RADON in a high karst area of Montenegro - A case study

The national radon surveys in Montenegro revealed that the highest annual average radon concentrations (C_Rn,ind) in ground floors of dwellings and schools were found in a rural region characterized as a typical high-karst area. In this region, spanning approximately 800 km², C_Rn,ind values in 9 houses and 16 schools ranged from 219 to 2494 Bq/m³, with AM = 977 Bq/m³. To investigate the causes of these elevated indoor radon concentrations, the following parameters were measured near the 25 surveyed buildings: soil humidity, electrical conductivity, pH, activity concentrations of ²²⁶Ra, ²³⁸U, ²³⁵U, ²³²Th and ⁴⁰K, radon concentration in soil gas (c), soil permeability for radon gas (k), and gamma dose rate in the air. The geogenic radon potential (GRP) of the location was calculated based on the measured values of c and k. As anticipated, the soil permeability in this karstic region was notably high, 1.53·10^-11 m² on average, resulting in elevated GRPs and radon indexes (RI). Therefore, 9 investigated locations were classified as having an Extremely High RI, and the other 9 as having Very High RI. Building characteristics, such as filling, wall material, floor slab quality (FSQ), window frames, and construction period, were also assessed. A multivariate regression analysis was performed to evaluate the relationship between C_Rn,ind and independent variables of geogenic origin, as well as those related to building construction. The optimal linear regression model, with predictor variables FSQ, c, k, GRP and ²³⁸U, can explain 29.1% of the variance of indoor radon concentrations.