Groundwater quality evaluation based on water quality indices (WQI) using GIS: Maadher plain of Hodna, Northern Algeria

In a semi-arid region of Maadher, central Hodna (Algeria), groundwater is the main source for agricultural and domestic purposes. Anthropogenic activities and the presence of climate change’s effects have a significant impact on the region’s groundwater quality. This study’s goals were to use water quality indices to evaluate the groundwater’s quality and its suitability for drinking and irrigation, as well as to identify contaminated wells using a geographic information system (GIS) and the spatial interpolation techniques of ordinary kriging and inverse distance weighting (IDW). The results reveal that all water samples exceeded the World Health Organization’s standards for nitrate ions and had alarming concentrations of calcium, chlorine, and sulfate (WHO). According to Piper’s diagram, the groundwater hydrochemical facies is composed of the elements sulfate–chloride-nitrate-calcium (SO 4 2− -Cl — NO 3 − -Ca 2+ water type). The majority of samples fall into the poor water category, slightly more than 10% fall into the very poor water category, and less than 10% fall into the good to the excellent quality category, per the water quality indices, which classify samples in a similar manner. According to irrigation water indices, every sample is suitable for irrigation. Depending on the direction of groundwater flow, the spatial distributions of Ca 2+ , Na + , Mg 2+ , SO 4 2− , and Cl − show that their concentrations are high north of the area and relatively low south of Maadher village (Fig. 3 ). Nitrate concentrations are high in the majority of samples, particularly those close to the Bousaada wadi. In most samples, particularly those close to the Bousaada wadi, nitrate levels are high. Various water quality models were described, and GIS spatial distribution maps were created using standard kriging and inverse distance weighting (IDW) techniques through selected semi-variograms predicted against measurements. To determine the origin of mineralization and the chemical processes that take place in the aquifer—which include the precipitation and dissolution of dolomite, calcite, aragonite, gypsum, anhydrite, and halite—the groundwater saturation index was calculated.