THE VULNERABILITY OF AFRICA'S SURFICIAL AND GROUNDWATER AQUIFERS TO URBAN POLLUTION

In preparing the Early Warning Bulletins and the Vulnerability Maps covering Bamako, Niamey, Ougadougou and their peripheral districts, the research teams undertook the following tasks and developed the following outputs:

1. Aquifer systems were sampled and analysed for hydrogeological and chemical parameters;
2. Pollutant sources were identified and, although the cartographic data requires some improvement. The approach of the Ouagadougou Early Warning Bulletin is slightly different due to the pattern of its aquifer (a granitic basement lying upon a network of faults, resulting in a heterogeneous aquifer);
3. Precipitation records were collected and stored. This information needs to be integrated into data relating to the flow regime of the Niger River recorded in Bamako and Niamey and into those relating to the replenishment of drinking water reservoirs in Ouagadougou;
4. Progression and trend indicators were collated (although still separately processed and stored), making it possible to identify parameters for raising awareness among city planners on the vulnerability and degree of pollution in their urban aquifers. In Bamako, only field analyses on water conductivity were carried out.

In conclusion, the situation in West Africa’s Sahelian Zone can be presented as follows:

Bamako, Mali and Niamey, Niger
The upper part of the aquifer is protected from pollution by a sewerage system and covered by a water supply network, while the deep aquifer is in direct natural contact with pollution leaching hot spots beside the river. Boreholes drilled into the deep aquifer are in hydraulic connection with the upper part of the groundwater.

Ouagadougou, Burkina Faso
The upper part of the aquifer is protected from pollution by a sewerage system and covered by a water supply network, while the lower, faulty aquifer is connected to the surface due to hill impoundments. Boreholes drilled into the faulty areas are in hydraulic contact with the upper part of the groundwater located immediately above the faulty areas.

Bulletins for Bamako, Niamey & Ouagadougou