Hydrochemical processes governing groundwater quality of sedimentary aquifers in Central Saudi Arabia and its environmental implications

The present study deals with the interpretation of the major processes governing the groundwater chemistry in parts of Qassim and Riyadh province of Saudi Arabia. The study area that is dominated by agricultural activities is represented by a multi-layered aquifer system with sedimentary formations ranging from Cambrian to the Quaternary present as outcrops. Groundwater samples from 97 agricultural bore wells in the area were collected and analyzed for 16 physio-chemical parameters. The evaluation of the main hydrochemical processes affecting the groundwater quality was carried out by interpreting the ionic relationships and hydrochemical facies analysis. The interpretation pointed toward evaporation, gypsum dissolution and ion exchange as main factors controlling the major ion groundwater chemistry. The piper plot showed SO₄–Cl type of groundwater with majority of the samples falling in the zone of permanent hardness due to the formation of non-carbonate salts. Principal component analysis that helps to understand the underlying natural and anthropogenic factors controlling the groundwater chemistry in an area was used in the present study, based on which four principal components (PCs) were extracted. The first PC as expected was dominated by the major ions and was attributed to natural processes, whereas the extracted components (mainly heavy metals) in PC 2, 3 and 4 pointed toward anthropogenic activities playing an active role in affecting the trace element hydrochemistry.