Geophysical surveys for improving the hydrogeological conceptual models in the semi-arid region of Valle Alto (Bolivia)

Geophysical methods provide important information for mapping the subsurface. In semiarid areas, a detailed knowledge of the aquifers geometry can assist to a better management of groundwater. In the Valle Alto (Bolivia), which is a semiarid region, there is gap in the knowledge about the aquifer system geometry and hydrogeological processes. Local reports indicated problems in some wells such as very low production and bad water quality (i.e. high concentrations of salts). In order to improve the knowledge about the aquifer system and identify the depth of the layers with saline water, the geophysical methods Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic (TEM) were applied. The main objective of this study is to refine the hydrogeological conceptual models and to delimitate the depth and thickness of saline layers. The TEM soundings are performed in a grid of 150 m separation, which provide significant information for proposing 2-D models that displays the lateral/vertical extent of the saline layers. While the ERT surveys were performed across the Valle Alto in order to obtain long cross sections where the aquifer geometry can be exposed. With the refined conceptual models, further planning and policies can be proposed for protection and sustainable groundwater exploitation.