Use of hydrogeochemical tools to evaluate seawater intrusion: a case study of Upper Pliocene Aquifer in the Ca Mau Peninsula, Vietnam

Abstract

Groundwater resources have been withdrawn significantly to meet the demands of agricultural economic development in the Ca Mau Peninsula, Mekong River Delta. As a result, aquifers face the risk of groundwater levels decline and high salinization potential. This study uses the groundwater quality index (GQI) and hydrochemical facies evolution diagram (HFE-D) to assess the hydrochemical characteristics and salinization potential of the Upper Pliocene aquifer (n2 2), which is one of the two most exploited aquifers in the Mekong River Delta. A total of 6 monitoring wells were used to observe groundwater level and water quality from 2017 to 2020. The GQI results ranged from 33.38 to 75.61, indicating that groundwater in Hau Giang and Soc Trang areas is salinized. The spatial distribution results of HFE-D stated that the boundaries of intrusion and freshening have varied in space and time. Specifically, the Upper Pliocene aquifer has been in the process of seawater intrusion. The freshwater area in the Ca Mau has been gradually shrinking in the East Sea area faster than the West Sea area. The displacement speed of the intrusion and freshening boundary varied considerably from 0.04 to 0.67 km/year from 2017 to 2020.