Basic Research Needs for Geosciences - Energetics Meetings and ...

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTinclude the quantification of aleatory and epistemic uncertainty in long-term estimates ofrecharge and discharge.3. Percolation and groundwater flow fieldsThe integrity of the engineered barrier system as well as waste dissolution, release, and transportof radionuclides to the accessible environment depend on the availability, amount, anddistribution of groundwater flow towards, into, and away from the repository. Delineation ofgroundwater flow paths through complex geologic media (i.e., porous and fractured rocks andsediments with complex stratigraphy which potentially contains faults) remains a majorchallenge in subsurface hydrology that strongly affects the predicted performance of a geologicrepository (Berkowitz 2002). Specifically, there is a need for robust methods for detecting andidentifying main flow features. This requires advances in science and technology to enable:1. Site-specific, high-resolution characterization of relevant hydrogeological properties2. Estimation of spatial and temporal distribution of water flow through these features underunsaturated and saturated flow conditions3. Appropriate upscaling, downscaling, and averaging procedures for hydrogeologicparameters, processes, and the resulting flow fieldsIn addition, there is a need to develop alternative models that include non-Darcy flow processes(e.g., film flow, rivulet flow, evaporation/condensation effects, liquid islands, flow acrossfracture intersections, non-equilibrium flows, etc.). Given the inherent difficulty to directlyobserve subsurface flow patterns, approaches need to be developed that estimate flow pathsusing combined hydrological, geochemical, and geophysical data. Finally, the long-term stabilityof identified groundwater flow paths needs to be assessed or predicted in response to geochem–ical and mechanical changes imposed by natural processes or the presence of the repository.4. Near-field effectsThe performance of a geologic repository is critically affected by the mutual impacts of thenatural and engineered systems. The geochemical and hydrological conditions of the naturalsystem affect the integrity of the engineered barriers. Conversely, the engineered barrier systemmay strongly affect natural processes in the near field, specifically through coupled thermalhydrological-chemical-mechanical-biologicalmechanisms. Potential effects include flow fieldalteration, evaporation, condensation, and the development of deliquescent brines, the generationof an excavation-disturbed zone, thermal effects, development of a drift shadow zone, andimpacts of introduced materials on the biogeochemical environment. There is a need to developmodels that describe, predict, and control the transport of fluids, radionuclides, chemicals, andheat across the interface between the natural and engineered systems. In addition, methods areneeded to optimize the repository design such that stable, passive, self-supporting, or self-healingmechanisms are induced at the interface between the natural and engineered barrier systems suchthat they are beneficial to repository performance.5. Radionuclide transportThe accurate prediction of radionuclide release and transport from the repository to theaccessible environment (including transport through and accumulation in the biosphere) is a keyelement of performance assessment calculations. Research is needed to identify the relevantprocesses and related hydrogeochemical properties affecting radionuclide transport (specificallyadvective transport pathways and transport velocity, fracture-matrix interaction, sorptionAppendix 1 • 40Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems