Environmental tracers and groundwater residence time indicators reveal controls of arsenic accumulation rates beneath a rapidly developing urban area in Patna, India

• DOI: 10.1016/j.jconhyd.2022.104043
• Publication Date: 2022-06-21T00:39:27Z
• Authors: Laura A. Richards; Rupa Kumari; Neha Parashar; Arun Kumar; Chuanhe Lu; George Wilson; Dan Lapworth; Vahid J. Niasar; Ashok Ghosh; Biswajit Chakravorty; Stefan Krause; David A. Polya; Daren C. Gooddy
• Keywords: Residence time indicators; GroundwaterBGS; Iron; 0208 environmental biotechnology; Ganga River Basin; India; 02 engineering and technology; 15. Life on land; IGRD; 6. Clean water; Arsenic; Water quality; 13. Climate action; Ammonium Compounds; 11. Sustainability; Humans; Redox zones; Groundwater; Water Pollutants, Chemical; Environmental Monitoring

Groundwater security is a pressing environmental and societal issue, particularly due to significantly increasing stressors on water resources, including rapid urbanization climate change. arsenic major public health challenge impacting millions of people in the Gangetic Basin India elsewhere globally. In rapidly developing city Patna (Bihar) northern India, we have studied evolution groundwater chemistry under following three-dimensional sampling framework multi-depth wells spanning central urban zone close proximity River Ganges (Ganga) transition into peri-urban rural areas outside boundaries further away from river. Using inorganic geochemical tracers (including arsenic, iron, manganese, nitrate, nitrite, ammonium, sulfate, sulfide others) residence time indicators (CFCs SF6), evaluated dominant hydrogeochemical processes occurring spatial patterns redox conditions across study area. The distribution other redox-sensitive parameters spatially heterogenous, elevated some locations consistent with mobilization via reductive dissolution iron hydroxides. Residence evidence modern (<~60-70 years) suggest important vertical lateral flow controls area, an apparent seasonal reversal regimes near center. An overall accumulation rate estimated be ~0.003 ± 0.003 μM.yr-1 (equivalent ~0.3 0.2 μg.yr-1), based average CFC-11, CFC-12 SF6-derived models, highest rates observed shallow, near-river groundwaters also exhibiting concentrations nutrients ammonium. Our findings implications management cities, potential future increased vulnerability associated surface-derived ingress large-scale abstraction or higher permeability zones river-groundwater connectivity.