Spatial distribution of dominant ions in the groundwater in Banyumudal Groundwater Basin, Central Java, Indonesia

Groundwater basin is an area with hydrogeological limits where it is happened all of hydrogeological processes. Banyumudal Groundwater Basin is one of groundwater basin with unique characteristic because of receiving water source from surroundings area, that would influence probably to the water quality. This study was conducted to: (1) know the spatial distribution of dominant ions concentration in the groundwater; (2) analyze surroundings factors that influence the spatial distribution of dominant ions in the groundwater. To realize the objectives, it was carried out the removal of groundwater samples in the observational wells that were determined by purposive sampling. The analyzed elements were Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄^2-, HCO_3-, CO₃^2-, Cl^- and Fe²⁺. The concentration of the dominant ions was realized in the form of Stiff Diagram and then was plotted in a map, so that it could be known the distribution. To analyze the process of mixing between the groundwater and water from the other sources with different chemical characteristics, it used the Piper Diagram, whereas to analyze the surroundings effects to the ionic concentration, it was conducted the analysis of quantitative descriptive. The study results showed that the groundwater from the northern part of Banyumudal Groundwater Basin has higher concentration of dominant ions compared with the southern ones. Viewed from each ion, the ionic concentration of Ca²⁺ and HCO_3- are higher than other dominant ions and have more varied values, so that the change of chemical characteristics of the groundwater would tend to be determined by the concentration change of them. Type of rocks is the most influencing factor to the concentration of dominant ions in the study area. Nevertheless, the domestic waste has also little effects related to the sanitary condition in around of samples location of the groundwater. © The Authors, published by EDP Sciences, 2019.