Annual maps of sites where % outliers ≥ 10% of the valid samples, e.g. sites which had ≥ 10% of their sample pairs with Z Scores outside of the range [-3,3]. Sites that meet the above criteria are identified with a colored dot. Furthermore the color of the dot indicates the dominant bias direction (red or pink) or lack of a dominant bias direction (blue). Legend: ● 0-40% of the outlier pairs had Z<-3 (SO 4 <<3*S) ● 41-60% of the outlier pairs had Z<-3 (SO 4 <<3*S) ● % of the outlier pair had Z<-3 (SO 4 <<3*S)