters to concrete structures. These indices are not absolute, but rather give some indication of the likelihood that the water will corrode concrete pipes and fittings.

The most commonly used indices are the Langelier Index, Calcium Carbonate Precipitation Potential (CCPP) and Larson Index. More details on these tests and how to interpret them can be found in Standard Methods (APHA 2004). (See also Table 2.1 with respect to Langeliers Index) The leaching of calcium and hydroxide ions and the resultant increase in pH may also be associated with a decrease in the aesthetic quality of the water. The water may have a soapy feel, and earthy or cement taste and may cause some skin irritation in susceptible people.

In most cases the most common and effective long term strategy to reduce water corrosivity is to introduce lime and carbon dioxide dosing at the front of the WTP to increase alkalinity and calcium hardness while controlling pH for coagulation. Final post filtration pH adjustment is also usually required. Lime is often also used here, although other alkalis such as caustic soda and soda ash are preferable. Caustic soda and soda ash generally have fewer impurities, do not impact on the turbidity of the treated water and are generally much easier to use.

Reduction of water age in the system can also limit the observed changes in water quality due to concrete corrosion. Decreasing the water age doesn’t stop the corrosion, it just means there has been less time for the calcium and hydroxide ions to migrate into the water. With less of them in the water there is less effect on water pH and hence less effect on disinfection effectiveness and less effect on taste. It is possible because of the underlying chemistry that reducing water age will actually enhance the rate of leaching. Whether this enhanced rate of leaching will significantly affect asset life will depend on your particular system. By minimising storage volumes and maximising flows, the degree of pH change that could induce corrosion or affect disinfectant residuals can be reduced. Hydraulic models are useful to help develop modifications to the operation of the system that might achieve these objectives. Alternatively simple field trials can be used where storage levels are changed and pH monitored in the distribution system. However once again it is important to ensure that by changing storage levels, minimum pressures in the distribution system are not lowered beyond a critical point such that backflow and ingress occur bringing with them an increased risk of contamination.

10. Minimise Copper Corrosion Copper corrosion is complex and only a brief account is provided here. The WSAA fact sheet (WSAA 2005) on copper corrosion should be consulted for further details.

Water found on the East Coast of Australia, and in Tasmania, is often low in alkalinity and hardness. Such water can be corrosive to metals such as copper and brass in pipes and fittings.

Copper corrosion may appear in different ways.

42

Chapter 4 – Distribution System Optimisation The water may appear a milky blue to green. This is particularly evident in a white bucket or bath but may also be noticeable in a glass. There will often also be blue staining of bathroom fixtures where there are dripping taps (Figure 4.30). The blue colouration is most easily seen when water has been taken from a pipe that has been stagnant for a short time. Typically this occurs overnight. The blue/green floc will settle rapidly. This condition is referred to as blue water. Copper levels in blue water generally exceed the ADWG maximum limit of 2 mg/L and represent a hazard to human health and should not be consumed. They may cause immediate vomiting and pose a long term risk for liver failure in susceptible individuals. This water is in fact seldom consumed since it has a distinct blue tinge and an unpleasant taste. It is rapidly flushed from the pipe. Consumption may however occur where water bottles have been filled and the colour of the water has not been checked first.

Figure 4.30. A hand basin stained blue by copper corrosion products

Another form of copper corrosion is seen as a physical deterioration of the pipe, in the form of very small holes in the copper pipe the size of a pin or less, known as pitting corrosion. This can lead to leaks and failures in homes with little other warning. Pitting corrosion is less common than blue water.

The exact cause of pitting corrosion and ‘blue water’ are not known but it is known to be worsened by bacteria growing on the surface of the copper pipe and releasing corrosion products to form blue water.

Specific incidents of copper corrosion and ‘blue water’ can occur apparently randomly throughout the distribution system and may occur in clusters particularly in soft water supplies where residual disinfectant is low and pH is elevated.

Mechanisms of corrosion within the distribution system are affected by a number of external factors. The characteristics of drinking water that affect the occurrence and rate of corrosion can be classified as physical, chemical and biological. In the majority of cases, corrosion is caused, or increased, by a complex interaction between pH, alkalinity, hardness, chlorine, silicates, chlorides, sulphates, and water temperature. Dissolved gases in the water including carbon dioxide, hydrogen sulphide, ammonia and oxygen also influence the corrosion reactions. Biofilm growth on surfaces is also implicated as a cause of corrosion. Recent work in Australia by CSIRO and WSAA suggests that one of the major causes of copper corrosion is in fact the presence of particular types of copper tolerant or corroding bacteria. Whether these initiate corrosion or simply worsen it once it has started is not completely clear.

Surface coatings of lubricant used in the manufacturing process may initiate some forms of corrosion while oxide coatings on the surface may protect against corrosion. The role of these coatings and how to manage them are still an area of active research.

43

Chapter 4 – Distribution System Optimisation Cuprosolvency involves a slow uniform rate of copper corrosion that may result in blue staining of bathroom fittings particularly where there is a dripping tap. The levels of copper in the water are generally below the ADWG maximum limit of 2mg/L. Cuprosolvency occurs more frequently in new copper pipes exposed to hard waters with a high concentration of bicarbonate or in water with a pH < 7. In hard waters the problem usually abates after a number of years.

A less common form of copper corrosion is erosion of the copper pipe at bends due to high water velocity, known as erosion corrosion.

In summary then, where soft poorly buffered water exists, copper will corrode under the right circumstances.

Therefore where this water type exists the only proven solution is to use a material other than copper, this includes the piping from the main to the meter. Plumbers responsible for connecting houses in new estates should be advised of this. If the type of pipe cannot be changed, then maintaining a free chlorine residual > 0.2 mg/L may limit such corrosion. Maintaining pH between 7.4 and 8.3 is recommended. A pH in the range of 9.0 to 9.5 in the presence of a low chlorine residual is the worst case scenario.

The extent of the problem can be estimated from logging consumer complaints, problems reported by plumbers and through community consultation. Proactive monitoring of pH and chlorine levels throughout the distribution systems will provide the utility with additional information. First draw copper sampling may also be carried out in areas identified as being at a higher risk. In first draw copper sampling, residents are asked not to use a particular tap overnight and first thing in the morning take a sample of the water from that tap for testing. The USEPA requires first draw copper levels to be below 1.3 mg/L. Levels above this suggest significant corrosion.

Once this information has been gathered over a lengthy period, a long term strategy can be pursued.

The response to any identified problems should be determined by the size of the system and number of customers affected.

Options for dealing with blue water and possibly pitting corrosion (although less is known about prevention of pitting corrosion) are: 1. General: • Where new copper pipes (including new buildings or house extensions) are installed it may be important to ensure that during testing, water is not allowed to remain in the pipes for long periods and become stagnant. It is better to drain the pipes than leave them with stationary water in them.

2. With soft water (negative Langeliers index < -1.5): • Add a hardening agent to the water such as calcium carbonate and stabilise the pH with carbon dioxide. This solution has been successfully implemented by Hunter Water.

• Implement localised chlorine dosing to maintain a chlorine residual of greater than 0.2 mg/L throughout the distribution system. This solution has been proven by CSIRO to work, but may be difficult to achieve reliably in a larger working distribution systems given variations in water age and chlorine decay.

• For individual houses, the CSIRO, WSAA and the Copper Development Association are developing an intermediate to long term solution involving treatment of the copper pipe. Individual utilities should contact WSAA for details of whether this solution has been commercialised and how it might be made available to your water utility.

• Implement a program to inform customers and tradespeople that copper pipe is not a suitable material to be used in contact with the water supplied by your utility where the water is cold, soft, has a very low or very high pH and has a low and variable chlorine residual. Such programs have been successfully implemented in Scotland.

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Chapter 4 – Distribution System Optimisation

3. With hard water (positive Langeliers index) • Use pH stabilisation techniques to maintain the pH in the system between 7.4 and 8.3.

11. Optimise Chloraminated Distribution Systems Chloramines are formed by reacting ammonia and chlorine. The reaction of ammonia with chlorine produces three different types of chloramines; monochloramines, dichloramines and trichloramines. Monochloramine is the principal and desired type of disinfectant as it has low taste and odour characteristics and is the most stable of the three. Dichloramines and trichloramines are undesirable in a water supply as they have strong,offensive odours and their levels need to be controlled by careful dosing of ammonia and chlorine so that they are not formed. For this reason monochloramines should make up over 95% of the total chlorine.

(More information on chloramine disinfection is provided in Mosse, Braden and Hourigan (2009).

While chloramines react with bacteria and organic material more slowly than chlorine, they are more stable and as a result last longer than free chlorine in a water supply system. In addition chloramines do not form significant by products like THMs (ADWG 2004). Chloramines are typically used as a secondary disinfectant but can be used as a primary disinfectant provided sufficient contact time is available to achieve the necessary Ct for the control of pathogens (See Table 4.1).

Where chlorine is used as the primary disinfectant, chlorine is added first and sufficient contact time provided to achieve the target Ct. Once this is achieved, ammonia is added to convert free chlorine to chloramines and thus provide secondary disinfection. When used in this way THM formation will still result.

Where sufficient time is available for the chloramines to achieve disinfection, chlorine and ammonia can be added virtually simultaneously to form the chloramines. In some systems where high levels of THMs will be formed by adding chlorine first, ammonia can be added prior to chlorine. This will ensure chloramines are immediately formed thereby limiting THM formation.

Monochloramine has approximately 1/150th the efficiency of chlorine as a disinfectant, while dichloramine has approximately 1/80th the efficiency of chlorine as a disinfectant.

If the efficiency of chloramine is so much lower than chlorine, the natural question is why would they be used in the first place. The answer is that chloramines, while less efficient than chlorine, have certain advantages that ensure their continued use. They do not form Trihalomethanes (THMs) and other disinfection byproducts (DBPs) to the same extent as chlorine and they also persist for longer in the distribution system.

Figure 4.31 shows the persistence of chloramine residuals through very long distribution systems operated

by SA Water.

Chloramine Decays 7

6

Figure 4.31. Persistence of chloramine residuals through SA Water systems.(Figure provided by SA Water)

Monochloramine (mg/L)

5

4

3

2

1

0 0

200 Summit SP 9208

400 Summit SP 1104

Hours TBK SP 2149

600 TBK SP 7052

800 SR SP 2139

1000 Loxton SP 2016

1200 Morgan SP 2137

45

Chapter 4 – Distribution System Optimisation Consequently chloramines are often used in long distribution systems where it is difficult to maintain a free chlorine residual because the residual disappears well before reaching the extremities of such systems.

Chloramine residuals persist for longer and therefore penetrate further into long distribution systems. There is also some evidence that chloramines are better able to control biofilms than chlorine.

Nitrification One problem associated with the use of chloramines for disinfection is that in the absence of a chlorine residual any excess ammonia, at any point in the system, for whatever reason, becomes available to nitrifying bacteria. In the process of nitrification these bacteria convert ammonia to nitrite and nitrate. While these bacteria are of no health concern they can cause serious disruption to maintaining adequate residuals in distribution systems. Therefore the control of ammonia becomes very important to limit the growth of nitrifying bacteria.

Regular monitoring at critical points within the system to verify disinfection stability is very important. If monitoring indicates that system performance is starting to deviate from normal operating bands, minor adjustments can often be made to restore performance. However if monitoring is insufficient, operators will have no early indication of the onset of nitrification and the emergence of a serious problem. Without specialised monitoring it is not uncommon for nitrifying bacteria to contaminate a significant part of the system before it is too late to implement effective control measures. In such cases the first indication of nitrification is the rapid loss of residuals throughout much of the distribution system.

Monitoring And Management Of Chloraminated Systems Table 3.2 provides some key target objectives for chloramination related parameters measured in the distribution system.

Where monochloramine is used as a primary disinfectant, typical concentrations range from 1.5 to 3.0 mg/L depending on length of the distribution system. Based on health considerations, the concentration of monochloramine should not exceed 3 mg/L (ADWG 2004) anywhere in the system. Monochloramines are normally measured by using field or laboratory instruments that measure total chlorine. When total chlorine is measured, the maximum level in distributed water should not exceed 4.1mg/L. This is equivalent to a monochloramine level of 3.0mg/L If higher levels of monochloramine can be maintained through all online tanks and storages some utilities report fewer problems with nitrification. A minimum level of 1.5mg/L of total chlorine is an operating guideline used by some utilities that manage long distribution systems with long detention times.

In long distribution systems with tanks en route, the occasional addition of chlorine tablets to the tanks and flushing has been shown to help maintain the system and ratios within the desired ranges.

Monochloramine levels below 0.2 mg/L are unlikely to control biofilm growth. HPCs above 200 are a concern and probably reflect a monochloramine residual that is too low.

Free ammonia levels within a distribution system can be controlled by topping up chlorine dosing to maintain the initial dosing ratio of between 3.5:1 to 4:1 (chlorine:ammonia). This may be necessary at different points in the distribution system if the free ammonia increases. Chlorine can be topped up using tablets in floating dispensers in tanks or treated water storages or by the installation of chlorine dosing systems.

If residual chlorine levels in a distribution system drop rapidly below normal operating levels nitrification is probably occurring. The presence of increasing levels of nitrite and nitrate in a system indicates the onset of nitrification. These processes need to be controlled in order to maintain continuous residual chlorine in a system.

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Chapter 4 – Distribution System Optimisation Nitrites/nitrates are key indicators of nitrification. They should be monitored weekly at critical points well into a system, particularly during warmer weather. If nitrite/nitrate levels increase, early action is required to prevent nitrification progression. Actions that can be taken to control and/or prevent further progression of the nitrification include • Reduce the storage time in tanks within the system. During the cooler low flow months isolate tanks from the system, or, if this is not possible, implement tank level control system changes to minimise storage levels.

• Check free ammonia levels at the dosing plant and reduce the chlorine:ammonia ratio to achieve 0.1mg/L free ammonia or less if possible.

• Check free ammonia levels in tanks and if excessive add chlorine to minimise the excess ammonia.

This will increase the monochloramine residual which provides an additional bonus.

• Increase the chloramine dosing level at the disinfection station.

Decreasing levels of dissolved oxygen (DO) may also indicate the onset of nitrification.

If nitrification has taken hold in the distribution system, the above actions will not eliminate the bacteria.

Temporary reversion to chlorination is considered to be the only effective way to eliminate them.

Caution. The change from chloramines to chlorine will be noticed by the customers. Free chlorine has a more pungent chemical odour which is likely to attract significant customer concern. A publicity campaign informing customers of the need for the essential chlorination work together with details of the change duration and the taste and odour changes expected is recommended as an essential part of the planning for such work.

Where chlorination is introduced to control nitrifiers, chlorine is dosed to achieve a free residual throughout the distribution system. This will often require dosing at relatively high levels (up to 5mg/L) to accelerate the progression of free chlorine though the system. If the distribution system is long, and the chlorine penetration is insufficient, a mobile booster chlorinator set up well into the system, may be needed. The optimum time to carry out a nitrification control program is during spring to early summer when the flow rates in the mains are significant. The resulting higher flows will facilitate chlorine front movement throughout the network. Mains flushing ahead of the chlorine front will also assist in achieving better chlorine penetration.

