[en] Fluor Hanford (FH) is designing and assessing the performance of engineered barriers for final closure of 200-UW-1 waste sites. Engineered barriers must minimize the intrusion of water, plants and animals into the underlying waste to provide protection for human health and the environment. The Pacific Northwest National Laboratory PNNL developed Subsurface Transport Over Multiple Phases (STOMP) simulator is being used to optimize the performance of candidate barriers. Simulating barrier performance involves computation of mass and energy transfer within a soil-atmosphere-vegetation continuum and requires a variety of input parameters, some of which are more readily available than others. Required input includes parameter values for the geotechnical, physical, hydraulic, and thermal properties of the materials comprising the barrier and the structural fill on which it will be constructed as well as parameters to allow simulation of plant effects. This report provides a data package of the required parameters as well as the technical basis, rationale and methodology used to obtain the parameter values

[en] Clastic dikes are subvertical sedimentary features that cut through horizontally layered sediments, and they are common at the Hanford Site. Because of their cross-cutting relationship with the surrounding matrix, they have been proposed as potential fast paths from former contaminant discharge sites at the surface to the water table. However, little was known of the detailed hydrogeologic properties of the dikes and detailed modeling of flow and transport through the dikes had not been performed. We excavated a 2 m wide clastic dike at the Hanford Site and characterized it using an air minipermeameter, infrared imagery, and grain size analyses. Field injection experiments were also used to characterize the system. The resulting data were used to prepare a detailed numerical model of the clastic dike and surrounding matrix for a portion of the excavation. Unsaturated flow and transport through the system were modeled for several recharge rates. The highly heterogeneous nature of the system led to complex behavior, with the relative flux rates in the matrix and clastic dike being highly dependent on the recharge rates that were imposed on the system. The study suggests that the potential role of clastic dikes in vertical transport at the Hanford Site would depend on the leakage rate, and that areas of contaminant deposition formed at high flow rates might become isolated at low flow rates, and vice-versa. The results may also help explain the occurrence of complex breakthrough patterns of contaminants at the water table

[en] Nuclear wastes are by-products of nuclear weapons production and nuclear power generation, plus residuals of radioactive materials used by industry, medicine, agriculture, and academia. Their distinctive nature and potential hazard make nuclear wastes not only the most dangerous waste ever created by mankind, but also one of the most controversial and regulated with respect to disposal. Nuclear waste issues, related to uncertainties in geologic disposal and long-term protection, combined with potential misuse by terrorist groups, have created uneasiness and fear in the general public and remain stumbling blocks for further development of a nuclear industry in a world that may soon be facing a global energy crisis

[en] The BC Cribs and Trenches, part of the 200 TW 1 OU waste sites, received about 30 Mgal of scavenged tank waste, with possibly the largest inventory of 99Tc ever disposed to the soil at Hanford and site remediation is being accelerated. The purpose of this work was to develop a conceptual model for contaminant fate and transport at the 216-B-26 Trench site to support identification and development and evaluation of remediation alternatives. Large concentrations of 99Tc high above the water table implicated stratigraphy in the control of the downward migration. The current conceptual model accounts for small-scale stratigraphy; site-specific changes soil properties; tilted layers; and lateral spreading. It assumes the layers are spatially continuous causing water and solutes to move laterally across the boundary if conditions permit. Water influx at the surface is assumed to be steady. Model parameters were generated with pedotransfer functions; these were coupled high resolution neutron moisture logs that provided information on the underlying heterogeneity on a scale of 3 inches. Two approaches were used to evaluate the impact of remedial options on transport. In the first, a 1-D convolution solution to the convective-dispersive equation was used, assuming steady flow. This model was used to predict future movement of the existing plume using the mean and depth dependent moisture content. In the second approach, the STOMP model was used to first predict the current plume distribution followed by its future migration. Redistribution of the 99Tc plume was simulated for the no-action alternative and on-site capping. Hypothetical caps limiting recharge to 1.0, 0.5, and 0.1 mm yr-1 were considered and assumed not to degrade in the long term. Results show that arrival time of the MCLs, the peak arrival time, and the arrival time of the center of mass increased with decreasing recharge rate. The 1-D convolution model is easy to apply and can easily accommodate initial contaminant inventory and water content depth distributions of any complexity. However, the results are somewhat conservative in that the model does not take credit for stratification and its dimensionality effects. Transient analysis shows transport to be controlled by small-scale stratification that resulted in laterally movement of contaminants and their failure to reach the ground water. Multiple discharges quickly merged into a single plume that migrated beyond the domain boundaries. However, it appears that this very feature that was effective in mitigating deep transport of the contaminants for almost 50 years now functions to confound expected barrier effects. Simulations suggest that a barrier provides no additional protection above the no-action alternative. Although continuous layers are assumed, in reality, there may be discontinuities that could lead to vertical movement. Episodic recharge events could also be conducive to downward movement. As more data becomes available, the conceptual model will be revised. Based on the analyses, capping appears to be no better than the no-action alternative. Projected 99Tc concentrations reaching the groundwater suggest that alternate source control actions may be necessary to reach soil screening levels. The benefits of active remediation are therefore readily apparent. Because none of the alternatives reduce soil concentrations, they effect no active reduction in the groundwater concentrations therefore the residual risk will remain high

