Abstract
Wadi Nisah which lies to the south of Riyadh city is an important source of groundwater supply and agricultural production in the central region of Saudi Arabia. Twenty-nine groundwater samples were collected from wells tapping the shallow alluvial aquifer as well as the Mesozoic Manjur and Dhruma aquifer in western Wadi Nisah. The interpretation of the results of the major ion analysis reveals that geogenic factors mainly rock-water interaction and mineral dissolution control the groundwater chemistry. The samples are characterized by high TDS and EC values. Saturation indices of the groundwater show that minerals dissolution is the primary factor affecting the groundwater composition Piper plot reveals groundwater mixing as Ca + Mg - Cl + SO4 facies, mixed Ca + Mg - Cl + SO4 facies and Na + K + Cl + SO4 facies is present in the study area. Gypsum and dolomite weathering coupled with reverse-ion exchange are responsible for the dominance of alkaline earth elements over alkali elements. Principal component analysis helped in the extraction of three principal components accounting for approximately 78% of the total data variability. The extracted components point mainly towards geogenic influences. However, the third principal component shows the influence of anthropogenic pollution, mainly nitrate pollution from agricultural activity in the area.