Factors Controlling DNAPL Migration in a Fracture Network: Experiments and Simulations

Groundwater contamination by dense nonaqueous phase liquids (DNAPLs) has received considerable attention in recent years, and the attention on characterizing and quantifying the migration of DNAPL in geological formations has been given to the migration of DNAPL in porous media, not much in fractured rock. The spilled DNAPL that is heavier than water migrates downward to fractured bedrocks under the influence of gravity and is a long-term contaminant source. Although the progress has been accomplished on the development of algorithms for the numerical solution of the macroscopic models of contaminant transport in rock fractures, a lack of fundamental understanding exists concerning the interactive effects of the structural characteristics of fractures and fluid rheology on the patterns of DNAPL migration in a fracture network. In particular, little experimental work has been done on DNAPL migration in a fracture network. The two-dimensional fracture network was built up. Water was applied to both sides of a fracture network to have intended hydraulic head, and TCE was injected into one of vertical fractures. TCE migration process was recorded with digital camcorder. The dynamic macro-modified invasion percolation (DMMIP) model is suggested by integrating groundwater flow factor with MMIP that reflects the capillary effect, gravity-destabilization condition and viscous force of DNAPL. The information gained from experiments was analyzed and used for testing the DMMIP model to characterize the DNAPL migration pathway in a fracture network. DMMIP simulations and laboratory experiments show a good agreement. The results of DMMIP simulations and laboratory experiments show that in addition to gravity force, water viscous force considerably affects migration of DNAPL in rock fractures. This study will provide a step-stone for further developing reliable numerical simulators of the DNAPL migration in a fracture network that are required for the implementation of rational and cost-effective risk assessment procedures to DNAPL-contaminated rock fractures.