Maintaining a free chlorine residual to the extremities of the system is recommended for up to one day prior to reversion back to chloramination.

Summary A summary of distribution system hazards, hazardous events and preventive measures is provided in tabular form in Appendix 3.

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Chapter 5 – Monitoring Distribution Systems

Since consumers “sample” their water every time they turn on a tap, water utilities should also sample their water at the consumers tap to assess whether the water quality targets are being achieved.

Many utilities have established routine monitoring programs. In general these tend to be verification monitoring programs. The ADWG Framework clearly recognises two forms of monitoring; process monitoring and verification monitoring (see Chapter 2). Both of these need to be carried out routinely. Some of the verification monitoring may be required by health departments or other regulators, but additional verification monitoring is generally necessary to really to ensure that the product water remains within specification.

Process monitoring should also be undertaken routinely to ensure that each control point from the catchment to the tap is functioning within limits. A simple way of looking at process monitoring is that if there are target criteria or critical limits defined, then there must be process monitoring in place to measure these parameters (see Chapter 2).

There will also be a need at times to implement special monitoring programs to help solve specific problems or gain greater understanding of the system in areas where that knowledge is deficient (see Appendix 2).

In our experience these situations arise quite frequently and because of this utilities should include some budget each year for “non routine” monitoring.

Essential Monitoring Equipment Operators with a responsibility for distribution system operation and maintenance must have ready access to portable Cl2, turbidity and pH meters and know how to use and maintain them. They must also know how to interpret the data provided by the instruments.

Table 5.1 provides a summary of equipment necessary for effective monitoring of distribution systems.

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Chapter 5 – Monitoring Distribution Systems Table 5.1. Monitoring equipment.

Essential Equipment

Desirable Equipment

Trained and observant operators!

Reliable portable Cl2 meters Reliable pH meters Reliable turbidity meters

On line Tb, UV absorbance, pressure and flow meters Data loggers usually associated with the on line instruments Hydraulic and disinfection models

On line Cl2 meters at primary disinfectant dosing sites Equipment for calibrating all equipment!!

On line equipment can provide information continuously and can be moved around the system to allow the development of a more complete picture. This is in contrast to data collected manually where operational staff can generally only monitor parameters intermittently at a limited number of sites without a major change in work practices and a considerable overtime cost. However in the absence of on line equipment, excellent data can be collected by careful grab sampling by field operators (see for example Figure 4.27). or by the collection of composite samples using automatic samplers.

More Sophisticated Monitoring Equipment More sophisticated equipment may be necessary to provide integrated monitoring of the entire distribution system.

Small portable “suitcase” data loggers can also be installed in the distribution system. These consist of a chlorine residual analyser and data logger mounted in a waterproof case (Figure 5.1). The unit can be deployed in a house or anywhere that a water feed can be provided and can collect data for as long as required. Data can be downloaded on site and the instrument left in place to collect more data.

Figure 5.1. A portable chlorine residual data logger

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Chapter 5 – Monitoring Distribution Systems Figure 5.2. A fire plug monitoring Figure 5.3. Inside the fire plug Figure 5.4. An example of data recorded system (Photo courtesy of monitoring system (Photo using the fire plug monitoring system.

C-Tech Services). courtesy of C-Tech Services). (Data courtesy of C-Tech Services).

Alternatively trailer systems can be designed that house monitoring equipment for pH, temperature, conductivity, turbidity and free chlorine residual. These monitoring trailers can be secured at a site and allowed to collect data. These are also systems that can readily be installed on fire plugs to monitor chlorine residuals, flow and other parameters (Figures 5.2, 5.3 and 5.4) The information can be telemetered back to a central location from the remote sites.

The CRC for Water Quality and Treatment (now Water Quality Research Australia) also developed some specialist equipment for assessing the distribution system. These include coupon chambers where water is allowed to circulate in an enclosed chamber that has been linked to the distribution system. Coupons are small pieces of copper, PVC or cement pipe that mimic the materials used in the construction of pipes.

Over time, biofilms will develop or corrosion may occur that will be similar to that actually occurring in the distribution system. The coupons can be removed at different time intervals and analysed in the laboratory.

The effect of modifications to treatment at the WTP or to changes in disinfection regimes can be monitored by sampling the coupons and studying the biofilms. Similar systems have been used extensively to study corrosion.

Monitoring Disinfection Table 3.1 lists target criteria for chlorine disinfection. These include a target limit of 0.2 mg/L at the end of the distribution system and a critical limit of 0.1 mg/L. The table also lists a target ratio of free chlorine: total chlorine of >0.9. This means that the free chlorine residual should be at least 90% of the total chlorine value.

A useful way to monitor these targets is to set up a residual mapping program. Depending on the size of the system, choose a number of sites sufficient to provide information on the disinfection residuals throughout the system. As a guide, twenty sites per 20,000 people has proved effective in monitoring rural cities. The sampling sites should be selected close to the mains so that water at the sample site represents the water in the main. It is also useful to choose sites that do not have dogs roaming in the front yard! Let the owners know that their tap has been selected for regular monitoring of water quality and they can expect to see a water utility person about once per week. To avoid issues of wasting water that the home owner has to pay for, sampling points can be introduced upstream of the customer’s meter so that the water sampled or flushed is not metered (Figure 5.5).

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Chapter 5 – Monitoring Distribution Systems Figure 5.5. A dedicated sampling point situated upstream of a customers meter.

Free and total chlorine residuals can be measured using portable analysers. Sites should be sampled once per week and the actual day and time varied to provide a more complete picture of the penetration of chlorine into the system. The data can be entered to a GIS system or very simply onto a photocopied street map. A colour code can be used to indicate whether the level is acceptable, too high or too low and a picture of water quality throughout the distribution system quickly established. By flicking from one map to the next, any changes in the distribution of residuals are immediately apparent. Gippsland Water in eastern Victoria used such a system for many years (Figure 5.6). Residuals greater than 0.6 mg/L were coded red, residuals less than 0.1 mg/L were marked with a blue cross. 0.1mg/L to 0.2 mg/L was marked with a blue dot and 0.2mg/L to 0.6 mg/L with a green dot.

Figure 5.6. An example of a chlorine residual map for part of the City of Traralgon

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Chapter 5 – Monitoring Distribution Systems This method of residual mapping has been used to • •

• • • • • •

Establish the overall disinfection status of the distribution system.

Identify problem areas with high or low residuals that could be due to Closed valves Poor circulation Need for secondary dosing.

Obtain a measure of chlorine demand throughout the system.

In conjunction with turbidity and Heterotrophic Plate Count (HPC) measurements, identify areas requiring cleaning.

Identify areas with infiltration or backflow. While rare, a sudden drop in residuals suggests that demand has increased suddenly at that point possibly as a result of infiltration or backflow or perhaps closing of a nearby valve.

Achieve balancing of chlorine levels throughout the system. This can be done by adjusting the dose at primary and secondary dosing sites.

Identify sites for the installation of secondary or booster dosing systems Calibrate hydraulic and disinfection models.

This basic level of residual monitoring can be supplemented with more detailed studies using portable on line monitoring equipment and data loggers. If these are not readily available, special work arrangements can be made to allow operational staff to sample sites, at say hourly intervals over the 24 hour cycle.

Such detailed studies are very valuable and provide a deeper understanding of what happens in identified problem areas, help to identify the cause of the problem and monitor the effectiveness of modifications to the management of the system.

Laboratory Testing While some distribution system testing, such as chlorine residuals can and should be carried out by operational staff, some tests require samples to be sent to laboratories. These include • • • • • • • • •

E coli Heterotrophic Plate Counts (HPC) (22oC or 37oC) Iron (Fe) Manganese(Mn) Disinfection by products Dissolved Organic Carbon MIB Geosmin Phenols and chlorinated phenols.

All of these tests should be part of routine verification monitoring. They will also be part of intensive monitoring associated with investigations to solve water quality problems.

One problem with laboratory testing is the delay between submitting the sample and receiving the result.

This is a particular problem where contamination with pathogens is suspected. Recently simple testing systems have been developed for the detection of E coli and coliforms. The kits can be purchased and held by the water utility and are available for immediate use. Coliform and E coli bacteria can be detected in 2 to 15 hours. The more bacteria the faster the results. Developments such as these provide water utilties with ways to monitor distribution systems that were not possible in the past. One particular application of these kits would be in monitoring known contamination events to assess the extent of the contamination and the recovery from such an event. These kits could be part of the “tool box” for all those with a responsibility to manage distribution systems.

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Chapter 5 – Monitoring Distribution Systems

To adequately investigate water quality problems it is often necessary to set up extensive long term monitoring programs that have been carefully designed to provide the information necessary to understand the problem. Routine monitoring programs will generally be insufficient to provide all the answers.

Having submitted samples for testing it is important to know how to interpret the data. Laboratory testing can provide useful information on the causes of dirty or poor tasting water, however most of these are likely to be no more than confirmatory to the experienced system operator who can detect problem levels of many of these compound by utilising their own senses of taste, smell or sight.

Of immediate interest to operators are any microbial test results since these will not necessarily be correlated with any field observations and cannot be detected by an operator. The main types of microbial indicators and the appropriate responses to detection are described in the following text.

E coli The presence of E. coli indicates fresh faecal contamination, and requires an immediate response. In the event that E. coli is reported in the distribution system, the following actions should be undertaken: • Notify the health department (or equivalent regulatory authority) immediately.

• Organise immediate re-sampling of the same site(s), and up and down stream sites, including the source reservoir and entry point to establish whether the contamination is widespread and where it has originated.

• Determine chlorine residuals at the site(s).

• Flush the mains to draw adequately chlorinated water (with a residual of at least 0.2 mg/L free chlorine) into the area. Consider increasing the chlorine dose and/or spot dosing to aid this.

• Check all relevant chlorination equipment and records of its function for the site(s).

• Resample the same site(s) after completion of an operational assessment of the situation.

• Check the integrity of treated water storages to look for any possible faecal contamination.

• Review recent works in the area looking for any low or zero pressure scenarios that may have permitted faecal ingress.

• In conjunction with the health department consider issuing a Boiled Water Alert.

• Continue with daily sampling until 0 E. coli are returned for two consecutive samples from the site(s).

• Document: the non-conformance itself the corrections undertaken to clear out the problem to bring the system back into compliance the probable root cause(s) identified for the problem the corrective action completed to prevent the problem happening again in future, at the affected site(s) and elsewhere, through similar causes.

Total Coliforms Total coliform bacteria are no longer required to be monitored according to regulations and guidelines.

However, the E. coli assays generally also detect total coliforms because the assays are usually combined, so the additional information may be useful and might as well be collected.

Total coliform data should be considered in conjunction with Heterotrophic Plate Counts.

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Chapter 5 – Monitoring Distribution Systems Heterotrophic Plate Counts (HPCs) HPCs are a measure of the microbial content of water. In the laboratory, samples of water from the distribution system are filtered through a membrane filter and the membrane filter placed on a non-specific general nutrient agar that encourages growth of most microbial organisms. Plates can be incubated at a range of temperatures between 20oC and 37oC. Standard Methods (APHA 2004) state that the highest counts typically will be obtained from 5-7d incubation at a temperature of 20oC to 28oC. Traditionally HPC were monitored at 37oC mimicking the temperature conditions of our bodies, making the test useful to detect the presence of potential pathogens in the water. In general the distribution of HPC (37oC) was similar to the distribution of coliforms (and to a lesser extent E coli) and for that reason the test was often considered unnecessary. However by measuring HPC at lower temperatures other information becomes available. HPC(22ºC) provides an indicator of the general microbial cleanliness of the water.

Testing at 22oC will help identify microbiologically active water that may cause increased asset corrosion, increased taste and odour formation and reduced penetration of disinfectant residual.

At the lower incubation temperature the counts will be higher than at the higher temperature. The higher numbers generated allow for improved interpretation of the data for management purposes. It is not possible to detect meaningful patterns with infrequent low numbers. Higher numbers provide an opportunity to identify poorly performing parts of the distribution system and take appropriate corrective action. Having said this, it is important to note that HPC data is very variable both within a system and between different systems. However long term monitoring can reveal definite trends within a given system.

Experience based on long term monitoring will help identify when HPCs are becoming elevated and the system might benefit from flushing or air scouring. This sort of proactive response may prevent or reduce taste, odour and corrosion problems. With HPC data it is generally inappropriate to respond to a single high value without repeated sampling and testing.

While the numbers of these organisms may vary considerably from sampling time to sampling time, in cooler climates with filtered water, any sites that consistently have HPC above 100 cfu/ml should be considered for cleaning, initially by flushing and maintaining a disinfectant residual. If however high levels persist despite flushing, the distribution system in that area should be cleaned using either unidirectional flushing, air scouring or swabbing. Samples with plate counts >500 cfu/ml should be a trigger for immediate cleaning using either unidirectional flushing, air scouring or swabbing. Once again however the emphasis should be on understanding your system and looking for inconsistencies or changes in your system.

Integrated Analysis In addition to thinking about individual results, it is also vitally important to look at results across space and time and to think about how the information from different tests can be interpreted to provide more complete information. For example, if turbidity and HPC are both quite high at the same time, flushing may be required to remove built up sediment. If high turbidity and HPC persist, there may be some ingress into the system that requires identification and elimination. A case study of an integrated approach to water quality optimisation is given in Appendix 2.

An important action is to note where high or low results are located. Use a simple street map or GIS if it is available and user friendly. Mark the actual plate count and coliform numbers on the map. Also mark the free and total chlorine residuals generated from the residual mapping program. Add turbidity and pH data.

Now look long and hard at the map. Is there a pattern? When do they occur and where do they occur? Is it at the end of a system or congregated in a particular area. There may be problems only downstream of a particular service reservoir, PRV or at the end of a system. If hydraulic models are available look at the flows in that area. Once a pattern has been determined, a full cleaning program should be initiated. Valves in the

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Chapter 5 – Monitoring Distribution Systems area may need to be changed to encourage flows through stagnant areas. Additional booster chlorine may be required in a main feeding the area. By plotting all the data and watching it over time, a more complete picture of the extent of the problem may be revealed, more so than just interpreting the data from a single test. It is likely that as the map builds up extra monitoring might be required. 24 hour continuous monitoring of chlorine residuals and pH may be necessary or grab water samples taken hourly over a one week period.

There are too many possibilities to provide definite guidelines, but as the data is reviewed appropriate responses and additional testing will become apparent.

If cleaning does not eliminate the problem, a more thorough analysis is required to check for ingress of dirty water from surface or subsurface assets due to holes, entry points or negative pressure transients.

The results from laboratory and field tests should also be considered in conjunction with consumer complaints.

Often repeated consumer complaints in a particular area correlate with poor results from laboratory and field tests and provide strong evidence of problems in that area.

