Assessment of hydrogeochemical characteristics of groundwater: link of AHP and PCA methods using a GIS approach in a semi-arid region, Central Tunisia

In semi-arid climate conditions (such as Central Tunisia), a crucial resource for satisfying the needs of socioeconomic development is groundwater. For water resource conservation and sustainable development, it is necessary to carry out an accurate estimation of groundwater quality to accurately assess the hydrogeochemical properties of the water. In this context, this study aims to assessment of hydrogeochemical characteristics of groundwater quality for irrigation by selection of the hydrogeochemical parameters by principal component analysis (PCA), along with the analytical hierarchy process (AHP) method, which combines with the geographic information system (GIS) approach. The PCA method was utilized to analyze 48 groundwater samples from the Regueb Basin. Ten physicochemical variables were measured [total dissolved solids (TDS, pH, SO42-, HCO3-, Ca2+, Mg2+, Na+, K+, Cl-, and NO3-] and data were analyzed using SPSS 2021 software. The most abundant chemical species were TDS, Na+, SO42-, and Cl-, with mean concentrations of 15.4 g/L, 2530 mg/L, 2600 mg/L, and 6000 mg/L, respectively. These were then selected and linked using the AHP method and determined in four steps. Six criteria (sodium adsorption ratio (SAR), electrical condictivity (EC), TDS, Na+, SO42- and Cl-) with high groundwater values were used in step one. The creation of a matrix A of pairwise comparisons for each criterion was the next stage. The weight of each criterion was determined in the third phase. Determining the reliability of the AHP model consistency index (CI) and consistency ratio (CR) (both with a value of 0.052) was the fourth step. The resulting map of the irrigation groundwater quality index (WQI) model was classified into five groups: excellent, good, permissible, doubtful, and unsuitable for irrigation purposes, accounting for 43.75%, 22.91%, 18.75%, 8.33%, and 6.25%, respectively. This study can be used as a foundation for new management strategies to minimize the degradation of groundwater quality in the Regueb Basin.