Application of Statistical and Spatial Outlier Identification for Evaluating the Environmental Baseline of Iron in Shallow Groundwater

Environmental baseline is essential for local environmental management, and a series of methods have been carried out for solving this issue. In this study, sixty-two shallow groundwater samples from the urban area in Suzhou, northern Anhui Province, China have been collected and analysed for their iron concentrations, and then processed by either statistical (box plot) or spatial analyses (spatial clustering) for outlier identification. The results indicate that four and five samples have been identified as outliers by box plot and spatial analysis, respectively, and the rest of the samples (fifty-four) have been set as environmental baseline samples. Their mean ± 2σ concentration is then set as environmental baseline (0-104.720 μg/L). The study demonstrated that spatial analysis is useful for assisting the outlier identification during evaluating the environmental baseline relative to statistical methods.