Consumers As Water Quality Monitors In the ideal world, operators would be aware of water quality problems before consumers noticed them.

Responses would be undertaken in good time, before consumers had any reason to complain. Whilst this should be the goal of water supply operators, it is inevitable that at least some consumer complaints will arise even with the best efforts of the utility.

In responding to consumer complaints the following actions should be undertaken.

• If possible fix the immediate problem and restore good quality water to the consumer • Establish the underlying root cause of the problem (this may take some time and require considerable investigation and testing).

• Identify appropriate corrective actions to correct the problem • Complete the corrective action(s) • Take steps to ensure that the problem is not repeated at the affected site(s) or elsewhere in the system • Carry out an incident debrief • Document a summary of the whole process to provide a record and to support learning by others.

In responding to consumer complaints it is important to treat all complaints relating to water quality seriously, even those from complaint “pests”. A good example is a case of a lady regularly complained that the water tasted like “cats piss”. The complaint was largely ignored. She was regarded by the field operations staff as being a bit “batty” and there were many quips as to “how did she know what cats piss tasted like anyway?”.

On reviewing the data and actually conducting a taste survey in the area, the presence of a real problem was identified. Subsequent laboratory testing revealed the presence of chlorinated phenols in the water.

Phenols have a very distinctive medicinal taste and odour. Perhaps her description was a little strange but she was right, there was a problem and as a result of taking her complaint seriously, the water quality in the town was improved. The problem was fixed by air scouring and cleaning the system. Biofilms were the likely source of the chlorinated phenols.

Pattern Analysis Consumer complaints are usually received through a call centre. The data is then usually entered into an electronic database. Because call centres are usually operated by many officers in different shifts, the

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Chapter 5 – Monitoring Distribution Systems opportunity to identify recurring or developing patterns is often missed. An effort should be made to either electronically or manually search the database for these patterns. In a manual system an officer charged with the responsibility to review the complaints can simply plot the sites of the complaints on a large scale map. Any emerging or short term recurring pattern will immediately become apparent. If the same officer is permanently charged with the responsibility for the task they will be able to recall that similar patterns may have occurred in the past and re investigate old complaint records. Once identified, the patterns should be notified to staff responsible for water quality to fully investigate and follow up. Electronic systems can be developed to carry out this sort of surveillance and provide electronic reports to appropriate officers within the utility and also track the responses.

Proactive Taste And Odour Surveys Relying on consumer complaints to alert a utility to problems with the aesthetic character of the supplied water is a poor substitute for regular proactive assessments of whether the product is fit for purpose.

Consumers are often reluctant to complain, either because they feel they are making a nuisance of themselves or because they feel they are not listened to. Many simply decide to purchase bottled water. In this way vital information is continually lost that would allow, and indeed demand, better operation of our water supply systems.

Regular tasting surveys should be undertaken by staff with a good sense of taste and smell and an interest in water quality. Standardised testing forms can be established and the data integrated into the water quality data and the information used to proactively manage the system for improved water quality.

Most utilities conduct some sort of annual customer survey but these seldom probe deeply enough to identify specific taste and odour problems. Due to modern privacy issues, the data is often presented without any access to actual addresses. Effective management of water quality problems in distribution systems requires specific site identification. Proactive taste and odour surveys provide superior data relating to taste and odour and therefore greater opportunities to identify and solve problems.

Phone surveys can also be used to obtain a better data set. Call centre staff, or indeed operational staff, can randomly select phone numbers from a phone book for a particular supply at a particular time and conduct a simple phone interview. As long as a suitable time is selected i.e. not at meal times, consumers are mostly more than willing to participate. The interview should be structured with a set number of questions and set series of descriptors for the water quality such as • Clarity Very clear Cloudy • Colour Red Brown Blue/black Milky • Smell None Chlorine Musty Fishy Medicinal Other

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Chapter 5 – Monitoring Distribution Systems The final question should be unstructured and allow the person to raise any issues at all to do with the water. Phone surveys such as these allow the collection of data from specific areas with specific addresses and can even allow before and after investigations.

Taste panels can also be established to evaluate specific water quality aesthetic questions (Figure 5.7) Figure 5.7. A taste panel assessing the acceptability of different types of water.

Consumer satisfaction, or dissatisfaction, depends on both physiological and psychological factors. Any experimental work designed to elucidate the degree of satisfaction or otherwise must take this into account and control for these factors.

In the assessment of taste and odour, it is important that testing be kept simple. While detailed chemical analysis is possible, the ultimate arbiter of acceptability is the consumer. The Australian Standard Triangle Test (AS 2542-2005 Sensory Analysis Method 2.2) can be used to evaluate consumer satisfaction or dissatisfaction with a particular water type. The principle of the Triangle Test is that volunteers will be presented with three water samples. Two of these will be identical and one different. The volunteers are invited to identify which sample is the different sample and whether that sample is superior, equivalent or less satisfactory from an aesthetic point of view. Even if the volunteer cannot detect a difference they are forced to make the identification.

Clearly if there is no discernible difference, based on chance they will choose each sample type the same number of times. The statistics behind the test are well established and provided in the Standard.

Volunteers should be screened for suitability to participate in such tests. The principal requirements are that the person actually consumes water during their normal daily activities and is a non smoker, however other requirements can be included. For example, for a particular assessment, participants of a certain age group might be required. On the day of the test, participants are asked to use a neutral soap and to not wear perfume.

Appendix 2 provides an example where the residents of the City of Sale in Victoria were engaged in a program to evaluate process changes at the WTP.

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Chapter 6 – Maintaining A Clean Distribution System

Cleaning removes sediments, removes biofilms and some scale, and replaces poor quality water. By comparing data relating to a range of parameters before and after cleaning, it is possible to see how much difference mains cleaning can make.

Utility Services, working for South East Water in Melbourne, quantified some of the benefits that came from air scouring. The results for turbidity, HPC(22oC), coliforms and free chlorine residual before and after air scouring are shown in Table 6.1. The results are impressive and clearly show significant reductions in turbidity, HPC, coliforms and an increase in free chlorine indicating improved penetration of chlorine into the system.

Table 6.1. Results of air scouring at a number of sites in part of a Melbourne system.

Site 1 2 3 4 5 6

Turbidity (NTU) Before After 5.2 0.6 3.1 0.5 1.7 0.8 180 1 41 0.7 6.9 0.9

HPC 22oC (orgs/100 mL) Before After 50 10 140 50 40 10 2800 10 170 10 40 10

Colilert Coliforms (orgs/100 mL) Before After 57 0 1 0 5 0 21 0 3 0 0 0

Free Chlorine (mg/L) Before After 0.01 0.05 0.01 0.01 0.01 0.03 0.03 0.22 0.03 0.1 0.03 0.07

(Data reproduced with kind permission of South East Water)

Sydney Water implemented a structured cleaning program in the Eastern Suburbs System between 1997 and 2000. As a result of this program, customer complaints reduced from 2.23 per 1000 in 96/97 to 1.28 per1000 in 00/01. Median HPC (20oC) count decreased from 200 to 10 and the mean chlorine residual increased from 0.48 mg/L to 0.66 mg/L over the same period (Vitanage 2000, 2005).

There are essentially three methods for cleaning mains in the distribution system, flushing, air scouring and swabbing. Each of these is described below.

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Chapter 6 – Maintaining A Clean Distribution System

Flushing Flushing involves simply opening the system, usually at a hydrant, and letting the water flow out. The increased velocity of water washes out any dirty water and some material that may have settled in the pipe.

Flushing is only really effective in pipes up to 150 mm diameter.

Flushing may be carried out reactively in response to dirty water complaints or proactively as a part of a system-wide, planned program to progressively clean all or a large part of the system. Reactive flushing may ease the localised problem but does very little to ensure the overall cleanliness of the system. This requires a well managed and systematic approach.

Unidirectional, systematic flushing involves flushing in a logical sequence from upstream to downstream.

The preferred method for unidirectional flushing is the “Leap Frog” method. This involves selecting a section of main with 2 or 3 hydrants. Valves are closed in such a way as to ensure water only flows in one direction and the maximum amount of water is passed along the pipe section. The 2 or 3 hydrants are opened and the water allowed to flow for a minimum of 5 minutes or until the water is clear. Sydney Water suggests a maximum flush period of 15 minutes. Once the flushing time has elapsed, the first or upstream hydrant is closed and moved to the next available hydrant downstream, effectively leapfrogging the other one or two hydrants. This is continued until the entire selected area has been cleaned.

For smaller mains, 100 mm and below, a single hydrant can be run to provide sufficient flushing velocity. For larger mains, 150 mm for example, two or more hydrants need to be flushed to get sufficient velocity. For very large mains, it is not possible to generate sufficient flushing so air scouring or swabbing is necessary.

Flushing should continue until water runs clear. However, this may take some time. If more than 5 min is required before the hydrants start to run clear it is likely that the dirty water problem is extensive and a systematic flushing program is probably required for the whole area. Every effort should be made to capture and reuse the flushed water. This is considered in more detail later in this chapter.

When undertaking flushing it is very important to flush at the highest velocity possible, with hydrants open as much as possible. Simply having water trickle out of a hydrant will do little more than turnover the water in the main, it will not travel fast enough to suspend, slough off and carry out sediments and biofilms.

Work in the Netherlands suggests that a flushing velocity of at least 1.5 m/sec is necessary for flushing to be effective. In larger pipes (150-200 mm pipes) where the sediment includes dense heavy materials, velocities up to 2 m/sec may be necessary to achieve satisfactory cleaning (Kirkmeyer 2003). Heavier materials such as sand require higher velocities to lift them than lighter materials such as alum or ferric floc.

Kirkmeyer (2003) also describes conditions where increased flushing velocities are necessary to provide effective cleaning. These include • pipes that are in poorer condition such as older DI or cast pipes with slight to heavy tuberculation • systems that have not been cleaned previously where the sediment in the pipes may have compacted • systems where routine daily flows do not achieve velocities greater than ~0.6 m/sec.

Air Scouring Air scouring uses pulses of air and water to clean the pipes. The turbulent flow generated by the air water mixture abrades and scours the pipe wall and carries out the loosened material. Air scouring is generally considered effective in mains up to 250 mm in diameter.

Filtered compressed air is introduced to the main via a hydrant. A section of main, typically 2 to 3 km in total, is isolated. The compressor is attached via the upstream injection hydrant. Prior to commencing

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Chapter 6 – Maintaining A Clean Distribution System compressor operation, the static pressure in the main is measured and the compressor overpressure valve set to approximately 50 kPa below the static pressure. This is done to minimise the risk of rupturing the pipe. The selected downstream valve is opened carefully and the main drained of water. Compressed air is introduced and the upstream valve opened slightly so that the discharge from the downstream hydrant is a pulsed mixture of air and water (Figure 6.1). Scouring is continued until the air water discharge runs clean. Samples can be taken during the scouring for water quality testing. This can be done on site using a turbidity meter or sent to the lab for further analysis. A turbidity end point of 1 NTU can be used to decide on the duration of the scour.

Figure 6.1. Air, water and suspended sediment being ejected from a hydrant

The process is then repeated in the next section of main and so on until the cleaning is completed. Typically it is possible to clean several km per day per scouring gang. As with flushing, for best results an air scouring plan needs to be developed to clean the mains from upstream to down stream with flow always occurring in one direction in the mains.

Swabbing Swabbing, or pigging, involves the introduction of hard foam rubber plugs (Figures 6.2 and 6.3) into a main (Figure 6.4) and allowing the swab to be pushed along by the water pressure. Figure 5.5 shows a swab emerging from a main. The size of the swab is chosen carefully so that it will pass along the main without getting stuck but tight enough to abrade the inside surface of the pipe. Swabbing is the only effective cleaning method for mains >250 mm in diameter.

Figure 6.2. Example of a foam swab

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Figure 6.3. Example of a foam swab

Chapter 6 – Maintaining A Clean Distribution System Figure 6.4. A swab launching site

Figure 6.5. A foam swab emerging from a main

The swab may have to be passed through the pipe several times until the water after the passage of the swab has cleared sufficiently. Once the discharged water is deemed to be satisfactory the main is flushed for 10 to 15 minutes and then chlorinated.

While the swabbing removes most of the sediment build up and the biofilm, it does leave some biofilm behind. The exposed biofilm may not have been adequately exposed to chlorine previously and viable microbes may be exposed to the water. This “new” surface needs to be disinfected. A swabbing team is able to clean several km of mains per day.

Which Cleaning Method Is Best?

This question can be difficult to answer but some idea can be obtained from the amount of material washed out of the pipes during the cleaning. In a comparison of swabbing and air scouring, Sydney Water (Vitanage 2005) found that swabbing removed nine times more sediment, and five times more metals. A look at what comes out during the process is also instructive. Table 6.2 gives some idea of the quality of the water discharged from a pipe during the peak of swabbing.

Table 6.2. Material expelled by swabbing in part of the Sydney system (Vitanage 2005) Parameter Suspended Solids (mg/L) Iron (mg/L) Aluminium (mg/L) Manganese (mg/L) Total Coliforms (orgs/100mL) HPC 20oC (orgs/100mL)

Levels 155-34,400 9.5-4720 1.3- 518 0.57-676 <2- 160,000 (average 7,100) 87-1,000,000

In general, swabbing removes the most material, followed by air scouring, and flushing the least. If pipe sizes are below 250 mm in diameter, air scouring is likely to be more effective than flushing and more cost effective than swabbing. If pipe sizes are greater than or equal to 250 mm in diameter, swabbing is likely to be more effective than air scouring and flushing.

The water volume used is also important. Because of their more direct effect, swabbing and air scouring can achieve the same, or better, cleaning effect with the use of less water. On the other hand, swabbing and air scouring are more expensive than flushing.

There are a number of companies in Australia able to offer these services. Some are listed in the Australian Water Association Directory (AWA 2007).

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Chapter 6 – Maintaining A Clean Distribution System

How Much Does Cleaning Cost?

In choosing between the different methods of cleaning, cost needs to be taken into consideration. Sydney Water calculated the costs of planning and management of the activity as well as the cost of the actual cleaning itself. Table 6.3 provides these Sydney Water estimates based on prices during the year 2000.

Table 6.3. Approximate cost (year 2000) of flushing, air scouring and swabbing (Vitanage 2005) Method Flushing Air scouring Swabbing (<250mm diam) Swabbing (250-375mm diam) Swabbing (>375 mm diam)

$/hydrant $40

$/m $12 $15.60 $19 ~$25

Yarra Valley Water quoted costs of $0.27/m for flushing, $0.60-$1.27/m for air scouring and $19.30/m for swabbing in 2003. All costs reported here should be considered indicative only.

How Often Should The System Be Cleaned?

The necessary cleaning frequency depends on • How much organic and particulate material enters the distribution system • How much iron and manganese enters the distribution system • How high the peak hour hydraulic velocity is in the distribution system • The stability of the assets in the ambient water quality.

