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Water Safety Plan Guide

Distribution System – Operation

Version 1, Ref D2.3

January 2014

Citation: Ministry of Health. 2014. Water Safety Plan Guide: Distribution System – Operation, Version 1, ref D2.3.

Wellington: Ministry of Health.

Published in January 2014by the Ministry of Health

PO Box 5013, Wellington, New Zealand

ISBN: 978-0-478-42766-0 (print)ISBN: 978-0-478-42767-7 (online)

Previously published in 2001 as Public Health Risk Management Plan Guide: Distribution System – Operation,

Version 1, ref D2.3. This publication’s title and any reference within the text to ‘public health risk management plan’ were

changed in January 2014 to reflect the December 2013 legislation change of the term ‘public health risk

management plan’ to ‘water safety plan’. No other changes have been made to this document.

This document is available at: www.health.govt.nz

This work is licensed under the Creative Commons Attribution 4.0 International licence. In essence, you are free to: share ie, copy and redistribute the material in any medium or format; adapt ie, remix, transform and build upon the material. You must give appropriate credit, provide a link to the licence and indicate if changes were made.

Contents

IntroductionRisk SummaryRisk Information TableContingency PlansWater Safety Plan Performance AssessmentAppendix 1: Good Hygiene Practices for Staff Working on Drinking-Water SuppliesAppendix 2: Cleaning and Disinfection of Mains

iv [Title]

Ref D2.3 Water Safety Plan Guide: vVersion 1, January 2014 Distribution System – Operation

IntroductionThis Guide is concerned with the following aspects of the operation of the distribution system: the repair and renewal of existing pipe and penetration of mains to

add fittings or connections flushing, scouring and pigging of mains to remove debris and

deposits leak detection programmes, by-pass operations using temporary

pipework for isolating distribution system zones and actual repair of the leaks

incorrectly operating valves that can give rise to problems in managing the distribution.

If an event to do with the operation of the distribution system occurs (ie, there are poor operation practices), the following could happen: If contamination gets into the distribution system, germs and

chemicals can cause sickness. If sediment or biofilm develops in the reticulation network, or is

stirred up, germs and chemicals contained in the sediment or biofilm can cause sickness.

If the pressure is too low, sickness may be caused by poor hygiene and by low pressure letting germs and chemicals get into the distribution system.

Operation of a distribution system can present risks to the health of staff involved. These are acknowledged, but are not discussed further as such risks are the subject of health and safety in employment legislation.

The management of the distribution system is based on the aspects of operation dealt with in this guide, and also the supply elements of water storage (Guide D1), construction materials (Guide D2.1), system pressure (Guide D2.2) and backflow prevention (Guide D2.4).

Several factors influence the management of drinking-water quality in the distribution system: negative, or fluctuating, pressure conditions performance of valves – these affect your ability to isolate, flush

and/or disinfect the affected area construction, repair and maintenance methods, including hygiene

and disinfection procedures use of suitable construction materials condition of alternative/disused mains and systems used during

repairs

Ref D2.3 Water Safety Plan Guide: 1Version 1, January 2014 Distribution System – Operation

characteristics of alternative water sources available for use during repairs

re-suspension of material in the distribution system by scour of pipe slimes, sediment and deposited minerals such as silicates or oxidised manganese

formation of floc after the treatment plant and its settling in the distribution system.

Opening mains for repair or renewal is a significant way by which contamination can get into the distribution system. The risk of contamination is reduced if good codes of practice concerning hygiene and the cleaning and disinfection of the mains are followed. Suggested approaches to good practice are given in the Appendices of this Guide.

Other sources of information that can be used as a basis for writing codes of practice are: AWWA Standard for Disinfecting Water Mains, ANSI/AWWA C651-92 Australian Water Industry Technical Standards, Chlorination of

Water Mains, 95-092.1 Water Reticulation Disinfection Code of Practice, Manukau Water,

February 2001.

