Causes Preventive measures Checking preventive measures Corrective action What to Signs that action is needed Event: CONTAMINATION GETS INTO THE TRUNK MAINS cont’d P2.1.3 Leaks. Management of pressure fluctuations and peak pressures to minimise stress on the system and eliminate negative pressure conditions. Annual leak detection and repair programme. Visual inspection. Regularity of observed leaks. Unexplained water loss. Modify leak detection programme and plan. P2.1.4 Incidental damage (eg, floods, slips, incidents). Quarterly inspection of vulnerable zones with appropriate follow-up during or after incidents (natural disasters, vehicle accidents, etc). Provide adequate physical protection for trunk mains. Inspection. Number of reported and detected failures. Determine viability of improving level of protection. P2.1.5 Poor repairs of breaks, incidental damage, and penetration of trunk mains. See D2.3 (D2.3.1.2–D2.3.1.9). Event: SEDIMENT CONTAINING CONTAMINANTS STIRRED UP Possible hazards: Germs; iron; manganese; possibly heavy metals; aluminium (from coagulant); organic particulate matter. Level of risk: Low P2.2.1 Sediment or biofilm allowed to develop. Intake designed to minimise introduction of sediment into the treatment plant. For distribution trunk mains see Guide D2.3 (D2.3.2). See Guide D2.3 (D2.3.2). P2.2.2 Velocity too high. See D2.3 (D2.3.2). Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: CONTAMINATION GETS INTO OPEN CHANNEL CONDUITS AND BREAK-PRESSURE TANKS Possible hazards: Germs; chemical determinands. Level of risk: High2
P2.3.1 Stock access to the channel and break tanks. Fence channel and tanks to keep stock clear. Ensure break pressure tanks have a well-fitting lid. Turbidity. quality. Abnormally high turbidity of water reaching plant. High E. coli counts. Elevated chlorine demand. Evidence of stock having gained access to the channel. Replace the open channel with pipes. Erect fence. Provide suitable lid. P2.3.2 Surface and leaching of water. Control land use practices in vicinity of open channel, particularly stock and chemical application (fertiliser, pesticides). Riparian margin channel. quality. Nutrients (depending on the nature of the fertiliser). Increasing nutrient levels. High E. coli counts. Elevated chlorine demand. Replace the open channel with P2.3.3 of water quality caused by increased biological activity in shallow, warm open channels. Ensure flow paths prevent regions of slow moving water. Develop maintenance plan to remove biological growths. Control land use practices in the vicinity to reduce nutrient input. quality. Flow. Algal toxins (if algae of concern are present). Visual inspection. Temperature. Nutrients (nitrogen and phosphorus). Algae of health significance present. Elevated levels of nutrients. Visual evidence of biological growths. Replace the open channel with pipes. P2.3.4 Collapse of the channel sides. Carry out regular checks of the state of the channel, and after heavy rain, and shore up sides as necessary. Fence channel and tanks to keep stock clear. Turbidity. quality. Abnormally high turbidity of water reaching plant. High E. coli counts. Elevated chlorine demand. Evidence of stock having gained access to the channel. Initiate checks. Replace the open channel with pipes. Erect fence. 2 The level of risk is high for those supplies using open channels and break-pressure tanks between the source and treatment plant, although treatment, including disinfection, should reduce the level of risk. Causes Preventive measures Checking preventive measures Corrective action What to Signs that action is needed