Groundwater geochemistry and hydrogeochemical processes assessment in Bantul, Yogyakarta, Indonesia

In Bantul, Southern Yogyakarta, groundwater is the main source of domestic water needs. Therefore, knowing the hydrogeochemistry of groundwater is crucial in order to manage a sustainable groundwater resource. To characterize the compelling geochemical processes that control the groundwater chemistry, further hydrogeochemical examinations were directed in the area. Thirty groundwater samples were collected from shallow dug wells during the early dry season (April 2021). Sampling procedures and chemical analysis were carried out as per standard methods with secondary data obtained in 2006. The geochemical evaluations were depicted using several graphical plots dependent on the ionic constituents, hydrochemical facies, and controlling factors of groundwater quality. Two major hydrochemical facies were identified: alkaline-earth water with higher alkali; bicarbonate predominated (62%) and alkaline-earth water; bicarbonate predominated (32%). Weathering of silicate minerals occurs in 70% of recent samples and predominantly regulates major ion chemistry such as calcium, magnesium, sodium, and potassium. Chloro-alkaline indices 1,2 values signify that there are two potential rock-water interaction processes in the study region, namely the ion exchange and reverse ion exchange. Concentrations of nitrate, sulfate, and chloride indicate that the water chemistry has not been heavily contaminated by the land use in the area and is still mainly controlled by geogenic processes rather than anthropogenic activities.