The report describes the results of the study of arsenic pollution in groundwater in Nadia as well as the hydro-chemical study of the river Hoogly in West Bengal. The alluvial tract along the river Hoogly covering a stretch of around 470 km encompassing eight districts is affected by arsenic pollution of ground water, the source being geogenic.
The occurrence of iron-pyrite and the change of geo-chemical environment due to over-exploitation of groundwater or excessive fluctuation of groundwater table are the possible reasons for decomposition of pyrite to ferrous sulphate, ferric sulphate and sulphuric acid. As a result, the groundwater of the region is characterized by high iron content.
In the study, the water samples collected from selected villages of Nadia district, West Bengal shows elevated concentrations of arsenic. The trace element data of lithological log of drill cuttings of the PHED bore-hole site at Ghetugachi in Chakdah block, Nadia district shows consistent arsenic contamination in the upper aquifer also.
The hydro-chemical study of the river Hoogly also shows consistent arsenic concentration in water and sediment samples of the river. The content of arsenic in the sediments was higher than the ones along the banks of the river Hoogly.
The Farakka Super Thermal Power Plant (STPP) operating in the state of West Bengal is another source of arsenic contamination in the nearby area. The analysis of fly ash deposited in the fly ash disposal ponds indicate arsenic content of the order of 400-500 µg/g. The ash generated from thermal plant finds its way into open environment i.e., air, water and soil from atmospheric precipitation, spillage from pipelines carrying fly ash slurry to ash ponds and from decanted water of ash pond. It contaminates groundwater due to seepage and mixing of fly ash into surface and subsurface water.
The study points out the urgent need for shifting to alternative drinking water sources and for implementation of watershed management programmes to develop small surface storages to address the problem.
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