Journal of Hazardous Materials 110 (2004) 139–149 Computational modelling of final covers for uranium mill tailings impoundments Guilherme Lu´ ıs Menegassi Leoni a , Márcio de Souza Soares Almeida a,∗ , Horst Monken Fernandes b a Federal University of Rio de Janeiro (UFRJ), COPPE—Graduate School of Engineering, Civil Engineering Program, Rio de Janeiro, Brazil b Institute for Radioprotection and Dosimetry/CNEN, Rio de Janeiro, Brazil Abstract To properly design a final cover for uranium mill tailings impoundments the designer must attempt to find an effective geotechnical solution which addresses the radiological and non-radiological potential impact and prevents geochemical processes from occurring within the tailings. This paper presents a computer-based method for evaluating the performance of engineered final covers for the remediation of uranium mill tailings impoundments. Three hypothetical final covers were taken from scientific literature to investigate the proposed method: (i) a compacted clay liner (CCL); (ii) a composite liner (CL) and (iii) a capillary barrier (CB). The processes investigated: (i) the saturated hydraulic flux; (ii) the unsaturated hydraulic flux (exclusively for the capillary barrier) and (iii) the radon exhalation to the atmosphere. The computer programs utilised for the analyses are: (i) Hydrologic Evaluation of Landfill Performance (HELP); (ii) SEEP/W and (iii) RADON. The site considered for the development of the research presented herein was the uranium mill tailings impoundment located at the Brazilian city of Poços de Caldas, in the Minas Gerais State. © 2004 Elsevier B.V. All rights reserved. Keywords: Final covers; Geotechnical modelling; Tailings impoundments; Soil remediation; Uranium mill tailings 1. Introduction A complete assessment of the efficiency of final soil cov- ers applied to uranium mill tailings impoundments must take into account the several particular aspects concerning non-radiological and radiological potential impacts. In this sense, final covers have to prevent water infiltration into underlying tailings as well as prevent radon gas emission from the underlying tailings into the atmosphere. In ad- dition, when pyrite is present in the tailings composition, the final covers have to prevent infiltration of gaseous oxy- gen into the tailings in order to avoid acid mine drainage formation. The long-term efficiency of final covers is a major im- portant concern when designing final covers for uranium mill tailings impoundments. Shackelford [1] writes that ∗ Corresponding author. Tel.: +55-21-2290-1730; fax: +55-21-2562-8464. E-mail address: almeida@geotec.coppe.ufrj.br (M.d.S.S. Almeida). “the costs associated with the assessment of the variety of materials, conditions and applications in environmental geotechnics are often prohibitive such that detailed testing and analysis is not always possible. In this regard, when laboratory and field data are available, modelling represents a promising approach due to the relative ease of implemen- tation and the potential for universal application of a given model to a given type of problem”. The approach presented herein for the assessment of the efficiency of final covers utilises different computer models in an integrated manner. Therefore, output data from one program is utilised as input data for another program. Lab- oratory investigations were performed in the Laboratory of Geotechnics at COPPE/UFRJ as well as in the labo- ratory for radiological investigations at IRD/CNEN. Field investigations were performed at the Poços de Caldas mill tailings impoundment. The results were used as input and background information. The uranium mill tailings im- poundment of Poços de Caldas was taken as the reference site under assessment. 0304-3894/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2004.02.047