Water Safety Plan Guide: Distribution System Post-Treatment Storage

Water Safety Plan Guide Distribution System – Post-treatment Storage Version 1, Ref D1

January 2014 Citation: Ministry of Health. 2014. Water Safety Plan Guide: Distribution System – Post-treatment Storage, Version 1, ref D1. Wellington: Ministry of Health.

Published in January 2014 by the Ministry of Health PO Box 5013, Wellington, New Zealand

ISBN: 978-0-478-42762-2 (print) ISBN: 978-0-478-42763-9 (online)

Previously published in 2001 as Public Health Risk Management Plan Guide: Distribution System – Post-treatment Storage, Version 1, ref D1. 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

4 [Title]

Introduction

Post-treatment storage facilities (service reservoirs) are used in many water supplies to: equalise demands on: water sources treatment plant pumping stations distribution mains maintain uniform pressures in the distribution system provide reserves for emergencies such as: power failure fires equipment failures in the supply.

This Guide is concerned with tanks and reservoirs used for this purpose. These facilities should not alter the quality of the water.

If an event occurs during the storage of treated water (ie, something happens to affect the quality or quantity of water available from the storage facility), the following could happen: If there is not enough water in storage to meet demand, sickness may be caused by poor hygiene and by low pressure allowing germs and chemicals to enter the distribution system. If contamination gets into the tank or reservoir, germs or chemicals can cause sickness. If sediment settles on the bottom of the tank or reservoir, or is stirred up, germs or chemicals in the sediment can cause sickness.

Maintenance of reservoirs can present risks to the health of staff. These are acknowledged, but are not discussed further as such risks are the subject of health and safety in employment legislation. Shortage of water can lead to fire-fighting problems, and hence to the possibility of injury. This is not dealt with in this Guide.

Post-treatment storage and the risks associated with it cannot be viewed in isolation. Having enough storage in the reservoirs depends on: being able to abstract enough water of adequate quality from the source (see P1 series of Guides) the operation of the treatment plant at a rate at which it can treat the water (see Guide P11) the system pumps working (see Guide P10) being able to transfer water from the treatment plant to the storage facility (see Guide P2) the community water demand.

Having water stored of acceptable quality depends on: the quality of the source water (see the S1 and P1 series of Guides)

6 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 the good operation of treatment processes before storage (see the P4, P5, P6, P7 and P8 series of Guides) events that affect the quality of the water once it is in the reservoir: introduction of contaminated material into service reservoirs: access by animals/birds/humans build up of sediment or living organisms (including algal growth) (see Guides S1.1 and P4.1) construction materials dissolving or corroding contaminated water running in from the surroundings or from the roof short-circuiting; disinfection is incomplete because the water does not stay in the reservoir long enough (see P7 series of Guides) regrowth/resuspension of material within service reservoir: biological regrowth or the disturbance of sediment or living organisms post-treatment floc formation.

Ref D1 Water Safety Plan Guide: 7 Version 1, January 2014 Distribution System – Post-Treatment Storage Risk Summary

The events creating the two greatest risks involved in treated water storage are having too little water stored to meet demand (see D1.1), and contamination getting into the reservoir (see D1.2).

The most important preventive measures are: construct another reservoir or tank if having too little water seems like being a continuing problem (see D1.1.3) restrict access to the reservoir to reduce the chances of contamination (see D1.2.1–3) carry out regular inspections for signs of structural deterioration or of contamination having got into the storage (see D1.2.1) make sure the facilities are designed to reduce the chances of contamination getting in, and that the construction materials will not contaminate the water (see D1.2.3–6) make sure there is enough disinfectant in the water to kill germs that get into the water (see D1.2.1–3).

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

8 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 Risk Information Table

Reliable 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: MAV – Maximum acceptable value – see Drinking-Water Standards for New Zealand:2000; NTU – nephelometric turbidity units

Ref D1 Water Safety Plan Guide: 9 Version 1, January 2014 Distribution System – Post-Treatment Storage Causes Preventive measures Checking preventive measures Corrective action

What to check Signs that action is needed

Event: NOT ENOUGH WATER IN POST-TREATMENT STORAGE TO MEET DEMAND Possible 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

D1.1.1 Provide sufficient raw water Pre-treatment storage Raw water storage Plan development of Insufficient storage to cover seasonal variations levels. levels or source new sources. supply of raw in source water availability, periods flows unacceptably Restrict development water. of untreatable raw water quality, low. in distribution area maximum limits on consent for until adequate water abstraction from the source. available. Develop auxiliary sources that can be used when secondary sources cannot meet demand. Refer also to Guide P1 series.

