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In Bangladesh, the majority of the irrigation and drinking water is supplied from underground sources due to the limitation of surface water. In recent years, arsenic contamination has emerged as a fresh blow to the country. This paper gives an overview of the extent and severity of groundwater arsenic contamination in Bangladesh, as well as a review of the latest statistics and findings of numerous investigations about this issue. Recent reports of the British Geological Survey show that the groundwater in all 61 surveyed districts out of 64 is now contaminated with arsenic. On the other hand, a survey report of School of Environmental Studies, Jadavpur University, and Dhaka Community Hospital shows 47 districts are contaminated. The population exposed to the arsenic poisoning through drinking water is more than 25 million. In regard to arsenic pollution, Bangladesh is the most vulnerable country in the world. Unfortunately, until now, the cause of groundwater arsenic contamination has not been detected. Initially, several anthropogenic sources of arsenic were presented. Gradually, all were rejected based on the field observations. Finally, it was recognized that the source of arsenic is in the geological deposits. The two prevailing hypotheses, pyrite oxidation and oxy-hydroxide reduction, describe the cause of contamination. However, neither has been studied thoroughly with accurate field data. Therefore, the verdict is still out whether to support one hypothesis over the other. Thousands of people are suffering from arsenic diseases ranging from melanosis to skin cancer and gangrene, and many have even died. Unfortunately, there is no specific treatment for chronic arsenicosis, other than ceasing further intake of arsenic contaminated water. To overcome this predicament, awareness of the problem and the creation of watershed management are necessary.

Abstract:This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holding water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than that at the apex and at the delta. For the second point, the concept of 'memory effect' of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus, a temporary increase of water level has about five times as long-term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics.

The groundwater arsenic contamination problem in Bangladesh is the worst in the world. Two hypotheses are prevailing as the cause (mobilization) of groundwater arsenic contamination in Bangladesh. One is called "pyrite oxidation" and the other is "oxy-hydroxide reduction." According to the first hypothesis, groundwater arsenic contamination is human-made, which has a relationship with excessive groundwater withdrawal. On the other hand, according to the second one, the contamination is natural. The British Geological Survey (BGS) conducted an investigation to identify the cause of groundwater arsenic contamination in Bangladesh. Based on their findings, they rejected the pyrite oxidation hypothesis and accepted the oxy-hydroxide reduction hypothesis. However, several experts are opposing their research findings. Therefore, a case study is undertaken to examine the validity of the BGS findings. Although we obtained results which are similar to the BGS, the errors in the estimates of percent of wells contaminated, the key parameter of these analyse show that the present as well as BGS results are not dependable to make any conclusion about the cause of contamination. Moreover, the validity test shows that space-dependent relationships among different hydro-geological parameters for the heterogeneous aquifer system are not valid to represent time-dependent phenomena. Therefore, the conclusion made by the BGS is not valid. Still, there is a possibility that the pyrite oxidation hypothesis could be accepted. For a final conclusion we must observe these relationships in a time domain by generating reliable time-dependent field data.