Impact of the geological and hydrogeological settings on the radon potential in Bulgaria (original) (raw)
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Analysis of the hydrogeological conditions in Bulgaria in connection with the radon potential
Review of the Bulgarian Geological Society, 2021
Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. Different types of rocks and soils possess different 226Ra content and different permeability. Radon has high mobility and is driven by diffusion and convection with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore, the radon potential of the area could depend on hydrogeology and its particular settings. The study deals with the general characteristics of the groundwater depths in Bulgaria based on the published since 1960’s sources. After analysis of the collected data several distinct regions have been elaborated based on different depth of the groundwater table regarding lithological, tectonic and geomorphological conditions. In addition, zones for screening assessment of groundwater table influence of radon potential have been precised.
Geologica Balcanica, 2021
Natural radon (222Rn) is a radioactive noble gas that occurs as the immediate decay product of radium (226Ra), part of the 238U family, in the lithosphere. Radon is driven by advection and diffusion with soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. The aim of the present study is to do a review of the existing so far research activities in Bulgaria in connection with the observation and/or evaluation of the degree of water saturation of the near-surface layer, and on that base to distinguish the up-to-date achievements in regards to the radon potential in situ evaluation. Due to this review, the studies in Bulgaria concerning moisture dynamics in the near-surface layers can be divided mainly into two groups. The first one investigates the hydraulic characteristics (parameters) of soils in the vadose zone. Based on that, conclusions or computer simulations for the saturation degree estimation can be drawn. The other group inclu...
Assessment of Radon Potential along Local Fault System in Sofia, Bulgaria (at Specific Test Site)
Dokladi na Bʺlgarskata akademiâ na naukite, 2024
Environmental spread of radon gas (222Rn) has been intensively investigated in the last few years due to its harmful effects on human health. A concept of radon index is used to characterize the geogenic radon potential of the terrain, as the latter gives the probability of the presence of radon gas concentration in a building, the genesis of which is directly related to the influence of the earth's surface. One of the approaches for quantifying the radon index is based on a multivariate cross-tabulation, which includes two parameters-radon concentration in soil gas and gas permeability of the earth layer (at 80 cm). The geology of the specific site (approx. 350 m 2) is characterized by the Pliocene clayey-sandy Formation, covered with Quaternary sediments. From tectonic point of view, the site as a part of Sofia Graben, has being subject of events related mainly with the Late Alpine deformations heading to very complex structures and fault systems. In situ measurements performed in the summer of 2023 at ten distinct points at the surface and 11 distinct points at two meters in depth from the surface vary as follows: from 44.2 to 189.0 kBq/m 3 (radon soil gas), from 2.0E−11 to 1.8E−13 m 2 (soil gas permeability), and from 0.10 to 0.17 µSv/h (gamma dose rate). Based on that, the radon index of the site is determined from "medium" to "high", with a predominance of the latter.
Environmental Geochemistry and Health, 2022
The paper describes research aimed at expanding scientific knowledge of radioactive isotope 222Rn occurrence in groundwaters flowing in crystalline rocks, including its spatial and temporal changes. The research, conducted in an area characterized by medium radon potential, was intended to determine the values of 222Rn activity concentration in groundwater in this type of areas. The 222Rn activity concentration in groundwaters discharged from investigated springs oscillated between 35.3 and 272.0 Bq/L. The authors discovered possible prevalence of radon groundwaters in areas with medium radon potential, which is the reason why all groundwaters intended for human consumption or household use in such areas should be subject to obligatory monitoring of 222Rn activity concentration. In the event of identifying occurrence of waters with 222Rn activity concentration of at least 100 Bq/L, their purification by removing radon is necessary before they are supplied to a water distribution net...
Radon in soil gas and constructed geogenic radon potential in Croatia
2017
Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the AlphaGUARD and from 2013with RM-2 measuring systems, while soil permeability was measured with the Radon-JOK device since 2015. Measurements of both parameters were performed at 412 locations, mostly in the vicinity of schools and kindergartens and the obtained average value of radon in soil gas was 48 kBq m -3 with standard deviation of 52 kBq m -3 . It is important to emphasize that there are areas with radon concentrations up to 550 kBq m 3 . Geogenic radon potential (GRP) has been constructed by “Neznal approach” and a new subclassification with 7 classes (1very low, 2 – low, 3 – medium lower, 4 – medium higher, 5 – high, 6 – very high, 7 – extremely high) is being introduced. The obtained average GRP of 28 ± 29 (“Neznal equation”) or 3.30 ± 0.96 (classes) classifies the soil of Croatia into soil of medium GRP.
Journal of radioanalytical …, 2002
This work characterizes the occurrence of radionuclides 222 Rn and 226 Ra in the mineralized groundwaters of Gorzanów. The village is situated in the Sudeten Mountains, which are known in Poland for having increased concentrations of the aforesaid radionuclides in their groundwaters. However, in Gorzanów, the measured concentrations of 226 Ra were low both in the reservoir rocks and mineralized waters. Consequently, the 222 Rn concentration in the groundwaters also turned out to be low. The 226 Ra content of these waters should mainly be associated with the dissolution of this nuclide, together with other main ions, at large depths, at slightly enhanced temperature. Radon-222, on the other hand, penetrates into the water during its outflow to the surface, in the zones of intensive friable deformations near fault zones. Thus, in the groundwaters of Gorzanów, the concentrations of these nuclides, subsequent in the uranium series, do not have a common genesis and they are not correlated with each other.
