Study of the Connection Between Yogyakarta – Sleman Groundwater Basin and Pajangan Hill (as a Non-Groundwater Basin Area) Using Groundwater Geochemistry and Isotope

Abstract This study investigates the hydrological connectivity between the Yogyakarta-Sleman Groundwater Basin (GWB) and the non-groundwater basin (non-GWB) area of Pajangan Hill using geochemical and isotopic methods. A total of 28 groundwater samples were analyzed for major ion content and isotopic composition, sampled from shallow wells, deep wells, and springs. Ion chromatography and cavity ring-down spectrometry were employed for analysis. The findings reveal that groundwater in Pajangan Hill predominantly consists of calcium bicarbonate, while Yogyakarta-Sleman GWB includes calcium bicarbonate, calcium nitrate, and sodium bicarbonate. Isotopic analysis indicates that water samples close to the Local Meteoric Water Line (LMWL) likely originate from local rainwater infiltration, maintaining their original isotopic composition. Despite some geochemical similarities, based on classification and composition analysis, significant differences in major ion concentration values suggest no hydrogeological connection between the two regions. The distinct lithologies, limestone in Pajangan Hill, and young volcanic deposits of Merapi in Yogyakarta-Sleman GWB further support this conclusion, indicating no hydrological connectivity between these areas.