Observations on elemental concentrations of groundwater in central Benin

SummaryGroundwater samples were collected at over 100 locations in Benin, West Africa, for the purpose of characterizing region-wide spatial variation in groundwater quality as indicated by concentrations of a number of elements measured within the samples. Analytic techniques ranged from field measures of conductivity and pH, to characterization of major and trace element concentrations using ICP-MS and ICP-OES. Five methods of data analysis were applied to the resulting data set: indicator variables, parameter plots, cluster analysis, variogram analysis, and principal component analysis (PCA). A number of observations are developed from these analyses including regional trends in concentrations and variation of concentration of major and trace elements in specific geologic settings. Perhaps most significant is the identification of a region in the southern portion of the study area where the element chemistry shows high spatial variability. This region had not been identified in prior studies of the regional geochemistry. The mechanisms leading to this variability remain under study. The results presented provide significant insight into the regional variation in groundwater elemental chemistry for Benin. Further, they provide further illustration of the utility of applying multiple data analysis techniques to assessment of regional water quality data sets.