2 Water Safety Plan Guide: Ref D2.3Distribution System – Operation Version 1, January 2014

Risk SummaryThe events creating the two greatest risks involved in the operation of the distribution system are the pressure being too low (see D2.3.4), and contamination getting into the distribution system (see D2.3.1).

The most important preventive measures are: monitoring changes in flows and pressure in the system (see Guide

D2.2) taking steps, including the development of backup sources of

water, the use of pressure-reducing and pressure-sustaining valves, to allow better control of pressure (see Guide D2.2)

monitoring the operation of network pumps and have preventive maintenance programmes for them (and bore pumps if part of the system) (see Guide D2.2)

constructing another reservoir or tank if having too little water seems like being a continuing problem (see Guide D1)

putting into action a water conservation programme (see Guide D2.2)

making sure maintenance crews follow good hygiene and disinfection practices when mains have to be opened (see D2.3.1.5)

training staff so they know about quality issues and good work practices (see D2.3.1.6)

making sure new or repaired mains are suitably flushed and disinfected (see D2.3.1.8)

maintaining a disinfectant residual in the distribution system (see D2.3.1.8).

(References in parentheses are to the Risk Information Table.)


Risk Information TableReliable information about water quality is essential for the proper management of a water supply. Knowledgeable and skilled staff are also essential for minimising the public health risks associated with water supplies. Please read the staff training (Guide G1) and the monitoring guides (Guide G2). While we haven’t pointed out every detail of how these documents are linked with the present document, the links are many and are important.

Abbreviations: DWSNZ – Drinking-Water Standards for New Zealand

Causes Preventive measures

Checking preventive measures Corrective action

What to check Signs that action is needed

Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEMPossible hazards: Germs; chemical determinands (dependent on the nature of the material).Level of risk: High1

D2.3.1.1Breaks, leaks, incidental damage to water mains.

See Guides P2 event P2.1 and D2.2. Breaks and leaks can appear as the result of the poor condition of the reticulation network. The role played by Asset Management in maintaining system integrity is noted in these Guides.

D2.3.1.2Affected area not correctly isolated.

Plan of pipes, valves and associated maintenance available.

Regularly exercise and service valves and/or determine their condition.

Adequately trained staff with knowledge to correctly open, shut and sequence valves.

Account taken of low pressure areas, hills, extremities, valves and hydrants.

All off-takes identified and consumer connections accounted for.

Job sheets. Network plans not updated regularly.

Knowledge of valve conditions and positions poor.

Complete audit of the network plans.

Staff not adequately trained.

Contamination risks not identified and documented.

Identify staff training needs and provide training.





D2.3.1.3System pressure drop (see Guide D2.2).

Install backflow prevention devices where appropriate (see Guide D2.4).

Low pressure areas, hills, extremities, valves and hydrants to be identified and mapped.

Pressure. Flow. Turbidity (if

there is concern about soil and associated contaminants being drawn into the supply).

E. coli and coliforms.

Backflow preventers not installed where necessary.

Low or negative pressures in part(s) of the reticulation network.

Install backflow preventers.

1 Microbiological contamination of the distribution system is a likely outcome. Such a contamination event can readily develop from a localised event to a widespread problem.




Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEM cont’d

D2.3.1.4Flow direction in affected area unknown or uncontrollable.

Determine flow direction from pressure information and chemical records before undertaking maintenance work.

For major mains, use a network model or chemical tracers to determine flow direction before undertaking maintenance work.

Job sheet and verification procedures.

Incorrect flows observed.

Review hydraulic model of system.

D2.3.1.5Standard hygiene practices not adopted.

Work practices for reticulation maintenance comply with standard procedures (see Appendix 1).

Screen water supply staff for water-borne diseases. They should not be permitted to work on potable water systems until they have obtained a medical certificate stating they are clear of the disease.

Indicator bacteria in water after maintenance.

Job sheets and procedures.

