Pleistocene aquifer is exploited for many purposes, including irrigation, domestic, production, and livestock use in Phu My town, Ba Ria – Vung Tau province. Groundwater Quality Index (GWQI) method combined with Geographic Information System (GIS) foundation is applied to determine the spatial variation as well as the suitability of groundwater in the study area. Water quality parameters in this study include pH, TDS, total hardness, Cl-, F-, NH4+, NO3-, SO42-, Pb2+, and Fe2+ were selected for analyzing from 17 monitoring wells in dry and wet seasons in 2017. The results indicate that water quality parameters such as Cl-, F-, NH4+-N, Pb2+ và Fe2+ exceed the maximum allowable levels by National Technical Regulation on Groundwater Quality. The groundwater quality, according to GWQI analysis results, shows that indicate 88% and 94% of the monitoring wells are from “good” to “excellent” type in the dry and wet seasons, respectively. The number of wells that have water quality from “poor” to “water unsuitable for drinking purpose” varies between the dry and wet seasons. Corresponding with the GWQI map, it shows that the area with good quality groundwater accounts for 98% of the total study area (331.44 km2) in the dry season and 94.5% of the study area (319.58 km2) in the wet season.

This research applied the groundwater quality index (GWQI) and principal component analysis (PCA) for assessing pollution levels and factors effecting groundwater quality of Pleistocene aquifer in Tan Thanh district, Ba Ria – Vung Tau province. Seventeen wells were colected in April (dry season) and October (rainy season) during 5 years (2012-2017). Nine parameters of water (pH, TDS, độ cứng, Cl-, F-, NO3-, SO42-, Cu2+ và Fe2+) were collected for analyses. The results of GWQI (dry season) divided into 17 wells in dry season with groundwater quality from good to very good which occupied to 82% databases, compared to 94% of rainy season. Meanwhile, the number of wells significantly changed from poor to very poor water between two seasons. PCA demonstrated that two specific factors, interaction of chemical components in river sediments and character of aquifer and anthropogenic, affected to the quality of groundwater in this study area. These explained 65.555% (dry season) and 61.562% (rainy season) of the variances. This result is provided specific information, and the useful tools in order to deal with the complicated databases, as well as zone the groundwater quality in the study area. This further help the authorities to plan suitable strategy for groundwater quality management.

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.