good aerator design (see P4.2.1.1) having intakes at different levels in the lake/reservoir or having a single intake that can be used at a range of depths (P4.2.1.3) starting the destratification process well before the different layers in the water are likely to start forming (P4.2.1.4). (References in parentheses are to the Risk Information 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 and the G1) monitoring guides (Guide While we haven’t pointed out every detail of how these G2). documents are linked with the present document, the links are many and are important. Abbreviations: MAV Maximum Acceptable Value; DWSNZ Drinking-Water Standards for New Zealand – – Preventive measures Checking preventive measures Corrective action Causes What to check Signs that action is needed Event: POOR MIXING OF THE WATER BODY, LEADING TO: algal blooms (under some circumstances) – raw water unsuitable for treatment – difficulties with treatment control because of variability in raw water quality. – Possible hazards: Germs (disinfectant demand1 too high); manganese, trihalomethanes, haloacetic acids and chloral hydrate (formed from elevated levels of organic matter), algal toxins. Level of risk: Low–high2 P4.2.1.1 Use a design that Dissolved Large Redesign has been oxygen (DO) differences Poor design of successfully used with depth. between DO and unit. aerator or previously. temperature hydraulic Temperature Redirect levels at (including In a long narrow with depth, to intake to different depths. insufficient reservoir (eg, a identify the upper levels of motor size). dammed river) formation of a Elevated levels the water body use a longitudinal thermocline.3 of Fe and Mn until aerator. It will be entering the FAC (free more hydraulically intake. can be available efficient than a resumed. chlorine) leaving Complaints of point source the treatment tastes and Use low-level aerator. plant and odours. intake to aid through the FAC distribution in the concentration system. springtime below 0.2 mg/L. and early Iron. summer. Manganese. Ammonia.
good aerator design (see P4.2.1.1) having intakes at different levels in the lake/reservoir or having a single intake that can be used at a range of depths (P4.2.1.3) starting the destratification process well before the different layers in the water are likely to start forming (P4.2.1.4). (References in parentheses are to the Risk Information 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; DWSNZ – Drinking-Water Standards for New Zealand Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: POOR MIXING OF THE WATER BODY, LEADING TO: – algal blooms (under some circumstances) – raw water unsuitable for treatment – difficulties with treatment control because of variability in raw water quality. Possible hazards: Germs (disinfectant demand1 too high); manganese, trihalomethanes, haloacetic acids and chloral hydrate (formed from elevated levels of organic matter), algal toxins. Level of risk: Low–high2 P4.2.1.1 Poor design of aerator or hydraulic (including insufficient motor size). Use a design that has been successfully used previously. In a long narrow reservoir (eg, a dammed river) use a longitudinal aerator. It will be more hydraulically efficient than a point source aerator. Dissolved oxygen (DO) with depth. Temperature with depth, to identify the formation of a thermocline.3 FAC (free available chlorine) leaving the treatment plant and through the distribution system. Iron. Manganese. Ammonia. Large differences between DO and temperature levels at different depths. Elevated levels of Fe and Mn entering the intake. Complaints of tastes and odours. FAC concentration below 0.2 mg/L. Redesign unit. Redirect intake to upper levels of the water body until can be resumed. Use low-level intake to aid in the springtime and early summer.
treatment-destratification-feb14-v2.docx