The palaeosol model of arsenic pollution of groundwater tested along a 32 km traverse across West Bengal, India.
The distribution of As-pollution in groundwater of the deltaic aquifers of south-eastern Asia may be controlled by the subsurface distribution of palaeo-channel sediments (As-polluted groundwaters) and palaeo-interfluvial sediments (As-free groundwaters). To test this idea, termed the palaeosol model of As-pollution, we drilled 10 sites, analysed groundwater from 249 shallow wells (screened <107 mbgl), field-tested another 149 for As, and used colour as a guide to the presence or absence of As-pollution in a further 531 wells. Our work was conducted along a 32-km traverse running W to E across southern West Bengal, India. At seven drill sites we logged a palaeo-interfluvial sequence, which occurs as three distinct units that together occupy 20 km of the traverse. These palaeo-interfluvial sequences yield As-free groundwaters from brown sands at depth<100 m. The palaeo-interfluvial sequences are separated by two deep palaeo-channels, which were logged at 3 sites. The palaeo-channel deposits host As-polluted groundwater in grey sands. Our findings confirm the predictions of the palaeosol model of As-pollution. We show again that well-colour can be used both to successfully predict the degree of As-pollution in groundwater, and to locate regions of buried palaeo-interfluve that will yield As-free groundwater for the foreseeable future.
Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK. m.hoque@ucl.ac.uk
M A
MA
Hoque
J M
JM
McArthur
P K
PK
Sikdar
D001151:Arsenic / Q000032:analysis*; D019015:Geologic Sediments; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D007194:India; D008962:Models, Theoretical; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060753:Water Quality
D014874:Water Pollutants, Chemical; D001151:Arsenic