Sources of low-arsenic groundwater in the Bengal Basin: investigating the influence of the last glacial maximum palaeosol using a 115-km traverse across Bangladesh

M A Hoque,J M Mcarthur,P K Sikdar

doi:10.1007/s10040-014-1139-8

Abstract

Abstract Pollution of groundwater in the Bengal Basin (Bangladesh and West Bengal, India) by arsenic (As) puts at risk the health of more than 100 million consumers. Using 1,580 borehole lithological logs and published hydrochemistry on 2,387 wells, it was predicted that low-As (<10 μg/L) groundwater exists, in palaeo-interfluvial aquifers of brown sand capped by a protective palaeosol, beneath at least 45,000 km2 of the Bengal Basin. The aquifers were predicted to be at a depth of as little as 25 m below ground level (mbgl), and typically no more than 50 mbgl. The predictions were confirmed along an east–west traverse 115 km in length (i.e. across half of Bangladesh) by drilling 28 new boreholes to 91-m depth to reveal subsurface sedimentology, and by mapping As distribution in groundwater. The aquifers identified occur at typically <40 mbgl and so are accessible with local drilling methods. A protective palaeosol that caps the palaeo-interfluvial aquifers prevents downward movement into them of As-polluted groundwater present in shallower palaeo-channel aquifers and ensures that the palaeo-interfluvial aquifers will yield low-As groundwater for the foreseeable future. Their use, in place of the shallower As-polluted palaeo-channel aquifers, would rapidly mitigate the health risks from consumption of As-polluted groundwater.

Highlights

In Bangladesh and West Bengal (India), i.e. the Bengal Basin, at least 85 % of the combined populations of 240 million use groundwater for domestic water supply, including for drinking
It is re-emphasised that the number of logs interpreted as representing a PI sequence is underestimated by the analysis of these Department of Public Health Engineering (DPHE) logs presented here, so the distribution shown should be viewed as representing the minimum number of such sites
Extent of low-As PI aquifers The analysis shows that low-As PI groundwaters that can be tapped from shallow depths accessible to local drilling methods are likely to be present under 45,000 km2 of the Bengal Basin, which is one third of its area (Fig. 4)

Summary

Introduction

In Bangladesh and West Bengal (India), i.e. the Bengal Basin, at least 85 % of the combined populations of 240 million use groundwater for domestic water supply, including for drinking. Mitigation strategies include rainwater harvesting, use of treated surface-water supplies, and exploitation of deep aquifers (>150 m below ground level (mbgl) and mostly >300 mbgl) which typically contain much less than 10 μg/L of As (DPHE 1999, 2001; Ahmed et al 2006; van Geen et al 2007; Ravenscroft et al 2009). These strategies require capital investment and maintenance that is beyond the capacity of most of the population, given that 90 % of it lives in a rural environment sustained by subsistence farming.

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Conclusion