The Huelva estuary, formed by the Tinto and Odiel rivers common mouths, it is a system of special interest, since these rivers present extreme physicochemical conditions due to mining activities, and in addition a Chemical Industrial Complex and phosphogypsum waste stacks are located at their surroundings. These facts make that this system is very altered and, therefore, an urgent remediation and environmental restoration is needed for these stacks. In this regard, the competent authorities, in collaboration with the responsible companies, are currently under design and approval of a project for the environmental remediation of these deposits.

From mid-60s until 31/12/2010 have been generated annually about 2.5 million tons of phosphogypsum by fertilizer plants located at this industrial complex. This residue is stored in big stacks built on the marshes of the right bank of the Tinto River, less than 1 km from the Huelva city, and accumulating them about 100-120 million tones covering an area of about 1000 ha. Previous studies have shown that phosphogypsum contains U-series radionuclides concentrations between 10-50 times higher than a typical soils depending of each isotope, and therefore this residue is classified as NORM (Naturally Occurring Radioactive Material). These deposits can emit radionuclides to the environment in the following ways: (1) atmospheric 222Rn emission and by particulate matter); (2) by waters released from these piles.

Therefore, the main objective of the project has been to characterize, evaluate and quantify the ability of these stacks of radioactively contaminate the environment, the radiation risks associated and, therefore, to apply the results to the recovery plan and environmental monitoring currently in development. To achieve the main objective, the project is structured in the following steps:

1) modeling the transport of 222Rn in the stacks calculating the total radon exhalation in order to introduce it as input to an atmospheric dispersion model, and thus assess the radon exposure of the population and the environment.
2) To study in laboratory the mobility and geochemical evolution of the radionuclides contained in the phosphogypsum under different environmental changes.
3) Characterization and quantification of the flows of radionuclides into the estuary.
4) To apply a hydrogeological model of the phosphogypsum stacks to quantify the radionuclides transport into the estuary by these stacks.
5) And finally, to assess of the radiological risks for the population.
6) Remediation proposal.

The expected results of the project are: to examine the processes of radionuclides transport (gas and solution) through phosphogypsum piles knowing the flows through their surface, and finally to know the ionizing radiation exposure associated to different scenarios (resident in the vicinity of the deposits, worker of the piles, recreational use, etc.). The results of the project, ans specially the methodology to asses the radiological risks of NORM repositories the evaluation of the effectiveness of different options engineering barriers, will carry out an important international impac due to the huge number of countries with this problem.

 RESUMEN DE LA PROPUESTA / SUMMARY OF THE PROPOSAL