The migration of uranium into peat-rich soils at Broubster, Caithness, Scotland, U.K

• Published in: CHEMISTRY AND MIGRATION OF ACTINIDES AND FISSION PRODUCTS Vol. 13; no. 1; pp. 291 - 308
• Main Authors: Read, D., Bennett, D.G., Hooker, P.J., Ivanovich, M., Longworth, G., Milodowski, A.E., Noy, D.J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.1993; Elsevier Science
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Freshwater; Geochemistry; Pollution, environment geology; Soil and rock geochemistry; United Kingdom; Scotland; Europe; radium; Retardation; ground water; radionucleids; complexing; sandstone; spatial distribution; apatite; thorium; bogs; soil profiles; radiometry; pH; fault zones; biochemical sedimentation; peat; clastic rocks; organic residues; models; clastic sediments; boulder clay; leaching; transport; mass transfer; sedimentary rocks; surface flow; fixation; migration; uranium; chemical composition; surface properties; Caithness
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/0169-7722(93)90067-3

Uranium is being actively transported from uraniferous sedimentary rocks into a peat bog at the Broubster natural analogue site in Caithness, Scotland. Massive calcareous sandstone within the Caithness Flags sequence is the main source of uranium which resides primarily within diagenetic apatite and dispersed USiTi phases. Supergene weathering processes have decalcified the sandstone and are effective in mobilising uranium by groundwater leaching, primarily along a fault zone. Uranium transport in solution by means of groundwater and surface flows is effectively terminated by retardation within 4-kyr-old peat deposits laid down on boulder clay. This process of secondary fixation has resulted in a young uranium anomaly in the peat which comprises in excess of 0.1 wt% U. The site has been investigated comprehensively to define the geometry of the anomaly together with the hydrogeology, hydrochemistry, petrology, mineralogy and the nature of the peat sink-term. The main physical and geochemical properties of the system, including the uranium decay series radionuclide distributions in water and solid samples, are documented in this paper. From these data, the processes governing the distribution of uranium have been quantified using a three-dimensional groundwater flow package and an equilibrium speciation model incorporating a recently developed electrostatic surface complexation model to account for cation-organic interactions. The results described form part of a coordinated project on natural radionuclide migration undertaken to improve confidence in predictive methods used for radiological assessment.