Water Safety Plan Guide Groundwater Abstraction Bores and Wells Version 1, Ref P1.3

Transcription

1 Water Safety Plan Guide Groundwater Abstraction Bores and Wells Version 1, Ref P1.3 January 2014

2 Citation: Ministry of Health Water Safety Plan Guide: Groundwater Abstraction Bores and Wells, Version 1, ref p1.3. Wellington: Ministry of Health. Published in January 2014 by Ministry of Health PO Box 5013, Wellington, New Zealand ISBN: (print) ISBN: (online) Previously published in 2001 as Public Health Risk Management Plan Guide: Groundwater Abstraction Bores and Wells, Version 1, ref p1.3. 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 12 Ref P1.3 Water Safety Plan Guide: iii Version 1, January 2014 Groundwater Abstraction Bores and Wells

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5 Introduction Source water abstraction is the process of taking water from the source for transmission to the treatment plant or pre-treatment storage. This Guide is concerned with the abstraction of groundwater from bores or wells. If an event occurs during abstraction (ie, the quantity or quality of water is affected during 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 enabling germs and chemicals to get into the distribution system If there is contamination of the bore or well during construction, germs and chemicals can cause sickness If contamination gets into the bore or well from shallower depths, germs and chemicals can cause sickness If contamination gets into the bore or well from the surface, germs and chemicals can cause sickness If contamination gets into the aquifer, germs and chemicals can cause sickness If a problem with the bore/wellhead does not allow enough water to be drawn from the aquifer, sickness can be caused by poor hygiene and by low pressure letting germs and chemicals get into the distribution system. Activities during the operation and construction of bores may 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. When constructing a bore or well you need to be aware of the requirements of: the Resource Management Act specific requirements of local authorities and regional councils the New Zealand Drilling Standard the information on well head construction given in Chapter 3.4 of Guidelines for Drinking-Water Quality Management for New Zealand Ministry of Health 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: Land use and activities carried out in the area where water enters the aquifer may affect the quality of the water being abstracted (see Guide S1.1) The quality of the groundwater will influence the treatment it requires (see P5, P6, P7, and P8 series of Guides). Several factors influence the likelihood of groundwater contamination: how close local pollution sources are: septic tanks or other waste disposal systems chemical or fertiliser stores Ref P1.3 Water Safety Plan Guide: 1 Version 1, January 2014 Groundwater Abstraction Bores and Wells

6 refuse dumps underground fuel tanks how easily the groundwater can be contaminated (influenced by, for example): water table abstraction depth confining layers hydraulic conductivity soil characteristics rainfall use of irrigation contamination of the aquifer due to: back-siphoning a poor seal between the casing and the ground cracks in the wellhead or casing. The risk to groundwater quality therefore depends on the quality of the water in the aquifer and the design, construction and operation of the bore or well. 2 Water Safety Plan Guide: Ref P1.3 Groundwater Abstraction Bores and Wells 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 P1.3.1), and contaminated water getting into the aquifer or the bore/well (see P ). The most important preventive measures are: take steps to conserve water when a water shortage looks likely (see P ) draw water from a secure aquifer if possible (one in which the water quality is not affected by water from the surface) (see P ) construct the bore/well head so that contamination cannot get in (see P ) install a device on the bore pump to stop backflow into the aquifer (see P ) restrict activities in the aquifer recharge zone that might contaminate the water (see P ). (References in parentheses are to the Risk Information Table.) Ref P1.3 Water Safety Plan Guide: 3 Version 1, January 2014 Groundwater Abstraction Bores and Wells

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; MAV Maximum acceptable value see DWSNZ; NZDS New Zealand Drilling Standard. 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 safe yield of the bore/well. 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 and sink more bores/wells. Water demand. Source usage rate. System pressure. Drop in system pressure. Customer complaints about low pressure. Find new sources. Increase storage capacity. Event: CONTAMINATION OF BORE/WELL DURING CONSTRUCTION Possible hazards: Germs and chemical determinands (eg, barium). Level of risk: Low P Crosscontamination by drilling equipment. Ensure that drills are cleaned and disinfected before drilling starts. Follow requirements of the NZDS. Development of nuisance organisms such as iron bacteria. Evidence of NZDS not having been followed. Disinfect bore/well. Flush bore/ well. Use a different contractor. 4 Water Safety Plan Guide: Ref P1.3 Groundwater Abstraction Bores and Wells Version 1, January 2014

