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DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK PROCEDURE

DISINFECTION OF WATER MAINS AND SERVICE PIPES

Document Title: Work Procedure - Disinfection of Water Mains and Service Pipes

Document Reference: DOM-WN-PRC-00000106 Version: D Date: August 2014 Approved By: Public Health Team Title: Public Health Manager

DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK PROCEDURE


Ref: DOM-WN-PRC-00000106

Version: D

Date: August 2014

Record of Changes and Amendments

Amendment No.

Document Section/ Reference

Number Document / Section

Title Version Number

Amendment Date

Archived Document / Section Text Affected

Archived Document /

Section Replaced

By

1 All sections All sections B May 2013 Changes to requirements for flushing and swabbing – keeping records & responsibilities

2 Section 3 Description B May 2013 Change text in relation to Carela / EpSolve name change.

3 Section 1 Preamble C Oct 2013 1.4 / New section inserted covering DOMS Training

4 Foreword Foreword D Aug 2014 New legal notice inserted

Sheet i

DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY

ASSET MANAGEMENT WORK PROCEDURE


Ref: DOM-WN-PRC-00000106 Version: D

Date: August 2014

FOREWORD

Background

DOMS stands for ‘Distribution Operation & Maintenance Strategy’ and is being used by Scottish Water to:

• Safeguard the quality of water to customers. • Ensure that Scottish Water apply due diligence to their Scottish Water distribution network.

The DOMS procedures and work instructions affect all functional staff who work on the network, which includes internal employees and employees of external organisations (i.e. planners, operators, delivery teams, Framework Contractors, or any other contractors).

Through the application of the DOMS principles in day-to-day network activities, Scottish Water and their approved contractors will operate and maintain their water distribution networks through operational ‘best practice’. This will allow Scottish Water to meet the following objectives:

• to maintain water quality. • to maintain continuity of supply. • to maintain water supply hygiene. • to undertake water quality incident management. • to maintain a cost-effective water supply. • to ensure a course of action for timely network intervention (Capex and/or Opex) to maintain

statutory obligations and customer satisfaction.

Responsibility The responsibility for adoption and implementation of all DOMS procedures and work instructions rest with Scottish Water General Managers and senior managers of external organisations. It is the responsibility of all Scottish Water employees and those of external organisations to comply with DOMS procedures and work instructions.

Document Control

This document is a CONTROLLED DOCUMENT when viewed on ‘Wavelength’.

The document becomes UNCONTROLLED if printed or downloaded from ‘Wavelength’ or any other source.

Refer to the ‘Wavelength’ site for the latest version of this document. Page i





Date: August 2014

Change Request

A change to this document can be requested by completing a Change Request Form - refer to document ‘DISTRIBUTION OPERATION and MAINTENANCE STRATEGY GOVERNANCE (DOM-WN-GOV-00000001)’ for change request procedure.

Legal Notice Copyright of this document is owned by Scottish Water. The document may not be copied or reproduced in any way. This document and the intellectual property rights in it belong to Scottish Water and except where you are specifically licensed to use this document, you have no right to re-use it. Disclosure of this document under freedom of information does not change the position on (i) ownership and (ii) re-use.

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CONTENTS FOREWORD…………………………………………………………………………………………………. i CONTENTS ……………………………………………………………………………………................... iii 1 PREAMBLE ………….………………………………………………………………………………….. 1 1.1 Procedure Objectives ……………………………………………..………………………….…. 1 1.2 Related Parent Documents………………………………………………….………………….. 1 1.3 Related External Controlled Documents…………………………………………................... 1 1.4 Related Internal Controlled Documents…………………………………………................... 1 1.5 DOMS Training Guidelines – Evidence of DOMS Training................................................. 1 2 PROCEDURE FLOW CHART………………………………………………………………………….. 3 3 DESCRIPTION…….……………………………………………………………………………………… 4 3.1 New Water Mains…………………………………………....................................................... 5 3.2 Rehabilitated Water Mains……………………………………………………………………….. 9 3.3 Water Main Tie-Ins…………………………………………………………………………………11 3.4 Water Main Repair Carried Out Under Positive Pressure……………………………………..12 3.5 Water Main Repair Where Water Has Been Turned Off……………………………………….13 3.6 Service Pipes……………………………………………………………………………………..…14 3.7 Gross Contamination……………………………………………………………………………….15 3.8 Disinfection Procedure for Water Mains and Services Pipes: where pipes have been unused for greater than 2 weeks…………………………………….. 16

