Delineation of trace metals contamination in groundwater using geostatistical techniques: A study on Dhaka City of Bangladesh

Abstract

Abstract Due to over-exploitation and unsustainable groundwater resource management, Dhaka the capital city of Bangladesh has posed an alarming risk of elimination in terms of quantity and its quality. Therefore, this study intended to evaluate the threat of groundwater contamination by geostatistical approach considering several major trace elementals concentrations. Besides, a number of pollution evaluation indices i.e., single-factor pollution index (I), nemerow pollution index (NI), heavy metal evaluation index (HEI), and the degree of contamination (Cd) were also used to quantify the level of the studied trace metal pollution in groundwater. The results of best-fitted semivariogram model showed the moderate spatial dependence for Fe, NI, and HEI; and weak spatial dependence for Mn. From cross validation result, it was found that, ordinary kriging produces the most accurate distribution maps for Fe, Mn, NI and HEI. Thematic maps showed the spatial distribution of Fe, Mn, NI and HEI, which exhibited an increasing trend of pollution towards the western and the south-western part in the study area. Besides, probability maps were developed using indicator and the probability kriging methods, to assess the risk of groundwater pollution, which also illustrated almost similar trend like thematic maps. However, standard error maps showed evidence that, the indicator kriging is more suitable method than that of the probability kriging to estimate the risk of groundwater metal contamination. Therefore, it has been suggested that, geostatistical method can be used for planners and policy makers to develop strategies for sustainable management of groundwater resources and to minimize the pollution.