75 Carpathian Journal of Earth and Environmental Sciences, August 2013, Vol. 8, No. 3, p. 75 - 80 FLUX MEASUREMENTS OF 222 Rn, CH 4 AND CO 2 ALONG WITH SOIL GAS CONCENTRATIONS ( 222 Rn, CO, NO 2 AND SO 2 ) OVER A METHANE RESERVOIR IN TRANSYLVANIA (ROMANIA) Nicolae FRUNZETI 1 , Mircea MOLDOVAN 1* , Bety-Denissa BURGHELE 1 , Constantin COSMA 1 , Calin BACIU 1 , Botond PAPP 1 , Gabriela Emilia POPITA 1 & Laurentiu Cristian STOIAN 2 1 Babeş-Bolyai University, Faculty of Environmental Science and Engineering, Fantanele street, 30, 400294, Cluj- Napoca, Romania. *E-mail: mircea.moldovan@ubbcluj.com 2 Babeş-Bolyai University, Faculty of Geography, Clinicilor Street, 5-7, 400006, Cluj-Napoca, Romania Abstract: The Transylvanian Basin is well known for its large and good quality methane accumulations. In many sites these accumulations are not completely sealed, and methane leaks into the atmosphere through faults or fractures. A soil gas survey was carried out after a rainy season at Sărmăşel, the largest methane seep in Transylvania. This study presents the first results of soil 222 Rn concentration measurements in relation with CH 4 flux, in an attempt to better understand the spatial distribution of soil gas concentrations and migration toward the surface in this area. Taking into account the particular situation in the field, the study area was divided in two sub-areas corresponding to the two main seeps with high methane emissions and everlasting fires. Accordingly, two sets of measurements were performed. The first set was distributed on a 36 meters transect with respect to seep 1. The soil gases concentrations ( 222 Rn, CO, NO 2 and SO 2 ) were measured at 80 cm depth along with CH 4 and CO 2 fluxes. The maximum values of 222 Rn concentration from soil was found at 17.5 kBqm -3 and quite high concentrations of other gases, such as 19 ppm of CO, 1 ppm of SO 2 and 0.7 ppm of NO 2 . The results suggest that concentrations of CO, NO 2 and SO 2 correlate with CH 4 and CO 2 fluxes. Radon concentration in soil seems to be more dependent on soil permeability than on the CH 4 flux. For the second set of measurements, the CH 4 and 222 Rn fluxes were randomly distributed around the main vents. It was observed a relatively high 222 Rn flux with a maximum value of 119.3 mBqm -2 s -1 and an average of 58.4 mBqm -2 s -1 , over an area with high CH 4 emission. Keywords: gas geochemistry, methane, radon, soil permeability 1. INTRODUCTION The importance of soil gas monitoring has been widely demonstrated in numerous applications in volcanology (Gal & Gadalia, 2011), petroleum exploration (Link, 1952; Abrams, 2005), and geophysics (Lombardi & Voltattorni, 2010; Papp et al., 2010). The gas migration toward the surface is strictly related to the existence of a gas reservoir, and the existence of a preferential pathway for degassing such as fractures or faults (Etiope & Martinelli, 2002). The variation of pressure, temperature, mechanical stress, and other tectonic factors lead to gas migration. Geogenic gasses include mainly CO 2 , H 2 O, H 2 S, NH 3 , H 2 , N 2 , CH 4 and heavier hydrocarbons, but also inert gases like He, 222 Rn or Ar. In sedimentary basins, the geogenic gas is mainly composed of CH 4 (very often up to 90- 99 %) followed by some trace amounts of other gases. The studies performed during the last decades, suggest that during the gas migration towards the surface, the large amount of CO 2 in volcanic-geothermal systems and CH 4 in sedimentary basins act as carrier gasses (Durrance & Gregory, 1990; Morner & Etiope, 2002). Radon ( 222 Rn) is a radioactive gas, chemically inert, which originates from the decay of the uranium ( 238 U) series. In general, soil 222 Rn has a near surface origin as its half-life is 3.82 days. But there are many cases when it may indicate the presence of an area where the advection or diffusion of other gasses like CO 2 or CH 4 occurs. Nazaroff (1992) estimated an average 222 Rn flux of about 22 mBqm -2 s -1 in an area without uraniferous formations. In the presence of a