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Trichloroethylene Residuals in the Capillary Fringe as Affected by Air-Entry Pressures

Geosciences Dep., Battelle Pacific Northwest Lab., P.O. Box 999, Richland, WA 99352.

^* Corresponding author.

ABSTRACT

Trichloroethylene (TCE) was allowed to drain through columns of soil with the capillary water fringe controlled at various depths. Outflow was measured as well as the TCE content when TCE drainage stopped. Two soils, a sand and a loamy sand, with air-entry values of 23 and 3 cm of water, respectively, were used. The sand with the large air-entry value retained more TCE below the capillary water fringe following TCE drainage than the loamy sand with a smaller air-entry pressure. The TCE below the saturated water fringe in both soils varied from almost 7% on a volume basis to <2%. The majority of the TCE in both soils was shown to resist further drainage when water was passed through the soils, suggesting the TCE phase was mostly fragmented. After 10 pore volumes of water was passed, the residual TCE content was 5.5 and 2.1% for the sand and loamy sand, respectively. Even though TCE has a greater specific gravity than water, it was shown in agreement with capillary theory, that TCE will not necessarily sink through the saturated water fringe to the bottom of an aquifer. Its tendency to do so is inversely proportional to the air-entry pressure of the porous mineral phase. The results bring out several practical points for managing contaminated areas.

Contribution from the Pacific Northwest Lab., Richland, WA 99325.

This research was supported by the Ecological Res. Div., Office of Health and Environ. Res. (OHER), U.S. Dep. of Energy (DOE) under Contract DE-AC06-76RLO 1830 as part of OHER's Subsurface Science Program. The Pacific Northwest Lab. is operated for DOE by Battelle Memorial Inst.

Received for publication March 7, 1988.