A potential source of low-manganese, arsenic-safe drinking water from Intermediate Deep Aquifers (IDA), Bangladesh

Elevated manganese (Mn) concentration in many drinking water tubewells in Bangladesh has made access to safe drinking water more critical despite providing arsenic (As) safe water to millions of people after decades of efforts to achieve latter. This study evaluates the potential of the Intermediate Deep Aquifer (IDA) in the Matlab area of Bangladesh as a source of As-safe and low-Mn groundwater. Based on observations from depth-specific piezometer nests, drinking water tubewells were installed at a targeted depth of 120 m in the Matlab region, an As-hot spot in the country. Water chemistry analysis of 243 Intermediate Deep Tubewells (IDTW) provided promising results which support the strategy of exploiting the IDA as a safe source for drinking water tubewells. Arsenic, manganese and other trace elements, along with the major ions, were analyzed by high-precision ICP-OES and ion chromatography. The Bangladesh drinking water standard for As (50 mu g/L) was exceeded only in 3 wells (1%) while 99% (n = 240) of the wells were found to be safe. More than 91% (n = 222) were within the WHO guideline value of 10 mu g/L. For Mn, 89% (n = 217) of the wells showed the concentration within or below the former WHO guideline value of 0.4 mg/L with a mean and median value of 0.18 and 0.07 mg/L respectively. Similar high permeability sand units at this depth range, if available could be targeted by the local tubewell drillers for tapping water at half the cost of deep tubewell installation, which will be quite encouraging for the local community, considering their affordability for installation of As-safe and low-Mn drinking water tubewells. This study's results could also be important for other relevant stakeholders, including the policy makers, implementing agencies and the water sector development partners, as well as water supply projects elsewhere in the world with similar hydrogeological settings.