In general the more organic material, particulate material and iron and manganese that enters the system the shorter will be the interval for cleaning. Independent of this, the higher the peak daily flow the less material will accumulate and therefore the longer the cleaning interval. Where mains are corroding, the cleaning frequency may also need to be increased.

In fully treated and filtered systems the interval for cleaning may be quite long. For example, Sydney Water estimates that a combination of swabbing every 10 to 15 years coupled with unidirectional flushing will maintain their system with low HPC, good chlorine residuals and few consumer complaints. Water entering the Sydney Water system is fully treated. Similarly in the Netherlands with exceptionally good water quality, mains are only cleaned every 10 years or so. However for unfiltered systems, or systems with poor quality water to achieve the same level of cleanliness will require cleaning every few years.

Monitoring data can be used to help dictate when and where to clean, including to some extent consumer complaints. Clusters of dirty water complaints or taste and odour complaints combined with high HPC and/or turbidity results and low chlorine residuals suggest cleaning may be necessary. Figures 6.6 and 6.7 show free chlorine and HPC (37oC) data from a small system. The bars on the left of the graphs are the sites closest to the WTP while the sites on the right are from sites well out into the distribution system.

The figures show a rapid consumption of free chlorine residual as the water moves through the system and in general, an increase in HPC further out into the system. The figures also reveal a tendency for higher HPC counts to be associated with sites where low free chlorine residuals are found. This system is a good candidate for a complete cleaning program. Although the data in Figures 6.6 and 6.7 are from a small rural system, similar studies are possible within water quality or pressure zones within large systems.

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Chapter 6 – Maintaining A Clean Distribution System Figure 6.6. Changes in mean free chlorine levels across a system over a period of approximately 4 years.

Sites on the left of the graph are close to the WTP while those to the right are well out into the distribution system.

Free Chlorine (mg/L)

2.5 2.0 1.5 1.0 0.5 0.0 CWS

Taver

Daris

Bowen

Yurana

Figure 6.7. Changes in mean HPC (37oC) across the same system as shown in Figure 6.6 over a period of approximately 4 years. Sites on the left of the graph are close to the WTP while those to the right are well out into the distribution system.

HPC 37 (orgs/mL)

2500 2000 1500 1000 500 0 CWS

Taver

Daris

Bowen

Yurana

One promising method to predict when cleaning is required has been developed in the Netherlands. This is called the Resuspension Potential Method. The method involves measuring changes in turbidity that result from increases in the water velocity in a selected pipe. The water velocity is increased and held for 15 minutes and the turbidity measured before, during and after the increase in velocity. The type of responseseen in the turbidity graph is given a numerical rating and used to predict if cleaning is necessary.

Verberk et al (2007) describe some early work with this method.

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Chapter 6 – Maintaining A Clean Distribution System Kirkmeyer (2003) summarises the conditions where cleaning should be considered • • • • • • • •

Elevated levels of HPCs Positive coliform results Planning to implement a treatment change Frequent customer complaints Difficulty maintaining disinfectant residual in portions of the system Absence of an aggressive valve/hydrant/tank exercising program Corrosive water supply Sediment accumulation in reservoirs or dead ends.

Monitoring data is necessary to establish whether the objectives of a cleaning program have been met, in particular before and after data. Ongoing monitoring is then required after a cleaning program to provide some guidance as to when cleaning is again necessary. Without monitoring data, a cleaning program remains ad hoc and reactive.

Mains Cleaning, Drought And Wasted Water All distribution system cleaning methods have the potential to “waste” significant quantities of water. Many parts of the country have suffered serious drought conditions for many years now, and security of supply is a major concern. Under such circumstances communities and utilities cannot afford to waste water.

Concerns with water wastage in the face of drought have prompted many utilities to cancel proactive cleaning of distribution systems. This is likely to have an adverse effect on water quality at a later stage. There are two issues here. One of the reasons that distribution system cleaning is not carried out is because of the concern about wasting water during drought periods. Although this is a serious concern, the consequences of not cleaning are also serious: increased biofilm growth, shielding of microbes in biofilms, accumulation of iron and manganese, taste and odour problems and dirty water.

Clearly, a balance between cleaning and water conservation needs to be established. Options are available to reuse the dirty water produced as part of the cleaning process. The water can be captured in tankers and “reused”. (Sydney Water have used this method in the past.) Options for reuse include returning the water to the raw water storage or using it in community projects such as parks and gardens or sporting facilities or using it to provide flushing water where sewer operations require this.

If the cleaning water is to be returned to the raw water source, a risk assessment should be carried out to assess the acceptability of this practice. The “cleaning” water may contain elevated levels of a variety of contaminants. Iron and manganese may be concentrated in biofilms, so water recycling could lead to increased levels of iron and manganese in the raw water. If these were elevated sufficiently they may contribute to a problem. While these levels may be increased in the biofilms it is unlikely that they would significantly increase the levels in the raw water storage, however monitoring of these two elements in the recycled water and in the raw water storage after dilution is recommended. Turbidity would settle in the raw water storage and any bacteria returned to the storage would be subjected to natural disinfection processes.

By attaching appropriate banners to the tankers and running a public relations campaign during the cleaning, utilities could benefit by demonstrating a dual commitment to water quality and responsible operations in the face of difficult drought conditions.

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Chapter 6 – Maintaining A Clean Distribution System

Keeping Treated Water Storages Clean Treated water storages need to be kept clean as well as the mains. Traditionally, reservoirs, basins and tanks were only cleaned when they were fully drained and offline. Cleaning was therefore infrequent. Modern expectations require treated water storages to be cleaned regularly and to remain on line during cleaning.

Specialist diving teams using purpose built equipment are now used routinely to clean storages while they remain on line (Figures 6.8, 6.9 and 6.10). Whichever method is used, sanitary operational procedures must be followed.

Figure 6.8. A diver being lowered into a storage

Figure 6.9. A diver vacuuming the bottom of a storage

Figure 6.10. A huge sediment build up being removed by divers

Cleaning can be initiated at appropriate intervals based on the rate at which contamination builds up on the bottom of treated water storages. Divers can help assess this by carrying out periodic inspections. These inspections can also include inspections of fittings, valves, ladders and any other structures in or over the storages (Figures 6.11 to 6.14).

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Chapter 6 – Maintaining A Clean Distribution System Figure 6.11A. Corroded ladder Figure 6.11B. Corroded pipe

Figure 6.11C. Corroding boat

Figure 6.11D. Concrete crack

Figure 6.13. Weed in outlet

Figure 6.12. Dead Possum

For filtered supplies with well maintained disinfectant residuals, service reservoirs may only need cleaning at intervals of 10 years. For unfiltered systems, cleaning intervals can be as short as one year.

The second priority in optimising water quality in treated water storages is to control the opportunity for build-up of microbial biofilms, to help reduce taste and odour formation and loss of disinfectant residual.

Examples of practical solutions to control such microbial activity and sludge build up include installation of mixers, installation of baffles, relocating inlet and outlet structures to prevent short circuiting and maintaining a disinfectant residual (see Chapter 4). Once again commercial diving companies can assist with these changes without the need to take storages off line.

There are a number of companies in Australia able to offer tank and reservoir cleaning services. Some are listed in the Australian Water Association Directory (AWA 2009).

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains

Sanitary Operating Procedures Whenever a new main is added into a distribution system, or a main breaks, the integrity of the system is disrupted and there is a potential for recontamination of the water inside the pipes. While the flow is generally outward, there is a possibility that non disinfected material may get into the system. To prevent this happening and to protect water quality, sanitary operating procedures need to be developed for all distribution system repair, maintenance, and construction activities. These procedures must aim to prevent contaminants getting into the system and to remove and/or disinfect any contaminated water that does get in before consumers are reconnected.

Distribution system operators should have ready access to the procedures and should be trained and regularly assessed as to their competence to perform them.

New And Replacement Mains Pipes and pipe fittings will become contaminated to some extent during installation from mud and water in the area around the work site. It is therefore necessary to ensure that before the pipe or repair is used to carry water to consumers it is thoroughly cleaned and disinfected (Figure 7.1).

Pipe lengths should be stored in a clean environment so as to prevent the entry of foreign materials into the pipe. Pest control is required to prevent stored pipes and fittings becoming infested with vermin that might contaminate the surfaces with infectious pathogens. Where possible, fittings and pipes should be capped (Figure 7.2 and 7.3), boxed or sealed. Pipes and fittings should be inspected prior to use. Any foreign material should be blown or swept out. During construction, all openings should be sealed with plugs or plastic wrapping when a work site is left unattended, both during the day and overnight (Figure 7.3).

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains Figure 7.1. Pipes ready for laying. This pipeline will require careful cleaning and disinfection prior to connection to consumer.

Figure 7.2. Pipes stored with end caps prevent contamination during storage and transport.

Figure 7.3. During construction, use of end caps prevents contamination of the inside of the pipe.

The WSAA Water Supply Code of Australia WSA 03-2002 and the Plumbing Code AS/NZS 3500:2003 requires that all mains are cleaned and swabbed or flushed, hydrostatically pressure tested and disinfected.

The complete details can be sourced from that document. A summary is provided below.

Swabbing All newly constructed mains between 100 mm and 825 mm diameter must be swabbed where practical to ensure the mains are free of foreign and possibly harmful material. The swabbing must be performed after completion of the pipe work and prior to flushing, hydrostatic pressure testing and disinfection. The swabs must be single use products that are pre-packaged and have been stored hygienically. Two swab runs are required.

Hydrostatic Pressure Testing All mains greater than 20m, after trench filling and compaction and sufficient time for concrete thrust curing to have occurred must be hydrostatically tested. Only potable water is to be used for testing. Up to 24 hrs must be allowed for the water to come to equilibrium and allow any released air to be removed from the system. The required test pressure specified in the code needs to be maintained for 15 minutes without loss of pressure.

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains Disinfection All mains >= 225mm diameter must be disinfected before they are placed in service. Any existing mains >= 225mm diameter that are taken out of service during construction must also be disinfected. Water mains <= 225 mm diameter should be disinfected where there is likelihood of contamination. The authors feel that it would be prudent to disinfect all mains prior to commencement of service. Chapter 1 provides the background to why disinfection of new and repaired mains is necessary. Without thorough flushing and disinfection, people are becoming ill.

The AWWA Water Distribution Systems Handbook provides guidelines for the disinfection of replacement and new mains (Walski, 2000). These are provided below.

• Continuous Feed Method : Flush the main at > 0.76 m/sec to remove any sediment from the pipe.

(For large mains it may be necessary to swab the pipe) Feed chlorine at a rate that maintains a free residual of 25 mg/L for 24 hrs. At the end of that time the free chlorine residual must be greater than 10 mg/L at all points in the pipe.

• Slug Method : Chlorine is added to the pipe so that a slug of highly chlorinated water with a free chlorine residual of at least 100 mg/L is held in the pipe for at least 3 hours. After this time the residual should still be greater than 50 mg/L. If not, the procedure needs to be repeated.

Sydney Water requires new or replacement mains to be super chlorinated with a standing dose of 20 mg/L for a minimum contact time of 24 hours. Chlorine is added to the pipe until the target free chlorine level is achieved. During the contact period all valves and hydrants on the new main are operated to ensure that all surfaces which will be in contact with water are exposed to chlorinated water.

Testing Bacteriological and other testing is required on all new mains prior to commissioning. New or replacement mains should only be placed into service when the microbiological results are satisfactory.

Sydney Water requires samples to be taken from the mid point of the new main, from the dead end of the new main and where the main is longer than 500m, additional samples are required every 250 m. The new main is only allowed to be placed into service if the microbiological testing returns 0 E coli and 0 Total Coliforms. If this is not the case the process needs to be repeated. In addition all samples must have a turbidity <5NTU prior to placing the main in service.

While there are some minor differences in the requirements for disinfection of new and replacement mains one thing is certain, there is agreement that replacement pipes and fittings must be disinfected before being brought on line. Water utilities should consider the information provided here and then decide on an appropriate method for that utility.

Mains Breaks Mains breaks vary in size and in their impact on the system. A small break can be fixed with a clamp without needing to depressurise the system. A break may however require a section of the main to be isolated and the application of a large clamp or replacement of a segment of the main.

The risk of contamination is quite different in both of these cases. The extent of the risk depends on

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains • • • • •

The amount of water lost and amount of mud around the work site The proximity to sewer mains The nature of the surrounding area whether it is swampy ground or dry hard ground The cleanliness of maintenance workers boots and equipment Whether the main needs to be shut down to repair it. Once a main is shut down, positive pressure is lost and flow of foreign material into the pipe is possible.

Once a repair is completed, the main needs to be brought back on line promptly in a way that minimises the risk of microbial contamination reaching a consumer. A risk assessment should be conducted to decide on an appropriate procedure. The following discussion is provided for guidance and information.

• In the case of a mains break, many utilities “flush till clear” after any repairs. The definition of “clear” is not provided.

• Other utilities extend this basic approach with a requirement to flush from the first hydrant downstream of the repair and continue flushing until the water runs clear and take chlorine free residual measurements every five minutes until a reading typical for the area is achieved. Flushing is also required for any side mains that come off the section of isolated pipe by using the first hydrant past the isolation valves. Free chlorine residuals are also measured in the side mains and flushing continued until a reading typical for the area is achieved. Operators in these situations generally have access to chlorine residual analysers, comparators and in some cases turbidity meters.

• One utility adds the extra requirement that if no free chlorine residual is recorded after 30 minutes, a works coordinator be notified and consideration be given to injecting sodium hypochlorite into the main through one of the hydrants.

• Another utility has developed a mobile disinfection trailer for the purpose of injecting disinfectant into the main (Figure 7.4).

Figure 7.4. An example of a mobile mains disinfection trailer

• Another utility requires that mains less than 200mm be flushed on either side of the main break until discoloured water is removed. Where the break is adjacent to a sewer, or in contaminated soils or where a large amount of dirt and dirty water has entered the main, the main must be disinfected using either a continuous dosing method at 10 mg/L for 30 minutes (Ct 300 mg.min/L) or by the standing dose method at 20 mg/L for 24 hours. For all mains greater than 200 mm the mains must be flushed on either side of the break until discoloured water is removed and then disinfected as described above.

Clearly there is considerable variation in the management of water quality after a mains break. So what should be done?

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains

In the authors opinion, regardless of the pipe diameter, where there is a risk that “environmental material” may have gained access to the distribution system, the repaired section needs to be thoroughly flushed and the affected area thoroughly disinfected. Clearly pipes need to be returned to operation as soon as possible and most utilities have key performance indicators for the restoration of water to consumers, but similar requirements for the resupply of safe drinking water are often not similarly emphasised. The important question is not how long it takes to return water to the consumer BUT how long it takes to return SAFE drinking water to the consumer.