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1. PREAMBLE

1.1 Procedure Objectives Scottish Water is committed to delivering the Ministerial Directions and other regulatory targets, within the financial limits set out in the Final Determination. To ensure that the risk of contamination of water in the Distribution System is minimised Scottish Water has produced a “Water Supply Hygiene Code of Practice”. This sets out the health and hygiene standards required of Scottish Water’s employees and its Contractors/Consultants. This procedure is designed to give Scottish Water staff and Contractors an awareness of the specific requirements of the Hygiene Code relating to the Disinfection of Water Mains and Service Pipes, including the action to be taken during repairs. Staff should refer to the Hygiene Code on a regular basis to ensure that they are working to the up to date requirements. Follow this file path on WaveLength to view the latest version of the Hygiene Code of Practice: Directorates > Asset Management > Scientific Services > Public Health Team > Useful Public Health & Scientific Links > SW Hygiene Code of Practice 1.2 Related Parent Documents

None 1.3 Related External Controlled Documents

None 1.4 Related Internal Controlled Documents • Water Supply Hygiene Code of Practice • DOM-WN-WIN-00000102 - Use and Disposal of Chlorine Solutions • DOM-WN-PRC-00000331 – Disinfection Methodology • DOM-WN-TBT-00000011 - Potable Water Sampling - Sample Details, Sample Registration &

Sample Results • DOM-WN-TBT-00000015 - Sampling Repairs and New Mains - Information for those taking

samples 1.5 DOMS Training Guidelines – Evidence of DOMS Training

In 2007, Scottish Water set the goal that all staff working on the water network receives the relevant DOMS training by the end of the year. The result - over 9,000 people have currently

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completed DOMS training to support their network activities since it has been introduced within SW.

All staff, both internal and external, who work on the water network, MUST complete the relevant Distribution, Operation and Maintenance Strategy (DOMS) training associated with their specific network activities and as a result MUST carry two cards which confirm their training.

DOMS training is available through a number of approved Training Providers and the registration of the training units taken by individuals is administered through EU Skills.

The first card relates to training given around the Hygiene Code of Practice (HCoP) and the card usually coloured light blue, confirms the cardholder has completed this element, which includes a health screening questionnaire.

The second card, usually coloured white, relates to training given around DOMS and the training units shown on the back of the card detail the type of DOMS related site activities that the cardholder can undertake.

Both cards detail the name of the cardholder, along with their picture, which will allow confirmation that the cardholder is the person holding the card.

Scottish Water staff may and will challenge all internal and external staff working on the water network at anytime to produce both their cards to ensure that cardholder has the relevant training and understanding of DOMS Procedures and Work Instruction for the specific task that they are undertaking.

The following guidelines should be followed for deciding the course of action to take when either internal of external staff were found to be working on the water network, or any infrastructure that will be connected to our network, without the requisite HCoP/DOMS cards confirming training

1) New starts - expectation that they will have their necessary HCoP/DOMS training organised by their employer within the first 4 weeks of them joining their company. They will not be allowed to work on the water network without the HCoP/DOMS training, even though they are being supervised by a person who has gone through the training. There is a minimal health risk here, which the health questionnaire, completed during the HCoP training, will confirm as acceptable or unacceptable.

2) Completed HCoP/DOMS Training but no card issued by EU Skills - staff in this situation can work on the water network as long as they can demonstrate that they have a 'cover note' issued by training providers. If a 'cover note' is produced, then the person challenging can ensure that 'cover note' refers to the actual person by checking the EU Skills web site against name or reference number.

This will be done in conjunction with the relevant DOMS Working Group representative.

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3) Person challenged on site and person has no HCoP/DOMS relevant training - if this scenario occurs then the person who has made the challenge will remove the person from working on the water network and contact the relevant business unit DOMS Working Group representative as the first point of contact. Together, the site contact and the DOMS Working Group representative will make the decision on whether work can or cannot continue after discussions with the employee’s relevant organisation.

