A better understanding of groundwater systems helps safeguard drinking water

Coastal communities rely heavily on groundwater for freshwater supplies. Seawater intrusion is common and worsened by the intensification of groundwater extraction due to urban development, tourism, and agriculture. It is a self-perpetuating problem, with smaller aquifers being particularly vulnerable. Recycling wastewater is a way to improve water supply while simultaneously mitigating seawater intrusion.

Port de la Selva, on the north-eastern coast of the Iberian Peninsula, has adopted a pioneering approach to Soil Aquifer Treatment (SAT) – recycling wastewater to recharge groundwater aquifers for human consumption. This initiative was prompted in part by the area's population surge from 1,000 in winter to 10,000 during the holiday months.

The hydrogeological conditions and processes involved mean that successfully realising the potential of SAT requires an intensely detailed understanding of all the intricacies within the hydrogeological system. In a study by the Universitat de Barcelona, electrical resistivity tomography (ERT), an advanced geophysical imaging technique using remote sensors, was employed to provide the detailed subsurface information needed for accurate groundwater modelling and solution design for Port de la Selva. An interdisciplinary team – comprising scholars, professionals, and students – gathered more than 6,300 data points from the local aquifers and utilised Seequent’s Leapfrog Geo and AGS Res2DInv software to manipulate and interpret the vast amount of information they collected.

Multiple data points were progressively and rapidly combined into a digital 3D model of the groundwater system, with the ability to update the interpretation dynamically as new data was added.

The ERT studies demonstrated low resistivity in the shallow coastal aquifer, indicating a high concentration of dissolved salts. Saltwater had intruded into the freshwater, drawn in by over-pumping to meet local needs.

These findings facilitated the town council’s decision to take action, including using a portable desalination plant at one location and recharging the shallow aquifer with treated wastewater to guarantee the water supply from local resources.

By ensuring a reliable water supply using only local water resources, Port de la Selva has safeguarded its future and can safely welcome the summer tourism trade upon which it relies.

The problems experienced at Port de la Selva are mirrored in many places across the EU and globally. The approach executed here is scalable to nearly all of these regions. The use of advanced web-based analysis and visualisation tools enhances informed decision-making, which is critical for addressing water supply issues.

“If we didn’t have the ease of integrating geophysical and lithological data from boreholes in Leapfrog Geo software, there’s no way we could have developed the aquifer and saltwater model that fast with a high degree of confidence,” says Alex Sendrós, a postdoctoral researcher at the Universitat de Barcelona.

#WaterWiseEU campaign 

This story has been submitted by a partner of the #WaterWiseEU campaign. The EU-wide campaign focuses on water resilience, aiming to change the way we see, use and value water. Find out more about the campaign and how you can get involved.