Radon and radium content of some cold and thermal aquifers from Bihor County (northwestern Romania)
Geofluids, 2010
In the present study, two of the major naturally occurring radionuclides (226 Ra and 222 Rn) were analyzed in water samples from shallow, medium-depth, and deep geothermal aquifers, all of which are located in Bihor County, northwestern Romania. Here, the results of radon and radium measurements, performed from 2008 to 2009 in 50 locations, are reported. Radon proved to have a wide range of activity, with values from 4.5 to 110.8 Bq l)1 for shallow aquifers, from 9.3 to 106.0 Bq l)1 for medium-depth aquifers, and from 10.1 to 34.8 Bq l)1 for deep geothermal aquifers. The shallow aquifers have lower radium concentrations (0.06 to 0.48 Bq l)1), compared to medium-depth aquifers (0.1 to 0.52 Bq l)1) and deep geothermal aquifers (0.27 to 1.8 Bq l)1). The principal aim was a thorough investigation into the possible correlations between the occurrence of radon and radium in different aquifers and the hydrogeological, hydrogeochemical, and geothermal features of the area. Besides the direct link between the occurrence of uranium and thorium and the 226 Ra and 222 Rn contents in groundwater, the measurements we performed have allowed us to identify a secondary control on radionuclide distributions caused by the adsorption of dissolved radium onto clay minerals in exchange for sodium (for the sandy clay aquifer of Sȃ cuieni), the high competition for adsorption sites in aquifers with high concentrations of dissolved calcium and magnesium (for the limestone dolomite aquifer of Oradea), and the role of thermal processes.
Geothermics, 2012
Geothermal waters originating from three aquifers in northwestern Romania have been analyzed for several physico-chemical parameters namely, pH, temperature, electrical conductivity, total dissolved solids, hardness, redox potential, and chemical oxygen demand. In addition, major dissolved ions and organic matter content and radium and radon occurrence have been analyzed. The three aquifers are the fissured Middle Triassic limestone/dolomite aquifer from Oradea, the Lower Cretaceous limestone aquifer from 1Mai-Felix Spa, and the Lower Pontian (Late Miocene) granular (sand) aquifer from Sȃcuieni. The first two aquifers belong to the Inner Dacides and the last to the Pannonian Basin. We have examined the relationships between the occurrence of radium and radon in the thermal waters and the hydrochemical and geothermal features of the aquifers, which may impart a secondary control on the activity of these radionuclides. According to their chemistry, the thermal waters were classified as sulfate-bicarbonate-calcium-magnesium (Oradea), bicarbonate-sulfate-calcium-magnesium (Felix-1Mai Spa), and bicarbonate-sodium-chloride (Sȃcuieni). The activities of radon and radium were higher in Sȃcuieni (up to 22.88 and 1.40 Bq/L) and Oradea (up to 34.82 and 1.82 Bq/L) than in Felix-1Mai Spa (up to 16.76 and 0.19 Bq/L). The data shows that the thermal processes may control the migration and distribution of radionuclides, and that the mobility of radionuclides may be influenced by several physico-chemical parameters, such as pH, total dissolved solids, and redox potential, or by some chemical processes, such as adsorption on humic acids or partitions into the organic (hydrocarbons) phase. The data illustrate no significant differences between the parameters analyzed from February to July 2009, proving that the production regime of the aquifers has a minor impact on their chemical and physical parameters.
Review of the Bulgarian Geological Society
Radon gas has high mobility and is driven by advection and diffusion with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore, there is a need for quantitative assessment of the saturation state, even on a daily-base in order to estimate the radon potential correctly. The more so as, the permeability is one of the key factors in the radon risk assessment. For the purpose of such investigation, a vertical profile model was elaborated for a study site in Northeast Bulgaria. On the base of pedotransfer function analyses, the hydraulic parameters describing the retention function and the hydraulic conductivity function were determined for each case study. The results show that even in a month with high amount of rainfall precipitation (13% of the total amount per year), the loess profile at certain depths remains unsaturated, regardless the difference in the hydraulic characteristics.
Measurements of radon concentration in soil gas of urban areas, Bulgaria
Romanian Journal of Physics
These work present results of preliminary study of radon concentration in soil gas at 64 locations within 13 urban areas of Bulgaria using AlphaGuard equipment. The measuring period was from 2008 to 2012. The temperature and humidity has been measured as well, including the gamma dose rate. The radon concentration in soil gas was found to be log-normally distributed within the range from 3?97kBq m?3, with arithmetic mean of 26 kBq.m?3. The influence of the meteorological and geological factors in relation to radon measurements was examined. Correlation between radon in soil gas and gamma dose rate was also present.