4) Person challenged on site and cannot produce HCoP/DOMS relevant training cards, but claims to have undergone training - if no cards can be produced, then the person challenging can not confirm that the person has had the relevant training by checking the EU Skills web site against name or reference number. This will be done in conjunction with the relevant DOMS Working Group representative.

5) Person challenged on site; DOMS CARD EXPIRED. If a DOMS card has expired and the person is waiting to attend a SW DOMS training course, a signed and dated cover note, with the course reference confirmation number and Registration Status clearly shown, must be issued by the person’s line manager, in order to allow access to the network.

The person must present this cover note on site.

(Failure to provide cover note will result in the individual being removed from working on the network until a cover note is issued, or the individual is retrained and re-registered with EUSR) The cover note will only be valid for 3 months after the original card expiry date. After 3 months has elapsed, if the person has not re-registered and is NOT in possession of a new card or a cover note stating the person is awaiting delivery of a new card, then access to work on the network will be refused.

All internal and external staff working on the water network must have completed the relevant training. If the site challenges are made by SW staff (and on occasions the DWQR) for all those working on the network, the message will be sent clearly that

'IF YOU HAVEN’T HAD THE TRAINING – YOU CANNOT WORK ON OUR NETWORK OR ANY INFRASTRUCTURE THAT WILL BE CONNECTED TO OUR NETWORK.’ While we all want to balanced and professional in our company approach to this matter, water quality and customer satisfaction in our product is our paramount concern.

Finally, can all Scottish Water staff note that for out-of-hours advice on public health issues, a representative from the Public Health Team can be contacted 24/7 through the ICC. 2. PROCEDURE FLOW CHART

No procedural flow chart is needed for this procedure.

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3. DESCRIPTION Newly installed pipes and fittings will inevitably be contaminated and need to be cleaned and disinfected before being connected to the ‘live’ distribution network. For bursts and alterations, whilst our network of pipes remains complete and under positive pressure, it should be safe from contamination. However, as soon as pipes are disconnected or network pressure is lost, contaminants could enter the network and put public health at risk. Before pipes and fittings are put back into service (made live) or connected for the first time they must be cleaned and disinfected. Pipes and fittings for new mains and service pipes should be stored and laid as hygienically as possible. All reasonable measures should be taken to exclude contamination in particular areas where animal faeces or hydrocarbons are present. During laying operations, the pipeline ends should be capped whenever work stops for an extended period (e.g. overnight). Uncapped pipe work must never be “pushed” through ground causing debris to enter the pipe resulting in gross contamination. This section provides checklists of the minimum steps you should take in the following circumstances: • New Mains • Rehabilitated Mains • Tie-ins • Repairs made under a positive water pressure • Repairs made under no positive pressure • Service Pipes • Gross Contamination of Pipework If you are dealing with something not covered by this list, seek advice from your Manager. This document is not intended to tell you how to carry out the actions: training should have been provided for that. If it hasn’t, talk to your Manager and ask for the appropriate training. This document should remind you of the steps you follow. More detailed procedures may be applicable depending upon site specific circumstances. In all cases the discharge of chlorinated / chloraminated water must be carried out with due regard for Health & Safety, the environment any requirements of SEPA. Consideration should always be given to the use of dechlorination equipment. Advice on this can be found in DOMS Work Instruction ‘Use and Disposal of Chlorine Solutions’ (DOM-WN-WIN-00000102). Alternative disinfection procedures using proprietary products (EpSolve, formally known as Carela) must be subject to the submission of a detailed method statement and written

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authorisation must be issued by a Scottish Water Operations Manager or depute before proceeding. Only registered, trained personnel should be allowed to use EpSolve on Scottish Water assets. The correct use of such products can remove the need for dechlorination, before discharge to the environment. Please refer to DOMS procedure ‘DOM-WN-PRC-00000328 Use of Epsolve for Disinfecting Pipe Work’. 3.1 New Water Mains Exceptions: mains installed by pipe bursting, swaging or slip lining. (i) Main is to be pressure tested (using clean, treated water; never use raw water), swabbed,

flushed and disinfected prior to permanent connection to live main. (ii) Any temporary connection provided to permit testing; swabbing and disinfection must be

provided with double check valve protection. (iii) The new main is to be swabbed using a swab soaked in 20 mg/l sodium hypochlorite

solution. A record of the time, date, number and size of swab/s being introduced and removed from the main should be kept for audit purposes.

