Application of Entropy weight in groundwater quality index (EWQI) and GIS for groundwater quality zoning in the Southeastern Coastal region, Vietnam

Abstract

Groundwater in the Southeastern coastal region of Vietnam is exploited for many purposes, including irrigation, livestock, domestic and production activities. In this study, Groundwater Quality Index calculated by Entropy weight method (EWQI) and Geographic Information System (GIS) are applied for zoning water quality through determining the weight of each parameter in accordance with the variation of each value in terms of. Spatial distribution the suitability of groundwater use in the study area. Groundwater samples were collected from 46 wells in the dry and wet seasons in 2018 for analyzing seven selected water quality parameters, including: pH, total dissolved solids (TDS), total hardness (TH), ammonium (NH4 +-N), nitrate (NO3 −-N), sulphate (SO4 2-) and ferrous (Fe2+). The groundwater quality is divided into five (05) categories corresponding to Entropy Water Quality Index (EWQI), comprising: excellent, good, medium, poor and extremely poor. The analysis results of Entropy weight indicated that pH, NH4 +-N, NO3 −-N are the most affected on the quality of groundwater at the study area. According to EWQI results, more than 41.30% of wells’ water quality are “very good” in both the dry and wet seasons, mainly in the coastal of Ba Ria - Vung Tau province and 13.04% of the total surveyed wells in the study area are “extremely poor”, mainly in Ho Chi Minh city. Accordingly, the zoning map of Entropy weighted Water Quality Index (EWQI), showed that the area with good quality of groundwater accounts for 34.3% and 37.72% of the total study area in the dry and the rainy season, respectively.