Phosphogypsum (PG) is a by-product of the phosphoric acid production process that contains high concentrations of U-series radionuclides. PG piles formed during the last
30 years cover about 1,200 hectares and are located close to the
town of Huelva (Spain) on a salt-marsh. The regional government of Andalusia restored the area beginning in 1990 by
covering it with a 25-cm-thick layer of natural soil. With this
restoration, the external gamma-dose rate in the zone has
decreased drastically, approaching near environmental background values. This conclusion is based on results obtained
through in-situ monitoring measurements and through a dosimetric model developed for that particular radiation source.
As the model uses average parameters of the studied site, its
output does not show a correlation point by point with the
in-situ monitoring measurements. However, a good agreement
is observed in average values over the covered piles. The model
gives an average dose rate of 0.41 mGy y21 and the in situ
monitoring 0.40 mGy y21
. Based on this model, it is possible to
calculate the necessary thickness of soil to reduce the dosimetric contribution from a similar extension of PG until the
desired level is reached. In our conditions, in a 25-cm-thick
soil, about 0.19 mGy y21 is the increase produced by the PG
layer in relation to an infinitum soil layer. Consequently, no
radiological concern exists in the restored zones with respect to
the external gamma radiatio