Multidisciplinary geophysical surveys for 3D hydrogeological conceptual model reconstruction in areas contaminated by fluoride in Nakuru area, East African Rift System (Kenya)

An extensive geophysical fieldwork was performed in Nakuru county (Kenya), Autumn 2018, aiming to study the shallow structure of the rift valley, within the framework of FLOWERED activities, an H2020 European Commission project (www.floweredproject.org). The overall objective of the project is to contribute to the development of a sustainable water management system in East African Rift areas affected by natural fluoride contamination. The investigated area is located in South-western Kenya near Nakuru, in the central part of the Kenya Rift. The area is characterized by a thick volcano-sedimentary succession of Pleistocene-Quaternary age, with volcanic rocks as lavas (phonolites, basalts, and trachytes) and pyroclastic flows and fall deposits (tephra, tuffs and fall deposits), intercalated with alluvial gravel and sands. The geophysical fieldwork was designed to implement a local detailed three-dimensional hydrogeological model of Nakuru area. We performed resistivity surveys at two different scales by using electrical resistivity tomography (ERT) and Hybrid-Source Audio Magnetotelluric (HSAMT), integrated by single station passive seismic measurements (HVSR). Overall, the performed surveys were helpful to delineate: a) depth and thickness of aquifers, b) aquitards or confining units and c) locating preferential fluid migration paths such as fractures and fault zones (Ghiglieri et al., 2017).