Geochemical Evolution of Groundwater Flowing Through Arsenic Source Sediments in an Aquifer System of West Bengal, India

Abstract

The source of geogenic arsenic (As) contaminating a shallow aquifer in West Bengal was traced to fine‐grained sediments deposited in an abandoned river channel. Along with As‐bearing phases, these sediments contain 0.46% codeposited organic carbon. The release of As and the geochemistry of groundwater within the channel‐fill deposits is investigated using a detailed mass balance model supported by aqueous, solid‐phase, and mineralogical data. The model describes the evolution of groundwater chemistry along a flow path extending from its recharge in an abandoned channel pond, through the channel fill, to the underlying aquifer. Variations in groundwater composition are explained in terms of mineral weathering of host sediments driven by organic carbon decay. Arsenic is released through the reductive dissolution of goethite and the weathering of chlorite. Concomitantly, some As is sequestered in precipitating vivianite. These competing processes reach equilibrium deeper in the channel‐fill sequence as groundwater As concentrations stabilize. The model yields estimates of mineral reaction (or precipitation) rates including rates of organic carbon oxidation (1.15 mmol C L−1 a−1) and net As release ( 4.57×10−4 mmol L−1 a−1). Fine‐grained, slightly permeable, deposits such as channel fill containing reactive organic carbon and As‐bearing goethite and phyllosilicates are centers of intense chemical weathering conducive to As mobilization.

Predicting geogenic Arsenic in Drinking Water Wells in Glacial Aquifers, North‐Central USA: Accounting for Depth‐Dependent Features

“…These variables are measures of proximity to surface water and are proxies of hydrologic position, which can represent geochemical evolution along a flow path; higher probability of elevated As was associated with shorter distance to larger streams. Redox condition, pH, water age, dissolved mineral content, and other factors can all be associated with well depth and hydrologic position, and these factors can also affect As mobilization (Aziz et al, ; Desbarats et al, ; Thomas, ).…”

“…Recent models for As‐affected aquifers in Southeast Asia have elucidated similar influential factors and variables (groundwater age, organic carbon, aquifer, depth, etc. ; Biswas et al, ; Biswas, Bhattacharya, et al, ; Biswas, Neidhardt, et al, ; Desbarats et al, ; Gillispie et al, ; McArthur et al, , , ; Mihajlov et al, ) related to modeled As hazard in aquifers (Biswas, Neidhardt, et al, ; Bonsor et al, ; Hoque et al, , , ; Mahmud et al, ; Mukherjee et al, ; Podgorski et al, ).…”

Conceptual Model of Arsenic Mobility in the Shallow Alluvial Aquifers Near Venice (Italy) Elucidated Through Machine Learning and Geochemical Modeling

“…Geogenic (i.e., naturally occurring) arsenic (As) contamination is a well‐known issue that affects unconsolidated and fractured aquifers worldwide (e.g., Choudhury et al, 2018; Desbarats et al, 2017; Erickson et al, 2018; Huang et al, 2018; Jakobsen et al, 2018; Pedretti et al, 2019), including Italian aquifers (e.g., Aiuppa et al, 2003; Carraro et al, 2013; Molinari et al, 2013; Rotiroti et al, 2014; Ungaro et al, 2008). Identifying a valid site‐specific conceptual model able to describe As mobility in groundwater is fundamental for many purposes related to As risk management.…”

Arsenic Pollution Characteristics and Variation Trends in Yangzonghai Lake, China

“…Arsenic exists in different binding states in the sediment and shows different mobility, bioavailability and ecotoxicity (Desbarats et al, 2017;Hossain et al, 2016). The mass fractions of water soluble fraction, ion exchange fraction and carbonate fraction are relatively low, and the sum of the three accounts for 0.55% of the total amount on average, and there is almost no change in the vertical distribution.…”