RADON IN GROUNDWATERS IN THE BAIKAL REGION AND TRANSBAIKALIA: VARIATIONS IN SPACE AND TIME

This study aimed to provide a systematic overview of water sources in the Baikal region and Transbaikalia by the content of radon (Q) and establish regularities in variations of Q values in space and time.

We collected and analyzed our evaluations of Q and the available published Q values for many dozens of water sources in the study area (Fig. 1), and reviewed the monitoring data of eight water sources that belong to the Angarsky fault impact zone in Southern Priangarie (Fig. 5). Radon content in water samples was measured in accordance with the standard procedure using a RRA-01M-03 radiometer (sensitivity of at least 1.4∙10–4 s–1∙Bq–1∙m3; maximum allowable relative error of 30 %).

Based on the frequency patterns of Q values measured in the Baikal region and Transbaikalia (Fig. 2) and the analysis of the known classifications of the water sources by radioactivity, we propose a uniform regional classification of groundwaters with respect to 222Rn content (Table 1). In seismically active Baikal region, wherein water sources with Q>185 Bq/l are practically lacking, we distinguish the first three groups with the following Q ranges: Group I – Q≤15 Bq/l, Group II – 16≤Q≤99 Bq/l, and Group III – 100≤Q≤184 Bq/l. Most of the water sources sampled in the Baikal region and Transbaikalia belong to Groups I and II, which allows us to recommend an objectively existing value of 100 Bq/l as the level of intervention in the preparation of drinking water in this region, instead of the limit of 60 Bq/l that is now approved in Russia.

In order to identify the special patterns of groundwater sources in the Baikal region and Transbaikalia, which belong to different radioactivity groups, we sampled these sources along the transect from Bayanday to Muhorshibir, across the Baikal rift and other large regional tectonic structures (Fig. 4). On a larger scale, we analysed the radon content variability in the groundwater sources within the zones influenced by the Tunka normal fault (Fig. 3), Primorsky normal fault, Angarsky strike-slip fault with a normal component, and other active faults located in the study region. 

Within the framework of the spatial aspect, the material and structural factors determining the radioactivity of groundwaters in the study region are identified. Our data support the results of the previous studies showing a generally lower radon content in groundwaters in the Baikal region in comparison with those in Transbaikalia that is characterized by a higher radioactivity due to the abundant granitoids of different types. The background concentrations of the radioactive gas in the Baikal region correspond to Group I, and in those in Transbaikalia to Group II. The boundary between the regions with different levels of radioactivity of groundwaters is shifted southeastward from the central structures of the Baikal rift. Within the Bayanday–Muhorshibir transect, it coincides with the known boundary between the Transbaikalia province of cold carbonic acid waters and the Baikal province of nitrogen and methan terms (see Fig. 4). The structural factor of formation of the emanation field refers to an increase in radioactivity of water associated with the faults, whereat an increased permeability and higher geodynamic activity cause a more intensive radon emanation and/or the occurrence of emanating reservoirs (see Fig. 3, and 4). In the Baikal region, water sources of Group II are generally associated with faults, while in Transbaikalia, groundwater sources belonging to groups III and VI are typically related to faults.

To clarify the pattern of temporal variations in groundwater radioactivity, we analysed long rows of the monitored Q values (9 to 30 months) in eight water sources in the Angarsky fault zone in Southern Priangarie (see Fig. 5, and 6).According to the adopted classification (see Table 1), three water sources belong to the near-surface sources (Group I), and there are five deeper near-fault water sources (Group II). Despite the distinct variations in radioactivity, the Q values recorded through most of the monitoring time do not exceed the threshold Q values for the respective groups. It appears that the observed periodic anomalously high and low contents of radon are due to seasonally variable meteorological parameters (see Fig. 6).

The correlation analysis of Q values and atmospheric pressure (P), air humidity (U) and temperature (T) shows a clear dependence of the content of radon in groundwater on T and P values (Table 3). Following the major seasonal trend of air temperature, the level of radioactivity is increased in the water samples taken in winter and decreased in summer (see Fig. 6). Q values are indirectly influenced by parameter T via changes of water temperature, variations in flow rates of water sources, freezing of the top layer of soil and other processes, which parameters require further research.

