Mobilization of transuranic radionuclides from disposal trenches by natural organic matter

• Published in: Journal of contaminant hydrology Vol. 30; no. 1; pp. 49 - 77
• Main Authors: McCarthy, John F, Czerwinski, Kenneth R, Sanford, William E, Jardine, Philip M, Marsh, J.Daniel
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31.03.1998; Elsevier Science
• Subjects: Actinides; americium; Anion exchanging; Chromatography; Complexation; Contaminant transport; Contaminants; curium; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fulvic acid; fulvic acids; Groundwater; groundwater contamination; humic acids; Humic substances; Hydrogeology; Hydrology; Hydrology. Hydrogeology; Natural organic matter; Pollution, environment geology; Radionuclides; Storms; Transuranic; Trenches; Waste disposal; Wastes; Tennessee; Complexation; Radionuclides; Actinides; Groundwater; Contaminant transport; Transuranic; Fulvic acid; Natural organic matter; Humic substances; Waste disposal; shale; actinides; waste disposal; mobilization; ground water; water table; radionucleids; pollution; saprolite; Am-241; fulvic acids; surface water; saturation; sedimentary rocks; curium; physicochemical properties; chromatography; organic materials; migration; silicates; seasonal variations; clastic rocks
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/S0169-7722(97)00032-6

Transuranic (TRU) radionuclides in groundwater at the Oak Ridge National Laboratory migrate rapidly and with little retardation of the radionuclides over distances of 80 m. Several interacting hydrogeochemical processes contribute to the observed releases of actinides ( 244Cm and 241Am) from the shallow unlined disposal trenches, through the highly weathered, fractured shale (saprolite) and to the surface-water seeps at White Oak Creek. Major releases are promoted when seasonal fluctuations in the water table permit groundwater to contact actinide-contaminated waste. Local recharge of stormwater into the trenches appears to permit minor releases, perhaps due to transient saturation within the trenches but above the local water table. Although the hydrogeology of the site permits contact of the TRU waste with the groundwater, the expected inorganic species of the actinides should strongly adsorb to the layer silicates and mineral oxides of the shale saprolite. Yet the timing of the actinide releases relative to when rising groundwater intercepts the trenches suggests that actinide transport is rapid, and the relative magnitude of peak actinide levels in wells near the trenches and at downgradient seeps suggests that there is very limited retention of the actinides by the formation. Based on anion exchange chromatography of the groundwater and geochemical modeling, the mobilization and transport of the actinides is demonstrated to result from complexation of the actinides by natural organic matter (NOM). Storm events contribute to mobilization by promoting hydrologic links between the TRU waste and groundwater, and by increasing the concentration of NOM in the mobile soil and groundwater. This study demonstrates that even in formations characterized by abundant mineral phases known to strongly adsorb actinides, the actinides can be transported essentially conservatively as NOM complexes.