Acid mine drainage from coal mines in the eastern Himalayan sub-region: Hydrogeochemical processes, seasonal variations and insights from hydrogen and oxygen stable isotopes

Vivek Kumar; Dibyendu Paul; Sudhir Kumar

doi:10.1016/j.envres.2024.119086

Acid mine drainage from coal mines in the eastern Himalayan sub-region: Hydrogeochemical processes, seasonal variations and insights from hydrogen and oxygen stable isotopes

Environ Res. 2024 May 7;252(Pt 4):119086. doi: 10.1016/j.envres.2024.119086. Online ahead of print.

Authors

Vivek Kumar¹, Dibyendu Paul², Sudhir Kumar³

Affiliations

¹ Department of Environmental Studies, North-Eastern Hill University, Shillong, 793022, India. Electronic address: naturevivek001@nehu.ac.in.
² Department of Environmental Studies, North-Eastern Hill University, Shillong, 793022, India.
³ National Institute of Hydrology, Roorkee, 247667, India.

PMID: 38723986
DOI: 10.1016/j.envres.2024.119086

Abstract

Uncontrolled coal mining using non-scientific methods has presented a major threat to the quality of environment, particularly the water resources in eastern himalayan sub-region of India. Water bodies in the vicinity of mining areas are contaminated by acid mine drainage (AMD) that is released into streams and rivers. This study attempted to assess the impact of AMD, deciphering hydrogeochemical processes, seasonal fluctuations, and stable isotope features of water bodies flowing through and around coal mining areas. Self-organizing maps (SOMs) used to separate and categorize AMD, AMD-impacted and non-AMD impacted water from the different study locations for two sampling seasons revealed four clusters (C), with C1 and C2 impacted by AMD, C3 and C4 showing negligible to no impact of AMD. AMD impacted water was SO₄^2- - Mg²⁺- Ca²⁺ hydrochemical type with sulphide oxidation and evaporation dominating water chemistry, followed by silicate weathering during both the sampling seasons. Water with negligible-to-no AMD-impact was Mg²⁺- Ca²⁺- SO₄^2- to Ca²⁺ - HCO₃^- to mixed hydrochemical type with rock weathering and dissolution, followed by ion exchange as major factors controlling water chemistry during both the sampling seasons. Most of physicochemical parameters of C1 and C2 exceeded the prescribed limits, whereas in C3 and C4 water samples, parameters were found within the prescribed limits. Stable isotopes of hydrogen (δ²H) and oxygen (δ¹⁸O) during post-monsoon (PoM) varied between -41.04 ‰ and -29.98 ‰, and -6.60 ‰ to -3.94 ‰; and during pre-monsoon (PrM) varied between -58.18 ‰ and - 33.76 ‰ and -8.60 ‰ to -5.46 ‰. Deuterium excess (d-excess) ranged between 1.57 ‰ and 12.47 ‰ during PoM and 5.70 ‰ to 15.17 ‰ during PrM season. The stable isotopes analysis revealed that evaporation, mineral dissolution and mixing with rainwater are the key factors in study area.

Keywords: Acid mine drainage (AMD); Coal mining; Eastern himalaya; Hydrogeochemistry; Northeast India; Stable isotopes.