According to the monitoring data (see Table 3, and Fig. 6, A), the content of radon in near-surface water sources (Group I) can vary by a few and the first dozens of units, while changes by tens of becquerel per liter are recorded in the deeper near-fault water sources (Group II). As a consequence, in short periods of extreme Q values, the content of radon in a water source may increase or decrease to a value corresponding to a neighbouring radon-radioactivity group.

This paper provides an overview of the radon activity of groundwater in the Baikal region and Transbaikalia with a focus on regularities in the spatial and temporal patterns of 222Rn in the water sources with Q<185 Bq/l. The nonradon waters are more abundant in the Baikal region, including areas of active use of natural resources. Although the content of 222Rn in low, such waters should be a target of further research aimed to explore medicinal water sources, assess drinking water quality, and discover the emanation precursors of strong earthquakes in the study region.

1. Adushkin V.V., Spivak A.A., 2014. Physical Fields in the Near-Surface Geophysics. GEOS, Moscow, 360 p. (in Russian) [Адушкин В.В., Спивак А.А. Физические поля в приповерхностной геофизике. М.: ГЕОС, 2014. 360 с.].

2. Baikal Branch of the Geophysical Survey. The main catalogue of events. Available from: http://seis-bykl.ru (last accessed February 10, 2016) (in Russian) [Байкальский филиал геофизической службы. Основной каталог событий. Режим доступа: http://seis-bykl.ru (дата обращения: 10.02.2016)].

3. Chernyago B.P., Nepomnyashchikh A.I., Medvedev V.I., 2012. Current radiation environment in the central ecological zone of the Baikal Natural Territory. Russian Geology and Geophysics 53 (9), 926–935. http://dx.doi.org/10.1016/j.rgg.2012.07.008.

4. Erdogan M., Eren N., Demirel S., Zedef V., 2013. Determination of radon concentration levels in wellwater in Konya, Turkey. Radiation protection dosimetry 156 (4), 489–494. http://dx.doi.org/10.1093/rpd/nct099.

5. Express Method for Measurement of 222Rn Volume Activity in Soil Air by PPA Radon Radiometers. Recommendation, 2004. Doza NPP, Moscow, 16 p. (in Russian) [Методика экспрессного измерения объемной активности 222Rn в почвенном воздухе с помощью радиометра радона типа РРА. Рекомендация. М.: НПП «Доза», 2004. 16 с.]

6. Ghosh D., Deb A., Sengupta R., 2009. Anomalous radon emission as precursor of earthquake. Journal of Applied Geophysics 69 (2), 67–81. http://dx.doi.org/10.1016/j.jappgeo.2009.06.001.

7. Guerra M., Etiope G., 1999. Effects of gas-water partitioning, stripping and channelling processes on radon and helium gas distribution in fault areas. Geochemical Journal 33 (3), 141–151. http://doi.org/10.2343/geochemj.33.141.

8. Koval P.V., Udodov Y.N., San’kov V.A., Yasenovskii A.A., Andrulaitis L.D., 2006. Geochemical activity of faults in the Baikal Rift Zone (mercury, radon, and thoron). Doklady Earth Sciences 409 (2), 912–915. http://dx.doi.org/10.1134/S1028334X06060171.

9. Kraynov S.R., Rizhenko B.N., Shvets V.M., 2012. Geochemistry of Groundwater. Theoretical, Applied and Environmental Aspects. CentrLitNefteGaz, Moscow, 672 p. (in Russian) [Крайнов С.Р., Рыженко Б.Н., Швец В.М. Геохимия подземных вод. Теоретические, прикладные и экологические аспекты. М.: ЦентрЛитНефтеГаз, 2012. 672 с.].

10. Kulikov G.V., Zhelvakov A.V., Bondarenko S.S., 1991. Mineral Medicinal Waters of the USSR: A Handbook. Nedra, Moscow, 399 p. (in Russian) [Куликов Г.В., Желваков А.В., Бондаренко С.С. Минеральные лечебные воды СССР: Справочник. М.: Недра, 1991. 399 с.].

11. Lomonosov I.S., Kustov Yu.I., Pinneker E.V., 1977. Mineral Waters of the Pribaikalie. East Siberian Publishing House, Irkutsk, 224 p. (in Russian) [Ломоносов И.С., Кустов Ю.И., Пиннекер Е.В. Минеральные воды Прибайкалья. Иркутск: Вост.-Сиб кн. изд-во, 1977. 224 с.].

