  A one-year monitoring study was conducted in a pilot house with high radon
levels to investigate the ability and efficiency of radon mitigation by soil
depressurisation (SD) both active and passive. The study included monitoring of
radon concentration, pressure field extension (pfe) under the slab and some
atmospheric parameters for different testing phases. Periods in which the house
remained closed to foster radon accumulation were alternated with phases of
active and passive soil depressurisation under different conditions. The
behaviour of the radon concentration in the pilot house was analysed along with
the influence of atmospheric variables, significant correlations were found for
the radon concentration with atmospheric pressure, outdoor temperature and
wind. From the pfe analysis it was proven that the pressure drop with distance
from the suction point of the SD system is proportional to the depressurisation
generated. It was found also that the permeability characterisation of the
pilot house agrees with the literature about granular fill materials
characterisation for radon SD systems across Europe. Radon reductions in excess
of 85% were achieved for the different testing phases in all cases. Finally,
from the results it was stated that a fan power of 23 W is sufficient to ensure
radon reductions over 85% for dwellings with similar aggregate layer and soil
permeability.