E. coli or coliforms detected in 100 ml water sample following system maintenance.

Errors detected by audit.

Identify staff training needs, and provide training.

Disinfection of the repaired section repeated.

Re-audit procedures.





D2.3.1.6Inadequate staff training.

Internal and external training provided to ensure that crews are aware of quality issues and the importance of good work practices.

On-site checklist of resources and training records.

Inadequate staff supervision by qualified personnel.

Inadequate resources/ training records.


D2.3.1.7Inappropriate materials used.

Only certified or approved materials used (see Appendix Guide D2.1).

Record of materials requirements.

Certification of materials used.

Non-approved materials used in the distribution system.

Records of materials in use inadequate.

Replace with items of suitable quality.


D2.3.1.8Inadequate flushing and disinfection practices during repairs or commissioning of new mains.

Develop and use a code of practice for the cleaning and disinfection of mains (see Appendix 2).

Ensure there is a chlorine residual upstream and downstream of repair/ commissioning site.

Maintain a disinfectant residual.

Free available chlorine (FAC) concentration.

Microbiological quality.

Turbidity.

No documentation of flow direction (see Appendix 2).

Excessive customer complaints, or suspected linked illnesses.

FAC residual cannot be maintained at more than 0.2 mg/L after cleaning, disinfection and flushing of the affected area.

FAC in affected section not maintained at more than 10 mg/L for 30 minutes.

E. coli or coliforms detected in 100 ml sample.

Turbidity more than 0.5 NTU.

Notify the MOH if there are more than 10 E. coli in a 100 ml sample, or if E. coli contamination persists.

Identify reasons for inadequate residual and correct.





D2.3.1.9Unsuitable temporary bypass and/or supply bypass.

Ensure equipment is cleaned and dedicated to water supply only (see D2.3.1.5).

Maintain chlorine residual.

Provide training of crews to ensure they understand issues of hygiene.

Use of a bypass is likely to result in a ‘dirty water incident’. Consumers, especially those with special water quality needs (eg, hospitals, food processors), must be informed of the likely deterioration in water quality.

FAC. Microbiological

quality.

Failure to meet the requirements of DWSNZ:2000.

Inadequate documentation.

Train staff. Re-audit

procedures. Identify

reasons for inadequate residual and correct.



D2.3.1.10Contamination during sampling.

Provide securable, safe sampling locations that allow access without risk of introducing contamination.


Appropriate determinands if chemical contamination is suspected.


Re-sample. Take steps

to avoid contamination recurring (Guide G2).

Retrain sampling staff.





D2.3.1.11Unsatisfactory location of water reticulation pipes.

Ensure that water mains have more than 3 m horizontal displacement from sewers (when in parallel). Closer location is acceptable for stormwater, or when the water main is at least 0.5 m above the sewer and the sewer has been constructed to water main standards (materials and joints).

Ensure that water mains are at least 0.5 m above sewers when there is a crossing, or if closer, that the sewer has been constructed to water main standards. Joints in the water pipe should be equidistant from the crossing. If the water mains passes under the sewer, 0.5 m minimum vertical separation is needed, and the sewer should be well supported to stop flexing of joints.

Avoid laying water mains through areas known to have sources of potential contamination (eg, chemical dumps, landfills, gasworks sites).

Avoid physically unstable terrain to reduce flexing of pipes.

Ensure pipes are deeper than frost penetration.


Chemical determinands (depending on potential contamination source).







D2.3.1.12Cross connections2

Inspection of the system for cross connections.

Ensure that only appropriately qualified persons are permitted to carry out connection work undertaken for the water supplier.

Inspection records.

Cross connections found during inspections.

Reports of gross visual contamination of tapwater by consumers.

Unexplained fluctuations in chemical and microbiological water quality.

Check on qualifications of staff undertaking connections.

Event: RE-SUSPENSION OF CONTAMINANTS IN SEDIMENTS IN THE DISTRIBUTION SYSTEMPossible hazards: Germs; chemical determinands, turbidity.Level of risk: Moderate3

D2.3.2.1Sediment or biofilm allowed to develop.