12. Lopatin M.N., 2015. Variations of dissolved radon concentrations in groundwater of the Southern Pribaikalie during earthquake preparation and occurrence. In: Lithosphere structure and geodynamics. Institute of the Earth’s Crust SB RAS, Irkutsk, p. 108–109 (in Russian) [Лопатин М.Н. Вариации концентраций растворенного радона в подземных водах Южного Прибайкалья при подготовке и реализации очагов землетрясений // Строение литосферы и геодинамика. Иркутск: ИЗК СО РАН, 2015. С. 108–109].

13. Mineral waters of the southern regions of East Siberia, vol. II. 1962. Publishing House of the USSR Academy of Sciences, Moscow, St. Petersburg, 200 p. (in Russian) [Минеральные воды южной части Восточной Сибири. Т. II. М.–Л.: Изд-во АН СССР, 1962. 200 с.].

14. Myasnikov A.A., Samovich D.A., Kokarev A.A., Gavrilov L.P., 2009. Uranium-bearing and radiation-ecological conditions of the southern regions of East Siberia. In: Radioactivity and radioactive elements in human environment. STT, Tomsk, p. 398–403 (in Russian) [Мясников А.А., Самович Д.А., Кокарев А.А., Гаврилов Л.П. Ураноносность и радиационно-экологическая обстановка территории юга Восточной Сибири // Радиоактивность и радиоактивные элементы в среде обитания человека. Томск: STT, 2009. С. 398–403].

15. Nevinsky I., Tsvetkova T., Nevinskaya E., 2015. Measurement of radon in ground waters of the Western Caucasus for seismological application. Journal of Environmental Radioactivity 149, 19–35. http://dx.doi.org/10.1016/j.jenvrad.2015.07.005.

16. Plyusnin A.M., Astakhov N.E., Peryazeva E.G., 2009. Radon in surface and ground waters of Transbaikalia: conditions and regularities of dissolution. In: Radioactivity and radioactive elements in human environment. STT, Tomsk, p. 444–448 (in Russian) [Плюснин А.М., Астахов Н.Е., Перязева Е.Г. Радон в поверхностных и подземных водах Забайкалья: условия и закономерности растворения // Радиоактивность и радиоактивные элементы в среде обитания человека. Томск: STT, 2009. С. 444–448].

17. Prasad Y., Prasad G., Gusain G.S., Choubey V.M., Ramola R.C., 2009. Seasonal variation on radon emission from soil and water. Indian Journal of Physics 83 (7), 1001–1010. http://dx.doi.org/10.1007/s12648-009-0060-9.

18. Przylibski T.A., 2011. Shallow circulation groundwater – the main type of water containing hazardous radon concentration. Natural Hazards and Earth System Sciences 11 (6), 1695–1703. http://dx.doi.org/10.5194/nhess-11-1695-2011.

19. Rudakov V.P., 1985. About barometric variations of subsoil radon. Geokhimiya (Geochemistry) (1), 124–127 (in Russian) [Рудаков В.П. О барических вариациях подпочвенного радона // Геохимия. 1985. № 1. С. 124–127].

20. Schery S.D., Gaeddert D.H., Wilkening M.H., 1982. Transport of radon from fractured rock. Journal of Geophysical Research 87 (B4), 2969–2976. http://dx.doi.org/10.1029/JB087iB04p02969.

21. Schubert M., Paschke A., Lieberman E., Burnett W.C., 2012. Air-Water partitioning of 222Rn and its dependence on water temperature and salinity. Environmental Science & Technology 46 (7), 3905–3911. http://dx.doi.org/10.1021/es204680n.

22. Seminskii K.Zh., Gladkov A.S., Lunina O.V., 2001. Tectonophysics of the Angara fault zone (Southern Siberian platform). Geologiya i Geofizika (Russian Geology and Geophysics) 42 (8), 1252–1262.

23. Seminsky A.K., Tugarina M.A., 2013. Specific features of radon distribution in groundwater of the Baikal region. In: Geology, exploration and survey of mineral resources and geological research methods. Irkutsk State Technical University, Irkutsk, p. 133–137 (in Russian) [Семинский А.К., Тугарина М.А. Особенности распределения радона в подземных водах Байкальского региона // Геология, поиски и разведка полезных ископаемых и методы геологических исследований. Иркутск: ИрГТУ, 2013. С. 133–137].

