Entropy weight application for calculating groundwater quality index (EWQI) in groundwater quality zoning in Pleistocene aquifer in the Phu My town, Ba Ria – Vung Tau province - Au, Nguyen; Bao, Tran; Nhi, Pham; Vy, Tat; Hien, Truong; Hiep, Tran; Linh, Luu (VNUHCM Journal of Environment and Earth Sciences, 2020)