The alteration wedge is unevenly distributed in the central region of Burkina Faso. Outcrops of
crystalline rocks can be seen everywhere on the sheet. Water drilling data made it possible to highlight
this inequality. The frequency of the encountered alteration depths associated with the water productivity of the
underlying aquifers made it possible to define four thickness bands. The average water productivities are depends on bands thickness. Geological, topographical, pedological, geomorphological and hydrographic maps are used for the correction, verification and validation of alteration maps. They are used to estimate and interpolate alteration depths in areas where drilling and geophysical data are not available. Taking into account the complexity of cartographic representation of alterations and the hydrogeological goal assigned to the map, it is necessary to define and determine reports and validity rates in order to better guide the users. The Validity Rate (VR) derived from the Validity Ratio (VR) which is the quotient of the statistical average over the average mapped alteration depths of a given interval.

lithology, phreatic surface, leaky phreatic aquifer, saturated alteration