This study, carried out in the framework of the MedProgramme Project, presents an evaluation of the intrinsic vulnerability of the Grombalia coastal aquifer in northeastern Tunisia using the GOD method, with particular attention to the Soliman Lagoon zone. The GOD method—based on Groundwater occurrence (G), Overall lithology of the unsaturated zone (O), and Depth to water table (D)—provides a qualitative framework for identifying zones most susceptible to contamination. The Grombalia aquifer system is under increasing pressure from intensive agriculture, urban expansion, and saline water intrusion, particularly near the Soliman Lagoon, a sensitive interface between groundwater and coastal ecosystems.

The resulting vulnerability map shows a spatial variation ranging from low to high vulnerability, with the highest risk zones concentrated along the Soliman Lagoon’s southern perimeter. These areas are characterized by shallow phreatic levels, highly permeable lithologies (sands and silty sands), and limited natural protective layers. The GOD index values in these high-risk zones exceed 0.6, placing them in the moderate-to-high vulnerability category. In contrast, more inland zones with deeper water tables and less permeable overburden exhibit lower vulnerability scores.

The findings underscore the necessity for integrated groundwater protection measures, especially in the lagoon’s vicinity, where both ecological and socioeconomic stakes are high. This study supports the implementation of land-use regulation, monitoring programs, and pollution mitigation strategies aimed at preserving water quality and ensuring the long-term sustainability of the aquifer system.