Deep Vadose Zone Treatability Test of Uranium Reactive Gas Sequestration for the Hanford Central Plateau: Final Report

Abstract

Over decades of operation, the U.S. Department of Energy (DOE) and its predecessors have released nearly 2 trillion L (450 billion gal.) of liquid into the vadose zone at the Hanford Site. Much of this liquid waste discharge into the vadose zone occurred in the Central Plateau, a 200 km 2 (75 mi 2 ) area that includes approximately 800 waste sites. Some of the inorganic and radionuclide contaminants in the deep vadose zone at the Hanford Site are at depths where direct exposure pathways (human health or ecological) are not of concern, but the contamination may need to be remediated to protect groundwater. The Tri-Party Agencies (DOE, the U.S. Environmental Protection Agency, and the Washington State Department of Ecology) established Milestone M-015-50, which directed DOE to submit a treatability test plan for remediation of technetium-99 (Tc-99) and uranium in the deep vadose zone. These contaminants are mobile in the subsurface environment and have been detected at high concentrations deep in the vadose zone, and, at some locations, have reached groundwater. Testing of technologies to remediate Tc-99 and uranium will also provide information relevant to remediating other contaminants in the vadose zone. The uranium reactive gas sequestration (URGS) test described herein was conducted as an element of the deep vadose zone treatability test plan published to meet Milestone M-015-50. The URGS technology was tested as a potential remedy to decrease the mobility of uranium in the vadose zone as a mechanism to protect groundwater. Information about URGS obtained from this test is intended for use in subsequent feasibility studies for Hanford Central Plateau waste sites with uranium contamination in the deep vadose zone.

Applied Science Investigations to Facilitate Closure of the F-Area and H-Area Seepage Basins

“…Yet, more refined humate solutions may not have this problem. Szecsody et al (2010) and Truex et al (2018) tested ammonia gas as an amendment to raise pH in the deep vadose zone at Hanford. Thus, there are several base solutions that could potentially replace the carbonate base used currently.…”