Groundwater monitoring in Niamey, Niger: Is groundwater an alternative drinking water supply under the current quality conditions?

Groundwater in Niger represents an essential resource for survival in remote areas far from the Niger River and a reserve in areas where access to surface water is secured as in Niamey itself. The monitoring of this resource offered as a part of the technical cooperation with the Niger Basin Authority NBA enabled to obtain data on groundwater quality and observe changes in groundwater levels over the last decade. The monitoring targeted the three main aquifers existing in the area: the alluvial aquifer, the Continental Terminal aquifer and the fractured basement aquifer. Several boreholes in the first and second aquifers show high concentrations of NH₄, NO₂ and heavy metals. The boreholes belonging to the third aquifer show concentrations of NO₃ considerably exceeding the WHO recommendation value between 100-1500 mg/l making this resource unfit for water supply. Reasons behind these excessive levels were mainly explained through the direct discharge of wastewater which is common in the Sahel region into the underground. However, the increased concentrations of NO₃ in some wells during the rainy season imply a source in the unsaturated zone which mobilizes the nitrate during the infiltration.

In addition to nitrate, elevated concentrations of heavy metals such as arsenic and cadmium were detected in the basement aquifer proving the possible infiltration of contaminants from the top layers.

These results show that the monitoring tools offered within the technical cooperation framework enable to detect and trace the contaminants. however, they alarm the authorities to meet measures to protect this resource urgently.