Groundwater withdrawal in randomly heterogeneous coastal aquifers

We analyze the combined effects of aquifer heterogeneity and pumping operations on seawater intrusion (SWI) in coastal aquifers, a phenomenon which is threatening Mediterranean and worldwide regions. We conceptualize the aquifer as a three-dimensional randomly heterogeneous porous medium, where the spatial distribution of permeability is uncertain. The geological setting of our study is patterned after the coastal aquifer of the Argentona river basin, in the Maresme region of 10 Catalonia (Spain). Numerical simulations of transient, three-dimensional, variable-density flow and solute transport are performed within a stochastic Monte Carlo framework. We consider a variety of groundwater withdrawal schemes, designed by varying the screen location along the vertical direction and the distance of the wellbore from the coastline and from the freshwater-saltwater mixing zone, in order to assess the impact of the pumping scenario on the contamination of the freshwater pumping well for a prescribed production rate. SWI is analyzed by examining isoconcentration curves and global 15 dimensionless quantities characterizing (i) inland penetration of the saltwater wedge and (ii) width of the mixing zone. Our results indicate that heterogeneity affects the (three-dimensional) seawater wedge either in the presence or in the absence of pumping, by reducing toe penetration and enlarging the width of the mixing zone. Simultaneous extraction of fresh and saltwater from two screens along the same wellbore located within the transition zone is effective in limiting SWI during groundwater resources exploitation. 20