Regionalization of arsenic release mechanics in the Bengal basin using fuzzy clustering approach

Abstract

India is predominantly an agro-oriented country where water has always played a vital role. In the Ganges delta, which covers nearly one-third of India’s total area, surface water was the primary source for irrigation and drinking until the 1960s. However, surface water bodies were often contaminated with pathogenic bacteria, leading to widespread waterborne diseases.

To prevent these diseases, groundwater was adopted as an alternative source, assumed to be more sustainable. Within decades, however, severe waterborne diseases emerged, reaching epidemic levels in the early 1990s. The primary symptoms included cancers of the skin, lungs, liver, and other internal organs. Investigations revealed that the main cause was arsenic contamination in groundwater.

This thesis addresses the problem by identifying the mechanisms of arsenic release responsible for contaminating groundwater in the Bengal delta of the Ganges River.

Geological and Hydrological Context The depositional history of the Bengal basin has been shaped by eustasy, sediment deposition, and tectonics, resulting in a complex geological setting.

Extensive irrigation and water abstraction have caused local-scale flow between aquifers, influencing arsenic distribution.

The combined complexity of geology and hydrology makes the region highly heterogeneous in terms of geochemical properties, complicating modeling efforts.

Methodology To address this complexity, a two-level fuzzy clustering approach was employed to identify arsenic release mechanisms. The study focused on Nadia district, located on the eastern side of the Ganges River.

Preliminary analysis showed that arsenic concentration varies significantly with time, necessitating a time-varying analysis using six chemical attributes.

Findings The release of arsenic in groundwater was found to be correlated with chloride ion concentration.

A hypothesis was proposed involving the intersection of two biogeochemical cycles:

One associated with chlorine.

The other associated with iron.

It was postulated that mineralization of organo-chlorine compounds leads to the release of arsenic into groundwater.