Based on the results of the hierarchical cluster analysis (see Fig. for the dendrogram), we classified the metal-contaminated sites into three groups (Group 1, 56 sites; Group 2, 104 sites; and Group 3, 34 sites). Although there is no absolute criterion for determining the number of clusters in hierarchical cluster analysis, using more than four groups resulted in clusters with fewer than 20 sites. We therefore used a three-group classification.