A framework for assessing groundwater vulnerability and pollution risk in transboundary aquifers: Insights from the Estonian-Latvian transboundary area

Estonian-Latvian transboundary area The primary aim of this study is to develop and apply a harmonized framework for assessing groundwater vulnerability and pollution risk in the Estonian-Latvian transboundary area. The DRASTIC and modified DRASTIC methods were employed to evaluate natural vulnerability, while DRASTIC-L and modified DRASTIC-L methods were used to integrate land use and assess pollution risk. Sensitivity analyses were conducted to identify the influence of key parameters, and results were validated using pollutant infiltration time calculations. This multi-method approach addresses the region's geological complexity and incorporates anthropogenic impacts to provide a comprehensive assessment. The study reveals significant spatial variability in groundwater vulnerability, influenced by sediment composition, groundwater level, and land use. High-risk areas are predominantly located in regions with sandy sediments, shallow groundwater, and intensive agricultural activity, while zones with deeper groundwater and clay-rich sediments show greater natural protection. By integrating pollution risk mapping with traditional vulnerability assessments, the study highlights the critical role of anthropogenic pressures in shaping contamination risks. The findings underscore the importance of harmonized cross-border data collection and provide a replicable framework for sustainable transboundary groundwater management. These insights contribute to protecting water resources and ensuring the availability of safe drinking water for present and future generations. • Harmonized groundwater vulnerability framework for transboundary aquifers. • DRASTIC-L reveals pollution risk by combining vulnerability and land use factors. • High-risk areas linked to sandy soils, shallow groundwater, and agriculture. • Infiltration time analysis supports index-based vulnerability assessments. • Cross-border data harmonization is crucial for reliable groundwater management.