•Stationary diffusion model was used to describe phosphogypsum particle transfer.•Active electronic dosimeters ALARA were used to measure dose rates.•The mass concentration of particles was determined fiducially and realistically.•The model enabled to reduce the expenses and time of the measurements. Phosphogypsum (PG), a waste product in phosphate fertilizer production, is characterized by technically enhanced natural radioactivity. The presented investigation was performed on a PG deposition site in Croatia. A new approach in the determination of the spread of PG particles from the deposition site into the environment based on the PG particle radioactivity measurements is suggested and explained. The stationary diffusion model was assumed and employed to describe long term PG particle transfer into the surroundings. The advantage of this method is that it requires a minimal number of measurement locations and offers a realistic and reliable distribution of PG particles. The mass concentration of PG particles decreased to the distance of about 3m, at most up to 10m from the deposition site edge. The results indicate that a unique mechanism of particle transport exists and the migration of PG particles by surface water is the dominant way of their spread. The particle current deduced from the measurements was very low, approximately 4.05×10−2kg/h, and the migration coefficient was approximately 1.69×10−5m2/h. The obtained results confirmed the initial hypothesis of the stationarity of the migration process, reached within about 6 years.