Evaluation of a Radioiodine Plume Increasing in Concentration at the Savannah River Site

Abstract

Field and laboratory studies were carried out to understand the cause for steady increases in (129)I concentrations emanating from radiological basins located on the Savannah River Site, South Carolina. The basins were closed in 1988 by adding limestone and slag and then capping with a low permeability engineered cover. Groundwater (129)I concentrations in a well near the basins in 1993 were 200 pCi L(-1) and are presently between 400 and 1000 pCi L(-1). Iodine speciation in the plume contained wide ranges of iodide, iodate, and organo-iodine concentrations. First-order calculations based on a basin sediment desorption study indicate that the modest increase of 0.7 pH units detected in the study site groundwater over the last 17 years since closure of the basins may be sufficient to produce the observed increased groundwater (129)I concentrations near the basins. Groundwater monitoring of the plume at the basins has shown that the migration of many of the high risk radionuclides originally present at this complex site has been attenuated. However, (129)I continues to leave the source at a rate that may have been exacerbated by the initial remediation efforts. This study underscores the importance of identifying the appropriate in situ stabilization technologies for all source contaminants, especially if their geochemical behaviors differ.

Iron mineralogy and uranium-binding environment in the rhizosphere of a wetland soil

“…S1). The larger plate-like crystals are likely hematite, which is frequently reported in these soils (Kaplan et al, 2011), was detectable by XRD in some of the bulk soils (Table 1), and also identified by Mössbauer spectroscopy (Fig. 4).…”

How mobile is iodide in the Callovo–Oxfordian claystones under experimental conditions close to the in situ ones?

“…Indeed, as previously shown by Reiller and Moulin (2003), Schlegel et al (2006) and Steinberg et al (2008), the iodination of the organic matter leads to the formation of covalent bonds, thus, to an immobilisation of iodine. Such a mechanism is capable of explaining the retardation of the iodide migrating through soils made of relatively fresh and reactive organic matter (see e.g., Kaplan et al, 2011;Zhang et al, 2011). However, extra cautions have to be taken for indurated clay rocks, in which NOM are kerogen-type, known to be mature and relatively inert (Deniau et al, 2008).…”

Radioiodine Biogeochemistry and Prevalence in Groundwater

“…The highest concentration reported to date, 1060 pCi/L, was in 1996 for a well adjacent to the largest basin. Concentrations of 129 I in this well have been rising over the past twenty years, while concentrations of most other radionuclide contaminants have been decreasing (Kaplan et al., 2011). The increase likely reflects release of adsorbed 129 I from vadose zone and seepage basin sediments as pH has risen with time (Denham and Vangelas, 2008; Kaplan et al., 2011).…”