An Unseen Contamination
Beneath the bustling Barcelona metropolitan area lies the Llobregat Delta aquifer, a freshwater resource historically used for urban, industrial, and agricultural supply. Geologically, the delta is a complex of Quaternary-era sand and gravel layers. The main aquifer is a confined body of permeable sediment, 10 to 20 meters thick, located 60 to 70 meters below the surface. For decades, intensive groundwater extraction—peaking at 130 cubic hectometers in 1973—lowered the natural water table. This overexploitation reversed the natural hydraulic gradient. Instead of freshwater pressing out to sea, the higher pressure of the denser saltwater now pushes it inland into the aquifer.
This process, known as saltwater intrusion, has been studied here since 1965. The contamination advances along preferential high-permeability zones, creating plumes of saline water that render wells unusable. By the late 2000s, approximately 30% of the aquifer was already salinized. Monitoring wells show a wide mixing zone where chloride concentrations can range from 1,000 to 15,000 milligrams per liter, far exceeding potable standards. The advance is tracked using a network of piezometers that measure electrical conductivity, an indicator of salinity.