Infiltration and Redistribution of Perchloroethylene in Stratified Water‐Saturated Porous Media

Abstract

Although infiltration, redistribution, and drainage of dense nonaqueous‐phase liquids (DNAPLs) in water‐saturated soils and aquifers are known to be sensitive to stratifications of the solid phases of the porous media, little experimental evidence is available to explain the behavior of DNAPL movement. To improve our understanding of DNAPL movement under these conditions, physical simulations were conducted with various perchloroethylene (PCE) spills in initially water‐saturated, stratified porous media in nominally one‐dimensional glass columns and in an intermediate scale, nominally two‐dimensional laboratory flow container. The columns and flow container were packed with two distinct layers of coarse sand, with a fine sand layer in between. Volumetric water and DNAPL contents, as well as bulk densities, were determined with a dual‐energy gamma radiation system. To obtain additional information required for the explanation of the displacement processes, in‐ and outflow rates of water and PCE were measured during each experiment. In the sand columns, PCE accumulated on top of the fine layer, while in the flow container, considerable lateral movement was observed just above the fine sand layer. In general, these phenomena were attributed to the small conductivity values of the fine layers relative to those of the coarse layers rather than to displacement pressures not being exceeded. Overall our results suggest that in field situations, continuous PCE spills are more likely to penetrate horizontal fine layers than short intermittent spills.

Two-dimensional DNAPL migration affected by groundwater flow in unconfined aquifer

“…Although experimental studies of DNAPLs are few, some research has been conducted in the 1990s. One-dimensional column tests for the measurement of DNAPL migration characteristics [13,14], two-dimensional tank tests for measuring NAPL migration in a heterogeneous ground system [15,16], tank modeling tests for DNAPL remediation by using a surfactant or a co-solvent [17][18][19], and the entrapment mechanism of DNAPL in porous media [20,21] were reported for the site characterization and remediation of DNAPL contamination sites. The concept of passive remediation is receiving much attention, because complete remediation to reach an environmental standard is considered to be uneconomical and technically difficult [22,23].…”

A review of non-invasive imaging methods and applications in contaminant hydrogeology research

“…The DNAPL and water saturation were then determined from γ-radiation imaging after no further migration of the injected DNAPL was apparent. In one case (Hofstee et al, 1998b), the system was water-saturated, in all others the fine-grained material and most of the coarse-grained material were unsaturated. Also in one case (Oostrom and Lenhard, 2003), the fine-grained material was caliche; in all others it was fine sand.…”

“…More complex experiments in heterogeneous systems with DNAPLs were reported by Hofstee et al (1998a,b), Oostrom and Lenhard (2003), and Oostrom et al (2003). In each of these four studies, DNAPL was released from a point source and allowed to infiltrate into a two-dimensional flow cell packed with a layer of fine-grained material surrounded by coarser grained material.…”

“…Also in one case (Oostrom and Lenhard, 2003), the fine-grained material was caliche; in all others it was fine sand. In two cases (Hofstee et al, 1998a,b), PCE was the DNAPL, while in the other two it was carbon tetrachloride (CT). A significant advancement in imaging for flow cells was the development of an automated track system that quickly moved the γ-radiation scanner to a desired location.…”

“…This allowed the same locations to be imaged at different imaging times, or many locations to be imaged at one imaging time. For example, more than 1,300 locations (1×1 cm 2 ) were imaged in a flow cell at one imaging time by Hofstee et al (1998b).…”