(iv) Flush main until running clear – re-swab if necessary (visibly inspect the water when

flushed and record if it is running clear). Report any incidences of low flows during flushing operations immediately to your line manager. This may indicate a blockage within the main e.g. a swab / rags etc. and could seriously impact on water quality and Customer Service. It is the responsibility of Contractor to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and it is the responsibility of the SW Project Manager to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(v) Generate flow at terminal hydrant(s) on new main(s) and add sodium hypochlorite

solution, via chlorine pump, to achieve free chlorine residual as noted below. If tablets are being used sufficient time should be allowed for them to dissolve before flushing through occurs (follow manufacturers guidelines). Remember Instachlor tablets dissolve immediately, HTH / Steadichlor tablets take longer to dissolve. Please refer to the tables in Appendix II of the Hygiene Code of Practice for guidance on tablet / concentration usage. Generally tablets should be used for smaller diameter new mains.

(vi) On detecting appropriate level of free chlorine at terminal hydrant(s) isolate and leave for

appropriate contact time.

Free Chlorine Residual

Contact Time

20 mg/l

24 hours

50 mg/l

2 hours

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(vii) Discharge chlorinated water (see DOMS Work Instruction ‘Use and Disposal of Chlorine

Solutions - DOM-WN-WIN-00000102 and the Hygiene Code of Practice Appendix II) then recharge with normal mains supply and stand for 24 hours.

(viii) Flush the main thoroughly until the chlorine residual downstream of the new main is

similar to that of the water entering the new main. Measure the free and total chlorine residual of both the discharged water and the incoming feed water to ensure the whole of the main has been adequately flushed. Record these chlorine residuals for audit purposes. It is the responsibility of Contractor to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and it is the responsibility of the SW Project Manager to ensure the data / measurements collected are reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(ix) Always take representative bacteriological samples following a new main installation.

Always ensure the bacteriological sample bottles used are not out of date. If samples are submitted to the laboratory in out of date bottles the samples will have to be cancelled and fresh samples will have to be taken. See the Hygiene Code of Practice for details of parameters to be tested or contact the Public Health Team.

(x) Measure the free and total chlorine residuals and take samples for bacteriological

examination (see test list below) from extremities of a new main and at intermediate points not exceeding 1000 metres where appropriate. For example:

• If the length of new main being commissioned is 1,400 metres then the minimum required number of samples that must be taken is 2 bacteriological samples from hydrant points up to 1000m and between 1000 – 1,400 metres.

• If the length of new main being commissioned is 2,400 metres then the minimum

required number of samples that must be taken is 3 bacteriological samples from hydrant points up to 1000m, between 1000 – 2000 metres and between 2000 metres and 2,400 metres.

(xi) Should the sample analysis results prove unsatisfactory the cause should be investigated

and the main flushed and re-chlorinated as above until acceptable results are obtained. (xii) Once satisfactory results have been obtained documentary evidence (from the Public

Health Team) should be obtained to confirm that the main is cleared for service, after which the main tie-in procedure should be followed.

Note: If the main is not connected to the live network within two weeks (14 days) of receiving the pass it must be re-tested before connection.

Bacteriological samples should be delivered for analysis to the laboratory or designated sample collection point within 12 hours of the sample being taken (bacteriological samples must be analysed within 24 hours of being taken – delivering them within 12 hours will

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ensure this target is met and will take account of any time necessary for onward transport to the analysing laboratory). If samples have to be stored awaiting transportation they should be kept in a designated fridge (2 – 8oC) or sample cold store. To avoid extremes of temperature during transportation in vans cool bags may be used. Cool bags must be cleaned on a regular basis to avoid bacteriological growth in order to prevent sample contamination. Please refer to DOMS Tool Box Talks (TBT) No 11 and 15 for additional information on sampling, sample registration and sample transportation.

For a New Main the following bacteriological tests should be carried out:

• Coliforms • E.coli • Faecal Streptococci • Clostridia • 22°C plate counts • 37°C plate counts

Remember – always measure and record the free and total chlorine residuals on the Sampling Pro-forma Sheet and on the sample bottle label, for each bacteriological sample that is taken.

