Estimation of the groundwater quality index and investigation of the affecting factors their changes in Shiraz drinking groundwater, Iran

This study aimed to determine the groundwater quality index (WQI) and investigate the anthropogenic factors causing changes in this index in Shiraz plain. This research studied the quality of groundwater of 35 wells for five years. Groundwater samples were analyzed for pH, TDS, TH, HCO3(-1), Cl-1, F-1, SO4-2, Ca+2, Mg+2, No-3(-1), and Na+1 and a microbial parameter was analyzed to compute the water quality index (WQI). Factors Affecting was evaluated using field studies, Google Earth, and multivariate statistical analysis and piper diagram. The computed WQI values ranged from 40.01 to 117.38. Overall, 5.7% of groundwater sites sampled had excellent water quality, while 65.7% were good. 28.6% of the samples indicated poor water quality. The zoning results showed that the water quality index (WQI) was worsening from northwest to southeast and from northeast to southeast. The correlation between water quality index WQI and changes in industrial land use and between water quality index (WQI) and changes in the unused lands were 0.46, and 0.35, respectively. Principal component analysis (PCA) on the chemical parameters revealed two factors that account for about 77.44% of the total variance in groundwater quality data set; the first factor (with high Eigen values) indicates that variation in water quality is due to natural origin. According to the results of hierarchical cluster analysis (HCA), there are three quality groups in groundwater of the research area: the first group of 8 wells, the second group of 11 wells, and the third group of 16 wells. In this context, the Piper diagram also indicates groundwater facies of the study area were Ca2+ - Mg2+ HCO3-; this is also due to water interaction, the limestone of a karst aquifer. The groundwater hydro-chemical in the study area is the majority of human activity, but it is influenced to some degree by the natural process.