D2.3.1.3 Install backflow Pressure. Backflow Install prevention devices preventers not backflow System Flow. where appropriate installed preventers. pressure drop Turbidity (if (see Guide D2.4). where (see D2.2). there is concern necessary. Low pressure about soil and areas, hills, Low or associated extremities, valves negative contaminants and hydrants to be pressures in being drawn into identified and part(s) of the the supply). mapped. reticulation E. coli and network. coliforms. 1 Microbiological contamination of the distribution system is a likely outcome. Such a contamination event can readily develop from a localised event to a widespread problem. Preventive measures Checking preventive measures Corrective Causes action What to check Signs that action is needed Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEM cont’d D2.3.1.4 Determine flow Job sheet and Incorrect Review direction from verification flows hydraulic Flow direction in pressure procedures. observed. model of affected area information and system. unknown or chemical records uncontrollable. before undertaking maintenance work. For major mains, use a network model or chemical tracers to determine flow direction before undertaking maintenance work. D2.3.1.5 Work practices for Indicator E. coli or Identify staff reticulation bacteria in coliforms training Standard maintenance water after detected in needs, and hygiene comply with maintenance. 100 ml water provide practices not standard sample training. adopted. Job sheets and procedures (see following procedures. Disinfection Appendix 1). system of the maintenance. Screen supply repaired staff for Errors section diseases. detected by repeated. They should not be audit. Re-audit permitted to work procedures. on potable water systems until they have obtained a medical certificate stating they are clear of the disease.
D2.3.1.3 System pressure drop (see D2.2). Install backflow prevention devices where appropriate (see Guide D2.4). Low pressure areas, hills, extremities, valves and hydrants to be identified and mapped. Pressure. Flow. Turbidity (if there is concern about soil and associated contaminants being drawn into the supply). E. coli and coliforms. Backflow preventers not installed where necessary. Low or negative pressures in part(s) of the reticulation network. Install backflow preventers. 1 Microbiological contamination of the distribution system is a likely outcome. Such a contamination event can readily develop from a localised event to a widespread problem. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: INTRODUCTION OF CONTAMINATING MATERIAL INTO THE DISTRIBUTION SYSTEM cont’d D2.3.1.4 Flow direction in affected area unknown or uncontrollable. Determine flow direction from pressure information and chemical records before undertaking maintenance work. For major mains, use a network model or chemical tracers to determine flow direction before undertaking maintenance work. Job sheet and verification procedures. Incorrect flows observed. Review hydraulic model of system. D2.3.1.5 Standard hygiene practices not adopted. Work practices for reticulation maintenance comply with standard procedures (see Appendix 1). Screen supply staff for diseases. They should not be permitted to work on potable water systems until they have obtained a medical certificate stating they are clear of the disease. Indicator bacteria in water after maintenance. Job sheets and procedures. E. coli or coliforms detected in 100 ml water sample following system maintenance. Errors detected by audit. Identify staff training needs, and provide training. Disinfection of the repaired section repeated. Re-audit procedures.