Shallow alluvial aquifers for drinking and agricultural purposes: a case study from Jia Bharali River Basin, North Brahmaputra Plain, India

A preliminary assessment of groundwater quality for drinking and irrigational purposes in the lower Jia Bharali river catchment and adjoining areas of North Brahmaputra Plain, India, was carried out with respect to major cations, anions, and trace elements. Water samples from 50 shallow alluvial dug wells were collected in wet and dry seasons for a period of 3 hydrological years (2008–2011). Seasonal analysis showed major cation and anion contents in a definite trend across the basin as Ca: 4.2–68.9 mg/L > Na 1.9–62.5 mg/L > Mg:1.0–29.2 mg/L > K (1.3–26.1 mg/L) and HCO₃ (16–118 mg/L) > Cl (2.8–138.3 mg/L) > SO₄ (1.2–99.5 mg/L) > PO₄ (BDL—1.50 mg/L) > NO₃ (BDL—1.20 mg/L) within WHO acceptable limit for drinking water in all the seasons. Low SAR (< 10) and RSC (< 1.25 meq/L) values of shallow wells showed their suitability as potential source for agricultural purposes, while a few wells were found unsuitable with respect to Na% > 60% and Kelly’s Index > 1. However, majority of the wells were found not suitable for drinking as well as irrigational purposes due to the presence of trace elements Cd (BDL—0.070 mg/L), Cr (BDL—0.24 mg/L), Fe (0.10–11.76 mg/L), Mn (BDL—1.37 mg/L), Ni (BDL—0.18 mg/L), and Pb (BDL—0.22 mg/L) beyond their respective standard limits. Piper trilinear diagram identified the major hydrochemical facies of the groundwater as alkaline earths (Ca, Mg) and weak acids (HCO₃) over alkalis (Na, K) and strong acids (SO₄, Cl).