Water Safety Plan Guide: Surface Water Abstraction – … · Web viewRef P1.2Water Safety Plan Guide:iv Version 1, June 2001 Surface Water Abstraction – Lakes and Reservoirs 12Water

Water Safety Plan Guide

Surface Water Abstraction –Lakes and Reservoirs

Version 1, Ref P1.2

January 2014

Citation: Ministry of Health. 2014. Water Safety Plan Guide: Surface Water Abstraction – Lakes and Reservoirs, Version

1, ref p1.2. Wellington: Ministry of Health.

Published in January 2014 by the Ministry of Health

PO Box 5013, Wellington, New Zealand

ISBN: 978-0-478-42706-6 (print)ISBN: 978-0-478-42707-3 (online)

Previously published in 2001 as Public Health Risk Management Plan Guide: Surface Water Abstraction – Lakes and Reservoirs, Version 1, ref p1.2. This publication’s title

and any reference within the text to ‘public health risk management plan’ was 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 Assessment

Ref P1.2 Water Safety Plan Guide: ivVersion 1, June 2001Surface Water Abstraction – Lakes and Reservoirs

Ref P1.2 Water Safety Plan Guide: vVersion 1, January 2014Surface Water Abstraction – Lakes and Reservoirs

IntroductionSource water abstraction is the process of taking water from the source to pipe to the treatment plant or pre-treatment storage. This Guide is concerned with the abstraction of water from static surface waters (lakes and reservoirs).

If an event related to abstraction occurs (ie, the quantity or quality of water is affected by the abstraction process), the following could happen: If there is not enough source water available to meet demand,

sickness can be caused by poor hygiene and by low pressure letting germs and chemicals get into the distribution system

If the water quality is so poor that the treatment plant can’t treat it, germs and disinfection by-products can cause sickness

If there is contamination of the lake or reservoir, germs and chemicals can cause sickness

If a problem with the intake does not allow enough water to be drawn from the source, sickness can be caused by poor hygiene and by low pressure letting germs and chemicals get into the distribution system.

Source water abstraction can present risks to the health and safety of the operators. These are acknowledged, but are not discussed further as such risks are the subject of health and safety in employment legislation.

When planning to draw water from a source you need to be aware of the requirements of: the Resource Management Act specific requirements of local authorities and regional councils.

Drawing water from the source, and the risks associated with it, cannot be viewed in isolation; the process influences, and is influenced by, other water supply elements: Which abstraction method is best for your situation will depend on

the availability and quality of the source water (see Guide S1.1):– drawing from a lake or reservoir is helpful if the water flow is

low, intermittent, or unlikely to meet demand under all conditions

– the use of lakes or reservoirs may make contamination from algal blooms more likely than use of flowing waters (see Guide P4.1)

– the development of layers of water near the bottom of lakes or reservoirs that are short of oxygen (anoxic) will influence the design of the intake (see Guide P4.2).

Ref P1.2 Water Safety Plan Guide: 1Version 1, January 2014Surface Water Abstraction – Lakes and Reservoirs

Which treatment processes are used to treat the water can be affected by the abstraction method chosen:– clarification/sedimentation may not be required if

impoundment can reduce the turbidity of the raw water, and limit its variability (see P5 series Guides)

– filtration processes that need relatively good quality feed water can be considered if the water can be improved by the abstraction method (see P6 series Guides)

– the effectiveness of disinfection is improved if the abstraction method can help reduce turbidity and colour (see P7 series Guides).

2 Water Safey Plan Guide: Ref P1.2Surface Water Abstraction – Lakes and Reservoirs Version 1,

January 2014

Risk SummaryThe events creating the two greatest risks involved in abstracting water from the source are not being able to draw enough water (see P1.2.1), and drawing water that cannot be properly treated because the quality is too poor (see P1.2.2).

The most important preventive measures are: make a plan to control the amounts of water that can be safely

drawn from the lake/ reservoir and the levels they are to be drawn from under certain conditions and obtain the necessary Resource Consents (see P1.2.1.1)

put an alarm on the flow from the intake to warn of an intake failure (see P1.2.1.4–4)

destratify the lake/reservoir to stop lower water levels becoming short of oxygen (see P1.2.2.2)

use multiple depth intakes to adjust the water quality apply algicide to the lake/reservoir early enough to stop algal

blooms (if this problem is know to happen) (see P1.2.2.2).

