Evaluation of Processes Affecting the Variation of Groundwater Quality in Quang Nam, Da Nang, Vietnam

Groundwater quality is vulnerable to various processes. In this study, processes affecting groundwater quality were evaluated in coastal aquifers of Quang Nam - Da Nang (QNDN). A chemical data of 426 groundwater samples from 27 monitoring wells in the period 2011-2018 were analyzed. Principal Components Analysis (PCA) and Base Exchange Indices (BEXD) were applied for the evaluation. The PCA results suggested the influences of natural processes and anthropogenic activities on the groundwater quality. Seawater influence contributed to the dominant ions in groundwater; mineral weathering and dissolution mainly increased the alkalinity, Ca2+, and Mg2+; SO42- reduction explained the low SO42- in the groundwater; and reductive dissolution of Fe (hydroxides) caused Fe exceeding WHO’s drinking standard. Intensive groundwater abstraction generated up coning of saline groundwater; discharge from agricultural practices, industrialization, and urbanization were considered as sources of high NO3- in groundwater. The integration of monitoring data and BEXD gave a better interpretation of salinization and freshening, which can be masked by the memory effects of seawater transgression and regression in history.