(especially arsenic is Install roof liners in tanks Replace lid after heavy more than with treated timber roofs. with more rain). 50% of its suitable MAV. material. 2 See Guide D2.1 regarding approved materials. Preventive measures Checking preventive measures Corrective action Causes What to Signs that action is needed Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO SERVICE RESERVOIR cont’d D1.2.5 Specify and audit roof FAC. Change in Repair leaky design: water quality joints/cracks/ Entry of roof following hatches rainwater to drain drainage. quality. rain. promptly. from (not into) tank Installation E. coli or restrict access to roof design. coliforms top Annual roof detected in hatches designed to inspection Replace badly 100 mL of exclude water report. designed water. ingress. hatches. Flaws in the design of the roof. D1.2.6 Repair leaks promptly. Unexplained Repair leaks. quality. change in Entry of Inspect tank 1–5 Isolate tank, water years (depending on the Tank chlorinate and quality. age of the tank and risks inspection check the groundwater caused by its location). report. E. coli or (for coliforms quality. If detected in there is gross tanks). 100 mL of contamination, water. dump the water, clean Line the tank with a Leaks and refill suitable waterproof identified by before material. the chlorinating. inspection. Complaints of petrol (if near underground fuel tanks). D1.2.7 Ensure there are screens Regular Taste and Replace and on the source outlet. screen odour clean screens. Animal entry inspection. complaints. from Isolate tank, upstream E. coli or chlorinate and source quality. coliforms the (animals detected in Turbidity. trapped and 100 mL of quality. If destroyed by water. there is gross action of contamination, Turbidity control dump the more than valves) water, clean – 0.2 NTU. where the and refill tank is filled before directly from chlorinating. the source.
(especially after heavy rain). arsenic is more than 50% of its MAV. Install roof liners in tanks with treated timber roofs. Replace lid with more suitable material. 2 See Guide D2.1 regarding approved materials. Causes Preventive measures Checking preventive measures Corrective action What to Signs that action is needed Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO SERVICE RESERVOIR cont’d D1.2.5 Entry of roof drainage. Specify and audit roof design: rainwater to drain from (not into) tank restrict access to roof top hatches designed to exclude water ingress. FAC. quality. Installation design. Annual roof inspection report. Change in water quality following rain. E. coli or coliforms detected in 100 mL of water. Flaws in the design of the roof. Repair leaky joints/cracks/ hatches promptly. Replace badly designed hatches. D1.2.6 Entry of groundwater (for tanks). Repair leaks promptly. Inspect tank 1–5 years (depending on the age of the tank and risks caused by its location). quality. Tank inspection report. Unexplained change in water quality. E. coli or coliforms detected in 100 mL of water. Repair leaks. Isolate tank, chlorinate and check the quality. If there is gross contamination, dump the water, clean and refill before chlorinating. Line the tank with a suitable waterproof material. Leaks identified by the inspection. Complaints of petrol (if near underground fuel tanks). D1.2.7 Animal entry from upstream source (animals trapped and destroyed by action of control valves) – where the tank is filled directly from the source. Ensure there are screens on the source outlet. Regular screen inspection. quality. Turbidity. Taste and odour complaints. E. coli or coliforms detected in 100 mL of water. Turbidity more than 0.2 NTU. Replace and clean screens. Isolate tank, chlorinate and the quality. If there is gross contamination, dump the water, clean and refill before chlorinating.
distribution-post-treatment-storage-feb14-v2.docx