24. Seminsky K.Zh., Bobrov A.A., 2012. Spatial and temporal variations of soil-radon activity in fault zones of the Pribaikalie (East Siberia, Russia). Chapter 1. In: Z. Li, C. Feng (Eds.), Handbook of radon: properties, applications and health. Nova Science Publishers, New York, р. 1–36.

25. Seminsky К.Z., Bobrov А.А., 2013. The first results of studies of temporary variations in soil radon activity of faults in Western Pribaikalie. Geodynamics & Tectonophysics 4 (1), 1–12 (in Russian) [Семинский К.Ж., Бобров А.А. Первые результаты исследований временных вариаций эманационной активности разломов Западного Прибайкалья // Геодинамика и тектонофизика. 2013. Т. 4. № 1. С. 1–12]. http://dx.doi.org/10.5800/GT-2013-4-1-0088.

26. Seminsky K.Z., Kozhevnikov N.O., Cheremnykh A.V., Pospeeva E.V., Bobrov A.A., Olenchenko V.V., Tugarina M.A., Potapov V.V., Zaripov R.M., Cheremnykh A.S., 2013. Interblock zones in the crust of the southern regions of East Siberia: tectonophysical interpretation of geological and geophysical data. Geodynamics & Tectonophysics 4 (3), 203–278 (in Russian) [Семинский К.Ж., Кожевников Н.О., Черемных А.В., Поспеева Е.В., Бобров А.А., Оленченко В.В., Тугарина М.А., Потапов В.В., Зарипов Р.М., Черемных А.С. Межблоковые зоны в земной коре юга Восточной Сибири: тектонофизическая интерпретация геолого-геофизических данных // Геодинамика и тектонофизика. 2013. Т. 4. № 3. С. 203–278]. http://dx.doi.org/10.5800/GT-2013-4-3-0099.

27. Smetanova I., Holy K., Mullerova M., Polaskova A., 2010. The effect of meteorological parameters on radon concentration in borehole air and water. Journal of Radioanalytical and Nuclear Chemistry 283 (1), 101–109. http://dx.doi.org/10.1007/s10967-009-0128-1.

28. Spivak A.A., 2010. The specific features of geophysical fields in the fault zones. Izvestiya, Physics of the Solid Earth 46 (4), 327–338. http://dx.doi.org/10.1134/S1069351310040051.

29. Steinitz G., Vulkan U., Lang B., Gilat A., Zafrir H., 1992. Radon emanation along border faults of the rift in the Dead Sea area. Israel Journal of Earth-Sciences 41 (1), 9–20.

30. Toutain J.-P., Baubron J.-C., 1999. Gas geochemistry and seismotectonics: a review. Tectonophysics 304 (1–2), 1–27. http://dx.doi.org/10.1016/S0040-1951(98)00295-9.

31. Trofimov V.T. (Ed.), 2000. Ecological Functions of the Lithosphere. Moscow State University, Moscow, 432 p. (in Russian) [Экологические функции литосферы / Ред. В.Т. Трофимов. М.: МГУ, 2000. 432 с.].

32. Weather Forecast, 2016. Irkutsk Weather Archive. Available from: http://rp5.ru (last accessed: February 10, 2016) (in Russian) [Расписание погоды. Архив погоды в Иркутске. Режим доступа: http://rp5.ru (дата обращения: 10.02.2016)].

33. Woith H., 2015. Radon earthquake precursor: A short review. The European Physical Journal Special Topics 224 (4), 611–627. http://dx.doi.org/10.1140/epjst/e2015-02395-9.

34. Zmazek B., Todorovski L., Dzeroski S., Vaupotic J., Kobal I., 2003. Application of decision trees to the analysis of soil radon data for earthquake prediction. Applied Radiation and Isotopes 58 (6), 697–706. http://dx.doi.org/10.1016/S0969-8043(03)00094-0.

35. Zmazek B., Vaupotic J., Zivcic M., Premru U., Kobal I., 2000. Radon monitoring for earthquake prediction in Slovenia. Fizika B (Zagreb) 9 (3), 111–118.