Radiation Measurements 43 (2008) 98 – 101 www.elsevier.com/locate/radmeas Radon occurrence in soil–gas and groundwater around an active landslide R.C. Ramola a , ∗ , V.M. Choubey b , M.S. Negi a , Yogesh Prasad a , Ganesh Prasad a a Department of Physics, H.N.B. Garhwal University, Badshahi Thaul Campus, Tehri Garhwal -249 199, India b Wadia Institute of Himalayan Geology, Dehradun 248 001, India Received 18 January 2007; received in revised form 11 April 2007; accepted 12 May 2007 Abstract This paper presents the results of investigation of radon levels in the soil–gas and groundwater of Uttarkashi, India within the distance of 5km in vertical and horizontal directions from the landslide of Varunawat hill. Radon release from the soil and groundwater was found higher than the normal values. Radon concentration in groundwater over and around the landslide was found to vary from 0.51 to 86kBq m −3 . The soil–gas radon concentration was found to vary from 219 to 3 kBq m −3 along the slope of landslide. Radon exhalation rate in collected soil samples was found to vary from 2.28 × 10 −5 to 9.01 × 10 −5 Bq kg −1 h −1 . Radon values were not found correlated with major and trace element contents in the upper soil of the area, which indicate that the migration of radon from deeper part of the earth along with landslide contribute to the surface radon concentration. Recorded values show a close association with local geology and Varunawat eruptions. © 2007 Elsevier Ltd. All rights reserved. Keywords: Radon; Soil–gas; Groundwater; Landslide 1. Introduction Exposure of person to high concentration of radon and its short-lived progeny for a long period leads to pathological ef- fects like the respiratory functional changes and the occurrence of lung cancer (Lubin and Boice, 1993; Ramola et al., 1997; UNSCEAR, 2000). Radium and radon are soluble in water. When ground water moves through radium/radon bearing soil and rocks they are dissolved and transported with the water. Radon concentration level and radon risk will be increased with high radium and Uranium content in ground water. The adverse health effects of radon in water are largely due to the transfer of radon to the air, where it decays and its short-lived radioac- tive daughter inhaled rather than direct ingestion (Cross et al., 1985). Large scale mobility characteristics are influenced by additional factors such as rock and soil geochemical character- istics and geological structures like faults, shears, thrusts, etc. (Choubey and Ramola, 1997). The Himalaya evolved due to intra-continental collision during the Cenozoic (Le Fort, 1975; Molnar and Tapponnier, ∗ Corresponding author. Tel.: +91 1376 232856; fax: +91 1376 256056. E-mail address: rcramola@gmail.com (R.C. Ramola). 1350-4487/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2007.05.054 1975). In Garhwal Himalaya, regional structures, namely the North Almora Thrust, Main Boundary Thrust, and Main Central Thrust are responsible for radon emanation, but sudden changes in geological structure released/controlled on tremendous ema- nation of radon. Uttarkashi area in Garhwal Himalaya was sub- jected to tectonic movements due to which several faults and weak planes have developed in the region (Saraf et al., 1996). Heavy landslide occurred in this region on 24 September 2003 (Fig. 1), which affected the central part of the town. The geo- logical map of the area is shown in Fig. 2. The fall of debris was continued for more than one month, which disturbed the entire activities in the town. Anthropogenic activities at the toe of hill slope have resulted in loosening of the rock mass and increase in slope gradient, which have disturbed the stability of the slopes by increasing the shear stress (Sarkar et al., 2004). This paper presents some results of radon measurements in drinking/groundwater samples around the landslide area. 2. Geology of the area Geologically the area around Uttarkashi is made up of two main lithotectonic units, which are the Higher Himalayan Crys- tallines and the Lesser Himalayan sediments (Valdiya, 1980).