Palaeosol Control of Arsenic Pollution: The Bengal Basin in West Bengal, India.

U Ghosal,P.K Sikdar,J.M Mcarthur

doi:10.1111/gwat.12251

Abstract

Groundwater in the Bengal Basin is badly polluted by arsenic (As) which adversely affects human health. To provide low-As groundwater for As mitigation, it was sought across 235 km(2) of central West Bengal, in the western part of the basin. By drilling 76 boreholes and chemical analysis of 535 water wells, groundwater with <10 µg/L As in shallow aquifers was found under one-third of a study area. The groundwater is in late Pleistocene palaeo-interfluvial aquifers of weathered brown sand that are capped by a palaeosol of red clay. The aquifers form two N-S trending lineaments that are bounded on the east by an As-polluted deep palaeo-channel aquifer and separated by a shallower palaeo-channel aquifer. The depth to the top of the palaeo-interfluvial aquifers is mostly between 35 and 38 m below ground level (mbgl). The palaeo-interfluvial aquifers are overlain by shallow palaeo-channel aquifers of gray sand in which groundwater is usually As-polluted. The palaeosol now protects the palaeo-interfluvial aquifers from downward migration of As-polluted groundwater in overlying shallow palaeo-channel aquifers. The depth to the palaeo-interfluvial aquifers of 35 to 38 mbgl makes the cost of their exploitation affordable to most of the rural poor of West Bengal, who can install a well cheaply to depths up to 60 mbgl. The protection against pollution afforded by the palaeosol means that the palaeo-interfluvial aquifers will provide a long-term source of low-As groundwater to mitigate As pollution of groundwater in the shallower, heavily used, palaeo-channel aquifers. This option for mitigation is cheap to employ and instantly available.

Highlights

The World Health Organization’s guideline value for arsenic (As) in drinking water is 10 μg/L (WHO 2011)
Some 25% of water wells tapping the shallow aquifers of the Bengal Basin (West Bengal and Bangladesh) contain more than 10 μg/L As (PHED 1991; DPHE 1999; van Geen et al 2003a; Jakariya et al 2007; Nickson et al 2007)
NGWA.org In DPHE (1999), it was shown that As pollution in the Bengal Basin is confined largely to groundwater in shallow sands deposited since the last glacial maximum (LGM), as sea level rose after its termination around 20 ka

Summary

Introduction

The World Health Organization’s guideline value for arsenic (As) in drinking water is 10 μg/L (WHO 2011). In DPHE (1999), it was shown that As pollution in the Bengal Basin is confined largely to groundwater in shallow sands deposited since the last glacial maximum (LGM), as sea level rose after its termination around 20 ka These post-LGM sands were laid down on a late Pleistocene landscape that had formed during the eustatic fall of sea level between 125 and 20 ka (Umitsu 1993; Davies 1995; DPHE 1999; Goodbred and Kuehl 2000a, 2000b). In DPHE (1999), it was shown that concentrations of As were usually much less than 10 μg/L in the groundwater in pre-LGM sands that underlay the now-buried late Pleistocene land surface These early observations have been repeatedly confirmed (DPHE 2001; van Geen et al 2003a; McArthur et al 2004; Zheng et al 2005 et seq). One option for As mitigation is to shift abstraction of groundwater for domestic supply away from the shallow, post-LGM, aquifers and into the deeper, pre-LGM, aquifers (DPHE 1999, 2001; van Geen et al 2003b; Ahmed et al 2005; Zheng et al 2005; Ravenscroft et al 2009; Mosler et al 2010; Ravenscroft et al 2013)

Methods

Results

Discussion

Conclusion