The Hidden Information in Observations of Groundwater Well Records in a Complex Multilayer Aquifer África de la Hera-Portillo, Eduardo Peña-Corriá, Rodrigo García-Lorenz, Julio López-Gutiérrez, Ester Rodríguez-Jiménez, Rocío Martín-Gamo, Carmen Macías, Cristian Cobaleda, Fortunato García-López, and Teresa Orozco-Cuenca Abstract The Los Arenales region in the Duero river basin (Spain) is an exten- sive area which today is formed by three adjoining groundwater bodies. The tradi- tional conceptual model for this area assumes three different hydrostratigraphic units: Quaternary (unconfined aquifer), and Upper (unconfined and semi/confined aquifers) and Lower Miocene (deep semi/confined aquifer) formations. The Medina del Campo groundwater body (GWB) occupies the central part of the Los Arenales region. Within this GWB, the La Moraña region is perhaps the most important groundwater irrigated area. An experimental project by the Castile-Leon regional government for the period 1999–2013 recorded data from a set of eight groundwater moni- toring wells. In this paper, we analyze the records of groundwater levels and Elec- trical Conductivity (EC) at the monthly scale and compare the records between the observed wells. Our interpretation highlights a transition from the Upper Miocene leaky aquifer (in the east) to the Lower Miocene semi/confined aquifer (in the west). If this hypothesis is confirmed with further research, it should be checked at the entire GWB. Keywords Electrical conductivity (EC) · Groundwater levels · Hydrogeology · La moraña · Medina del Campo Á. de la Hera-Portillo (B ) · E. Peña-Corriá · R. García-Lorenz · J. López-Gutiérrez · T. Orozco-Cuenca Instituto Geológico y Minero de España (IGME), Ríos Rosas 23, 28003 Madrid, Spain e-mail: a.delahera@igme.es E. Rodríguez-Jiménez Confederación Hidrográfica del Duero (CHD), C/Muro 5, Valladolid, Spain R. Martín-Gamo · C. Macías · C. Cobaleda TRAGSA, Calle Julián Camarillo 6 B -3 A, 28037 Madrid, Spain F. García-López Servicio Territorial de Agricultura y Ganadería de Ávila, Pasaje del Císter nº 1, 05001 Ávila, Spain © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. Ksibi et al. (eds.), Recent Advances in Environmental Science from the Euro-Mediterranean and Surrounding Regions (2nd Edition), Environmental Science and Engineering, https://doi.org/10.1007/978-3-030-51210-1_263 1657