Qualified well contruction in Bangladesh (January to December 2023)

Background/Summary

In the search for arsenic-free water in Bangladesh, wells are often drilled unnecessarily deep - up to 300 m and more. The decision about the suitable depth of wells is often based on the experience of unqualified drilling companies and the lack of information about local arsenic contaminations. With this project, we intended to find simple tools to evaluate groundwater quality prior to drilling and to evaluate more sustainable water sources.

In cooperation with the NGO AGAPE e.V. (www.agape-ev.de) and the local Department for Public Health Engineering (DPHE), in an area-wide survey near the city of Nabiganj (NE Bangladesh), existing wells were sampled and analyzed using simple methods (rapid arsenic test, conductivity measurement, filling a water sample for iron content determination). At the same time, samples were taken from the same wells for professional analysis at the University of Heidelberg. In comparison of 4 sites, we concluded, that the electric conductivity is a suitable tool for evaluating groundwater quality, as it is positively correlated with Arsenic content. Some exceptions were extremely high conductivities, indicating sewage water interactions and low water quality, respectively. Bottle tests were done by filling a plastic bottle with water and waiting for 24h, in order to investigate the iron precipitation in color and also consistence. We found that iron precipitates of Bangladesh waters react differently than common precipitates and formed flocks re-precipitate quickly after shaking. This gives sustainable opportunities of Arsenic filtration in sand filters, as provided and maintained by AGAPE e.V. alternatively to deep wells. In a second step, deep wells of the same area were investigated using geophysical methods (gamma log). As during drillings no sediment logs are taken, this depth profile can give important insight to subsurface layers.

We also found out, that wells outside of settlement area tendentially have lower arsenic concentrations than nearby houses or ponds. The reasons therefor are still under investigation and will continue soon.