Evaluation of groundwater quality in northern Saudi Arabia using multivariate analysis and stochastic statistics

Groundwater resources available in the Paleozoic sedimentary formations form the most prolific source of water supply in the Kingdom of Saudi Arabia. In the absence of surface water supplies the available groundwater reserves in these aquifers have been used extensively to fulfill the agricultural and domestic water demands. The main purpose of this paper was to evaluate the groundwater quality in the Northern Western part of Saudi Arabia using the classical water facies diagram (Piper and Durov plot). The more advanced methods of principal component analysis (PCA) for determining the factors controlling the groundwater chemistry and stochastic geostatistics to understand the spatial distribution of different major elements in the groundwater of the study area were employed. 40 groundwater samples from bore wells tapping the Saq aquifer were collected and analyzed for the major ion chemistry and nitrates. Groundwater occurs within detrital sandstones of Phanerozoic era in Saq Formations. Piper plot revealed that most of the water samples belonged to the mixed class (Ca–Mg–Cl–SO₄ type) and few samples falling within the Ca–Mg–HCO₃ type, Na–Cl type, and Ca–Mg–SO₄ type of groundwater facies. Durov plot pointed towards simple dissolution, silicate weathering, ion exchange, and reverse ion exchange as the main processes governing the chemistry of the area. PCA resulted in the extraction of two PC accounting for 78.11 % of the data variability. The extracted PCs pointed towards geogenic factors governing the groundwater quality. Stochastic geostatistics involved prediction maps of ordinary kriging and indicator kriging which provided detailed indications of spatial distribution of the chemical elements.