The only alternative would be to issue a “Boiled Water” alert and keep it in place for the time taken for the water to pass from the break area and out of the system, plus some extra period to be conservative. Walski (2000), in the American Water Works Association (AWWA) Water Distribution Systems Handbook, also makes the point that the mains may need to be disinfected if pressure was lost and that “if there is concern that contamination has occurred during repair, a precautionary “boiled water” notice should be posted.”

When disinfecting mains after a break, it is important to remember that viruses are generally more resistant than bacteria to disinfection but can be controlled with common disinfectants used in the water industry (ADWG 2004) (see also Chapter 4 page ??). However the Ct required for disinfection of Cryptosporidium is several thousand and therefore requires very high chlorine concentrations such as 20 mg/L chlorine left in place overnight. Such requirements are often impractical in field circumstances, leaving a Boiled Water alert as the only suitable management option if there is a significant risk that major sewer contamination may have occurred.

Any procedure for the disinfection of mains should be based on a high Ct value to provide a margin for uncertainty and variations in temperature and operational conditions and in the case of new pipes, the condition of the walls of the pipe.

An arbitrary value of Ct = 300 mg•min/L has been selected for the following example. This figure should not be taken as a requirement or even a recommendation. That decision needs to be taken by the individual utility based on their own individual risk assessments. Table 7.1 provides an example of chlorine residuals and time necessary to achieve a Ct of 300 mg•min/L. Note that it is the chlorine concentration at the end of the contact period that is used to define the Ct, not the dosed amount of chlorine.

Table 7.1. Examples of chlorine residuals and contact time requirements to achieve a Ct of 300 mg.min/L Free Chlorine Residual at the End of the Holding Period (mg/L) 1 5 10 20

Minimum Contact Time Required(mins) 300 60 30 15

The figures provided above are only an example and tables of necessary Ct values to achieve disinfection of different micro-organisms can be obtained from Hrudey and Hrudey (2004) or the ADWG (2004).

Once an effective and efficient mechanism has been developed to inject sodium hypochlorite into the main, the process can be manipulated to disinfect the main and achieve the required resumption of service.

Higher concentrations of chlorine for shorter times allow quicker resumption of service. Therefore, the

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Chapter 7 – Mains Breaks, Mains Replacement And New Mains disinfection of a main after repair doesn’t need to delay the restoration of water significantly, if the proper equipment and training is provided. In reporting data on the restoration of service, it would be very useful to also report the actual Ct achieved prior to reconnection of supply.

Fittings such as clamps or tapping saddles should be thoroughly sprayed with a sodium hypochlorite solution (1% –1.5% is suitable) prior to attachment to the pipe to further reduce any risk of contamination.

Dahm and Schulz (2006) report on the use of a trailer mounted ozone system for disinfecting mains. The system has many advantages including the possibility of bringing mains back on line more quickly and simpler management of the water from within the main.

Where mains installation and mains repairs are contracted out to private companies or indeed even if these functions are performed “in house”, utilities are well advised to conduct periodic spot audits to gauge compliance with requirements (see Chapter 7). This activity is not one of policing but is simply part of a quality assurance program to ensure that consumers are supplied with safe drinking water at all possible times. The audit process is an integral part of the ADWG 2004 and AS/NZS ISO 22000:2005.

Figure 7.5 and Table 7.2 provide a summary of the key aspects of ensuring safe water is returned to consumers after mains repairs or laying of new mains.

Broken water main

Hygienic work practices

Disinfect fittings Ct 10,000

Repair

Can it be fixed under pressure?

Is there an mmediate risk of contamination

No Hygienic work practices

Disinfect fittings Ct 10,000

Hygienic work practices

Disinfect fittings Ct 10,000

Isolate fix and flush thoroughly

Check residual = upstream residual

Has water entered the pipe?

Process Complete

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Isolate and repair

Disinfect fully Ct >300

Is significant contamination possible

Issue Boil Water Alert

Dispose of chlorinated water appropriately

Dispose of chlorinated water appropriately

Process Complete

Process Complete

Chapter 7 – Mains Breaks, Mains Replacement And New Mains Table 7.2. Summary of activities for management of repairs and new mains.

No loss of pressure

Loss of pressure

New mains

Low risk

High risk

Medium risk

Keep trench water out of pipes!!

Disinfect all fittings (1% hypo 10 minutes = 100,000 Ct)

• • • • • • • • • •

• •

• • •

• •

Excavate under pressure Excavate pump sump Install suitable sized sump pump (big is good!!!)

Remove water from any hydrant points Prevent water being sucked into isolated section through hydrants (use hydrant extensions) Slowly isolate section Pump out water before all pressure discharged Keep trench dewatered for duration of repair Drain section using fire plugs and hydrants (try to minimise the length of main drained) Clean all fittings and pipe sections before installation (this should not be necessary if they have been stored appropriately) Disinfect all fittings and pipe sections (1% hypo for 10 minutes = 100,000 Ct) Swab liberally with 1% hypo all internal surfaces of adjoining mains and external surfaces where clamps are to be fitted Remove water from any hydrant points Flush till clear and upstream free chlorine residual is stable at downstream sample point If there is any risk that water has entered the pipe then the main MUST be fully disinfected. If serious risk due to nearby septic tanks, sewer or swampy livestock farmland higher Ct required.

If site left unattended, exposed ends of pipes must be sealed Still in doubt?… Boil Water Notice

WSAA Code All new mains between 100 mm and 825 mm must be • Swabbed (Single use swabs, two swab runs) • Flushed • Hydrostatically tested (no change in 15 mins) All mains >225 mm must be disinfected.

Bacteriological testing

What To Do With The Discharged Water The question of what to do with discharged water during cleaning was addressed in Chapter 5. Disinfection of repaired, new or replacement mains also requires the disposal of water, often with a high chlorine residual. If the water is not going to be captured and reused i.e. in situations where water is not in short supply, the question is how to dispose of the discharge in an environmentally sensible manner. If possible, dischargethe water to land rather than to water ways. In discharging to land ensure that the discharge does not cause erosion or unwanted flooding. Permission from the land owner should be obtained before

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discharging the water. If the water must be discharged to a natural water way then this must comply with relevant state regulations or guidelines. Maximum dilution should be achieved at all times. Water with a high chlorine residual requires dechlorination using a reducing chemical such as sodium sulphite or sodium metabisulphite prior to discharge. Mobile trailer based chlorination/dechlorination systems can be built or alternately several companies are available to provide this service. Some of these are listed in the Australian Water Directory (AWA 2009).

Chloraminated water is highly toxic to aquatic organisms and therefore extra care is required where the water is chloraminated to avoid discharge to waterways.

Approved Materials All piping, joints, clamps, linings, paints, coatings and sealants used in the maintenance or construction of a distribution system must be specifically approved for use in contact with potable water. Purchasing and storage procedures are required to ensure that only materials that have satisfactorily passed the requirements for Testing of Products for Use in Contact with Drinking Water AS/NZS 4020:2005 are obtained and made available in stores and depots. Non-compliant materials should not be stocked.

Work Teams And Management Practices IEductor pumps, shovels, work boots, clothing and tools could all transport pathogens from the site of a sewer repair to the site of a water main repair. This risk needs to be recognised and appropriate measures put in place to prevent potential cross contamination. It is easy to prevent such transfer as long as the risk is recognised. The basis of management of this risk is to ensure that anything that may have contacted sewage must never come in contact with water. This includes pumps and hoses, backhoe buckets, shovels, crow bars and spanners.

The best option is the complete separation of work groups and work materials. There are several ways to do this. Many larger utilities have work teams dedicated to water operations or sewer operations with no crossover of workers or equipment. Some utilities opt to contract out one function, usually sewer maintenance and keep water system maintenance “in house”.

For smaller utilities, such separation may not be possible due to the number of staff available and the geographic area covered. In this case the second best option is to ensure complete separation of work materials including personal clothing. All tools and equipment should be colour coded e.g. white or blue for water and red or black for sewer. These tools and equipment should be kept in well defined and separated areas in depots and sheds or in separate colour coded trailers. For example one Victorian utility has set up separate response trailers. They have a fully equipped sewer response trailer and a fully equipped water response trailer. The trailers are colour coded. The sewer response trailer is coloured red and the water response trailer is blue (Figures 7.6 and 7.7).Alternatively vehicles can be set up with separate sets of boots and tools in separate compartments. White boots would be used for water operations while dark coloured boots would be used for sewer operations.

If in an emergency separation is not possible then all equipment including boots and tools must be meticulously decontaminated before commencing work on potable water systems. This involves immersing boots, shovels and pumps and any other equipment on site in high strength chlorine solution. A suitable procedure involves immersing all surfaces that may come into contact with water in 1% chlorine for 10 minutes (Ct = 100,000 mg.min/L). Disposable overalls should be used to cover possibly contaminated clothing. trailers.

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Figure 7.6. The sewer response trailer

Figure 7.7. The water response trailer

In situations where staff may be involved in work on sewers and on drinking water systems it is absolutely essential that sufficient training is provided to ensure that all operators recognise the risks their actions pose to the safety of the drinking water. Remember, recontamination after primary disinfection has occurred is a serious risk.

Residual chlorine in the system cannot be relied on to manage bacteria, viruses or protozoans. They must be prevented from gaining access in the first place, or if there is a risk that they might have gained access, they must be thoroughly flushed from the system and the part of the system re disinfected. Remember also that the final barrier is a Boil Water alert and that this may need to be invoked to protect public health.

Whatever system is set up it is imperative that it be audited periodically to ensure that it is in fact in use.

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Chapter 8 – Operational Verification Audits

Given the pressure on water utilities, it is easy for some activities to be overlooked or for untrained, inexperienced staff or external contractors to become involved in operations. The ‘head office syndrome’ of becoming buried in paperwork and meetings means that it is quite possible that supervisory and management staff will be unaware of potentially major omissions in operational procedures. Where these omissions affect water quality there is a real potential for an adverse impact on public health.

Operators may not feel comfortable coming forward to request more support, they might not even be aware that they need it. Contractors working on site for large contract companies may not understand what is required to protect public health. Therefore it is vital that operational audits are performed to establish what actually happens in the field. These may be conducted by utility staff or by suitably trained external auditors.

The audits need to verify that the work is being done properly and in such a way as to protect public health.

Audits usually involve interviews with staff to establish their understanding of processes as well as checks of records of operational activities and monitoring data to confirm compliance with requirements. Where possible, “surprise” field audits should also be carried out. These can be formal or just informal when a water quality officer arrives on site to watch a repair or other distribution system task.

Remember auditing is not about catching someone out. It is a part of a cooperative mechanism to ensure that public health gets the appropriate attention at all times.

Table 8.1 provides examples of operational audit verification activities.

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Table 8.1. Examples of possible operational verification audit activities for good distribution system management.

Item to be verified Auditor Frequency Comments Conformance to sanitary operating procedures.

Supervisor

Supervisor

Auditing should be reasonably random and involves attending sites whilst works are in progress, observing the whole activity.

The audit must check the aspects of the procedures relating to drinking water safety, not just occupational safety or environmental management system compliance.

Operators should be interviewed to ensure that they understand the importance of the preventive control measures and are able to perform the works satisfactorily.

Conformance to treated water storage inspections.

Supervisor

Quarterly

Auditing should sample records to establish that water quality protection inspections are taking place and that records are retained.

Operators should be interviewed to ensure they understand the importance of the preventive control measures and are able to perform the inspections satisfactorily.

Completion of corrective actions in response to non-conformances

Supervisor

Monthly

Auditing should sample records to establish that corrective actions are being taken in response to non-conformances, such as high E. coli results or customer complaints.

The audit should also check how corrective actions are programmed and completed in response to non-conformances.

Auditing should specifically consider the adequacy of the response in terms of timeliness and coverage.

Operators should be interviewed to ensure they understand the importance of the performing corrective actions and have the authority and support required to do so.

Training and competency Manager of operators.

Annually

Auditing should check the competency and recognised skills records for staff to ensure aspects related to water quality management are current and sufficient.

All aspects of water quality management system.

Annually

Auditing should sample all aspects related to water quality management.

External auditor

A combination of office-based, depot-based and field auditing should be employed.

Auditors should be skilled in practical aspects of water quality management in distribution systems.

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Chapter 9 – Closing Words Provision of safe drinking water requires diligence, attention to detail and effective process monitoring.

Distribution systems are a key element in the process of delivering safe water to the consumer.

This practical guide has provided a sound background to the operation of distribution systems. Distribution systems because of their nature, being mostly below ground and spread out, may appear at first to be difficult to manage, however if the advice provided here is implemented and incorporated into the routine work practices of the operations teams responsible for the distribution system, the chances of producing safe drinking water will be greatly increased.

The advice provided here might seem to some like more work, BUT, it IS the work of operating distribution systems. Time simply must be found. Managers need to fully support operators in this to facilitate the implementation of these tasks.

Think about it? A well run distribution system means peace of mind that the water delivered to consumers is safe to drink and will not result in an outbreak of waterborne disease of the types that have been described all around the developed world.

Take the first step now!

Good Luck Sleep Soundly Enjoy!!

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Appendix 1 – Distribution System Contamination Case Studies

Appendix 1 – Distribution System Contamination Case Studies Case Study 1. Central Queensland, Australia, 1999 This case study proves that pathogens getting into water tanks via animal faeces can cause disease in humans and clearly proves the importance of protecting reservoirs from such incidents.

“Two cases of salmonellosis were notified by General Practitioners from towns 250 km apart, on 15 March and 24 March 1999. Both worked at the same site and both were faeces culture-positive for Salmonella spp, later typed as S. saintpaul. Telephone follow-up of the first suggested no associated cases, but follow-up of the second did, prompting an immediate site visit and further investigation.

An assessment of water carted to the site was conducted. The carter servicing the site obtained water from a reticulated water supply for which there were no indications of recent problems. Supplementary chlorine was added to it prior to delivery. Samples taken from the carter’s tankers complied with NHMRC Australian Drinking Water Guidelines.

On delivery, water was stored without further chlorination in six new 5,000-litre tanks located at three points around the construction site. Two of the six tanks (1 and 2) were interconnected and supplemented with rainwater collected from a workshop roof. One of these tanks had an uncovered inlet.

The most significant rain during February/March was a fall of 125 mm on 6 March, and it is possible this marked the actual beginning of the outbreak. Although the original source of contamination of the water tanks is uncertain, there are at least two plausible explanations.

Salmonellae may have been introduced via mice and/or their excreta washed into the tanks from the roof collection area. Mice were evident during site inspections despite rodent control measures. On cleaning, no dead mice were found inside the Salmonella contaminated interconnected tanks, but a number of live green tree frogs were and these may have introduced contamination directly. Alternatively, Salmonella from animal excreta flushed into the tank by the heavy rainfall event multiplied in the frogs and were effectively ‘amplified’.

Local Parks and Wildlife staff confirm that inquiries from the public about removal of frogs from water tanks are common. Maintenance of barriers across water tank inspection ports is the obvious (but frequently neglected) intervention to prevent ingress of frogs. Further research may be warranted to investigate the potential role of frogs as vectors in human Salmonella infection.

