Occurrence of radon in groundwater of Saudi Arabia

Samples were collected from 1025 wells supplying drinking water to the 13 regions of Saudi Arabia and analyzed for radon concentrations. The weighted radon median value for the entire country was found to be 4.62 Bq L(-1) with a range of 0.01-67.4 Bq L(-1). The percentage of samples with radon concentration equal to or greater than 11.1 Bq L(-1) (US EPA proposed MCL) was found to be 19.22%. The range of radon in shallow wells varied between 0.06 and 67.4 Bq L(-1) (median value 5.1 Bq L(-1)) and between 0.06 and 40.9 Bq L(-1) (median value 5.34 Bq L(-1)) for deep wells. However, 50% of the samples had radon concentrations equal to or greater than 4.0 and 2.87 Bq L(-1) for the shallow and deep wells, respectively. Correlation of well depth with radon levels revealed that wells drilled in Saq aquifer consisting of predominantly sandstone with significant shale layers in the upper parts, gave higher median radon levels than in Manjur aquifer which consists of predominantly limestone and sandstone.