Uranium Immobility in Tims Branch Wetland

Technical Report · Mon Mar 01 04:00:00 EST 2021

DOI:https://doi.org/10.2172/1770287· OSTI ID:1770287

Kaplan, D. I. ^[1]; Parker, C. ^[2]; Powell, B. A. ^[2]

---

1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2. Clemson Univ., SC (United States)

The objective of this study was to address an item identified by the Low-Level Waste Disposal Facility Federal Review Group (LFRG) panel during their review of the Savannah River Site’s Composite Analysis. Their concern was that the Tims Branch wetland, which has elevated levels of uranium (U) originating from site operations between 1952 to 1985, may be a secondary source term, posing a human health risk. This report briefly describes three studies dealing with: 1) quantifying the mass of U remaining in the wetland, 2) quantifying the tendency of U to release from Tims Branch sediment, and 3) describing the distribution of U in aqueous and suspended solids in Tims Branch water during episodic storm events. The Tims Branch wetland has been extremely effective for the last 50 years at immobilizing U released to the system. A detailed map including 270,000 gamma spectra of the U distribution in the wetland indicated that 84% of the initial 43,500 kg U introduced in the system remain there after 50 years (Kaplan et al., 2020). The effectiveness of immobilizing U is supported by stream water measurements collected over the last several decades indicating that U concentrations have been consistently below drinking water regulatory limits (i.e., the EPA Maximum Contaminant Level, 30 pg/L (SRNS, 2019)). Furthermore, using contaminated Tims Branch sediments, in situ desorption Kd values (ratio of U sediment/U Water) were extremely high, ranging from 104to 106 L/kg, suggesting the U is strongly bound to these wetland sediments. Finally, a detailed study of Tims Branch stream water properties during episodic rain events indicated that essentially all the U transported in this stream was associated with suspended solids (Batson et al., 1996). Together these findings indicate that the Tims Branch wetland is extremely effective in its present state at immobilizing U and that the small masses of U released downstream will be predominantly in association with suspended solids.

• Research Organization: Savannah River Site (SRS), Aiken, SC (United States); Savannah River National Lab (SRNL), Aiken, SC (United States); Clemson Univ., SC (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• DOE Contract Number: AC09-08SR22470
• OSTI ID: 1770287
• Report Number(s): SRNL-STI--2021-00081
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES