Radon (²²²Rn) occurrence in quaternary deposits, annual dosage, and groundwater recirculation in Hashimiya, Iraq

Due to many cancer cases and deaths in a population of 80,000 in Hashimiya, mid-Iraq, a radiologic and hydrogeologic study was carried out. ²²²Rn, among many pollutants, was encountered in concentrations exceeding the allowable limit of 100 Bq L⁻¹ according to the WHO, during continuous groundwater pumping for > 3 hours from unconfined Quaternary aquifer deposits at many locations. Investigations used 20 wells and the Alpha GUAR PQ2000 PRO, Alpha PUMP and Aqua KIT device for 140 groundwater sample tests, revealing that radon concentrations reached 113 Bq L⁻¹. Geologically, Hashimiya consists of Quaternary deposits of unconsolidated fine-grained sediments of the flood plains of the Euphrates River and are mainly of layers of clay, silt, sand and gypsum. It was found that piezometric and groundwater velocities of ∼ 1 cm day⁻¹ and ∼ 0.3 cm day⁻¹, respectively, are low enough to cause the immediate local creation of ²²²Rn beneath the rocks and soil and to produce concentrations that increase preceding pumping, rather than ²²²Rn being carried from a distance. It was found that the annual dosages reached 0.28 mSv year ⁻¹ with residence times of 12 day⁻¹. A mathematical model was used to simulate the groundwater scheme and recirculation to remediate ²²²Rn contamination using the property of radon release during exposure to air. The results indicated that the recirculation process reduced radon concentrations from > 100 Bq L⁻¹ to range of 1.06–1.21 Bq L⁻¹ at the Kids and Sareaa streams. The number of pumping and injection wells needed per annum for conducting the recirculation process for the selected contaminated sector are 216 and 112, respectively.