(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: NOT ENOUGH SOURCE WATER AVAILABLE FOR ABSTRACTIONHazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene.Level of risk: High

P1.2.1.1Drought.

Start water conservation measures as soon as water shortage becomes likely.

Plan the development and use of the water source, and the need to identify and develop new sources, based on the lake/ reservoir’s safe yield and drought probability.

Water demand.

Source usage rate.

System pressure.

Drop in system pressure.

Customer complaints about low pressure.

Prepare new resource consent application.

Find new sources.

Increase storage capacity.

Partially close valves through the network to equalise pressures.

P1.2.1.2Resource consent limitations.

Negotiate new resource consents or emergency provisions.

Water demand.

Source usage rate.

System pressure.

Drop in system pressure.

Customer complaints about low pressure.

Find new sources.

Increase storage capacity.


January 2014



Event: RAW WATER QUALITY TOO POOR TO TREATPossible hazards: Germs and chemical determinands particularly disinfection by-products (trihalomethanes, haloacetic acids, chloral hydrate).Level of risk: High1

P1.2.2.1Heavy rain leading to high levels of turbidity and organic matter in water entering the plant.

Take steps to allow close down of intake when necessary:– establish levels of

raw water quality that the plant cannot treat

– automatic measurement of raw water turbidity and telemetric warning

– use regional council upstream river levels as an early warning system

– manage treated reservoir levels to maximise period intake can be shut down

Raw water quality (to determine when quality is approaching the limits of the plant’s treatment capabilities).

River levels. Storm

warnings.

Non-compliance with DWSNZ: 2000, particularly turbidity, particle counts, and E. coli.

Increased filter backwash frequency.

Unable to achieve effective chemical coagulation.

Difficulty in achieving free residual chlorine in treated water.

Review alternative source options.

Review pre-treatment options.

Slow the rate of treatment.

Optimise application of coagulant chemicals and chlorine.

– install multi-level intakes.

Turn off treatment. Inspect catchment

for signs of erosion and slips that will potentially be ongoing problems.

Choose best abstraction depth.




P1.2.2.2High algal content.

Adjust intake or change offtake to approximately2–3 metres below surface.

Surveillance of water quality and temperature as warning of the need to destratify(see Guide P4.2) the water body or apply algicide (see Guide P4.1) before a bloom develops.

Algal content. Water

temperature. Colour and

development of scum in raw water.

As for P1.2.2.1.

Taste and odour problems.

Increased chlorine demand.

High algal counts.

Modify intake system.

Improve surveillance procedure.

Activated carbon dosing system available.

Ensure adequate contact time with chlorine/ ozone to destroy algal toxins.

Instigate destratification if appropriate.

Carry out algicide application, if appropriate.

1 Treatment plants are usually designed to be able to treat raw waters with a range of turbidity and colour (see Guide P11). From time to time the raw water quality may exceed these limits, and the treated water quality may not meet that required by DWSNZ.


January 2014



Event: RAW WATER QUALITY TOO POOR TO TREAT cont’d

P1.2.2.3Seasonal turnovers typical of deep lakes and reservoirs.

Plan for managing seasonal turnover of water typically November/December and April/May by:– carrying out

destratification of reservoir (see Guide P4.2)

– slowing treatment plant rate

– placing emphasis on using stored treated water

– determining whether different coagulants are necessary for changed water quality

– planning supplementary treatment eg, potassium permanganate dosing (see Guide P4.3).

Temperature at various depths (indicating turnover).

Dissolved oxygen concentration with depth.

As for P1.2.2.1.

Iron and or manganese staining on washing and/or sloughing from distribution pipes.

Increased chlorine demand.

Improve surveillance procedure to give better warning of stratification.

Use of additional treatment processes (eg, pre-oxidation, algicide application, activated carbon).

P1.2.2.4Water level too low so forced to take poorly oxygenated water.

