Drinking Water Supply from Unconsolidated Aquifers in Cold Climates: Evaluation of Factors Influencing Hygienic Safety Barriers Emphasizing Viruses
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The overall aim of this doctoral thesis was to provide insight into factors affecting the hygienic safety of groundwater abstracted from cold-climate unconsolidated aquifers. An understanding of such factors is essential for the dimensioning of both natural and engineered microorganism elimination solutions. In papers I – IV, factors directly associated to groundwater-related disease outbreaks and aquifer-dependent characteristics were assessed and evaluated trough correlational (paper I) and experimental (paper II – IV) research. It was found that viruses probably represent the main threat to public health related to the consumption of untreated groundwater in Norway, and that physicochemical filtration processes and the presence of preferential flow paths are the dominating mechanisms controlling the removal and transport of viruses during aquifer passage in cold-climate, unconsolidated aquifers. It was demonstrated that inactivation had a negligible influence on the overall virus removal. Hence, the formulations in the current Norwegian Drinking Water Guidelines, with respect to recommendations for the dimensioning of microbial protection zones around groundwater abstraction wells in unconsolidated aquifers, should be reconsidered. In particular, the role of permanent virus attachment and variabilities in aquifer hydraulics on overall virus removal should be recognized and further investigated. The importance of microbial transport along preferential flow paths highlighted the need for permanent disinfection treatment when supplying drinking water from geographically limited, heterogeneous cold-climate aquifers. In paper V, the natural hygienic safety barriers at two waterworks applying the bank filtration principle were evaluated using naturally occurring microorganisms and natural organic matter as response parameters. Because Norwegian water management terms to such water supplies at groundwater supplies, limited information has been available on the actual barrier efficiencies achieved. The study showed that bank filtration and aquifer passage has a high potential as a pretreatment method for production of hygienically safe drinking water in Norway in the context of a changing climate. The main advantage of using bank filtration and aquifer passage in the Nordic region is related to the considerable improvement of the chemical and hygienic water quality of surface water, reducing the need for additional water treatment and increasing the effectiveness of disinfection processes. Subsurface water passage dampens water quality fluctuations observed in surface waters, and thus, provides a more stable operation of subsequent water treatment and disinfection processes at the water treatment plant.