Seasonal variation in major ions chemistry and radionuclide concentrations in groundwater: a case study in the Amman-Zarqa Basin (Jordan)

Abstract

This research was conducted in Amman-Zarqa basin (Upper Cretaceous system) which hosts the main aquifer of Jordan. The region has intensive anthropogenic activities and the geology is dominated by phosphate rocks, which contain high concentrations of uranium. The study aimed to evaluate the water quality and the radioactivity exposure from intake of radionuclides contained in water and assessed through total alpha, total beta, 238U, and 232Th activity concentrations. Groundwater samples were collected from 29 boreholes for determination of major ions and radionuclide concentrations. The sampling was carried out during the rainy season (February) and dry season (June) of 2019 in order to assess the seasonal variation of analyte concentrations. The mean concentrations of major ions varied between seasons as follows: chloride (Cl−1) 162 to 180 µg L−1, sulfate (SO4−2) 47 to 57 µg L−1, bicarbonate (HCO3−1) 288 to 313 µg L−1, and nitrate (NO3−) 42 to 50 µg L−1, in February and June respectively. The ion concentrations of potassium (K+), sodium (Na+), magnesium (Mg+2), nitrate (NO3−), sulphate (SO4−2), and chloride (Cl−) as well as radioactivity levels were within regulatory limits, whereas calcium (Ca+2) and bicarbonate (HCO3−1) concentrations were higher than the recommended limits in national legislation. Statistical test (ANOVA) results indicated significant differences between seasons for Mg+2, NO3−, SO4−2 concentrations. The ion chemistry of groundwater was dominated by HCO3−, Cl−, Na+ and Ca+2, with minor contributions from SO4−2, NO3−, K+ and Mg+2. The annual effective dose due to ingestion of groundwater radionuclides, based on total alpha and total beta activity averaged 0.49 mSv y−1 corresponding to a risk of an extra cancer over lifetime of 25 × 10–4, which is comparable to the national admissible cancer risk limit of 25 × 10–4. The results of this study were compared with national and international water quality standards. Several water parameters attained the recommended limits for the protection of public health, and a thorough water quality monitoring programme and enhanced measures for protection of the aquifer are recommended.