Occurrence of (222)Rn and (226,228)Ra in underground water and (222)Rn in soil and their mutual correlations for underground water supplies in southern Greater Poland

European Union Council Directive 2013/51/EURATOM recently sets out so-called indicator parameters for: radon, tritium and indicative dose of water intended for human consumption. The aim of this research was to elaborate an effective procedure for determination of radon and radium (226,228)Ra isotopes (which are potentially the main contributors to the internal dose from drinking and cooking water) and to find the possible relationships between these radionuclides in underground water reservoirs and (222)Rn concentration in the soil gas in their vicinity. The research was performed by applying a non-volatile and water-immiscible scintillation cocktail based on a pure diisopropylnaphthalene (Ultima Gold F: UGF), which allow for efficient radon extraction from 0.5 dm(3) of water samples to 20 cm(3) of scintillation phase and its direct determination with a detection limit of 5 × 10(–3) Bq dm(−3). The further preliminary concentration of 3 dm(3) of crude water samples by evaporation to 0.5 dm(3) samples led to the removal of all unsupported (222)Rn activity and allowed the (226)Ra determination via equivalent (222)Rn detection after one-month samples storage using a low-background Triathler liquid scintillation counter in the α/β separation counting mode. Together with determination of (226)Ra isotope in water samples, the simultaneous measurements of (228)Ra and (222)Rn radionuclides concentrations in water as well as (222)Rn activity in the soil gas around the water supply sites were performed. The achieved limit of (226)Ra detection was at a very low level of 10(–3) Bq dm(−3). The measured values of (226)Ra concentration in 50 public underground water supply units for the Kalisz district of Poland were relatively low and ranged from below detection limit to 28.5 × 10(–3) Bq dm(−3) with arithmetic mean and median values of 12.9 and 12.2 × 10(–3) Bq dm(−3), respectively. Weak correlations were observed between activity concentrations of (226)Ra and (222)Rn in the crude water samples (R(2) = 0.31) and (222)Rn in water and its concentration in the nearby soil gas (R(2) = 0.48).