INSTALLATION OF ARSENIC-SAFE AND LOW MANGANESE WELLS BY LOCAL DRILLERS FOR MEETING THE CHALLENGES OF SAFE DRINKING WATER IN BANGLADESH

A significant proportion of shallow wells (usually < 80m) in general are As-contamination, deep wells are drilled to depths of around 250 m has been a common mitigation option. However, the number of deep wells is still very low, compared to the safe water demand in the country. Since the past decade and half the local drillers are installing new wells in regions with high-arsenic shallow wells to provide safe drinking water through well switching practice (viz. in Matlab and Araihazar regions), at relatively low costs of installation. The KTH-Groundwater Arsenic Research Group has closely worked with the team of local drillers in one of the hot spot areas of Matlab in southeastern Bangladesh. We have followed up their practice of new tubewell installations based on their simple perspective evaluation of water quality based on the color of the aquifer sediments.

In order to evaluate this practice we have carried out systematic scientific research to unravel the hydrochemical characteristics in the shallow, intermediate deep and deep aquifer systems through monitoring of groundwater using depth-specific piezometers (n=82) installed in 15 locations in Matlab area of Bangladesh and monitored over a 3 year period. For the installation of shallow drinking water wells, one aim of this study was to develop a sediment color tool on the basis of local driller’s color perception of sediments (Black, White, Off-white and Red), As concentration of tubewell waters and respective color of aquifer sediments. The median values of As was generally less than the WHO guideline value of 10 µg/L in wells installed in red sands aquifer implying that red sediments provide As-safe water. On the contrary, levels of As in more than 90% of shallow wells installed in black sands were high with median value of 239 µg/L. Therefore, it is recommended to avoid installation of shallow wells in aquifers consisting of black sands.

This study also pioneered Intermediate Deep Aquifer (IDA) as a potential source for As-safe and low Mn drinking water. Installation of 245 Intermediate Deep Tubewells (IDTW) at a depth of 120 m provided promising results (99% As-safe and 91% low Mn) which supports the strategy of exploiting IDA as safe aquifers for installation of drinking water wells almost at half of the deep tubewell installation.