See D2.3.3 Causes and Preventive Measures.

Scour, pig, flush distribution system.

Restore acceptable quality.

D2.3.2.2Water velocity too high.

Controlled opening/closing valves and starting pumps.

Size pipe diameters to accommodate demand for water without high water velocities re-suspending sediment. (In some situations it may not be possible to accommodate fire flows.)


quality. Turbidity.

Customer complaints.

Failure to meet requirements of DWSNZ:2000.

Restore acceptable quality.

Amend flushing protocol.

2 Examples of situations where cross connections might be a concern include premises: with an auxiliary water supply; having a swimming pool; where connection is provided to for supplying ships; and where a substance or material (included processed water or water from the public supply which might be contaminated) is handled, stored or contained.

3 The condition of the mains, the type of water source used and the performance of the treatment plant are key factors. Re-suspension of deposited manganese or silicates in volcanic areas, exposure of rusted surfaces or detachment or nodules, and possible subsequent release of bacteria are potential problems arising from flow fluctuations or reversals.





Event: DEVELOPMENT OF SEDIMENT OR BIOFILMPossible hazards: Germs; chemical determinands, turbidity.Level of risk: Moderate

D2.3.3.1Poor chemical water quality leaving the treatment plant – eg, post-treatment precipitation of floc, iron/ manganese precipitation.

Ensure treatment is in place to remove raw water-derived constituents that could otherwise deposit in the distribution system.

Ensure treatment is operating effectively so that it does not add constituents that could deposit in the distribution system.

Ensure a regular cleaning/flushing programme, especially through low-flow and dead-end areas, being mindful of D2.3.1.7 and D2.3.2.1.

Turbidity. Aluminium. Iron,

manganese. Inspection.


Improve treatment performance.

Scour, pig and flush the distribution system.

D2.3.3.2Poor microbiological water quality leaving the treatment plant and in the distribution system.

Ensure continuous FAC throughout distribution system.

Ensure a regular cleaning/flushing programme, especially through low-flow and dead-end areas, being mindful of D2.3.1.7 and D2.3.2.1.


quality. Turbidity.

Failure to meet requirements of DWSNZ:2000, especially FAC not maintained.

D2.3.3.3Water flows too low resulting in: decay of

chlorine microbiologic

al colonisation of surfaces.

Review the zones of concern, and put in place a plan to increase flows through these areas.

Design the reticulation network on a grid rather than tree model to allow greater flexibility in routing water flows, so reducing areas with little flow.

Flow. Pressure.

Model flow patterns and FAC residuals to identify the required changes.





D2.3.3.4Poor repair practices allowing colonisation.

See D2.3.1.5 and D2.3.1.8.

Select materials that are resistant to biofilm development (smooth) and do not promote biofilm development (some plastics do).


Turbidity.


Review maintenance practices.

Change construction and repair materials.

Event: DEVELOPMENT OF SEDIMENT OR BIOFILM cont’d

D2.3.3.5Inadequate cleaning programme.

Ensure a regular cleaning programme, especially through low-flow and dead-end areas, being mindful of D2.3.1.7 and D2.3.2.1.

FAC. E. coli or

coliforms. Turbidity. Aluminium. Iron,

manganese.

Maintenance log not signed off.



Amend cleaning programme.

Event: FAILURE TO MAINTAIN SUFFICIENT WATER PRESSUREPossible hazards: Low pressure in the water supply system may allow entry of germs and chemical determinands; hazards associated with poor hygiene.Level of risk: High

D2.3.4.1Insufficient water available from the source, treatment plant or post treatment reservoir.

See Guides regarding abstraction of water from sources (P1 series),pre-treatment storage (P3), design and construction of the treatment plant (P11)

and post-treatment storage (D1).

D2.3.4.2Leaks in the reticulation network.

