Evaluation of groundwater chemistry and its impact on drinking and irrigation water quality in the eastern part of the Central Arabian graben and trough system, Saudi Arabia

• Groundwater quality assessment in Wasia/Biyadh aquifer, Central Saudi Arabia.
• Groundwater belongs to the SO4Cl and mixed CaMgSO4/Cl type.
• NaCaMg concentrations are related to ion exchange phenomenon.
• DWQI ranges between poor to unsuitable category for majority of the samples.
• TDS, NO3 concentration and reverse ion exchange is higher in Wasia aquifer.

The present study deals with the assessment of groundwater with respect to the main hydrological processes controlling its chemistry and its subsequent impact on groundwater quality for drinking and irrigation purposes in the eastern part of the Central Arabian graben and trough system. Groundwater samples were collected from 73 bore wells tapping the Cretaceous Biyadh and Wasia sandstone aquifers. The main groundwater facies in the area belong to the mixed CaMgSO4/Cl type and the SO4Cl type. Prolonged rock water interaction has resulted in high TDS (average of 2131 mg/l) and high EC (average of 2725 μS/cm) of the groundwater. The average nitrate (56.38 mg/l) value in the area is higher than the WHO prescribed limits of 50 mg/l in drinking water and is attributed to agricultural activities. The Drinking Water Quality Index (DWQI) shows that 33% of the water samples fall within the excellent to good category whereas the remaining samples fall in the poor to unsuitable for drinking category. In terms of Sodium Adsorption Ratio (SAR), Sodium percentage (Na %) and Residual Sodium Carbonate (RSC) the groundwater is suitable for irrigation however the high salinity values can adversely affect the plant physiology.