多変量解析による伊豆大島水源地下水の水質特性の解明

抄録

To supply safe and high-quality drinking water to the inhabitants of the volcanic Izu-Oshima island during periods of volcanic inactivity, quality analysis of groundwater from 17 sites and multivariate analysis were performed. The analytical indices were divided into four groups by cluster and correlation analyses : (a) 11 indices (Na, Ca, Cl^-, etc.) were that related to seawater intrusion, (b) 6 indices (HCO₃^-, B, As, Li, SiO₂ and water temperature) were that related to water-rock interaction in the volcanic area (WRI), (c) 2 indices (pH and NO₃^--N) were that inversely related to WRI and (d) the 4 other indices. Principal component analysis revealed that 68% of the original data set could be explained by only 2 principal components and that the water quality was influenced mainly by seawater intrusion and WRI. The first principal component corresponded to the overall influences of seawater intrusion as the major factor and WRI as the minor factor. The second principal component represented the influence of WRI. The samples of groundwater were grouped according to scores of each first and second principal component. Although the sites of water wells were contiguous, they showed different water quality owing to the influences of seawater intrusion and WRI. Concentrations of arsenic and boron in groundwater from some sites were strongly influenced by WRI and exceeded the Japanese criteria for drinking water. This indicates the importance of monitoring these elements in the groundwater of Izu-Oshima island.