Evaluation of arsenic contamination potential using indicator kriging in the Yun-Lin aquifer (Taiwan)

Data on the quality of groundwater obtained from several multi-level monitoring wells indicated that arsenic (As) concentration far exceeds the drinking water supply standard in the coastal aquifer of the Yun-Lin, Taiwan. In this study, an estimated As probability risk was computed using indicator kriging to assess the As contamination potential of exceeding the drinking water supply standard in the Yun-Lin county. A three-dimensional (3D) spatial variability model was presented to analyze anisotropically the variation of As concentration using a multi-level threshold indicator variable. This 3D estimator overcomes the scarcity of the data and establishes a vertical correlation of measured As data. The results indicate high As pollution probability in the coastal area and in the Pei-Kang river basin. The highest probability, 0.92, of the As pollution is in the shallow aquifer of the Kou-Hu. The contamination potential of As is primarily within an aquifer depth of 180 m. The contaminated aquifer (<180 m) is not suitable for supplying drinking water. The contamination potential of As is low at the depths of more than 190 m. However, the probabilities associated with the As pollution still exceed 0.2 in the deep aquifer of four coastal townships of the Yun-Lin, and may pose risks to human health if the groundwater is used for drinking.