D1.1.2 Design treatment plant to meet Post-treatment Calculate future water Insufficient expected demand for projected life storage levels use and plan actions water treatment of the plant. unacceptably low. to meet likely capacity, or Identify treatment stages that are demand. output limited limiting capacity and undertake Identify problem by one or more modification of these. treatment stage and treatment Ensure appropriate water safety increase throughput if stages not plans are operational for all possible. operating. treatment processes to avoid or limit down time.

D1.1.3 Construct additional storage. Water consumption. Need for water use Water use restrictions. Inadequate Encourage water conservation restrictions. post-treatment during periods when demand is Post-treatment storage likely to be high. storage levels capacity. unacceptably low.

Event: NOT ENOUGH WATER IN POST-TREATMENT STORAGE TO MEET DEMAND cont’d

D1.1.4 Ensure pumps have stand-by Inspection log. Water transmission Re-fuel generators (if Inability to generators. Electricity supply. ceases. necessary). transmit water Routine inspection and Maintenance and Clear blockages/ from source to maintenance of pipelines. inspection not repair pump plant, or plant carried out. breakdowns or pipe to post- failures. treatment storage (including power failure).

D1.1.5 Carry out routine testing of storage Change in storage Change in storage Locate and fix leak. Leakage from for leaks. level. level does not equal the storage water input minus facility. water output (including evaporation).

Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO SERVICE RESERVOIR Possible hazards: Germs, arsenic, copper, chromium, iron, chlorine, aluminium. Level of risk: High1

10 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 Causes Preventive measures Checking preventive measures Corrective action

D1.2.1 For tanks in general: Inspection reports. Unexplained Replace damaged Access by ensure the storage is covered Free available change in water screens, etc. animals/birds. install mesh, grills, vents, etc chlorine (FAC). quality. Isolate tank, undertake regular tank Taste and odour chlorinate and check inspections complaints. the microbiological document condition of Visual evidence of quality. If there is structure, mesh, grills, gross contamination, vents, tank liner (for gaps) entry of animal or bird. dump the water, clean etc and take action. and refill before For wooden tanks: FAC concentration chlorinating. install metal band around less than 0.2 mg/L. wooden tanks to prevent access from ground level remove vegetation near tanks install internal liner for tank roof. Maintain an FAC residual.

1 The level of risk from microbiological contamination is less if a chlorine residual is maintained.

Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO SERVICE RESERVOIR cont’d

D1.2.2 Provide: Regular site Evidence of break- See Contingency Unauthorised locked perimeter fence inspections with ins or damage. Plan. access/ locked access towers and checks on security Unexplained Determine how access vandalism/ ladders measures. change in water was obtained and sabotage. locked hatches on tanks FAC. quality. rectify shortcoming in intruder alarm. Microbiological FAC residual less security. Maintain chlorine residual. quality. than 0.2 mg/L and Isolate tank, cannot be chlorinate and check maintained. the microbiological E. coli or coliforms quality. If there is detected in 100 mL gross contamination, of water. dump the water, clean and refill before chlorinating.

D1.2.3 Train personnel who need access to Microbiological Deterioration of Isolate tank, Human access tanks. quality. water quality chlorinate and check for sampling, Design internal walkways that do Reservoir following operation the microbiological etc. not become submerged with a solid construction. involving tank quality. If there is floor and raised edges to avoid access, in particular gross contamination, shoe scrapings entering the water. E. coli or coliforms dump the water, clean detected in 100 mL and refill before Maintain chlorine residual. of water. chlorinating. Isolation of tank. Procedures for staff entering tanks to clean footwear, then to cover their shoes with clean plastic bags, or to go through a chlorinated foot- bath. Test sampling staff to ensure they are not carriers of water-borne disease, and relieve them of sampling duties if necessary.

