Natural radioactivity in the groundwater of Wadi Nu'man, Mecca Province, Saudi Arabia

Twenty-nine groundwater samples, collected from Wadi Nu'man wells, were analyzed for natural radioactivity to check for compliance with the national guideline values. Gross alpha and gross beta screening, in addition to radon (Rn-222) measurements, were performed for all samples. Samples of gross activity levels exceeding the national guideline values set out for drinking water were subjected to further investigation for radium and uranium isotopes using liquid scintillation counting and alpha-spectrometry, respectively. The results showed that the anomalous source was natural uranium. The water contains high concentrations of Rn-222 and considerable levels of natural uranium. The Rn-222 concentration ranged from 10-100 Bq/L with an average value of about 40 Bq/L. The uranium concentration, in samples of gross activity levels exceeding the national guideline value, ranged from 9 to 55 mu g/L. The levels of Ra-226 and Ra-228 were below the detection limit of the counting system in all samples. The variation in the Rn-222 and uranium concentrations was found to be linked with the local Ethology. The higher values were recorded in the wells of Nu'man complex aquifer, where the predominating mineral is foliated monzonite. Recommendations and advices for water management to reduce radiation exposure to users are presented.