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...

Carbon tetrachloride (CT) was discharged to waste sites that are included in the 200-PW-1 Operable Unit in Hanford 200 West Area. Fluor Hanford, Inc. is conducting a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) remedial investigation/feasibility study (RI/FS) for the 200-PW-1 Operable Unit. The RI/FS process and remedial investigations for the 200-PW-1, 200-PW-3, and 200-PW-6 Operable Units are described in the Plutonium/Organic-Rich Process Condensate/Process Waste Groups Operable Unit RI/FS Work Plan. As part of this overall effort, Pacific Northwest National Laboratory (PNNL) was contracted to improve the STOMP simulator (White and Oostrom, 2006) by incorporating kinetic volatilization of nonaqueous phase liquids (NAPL) and multicomponent flow and transport. This work supports the U.S. Department of Energy's (DOE's) efforts to characterize the nature and distribution of CT in the 200 West Area and subsequently select an appropriate final remedy.Previous numerical simulation results with the STOMP simulator have overestimated the effect of soil vapor extraction (SVE) on subsurface CT, showing rapid removal of considerably more CT than has actually been recovered so far. These previous multiphase simulations modeled CT mass transfer between phases based on equilibrium partitioning. Equilibrium volatilization can overestimate volatilization because mass transfer limitations present in the field are not considered. Previous simulations were also conducted by modeling the NAPL as a single component, CT. In reality, however, the NAPL mixture disposed of at the Hanford site contained several non-volatile and nearly insoluble organic components, resulting in time-variant fluid properties as the CT component volatilized or dissolved over time. Simulation of CT removal from a DNAPL mixture using single-component DNAPL properties typically leads to an overestimation of CT removal. Other possible reasons for the discrepancy between observed and simulated CT mass removal during SVE are differences between the actual and simulated 1) SVE flow rates, 2) fluid-media properties, and 3) disposal history (volumes, rates, and timing).In this report, numerical implementation of kinetic volatilization and multicomponent DNAPL flow and transport into the STOMP simulator (White and Oostrom, 2006) is described. The results of several test cases are presented and explained. The addition of these two major code enhancements increases the ability of the STOMP simulator to model complex subsurface flow and transport processes involving CT at the Hanford site.v