P7.1.1.2 Regular manual FAC. FAC Recalibrate checks on calibration concentration is controller. Dose of sensor (see less than controller’s quality. Increase DWSNZ:2000). 0.2 mg/L. sensor chlorine Calibration incorrectly E. coli or dose rate schedule. calibrated. coliforms detected in recalibration 100 mL sample undertaken. of water leaving the treatment plant. Calibration schedule not signed off. 1 The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water and the effectiveness of treatment processes prior to the chlorination process. Preventive measures Checking preventive measures Corrective Causes action What to check Signs that action is needed Event: NOT ENOUGH FREE AVAILABLE CHLORINE cont’d P7.1.1.3 Periodic manual FAC. FAC Adjust checks on FAC concentration is controller Dose concentration, less than set-point. controller’s quality. especially during 0.2 mg/L. set-point Recalculate periods of quality incorrect, or E. coli or dose rates variability Dose flow incorrect dose coliforms and change rates and dose calculation. Independent on detected in settings. calculations. calculations 100 mL sample staff in (especially after a of water leaving making dose system change when the treatment calculations. expected dose rates plant. are uncertain. Frequent Install visual flow calculation meters to allow errors chlorine flow to be Flow rates lower checked by eye. than expected.
P7.1.1.2 Dose controller’s sensor incorrectly calibrated. Regular manual checks on calibration of sensor (see DWSNZ:2000). FAC. quality. Calibration schedule. FAC concentration is less than 0.2 mg/L. E. coli or coliforms detected in 100 mL sample of water leaving the treatment plant. Calibration schedule not signed off. Recalibrate controller. Increase chlorine dose rate recalibration undertaken. 1 The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water and the effectiveness of treatment processes prior to the chlorination process. Causes Preventive measures Checking preventive measures Corrective action What to check Signs that action is needed Event: NOT ENOUGH FREE AVAILABLE CHLORINE cont’d P7.1.1.3 Dose controller’s set-point incorrect, or incorrect dose calculation. Periodic manual checks on FAC concentration, especially during periods of quality variability Independent on calculations (especially after a system change when expected dose rates are uncertain. Install visual flow meters to allow chlorine flow to be checked by eye. FAC. quality. Dose flow rates and dose calculations. FAC concentration is less than 0.2 mg/L. E. coli or coliforms detected in 100 mL sample of water leaving the treatment plant. Frequent calculation errors Flow rates lower than expected. Adjust controller set-point. Recalculate dose rates and change settings. staff in making dose calculations.
treatment-chlorination-feb14-v2.docx