A copy of the Sampling Pro-forma Sheet (MCL1158) can be obtained on Wavelength at:

Directorate > Asset Management > Scientific Services > Technical Logistics > Logistics Note: If guidance is required on any aspect of sampling and analysis (chemical or bacteriological) of New Mains please contact the Public Health Team for advice. Contact details can be obtained from the corporate systems (Standby Log), the ICC, Call Centre or alternatively there are details listed in DOMS TBT No 11. For New Mains being commissioned in or using:

1. Contaminated Ground 2. Ductile Iron 3. Cement Lined 4. Epoxy Lined

the following tests (contamination suite) should be carried out:

Chemical • pH • Colour • Turbidity • Conductivity • Iron

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• Manganese • Aluminium • Calcium • Magnesium • Zinc • Lead • Copper • Hydrocarbons by GCMS Scan • Phenols

Bacteriological + Taste & Odour

• Qualitative Taste & Odour • Coliforms • E.coli • Faecal Streptococci • Clostridia • 22°C plate counts • 37°C plate counts

In any of the cases listed above the following approach must be taken:

1. Swab, flush & chlorinate the new main as detailed in (a) above 2. Flush the main (recommended with 10 times the volume of the new main), dechlorinating

the discharge as per standard procedure 3. Samples are required from the incoming main and the new main including any branches. 4. Take the Chemical samples listed above immediately after the flushing exercise and

submit for analysis. Some of these tests can take up to 14 days to complete. 5. Take the Bacteriological and the Taste & Odour samples after 7 days and submit for

analysis. Remember – always measure and record the free and total chlorine residuals on the Sampling Pro-forma Sheet (MCL1158) and on the sample bottle label, for each bacteriological sample that is taken.


Directorate > Asset Management > Scientific Services > Technical Logistics > Logistics (xiii) Should the sample analysis results prove unsatisfactory the cause should be investigated

and the main flushed and / or cleaned and re-chlorinated as above until acceptable results are obtained, as necessary.

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(xiv) Once satisfactory results have been reported, documentary evidence (from the Public

Health Team) should be obtained to confirm that the main is approved for service, after which the main tie-in procedure should be followed.

Note: This should be within two weeks (14 days) of receiving confirmation from the Public Health Team. Should the main be left longer then the main should be re-tested for bacteriological quality.

3.2 Rehabilitated Water Mains Notice MUST be given to the Public Health Team in advance of the work starting. This notice MUST include any intention to issue boil water notices to customers as part of the work being carried out. (i) All services must be isolated throughout the rehabilitation and disinfection process. (ii) Throughout the rehabilitation process and until such time as the main is tied-in, all

excavations should be pumped dry to a minimum of 150mm below pipe invert, to ensure that no contaminated water enters the main. End caps should be fitted to the main wherever possible.

(iii) Temporary connection to permit testing, swabbing and disinfection to be provided with

double check valve protection. (iv) Rehabilitated main to be swabbed using a swab soaked in 20 mg/l sodium hypochlorite

solution. A record of the time, date, number and size of swab/s being introduced and removed from the main should be kept for audit purposes.

(v) Flush main until clear (visibly inspect the water when flushed and record if it is running

clear). It is the responsibility of Contractor to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and it is the responsibility of the SW Project Manager to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(vi) Generate flow at terminal hydrant(s) on new main(s) and add sodium hypochlorite

solution, via chlorine pump, to achieve free chlorine residual as noted below. If tablets are being used sufficient time should be allowed for them to dissolve before flushing through occurs (follow manufacturers guidelines). Remember Instachlor tablets dissolve immediately, HTH / Steadichlor tablets take longer to dissolve. Please refer to the tables in Appendix II for guidance on tablet / concentration usage. Generally tablets should be used for smaller diameter pipes.

(vii) On detecting appropriate level of free chlorine (by measuring the chlorine residuals) at

terminal hydrant(s) isolate and leave for appropriate contact time. Free Chlorine Residual Contact Time

20 mg/l 24 hours

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50 mg/l 2 hours

(viii) Measure the chlorine residual at the end of the contact period. Any significant decrease in measured residual could indicate serious contamination of the new main. Consult a member of the Public Health Team for advice.