D1.2.4 Specify materials certified for Conduct regular Deterioration of Replace sub-standard 2 Leaching/ potable water use in tenders and inspection of tanks. water quality materials. corrosion from check these specifications are being Check residence following new construction met during construction. times. installation. materials. Use accredited contractors. If roof is unlined – Change in water Low residence time of water in copper/ chromium/ quality after rain. tanks (while maintaining arsenic (especially Concentration of disinfection contact time). after heavy rain). copper, chromium or arsenic is more Install roof liners in tanks with Replace lid with more than 50% of its treated timber roofs. suitable material. MAV.

2 See Guide D2.1 regarding approved materials.

12 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 Causes Preventive measures Checking preventive measures Corrective action

D1.2.5 Specify and audit roof design: FAC. Change in water Repair leaky Entry of roof rainwater to drain from (not Microbiological quality following joints/cracks/ hatches drainage. into) tank quality. rain. promptly. restrict access to roof top Installation design. E. coli or coliforms hatches designed to exclude detected in 100 mL water ingress. Annual roof of water. inspection report. Replace badly Flaws in the design designed hatches. of the roof.

D1.2.6 Repair leaks promptly. Microbiological Unexplained Repair leaks. Entry of Inspect tank every 1–5 years quality. change in water Isolate tank, contaminated (depending on the age of the tank Tank inspection quality. chlorinate and check groundwater and risks caused by its location). report. E. coli or coliforms the microbiological (for in-ground detected in 100 mL quality. If there is tanks). of water. gross contamination, dump the water, clean Line the tank with a suitable Leaks identified by and refill before waterproof material. the inspection. chlorinating. Complaints of petrol smell (if near underground fuel tanks).

D1.2.7 Ensure there are screens on the Regular screen Taste and odour Replace and clean Animal entry source outlet. inspection. complaints. screens. from upstream Microbiological E. coli or coliforms Isolate tank, source (animals quality. detected in 100 mL chlorinate and check trapped and Turbidity. of water. the microbiological destroyed by Turbidity more than quality. If there is action of 0.2 NTU. gross contamination, control valves) dump the water, clean – where the and refill before tank is filled chlorinating. directly from the source.

D1.2.8 Train staff in calculation of dose Treatment chemicals. Elevated turbidity/ See Contingency Chemical rates and in the use of methods for Turbidity. treatment chemical Plan. contamination optimising treatment plant concentration post- from incorrect operation. treatment. chemical Document treatment plant dosing Absence of written dosing. procedures (especially calculations descriptions of of type and quantity of materials dosing procedures. used), and those for the reservoir if Turbidity more than it is dosed. 0.2 NTU.

D1.2.9 Ensure that there is an airgap or Microbiological Change in water Disconnect any direct Backflow from other suitable backflow prevention quality. quality after rain connections. drains. device between tank overflow and Turbidity. events. Isolate tank, dump the sewer or stormwater drains. Overflow Turbidity more than water, clean, construction. 0.2 NTU. chlorinate and check E. coli or coliforms the microbiological detected in 100 mL quality before of water. refilling.

Event: DEVELOPMENT, OR RE-SUSPENSION, OF SEDIMENT WITHIN TANK OR RESERVOIR Possible hazards: Germs; manganese, disinfection by-products (trihalomethanes, haloacetic acids, chloral hydrate). Level of risk: Low–moderate

D1.3.1 Avoidance of rapid drain/fill. FAC. Visible slime/ Review cleaning Sediment/ Undertake regular cleaning of Microbiological sediment. procedures and plant slime reservoirs (every 1–5 years quality. Customers operation. accumulation depending on the quality of the Turbidity. complain of slime/ Isolate tank, and release. source water, flow through and sediment. chlorinate and check Manganese. degree of stagnation in the tank FAC residual the microbiological etc). Audit cleaning concentration less quality. If there is Cleaning procedures need to procedures and than 0.2 mg/L. gross contamination, operation. dump the water, clean consider disinfection of all E. coli or coliforms equipment, satisfactory training and refill before detected in 100 ml chlorinating. procedures, preferably isolation of water. during cleaning, minimisation of sediment stir-up if online during Turbidity more than cleaning. 0.2 NTU. Maintain chlorine residual. Minimise conditions leading to post-treatment floc formation.

