Torres Negrón, Alexander

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    Vapor phase transport of explosive related compounds through unsaturated sandy soils
    (2008-08) Torres Negrón, Alexander; Padilla Cestero, Ingrid Y.; College of Engineering; Camacho, Beatriz I.; Harmsen, Eric; Department of Civil Engineering; Torres, Ramón
    Chemical detection of buried explosives devices through chemical sensing is influenced by factors affecting the transport of chemical components associated with the devices. Explosive-related chemicals (ERCs), such as 2,4-Dinitrotoluene (DNT) and 2,4,6-Trinitrotoluene (TNT), are somewhat volatile and their overall transport is influenced by vapor-phase diffusion. Gaseous diffusion depends on environmental and soil conditions. The significance of this mechanism is greater for unsaturated soil, and increases as water content decreases. Other mechanisms, such as sorption, which affect the overall fate and transport, may be more significant under diffusion transport due to the higher residence time of ERCs in the soil system. Vapor transport in soil of DNT and TNT was analyzed using one-dimensional physical model (1-D column). Experiments were conducted at different soil water contents and temperatures. Variation of the vapor phase concentrations were analyzed spatially and temporally. Vapor samples were obtained from the columns using Solid Phase Microextraction (SPME) and analyzed using Gas Chromatography. In addition, soil samples were extracted and analyzed using High Performance Liquid Chromatography. Measured data was modeled using the HYDRUS 1-D code, in order to determine the most important transport parameters affecting the vapor transport. Results suggest that DNT and TNT overall vapor transport is influenced by diffusive and retention processes, water content, source characteristics, and temperature. Vapor concentrations of DNT and TNT at a given temperature tend to increase with increasing water contents at very dry conditions (θw < 8%), reach a maximum value, and decrease with further increase in water contents at the higher water content regime. Higher temperatures induced higher vapor concentrations, principally, due to increments of the explosive source volatilization. Vapor sorption was more dominant at low water contents (< 1%) and decreases several orders of magnitude (3) with increments in water contents. This sorption process was rate-limited. Vapor fluxes were higher near the explosive source than further away. Results suggest that the main parameter affecting the vapor transport is the soil water content and temperature.