ABSTRACT

This chapter analyzes the spatial arsenic discontinuity with geostatistics that shows the pattern of arsenic concentrations in different areas. It examines how the nugget effects, sills, and ranges have shown locally erratic variations of arsenic concentrations. The deviating relationships between aquifer depths and arsenic concentrations are also a central issue. It shows that deep tubewells were also found to be contaminated, but at a low level of concentration. There is no uniformity in spatial arsenic concentrations corresponding to surface geology. The unevenness is due to the aquifer characteristics and surface geology. The Ganges-deltaic flood plain deposits contain very high and erratic concentrations of arsenic. The sharp micro-level variation of arsenic concentrations in the same aquifer raises a number of issues. Is geological variability the main cause of the differences? The variation of arsenic concentrations over time also raises the issue of the mechanism of arsenic in Bangladesh groundwater. What are the reasons for the variation of arsenic concentration with tubewell age: heavy withdrawal of groundwater for irrigation and domestic uses or geological origin and lithology? The chapter concludes that more research is therefore needed on depth-specific distribution in different geological settings to investigate the nature of arsenic mobilization as well as the role of organic matter in the mechanism of arsenic release in groundwater.