Plan for this problem by:– changing intake

to lower level earlier than required to draw oxygenated water into lower depths (precipitation and settling of iron and manganese).

– carrying out aeration of reservoir (see Guide P4.2).

Water level. As for P1.2.2.1.

Review effectiveness of procedures.

Review destratification system management.




Event: CONTAMINATION OF THE LAKE OR RESERVOIRPossible hazards: Germs and chemical determinands appropriate to contamination sources.Level of risk: Moderate2

P1.2.3.1Contamination sources (eg, stock, septic tanks, chemical sources) in the catchment of lake/reservoir or the river catchment.

Identify potential sources of contamination when abstraction site is being selected (see Guide S1.1).

Ensure that changes in land use (including urban developments) and the potential for contamination they create, are well monitored after commissioning of the source.

Restrict activities in the catchment that may contaminate the water (see Guide S1.1).

Gather information about the hydrology of the catchment before undertaking development.

Microbiological quality.

Chemical determinands appropriate for likely contamination source.

No survey of potential sources of contamination undertaken.

No hydrological information gathered.

No system for obtaining information about changing land use in place.

High E. coli counts in raw water.

Add treatment processes to remove identified contaminants.

Instigate system for gathering information about land use changes.

Review procedures for restricting access, and change as necessary.

P1.2.3.2Human or boat contamination in intake area.

Zone the area and restrict access by signage and physical barriers.

Publicise public health issues in local boating literature.

Physical inspection.

Microbiological quality.

Chemical determinands arising from recreational activities, if necessary (eg, aromatics and their derivatives from fuel).

High E. coli counts in raw water.

Observation of public use of zone.

Review procedures for exclusion zone, and change as necessary.

2 The consequences of the event, and therefore the level of risk, will be influenced by the nature of the contaminants and whether any treatment processes in use are capable of removing the contaminants.


January 2014



Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMANDPossible hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene).Level of risk: High3

P1.2.4.1Screens damaged or clogged.

Regular inspection and cleaning of screens, intensified during times of flood.

Limit nutrient input into the raw water to reduce clogging by algae and weed under low-flow conditions.

Particularly for a lake accessible to the public, restrict access by zoning, signage, physical barriers.

Booms and screens to trap weed/algae.

Treatment plant flow meters.

Reduced flow. No records of

inspection and cleaning programme.

Modify intake to protect against damage, and reduce likelihood of clogging.

Implement plan to reduce nutrient input into source.

P1.2.4.2Failure of the intake structure due to mechanical or structural failure.

Regular preventive maintenance, as required by the conditions, and manufacturers’ specifications: lubrication, component replacement, exercise valves.

Regular inspections of intake.

Telemetric alarm for low flows from intake.

Flows (from intake).

Inspection records.

Preventive maintenance log.

Failure of significant componentry.

No record of maintenance programme.

No water. Alarm

activated.

Review maintenance and inspection schedule.

P1.2.4.3Catastrophic failure (eg, flood, slips or earthquake-related damage).

Intake inspections, regularly and directly after floods etc., with follow-up action if required for existing protection (eg, fences, vegetation and soil instability).

Telemetric alarm for low flows from intake.

Flood levels. Flows (from

intake). Inspection

records.

No water. Reduced flow. Alarm

activated.




P1.2.4.4Pump failure (see also Guide P10).

Maintenance according to manufacturers’ recommendations.

Standby pump with auto switch to alternate pumps.

Operate duty and standby pumps using an alternate ‘number of days cycle’.

Telemetric alarm for low flows.

Telemetric records.

No water. No record of

maintenance programme.

Alarm activated.

New pumps.

3 The level of risk will probably increase the lower the flow of the water is.Causes Preventive measures Checking preventive measures Corrective

actionWhat to check Signs that

action is needed

Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMAND cont’d

P1.2.4.5Power failure.

Regular inspection of cabling, power lines and connectors.

Stand-by generator. Battery backed-up

alarms.

No water. Alarm

activated.

Consult with power supply authority.

P1.2.4.6Vandalism/ sabotage.

Construct a fence around the intake site.

Install intruder alarm.