In concluding, contamination of a tank water supply system led to an outbreak of Salmonella saintpaul with 28 cases of gastroenteritis amongst over 200 workers at a large construction site. The outbreak was identified following notification of two salmonellosis cases by general practitioners from different towns during March 1999. The source of infection, contaminated drinking water, was identified through environmental sampling and confirmed by epidemiological investigations. Frogs and/or mice may have been the original source of the contamination”.

Source: Abridged extract from © Roscoe Taylor, David Sloan, Toni Cooper, Bruce Morton, Ian Hunter. 2000.

A waterborne outbreak of Salmonella Saintpaul. Commun Dis Intell 24:336-340.

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Appendix 1 – Distribution System Contamination Case Studies

Case Study 2 Gideon, Missouri, 1993 This case study proves that pathogens getting into water tanks via bird faeces can cause disease in humans and clearly proves the importance of protecting reservoirs from such incidents.

An outbreak of waterborne disease was recorded in the small city of Gideon, Missouri in 1993. The outbreak affected 44% of the of the 1104 residents. 28% of non residents who drank the water were also infected.

Seven residents were thought to have been killed by the particularly virulent strain of infectious bacteria present.

A sequential flushing program involving all 50 of the towns hydrants was initiated in an attempt to control a taste and odour problem. The increased flow caused previously full tanks that never adequately turned over to empty. The increased flow stirred up the sediments in the tank and allowed a stagnant surface layer that normally didn’t distribute to travel into the distribution system. Contaminated stagnant surface water from the top of the tank or contaminated sediments at the bottom of the tank entered the system.

Upon inspection, one of the tanks was found to have a rusted cover with several holes in it. Large numbers of pigeons were found roosting on the roof of the tank. Feathers were observed floating in the water. In their consideration of the outbreak, investigating authorities gave consideration to a number of contributing factors including: • • • •

The probable source of faecal contamination was the pigeons on the tank roof Salmonella spp bacteria were probably present in the faecal material Poor maintenance meant that holes in the water tank had let faecal material into the tank The faecal contamination has built up in the sediment at the bottom of the tank and in the stagnant surface layer of the tank • Extensive flushing lowered pressure in the system • The increased flow of water during the flushing caused tanks to turnover, entraining stagnant surface layers and scouring sediments from the bottom of the tank.

Source: Based on © Clark, R. (2000) Water quality modelling case studies. In: Water distribution systems handbook. Ed. Mays, L.W. McGraw Hill New York.

Case Study 3. Queensland, Australia, 2005 This case study proves that pathogens getting into water tanks via animal faeces can cause disease in humans and clearly proves the importance of protecting water storages from such incidents.

“During the quarter, there were two outbreaks potentially associated with drinking water. One was associated with a prolonged outbreak of salmonellosis at an aged care facility.

Eight residents were ill with salmonellosis thought to be caused by a contaminated rainwater tank.

Patients were infected with multiple serotypes of Salmonella, including Muenchen, Chester, and Subspecies 3b over a three month period. Subspecies 3b was isolated from water from the facility’s rainwater tank. The tank water was also heavily contaminated with E. coli. The source of the pathogens is unknown but may have been due to amphibians or reptiles.

The aged care facility used rainwater tanks as the source of drinking water. The tanks may have been contaminated by animals on roof catchment areas. This outbreak and previous microbiological surveys illustrate that tanks may be unsuitable as a source of drinking water for aged care facilities.

Rainwater tanks have been implicated as a source of disease previously and they are difficult to clean and maintain. Rainwater tanks may be a more common cause of disease than previously recognised”.

Source: Abridged extract from © OzFoodNet 2005, Enhancing foodborne disease surveillance across Australia: Quarterly report, January to March 2005: Communicable Diseases Intelligence 29:197-8.

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Appendix 1 – Distribution System Contamination Case Studies

Case Study 4. Pennsylvania, USA, 2005 This case study proves that chemicals can readily enter water distribution systems following pressure loss and clearly proves the importance both of taking all reasonable precautions to prevent negative pressure events and the importance of flushing to remove possible contaminants.

“The idea that harmful substances could be slowly invading our nation’s water supply sounds like something straight out of a low-budget horror movie. However, it is a possibility that all water systems, regardless of size, need to address.

When “yellow gushy stuff” began pouring out of water faucets in a sleepy Pennsylvania community a few years ago there wasn’t a movie director around to yell “cut” when people started getting ill.

Without Superman or Wonder Woman to step onto the scene and “save the day,” the water system of a 75-unit apartment complex was quickly infiltrated by the mysterious “yellow” substance.

Was this a case of alien invaders or mutant creatures from the “black lagoon” seeking to destroy the planet?

No, in fact it turned out to be a much spookier scenario.

According to investigators, the yellow substance residents discovered “oozing” out of their faucets turned out not to be a mind-controlling ectoplasm, but rather a combination of pesticides that had been siphoned into the public water system through a hose that had been left in a local exterminator’s tank truck.

When a nearby waterline was cut, a siphon (or backflow) was created, which pulled the poisonous chemical cocktail into the water hose that was connected to the community’s water distribution system.

Had the community clearly understood the dangers associated with cross connections, this tale might have had a happier ending.”

Source: Abridged extract from © Safe Drinking Water Trust eBulletin, Rural Community Assistance Partnership, United States Department of Health and Human Services, November 12 2005. http://www.crg. org/bulletin/articles.asp?name=FeatureArticle&ID=768

Case Study 5. Alabama, USA, 1986 This case study proves that chemicals can readily enter water distribution systems following pressure loss and clearly proves the importance both of taking all reasonable precautions to prevent negative pressure events and the importance of flushing to remove possible contaminants.

“A resident of a small town in Alabama, jumped in the shower at 5 a.m. one morning in October, 1986, and when he got out his body was covered with tiny blisters. “The more I rubbed it, the worse it got,” the 60 year old resident said. “It looked like someone took a blow torch and singed me.” He and several other residents received medical treatment at the emergency room of the local hospital after the water system was contaminated with sodium hydroxide, a strong caustic solution. Other residents claimed that, “It (the water) bubbled up and looked like Alka Seltzer. I stuck my hand under the faucet and some blisters came up”. One neighbor’s head was covered with blisters after she washed her hair and others complained of burned throats or mouths after drinking the water.

The incident began after an 8-inch water main, that fed the town, broke and was repaired. While repairing the water main, one workman suffered leg burns from a chemical in the water and required medical treatment.

Measurements of the pH of the water were as high as 13 in some sections of the pipe. Investigation into the

81

cause of the problem led to a possible source of the contamination from a nearby chemical company that distributes chemicals such as sodium hydroxide. The sodium hydroxide is brought to the plant in liquid form in bulk tanker trucks and is transferred to a holding tank and then pumped into 55 gallon drums. When the water main broke, a truck driver was adding the water from the bottom of the tank truck instead of the top, and sodium hydroxide back-siphoned into the water main”.

Source: Abridged extract from © USEPA 2003 Cross-Connection Control Manual. United States Environmental Protection Agency Office of Water, Office of Ground Water and Drinking Water.

Case Study 6. Oulu, Finland, 1998 This case study proves that microbial pathogens can readily enter water distribution systems following line repairs and clearly proves the importance both of taking all reasonable precautions to prevent line breakages, of sanitary repair procedures and of flushing and disinfecting to remove possible contaminants.

“The municipality has a population of approximately 15,000 people and is located in northern Finland, 20 km north of the city of Oulu. Practically all (99%) residents receive drinking water from the non-chlorinated municipal water supply. On Monday 10 August, the National Public Health Institute (KTL) was notified that during the weekend of 7–8 August 1998, approximately 50 persons had sought care at the municipal health centre because of gastrointestinal symptoms. On 11 August, Campylobacter jejuni was isolated from stool samples of 15 patients with gastrointestinal symptoms. The wide geographical distribution of cases and preliminary interviews with patients suggested drinking water as the source of the outbreak. A boil-water notice was, therefore, issued on 11 August, and chlorination of water began on 13 August.

During mains repair work close to the centre of municipality on 29 July, sewage water had flooded and probably mixed with mains water. After the incident, the pipes were thoroughly flushed in order to prevent contamination of the main water system. Initial samples from the water supply were negative for coliforms.

Subsequent water samples from various points of the water system from 11, 12 and 13 August were negative for Campylobacter and indicator bacteria. Noroviruses or parasites were not detected in water samples.

In this community-wide outbreak associated with consumption of non-chlorinated drinking water from a ground-water supply, we found that almost one fifth of the population in the affected municipality fell ill with gastroenteritis. In addition to a strong association between illness and consumption of municipal water, the risk of illness increased with increasing daily consumption of unboiled tap water. C. jejuni was isolated from a majority of the investigated stool samples, and the studied strains had indistinguishable genotypes indicating a common source of infection. Together with the temporal association and a plausible contamination mechanism from mains repair work, these findings provide strong evidence that the outbreak was waterborne The environmental investigation revealed several risk points in the water system. The mains repair work on 29 July is the most plausible source of contamination on the basis of epidemiological and environmental evidence as well as temporal association. The work was done close to the centre of the municipality and water tower where the attack rate was highest. It probably caused a cross-connection between sewage water and drinking water. According to the epidemic curve, contamination during the construction work is temporally compatible with the epidemiologically determined exposure period in the outbreak. Previously, cross-connection has resulted into community-wide waterborne outbreaks”.

Source: Abridged extract from © Kuusi M, Nuorti JP, Hanninen ML, Koskela M, Jusilla V, Kela E, Miettinen I and Ruutu P. 2005. A large outbreak of campylobacteriosis associated with a municipal water supply in Finland. Epidemiol Infect 133:593-601.

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Appendix 2 – Optimisation Case Study

Appendix 2 – Optimisation Case Study The case study presented here is quite long. It is presented in full detail to give readers some idea of the commitment and work necessary to solve problems involving the distribution system. The details herein may also give readers ideas as to how they might tackle problems within their own systems.

Dirty Water, Taste And Odour In Sale Victoria Dirty water and taste and odour problems are common in the water industry. The key to understanding and finding solutions to such problems involves a logical sequence of steps.

• • • • • • •

Making observations Collecting data Suggesting a possible reason for the problem based on the data collected Collecting more data to see whether the explanation is reasonable Modifying the explanation if necessary Developing possible solutions Implementing the solutions.

The method is exactly the same as that used by scientists investigating any scientific problem. Solving problems requires patience and you must be prepared to invest time and some money to set up a well structured monitoring program. Relying on routine monitoring data will seldom provide the answers.

Additional monitoring is nearly always necessary.

The following case study is presented to illustrate the methodology available to identify and solve a wide range of problems. The actual example won’t necessarily apply to many situations but the steps taken to resolve the problems can serve as a guide to how to solve similar sorts of problems. The rural city in this case study had persistent long term dirty water as well as taste and odour problems.

Background to the Problems The City of Sale ( population 13,500) in Victoria has a history of water supply problems dating back to the mid 1800’s. Initially raw water was taken from the Thomson River, but this source became progressively polluted from goldmining, pig farming and slaughter yard operations. In 1880, after more than 20 years of debate, a bore was sunk, but the ground water was sulphurous and corrosive to the early cast iron reticulation system. In 1888, the supply reverted to the still polluted Thomson River and in 1935, a filtration plant was built. The plant was expanded as the City grew until 1965 when colour and taste and odour problems associated with effluent from a milk factory 30 km upstream became insurmountable. On Christmas Day 1970 after a period of over 80 years, Sale returned to a ground water source for its raw water supply.

Water can be drawn from any one of five bores. These bores are all less than 1 km apart and supposedly draw from the same aquifer but at different depths. Typical raw water quality for the bores is shown in Table 1.

83

Appendix 2 – Optimisation Case Study Table 1. Raw water quality. Data is for the period 1995 to 2001. Data are means and standard deviations.

Bore 1 Alkalinity (mg/L) 24 (3) Turbidity (NTU) 2.2 (3.8) Colour (PtCo) 6 Iron (mg/L) 0.39 (0.60) 0.052 Manganese (mg/L) (0.005)

Bore 2 28 (5) 3.9 (5.6) 5 0.55 (0.45) 0.059 (0.018)

Bore 3 24 (2) 1.0 (1.0) 5 0.25 (0.14) 0.051 (0.003)

Bore 5 24 (5) 0.90 (1.2) 5 0.32 (0.16) 0.055 (0.006)

Bore 6 24 (7) 2.1 (4.0) 5 0.99 (2.4) 0.059 (0.016)

The data in the table indicates that there are very subtle differences in the water quality from the different bores. The raw water has a pH of around 5.6 and a TDS of around 200 mg/L. The Sale Water Treatment Plant (WTP) consists of two cascade aeration towers for the removal of hydrogen sulphide and partial oxidation of iron and manganese. Lime and alum were originally added in a mixing chamber and the chemically treated water then flowed through a flocculation tank and then to a sedimentation tank. The clarified water passes through three dual media rapid gravity filters and is disinfected with gaseous chlorine.

The majority of the sulphides are removed in the aeration towers, pH increases from about 5.8 to 7.2, and the iron is reduced to around 0.2 mg/L. There is little reduction in manganese with the typical levels entering the plant after the aeration towers being around 0.06 mg/L.

Dirty Water Complaints Early investigations of the dirty water problem included a comparison of the levels of iron, manganese and aluminium in water samples taken from the Sale distribution system with that from similar samples taken in other major towns supplied by Gippsland Water where dirty water complaints were less common. The levels for Sale were all less than the Australian Drinking Water Guideline (ADWG) values and were within the range found at all Gippsland Water towns. The manganese levels (mean 0.042 mg/L) were however at the upper end of the range for all the towns. The iron levels (mean 0.08 mg/L) were generally low. The aluminium levels (mean 0.06 mg/L) were also low.

The evidence at that time therefore pointed to the distribution system.

Removal of Cast Iron Fittings Provides Some Localised Improvement The distribution system had a large number of cast iron fittings that showed signs of corrosion, so a program was initiated to remove these wherever possible. This produced some localised improvements in the immediate region where the fittings were removed but no general improvement. Since the distribution system had never been systematically cleaned an air scouring program was initiated.

Air Scouring Provides Some Improvement The distribution system was air scoured in May and June1997, September and October 1999 (in part) and again in July 2000 (in part). Although there was apparently some reduction in dirty water complaints for a few months there was no sustained overall improvement based on the number of dirty water complaints.

84

Appendix 2 – Optimisation Case Study Dirty Water Complaints Persisted During the period when the problems were being investigated, data was presented by Hunter Water and Gold Coast City Council that suggested that dirty water complaints were likely with manganese levels as low as 0.02 mg/L, well below the ADWG guideline limit.

A program was initiated to test water from households in Sale complaining of dirty water. The sample was taken as close to the time of the complaint as possible. This occurred for a period of 8 months from December 1999 to August 2000. A total of 45 samples were analysed for Fe, Mn, Cu and Al. Results for Fe and Mn are shown in Figure 1 and 2.

