Physico-chemical properties and the stable isotope composition of groundwater in Mandalika and its surrounding, West Nusa Tenggara, Indonesia

Abstract Groundwater is a very important source of clean water in coastal areas such as the Mandalika area, Central Lombok Regency, and its surroundings. The Mandalika area is one of the special economic zones in Indonesia, and it is a world-class tourist destination. However, in terms of hydrogeology conditions, Mandalika is located in a poorly productive aquifer area. Therefore, it is necessary to identify the quality and existence of groundwater. The objective of this study is to assess the viability of groundwater as a source of clean water by analyzing its physico-chemical properties. Additionally, the study intends to pinpoint the origin of groundwater sources by examining stable isotopes of hydrogen (δ 2 H) and oxygen (δ 18 O). In order to achieve the objectives, a campaign of water sampling was conducted on several springs, drill wells, and also rainwater at different elevations. As a result, the range of physico-chemical characteristics of groundwater found with temperature values 30.60 °C-31.80 °C, pH 6.50-7.11, Total dissolved solids (TDS) 393.00 mg/L-1,384.00 mg/L, and Electric Conductivity (EC) of 789.00 μS/cm-2,780.00 μS/cm. Most of the groundwater samples collected met the drinking water criteria. According to isotope data, all groundwater samples are estimated to come from meteoric water and originated from a recharge area, which is located at an elevation of 15-285 masl. Based on these results. It can be concluded that groundwater is actually a potential source of clean water supply in this area, and research on the potential of groundwater quantity is urgently needed.