See Guides P2 and D2.2.

D2.3.4.3Transmission pump failure.

See Guides P10 and D2.2.


Contingency PlansIf an event happens despite preventive and corrective actions you have taken, you may need to consult with the Medical Officer of Health to assess how serious a problem is.

Event – Contamination enters the distribution system

Indicators: Inability to maintain a chlorine residual when one can normally be maintained.

In 100 ml samples of water from the reservoir, E. coli is continually detectable or is present at elevated levels (more than 10 per 100 mL).

Widespread complaints of taste and odour from consumers.

Widespread levels of illness in the community. Turbidity fluctuations and levels greater than that

in water leaving the treatment plant.

Required actions:

Follow the actions given in Figure 3.3 of the DWSNZ:2000.

Identify the reason for the failure and rectify. Record cause of system failure and steps taken to

correct. Modify water safety plan if necessary.

Responsibility:

Manager designated responsible for the water supply.


Water Safety Plan Performance AssessmentTo make sure that your supply’s water safety plan (formerly known as a Public Health Risk Management Plan, PHRMP) is working properly, periodic checks are needed. The overview document outlines what needs to be done. The following table provides the detailed information for checking this particular supply element.

What to measure or observe:

Bacteriological sampling of burst main repairs and mains renewal projects.

Chemical Priority 2 determinands (if any exist). Hygiene and disinfection practices. Job sheets to record procedures used,

observations made and problems encountered. Continuous chlorine residual. Minimal consumer complaints about suspected

waterborne disease, discoloration, staining and taste and odours.

E. coli, coliforms or heterotrophic plate count. Turbidity.Remember that these measurements can be influenced by a wide range of factors including site-specific characteristics of the distribution system and the performance of the treatment plant.

How often: DWSNZ:2000 (see Note 7 Table 3.1) requires sampling to be done within 12 hours of completion of construction or repair work, or restoration of flow. Bacteriological sampling for three consecutive days after work is completed should be carried out. Test for E. coli and coliforms. E. coli should not be detected in any of these samples. If E. coli is detected, advise the MOH and institute normal corrective procedures (Section 3.4.1.2 DWSNZ:2000).

Procedures, details and outcomes should be logged for all events.

Turbidity, FAC and pH should be measured after every event.


What to do with the results:

Results need to be recorded to meet legislative requirements or to allow water safety plan performance assessment. The WINZ database is good for this.

The collected data need to be periodically reviewed to see whether problems with this supply element are developing. This should be done as frequently as the manager responsible considers necessary to minimise risk to public health arising from this supply element.

Should the review flag any unusual incidents, indicate that proper procedures are not being carried out, highlight poor laboratory results or indicate that poor water quality is reaching customers, then review the procedures for managing distribution system operations.

Evaluate the monitoring results, and any actions taken as the result of having to implement a contingency plan, to see if the water safety plan needs modification, eg, preventive measures are up to date; the contingency plan steps are still adequate; and changes to distribution system operation are recognised in the plan.

Responsibility: Manager designated responsible for water supply.


Appendix 1: Good Hygiene Practices for Staff Working on Drinking-Water SuppliesOnce distribution systems have been opened for repair or construction, the chances of contamination are increased. To minimise contamination by germs, it is recommended codes of practice for worker hygiene should include (but not be limited to) the following: The same maintenance personnel are not to work on both water

and sewer systems. Vehicles and equipment are to be dedicated to water operations

and kept totally separate from those used for sewage work. A high standard of cleanliness is required for vehicle interiors.

All equipment is to be cleaned of dirt and debris, and disinfected (100 mg/L chlorine solution) before use. Biocidal lubricants should be used where necessary.

All new system components should be sealed by the manufacturer and are to be kept sealed until just prior to installation.

Components that have been worked on, and disinfected, but not returned immediately to use, are to be sealed (blank flanges are to fitted to pipes and pumps while in storage to prevent contaminant entry and only removed just prior to installation).

