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Spatial variability of geogenic contaminants in drinking water sources

Insights into hydrogeological controls, geospatial data for safe water supply and groundwater resource management

Time: Wed 2022-02-16 13.00

Location: Sahara Plan 2, Teknikringen 10B, Campus, Videolänk, Stockhom

Video link: https://kth-se.zoom.us/j/66560331182

Language: English

Subject area: Land and Water Resources Engineering

Doctoral student: J. Ijumulana , Vatten- och miljöteknik, DAFWAT Research Group, Department of Water Resources Engineering, College of Engineering and Technology, University of Dar es Salaam, Dar es Salaam, Tanzania, KTH-International Arsenic Research Group

Opponent: Professor Steve W. Lyon, College of Food, Agricultural and Environmental Resources School of Environment and Natural Resources, Wooster, The Ohio State University, Wooster, Ohio, USA

Supervisor: Professor Prosun Bhattacharya, Vatten- och miljöteknik; Professor Felix Mtalo, DAFWAT Research Group, Department of Water Resources Engineering, College of Engineering and Technology, University of Dar es Salaam, Dar es Salaam, Tanzania

QC 20220124

Abstract

The presence of geogenic contaminants in drinking water is a major health concern in many parts of the world. The interaction of groundwater with different rock types and sediments in the natural geochemical environment play an important role in controlling their mobility. Due to limited resource allocations, water quality investigations are mostly limited only to the drinking water sources serving the communities. As a consequence, most aquifer systems remain unexplored in terms of groundwater quality through conventional methods. The present study aims to investigate the status of groundwater quality in the nine drainage basins of Tanzania focusing on the occurrence of fluoride (F¯) and other potentially toxic elements especially in the northern development zone (NDZ). The specific objectives were to model the spatial distribution of geogenic F¯- in groundwater systems and the health risk among the population as well as to evaluate the key influencing hydrogeological factors for the observed variability in F¯ concentrations in water sources using modern geospatial methods and technologies. Both literature and community perspectives indicate a serious problem in terms of F¯ in the Internal, Pangani, and Lake Victoria basins in the NDZ where the prevalence of mild to severe fluorosis is a health risk among the communities dependent on groundwater for drinking. In order to understand the spatial variability, machine learning methods were developed during this research by applying a combination of the concepts of spatial statistics, geostatistics, different Geographical Information Systems (GIS) tools as well as non-parametric methods to study the occurrence of geogenic contaminants in groundwater systems. Spatial statistical methods such as Moran’s I statistics and GIS tools revealed two positive significant high-high spatial patterns along the Pliocene-recent volcanic and the Mozambique belt as well as around Meru and Hanang’ stratovolcanoes in the northeast and southwestern part of the study regions, respectively. The positive low-low spatial patterns were determined around the major and minor rift valley escarpments both in the west and east of the East African Rift Valley (EARV) graben and around the stratovolcanoes within the graben. Other potentially toxic elements were found in elevated concentration around the Meru stratovolcano creating another risk of health concern to the communities which depend on such sources of drinking water. Factors controlling the spatial variability of fluoride in groundwater included, in the descending order, the mineralization, topography, tectonic processes, pH and water exchange between hydrogeological units during water movement. Other factors included depth to groundwater, well depth, screen depth and irrigation practices in the Sanya alluvial plain. The spatial heterogeneity of geological characteristics may lead to the spatial variability of various geogenic contaminants at spatial scales besides several other factors like topography, soil type, surface water-groundwater interaction, climate, volcanic activities, tectonic processes.The results of this study are important to the water safety planning implementation in the naturally contaminated aquifer systems especially in the EARV regions and volcanic areas.

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Belongs to: About KTH
Last changed: Jan 24, 2022