Integration of Stratigraphic Data, Pump Test and Geophysics for the Analysis of Shallow Unconsolidated Aquifers in West Africa and Identification of Suitable Condition for Manual Drilling

Manual drilling relies on human energy to construct a borehole (Danert, 2015). It can be an effective strategy to increase access to groundwater but it can be applied only where shallow geological layers are relatively soft and water table is not too deep. Therefore it is important to identify those zones with suitable conditions, investigating the characteristics of shallow porous aquifers. Hydrogeological studies are often focused in deep fractures aquifers, more productive and able to ensure water supply for large settlements. Shallow porous aquifers are not considered. This research propose a method to characterize shallow aquifers through the integration of borehole logs data processing, pump test in large diameter wells and geophysical investigations. A dataset of 160 borehole logs was processed using the software TANGAFRIC with the following procedure: a) identification of common categories (nouns and adjectives) in the dataset of Senegal and Guinea; b) codification of each stratigraphic layer; c) extraction of textural composition of layers by means of a weighted average process for 2 m depth intervals and then aggregated for user defined intervals; d) estimation and extraction of hydraulic conductivity (K), using available published table comparing texture and estimated K. Pump and recovery tests in 11 large hand dug wells was carried out in order to provide information on hydraulic parameters and texture of shallow porous aquifers (as pump tests data in deep boreholes are not representative of shallow aquifers) ; different methods to calculate K and T has been applied and results are compared to K values estimated from nearby stratigraphic logs and geophysics survey (vertical electrical soundings). The integration of these 3 methods allowed to define geometry and hydraulic behavior of shallow unconsolidated aquifer, identifying suitable areas for manual drilling.