Despite the observed large variations in concentrations of metals, the levels of concentrations at the 194 metal-contaminated sites generally increased in the order: Cd (median: 0.013 μg/L)  Pb (0.072 μg/L) < Ni (0.45 μg/L) < Cu (1.2 μg/L) < Zn (9.1 μg/L)  Al (22 μg/L) (Fig. ). Compared with Group 2, where the overall metal concentration levels were similar to those at all metal-contaminated sites, the Cd concentrations in Group 1 were notably higher (median: 0.12 μg/L in Group 1 vs. 0.007 μg/L in Group 2).