Vapor phase transport of unexploded ordnance compounds through soils

Abstract

Unexploded ordnance (UXO) is a source of concern at several U.S. Department of Defense (DOD) sites. Localization of munitions and fate and transport of the explosive compounds from these munitions are a major issue of concern. A set of laboratory experiments were conducted in specially designed flux chambers to measure the evaporative flux of three explosive compounds (2,4-dinitrotoluene, 2,6-dinitrotoluene, and 1,3-dinitrobenzene) from three different soils. The effect of different soil moisture contents, the relative humidity of air contacting the soil surface, and soil temperature on the chemical fluxes were evaluated. A diffusion model was used to describe the chemical transport mechanism in the soil pore air. The soil-air partition constant was treated as a fit parameter in the model because of the uncertainty in the a priori estimation. The model predicts the qualitative trends of the experimental fluxes satisfactorily. Under extremely dry conditions, the flux decreased more rapidly than that predicted by the model. The fluxes from soils at 24 degrees C were higher than those at 14 degrees C, indicating a larger volatilization driving force at the higher temperature.