Assessment of groundwater quality of unconfined aquifers in an urbanized area using the water quality index method

This study performed an evaluation of the groundwater quality of unconfined aquifers in Yangzhou, located in the Yangtze River Delta, eastern China. The study area is the source area of the Eastern Route (ER) of the South-to-North Water Diversion Project (SNWDP), typical of the lower alluvial plain of the lower Yangtze River. Water samples from monitoring wells and domestic wells were collected to analyze common variables (pH, EC), major ions, trace metals, etc. The water quality index method was employed to evaluate groundwater quality in both eastern and western parts of the study area. The study found that the groundwater hydrochemistry is typical of HCO₃-Ca and HCO₃-Na, similar between the eastern and western parts of the study area. In addition, the eastern part of the study area is more affected by nitrate pollution than the western part due to agricultural activities. The water quality analysis suggests that the groundwater in the western region was slightly better than that in the eastern region. The comparison between different scenarios indicates that the water quality using only major ions can differ significantly from that using all chemical parameters, but may offer some preliminary insights into the groundwater quality useful for conducting further more detailed analysis. Our study shows that using the combination of major ions and heavy metals could provide relatively robust results of the groundwater quality in our study area. Our study has important implications for the assessment of groundwater quality in regions with similar conditions.