Assessment of hydraulic conductivity distributions through assimilation of travel time data from ERT-monitored tracer tests

Assessing the spatial distribution of hydraulic conductivity (K) in natural aquifers is fundamental to predict the spatio-temporal evolution of solutes, a process that is mainly controlled by the heterogeneity of K. In sedimentary aquifers, the vertical variations of K are typically more relevant than the horizontal ones in controlling the plume evolution at the local scale; such K vertical distributions can be inferred by combining the Lagrangian formulation of transport with the assimilation of tracer test data via the esemble Kalman filter (EnKF). In this work, the data for the assimilation procedure are provided by monitoring tracer tests with electrical resistivity tomography (ERT). Our main objective is to show the possibility of directly using ERT data by assimilating the solute travel times, instead of the concentration values, thus avoiding the need for a petrophysical law. The methodology is applied to both a synthetic and a real test case and gives a satisfactory retrieval of the K field distribution, as well as of the solute evolution.