تطوير نموذج لإدارة سلامة المياه من المخاطر لنظام الإمداد بالمناوبة

Abstract

Water Directorates in Kingdom of Saudi Arabia (KSA) are facing challenges related to both the quantity and quality of water due to low annual rainfall, depleting water resources, and presence of naturally occurring substances in groundwater. As a result, they are striving to meet municipal water demand with adequate water quality through intermittent water supply. Although, raw groundwater is being treated with expansive treatment processes, intermittent water supply and in-house storage have led to various water quality problems at the consumer end, such as possibility of bacterial contamination. In this research, a comprehensive risk-based water safety management model was developed to identify, analyse, and reduce the water quality problems from source to the consumer tap. Risk analysis was carried out at two levels, including coarse risk analysis detailed risk assessment. Original Canadian Council of Minster of the Environment Water Quality Index (CCME WQI) was being used for assessing the water quality of surface water sources and distribution systems on a case by case basis. Its full potential as a management tool for complete water supply systems (WSSs) has yet to be recognized at global level. In coarse risk analysis, a framework was developed using the modified CCME WQI to assess spatiotemporal water quality from groundwater source to treatment and distribution networks in smaller systems. The modified index resolves a limitation of the original index by also evaluating the microbiological water quality parameters which have to be completely absent for meeting desired drinking water quality standards. The framework divides the distribution network in different zones, which are further segregated into districts, to improve the decision-making process. Temporal assessment identifies the seasons with higher probabilities of failures, while the spatial assessment provides an insight on the performance (i.e., Excellent to Poor) of each district in a distribution network. In addition to failure probability, risk mapping gives appropriate attention to the number of consumers in different districts. Application of the framework on two smaller WSSs (population less than 50,000) in Qassim region revealed that the remotely located districts from the treatment facility underperform in comparison to the closely situated districts. In detailed risk assessment, the districts highlighted with higher risk (i.e., potential of water quality failure) were evaluated in detail. Root cause analysis was conducted to identify potential hazards in water source, treatment plant operations, treated water storage, distribution networks, and the in-house plumbing system. Subsequently, fuzzy-failure mode and effect analysis (Fuzzy-FMEA) were applied to assess and prioritize different hazards. The fuzzy sets effectively addressed the uncertainties associated with the data limitations in calculating the exceedance probabilities (Pe) and vagueness in expert opinion for subjective evaluation of severity and detectability of failure. The framework was applied on a smaller system serving 18,000 consumers in Unayzah, Saudi Arabia. Potable supplied water underwent reoccurrence of TDS (Pe = 20 %), turbidity (Pe =10 %), and Fe (Pe = 2 %) in distribution that further increased up to 44 %, 33 %, and 11 % at the consumer end. The Pe for residual chlorine failure soared up to 89 %. Up to 50 % cumulative risk reduction was achieved through economical controls. Only the shift to continuous supply can limit the remaining failures under the acceptable risk. The framework will help the decision-makers for source to tap risk assessment of intermittent supply systems in Saudi Arabia, Gulf Region, and elsewhere. Utility managers can effectively apply the coarse risk analysis to identify the locations and periods of water quality failures in each component (i.e., source, treatment, and distribution) of a smaller WSS for effective utilization of their resources. Based on the results of detailed risk assessment, the Water Directorates and water utilities can plan their available investments to minimize the hazards with highest risk priorities. The model has also been implemented on the water supply system in Unayzah to evaluate its practicality for other Water Directorates in Qassim, other regions in KSA, and elsewhere in the world.