9 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATION OF BORE/WELL DURING CONSTRUCTION cont d P Residual substances used in drilling releasing health significant determinands (eg, barium from baryte). Follow requirements of the NZDS. Ensure the bore is well flushed before being put into use. Healthsignificant determinands used in drilling. Concentrations of chemical determinands more than 50% of their MAV. Evidence of NZDS not having been followed. Flush well/bore until chemical determinand concentrations less than 50% of their MAVs. Flushing not undertaken. Event: CONTAMINATED WATER GETTING INTO THE BORE/WELL FROM SHALLOWER DEPTHS Possible hazards: Germs and chemical determinands (eg, manganese, nitrate). Level of risk: High P Poor joints, cracks or corrosion, in the bore casing. Select appropriate casing material from knowledge of the water chemistry. Ensure bore construction follows the NZDS. Microbiological quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). High E. coli counts. Evidence of NZDS not having been followed. Inappropriate casing material selected. Withdraw casing and replace or repair. No system for backflow prevention. P Drawdown bringing contaminants from shallower regions of the aquifer. Carry out initial aquifer tests to determine a rate at which water can be abstracted without excessive drawdown. Microbiological quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). High E. coli counts. Evidence of NZDS not having been followed. Inappropriate casing material selected. Implement conservation measures and reduce pumping rate. No system for backflow prevention. Ref P1.3 Water Safety Plan Guide: 5 Version 1, January 2014 Groundwater Abstraction Bores and Wells

10 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATED WATER GETTING INTO THE BORE/WELL FROM THE SURFACE Possible hazards: Germs and chemical determinands appropriate to contamination sources. Level of risk: High P Inappropriate bore/well head design, or poor construction. Ensure bore construction follows the NZDS with particular emphasis on the following: the cement sanitary seal is watertight or is raised 0.5 m above 100-year flood level, and extends at least 3 m down the casing air vent openings are screened, facing downwards and are 0.5 m above 100 year flood level bore/well head is surrounded by a cement apron (at least 2 m in diameter) sloping away from the head. Microbiological quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). Inspection of bore/well head shows noncompliance with NZDS. Make necessary changes to bore/well head to meet NZDS requirements. Ensure well tops are properly sealed. Ensure pumps are sealed or situated so that wastewater cannot re-enter the well. P Bore/well head or casing damaged. Provide protection for the bore/well head against stock and human damage. Carry out regular visual checks for damage. Microbiological quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). Inspection of bore/well head shows noncompliance with NZDS. Repair bore/ well head. Remove casing and replace or repair. P Contamination sources (eg, stock) too close to the bore/well head. Identify potential sources of contamination when well is being sited (see Guide S1.1). Ensure that changes in land use (including urban developments), and the potential for contamination they create, are well monitored after construction of the bore/ well. Provide a fence around the bore/well head to keep stock at a suitable distance (at least 10 m). Construct fence. 6 Water Safety Plan Guide: Ref P1.3 Groundwater Abstraction Bores and Wells Version 1, January 2014

