2D and 3D-modelling as a support tool for aquifer mapping and large-scale knowledge transfer : Targeting safe aquifers in Towakull region inGowainghat Upazilla, Sylhet, Bangladesh

Sammanfattning

Arsenic has been discovered in the groundwater of Bangladesh and affects millions of people. Many parts of the country experiences elevated levels of As above the drinking water limit set by Bangladesh at 50 μg/L. Tube wells installed at a shallow depth is the main source of drinking water in Bangladesh for local communities. Previous investigation has identified elevated levels of As in these shallow tube wells. Color of sediments as well as depth below surface was also identified as important properties in determining As safe aquifers. Despite the knowledge surrounding the elevated As concentrations and mitigation efforts there has been a lack of large scale, successful mitigation methods. The problems have been identified as a lack of large scale knowledge transfer regarding the subsurface geology to local drillers and communities as well as a lack of coherent and country wide data capturing, management and storage. The aim of this study was to investigate how already captured data in Bangladesh from previous projects could be compiled, formatted, visualized and communicated to facilitate large scale knowledge transfer as well as increasing the understanding off what geological and hydrogeological data is necessary to accurately and with a high degree of confidence map the aquifers of Bangladesh. This study was conducted as a pilot study for aquifer mapping in the EPSC-DDM project together with the International Groundwater Research Group at KTH. To understand data necessity and how to effectively map aquifers in Bangladesh data from various sources needed to be compiled. The data was cleaned and investigated as 2D and 3D models. Hydrographs was created from water level data in GeoGIS. Water quality data was used together in modelling processes and alone to investigate the water quality of potential aquifer systems. The modelling was conducted in GeoGIS for 2D cross sections and Earth Volumetric Studios for 3D models. The results showed two distinct aquifer in the study area of Towakull union, at a depth of 50-150 m as well as around 200-250 meters. The shallow aquifer was deemed unsafe in terms of As concentrations while the deep was deemed safe. The results from the modelling indicated that data already gathered for previous projects could be used as a base for aquifer mapping. Lithological data with main grain size together with water quality data at depth was deemed as the minimum data needed for 3D model aquifer mapping and water level data as well as color of the sediments was deemed as important data to collect if possible. The results also indicated that automatic capturing and storage of data into one coherent format would greatly decrease the time of data cleaning before modelling as well as increasing the accuracy and limiting the need for interpretation of the modeler. In conclusion the usage of 2D or 3D models for aquifer mapping shows great promise and the usage of already captured data to create these models was possible. The models had the potential to be easily communicated and distributed in digital format or in print to facilitate large scale knowledge transfer and increase evidence-based decision making in Bangladesh.