Groundwater Chemistry at Deep Aquifer in Koyra: Khulna, Bangladesh

Abstract

Koyra (Khulna District) is the coastal Upazila of Bangladesh and is very susceptible to salinity intrusion. The surface and shallow tube well water in the Upazila is naturally saline. The quality of subterranean tube well water in the deliberate area is hardly presented for different Unions of Koyra. Dakshin Bedkashi Union of Koyra is very saline prone. Therefore, the groundwater chemistry of Dakshin Bedkashi Union was determined to legalize if the groundwater is fit for drinking and irrigation or not. Spatially dispersed 30 water samples were collected from the deep aquifer (550 to 700 feet depth) in December, 2016 and analyzed for physico-chemical properties. The outcomes were compared with WHO, USEPA and BBS drinking water quality standard and with FAO standard for irrigation purpose. The pH varied from 6.73 to 8.33, indicating that the water samples were within the WHO drinking water quality standard. The TDS showed a long range variation (230.5 to 2052.0 ppm) with an average of 841.23 ppm, of which 33% of water sources exceeded BBS standard value. The mean value of salinity was 0.65 (±0.43) ppt and EC was 1,400.9 (±904.18) µS cm-1. The loads of key ions were ranked as Na+> Ca2+> Mg2+> K+ and HCO3-> Cl-> SO42-> NO3-> PO4-. The Piper diagram demonstrated that the existing hydro-chemical facies of groundwater were Na+-Cl--HCO3- and Na+-Ca2+-HCO3- type. The Gibbs diagram illustrated that the chemical arrangement of groundwater is mainly misrepresented by rock weathering. Silicate weathering was the profuse process along study area. The Wilcox diagram proved that the greater water sources were allowable to suspicious for irrigation. The core component analysis ensured that rock suspension and sea water intrusion was the primary source of ions in groundwater. The controlling factors of groundwater chemistry were typically related to geologic factors, while the anthropogenic factors have not any momentous effects.