(ix) Discharge chlorinated water (see Appendix II) and flush the main with normal mains supply.

(x) Flush the main thoroughly until the chlorine residual downstream of the new main is similar to that of the water entering the new main. Measure the free and total chlorine residual of both the flushing water and the incoming feed water to ensure the whole of the main has been adequately flushed. Record these chlorine residuals for audit purposes. It is the responsibility of Contractor to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and it is the responsibility of the SW Project Manager to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(xi) Complete tie-in in accordance with Water Main Tie-In procedure and always measure the free & total chlorine residuals. As soon as possible take representative samples for bacteriological examination.

For a Rehabilitated Main the following bacteriological tests should be carried out: • Coliforms • E.coli • Faecal Streptococci • Clostridia • 22°C plate counts • 37°C plate counts

Remember – always measure and record the free and total chlorine residuals on the Sampling Pro-forma Sheet and on the sample bottle label, for each bacteriological sample that is taken.


Directorate > Asset Management > Scientific Services > Technical Logistics > Logistics Note: If guidance is required on any aspect of sampling and analysis (chemical or bacteriological) of Rehabilitated Mains please contact the Public Health Team for advice. In the event of a sample failure Scottish Water’s bacteriological sample failure procedure should be implemented. Contact the Public Health Team for guidance. Contact details can be obtained from the corporate systems (Standby Log), the ICC, Call Centre or alternatively there are details listed in DOMS TBT No 11.

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Note: Pre-chlorination of coiled pipes or liners may be carried out as an additional precaution but not as an alternative to disinfection after installation. 3.3 Water Main Tie-Ins (i) Drain the new, or rehabilitated, branch main.

(ii) Excavate below existing main (and branch main where temporary pipe work is to be

removed) and keep excavation dry to minimum depth of 150mm below pipe invert, including pumping out of the excavation if required, to ensure no contaminated water can enter main during the Tie-In operation.

(iii) Before shutting off main, STOP AND THINK, the area to be cut must be inspected for

signs of contamination. Should contamination be suspected, the area must be cleaned and free of the contaminant before shutting and draining of the main occurs? See Appendix III – Cryptosporidium of the Hygiene Code of Practice for further information or contact the Public Health Team for guidance.

(iv) Spray all new pipe and fittings which are to come into contact with potable water with a

solution containing 250mg/l chlorine. (v) After recharging, flush the main thoroughly until the chlorine residual downstream of the

Tie-In is similar to that of the water upstream of the Tie-In (i.e. the incoming feed water). Record the free and total chlorine residuals for audit purposes. It is the responsibility of Contractor to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and it is the responsibility of the SW Project Manager to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(vi) Take representative samples as soon as possible for bacteriological examination. For a Water Main Tie In the following bacteriological tests should be carried out:

• Coliforms • E.coli • Faecal Streptococci • Clostridia • 22°C plate counts • 37°C plate counts

Note: If guidance is required on any aspect of sampling and analysis (chemical or bacteriological) of a Water Main Tie In please contact the Public Health Team for advice.

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(vii) In the event of a sample failure, Scottish Water’s bacteriological sample failure procedure

should be implemented. Contact the Public Health Team for guidance. Contact details can be obtained from the corporate systems (Standby Log), the ICC, Call Centre or alternatively there are details listed in DOMS TBT No 11.

The need for further disinfection should be assessed based on the level of contamination having occurred. Where a significant amount of dirty / non-potable water has entered the pipe, the affected section of pipe must be flushed until the water is clear (visually check the flushing water and record if it is running clear) and the main disinfected as far as is practicable, to achieve 50mg/l of free chlorine for a minimum of 30 minutes. Service connections should be isolated or customers warned not to use the water until the main has been flushed.

If this occurs the Public Health Team must be informed as soon as possible. Where gross contamination has occurred refer to Section 3.7. 3.4 Water Main Repair Carried Out Under Positive Pressure (i) Keep a nominal positive pressure within the main at all times. (ii) Particular care must be taken when carrying out repairs in areas of obvious, or suspected,

surface or sub-soil contamination (e.g. wastewater treatment works, lagoons, farmyards, agricultural land, industrial sites, tips, garages, etc).

