Geofluids (2010) 10, 571–585 doi: 10.1111/j.1468-8123.2010.00316.x
Radon and radium content of some cold and thermal aquifers from Bihor County (northwestern Romania)
C. A. ROBA1 ,V.CODREA2 ,M.MOLDOVAN1 ,C.BACIU1 AND C. COSMA1 1Faculty of Environmental Sciences, Babes¸-Bolyai University, Cluj-Napoca, Romania; 2Biology and Geology Faculty, Babes¸-Bolyai University, Cluj-Napoca, Romania
ABSTRACT
In the present study, two of the major naturally occurring radionuclides (226Ra and 222Rn) 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 differ- ent aquifers and the hydrogeological, hydrogeochemical, and geothermal features of the area. Besides the direct link between the occurrence of uranium and thorium and the 226Ra and 222Rn contents in groundwater, the mea- surements 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 Sa˘ 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.
Key words: geology, geothermal waters, radioactivity, radionuclide migration
Received 31 December 2009; accepted 9 September 2010
Corresponding author: Carmen Andreea Roba, Faculty of Environmental Sciences, Babes¸-Bolyai University, Cluj-Napoca, Romania. Email: [email protected]. Tel: +40 728 261045. Fax: +40 264 307032.
Geofluids (2010) 10, 571–585
the subsurface migration and behavior of non-aqueous- INTRODUCTION phase liquids (Schubert et al. 2002), and ⁄ or for investigat- The naturally occurring radionuclides, commonly found in ing seismic activity (Yang et al. 2005; Einarsson et al. surface- and groundwaters, belong to the uranium (238U, 2008). Radon and radium are also analyzed for radiation 235U) and thorium (232Th) decay series. Most attention protection purposes (UNSCEAR 2000). High radon and 226 has been focused on Ra (with a half-life of T½ = 1600 radium concentrations occur in groundwater in many areas 222 years) and Rn (T½ = 3.8 days), two of the daughter where this resource is used for domestic water supply. 230 isotopes produced during the alpha decay of Th (T½ = Geothermal waters are often used for heating (in dwellings, 238 9 75200 years) in U(T½ = 4.468 · 10 years) decay hospitals, schools, public buildings, churches, etc.), in agri- series. Radon is frequently investigated in hydrogeological culture (in greenhouse heating, or in cereals drying), studies and used to identify buried uranium deposits for entertainment facilities (swimming pools), or for medi- (Ramola et al. 1989), for searching for hidden faults ⁄ cal purposes (balneotherapy). The use and release of thrusts (Etiope & Martinelli 2002; Ramola et al. 2008; these waters to the environment may raise concerns regard- Gonza´lez-Dı´ez et al. 2009), as a tracer for the examination ing aquatic ecology and health risks for local residents of groundwater inflows (Burnett et al. 2003; Kluge et al. (UNSCEAR 2000; Durand & Scott 2005). As a conse- 2007; Barragan et al. 2008), for better understanding of quence, continuous monitoring of these radionuclides in