Workers are to report any gastrointestinal illness, to have faecal specimens taken for analysis when the illness starts, and are not to work with reticulation system components until they can provide a medical certificate stating that they are clear of the disease.

Workers are to obtain a medical clearance against being carriers of potentially water-borne disease:– prior to employment on the water reticulation system– on an annual basis– following overseas travel to countries with a significant level of

endemic water-borne disease.


Appendix 2: Cleaning and Disinfection of MainsThe following procedures are recommended for the cleaning and disinfection of mains following construction or repair.

Procedure for new mains Clean loose deposits from the mains using unidirectional flushing

(minimum velocity of 1.5 m/s). Ensure that the water is drawn from the trunk main or one that has previously been cleaned. Swabbing the main may be used in preference to flushing where the pipe diameter makes developing sufficient velocity difficult.

Disinfect with 50 mg/L of chlorine for a minimum of two hours. Dispose of the chlorinated water to waste, do not discharge into the

ground or stormwater drain. Neutralisation of the chlorine may be used to reduce the problems associated with the disposal of elevated chlorine concentrations. (Depending on the disposal options available, prior arrangements may need to be made with the regional council for disposal of water.)

Procedure for existing mains The procedure for disinfection of mains undergoing maintenance

(repair, replacement etc) should be dictated by the situation. The need to use high chlorine concentrations to disinfect the main can be avoided under some circumstances. Someone with suitable training should have responsibility for assessing the situation and deciding which action is appropriate.

Disinfection is unnecessary where there is a very low risk of contamination having entered the system. Such situations include those:– where repair can be done under positive pressure– where there is a loss of pressure but no contamination enters

the main. This situation requires that some positive pressure be maintained while the trench is excavated, and the trench thoroughly de-watered before the flow is cut totally and repair undertaken.

Disinfect all fittings surfaces, and the exterior of the main, with 1 percent chlorine solution (applied by spray of wash), and where pressure has been lost, disinfect the internal surfaces at the openings.


Where pressure has been lost, thoroughly flush the main (minimum of 1.5 m/s velocity or ‘run to clear’) after completion of the work, and maintain a chlorine concentration of 5 mg/L in the main for a minimum of 30 minutes.

Disinfection is necessary where it has not been possible to stop the entry of contaminants into the main.– The area affected by the operations should be fully isolated,

including all known connections to consumers. The high levels of chlorine that need to be used to disinfect mains in this situation pose a risk to health if consumers are exposed to them. After disinfection, careful flushing of all the affected area is required, and notification to consumers to flush their systems is also needed to ensure they will not be exposed to slugs of water with high chlorine concentrations which are still in the system. Notifying consumers may help to avoid incidents arising from unknown mains connections.

– After the maintenance has been carried out, thoroughly unidirectionally flush, or swab the main where possible, and disinfect with 50 mg/L of chlorine for a minimum of two hours. Flushing should be carried out at a minimum velocity of 1.5 m/s or ‘run to clear’. A free available chlorine residual of not less than 5 mg/L should be measurable in the water after the two hours contact time.

– Dispose of the chlorinated water to waste, do not discharge into the ground or stormwater drain. Neutralisation of the chlorine may be used to reduce the problems associated with the disposal of elevated chlorine concentrations. (Depending on the disposal options available, prior arrangements may need to be made with the regional council for disposal of water.)

– Thoroughly flush the affected area with fresh water. In all cases, microbiological sampling both upstream and

downstream of the repair should be undertaken to confirm the microbiological acceptability of the water. Samples must be taken within 12 hours of taking completing the repair or placing the line back in service. Should the tests show the water quality to be unsatisfactory, disinfect the mains again and follow the responses give in Figure 3.3 of the Drinking-Water Standards for New Zealand:2000.

Where entry of a chemical contaminant into the main may have occurred, sampling should also be undertaken to confirm that its concentration is not a health concern.


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