Application of groundwater quality index (GWQI) and principle component analysis (PCA) to assess the groundwater quality of Pleistocene aquifer in Tan Thanh district, Ba Ria – Vung Tau province - Nguyen, Au; Hoang, Truong; Pham, Nhi; Tat, Vy; Phan, Ngoc; Nguyen, Quyet (VNUHCM Journal of Earth Science and Environment, 2019)