The Behavior of Dense, Nonaqueous Phase Liquids in Fractured Clay and Rock

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Abstract
This paper examines the behavior of dense, nonaqueous phase liquids (DNAPLs) in fractured clay and rock. The conditions under which a DNAPL will enter an initially water‐saturated, rough‐walled fracture are outlined and expressed in a number of ways, including the height to which a DNAPL pool can accumulate above a fracture prior to initial entry. To study the behavior of DNAPL in a rough‐walled fracture following initial entry, numerical simulations are carried out both in the plane of a fracture using a discrete representation of fracture roughness, and at a larger scale of averaging using an equivalent homogeneous porous media approach. The simulations illustrate that DNAPL will migrate through the larger aperture regions of a fracture plane, and that the DNAPL has the potential to enter progressively smaller aperture fractures with depth as it migrates. Additional numerical simulations indicate that the time taken for a nonaqueous phase liquid to traverse a fractured aquitard is inversely proportional to the fracture aperture, the fracture dip from the horizontal, and the height of the pool collected above the aquitard. It is also demonstrated that upward hydraulic gradients across a fractured aquitard can significantly slow the downward rate of DNAPL migration while downward water gradients enhance the rate of DNAPL migration across the aquitard.