The transport of Explosive Related Compounds (ERCs) has been studied as part of a research program aiming to the
development of chemical sensors for detecting landmines. TNT and its degradation products typically make up the
explosive charge in buried mines. The spatial and temporal distribution of concentrations of ERCs depends primarily on
the mobility of the water phase since the main chemicals are transported through the liquid phase of the soil (water). This
work presents an analytical approach to the description of the transport process. The model is based on the conservation
equations applied to the vadose zone and predicts the concentration profiles of water and ERCs as a function of time.
Techniques, such as linearization, variable transformations, and perturbation analysis are used in the development of the
model. Results agree with experiments and numerical simulations previously reported.
As part of a large research program aiming to the development of chemical sensor for detecting landmines, we
have studied the fate and transport of TNT subject to different ambient parameters. The space and temporal
concentration profiles of TNT, and its degradation compounds have been measured using soil tanks. The following
ambient parameters were controlled to emulate environmental factors: water content, temperature, relative humidity,
and UV-VIS radiation. A series of soil tanks were kept under controlled conditions for longer than a year and
sampled periodically at the surface. After several months, all tanks were sampled vertically and disposed of.
Chromatography (GC-&mgr;ECD) with direct injection was used for the analysis of the samples. Of particular interest is
the presence of several degradation compounds, as time evolves, responding to the ambient parameters imposed.
The vertical concentration profiles of the several chemicals found, gives an interesting view of the degradation
process as well as of the transport mechanisms. The results agreed with our computer simulations, and are used to
validate previous numerical analyses.
New analytical methods have been developed and existing methods have been improved for the detection of explosives and their degradation products by increasing their sensitivity and selectivity. Some of the analytical methods available for detection of explosives and degradation products are gas chromatography, mass spectrometry, high performance liquid chromatography, and gas chromatography with mass spectrometry. This work presents the design and development of the experiments for the detection of the spectroscopic signature of TNT buried in sand and its degradation products. These experiments are conducted using a series of soil tanks with controlled environmental conditions such as: temperature, soil moisture content, relative humidity and radiation (UV and VIS). Gas chromatography and solid-liquid extraction with acetonitrile were used for the analysis of explosives. Sampling of tanks was performed in three points on the surface. The results show that TNT and 2,4-DNT are the main explosives that reach the surface of tanks. Temperature and water content play a most important role in the degradation and diffusion of TNT. Finally, the tanks were disassembled and sampling in deep with the objective to obtain a concentration profile. The results demonstrated that the highest concentration was located at 5 cm from surface.
The transport of the chemical signature compounds from buried landmines in a three-dimensional (3D) array has been numerically modeled using the finite-volume technique. Compounds such as trinitrotoluene, dinitrotoluene, and their degradation products, are semi volatile and somewhat soluble in water. Furthermore, they can strongly adsorb to the soil and undergo chemical and biological degradation. Consequently, the spatial and temporal concentration distributions of such chemicals depend on the mobility of the water and gaseous phases, their molecular and mechanical diffusion, adsorption characteristics, soil water content, compaction, and environmental factors. A 3D framework is required since two-dimensional (2D) symmetry may easily fade due to terrain topography: non-flat surfaces, soil heterogeneity, or underground fractures. The spatial and temporal distribution of the chemical-signature-compounds, in an inclined grid has been obtained. The fact that the chemicals may migrate horizontally, giving higher surface concentrations at positions not directly on top of the objects, emphasizes the need for understanding the transport mechanism when a chemical detector is used. Deformation in the concentration contours after rainfall is observed in the inclined surface and is attributed to both: the advective flux, and to the water flux at the surface caused by the slope. The analysis of the displacements in the position of the maximum concentrations at the surface, respect to the actual location of the mine, in an inclined system, is presented.
Detection and removal of antipersonnel and antitank landmines is a great challenge and a worldwide enviromental and humanitarian problem. Sensors tuned on the spectroscopic signature of the chemicals released from mines are a potential solution. Enviromental factors (temperature, relative humidity, rainfall precipitation, wind, sun irradiation, pressure, etc.) as well as soil characteristics (water content, compaction, porosity, chemical composition, particle size distribution, topography, vegetation, etc), have a direct impact on the fate and transport of the chemicals released from landmines. Chemicals such as TNT, DNT and their degradation products, are semi-volatile, and somewhat soluble in water. Also, they may adsorb strongly to soil particles, and are susceptible to degradation by microorganisms, light, or chemical agents. Here we show an experimental procedure to quantify the effect of the above variables on the spectroscopic signature. A number of soil tanks under controlled conditions are used to study the effect of temperature, water content, relative humidity and light radiation.