Geochemical characterization of groundwater in a Miocene Aquifer, Southeastern Tunisia

Groundwater plays a dominant role in the southern part of Tunisia. Because of the lack of permanent surface-water reservoirs owing to the harsh climate, groundwater is the principal source of freshwater. Groundwater resource assessments and sustainability considerations are required for water management. Sampling surveys were undertaken in July 2004 from 18 wells. Eighteen variables (temperature [T, °C], pH, total dissolved solids [TDS], Na+, Cl-, Ca2+, Mg2+, SO42-, K+, HCO3 2, Fe3+, Mn2+, Zn2+, Al 3+, Pb2+, Cr3+, Cu2+, and F2) were determined from the water samples. We applied conventional classification techniques, such as Piper diagram and scatter plots, to evaluate geochemical processes. In addition, two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a sub-group of the data set to evaluate their usefulness and to classify the groundwater samples. Results show that groundwater in the area is generally brackish and highly to very highly saline. The abundance of the major ions is as follows: Na+ . Ca2+ . Mg2+ . K+ = Cl2 . SO4 22 . HCO3 2. Concentrations of trace elements were low, and under the maximum recommended level for human use. PCA indentified three major factors explaining 74 percent of the total variance in water quality; the major variations are related to the degree of groundwater mineralization. HCA shows that the wells are broadly divided into three major groups based on similar groundwater characteristics. Finally, results indicate that groundwater properties are varied spatially, and groundwater evolution in the study area is generally controlled by the prevailing geochemical processes of dissolution and precipitation of salts and minerals, ion exchange, and water recharge origin. © 2012 Association of Environmental & Engineering Geologists.