(iii) Before repair is carried out, STOP AND THINK, the area around the burst must be

inspected for signs of contamination. Should contamination be suspected the area must be cleaned and free of the contaminant before repair commences. See Appendix III – Cryptosporidium for further information or contact the Public Health Team for guidance.

(iv) Carry out repair, ensuring that all new pipes and fittings which are to come into contact

with potable water are sprayed with a solution containing 250mg/l chlorine. (v) After recharging and flushing the main, if the Responsible Person is confident the main

has remained under pressure throughout the repair and if an Impact Assessment Form has been completed and the excavation has remained free from contamination, there is no need to take samples for bacteriological examination. It is the responsibility of Contractor / person carrying out the repair to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(vi) The Responsible Person must ensure that any decisions made as to whether the main

has remained under pressure or not, are clearly communicated, preferably in writing if possible, to any other Responsible Person during handover of shifts. This will ensure appropriate sampling and analysis will be carried if necessary.

(vii) If there is any doubt that the main has remained under pressure during the repair,

representative bacteriological samples must be taken downstream of the repair. Samples

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need not be taken from repairs on service pipes below 50 mm diameter. DOMS Procedures & Toolbox Talks can be viewed on Wavelength by following the path below:

Directorates > Asset Management > Asset and Investment Management > Water Planning > DOMS > Tool Box Talks

If samples are necessary following a Mains Repair always measure the free and total chlorine residuals and the following bacteriological tests should be carried out:

• Coliforms • E.coli • Faecal Streptococci • Clostridia

Note: If guidance is required on any aspect of sampling and analysis (chemical or bacteriological) of a Mains Repair please contact the Public Health Team for advice. If, after an appropriate time (up to 1 hour) the water is not running clear after flushing, take a bacteriological sample and send it for analysis. Take a further bacteriological sample within 24 hours of the first ‘dirty’ sample, after allowing the network to settle.

(viii) In the event of a sample failure Scottish Water’s bacteriological sample failure

procedure should be implemented. Contact the Public Health Team for guidance. 3.5 Water Main Repair Where Water Has Been Turned Off (depressurised) (i) Where possible keep a positive pressure within the main until excavation has taken place

to uncover the failed pipe and the excavation pumped dry to a minimum of 150mm below invert. Excavate below existing main and keep excavation dry to minimum depth of 150mm below pipe invert, including pumping out of the excavation if required, to ensure no contaminated water can enter main during the repair. Excavations must be of an adequate depth below the main to enable dewatering and the digging of drainage sumps must be carried out, so as not to hinder dewatering. Adequate sump pumping capacity should always be utilised to facilitate dewatering of excavations.

(ii) Particular care must be taken when carrying out repairs in areas of obvious, or suspected,

surface or sub-soil contamination (e.g. wastewater treatment works, lagoons, farmyards, tips, garages, etc).

(iii) Before shutting off main, STOP AND THINK, the area around the burst must be

inspected for signs of contamination. Should contamination be suspected, the area must be cleaned and free of the contaminant before shutting and draining of the main occurs. See Appendix III – Cryptosporidium for further information or contact the Public Health Team for guidance.

(iv) Shut down main, preferably by closing downstream valve first, and carry out repair; clean

existing pipe ends and all new pipes and fittings which are to come into contact with potable water with a solution containing 250mg/l chlorine.

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(v) After recharging, flush the main thoroughly until the chlorine residual downstream of the

repair is similar to that of the water upstream of the repair (i.e. the incoming feed water). Record the free and total chlorine residuals for audit purposes. It is the responsibility of Contractor / person carrying out the repair to ensure flushing and monitoring is carried out correctly. It is the responsibility of the SW Responsible Person to ensure these actions are adequately supervised and to ensure the data / measurements collected is reviewed, within a suitable time frame, to ensure water quality and public health is not put at risk.

