The exploitation of radium and uranium in Europe during the 20th century left a legacy of mining sites and milling facilities with radioactive contaminated materials that today fall in the framework of the European Basic Safety Standards (BSS) as existing situations of radiation exposure. In Europe the former radium and uranium producers are currently dealing with environmental remediation of such sites in order to meet the requirements of the European BSS. This is the case for example of Germany, France, Spain, Hungary, and Portugal amongst several former uranium producing countries.
The uranium production in Portugal took place mainly in the vein deposits of the granite region of center north of the country where sixty deposits of secondary uranium minerals were exploited. Uranium milling took place mainly at Urgeiriça, Bica, Guarda and Senhora dos Remédios and Castelejo mines. After closure of the last mine in 2001, public concerns about the fate of uranium residues motivated an assessment of the environmental contamination and public health risk of such residues in the former mine areas.
The environmental and radiological risk assessment investigation identified the amounts of waste, radionuclide concentrations and the situations were environmental dispersal of radionuclides were occurring and could expose local populations through water and food consumption, as well as the risk of radon exposure and radioactive dust inhalation. Following this radiation risk assessment the government approved an environmental remediation project for abandoned mine areas and, from 2005 to the present, about thirty of those former uranium sites were cleaned and remediated. Environmental radioactivity measurements in soils, water, agriculture products and livestock produced in the region were made and are made every year in order to maintain surveillance over the environmental contamination and radiation risks to man and biota.
The case study of the former uranium mine of Cunha Baixa is described in detail to provide insights into the concentrations of uranium radionuclides in mining and milling waste, mine drainage and in water from irrigation wells in the area of this mine. Furthermore, the agriculture products from the local farms, mostly products from irrigated horticulture and farm animals were analyzed as well and the radiation doses for consumers have been estimated. It was found that the ingestion of horticulture products grown with irrigation water from contaminated wells was originating a potential radiation exposure of members of the population of the village nearby, exceeding 1 mSv/year from mine radionuclides.
Remediation measures applied in Cunha Baixa mine included the coverage of the tailings, the continued treatment of mine water drainage, and removal of surface soil in contaminated areas. As the drinking water in the past was partially met with water wells, the supply of tap water through public waterways was accomplished decades ago. Irrigation of local farms was however an issue, because the contamination of the local aquifer with acid and radioactivity is high, and water is not adequate for irrigation. A surface water supply for irrigation was recently built and wells were sealed. These remediation measures reduced local contamination and exposure of the population to radioactivity and already improved the environmental and radiological conditions.
Lessons from the past practices in uranium mining and milling and radiation protection measures adopted are similar amongst the former uranium mining countries. Lessons to retain and procedures currently recommended to avoid generating new uranium legacies are summarized.