Mixed Waste Management Facility Research Articles

Influence of irrigation approaches and spatial geolocation on tritium speciation, uptake and depuration

Pine needles and tree cores from a tritium (T) contaminated phytoremediation forest at the Savannah River Site (SRS in Aiken, SC) Mixed Waste Management Facility (MWMF) were measured for total T and T speciation and compared to other locations at the SRS and the surrounding area. Tree core ages ranged from 9 to 14 years old, covering over half of the ∼20-year on-going remediation efforts, while pine needles represent more recent time periods of 1-to-2-year increments. Remedial irrigation efforts at the MWMF are found to directly influence the pine needle T concentrations. The T content in the MWMF samples is higher than non-irrigated needle samples from other locations around the SRS. Further, the different forms of organic bound T are preferentially stored in tree core tissue, compared to pine needles where tritiated water dominates.

The use of dynamic modeling in assessing tritium phytoremediation

To minimize movement of tritium into surface waters at the Mixed Waste Management Facility at the Savannah River Site, tritium-contaminated groundwater released to the surface along seeps in the hillside is being retained in a constructed pond and used to irrigate forest acreage that lies over the contaminated groundwater. Management of the application of tritium-contaminated irrigation water needs to be evaluated in the context of the large amount of rainfall relative to evapotranspiration, the strong seasonality in evapotranspiration, and intra-annual and interannual variability in precipitation in this region. A dynamic simulation model of water and tritium fluxes in the soil-plant-atmosphere continuum was developed to assess the efficiency (tritium transpired/tritium applied) of several irrigation management strategies. The model was parameterized using soil-water content data measured at 18 sites for the first year of the project and evaluated using tritium activity measurements made at the same 18 sites over 2.5 yr. The model was then used to evaluate several irrigation strategies. The 25-yr efficiencies (tritium transpired/tritium applied) of the irrigation strategies were related to the quantity of irrigation water applied. There was a strong (r2 = 0.99) negative linear relationship between irrigation water applied and efficiency. When a quasi-steady state has been reached in the system, the annual efficiencies of all the irrigation strategies were negatively correlated with annual rainfall. Quantification of these relationships allows irrigation managers to choose irrigation strategies based on desired long-term system efficiency, which differ with climate and irrigation strategy.

Immobilization in Ceramic Waste Forms of the Residues From Treatment of Mixed Wastes

ABSTRACTThe Environmental Restoration and Waste Management Applied Technology Program at LLNL is developing a Mixed Waste Management Facility to demonstrate treatment technologies that provide an alternative to incineration. As part of that program, we are developing final waste forms using ceramic processing methods for the immobilization of the treatment process residues. The ceramic phase assemblages are based on using Synroc D as a starting point and varying the phase assemblage to accommodate the differences in chemistry between the treatment process residues and the defense waste for which Synroc D was developed. Two basic formulations are used, one for low ash residues resulting from treatment of organic materials contaminated with RCRA metals, and one for high ash residues generated from the treatment of plastics and paper products. Treatment process residues are mixed with ceramic precursor materials, dried, calcined, formed into pellets at room temperature, and sintered at 1150 to 1200°C to produce the final waste form. This paper discusses the chemical composition of the waste streams and waste forms, the phase assemblages that serve as hosts for inorganic waste elements, and the changes in waste form characteristics as a function of variation in process parameters.