| Abstract |
Introduction: The provision of good and safe drinking water is globally recognized as a fundamental public health issue and should be the primary goal of water supply systems. Drinking water quality control is based on the detection of pathogenic and toxic concentrations of chemicals through monitoring programs and compliance with national or international guidelines and standards, mainly based on indicator bacteria and maximum concentration levels of chemicals. However, this methodology is often slow, complex and expensive. Even for sophisticated and well-functioning systems, these monitoring systems have proven ineffective in preventing waterborne diseases such as, for example, Giardia or Cryptosporidium outbreaks. From this evidence we can conclude that final product testing is a reactive rather than a proactive way to ensure the availability of safe drinking water. This justifies the need to formulate a new approach to the quality control of drinking water based on the understanding of the vulnerability of the system to contamination and the preventive measures and actions necessary to guarantee the safety of the water supplied to the consumer. A water safety plan is a concept for risk assessment and risk management throughout the water cycle from catchments to the point of consumption. This approach involves identifying hazards and introducing control points that serve to minimize these potential hazards, providing more effective control of drinking water quality.
Aim: The purpose of this work is to assess risks and assess their risk in the operation of the Aposelemis’ Dam Water Treatment Plant, in accordance with the guidelines of the World Health Organization (WHO) and IWA, with the perspective of utilizing the results of in the implementation of a Water Safety Plan for the benefit of Public Health.
Methodology: The present study follows the first steps from the World Health Organization protocol on the design of Water Safety Plans and for risk assessment and risk assessment it used the semi-quantitative method according to Deere et al 2009 which is based on the production of a product of the probability of the occurrence of a risk times the severity of its occurrence. It focused on the very important part concerning the system assessment, having the valuable help of the interdisciplinary team of safe operation of Aposelemis’ dam water treatment plant. The assessment of the system included the recording and description of the system and the creation of a flow diagram, the assessment of risks and their classification by risk priority (low impact with a score of <6, medium impact with a score of 6-9, high impact with a score of 10 -15, very high impact with a score >15) and finally the identification of control measures with which the risk can be reduced.
Results: Aposelemis’ Water Treatment Plant (WTP) is located in Agriana in Hersonissos, Crete and is a modern surface category A2 water treatment plant, with physicochemical processes. The water of the reservoir of the Aposelemis dam, in the area of Potamies of Crete, which receives water from 2 catchment basins, is treated. That of the Aposelemis’ stream as well as that of Lasithi Plateau. Since 2019, it also receives the flood waters of the Lasithi Plateau through a pipeline inside a tunnel. Aposelemis WTP uses 4 main processes, those of Ozonation, Flocculation using an anionic polyelectrolyte and Aluminum Sulphate or Polyaluminum Chloride, Filtration with sand filters, Chlorination with chlorine gas and/or Sodium Hypochlorite produced in the electrolysis unit, as well as 2 secondary ones, those of thickening and dewatering of the sludge from the flocculation tanks, for the treatment of the reservoir water. The WTP has an aqueduct to Heraklion as well as to Agios Nikolaos and supplies water for human consumption to up to 300,000 permanent residents and visitors. The entire WTP water supply system, from the Lassithi plateau water diversion projects to the end points of the aqueduct, is supervised by a SCADA monitoring and telemetry system. While a sampling and control plan is followed in the frequencies as well as the parameters defined by both the surface water legislation and the human consumption water legislation with satisfactory results as a whole, it was found that no controls are carried out on Cryptosporidium & Giardia Lamblia even though surface water is treated at risk contamination by these species. Also, there are no tests for Legionella spp which there is a risk of being detected due to surface water and colonizing the water distribution networks or parts of the processes. It is very important to add the lack of bromate controls in the incoming water which makes it a risk and condition for more likely bromate formation in case of residual ozone overdose. Finally, the definition of strict reservoir protection zones is absent. It is a basic condition for the safety of the reservoir and the quality of the surface water. After the water supply system flow diagram was drawn and its critical control points were marked, the risks were assessed. A total of 46 low impact hazards, 21 medium hazards and 49 high impact hazards were identified and characterized throughout the system, with the critical point of the reservoir and WTP showing the most. The most important risks identified have to do with contamination of surface water with either microorganisms or chemicals, with operational parameters such as dosage of treatment chemicals or proper functioning of instruments as well as with the condition of water distribution pipelines. There was no very high incidence risk identified. There is scope for improvement and further reduction, and for this reason, tables were drawn up with proposals for measures and corrective actions.
Conclusions: The operation of Aposelemis’ dam WTP, seems to have considerably reduced the probability/frequency of occurrence of risks. Their evaluation did not reveal any risk with a very high impact. This study confirmed the necessity for the preparation and implementation of a Water Safety Plan since it provides the possibility of an integrated management approach and a detailed risk analysis plan in all stages of water management and will contribute to the maximum in this direction.
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