2014 IR&D Annual Report

Detection of Uranium Mill Tailings Cover Erosion Rates and Settlement Using Satellite-Based Radar Interferometry, 20-R8449

Principal Investigators
D. Marius Necsoiu
Gary R. Walter

Inclusive Dates: 01/20/14 – 06/20/14

Background — The Institute is actively expanding work related to land disposal sites with the U.S. Nuclear Regulatory Commission and other clients. Closure of uranium mill tailings impoundments requires construction of earthen covers that limit radon emissions and dispersal of radionuclides to the environment. NRC10 CFR Part 40 requires reasonable assurance that control of radiological hazards will be effective for at least 200 years. and for 1,000 years to the extent reasonably achievable.

This project investigated the feasibility of using synthetic aperture radar (SAR) coherence analysis, differential radar interferometry (DlnSAR) and multitemporal interferometry, in particular the small baseline subsets (SBAS) technique to monitor the performance and stability of soil covers at uranium mill tailings sites and other land disposal sites with earthen covers. The methodology promises to provide a low-cost means for routinely monitoring changes across the entire site, infeasible with groundbased methodology.

Approach — Archived satellite SAR data were acquired to include two uranium mill tailings sites in northwestern New Mexico: the Bluewater site and the Grants Homestake site. Mill tailings covers may consist of vegetated soil, rock mulch (a mixture of rock and soil), or rip rap. These various cover conditions affect the strength of the SAR signal and may affect its coherence, which in turn affects the ability to use lnSAR techniques in estimating surface displacement measurements. For the Bluewater site, the DlnSAR and SBAS analyses provided consistent centimeter-scale changes in ground surface displacements, mapped over the entire tailings impoundment. The displacements correlate with variations in the slope of the tailings impoundment cover and nature of the underlying tailings. At the Grants site, only the rock-covered side slopes maintained sufficient coherence to perform quantitative SBAS lnSAR analysis because reclamation activities disturbed the surface soil of the impoundment cap during the time period covered by the SAR data.

Accomplishments — This project provided a proof of-concept that InSAR techniques can be used to monitor the performance and stability of soil covers at uranium mill tailings sites and other land disposal sites with earthen covers. The research also advanced the understanding of how rip rap (coarse rock) affects the SAR signal response. Although the extent of the analysis was limited by the availability of archived data, the results demonstrated that future monitoring using on-demand SAR data acquisitions should yield reliable measurements of ground surface displacements.

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