Assessment of the hydrodynamics role for groundwater quality using an integration of GIS, water quality index and multivariate statistical techniques

To explore the impact of groundwater hydrodynamics on water quality, a cost-effective geospatial model was developed using geographic information system (GIS) technology and the Dupuit assumption. Meanwhile, the groundwater quality in the Dagu River Basin was evaluated based on the water quality index (WQI) and multivariate statistical analyses. In April (dry season) and September (rainy season) 2017, the groundwater level was automatically monitored from 115 wells, and the water quality including 21 hydrochemical parameters was sampled from 37 wells. Results reveal that the WQI values varied from 35.01 to 64.74, with mean values of 51.89 and 47.87 in the rainy and dry seasons. Approximately 80% of the samples exhibited moderate water quality, with no significant difference between the rainy and dry seasons. Nitrate pollution and the integrated water quality in the central and northern regions were generally worse than that in the southern region. The Darcy velocity in the central and northern regions was relatively high with a maximum rate of 0.56 m/d, compared with the southern region. This correlation illustrates the effect of groundwater hydrodynamics on quality. The sowing of greater chemical fertilizers combined with faster groundwater movement is likely responsible for the large-scale nitrate pollution in the central and northern regions. Results also proved the accuracy of the geospatial model with a valid uncertainty. The geospatial model provides a valuable alternative for the spatial analysis of the effect of groundwater hydrodynamics on water quality.