Challenge. Perform studies of hydrogeologic characterization and modeling methods in preparation for siting deep geologic repository for radioactive wastes

Solution. In support of NDA’s development of a geosphere characterization program, INTERA has provided expertise and services in a number of technical areas including hydrogeology, hydrogeochemistry, transport of radionuclides, and site investigation techniques. We completed a study to develop an understanding of approaches that can be adopted for evaluating the geological aspects of candidate sites. The study examined the nature and content of geoscientific information available as input to the studies of candidate sites; the various means by which geoscientific information can be presented to non-geoscientific audiences; and the approaches that can be adopted for evaluating and presenting geoscientific information and site investigation issues. INTERA updated a previously conducted review of available instrumentation systems for the monitoring of groundwater pressure, with an emphasis on use in low-permeability environments. This study reviewed and documented issues such as the benefits and constraints of each system; the accuracy and resolution of data collected, commercial availability of each technique, and anticipated design life of the equipment; borehole design requirements associated with each system; and approaches to data transmission and management. We completed a comprehensive study to define the information requirements for developing a hydrogeology site descriptive model, including the interpretation of fluid logging tests to delineate flowing and non-flowing strata or features, the interpretation of borehole fluid density surveys, the interpretation of hydrogeologic tests in fractured and unfractured media to determine hydraulic conductivity and storativity, the development of discrete and spatially varying input parameters (e.g., transmissivity), and the modeling of near- and far-field state variables (e.g., groundwater pressures or heads, groundwater velocities, and travel times) to assess the performance of the geosphere system. INTERA also participated in an evaluation of the long-term stability of materials that can be used as components in sealing systems for investigation boreholes. The review included an assessment of the plans and experience of radioactive waste management programs worldwide, most notably Nagra and SKB/Posiva, as well as on other geoscientific sectors concerned with long-term isolation of resources and/or wastes. In the area of hydrogeochemistry, we have reviewed and evaluated sampling, testing, and modeling techniques for developing the conceptual understanding of undisturbed hydrochemical conditions and how site-specific hydrogeochemistry supports and interacts with the design and the safety case development.