(vi) Take representative samples downstream of the repair as soon as possible for

bacteriological examination. Always take samples following a Mains Repair (depressurised) & always measure the free and total chlorine residuals. The following bacteriological tests should be carried out:

• Coliforms • E.coli • Faecal Streptococci • Clostridia

(vii) In the event of a sample failure Scottish Water’s bacteriological sample failure procedure

should be implemented. Contact the Public Health Team for guidance. In the event of a positive pressure not being maintained prior to excavation or repair, the procedure remains as Parts (ii) – (vi) above, but in addition the need for further disinfection should be assessed based on the level of contamination having occurred. Where a significant amount of dirty water has entered the pipe, the affected section of pipe must be flushed until the water is clear (visibly inspect the water when flushed and record if it is running clear) and the main must be disinfected as far as is practicable to achieve 50mg/l of free chlorine for a minimum of 30 minutes. The residual should be checked after 30 minutes to ensure is hasn’t significantly deteriorated. This could indicate significant contamination, and may require swabbing of the main. Service connections should be isolated or customers warned not to use the water until the main has been flushed. If this occurs, the Public Health Team must be informed as soon as possible. Where gross contamination has occurred refer to Section 3.7. 3.6 Service Pipes The procedure is applicable to all new communication pipes, transfers of connections, communication pipe repairs, etc, (i.e. all operations which involve exposing communication pipe work to the atmosphere). Clearly there is no point in going through detailed procedures to disinfect water mains and then risking contamination of the service pipe work – hence the importance of complying with this procedure.

(i) Excavate below existing main and keep excavation dry to minimum depth of 150mm

below pipe invert, including pumping out of the excavation if required, to ensure no contaminated water can enter service pipe.

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Date: August 2014

(ii) Before connecting pipe, STOP AND THINK, the excavation must be inspected for signs

of contamination. Should contamination be suspected the area must be cleaned and free of the contaminant before pipe connections are carried out? See Appendix III – Cryptosporidium for further information or contact the Public Health Team for guidance.

(iii) Spray all new pipe and fittings which are to come into contact with potable water with a

solution containing 250mg/l chlorine. (iv) Whilst the necessary works are in progress place fizzy ‘Instachlor’ tablets in the open

communication pipe at a point as close to the connection to the main as possible. (See Appendix II). Never use disinfection tablets on “live” supplies that customers could be using.

(v) On completion of the works fill the service pipe (restricted to the communication pipe in

some cases) slowly to allow the tablets to dissolve. Allow to stand in contact with chlorine for 30 minutes.

(vi) Where the service pipe work supplies existing customer(s) advise the customer(s) by card

to flush their pipe work for an appropriate length of time depending in the length / diameter of their service pipe, before use.

3.7 Gross Contamination In the event of an actual or suspected gross contaminant entering a water main or service pipe particularly rigorous corrective actions must be taken to minimise the risk of any contaminated water being consumed. Such an occurrence must be escalated to a Scottish Water Manager / Team Leader in all cases as soon as possible.

(i) Examples of gross contaminants include -

• Sewage

• Petrol, diesel, lubricants and other fuel oils

• Agricultural waste/silage

• Industrial effluent / industrial ground

• Chemicals

• Groundwater / Surface water of unknown quality

(ii) The severity of gross contamination incidents can vary widely and subsequently corrective actions required tend to be site specific. It is not practical to detail a set of procedures to be applied for each type of event; it is best to contact the Public Health Team for advice if in any doubt. As a minimum response, the following must be actioned / considered:

(a) The section of pipe work that could be contaminated must be isolated as quickly as possible. Particular attention must be paid to the sequence in which valves are closed - where practicable the downstream valves should be closed first to limit any contaminated material being drawn downstream.

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(b) The Scottish Water Manager / Team Leader in the first instance should be contacted, who will make the decision as to whether it will be necessary to initiate Scottish Water’s Emergency Procedures and invoke the Scottish Waterborne Hazard Plan.

(c) The supply should not be restored to normal until such time as satisfactory

bacteriological, chemical and organics (as appropriate) water sample results have been obtained and approval obtained from the Public Health Team.

3.8 Disinfection Procedure for Water Mains and Services Pipes - where pipes have

been unused for greater than 2 weeks.

(a) If in the event the water main or service pipe remains unused after a period of 2 weeks, from notification that sample analysis was satisfactory, the pipe should be flushed and re-tested for bacteriological analysis. Contact the Public Health Team for guidance.

(b) This applies to all pipe work, service reservoirs and tanks where water has been

allowed to stand. If in doubt contact the Public Health Team for guidance.

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