Geospatial assessment of groundwater arsenic contamination in the Holocene aquifers of Bengal Delta from western parts of the Bhaghirathi River in West Bengal, India

Abstract

The spatial and subsurface distribution of groundwater arsenic (As) and iron (Fe) in tubewell water were studied with the help of geospatial technique in Purbasthali Blocks I and II of Purba Bardhaman district in Bengal Delta of West Bengal. About 50.40% of tubewell samples (N = 127) have As above the WHO guidelines’ value (> 10 μg/l). Among these contaminated tubewells, about 82.81% tubewells are installed within 60 m depth. All the samples (N = 127) have Fe concentration above 300 μg/l. Maximum concentrations of As and Fe in tubewell samples are 374 μg/l and 17,600 μg/l, respectively. Mean values of As and Fe concentrations are 48 μg/l and 4016 μg/l, respectively. About 29.92% and 33.86% of samples have As and Fe above mean values, respectively. The correlation between As and Fe is significantly positive (R = 0.618) and presence of high concentration (17,600 μg/l) of dissolved Fe indicates strong reducing condition of the aquifers. Maximum number of samples (34.64 %) are from 21 to 40 m depth. Most of the As-contaminated tubewells are located within the depth of 21 to 40 m in the Holocene Newer Alluvium aquifers. Static water level (SWL) depth 10.1 to 15 m below ground surface, occurring in most part of the Katwa Formation, is found to be As-contaminated. Arsenic pollution in the Holocene aquifers is mostly confined in Katwa Formation. Sijua Formation is almost As-safe in groundwater which is in the upper Pleistocene to lower Holocene in age. Most of the As-contaminated tubewells in Katwa Formation are located in the Holocene Newer Alluvium and spatially associated with meander cut-offs, paleo-meander scars, abandoned channels, and back swamp areas.