Event: CHLORINE CONTACT TIME TOO SHORT Possible hazards: Germs not killed. Level of risk: High

D1.4.1 Check calculations of tank Flow rates (measured E. coli or coliforms Increase size of tank. Storage tank hydraulics and the hydraulic profile through tank). detected in 100 mL too small. of the network before construction; Microbiological of water despite make use of hydraulic models if quality. adequate FAC necessary. residual Installation design. concentration. Check residence Unexplained times. fluctuations in water quality.

Event: CHLORINE CONTACT TIME TOO SHORT (cont’d)

D1.4.2 Specify and audit suitable tank Flow rates (measured E. coli or coliforms Operate the tank to Short- design to include: through tank). detected in 100 mL force turnover circuiting. baffles Microbiological of water despite (deliberately run up fill at the top and empty from quality. adequate FAC and down). the bottom. residual Installation design. If necessary, redesign the concentration. inlet/outlet or install baffles. Check residence Unexplained times. fluctuations in water quality.

14 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 Contingency Plans

If 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 – Breach of the post-treatment storage tank/reservoir

Indicators: Visual inspection shows evidence of structural deterioration or a leak. Water levels cannot be maintained despite water being pumped into storage at an adequate rate.

Required Identify the location of the leak, and repair. actions: Bypass the tank/reservoir and take water directly from the treatment plant. If the normal water source does not meet the needs of the community or treatment plant capacity (ie, the quantity is too low at that time of year): investigate and obtain alternative source(s) of water implement water use restrictions. Repair the storage tank/reservoir if a leak is the cause of the shortage. Record cause of system failure and steps taken to correct. Modify water safety plan if necessary.

Responsibility: Manager designated responsible for the water supply.

Event – Germs detected in the stored water

Indicators: A detectable chlorine residual cannot be obtained in the water leaving the reservoir. In 100 ml samples of water from the reservoir, E. coli or coliforms are continually detectable, or E. coli is present at elevated levels (more than 10 per 100 mL). Widespread levels of illness in the community. Knowledge of sabotage or vandalism.

Required Follow the actions given in Figure 3.3 of the DWSNZ:2000. In actions: consultation with the MOH, consider dumping the stored water, even though indicators are clear, if there have been high levels of microbiological contamination. Record cause of system failure and steps taken to correct. Modify water safety plan if necessary.

Ref D1 Water Safety Plan Guide: 15 Version 1, January 2014 Distribution System – Post-Treatment Storage Event – High levels of chemical contaminants in the stored water

Indicators: Knowledge of a major chemical spill, or chemical overdose (eg, chlorine), into the reservoir; sabotage or vandalism. Change in the appearance, smell or taste of the water. Widespread levels of illness in the community. Chlorine residual not restored.

Required Close down the reservoir, and if necessary the supply. Provide another actions: source of potable water until water of acceptable quality can again be supplied. Inform the MOH of the situation. Identify the source of contamination and take steps to avoid recontamination. Dump the reservoir water. Consultation with the regional council will probably be required with regard to disposal of the flushed water. Flush the reticulation system and monitor water quality until determinand concentrations are again less than 50% of the MAV. Warn consumers to thoroughly flush their taps before drawing water for use. Record cause of system failure and steps taken to correct. Modify water safety plan if necessary.

16 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014 Water 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 Inspection and sampling of service reservoirs. or observe: E. coli and coliforms Turbidity Chemical Priority 2 determinands (if any exist) FAC. Follow the protocols set out in DWSNZ:2000.

How often: For the monitoring frequencies for E. coli, turbidity and FAC measurements see DWSNZ:2000 Section 3.3.2. For chemical determinands see DWSNZ:2000 Table 4.1. Other regular inspection and sampling should include, but not be limited to, the following: evidence of human or animal access assessment of security evidence of cracks or holes that may allow contaminants to enter appearance and odour of the water. The frequency will be site-dependent and should be based on previous findings.

Ref D1 Water Safety Plan Guide: 17 Version 1, January 2014 Distribution System – Post-Treatment Storage What to do with Results need to be recorded to meet legislative requirements or to the results: 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 this review show 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 service reservoirs. 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 the operation of post-treatment storage are recognised in the plan.

18 Water Safety Plan Guide: Ref D1 Distribution System – Post-Treatment Storage Version 1, January 2014