Hydrogeochemical characteristic and water quality index of groundwater and streamwater at Nam Mu River basin, Lai Chau province in northwest Vietnam

Assessing the quality of groundwater and upstream water in regions experiencing water scarcity during the dry season, such as the mountainous districts of Northern Vietnam, holds immense significance in the management, utilization, and preservation of natural water resources. In this study, we collected and analyzed 54 samples of groundwater and upstream streamwater within the Nam Mu river basin in Lai Chau province during the dry season. These samples underwent thorough analysis for physicochemical parameters, major ion concentrations, and trace elements. Some results revealed a close relationship between streamwater and groundwater, indicating a similar chemical composition. These waters could be classified based on geological formations, yielding two primary water types in the area. The first type, characterized by Ca ^2+ - Mg ^2+ - HCO _3 ^− is prevalent in Triassic terrigenous sediments. The second type is a mixed water type, ranging from Ca ^2+ - Mg ^2+ - Cl ^− to Ca ^2+ - Na ^+ - HCO _3 ^− , primarily distributed in Permian felsic volcanic formations. These distinct water types are primarily the result of interactions between water and rock, precipitation processes, and ion exchange phenomena. Geochemical simulation results demonstrated the supersaturation of aragonite, calcite, and dolomite minerals, leading to the precipitation of carbonate minerals. Concurrently, the simulation indicated a tendency to dissolve minerals such as fluorite, gypsum, halite, and sylvite. The assessment of water quality using the WQI indicates that, in accordance with QCVN 01-1:2018/BYT 2018 standards, the majority of groundwater and streamwater are suitable for domestic use. However, exceptions exist in certain sample locations where water quality exceeds permissible standards, primarily due to elevated levels of Fe, Mn, and NO _3 ^− concentration. Hence, it is important to implement water treatment processes for the water sourced from these specific locations before their utilization in daily activities to ensure the safety and well-being of the local population.