Hydrochemical characteristics and salt intrusion in groundwater of the lower Chao Phraya river basin: Insights from stable isotopes and hydrochemical analysis

Abstract

Saltwater intrusion is a significant hydrogeological challenge in coastal regions. This study investigates salt intrusion and hydrogeological processes in the Lower Chao Phraya River basin using stable isotopes and hydrochemical analysis. One Hundred groundwater wells sampled from different aquifers were analyzed for major ions spanning from 2010 to 2021, as well as stable isotopes specifically for the samples in the year 2021. The results reveal four distinct groundwater types: Ca(HCO3)2, NaHCO3, NaCl, and CaSO4, based on their predominant cations and anions. Shallow groundwater, which represents the discharge zone affected by salt intrusion, halite dissolution, and cation exchange reactions, exhibits a significant concentration of NaCl. Water-rock interactions play a crucial role in shaping groundwater chemistry, with carbonate dissolution and precipitation dominating the Ca(HCO3)2 type and silicate weathering influencing the CaSO4 type. The NaHCO3 type is associated with ion exchange and seawater intrusion. Silicate and carbonate rock weathering are the dominant processes in the region. Stable isotope analysis indicates that groundwater recharge primarily comes from rainfall and surface water, with limited contributions from deep sources. Overall, this study provides valuable insights into the hydrochemical characteristics and complex water-rock interactions within the groundwater system of the Chao Phraya River basin. As a result, it holds significant potential for informing effective groundwater management practices and facilitating resource planning in the region. Furthermore, the findings and methodologies presented here offer valuable lessons for addressing saltwater intrusion and hydrogeological challenges in other coastal regions worldwide.