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: – 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 P1.3.1.1 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. 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. P1.3.1.2 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. CONTAMINATION OF BORE/WELL DURING CONSTRUCTION Possible hazards: Germs and chemical determinands (eg, barium). Level of risk: Low P1.3.2.1 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. Event: CONTAMINATION OF BORE/WELL DURING CONSTRUCTION cont’d
P1.3.2.2 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. determinands used in drilling. of chemical determinands more than 50% of MAV. Evidence of NZDS not having been followed. Flushing not undertaken. Flush well/bore until chemical determinand less than 50% of their MAVs. Event: CONTAMINATED WATER GETTING INTO THE BORE/WELL FROM SHALLOWER DEPTHS Possible hazards: Germs and chemical determinands (eg, manganese, nitrate). Level of risk: High P1.3.3.1 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. 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. No system for backflow prevention. Withdraw casing and replace or repair. P1.3.3.2 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. 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. No system for backflow prevention. Implement conservation measures and reduce pumping rate. CONTAMINATED WATER GETTING INTO THE BORE/WELL FROM THE SURFACE Possible hazards: Germs and chemical determinands appropriate to contamination sources. Level of risk: High
P1.3.4.1 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 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. Ensure well tops are properly sealed. Ensure pumps are sealed or situated so that wastewater cannot re-enter the well. quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). Inspection of bore/well head shows with NZDS. Make necessary changes to bore/well head to meet NZDS requirements. P1.3.4.2 Bore/well head or casing damaged. Provide protection for the bore/well head against stock and human damage. out regular visual checks for damage. quality. Chemical determinands possible at shallower depths (eg, nitrate, manganese). Inspection of bore/well head shows with NZDS. Repair bore/ well head. Remove casing and replace or repair. P1.3.4.3 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.
P1.3.6.1 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. Fence off bore/well head to protect against animal damage (stock should be at least 10 m away). Flow. Low or no flows. No inspections or maintenance records. No protection for bore/well head. Redevelop well area. Review maintenance and inspection procedures. P1.3.6.2 Catastrophic failure (eg, flood, slips or 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). Telemetric alarm for low flows from the intake. Flood levels. Flows (from bore/well head). Inspection records. No water. Reduced flow. Alarm activated. Consider alternative source. Evaluate existing protection system. P1.3.6.3 Pump failure (see Guide P10). Maintenance according to manufacturers’ recommendations. Standby pump with auto-switch to alternate pumps. Operate duty and standby using an alternate ‘number of days‘ cycle. Telemetric alarm for low flows. Telemetric records. No water. Alarm activated. No maintenance record. New pumps. Instigate maintenance programme. P1.3.6.4 Power failure. Regular inspection of cabling, power lines and connectors. Stand-by generator. Alarm for power failure, with battery back up. Alarm to indicate faults. No flow. Consult with power authority. Obtain generator. 1 The of risk will probably increase the lower the flow of the water is. Causes Preventive measures Checking preventive measures Corrective action What to that action is needed