Diana H. Bacon

Probabilistic evaluation of shallow groundwater resources at a hypothetical carbon sequestration site

Carbon sequestration in geologic reservoirs is an important approach for mitigating greenhouse gases emissions to the atmosphere. This study first develops an integrated Monte Carlo method for simulating CO2 and brine leakage from carbon sequestration and subsequent geochemical interactions in shallow aquifers. Then, we estimate probability distributions of five risk proxies related to the likelihood and volume of changes in pH, total dissolved solids, and trace concentrations of lead, arsenic, and cadmium for two possible consequence thresholds. The results indicate that shallow groundwater resources may degrade locally around leakage points by reduced pH and increased total dissolved solids (TDS). The volumes of pH and TDS plumes are most sensitive to aquifer porosity, permeability, and CO2 and brine leakage rates. The estimated plume size of pH change is the largest, while that of cadmium is the smallest among the risk proxies. Plume volume distributions of arsenic and lead are similar to those of TDS. The scientific results from this study provide substantial insight for understanding risks of deep fluids leaking into shallow aquifers, determining the area of review, and designing monitoring networks at carbon sequestration sites.

Changes in hydrologic properties of aquifer media due to chemical reactions: A review

Hydrologic properties that govern fluid flow through the subsurface are porosity, permeability, relative permeability, fluid-fluid and fluid-solid interfacial areas, pore and particle size distributions, which may change due to dissolution/precipitation of minerals, fine particle release and capture, ion exchange, and clay swelling. Provided here is a review on the change of hydrologic properties in subsurface media due to chemical processes, and the modeling of such changes. Precipitation and dissolution processes affecting the hydrologic properties, their kinetics and the effect of hydrodynamic factors on such processes are discussed. Precipitation in carbonaceous, siliceous, alkaline and acidic environments, and the role of dissolution and clay swelling in formation damage are reviewed. Changes in properties of unsaturated and fractured media were also discussed. Traditionally, different approaches were used to model various physico-chemical processes and their effect on the hydrologic properties. A detailed review of these methods, including the geochemical equilibrium and kinetic models, chemical divide pathway models, flow and transport models, precipitation/dissolution wave theory, network models, porosity and permeability reduction models, is presented. Recommendations are provided for the assessment of changes in the hydrologic properties of subsurface media attributable to chemical reactions, and modeling flow and transport in their presence. Further, research needs on the changes in hydrologic properties and constitutive relationships among such properties in unsaturated media are identified.

Near-Field Performance Assessment for a Low-Activity Waste Glass Disposal System: Laboratory Testing to Modeling Results

Abstract Reactive chemical transport simulations of glass corrosion and radionuclide release from a low-activity waste (LAW) disposal system were conducted out to times in excess of 20 000 yr with the subsurface transport over reactive multiphases (STORM) code. Time and spatial dependence of glass corrosion rate, secondary phase formation, pH, and radionuclide concentration were evaluated. The results show low release rates overall for the LAW glasses such that performance objectives for the site will be met by a factor of 20 or more. Parameterization of the computer model was accomplished by combining direct laboratory measurements, literature data (principally thermodynamic data), and parameter estimation methods.

Subsurface Transport Over Reactive Multiphases (STORM): A general, coupled, nonisothermal multiphase flow, reactive transport, and porous medium alteration simulator, Version 2 user's guide

The Hanford Site, in southeastern Washington State, has been used extensively to produce nuclear materials for the US strategic defense arsenal by the Department of Energy (DOE) and its predecessors, the US Atomic Energy Commission and the US Energy Research and Development Administration. A large inventory of radioactive and mixed waste has accumulated in 177 buried single- and double shell tanks. Liquid waste recovered from the tanks will be pretreated to separate the low-activity fraction from the high-level and transuranic wastes. Vitrification is the leading option for immobilization of these wastes, expected to produce approximately 550,000 metric tons of Low Activity Waste (LAW) glass. This total tonnage, based on nominal Na{sub 2}O oxide loading of 20% by weight, is destined for disposal in a near-surface facility. Before disposal of the immobilized waste can proceed, the DOE must approve a performance assessment, a document that described the impacts, if any, of the disposal facility on public health and environmental resources. Studies have shown that release rates of radionuclides from the glass waste form by reaction with water determine the impacts of the disposal action more than any other independent parameter. This report describes the latest accomplishments in the development of a computational tool, Subsurface Transport Over Reactive Multiphases (STORM), Version 2, a general, coupled non-isothermal multiphase flow and reactive transport simulator. The underlying mathematics in STORM describe the rate of change of the solute concentrations of pore water in a variably saturated, non-isothermal porous medium, and the alteration of waste forms, packaging materials, backfill, and host rocks.

A Strategy to Assess Performance of Selected Low-Activity Waste Forms in an Integrated Disposal Facility

An overall strategy for evaluating the long-term performance of three waste forms being considered for supplemental treatment of low-activity waste at Hanford is discussed. The same computational framework used to conduct the 2001 ILAW performance assessment will be used for all three waste forms. Cast stone will be modeled with a diffusion-advection transport model and bulk vitrified glass and steam reformed LAW will be modeled with a reactive chemical transport simulator. The recommended laboratory testing to support the supplemental LAW form selection includes single-pass flow-through (SPFT), product consistency (PCT), and vapor hydration tests for glass, SPFT and PCT tests for steam reformed LAW forms, and ANS 16.1 tests for cast stone. These and potentially other laboratory tests for the selected waste form(s) would also be the basis for more detailed studies needed to support a comprehensive long-term performance assessment should one or more of these waste forms be selected for disposal in an integrated disposal facility.

The Sim-SEQ Project: Comparison of Selected Flow Models for the S-3 Site

Sim-SEQ is an international initiative on model comparison for geologic carbon sequestration, with an objective to understand and, if possible, quantify model uncertainties. Model comparison efforts in Sim-SEQ are at present focusing on one specific field test site, hereafter referred to as the Sim-SEQ Study site (or S-3 site). Within Sim-SEQ, different modeling teams are developing conceptual models of

300 Area Treatability Test: Laboratory Development of Polyphosphate Remediation Technology for In Situ Treatment of Uranium Contamination in the Vadose Zone and Capillary Fringe

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Waste Form Release Calculations for the 2005 Integrated Disposal Facility Performance Assessment

CO2 injection at the S-3 site. In this paper, we select five flow models of the S-3 site and provide a qualitative comparison of their attributes and predictions. These models are based on five different simulators or modeling approaches: TOUGH2/EOS7C, STOMP-CO2e, MoReS, TOUGH2-MP/ECO2N, and VESA. In addition to model-to-model comparison, we perform a limited model-to-data comparison, and illustrate how model choices impact model predictions. We conclude the paper by making recommendations for model refinement that are likely to result in less uncertainty in model predictions.