EVALUATION OF GROUNDWATER CONTAMINATION USING GEOCHEMICAL ANALYSES AND FUZZY TECHNIQUE

The evolution and degradation of the groundwater quality in a municipal area of Busan City, Korea were investigated by the geochemical analyses and the fuzzy technique. The mean concentrations of cations and anions in groundwater were shown in the order of Na>Ca>Mg>K and Cl>HCO₃>SO₄>NO₃, respectively. By Gibbs and Piper plots, rock weathering was a main factor controlling the groundwater chemistry in the study area, and salinized river water and municipal contaminants also influenced the groundwater quality. The Ionic relationship and mineral saturation index exhibited the geological and geochemical processes of evaporation, weathering, and mineral dissolution. The predominant influence of the gypsum, anhydrite and halite minerals suggested the over to under saturated condition under precipitation, deposition and dissolution processes of the host rocks. The fuzzy logic membership tool was used to describe the input data of groundwater chemical components as 0.0 – 1.0 scale based on the possibility of being a member of a detailed set. The spatial maps of the fuzzy membership values of all the chemical parameters were produced using the inverse distance weighted interpolation method (IDW). The final fuzzy membership map was overlaid in the fuzzy overlay tool. The fuzzy overlay tool allowed the analysis of the possibility of a phenomenon belonging to multiple sets in a multicriteria overlay analysis. The characteristics of groundwater were primarily due to the natural processes such as mineral dissolution, ion exchange and leaching. Secondarily, the salinized Suyeong River and municipal contaminants increased the degradation of the groundwater quality. This research concluded that the geochemical analyses and the fuzzy GIS method were very useful to identify the sources and distributions of groundwater contamination.