Engineering topics

Truex, Michael

Publications and source records attributed to Truex, Michael.

6 records

DOE OSTI2020

Evaluating Remediation Options for a Perched-Water Unit at the Hanford Site - 20378

At the U.S. Department of Energy's Hanford Site, liquid-phase waste was discharged using surface disposal features such as ponds, trenches, and cribs. These practices distributed contaminants in the subsurface, some of which are currently in the vadose zone above the groundwater. At the 200-DV-1 operable unit (OU) at the Hanford Site, a key feature is a perched-water zone. This perched-water zone contains several million liters of water contaminated with high concentrations of uranium, technetium-99 (Tc-99), and nitrate that serves as a continuing source of contamination to the underlying aquifer. Currently, a pumping system is used to remove contaminant mass from the perched-water zone. However, water extraction will become more challenging as the perched unit dewaters. As a result, residual contaminants remaining after pumping is no longer effective needs to be addressed with post-extraction mitigation approaches, appropriate monitoring, and selection of suitable remediation endpoints. Thus, a remedy evaluation needs to include the unique conditions of this perched-water zone. As part of the initial evaluation, a set of technologies have been preliminarily identified as potentially applicable to the perched-water zone, including in situ remediation technologies to sequester uranium and Tc-99 and to degrade nitrate. While there is sufficient information available for direct consideration of some of the reviewed technologies in a feasibility study, five in situ remediation technologies were identified as needing additional information on their effectiveness under the geochemical and contaminant conditions of the perched-water zone. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Field Test Bed for Vadose-Zone Monitoring Approaches - 20404

In the Central Plateau at the U.S. Department of Energy Hanford Site, a large inventory of contaminants resides in unsaturated sediments within the approximately 100-meter-thick vadose zone, posing a potential continuing risk to groundwater. Vadose zone remedies used to address these contaminants will require performance monitoring to provide feedback during implementation and for long-term verification that remedial action objectives have been met. Passive approaches may also need long-term monitoring to demonstrate that the flux of contaminants from the vadose zone to the groundwater are below thresholds established to meet groundwater protection goals. Collection of physical (e.g., groundwater or sediment) samples is a common method for identifying contaminant concentration distributions, but this approach is limited by the number of locations and the frequency with which data can be collected. In situ vadose zone measurements have evolved over the past few years to include key measurements of water content, soil water pressure, temperature, and chemical concentration. However, the current generation of sensors is designed for relatively short-term use in near-surface soils or sediments. Geophysical methods have been evolving but are also limited in that they have not been designed for the specific long-term vadose zone monitoring needs at the Hanford Site. Overall, monitoring under unsaturated conditions can be difficult due to the need to install and maintain instrumentation over a large area and depth and the need to identify preferential flow pathways due to geologic and chemical heterogeneities over long periods. Thus, a vadose zone monitoring test bed was initiated to address these challenges and identify cost-effective approaches for implementation and postclosure monitoring of the deep vadose zone. The monitoring test bed is expected to provide valuable field-scale information for the design of vadose zone monitoring systems. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Technology Assessment for Radioiodine at the Hanford Site - 20240

An evaluation was conducted to assess the practicability of technologies of sufficient promise and maturity to warrant treatability tests for remediating radioiodine (I-129) in groundwater at the 200-UP-1 operable unit at the U.S. Department of Energy Hanford Site. Technologies were evaluated based on recent updated knowledge of subsurface iodine transport behavior at Hanford, and the effectiveness, implementability, and cost of potential treatment technologies for I-129. Because more than two-thirds of the iodine at Hanford is estimated to be present in its oxidized form as iodate, treatment technologies were evaluated with respect to addressing iodate. In situ treatments were identified as having limited implementability because the plume core is located directly beneath the Environmental Restoration Disposal Facility disposal cells, a landfill used for the disposal of low-level radioactive, hazardous, and mixed wastes generated from Hanford cleanup activities. Further limitations in treatment technologies for radioiodine were due to the isotopic distribution of subsurface iodine. Data indicate that stable iodine (I- 127) concentrations are up to three orders of magnitude greater than I-129, limiting the effectiveness of potential technologies because they are not isotope-specific. Ex situ approaches also lacked the effectiveness and maturity required to treat I-129. Hence, the technology evaluation did not identify any technologies that needed treatability testing, driven by site and contaminant properties that hinder effectiveness and/or implementability of the technologies. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Opportunities for an Integrated Web-Based Workbench for Data Access and Analysis - 20244

