Citation: Ministry of Health. 2014. Water Safety Plan Guide: Distribution System – Operation, Version 1, ref D2.3. Wellington: Ministry of Health. Published in January 2014 by 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.
D2.3.1.6 Inadequate 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. Identify staff training needs and provide training. D2.3.1.7 Inappropriate 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. Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEM cont’d D2.3.1.8 Inadequate 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 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 persists. Identify reasons for inadequate residual and correct.
D2.3.1.9 Unsuitable 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 Train staff. Re-audit procedures. Identify reasons for inadequate residual and correct. Identify staff training needs and provide training. Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEM cont’d D2.3.1.10 Contamination during sampling. Provide securable, safe sampling locations that allow access without risk of introducing contamination. Microbiological quality. Appropriate determinands if chemical contamination is suspected. Failure to meet the requirements of DWSNZ:2000. Re-sample. Take to avoid recurring (Guide G2). Retrain sampling staff.
D2.3.1.12 Cross 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 water quality. on of staff undertaking connections. Event: RE-SUSPENSION OF CONTAMINANTS IN SEDIMENTS IN THE DISTRIBUTION SYSTEM Possible hazards: Germs; chemical determinands, turbidity. Level of risk: Moderate3 D2.3.2.1 Sediment or biofilm allowed to develop. See D2.3.3 Causes and Preventive Measures. Scour, pig, flush distribution system. Restore acceptable quality. D2.3.2.2 Water velocity too high. Controlled opening/closing valves and starting pumps. Size pipe diameters to accommodate demand for water without high water velocities sediment. (In some situations it may not be possible to accommodate fire flows.) FAC. Microbiological 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. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: DEVELOPMENT OF SEDIMENT OR BIOFILM Possible hazards: Germs; chemical determinands, turbidity. Level of risk: Moderate
D2.3.3.1 Poor chemical water quality leaving the treatment plant – eg, 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 areas, being mindful of D2.3.1.7 and D2.3.2.1. Turbidity. Aluminium. Iron, manganese. Inspection. Customer complaints. Improve treatment Scour, pig and flush the distribution system. D2.3.3.2 Poor 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 areas, being mindful of D2.3.1.7 and D2.3.2.1. FAC. Microbiological quality. Turbidity. Failure to meet requirements of DWSNZ:2000, especially FAC not maintained. D2.3.3.3 Water flows too low resulting in: decay of chlorine 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. D2.3.3.4 Poor 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). Microbiological quality. Turbidity. Failure to meet requirements of DWSNZ:2000. Review maintenance practices. Change construction and repair materials. Event: DEVELOPMENT OF SEDIMENT OR BIOFILM cont’d
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. Safety Plan Performance Assessment To 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.