Deep Vadose Zone Treatability Test for the Hanford Central Plateau: Soil Desiccation Pilot Test Results
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- CH2M Hill Plateau Remediation Co., Richland, WA (United States)
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 km2 (75 mi2 ) 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 below the limit of direct exposure pathways, but may need to be remediated to protect groundwater (DOE 2008a; Dresel et al. 2011). The Tri-Party Agencies (DOE, U.S. Environmental Protection Agency, and Washington State Department of Ecology) established Milestone M-015-50, which directed DOE to submit a treatability test plan for remediation of 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 technologies for remediating Tc-99 and uranium will also provide information relevant for remediating other contaminants in the vadose zone. The desiccation test described herein was conducted as an element of the test plan published in March 2008 to meet Milestone M-015-50 (DOE 2008a). This field test report was prepared and submitted in response to Milestone M-015-110D, which set a date for desiccation field test activities to be reported to the Tri-Party Agencies. The desiccation field test was conducted at the Hanford Site 200-BC-1 Operable Unit. This waste site contains 26 cribs and trenches that received about 110 million L (29 million gal) of liquid waste primarily in the mid-1950s. The waste contained about 410 curies of Tc-99 (Corbin et al. 2005). There is no evidence the contamination has reached groundwater, located about 100 m (330 ft) below ground surface (bgs) in this area. Initial characterization efforts indicated the Tc-99 inventory is located mostly at a depth in the vadose zone of between about 30 and 70 m (98 and 230 ft) bgs. However, transport model predictions have indicated the potential for this contamination to adversely impact groundwater in the future (Ward et al. 2004). The test was conducted in two steps to provide information about desiccation that is intended for use in subsequent feasibility studies for waste sites with inorganic and radionuclide contaminants in the deep vadose zone. The first step was field-scale test site characterization conducted as described in a characterization work plan (DOE 2008b). Results of the characterization effort have been previously reported in DOE (2010a) and Um et al. (2009). A field test plan (DOE 2010b) was prepared and used to guide the desiccation field testing effort. Laboratory and numerical modeling efforts (Truex et al. 2011; Ward et al. 2008; Oostrom et al. 2009, 2011, 2012, In Press) preceded and accompanied the field test and are incorporated herein as their results pertain to assessment of desiccation for future feasibility studies.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1095466
- Report Number(s):
- PNNL--21369; 830403000
- Country of Publication:
- United States
- Language:
- English
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