Groundwater hydrogeochemistry in the southern part of Pujut sub-district, West Nusa Tenggara, Indonesia

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Abstract The southern sub-district of Pujut, which encompasses Mandalika’s Special Economic Zone, is a region focused on industrial and tourism growth. Groundwater supplies are necessary to fulfill the demands of the local population and the tourism sector. In groundwater exploration, one of the important parameters is hydrochemistry, whereas, in the research area, more studies are needed on this topic, especially in relation to hydrogeological conditions. The objective of this research is to comprehend the hydrochemical properties of the groundwater system present in this region. A total of 9 samples from drilled wells and 2 samples from springs were collected and assessed to ascertain the concentration of primary ions. The diagrams developed by Piper and Stiff were employed to categorize the groundwater facies and establish their correlation with the geological conditions. The results revealed that the chemical composition of the groundwater was classified into four unique categories, demonstrating differences in facies and groundwater systems. Group 1 comprises Ca-Mg-HCO3 facies characterized by bicarbonate water and is associated with calcarenite limestone and volcanic breccia. Group 2 is the Ca-Cl facies, distinguished by the presence of water rich in chloride. These facies are characterized by the occurrence of saline or brackish water associated with calcarenite limestone and are frequently observed in close proximity to the shoreline. A mixture of Na-Cl-SO4 characterizes group 3. The concentration of sulfate ions is high in this group, and their existence is due to the oxidation of sulfide minerals in altered volcanic breccias. Group 4 is the mix of Ca-Na-HCO3 type and is associated with alluvium deposits. Based on the previous explanation, groundwater that has the potential to be exploited is groundwater in the Ca-Na-HCO3 and Ca-Mg-HCO3 facies. According to the explanation, the groundwater that can be utilized is the groundwater in the Ca-Na-HCO3 and Ca-Mg-HCO3 facies.