Contaminants in the vadose zone may be a long-term source of groundwater contamination and need to be considered in remedy evaluations. In many cases, remediation decisions for the vadose zone will need to be made all or in part based on projected impacts to groundwater. There are significant natural attenuation processes inherent in vadose zone contaminant transport. Attenuation processes include both hydrobiogeochemical processes that serve to retain contaminants within porous media and physical processes that slow the vertical rate of movement for disposed water and waste solutions. In particular, the physical processes controlling fluid flow in the vadose zone are quite different and generally have a more significant attenuation impact on contaminant transport relative to those within the groundwater system. A remedy evaluation framework is presented herein that uses an adaptation of the established EPA Monitored Natural Attenuation evaluation approach integrated into an approach based on a conceptual model focused on identifying and quantifying features and processes that control contaminant flux through the vadose zone. This report presents a framework to support evaluation of contaminant fate and transport in the vadose zone and bridges this analysis to refinement of the site conceptual model, assessment of risk, and support for baseline risk assessment and remedy selection.v

No abstract

Soil flushing was included in the Deep Vadose Zone Treatability Test Plan for the Hanford CentralPlateau (DOE-RL 2008 1 ) as a technology with the potential to remove contaminants from the vadose zone. Soil flushing operates through the addition of water, and if necessary an appropriate mobilizing agent, to mobilize contaminants and flush them from the vadose zone and into the groundwater where they are subsequently captured by a pump-and-treat system. There are uncertainties associated with applying soil flushing technology to contaminants in the deep vadose zone at the Hanford Central Plateau. The modeling and laboratory efforts reported herein are intended to provide a quantitative assessment of factors that impact water infiltration and contaminant flushing through the vadose zone and into the underlying groundwater. Once in the groundwater, capture of the contaminants would be necessary, but this aspect of implementing soil flushing was not evaluated in this effort. Soil flushing was evaluated primarily with respect to applications for technetium and uranium contaminants in the deep vadose zone of the Hanford Central Plateau. SummarySoil flushing operates through addition of water, and if necessary an appropriate mobilizing agent, to mobilize contaminants and flush them from the vadose zone and into the groundwater where they are subsequently captured by a pump-and-treat system. As described in the Deep Vadose Zone Treatability Test Plan for the Hanford Central Plateau (DOE-RL 2008), investigation of these vadose zone processes through modeling and laboratory evaluation is needed as a first step in providing information for considering soil flushing in subsequent feasibility studies for the Hanford Site deep vadose zone.Numerical modeling and laboratory flow-cell experiments were conducted to investigate the characteristics of water flow and solute transport through the vadose zone as a function of the imposed infiltration condition, subsurface properties, and properties of the leaching solution. Information on previous uranium leaching studies, infiltration studies at the Hanford Site data, and relevant uranium mining operations were compiled and evaluated with respect to how these approaches potentially apply to soil flushing in the Hanford Central Plateau.There are uncertainties associated with applying soil flushing technology to contaminants in the deep vadose zone at the Hanford Central Plateau. Modeling and laboratory efforts reported herein are intended to provide a quantitative assessment of factors that impact water infiltration and contaminant flushing through the vadose zone and into the underlying groundwater. Once in the groundwater, capture of the contaminants would be necessary, but this aspect of implementing soil flushing was not evaluated in this effort. Soil flushing was evaluated primarily with respect to applications for technetium and uranium contaminants in the deep vadose zone of the Hanford Central Plateau.Contaminants such as technetium do not interact significantly...

No abstract

No abstract