Groundwater geochemistry and hydro-geochemical processes in coastal area South Phan Thiet, Binh Thuan Province, Vietnam

Abstract

As one of the largest dragon fruit areas and many tourism projects, the southern coastal area of Phan Thiet (including three communes: Tien Thanh, Thuan Quy, and Tan Thanh) has been a bright spot in the economy of Binh Thuan. Economic development puts pressure on water resources, especially groundwater resources, the main supply for irrigation and domestic water in the region. In this research, 19 groundwater samples from the Holocene and Pleistocene aquifers were collected in February 2023 and analyzed for the concentration of Ca2+, Mg2+, Na+, K+, NH4 +, NO3 −, PO4 3-, Cl−, HCO3 –, and SO4 2-, thereby evaluating groundwater geochemistry, hydro-geochemical processes, and the suitability for irrigation purposes. The rank of cations in the aquifers of the region is Na+ > Ca2+ ∼ Mg2+, and Ca2+ ∼ Mg2+ > Na+ respectively. The concentrations of major anions in the study area are in order Cl− > HCO3 − > SO4 2- respectively. The predominant processes in the aquifer involve the interplay between rock and water as well as anthropogenic activity. The saturation indices of dolomite, gypsum, and halite are under-saturated in all collecting sample sites. According to the quality evaluation for irrigation, 14 of the 19 samples with % sodium levels less than 60 are suitable, while the others should be treated before use. The study area also indicated nitrate pollution (4/19 groundwater samples exceeding 15 mgN L−1 of the Nitrate limited for groundwater, National technical regulation on underground water quality). It is recommended that local authorities have strategies to supply water for different purposes, control pollution sources, and treat water waste to protect these aquifers.