Importance of rock matrix entry pressure on DNAPL migration in fractured geologic materials

The capillary pressure versus saturation relationship for various carbonate rocks exhibits a wide range of entry pressures depending on the deposition al and diagenetic environment of the rock. The results of a numerical study are presented that focus on the effect of the DNAPL entry pressure of the porous rock matrix on the migration of DNAPL within the fracture network of carbonate rocks. Representative numerical experiments involving the releas e of DNAPL into a single vertical fracture terminating within a porous carb onate rock that was assigned a variety of measured capillary pressure versu s saturation relationships showed that the volume of DNAPL that entered the rock matrix increased dramatically as the entry pressure of the rock matri x decreased. Simulations of a DNAPL-contaminated site located on fractured carbonate bedrock in southern Ontario are also presented which highlight th e sensitivity of the extent of the zone of DNAPL contamination within the b edrock to the capillary pressure curves assigned to the rock matrix. One sc enario presented demonstrates that the penetration depth and horizontal ext ent of the zone of DNAPL contamination within the bedrock can be large if t he carbonate rock has a high entry pressure, because much of the DNAPL Bow is restricted to the fracture network. Another case involving a lower entry pressure for the rock matrix produced a smaller zone of DNAPL contaminatio n, but the bulk of the DNAPL was contained in the rock matrix. The results for both cases suggest that attempts at DNAPL-zone restoration in fractured rock using technologies that are available today would be problematic.