Water Safety Plan Guide Surface Water Abstraction Rivers, Streams and Infiltration Galleries Version 1, Ref P1.1

Transcription

1 Water Safety Plan Guide Surface Water Abstraction Rivers, Streams and Infiltration Galleries Version 1, Ref P1.1 January 2014

2 Citation: Ministry of Health Water Safety Plan Guide: Surface Water Abstraction Rivers, Streams and Infiltration Galleries, Version 1, ref p1.1. Wellington: Ministry of Health. Published in January 2014 by the Ministry of Health PO Box 5013, Wellington, New Zealand ISBN: (print) ISBN: (online) Previously published in 2001 as Public Health Risk Management Plan Guide: Surface Water Abstraction Rivers, Streams and Infiltration Galleries, Version 1, ref p1.1. 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:

3 Contents Introduction 1 Risk Summary 3 Risk Information Table 4 Contingency Plans 10 Water Safety Plan Performance Assessment 13 Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: iii

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5 Introduction Source 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 flowing surface waters (rivers, streams) including the use of infiltration galleries. 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 the treatment plant can t treat it, germs and disinfection by-products can cause sickness If there is contamination of the river or stream, germs and chemicals can cause sickness If the water quality is not improved enough by the infiltration gallery, germs and disinfection by-products can cause sickness If a problem with the intake, or infiltration gallery, 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): impoundment may be considered if the water flow is low, intermittent, or unlikely to meet demand under all conditions an infiltration gallery or bankside storage can be used to improve poor raw water quality, and reduce variability in quality. Which treatment processes are used to treat the water can be affected by the abstraction method chosen: clarification/sedimentation may not be required if an infiltration gallery can reduce the colour and turbidity of the raw water, and limit their variability (see P5 series Guides) Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 1

6 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 Safety Plan Guide: Ref P1.1, Version 1, January 2014

7 Risk Summary The events creating the two greatest risks involved in abstracting water from the source are not being able to draw enough water (see P1.1.4, P1.1.5), and drawing water that cannot be properly treated because the quality is too poor (see P1.1.3). The most important preventive measures are: regularly inspect the intake for damage or clogging (see P , P ) put an alarm on the flow from the intake to warn of an intake failure (see P ) use an abstraction method that reduces water quality variability so periods of very poor quality are avoided (see P ). (References in parentheses are to the Risk Information Table.) Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 3

8 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: 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 ABSTRACTION Hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene. Level of risk: High P Drought. 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 river/stream s safe yield. 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. P Resource 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. 4 Water Safety Plan Guide: Ref P1.1, Version 1, January 2014

9 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: RAW WATER QUALITY TOO POOR TO TREAT Possible hazards: Germs and chemical determinands particularly disinfection by-products (trihalomethanes, haloacetic acids, chloral hydrate). Level of risk: High 1 P Heavy rain leading to high levels of turbidity and organic matter in water entering the plant. Stabilise raw water quality (using, eg, infiltration gallery or raw water reservoir) to avoid periods of very poor quality. Take steps to allow close down of intake when river conditions are such that water cannot be adequately treated: 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 pretreatment options. Slow the rate of treatment. Optimise application of coagulant chemicals and chlorine. Turn off treatment. Inspect catchment for signs of erosion and slips that will potentially be ongoing problems. 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. Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 5

10 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATION OF THE RIVER OR STREAM Possible hazards: Germs and chemical determinands appropriate to contamination sources. Level of risk: Moderate 2 P Contamination sources (eg, stock access to river, septic tanks, chemical sources) present in the 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 to gather information about land use changes. Event: WATER QUALITY NOT IMPROVED BY INFILTRATION GALLERY Possible hazards: Germs and, if water is coloured, disinfection by-products (trihalomethanes, haloacetic acids, chloral hydrate). Level of risk: Low high 3 P Sediment load in raw water too high. Establish levels of raw water quality that the gallery cannot handle, and turn the gallery pumps off when these are exceeded. Water quality before and after the gallery: turbidity and suspended solids. Turbidity exceeds gallery design guidelines and treatment capability. Review gallery design. Clean gravel packs with compressed air lances. Slow abstraction rate to reduce filtration velocities through the gravel packs. 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. 3 The main consideration is to match the gallery design to the raw water quality. 6 Water Safety Plan Guide: Ref P1.1, Version 1, January 2014

