Hydrogeochemical investigation of groundwater in Dhaka City of Bangladesh using GIS and multivariate statistical techniques

GIS and multivariate statistics along with the geochemical approaches were applied in this study to investigate the hydrogeochemical behavior, source apportionment of groundwater pollutants and their spatial distribution in the aquifer system of Dhaka City, Bangladesh. A total of 33 groundwater samples were collected and analyzed, in order to evaluate the geochemical constituents of groundwater. Results found that, the trends of cations and anions are Na+> Mg2+> Ca2+> K+ and HCO3- > Cl- > SO42- > NO3- respectively, and Ca2+-Mg2+-HCO3- is the dominant groundwater type. Except Na+, K+, Cl-, F- and NO3- all others measured parameters fall within the permissible limits. However, silicate weathering was identified as the major processes of controlling the groundwater solute content. Besides, cation exchange plays a significant role, influencing the water chemistry of the aquifers. Aqueous speciation model revealed that, aquifer materials were more saturated with aragonite, calcite and dolomite, and under-saturated with halite. From regression and correlation analysis it was found that, EC, Cl- and SO42- were correlated with each other's; which might helpful for site specific monitoring of groundwater quality. Principal component analysis (PCA) and cluster analysis (CA) were also employed to appraise the sources of contaminants, and it was explored that both natural and anthropogenic factors were influencing the groundwater quality. Groundwater was contaminated due to induced river recharge and rapid infiltration of contaminated water through the recharge areas. In this situation it is expected that, outcomes of this study will provide useful insights to planners for sustainable management of groundwater resources of this megacity.