Hydrodynamics of Groundwater Flow in the Arsenic-Affected Areas of the Gangetic West Bengal, India

Abstract

Hydrostratigraphy and groundwater flow in a ~21,000 km2 area of the arsenic-contaminated districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)], India, have been delineated. Based on 143 lithologs, a regional hydrostratigraphic model has been developed to a depth of 300 m below mean sea level. Lithologic interpolations that were done manually and by computer models (resolution: 1000 m × 1000 m × 2 m) demonstrate a near-continuous, unconfined to semi-confined aquifer dominated by sand underlain by a thick clay aquitard. The aquifer thickens toward basin center in Bangladesh, toward south and east. Toward the Bay of Bengal, at the southern boundary, several heterogeneous aquitard layers of clay sub-divide the primary aquifer, into several deeper, regionally-discontinuous but laterally-connected, confined to semi-confined aquifers. Eight 21-layer regional groundwater models are based on observed topography and hydrostratigraphy. Groundwater flows were simulated in the pre-monsoon, monsoon and post-monsoon seasons with presence (2001) and absence (pre-1970s) of irrigation pumping and projected pumping for pre-monsoon seasons of 2011 and 2021. Modeling results indicate topographically dominated, seasonally variable, continuos regional-scale groundwater flow, which have been largely distorted by pumping. Groundwater flow is predominantly in the upper ~100 m of the aquifer but occurs to a depth of ~200 m.