Hydrochemical characterization of aquifers using sequential multivariate analyses and geographic information systems in a tropical setting

Abstract

This study demonstrates yet another innovation in the application of multivariate analysis to the understanding of regional hydrochemical processes in a tropical setting. Sequential Q-mode hierarchical cluster analysis (HCA) and factor analysis were used jointly with geographic information systems (GIS) and conventional graphical methods to determine spatial groundwater types in Ghana, and the spatial variation of the major sources of hydrochemical change in groundwater in Ghana. This study finds that two major groundwater types exist in the country: the Na-Cl groundwater types, which dominate the coastal aquifers where groundwater salinity is high, and Na-K-HCO3 groundwater types, which dominate aquifers farther inland. The major source of variation in hydrochemistry of groundwater in Ghana is mineral weathering and saline water intrusion. Silicate mineral weathering has strong effects in the more inland aquifers whereas saline water intrusion has the greatest effects along the coast. Chemical fertilizers, organic manure, and domestic sewage represent the second-most important source influencing groundwater hydrochemistry in Ghana. Effects of these are highest in areas where aquifers are relatively shallow and chemicals are heavily used, such as the Keta Basin. The third-most important source is the oxidation of organic carbon by nitrate. Maps showing the variation of these three sources across the country have been generated using ordinary kriging and are discussed here. © 2011 American Society of Civil Engineers.