INFLUENCE OF EMBEDDED FRACTURES ON CONTAMINANT DIFFUSION IN GEOLOGICAL FORMATIONS

Crystalline rock formations are prime candidates for siting of reposit ories for radioactive and toxic wastes. Even the possibility of tenuou s proximity of these sites to the biosphere requires realistic means o f predicting subtle features of contaminant migration, such as very lo w-level seepage. We generate percolation clusters to reproduce the oft en observed ramified embedded fracture structures in these formations. Diffusion paths through these clusters and the shortest spans of rock between them can so significantly decrease contaminant breakthrough t imes that previous estimates can be in error by up to an order of magn itude. Our analysis suggests that current methods for determining the suitability of geological formations as natural barriers to contaminat ion are inadequate, and may result in dangerously misleading conclusio ns.