Groundwater vulnerability and pollution risk assessment in the Estonian-Latvian transboundary area

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Protecting groundwater resources is of fundamental importance as groundwater is a crucial source of drinking water worldwide. Despite its overall abundance, the task of maintaining both the quality and quantity of groundwater is challenging due to population growth and intensified agricultural activities. Therefore, proactive protection measures are needed to prevent the contamination of this vital resource. In order to improve groundwater management and protection, groundwater vulnerability assessment methods are developed to identify the most vulnerable areas. This study focuses on the Estonian-Latvian transboundary area, recognizing the need to effectively manage the protection of the shared resource between the countries. The assessment of the natural groundwater vulnerability in the Estonian-Latvian transboundary area is conducted with the index-based modified DRASTIC method. Particularly crucial in areas characterized by diverse Quaternary sediments and a confined aquifer, a modified version of the DRASTIC method increases precision in vulnerability assessment results. Additionally, a numeric vulnerability assessment method based on pollutant movement time is used to compare and validate the results, enhancing the reliability of the vulnerability maps. In addition to the natural vulnerability assessment, the pollution risk map serves as a valuable tool in identifying areas in need of protection by connecting the impact of anthropogenic pressure with the vulnerability defined by hydrogeological factors. To accomplish this, the DRASTIC-L method is used to determine the pollution risk in the Estonian-Latvian transboundary area. The DRASTIC-L method uses an additional parameter, land use, for a more precise vulnerability assessment. The results emphasize the importance of developing accurate vulnerability assessment methods based on regional geological conditions. While natural vulnerability maps offer insights to the intrinsic vulnerability of an area to groundwater contamination, a comprehensive risk assessment requires the inclusion of pollution risk maps, highlighting the significance of anthropogenic activities in shaping contamination risks. In addition to advancing groundwater vulnerability and pollution risk assessment methodologies, this study emphasizes the necessity of international collaboration. Groundwater flow knows no national borders, highlighting the collective responsibility for protecting this shared resource and ensuring the availability of safe drinking water for present and future generations.