Groundwater Quality Assessment Using EWQI With Updated Water Quality Classification Criteria: A Case Study in and Around Zhouzhi County, Guanzhong Basin (China)

The entropy water quality index (EWQI) is a simple method of comprehensively assessing water quality. This method has been widely used in groundwater quality assessment. However, the number of hydrochemical parameters selected for the evaluation can lead to inconsistent classification criteria. In this study, 12 parameters were selected, based on their importance in the groundwater quality, to redefine the classification criteria of EWQI. Therefore, the modified EWQI approach with updated classification criteria was applied to evaluate groundwater quality in the Zhouzhi Country of the Guanzhong Basin, China. The results show that considering heavy metals in the groundwater quality resulted in different EWQI classification criteria from those previously used in other studies due to the large difference in the national standard limits for heavy metals in different water quality categories. In addition, the improved EWQI showed that 1.41, 63.38, and 35.21% of the groundwater samples in the Zhouzhi County were of excellent, good and moderate groundwater quality, respectively. Compared with other classification criteria, the improved EWQI method considering more water hydrochemical parameters and heavy metal elements is more suitable and reliable for comprehensively evaluating groundwater quality.