Impact of the loess’ hydraulic characteristics on its degree of saturation for the purpose of radon index measurements (Northeast Bulgaria case study)

Radon gas has high mobility and is driven by advection and diffusion with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore, there is a need for quantitative assessment of the saturation state, even on a daily-base in order to estimate the radon potential correctly. The more so as, the permeability is one of the key factors in the radon risk assessment. For the purpose of such investigation, a vertical profile model was elaborated for a study site in Northeast Bulgaria. On the base of pedotransfer function analyses, the hydraulic parameters describing the retention function and the hydraulic conductivity function were determined for each case study. The results show that even in a month with high amount of rainfall precipitation (13% of the total amount per year), the loess profile at certain depths remains unsaturated, regardless the difference in the hydraulic characteristics.