Management of environmental issues can require integration of multiple types of data and information, conducting data analysis and interpretation, and providing data visualization for effective communications. These data elements are important for site management to support regulator interactions and provide defensibility for remedial decisions. Databases and information repositories are core elements of managing data; however, efficient data access and analysis also enable effective site management. The U.S. Department of Energy (DOE) Hanford Site is an example of a complex site with a voluminous quantity of environmental data and a need for efficient site management. Different tiers of data and information tools have been developed and deployed to address site needs. These tools are configured for ready access via the web site interfaces and meet the rigorous quality requirements for environmental site management. Evolving efforts are focused on an integrated platform to meet site environmental management needs. In this platform, users can access site information at multiple levels of detail based on their need and permissions, so that data and associated analyses are presented within the context of the site mission and the user's management or technical needs. This concept is not only applicable at individual sites like Hanford but also applicable at other sites within the DOE complex. An integrated web-based architecture that links data visualization, data analytics, and management tools can provide holistic access to large data sets, minimize complexity, and maximize interactivity and technical communication. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

Integrating Electrical Resistivity Tomography with Vadose Zone Characterization - 20246

The environmental management mission at the U.S. Department of Energy Hanford Site includes addressing subsurface contaminants that are present in the vadose zone because of historical waste discharges. Characterization is needed to support evaluation of whether contaminants at specific disposal sites will migrate to and contaminate the groundwater in the future. Drilling of boreholes and analysis of retrieved sediment samples is a standard approach to evaluating contaminant distribution in the vadose zone for the types of inorganic and radionuclide contaminants at the Hanford Site. However, borehole sampling has limitations for understanding the volumetric distribution of contaminants. The Hanford Site is now applying electrical resistivity tomography to characterize the path and volumetric extent of contaminant migration in the vadose zone. This information aids selection of appropriate locations for obtaining borehole samples and provides three-dimensional contaminant distribution information for incorporation into conceptual site models and to help configure fate and transport models. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2020

In-Situ Uranium Source Treatment Performance Assessment Elements - 20247

Field-scale in situ injection of an aqueous polyphosphate amendment was conducted to decrease uranium leaching from a vadose zone source to groundwater near the Columbia River at the U.S. Department of Energy's Hanford Site. After an initial phase of application in November 2015, this treatment was applied as an enhanced attenuation approach in September 2018, targeting uranium in a subsurface zone where water table periodically rises in response to the seasonal high river stage. Uranium within this zone is aqueous, adsorbed, and in low- and high-solubility precipitates and is mobilized into the groundwater at high river stage, resulting in a persistent groundwater plume. The polyphosphate amendment creates phosphate coatings on uranium (potentially including low solubility uranium-phosphate precipitates) that decrease the uranium leached into groundwater when the zone is periodically rewetted to improve the ability of natural attenuation to meet groundwater concentration objectives. For treatment, the amendment was injected into a network of wells within the periodically rewetted source area. Multiple lines of evidence are being applied to evaluate the performance of the phosphate treatment. Three elements of this performance assessment include 1) identifying the distribution of injected phosphate amendment to the targeted treatment zone using cross-borehole electrical resistivity tomography and comparisons of phosphate precipitates between pre- and post-treatment samples, 2) demonstrating the functional reduction in uranium mobility and leachability using laboratory tests with pre- and post- treatment sediments from the source zone, and 3) evaluating the presence of low-solubility uranium phosphate minerals and/or coatings associated with reduced uranium mobility. (authors)

07 ISOTOPE AND RADIATION SOURCES↗