Groundwater Quality of the Northern Lake Chad Basin

Christoph Neukum1, Helene Rieckh1, Mélanie Ndedje-Allah Ronelngar1, Djoret Daïra2, Sara Vassolo2
1 Bundesanstalt für Geowissenschaften und Rohstoffe
2 Tschadseekommission, N’Djamena, Tschad

P 11.2 in Beiträge zur Hydrogeologie Südamerikas und Afrikas

In the last years the Lake Chad Region has experienced a serious humanitarian crisis due to the Nigerian refugees fleeing from Boko Haram. People face food insecurity and malnutrition and they lack access to water in adequate quantity and quality as well as basic hygiene services. Groundwater is the most important source for water supply and its quality with respect to human consumption is of high priority. In order to improve the knowledge of groundwater characteristics in the northern basin of the Lake Chad, a field campaign was conducted. A total of 63 samples were taken: 62 from the uppermost aquifer at drilled wells and hand-dug wells and one sample from surface water. The water samples were analysed at BGR laboratories in Germany for stable isotopes, total ions and trace elements. In-situ pH, temperature, and electrical conductivity of all collected samples were measured using a handheld device.

Results show that the majority of the sampled groundwater is not suitable for drinking purposes, as 38 out of 63 water samples (60%) have a chemical composition that does not meet the WHO recommendation concerning drinking-water quality. Furthermore, if ammonia, aluminium, manganese, sodium, iron, and sulphate are considered additionally, only five out of 63 collected samples are suitable for drinking-water purposes. Fluoride concentration is the major limitation of water quality according WHO (2011) in the northern sub-area of the studied region. Concerning limitations in taste, sodium concentration is the responsible ion, which exceeds the threshold value of 200 mg/l in more than 75 % of all samples.

Although improved protection of groundwater may solve only some of the quality aspects in the study area, problems associated with the dissolution of specific ions in water during infiltration, percolation and groundwater flow may not be solved using the common tools of drinking-water protection. To overcome these problems, identification of other sources of drinking-water might be appropriate. Groundwater currently used for water supply is extracted from rather shallow depths compared to the total thickness of the upper aquifer. Consequently, it is recommended to investigate the deeper parts of the Quaternary aquifer for its suitability as drinking-water resource. Additionally, collecting more data about the lower, confined Neogene aquifer is recommended since it might be a reasonable alternative source for future water supply.