Figure 1. Levels of manganese in water samples collected from dirty water complaint sites over the period December 1999 to August 2000.

2 Mn (mg/L)

1.5 1 0.5 00 7/

20

00 /0 30

30

/0

6/

20

00 20

5/

00 /0 30

4/

20

00 /0 30

3/

20

00 /0

2/

20 30

00 /0 29

/0

1/

20

99 19 30

2/ /1

30

30

/1

1/

19

99

0

Figure 2. Levels of iron in water samples collected from dirty water complaint sites over the period December 1999 to August 2000.

Fe (mg/L)

1 0.8 0.6 0.4 0.2 20 00

30 /0 7/

20 00

30 /0 6/

20 00

30 /0 5/

20 00

30 /0 4/

20 00

30 /0 3/

20 00

29 /0 2/

20 00

30 /0 1/

19 99

30 /1 2/

30 /1 1/

19 99

0

Figures 1 and 2 show clearly that, in contrast to the regular reticulation samples, these dirty water samples regularly exceeded desirable levels of iron and manganese. It is also likely that some of the samples that returned a satisfactory level were in fact sampled after the immediate event had passed, so the data presented here may underestimate the extent of the problem.

85

Appendix 2 – Optimisation Case Study Iron and Manganese Levels Need to be Reduced There was clearly a need to reduce the level of Fe and Mn in the water supplied to Sale. Based on discussions within the Australian Water Industry, a target level of 0.01 mg/L was set for manganese and 0.1 mg/L for iron.

Potassium permanganate and chlorine have both been used for the removal of iron and manganese from potable water. For Sale, the use of chlorine was rejected because, at the dose needed to achieve some removal of manganese, a strong and unacceptable chlorine odour was present in the water.

A series of jar tests were undertaken to determine the best treatment regime for the Sale water. Based on the outcomes of the jar testing a full scale plant trial using potassium permanganate, alum and lime was conducted.

A Solution to the Problem Leads to New Problems that Must be Solved While good manganese removal and acceptable aluminium residuals were obtained, the new treatment regime resulted in shortened filter run-times.

An alternative method for removal of manganese involves the use of lime as coagulant. Additional jar tests were carried out using potassium permanganate and lime without any other coagulant. These tests showed that manganese levels less than 0.01 mg/L could be achieved at a pH of around 8.2. The resultant high pH raised some concerns for disinfection efficiency however a full plant trial was planned.

Permanganate and lime were used but the pH was limited to 7.5 to ensure effective disinfection.

The target levels for both manganese and iron were readily achieved even at the lower pH. During the following 9 months, treated water leaving the plant averaged 0.001 mg/L manganese and 0.004 mg/L iron.

Low Iron and Manganese Levels Result in a Sustained Reduction in Dirty Water Complaints A monitoring program was established to monitor the impact of the changes at the WTP on the distribution system. Eight sites were selected to represent the entire distribution system, including sites in the general areas where dirty water complaints were prevalent. Sites were sampled weekly over the period October 2000 to July 2001. The results presented in Figures 3 and 4 clearly show that the low manganese levels leaving the plant were maintained throughout the distribution system; however there was some variable elevation in the iron levels. This was more marked for some of the sites than others. The interesting observation is that the relative variation has been largely retained over the sampling period. There is a rough correlation between the level of iron and the distance from the WTP. Although the iron levels in the distribution system are higher than those in the water leaving the treatment plant, the levels are all well below the target level of 0.1 mg/L. These results suggest that the deterioration in water quality is unlikely to be biofilm derived, since, if this were the case, one might expect occasional higher levels of both manganese and iron. The fact that only iron is elevated is strongly suggestive of an inorganic source, most likely cast iron fittings themselves. The system was reviewed and additional cast iron fittings and hydrants removed.

86

Appendix 2 – Optimisation Case Study

Figure 3. Iron levels in water sampled weekly from the 8 sample sites over the period October 2000 to July 2001.

0.06

Fe (mg/L)

0.05 0.04 0.03 0.02 0.01

Ja ck s Be on nn is on Jo hn W an s da G na ut he La ridg e ns do w ne R ag la n R ho de s

0

Figure 4. Manganese levels in water sampled weekly from the 8 sample sites over the period October 2000 to July 2001.

Mn(mg/L)

0.06 0.05 0.04 0.03 0.02

Ja

ck

so

n Be nn is on Jo hn W s an da G na ut he rid La ge ns do w ne R ag la n R ho de s

0.01 0

Figure 5 shows the number of formal dirty water complaints received by Gippsland Water since 1996. The total numbers are not high; however they are likely to very much underestimate the dissatisfaction with the water, because only a relatively small proportion of concerned customers take the step to actually register a formal complaint. Figure 5 however shows very clearly that after the change in treatment process at the WTP, there was a significant decrease in the number of dirty water complaints. The figure also shows that air scouring was only effective in reducing dirty water complaints for a relatively short time.

87

Appendix 2 – Optimisation Case Study Figure 5. Dirty water complaints received by Gippsland Water for the City of Sale from 1996 to 2001. The larger dark arrow indicates the commencement of the altered treatment regime at the WTP. The smaller arrows indicate when air scouring was carried out. A small area of the town was also air scoured in July 2000.

25

Complaints

20 15 10 5 0 J FMAMJ JASONDJFMAMJ JA SONDJ FMAMJ JA SONDJ FMAMJ JA SONDJ FMAMJ JASONDJFMAMJ JA S 1996

1997

1998

1999

2000

2001

Taste and Odour Problems Sale also had a long history of taste and odour complaints.

The Australian Drinking Water Guidelines state that “the taste and odour of drinking water should be acceptable to most people”. Most Water Authorities make some assessment of the palatability of the water they supply usually via customer questionnaires. These may identify some problems however the solution to the problems are difficult and often not addressed further.

Customer Surveys Note Significant Improvement in Taste but Problems Still Remain in Some Areas Since potassium permanganate is a strong oxidant it was possible that it might have helped control some of the taste and odour problems. A doorknock survey was conducted in the early evenings. The evening was chosen as a suitable time to find people at home without disrupting their activities too much. The majority of those interviewed felt that there had been some recent improvement in the taste and odour of the water.

When asked for how long the water quality had been improved, most of the responses correlated with the introduction of the permanganate treatment.

Although there was an overall improvement in the taste profile of the water, a new taste became apparent.

This new taste occurred irregularly and was more noticeable in certain parts of Sale. The unpleasant and very characteristic taste, although detectable in the treated water, was most noticeable when the water had been boiled and used for tea or coffee. The taste was described as “medicinal” or “phenolic”.

Laboratory testing found that the taste compounds were only present after chlorination, the higher the chlorine dose the more noticeable the unpleasant taste.

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Appendix 2 – Optimisation Case Study A New Instrument Reveals some Interesting Clues A new instrument, the SpectrolyserTM , became available during the investigation. The instrument measures the UV Vis spectrum of water samples. The instrument was able to detect subtle changes in the nature of the water. There were quite significant differences in the spectra obtained from water from the different bores (Figure 6). This was a little surprising since the bores are all close together and supposedly draw from the same aquifer but at depths between 70m and 180m.

Figure 6. UV-Vis spectra obtained for water originating from 3 different bores.

1.4 1.2

Abs/m

1 0.8 0.6 0.4 0.2 0 -0.2

200

300

400

500

600

700

Wavelength Bore 1.

Bore 2.

Bore 6.

The instrument was also able to detect differences between the cold and boiled water.

Samples were also tested from various parts of the distribution system. Figure 7 shows UV-Vis spectra of water obtained from a number of sites within the distribution system. The sites were chosen to reflect a range of residence times within the system and include sites with taste problems. In general, the higher the absorbance the poorer the quality of the water. Although there was a tendency for absorbances to increase the longer the water is in the system, there were notable exceptions. The sample with the longest residence time (Wandana 51 hrs) had an absorbance spectrum more similar to sites with much shorter residence times. Two sites with the same residence time, but which were geographically separate (Lansdowne 16 hrs and Dawson 16 hrs), had significantly different absorbance spectra. Taste complaints were received from the Dawson site but not the Lansdowne site. Complaints had also been received from the Chalmers (43hrs) site.

89

Appendix 2 – Optimisation Case Study Figure 7. Spectra obtained from sites within the distribution system with different retention times.

0.4 0.3

Abs/m

0.2 0.1 0 -0.1

200

250

300

350

400

450

500

-0.2 Wavelength 338 Raglan (18 hrs)

15 Chalmer (43 hrs)

8 Rhodes (30 hrs)

5 Daw son Front (16 hrs)

3 Wandana (51 hrs)

93 Lansdow ne (16 hrs)

10 Hazel (35 hrs)

13 Treloar (31 hrs)

Notably the two sites with the highest absorbances are those where complaints had been recorded.

The Raw Water Contains an Organic Chemical that is Modified by Treatment and During Passage through the Distribution System Some samples were sent for detailed chemical analysis (gas chromatography). The results suggested that the chemical responsible for the taste was a bromophenol that became chlorinated during treatment.

Passage through certain parts of the distribution system seemed to result in worse taste problems.

Laboratory Trials Suggest Ways to Remove the Taste and Odour Chemicals A number of laboratory trials were conducted. Since the most likely cause of the taste and odour was an organic chemical it was likely that activated carbon might remove it.

Powdered Activated Carbon (PAC) dosing was trialled in bench tests. Figure 8 shows the effect of this treatment. A time dependent improvement in the absorbance spectra is apparent. This time dependent improvement in water quality was confirmed by tasting the water. Samples at the 20 and 30-minute time periods were free of the taste.

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Appendix 2 – Optimisation Case Study Figure 8. UV-Vis spectra of water samples treated with a Powdered Activated Carbon for different periods 2

Abs/m

1.5 1 0.5 0 200

250

300

350

400

450

-0.5 Wavelength

Boiled and Cooled

10mg A6 10 mins

10mg A6 20 mins

10mg A6 30 mins

Whole City Trials A number of alternative treatment regimes were planned to see if they could improve the taste and odour of the water in Sale. The treatments were selected based on laboratory trials or information from the literature.

Since the residents of Sale were the ones most affected by the taste and odour of the water, Gippsland Water felt it was appropriate to ask the residents themselves to judge whether the proposed treatments were successful. To this end, a customer reference group was established.

Consumers are the Best Judges A customer reference group was set up of residents who were able to taste the chemical and were willing to participate in a fairly long trial that required them to keep a record diary. The reference group represented 29 sites spread widely and relatively evenly across the Sale distribution system.

The trial lasted for approximately 3.5 months and involved 6 treatment types.

• • • • •

High chlorine dose ( 0.80 mg/L free chlorine) Low chlorine dose (0.10 mg/L free chlorine) Normal chlorine dose (0.35 mg/L free chlorine) Chloramination (0.8 – 1.2 mg/L total chlorine) PAC dosing (20 mg/L, approximately 20 minutes contact time).

The customers maintained daily log sheets and scored the water for both taste and odour. The results are shown in Figure 9. Higher scores represent poor quality water.

91

Appendix 2 – Optimisation Case Study Figure 9. Summary of responses to the different treatments. The blue bars represent the total numerical score while the brown bars represent the total of the averaged water quality scores. A higher score represents water with a poorer taste and odour profile.

2000

Total and Average Water Quality Score

1800 1600 1400 1200 1000 800 600 400 200 0 Chlorine 0.35 Chlorine 0.80 Chlorine 0.10 Chlorine 0.35 Chloramine

PAC

Chlorine 0.35

While these results clearly indicate that PAC and low chlorine doses produced more acceptable water, the consolidated data conceals some additional information. Figure 10 shows individual data from four sites.

These have been selected to demonstrate the range of responses seen.

Figure 10. Results obtained at four individual sites showing the range of responses from the participants. A higher score represents water with a poorer taste and odour profile. For Site 4 the PAC score was zero.

300

Water Quality Score

250

200

150

100

50

0

Site 1 Chlorine 0.35

Site 2 Chlorine 0.80

Site 3 Chlorine 0.10

Chlorine 0.35

Site 4 Chloramine

PAC

Quite different patterns are apparent. This may represent individual sensitivity to the taste chemical or differences imparted to the water by the distribution system. Other evidence suggests that at least some of the difference is due to the impact of the distribution system.

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Analysis of the individual results show that the majority of the participants found the chloraminated water unpalatable and the PAC dosed water the most palatable.

Because of the way the trial was conducted it was also possible to get some limited data on the effect of water from the different bores. This is shown in Figure 11. The figure shows that while bore 6 was in use the water quality was generally perceived to be better.

Figure 11. Averaged water quality scores for the different bores used during the period that the plant was operated at 0.35 mg/L free chlorine.

350

300

Water Quality Score

250

200

150

100

50

0 Bore 6

Bore 2

Bore 1

This was interesting because the UV Vis data suggested bore 6 had higher levels of organic material, but it could not tell us whether or not the organic chemical responsible for the unpleasant taste was in it or not.

The customer responses suggest that despite the higher organic load, the chemical responsible for the taste was not in that bore.

Conclusions The solution to the problem involved dealing with both the source water and the distribution system. Where the source water contains substances that subsequently have an impact on the customer, then the only option is to deal with these at the treatment stage. In this case study, this included removal of the iron and manganese and the organic chemical leading to the taste problems. Where the distribution system contributes to the problem then this must be managed within the distribution system. In this case removal of cast iron fittings and removal of biofilm by air scouring assisted the solution to both the dirty water and taste and odour problems.

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Appendix 3 – Summary Of Distribution System Hazards, Hazardous Events and Preventative Measures

Appendix 3 – Summary Of Distribution System Hazards, Hazardous Events and Preventative Measures The following table provides a summary of the key hazards and hazardous events associated with the operation of distribution systems. The table is structured with more serious risks at the top and lesser risks lower down.

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Hazard or Hazardous Event

Consequences

Preventive Measures

Contamination of water in service reservoirs with faecal material from mammals, birds, reptiles and amphibians.

Waterborne disease outbreaks.

Keep service reservoirs closed to animals and birds.

Prevent rain-washed and wind blown faecal material entering reservoirs by maintaining bird proofing structures, repairing holes in roofs, using raised gatic lids and sealing around access points.

Remove overhanging branches and other roosting sites.

Maintain disinfectant residuals above 0.2 mg/L free chlorine.

During repairs to mains or during the installation of new mains, contaminants may enter the water.

Where water mains are close to sewer mains, a particular risk arises from sewer to water cross contamination.

Waterborne disease outbreaks.

Backflow from service connections can result in contaminants siphoning back into the distribution system. This can happen when the distribution system loses pressure during high demand periods.

Waterborne disease outbreaks.

In large overland pipelines in hot summers, where the reticulated water is often at or above 18ºC, some microbial pathogens (e.g. Naegleria, Acanthameoba, Burkholderia ) can reach high enough densities to present a health risk.

Waterborne disease outbreaks.