11 Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATED WATER GETTING INTO THE BORE/WELL FROM THE SURFACE cont d P Bore/well sited in low ground. P Back-siphoning. Consider elevation of bore/well head when siting bore/well. Ensure bore is equipped with backflow prevention. Ensure site is well drained to avoid pooling of water. Event: CONTAMINATION OF THE AQUIFER (the source) Possible hazards: Germs and chemical determinands appropriate to contamination sources. Level of risk: High P Contamination sources (eg, stock, septic tanks, chemical sources) too close to the bore/well head, or bore/well too shallow. Identify potential sources of contamination when well is being sited (see Guide S1.1). Ensure that changes in land use (including urban developments) and the potential for contamination they create, are well monitored after construction of the bore/ well. Microbiological quality. Chemical determinands appropriate for likely contamination source. No survey of potential sources of contamination undertaken. No aquifer tests carried out. No system for obtaining information about changing land use in place. Add treatment processes to remove identified contaminants. Instigate system for gathering information about land use changes. Restrict activities in the aquifer recharge zone that may contaminate the water (see Guide S1.1). Gather information about the vulnerability of the aquifer before undertaking development. P Aquifer is not secure. Assess the security status of the aquifer before undertaking development so that treatment needs can be identified, and the importance of restrictions on activities in the recharge zone evaluated (see DWSNZ:2000 Section 3.2.4). Isotope and CFC determinands, and/or Conductivity Chloride Nitrate (See DWSNZ:2000 Section ) Tests to demonstrate security do not meet the requirements of DWSNZ:2000. Changes in turbidity and/or colour of water with weather conditions. Take actions to reduce possible contamination sources. Ensure treatment processes are in place to compensate for unsecure source. Ref P1.3 Water Safety Plan Guide: 7 Version 1, January 2014 Groundwater Abstraction Bores and Wells

12 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 BORE OR WELL 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 1 P Damage to the pump or bore/ well head by animals. Regular maintenance and inspections of the bore/well head and the pump(s) (see Guide P10). Early warning system installed to indicate change in flow. Flow. Low or no flows. No inspections or maintenance records. No protection for bore/well head. Redevelop well area. Review maintenance and inspection procedures. Fence off bore/well head to protect against animal damage (stock should be at least 10 m away). P Catastrophic failure (eg, flood, slips or earthquakerelated damage). Provide protection against flood damage, and carry out inspections after natural disasters. Bore/well head inspections, regularly, and directly after floods etc, with follow-up action if required for existing protection (eg, fences, vegetation and soil instability). Flood levels. Flows (from bore/well head). Inspection records. No water. Reduced flow. Alarm activated. Consider alternative source. Evaluate existing protection system. Telemetric alarm for low flows from the intake. P Pump failure (see Guide P10). Maintenance according to manufacturers recommendations. Standby pump with auto-switch to alternate pumps. Telemetric 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. Regular inspection of cabling, power lines and connectors. Stand-by generator. Alarm to indicate faults. No flow. Consult with power authority. Obtain stand-by generator. Alarm for power failure, with battery back up. 1 The level of risk will probably increase the lower the flow of the water is. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed 8 Water Safety Plan Guide: Ref P1.3 Groundwater Abstraction Bores and Wells 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 BORE OR WELL TO MEET DEMAND cont d P Vandalism/ sabotage. Construct a security fence around the bore/ well head, or place inside a locked shed. Install intruder alarm. Damage to the intake. Evidence of attempts to gain access to the intake. P Screens clogged. Develop a maintenance plan to ensure debris is regularly cleared from the screens. The frequency of the clearing will depend, amongst other things, on the quality of the water. Aquifer tests. Reduced flow from bore. Clear screens. Develop well. Ref P1.3 Water Safety Plan Guide: 9 Version 1, January 2014 Groundwater Abstraction Bores and Wells

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 Not enough water reaching the treatment plant Indicators: Reduced, or no, flow reaching the treatment plant. Unexpectedly high usage. Structural failure of bore/wellhead, 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 (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 P1.3 Groundwater Abstraction Bores and Wells Version 1, January 2014

15 Event Contamination enters the aquifer or bore/well 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. Ref P1.3 Water Safety Plan Guide: 11 Version 1, January 2014 Groundwater Abstraction Bores and Wells

16 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: Responsibility: Results need to be recorded to meet legislative requirements or to 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, or indicate that poor water quality is reaching customers, then review the procedures 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. Manager designated responsible for water quality. 12 Water Safety Plan Guide: Ref P1.3 Groundwater Abstraction Bores and Wells Version 1, January 2014