HETEROGENEOUS FLOW AND TRANSPORT MODEL FOR THE SUBSURFACE NEGEV DESERT, ISRAEL

The disposal of long-term nuclear waste remains a challenge for many countries where isolation, safe storage and security concerns are paramount. The adverse effects of radiation from waste can create unique issues for long-term isolation. Strategies for disposing of nuclear waste have been explored, including but not limited to placing the waste in caverns, boreholes and mined facilities. All of these strategies are solutions that rely on subsurface geologic settings. In addition to a geology with well characterized properties, this requires low infiltration and groundwater flow rates and a realistic model for predicting the effects of future climate scenarios on waste migration.

In this US-Israeli collaborative study, the subsurface of the Negev Desert is being evaluated as a potential vadose zone site for nuclear waste disposal. The region consists of alluvial plain sediments with low yearly precipitation, high evaporation conditions, underlain by layered shallow marine sediments. Combined with little or no surface infiltration and a site location away from large population centers, the Negev desert subsurface may represent a suitable nuclear waste disposal site.

Having constructed the first 3D computational mesh of the NE Negev subsurface, the effects of a layered stratigraphy on plume migration subjected to different infiltration scenarios are simulated using a flow and transport model of radioactive contaminant migration. Because subsurface properties cannot be described deterministically due to spatial variations, we use a variety of geostatistical methods to account for variations within the model, including sampling based on correlation lengths and Monte Carlo simulations. Additionally, we use past climate data and infiltration models to test scenarios that include wet and dry periods that represent future climate changes. In this way we hope to characterize the response of the NE Negev desert subsurface to low, medium, and high infiltration rates, and cyclic ponding events. Our preliminary results show that increased infiltration from wetter climates has the potential to modify the hydrologic setting (saturations and groundwater velocities) at a hypothetical disposal site that could influence radionuclide plume migration.