Damage to the intake.

Evidence of attempts to gain access to the intake.


January 2014

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 – Water quality too poor to treat

Indicators: Water too turbid or too coloured to treat. Turbidity of water leaving plant consistently

greater than 0.2 NTU‡ (See DWSNZ:2000).

Required actions:

Consider whether to cease abstraction and switch to an alternative source of potable water until water of acceptable quality can again be supplied, or to use storage. (Make sure that the history of any tanker used to cart water has been investigated before it is used and that the tanker will not contaminate the water.)

If inadequately-filtered water has entered the reticulation, inform the MOH.

Monitor particle counts, turbidity or colour levels until they reach acceptable limits.

Increase chlorine residual as an interim measure.

Restart plant operation, perhaps at a slower rate.

If very poor raw water quality is likely to be a frequent problem, consider an alternative source, or changes to abstraction method or treatment.

Record cause of failure and corrective steps taken.

Plan and develop long term countermeasures if needed.

Modify water safety plan (formerly known as a public health risk management plan, PHRMP) if necessary.

Responsibility: Manager designated responsible for water supplies.


Event – Not enough water reaching the treatment plant

Indicators: Reduced, or no, flow reaching the treatment plant.

Unexpectedly high usage. Structural failure of intake, or pump failure.

Required actions:

Implement the water supplier’s emergency demand management strategy.

Consider whether to switch to an alternative source of water until adequate water of acceptable quality can again be supplied, or to use storage. (Make sure that the history of any tanker used to cart water has been investigated before it is used and that the tanker will not contaminate the water.)

If inadequately-filtered water has entered the reticulation, inform MOH of the transgression.

Put conservation measures in place. Close valves at reservoirs to restrict supply if

necessary. Increase chlorine residual as an interim

measure. If appropriate, identify intake problem and

rectify. When restarting the treatment plant, consider

doing this at a slower rate. Record cause of failure and corrective steps

taken. If shortages occur frequently because of too

little water available at the source, plan for finding and developing a new source.

Modify water safety plan if necessary.

Responsibility: Manager designated responsible for water supplies.


January 2014

Event – Contamination enters the lake or reservoir

Indicators: Complaints of discoloured, tasting or smelling water coming from taps.

Continued contamination of water supply: E coli detected or Priority 2 chemical concentrations more than 50% of MAV.

Reports of illness in parts of the community that may be linked to water quality.

Required actions:

Close intake. Notify the MOH, and in consultation warn

consumers in the affected area of alternative water supply measures until further notice.

Identify the source of the contamination, and determine whether it is likely to be a transient problem and whether temporary treatment is available.

If problem is transient:– drain and flush the affected part of the

distribution system, considering the need to flush with elevated chlorine concentrations if the incident may have involved microbiological contaminants (consultation with the regional council will probably be required with regard to disposal of the flushed water)

– monitor an appropriate determinand in the affected area to determine the success of the contingency measures, and notify consumers, when the supply is safe to use, that they will need to flush their taps until good quality water can again be drawn.

If problem is likely to be long-lasting or permanent:– investigate and develop an alternative

supply and/or treatment– provide another source of potable water

until water of acceptable quality can again be supplied.

Record cause of system failure and steps taken to correct.

Modify water safety plan if necessary.


Responsibility: Manager designated responsible for the water supply.

‡ Nephelometric turbidity units.


January 2014

Water Safety Plan Performance AssessmentTo make sure that your supply’s water safety plan 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:

Flow records. Turbidity. State of intake.

How often: Regular inspection of intake and records (frequency will be site-dependent and should be based on previous findings). The inspection should include, but not be limited to, the following:– after natural or high-risk events– chemical and microbiological analysis

results– inspection reports.

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 provides a useful tool for this purpose.

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 the abstraction of water.

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 abstraction system are recognised in the plan.

Responsibility: Manager designated responsible for the water supply.


January 2014

Documents

Water Safety Plan Guide: Surface Water Abstraction – … · Web viewRef P1.2Water Safety Plan Guide:iv Version 1, June 2001 Surface Water Abstraction – Lakes and Reservoirs 12Water