[en] The Department of Energy (DOE) Carlsbad Field Office (CBFO) is required by Title 40 CFR Part 191.14(c) and Title 40 CFR Part 194.43 to develop a Passive Institutional Controls (PICs) program to prevent the likelihood for future human intrusion into the Waste Isolation Pilot Plant (WIPP). The purpose of this paper is to explore how the exploitation of resources under nuclear waste repositories as a part of PICs could reduce the risk of future human intrusion. The WIPP, located in the northern Permian Basin near Carlsbad, New Mexico, is a geologic repository for the permanent isolation of defense-related transuranic waste. In 1995, a series of geophysical surveys by the New Mexico Bureau of Mines and Mineral Resources estimated the total hydrocarbon reserves underneath the WIPP, which included a 16-section area plus a one mile buffer. Since that time the Delaware Basin well database has been maintained to closely monitor hydrocarbon extraction activities. The database was used in compiling relevant oil and gas extraction data retrieved from The New Mexico Oil Conservation Division. The volume of hydrocarbons extracted from 1995 to the present suggests that if current extraction growth trends continue (as historic market and production data indicate they will), all known crude oil reserves under the WIPP, obtainable through current extraction technology, will be depleted within approximately 10 years, i.e., by 2026. This is well before the anticipated WIPP closure and start of the Active Institutional Controls (AICs) program called for in 40 CFR Part 194.41(b). In addition, gas resources, although more difficult to forecast, are not expected to last beyond 2137. Title 40 CFR 194.33 states, 'Inadvertent and intermittent intrusion by drilling for resources... is the most severe human intrusion scenario'. This human intrusion scenario is the feature, event, and process (FEP) that performance assessment (PA) has identified as having the most significant impact on radionuclide releases during the 10,000 year regulatory period for the WIPP. Title 40 CFR 194.43 requires a PICs program which contains '... [records] in the international archives that would likely be consulted by individuals in search of unexploited resources'. Due to political, social, and economic motivators for resource exploration and exploitation, the potential future absence of hydrocarbon resources under the WIPP is important in deterring possible human intrusion. To minimize the risk of future human intrusion, it may be necessary to consider actively removing as many of the exploitable hydrocarbon resources under and around a nuclear waste repository as is practicable before the end of the period of AICs (i.e., 100 years after closure of the repository). Additionally, communicating the absence of hydrocarbon resources under a nuclear repository should take a prominent role in any PICs program. Due to its high-cost nature, exploratory drilling of any kind currently involves cost/benefit analysis. If in the future the economic realities of resource exploration remain similar to today, and future oil companies know the resources for a particular area have already been heavily exploited, hypothetically, they would become less motivated to drill in that area. They would instead opt to explore an area with better prospects. It is important then that the remaining hydrocarbon reserves be clearly stated and prominently displayed. In essence we should communicate the message, loud and clear, 'There is nothing here for you'. (authors)