Contaminants dumped into water tanks and service reservoirs by malicious individuals.

Waterborne disease outbreaks or illness.

Some fatalities have been recorded overseas and some serious illness recorded in Australia.

Some serious illness has been recorded overseas.

Some fatalities have been recorded.

Some fatalities have been recorded.

Some illness has been recorded from this cause.

Exclude contaminated water during works.

Thoroughly flush and disinfect the mains once the works are complete.

Fit and maintain backflow prevention devices in compliance with the Plumbing Code AS/NZS 3500:2003.

Maintain positive pressure in the system

Keep water temperatures below 18ºC. Where this is not possible, increase monitoring and ensure disinfectant residuals are maintained at all times.

Minimise hydraulic residence times.

Maintain disinfectant residuals above 0.2 mg/L. Higher residuals may be necessary.

Install security fencing with locked gates.

Lock hatches.

Lock ladder shrouds.

Install tamper detection, cameras, motion sensors and telemetry alarms.

Appendix 3 – Summary Of Distribution System Hazards, Hazardous Events and Preventative Measures Hazard or Hazardous Event

Consequences

Preventive Measures

Cross connections can lead to problems where pressure sewers, rising sewer mains, third pipe systems or other pressurised piped contaminants get into the water supply through cross connections.

Waterborne disease outbreaks.

Ensure compliance with Plumbing Code AS/NZS 3500:2003

Potential fatalities in extreme cases.

If possible increase pressure in the water mains above that in any surrounding sewer mains.

Cross connections between raw water and treated water systems may allow untreated water to enter the distribution system

Waterborne disease outbreaks.

Infiltration from surrounding ground water can cause contamination. Studies have shown that it is possible to have short periods of extremely low pressure and even negative pressure in mains at some times. Clearly if the pressure in the main is lower than water surrounding the pipe and if the pipe has leaks or poor joints, water may be sucked back into the pipe. This problem may occur during periods of high pumping creating negative pressure in suction lines.

Waterborne disease outbreaks.

In one bizarre case, a flammable gas under pressure found its way into the water supply through this mechanism.

Conduct regular manual cross connection checks in areas with third pipes or other high risk areas.

Identify and remove all old raw water treated water cross connections.

Potential fatalities in extreme cases.

Potential fatalities in extreme cases.

Design all systems such that the pipe work is above the level of groundwater at all times.

If there is a significant likelihood that groundwater could enter a main, either replace the main with a continuous impermeable pipe or install some form of monitoring to assess if contamination is entering. For example on line conductivity sensors.

Maintain positive system pressure where possible. Hydraulic modelling can be useful to understand the risks and identify possible improvements.

Make changes in pumping rates and valve operations slow and smooth.

Fire plugs may allow contaminated water to get into the mains through faulty sealing mechanisms during low pressure periods. Faulty seals can arise due to improper re-seating of the fire plug following hydrant use or through failure of the closure springs.

Waterborne disease outbreaks.

During design, ensure that fire plugs are not installed at low points or depressions.

Potential fatalities in extreme cases.

Maintain positive system pressure.

Taste and odour from petrol and oil products.

Inspect, clean and maintain all fire plugs and hydrants points.

Replace faulty plugs.

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Appendix 3 – Summary Of Distribution System Hazards, Hazardous Events and Preventative Measures Hazard or Hazardous Event

Consequences

Preventive Measures

Corrosion of copper pipes and fittings can release unsafe levels of copper into the water supply. Copper is mostly used in household plumbing rather than utility assets, however, some 40 mm reticulated water mains have been found to cause this problem.

Metallic taste.

Work done by CSIRO and WSAA found that copper pipe will corrode in soft, poorly buffered water under the right circumstances. Therefore where this water type exists the only two proven solutions are to use a material other than copper for the main to meter and to maintain a residual of >0.2 mg/L free chlorine.

Relatively minor, shortterm health impacts, such as vomiting.

During commissioning do not allow water to sit for long times in new copper pipes.

Increase disinfectant residuals.

Maintain pH between 7.4 to 8.3.

In areas with older plumbing, lead can reach harmful levels in water supply systems. This is more of a problem in ‘old world’ water supplies, such as in the UK, however, high lead levels have been found in Australian distribution systems.

Lead poisoning after prolonged periods, particularly among children.

Ensure lead is not used in water distribution systems.

Biofilms and organic matter can interact with disinfectant residuals to increase disinfection by-products during distribution.

There is uncertainty regarding the health risks. The risks are not high and disinfection should not be compromised to control them.

Reduce organic precursors in source waters.

Replace lead fittings and pipes.

Reduce organic precursors through treatment.

Reduce hydraulic residence times during water distribution.

Consider alternative disinfection technologies. Chlorine dioxide has been shown to control some biofilms.

Do NOT compromise disinfection

Sedimentation of particles may lead to accumulation of sediments in low flow areas, such as in courts or other dead ends. During high flow events, this sediment may become dislodged.

Dirty water.

Flush, scour and swab the system.

Note that flushing may increase customer complaints, mainly because it causes an increase in velocity in the pipe and consequently stirs up sediments.

Air scouring or swabbing may be the preferable alternative.

The rate of sediment accumulation is important. If the rate is high then investigate methods to reduce particles in the source water or through treatment.

Control flows in distribution systems and seek to minimise low flow periods and zones.

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Appendix 3 – Summary Of Distribution System Hazards, Hazardous Events and Preventative Measures Hazard or Hazardous Event

Consequences

Preventive Measures

Bacteria in biofilms can release taste and odour compounds, such as geosmin and methyl isoborneol (MIB), that are readily perceived by humans.

Off taste and odour.

Reduce DOC in source waters or through treatment.

Reduce hydraulic residence times.

Control flows in distribution systems and seek to minimise low flow periods and zones.

Maintain disinfectant residuals.

Flush, scour and swab the system.

Biofilms can accumulate iron and manganese and then, when the biofilms slough off during periods of high flow or periods of high disinfectant residual, dirty water results.

Dirty water.

Stained washing.

Reduce nutrient, iron and manganese levels in source waters.

Reduce nutrient, iron and manganese levels through treatment.

Reduce hydraulic residence times.

This phenomenon may also occur when distribution systems are disinfected for the first time, or when changing over from chlorine to chloramine for the first time.

Control flows in distribution systems and seek to minimise low flow periods and zones.

Avoid rapid increases in flow.

Maintain even disinfectant residuals.

Flush, scour and swab the system.

Where multiple Pressure Reduction Valves (PRVs) are present with staggered operating pressures it is likely that one or more of the valves seldom operates, thereby allowing water to stagnate in the region near the valve. The low free chlorine residuals allow the proliferation of bacteria such that when the valve does open, the system is seeded with bacteria that can then colonise biofilms and flourish, particularly if chlorine residuals are low.

Adverse taste and odour.

Reduce hydraulic residence times.

Seeding of downstream system with bacteria.

Remove redundant PRVs.

Excessive release of alkali from cement linings can occasionally lead to extremely high pH. The pH can reach 11 in systems that have very low water turnover.

Soapy feel.

Stagnation in large pipe systems leading to excessive water age. The reduced ratio of free to combined chlorine and/or the build up of odorous bacterial metabolites can cause problems

Adverse taste and odour.

Exercise PRVs regularly Ensure regular operation of PRVs

Increase water turnover to reduce pH.

Relatively minor, short-term Stabilise water through increasing discomfort, such as irritation buffering capacity by the addition of of skin. lime and CO2.

Reduce hydraulic residence times.

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Hazard or Hazardous Event

Consequences

Preventive Measures

Corrosion (rusting) of iron fittings.

Adverse taste.

Use lined fittings.

Discolouration.

Replace unlined fittings.

Stained washing.

Replace corroded fittings.

Reduce hydraulic residence times.

Increase disinfectant residuals.

Maintain pH between 6.5 to 8.5.

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In some systems, water may be sourced from different supplies with one supply of a higher or different quality to another. When these are mixed in the distribution system, consumers may notice changes in quality.

For some this may not be favourable.

Adverse taste and odour.

Plastic pipe near service stations. There is potential for contamination with petrol and hydrocarbons.

Adverse taste and odour.

Where aluminium or iron residuals are not controlled adequately at the WTP and they pass into the distribution system they may slowly form floc. This can accumulate in low flow areas and lead to dirty water complaints particularly when flows increase for some reason e.g. flushing, fire flows or peak demand flows.

Dirty water.

Apply cautious blending practices.

Assess consumer acceptance prior to blending using taste and odour panels.

Monitor to assess if contamination is entering.

Replace the main with a continuous impermeable pipe.

Stained washing.

Optimise coagulant dosing at treatment plants using jar testing or Streaming Current Detectors.

Control pH.

Appendix 4 – A Simplified Method For The Measurement Of Chlorine Demand

Appendix 4 – A Simplified Method For The Measurement Of Chlorine Demand Reagents Chlorine Stock Solution -approximate 500mg/L Add 1.0ml of 5%w/v sodium hypochlorite solution to 99ml of distilled water and store in a clean container. This stock solution will deteriorate over time, so must be freshly prepared prior to use. pH buffers 4.0, 7.0 & 10.0.

Free & Total DPD reagents.

Equipment 2 x 1 litre glass bottles with plastic lids. (Schott bottles are suitable) The bottles should be cleaned and thoroughly rinsed and kept aside as dedicated bottles for the chlorine demand test.

1 x 500ml glass bottle with plastic lid. (Schott bottles are suitable) Calibrated pH meter capable of reading to at least one decimal place.

Thermometer capable of reading from +5 to +300C. Chlorine meter. (Using the DPD method)

Method 1. Rinse the bottles with the sample three times before filling. Fill two 1L bottles and one 500ml bottle with un-chlorinated water from the filters.

Note: Keep samples away from direct sun light by covering the bottle in Aluminium foil and store bottles in a cupboard between analyses.

2. Analyse the 500ml sample for pH, Temperature, Turbidity, True Colour, Aluminium, Iron and Manganese, and record results.

3. Add 3 ml of the Stock chlorine solution to each of the 1L bottles and immediately mix the solution by briskly stirring to avoid over aerating the sample. (3ml of the stock chlorine solution added to the un-chlorinated filtered water sample should give a free chlorine concentration of approximately 1.5mg/L.) 4. After mixing, immediately analyse for Total & Free chlorine and record the time and the free & total chlorine measurements for each bottle and re cap tightly.

5. Store samples in the cupboard for 10 minutes.

6. Remove a sample from the cupboard and stir (10 turns to the right, 10 turns to the left, then 10 turns to the right again) and take a 10ml sub sample from each bottle and record the time.

7. Measure the free & total chlorine of the samples and record the results.

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Appendix 4 – A Simplified Method For The Measurement Of Chlorine Demand 8. Return the bottles to the cupboard promptly when analysis is completed.

9. Repeat steps 5 through 8, twice more. Total number of readings, including the initial reading will be four (4).

10. After the final chlorine analyses, measure the test samples pH and temperature and record the results with the 30 minute test.

Calculate and record the following.

Free Chlorine Demand (mg/L)= Chlorine consumed over 30 minute contact period

= Free chlorine at zero minutes – Free chlorine at 30 minutes Free Chlorine Decay (%)=Percentage chlorine lost over 30 min relative to the initial dose. = Free chlorine at zero minutes – Free chlorine at 30 minutes x 100 Free chlorine at zero minutes

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Chlorine Demand Test Result Sheet Date: _____________

Time: ____________

Site: ______________________

Operator: _____________

Sample Point or Location: ________________________

Un-chlorinated filtered water, analysis: pH

Turbidity

True Colour

Iron

Aluminium

Manganese

Test sample analysis: Sample Number

Test Time (minutes)

1

Zero

2

10

3

20

4

30

Free Chlorine Demand

Free Chlorine Decay

Free chlorine (mg/L) Bottle 1

Bottle 2

Total chlorine (mg/L) Bottle 1

Bottle 1 Bottle 2 Bottle 1 Bottle 2

Bottle 2

pH

Temperature (oC)

mg/L

%

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References ADWG (2004). Australian Drinking Water Guidelines. National Health and Medical Research Council, Canberra APHA (2004). Standard Methods for the Analysis of Water and Wastewater. American Public Health Association.

AWA (2009). The Australian water directory. Australian Water Association, Sydney Clark, R.(2000). Water quality modelling case studies. In: Water distribution systems handbook. Ed. Mays, L.W. McGraw Hill New York Chase, D.V.(2000). Operation of water distribution systems. In: Water distribution systems handbook. Ed. Mays, L.W. McGraw Hill New York Dahm, B. and Schulz, C.R. (2006). Disinfecting mains with ozonation. Alternative saves time and environment. Opsflow September 2006 p 18-21 Deere, D., Stevens, M., Davison, A., Helm, G. and Dufour, A. (2001). Management Strategies. In: Water Quality: Guidelines, Standards and Health. Assessment of risk and risk management for water-related infectious disease. Fewtrell, L., Bartram, J. (eds). IWA Publishing, London. ISBN 1 900222 28 0. Ch 12. p 257-288 Ford, R. (1998). Preventing backflow contamination. Water March/April 1998 p 43-45 Hrudey,S.E. and Hrudey,E.J. (2004). Safe Drinking Water. Lessons from Recent Outbreaks in Affluent Nations. IWA Publishing. London UK. Kirkmeyer, G (2003). Customer expectations and setting goals. Presented at: Maintenance and Assessment of Distribution Systems to Improve Water Quality. Cooperative Research Centre for Water Quality and Treatment. Sydney September 2003.

USEPA. (1999). Enhanced coagulation and enhanced precipitative softening guidance manual.

Verberk, J.Q.J.C. et al (2007) International collaborative research on discoloured water. Water 34: 144149.

Vitanage, D. (2000) Network Cleaning. Presented at: Particles in the Distribution System. A Planning Workshop. Cooperative Research Centre for Water Quality and Treatment. Melbourne September 2000.

Vitanage, D. (2005). Advantages and disadvantages of flushing, air scouring and swabbing. Presented at: Water Quality and Distribution Systems Management. Issues for Operators. Water Industry Operators Association. Melbourne July 2005.

Walski, T.M. (2000). Water quality aspects of construction and operation. In: Water distribution systems handbook. Ed. Mays, L.W. McGraw Hill New York WSAA (2005). Corrosion of copper pipe in Australian drinking waters. Materials Fact Sheet No 5.

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Disclaimer This document does not purport to be a comprehensive statement on the management of distribution systems but rather aims to create awareness of what is possible, what might be done and indeed what has been done. However the authors, reviewers and the organisations supporting the production of this manual (WIOA,AWA,WSAA and CRCWQT) are not responsible for the outcomes of any actions taken on the basis of information in this document, nor for any errors or omissions. The authors and the afore mentioned organisations disclaim all and any liability to any person in respect of anything and the consequences of anything done or omitted to be done by a person in reliance upon the whole or any part of this document. If further expert advice is required the services of a competent professional should be sought.

WILLPRINT SHEPPARTON 03 5831 6565