Use of WSP concepts in risk mitigation of distribution systems at under capacity operation - a case study on Kandy South water distribution system

Abstract

A Water Safety Plan is one of the most effective ways of ensuring that a water supply is safe and reliable for human consumption and that it meets the health and demand based standards and other regulatory requirements. WSP is based on a comprehensive risk assessment and risk management approach to all the steps in a water supply chain from source to consumer. Recently introduced WSP for distribution systems is a new concept to NWSDB. However, the NWSDB, being the authority directly responsible for treatment and delivery of drinking water to the consumer, has commenced implementation of the WSP approach to the distribution system as a first step. Numerous studies were found in literature for assessing the formation and behavior of disinfection by products, residual chlorine and other hydraulic parameters in water distribution systems. Yet the studies related to WSP for distribution system approach were not frequently found. The risk assessment of an under capacity operating system is carried out throughout this study and the recommendations were made to mitigate those in future. Maligathenna scheme, which is a sub-scheme coming under Kandy South Region was analyzed in detail. The main parameters concerned were Trihalomethane, Residual Chlorine, Pressure, Water Age, Total Organic Carbon, Turbidity and Conductivity. Water quality parameters were tested at site or in the laboratory. A hydraulic model was built using Water GEMs software to determine the hydraulic parameters such as pressure, water age. A special water quality model was developed to assess the performance of the distribution network and predict the parameter values for the future. General conclusions along with the specific recommendations were made based on the results and observations met throughout the study. WSP hazard identification and assessment approach is followed throughout the study. Some alarming findings were listed with respect to TTHM and RCl. However clear and significant relationships among the parameters could not be found. Most of the recommendations which were made at the end of the study are expected to be implemented either in design stage or during operation and maintenance period