11 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: WATER QUALITY NOT IMPROVED BY INFILTRATION GALLERY (cont d) P Poor infiltration gallery design. Take account of the range of possible raw water qualities when designing the gallery. Water quality before and after the gallery: turbidity and suspended solids. Insufficient difference between turbidities of raw water and gallery outlet. Review gallery design and modify if necessary. Consider alternative abstraction/ pre-treatment system. Slow abstraction rate to reduce filtration velocities through the gravel packs. Clean gravel packs with compressed air lances. Event: INFILTRATION GALLERY PRODUCES LESS WATER THAN IT WAS DESIGNED TO Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene. Level of risk: Low high 4 P Clogged gravel packs in the infiltration gallery. Turn off the gallery under extreme conditions to minimise drawing sediment deep into the gravel packs. Regular programme to scarify gravel pack with tractor mounted unit. (NB: If gallery is in the stream bed a resource consent will be required.) Regular programme of cleaning gravel packs using compressed air lances. Flows. Regular checks on raw water quality. Reduction in flow. Abstraction pump cavitation. Staining in stream bed gravels. Determinands of concern found in gallery filtered water. Scarify the gravel packs, or clean with compressed air lances. P Gravel packs and/or screen slots calcified or clogged with oxidised iron or manganese. Regular programme of cleaning gravel packs using compressed air lances Use raw water quality data when planning the abstraction process to help decide whether a gallery is appropriate given the quality of water. In the raw water: determinands to calculate the Langelier Saturation Index (hardness, ph, alkalinity) iron and manganese turbidity/ suspended solids. Langelier Saturation Index is zero or positive. Elevated levels of iron and manganese. Review extent of problem and consider alternative pretreatment options. Scarify the gravel packs, or clean with compressed air lances. 4 The high level of risk results when there is a severe lack of water. High sediment floods can cause problems for a gallery because packed gravel beds become blocked. Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 7

12 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: INFILTRATION GALLERY PRODUCES LESS WATER THAN IT WAS DESIGNED TO (cont d) P Gallery clogged by tree roots. Avoid planting trees near the gallery. Remove trees already present, and determine appropriate method for killing roots. Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMAND Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated with poor hygiene). Level of risk: High 5 P Screens 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. Booms and screens to trap weed/algae. State of intakes. Treatment plant flow meters. Algal counts in river. Reduced flow. Elevated algal count. Modify intake to protect against damage, and reduce likelihood of clogging. Implement plan to reduce nutrient input into source. P Failure of the intake due to mechanical or structural failure. Regular preventive maintenance, as required by the conditions, and manufacturers specifications: lubrication, component replacement, exercise valves. Flows (from intake). Inspection records. Preventive maintenance log. Failure of significant componentry. No water. Alarm activated. Review maintenance and inspection schedule. Regular inspections of intake. Telemetric alarm for low flows from the intake. P Catastrophic failure (eg, flood, slips or earthquakerelated damage). Intake inspections, regularly and directly after floods etc, with follow-up action if required for existing protection (eg, gabions, piling, screens and grates, etc). Telemetric alarm for low flows from the intake. Flood levels. Flows (from intake). Inspection records. No water. Reduced flow. Alarm activated. Consider alternative source. Review the options for bankside storage. Evaluate existing protection system. 5 The level of risk will probably increase the lower the flow of the water is. 8 Water Safety Plan Guide: Ref P1.1, Version 1, January 2014

13 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMAND (cont d) P Pump failure (see also Guide P10). Maintenance according to manufacturers recommendations. Standby pump with auto-switch to alternate pumps. Telemetric records Maintenance records. No water. Alarm activated. No maintenance record. New pumps. Instigate maintenance programme. Operate duty and standby pumps using an alternate number of days cycle. Telemetric alarm for low flows. P Power failure. P Vandalism/ sabotage. Regular inspection of cabling, power lines and connectors. Stand-by generator. Battery backed-up alarms. Construct a fence around the intake site. Install intruder alarm. No water. Consult with power authority. Obtain stand-by generator. Damage to the intake. Evidence of attempts to gain access to the intake. Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 9

14 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 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 counter-measures 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. 10 Water Safety Plan Guide: Ref P1.1, Version 1, January 2014

15 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. Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 11

16 Event Contamination enters the river or stream Indicators: Complaints of discoloured, tasting or smelling water coming from taps. Required actions: Close intake. 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. Notify the MOH, and in consultation warn consumers in the affected area not to draw water 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 an 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. 12 Water Safety Plan Guide: Ref P1.1, Version 1, January 2014

17 Water Safety Plan Performance Assessment To 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. Ref P1.1, Version 1, January 2014 Water Safety Plan Guide: 13