KEYWORDS: 3D modeling, Solar radiation models, Solar radiation, Explosives, Sensors, Process control, Diffusion, Visible radiation, Ultraviolet radiation, Data modeling
Chemical, biological, and canine detection of buried explosive devices (BEDs) rely on the presence of explosive related
compounds (ERCs) near the soil-atmospheric surface. ERC distribution near this surface and its relation to the location
of BEDs is controlled by fate and transport processes. Experimental work was conducted in a 3D laboratory-scale
SoilBed system to determine the effect of cyclic rainfall, evaporation, temperature, and solar radiation on on the fate,
transport and detection of ERCs near soil surfaces. Experiments were conducted by burying a TNT/DNT source under
the soil surface, and applying different rainfall and light radiation cycles while monitoring salt tracers and TNT solute
concentrations temporally and spatially within the SoilBed. Transport of non-reactive solutes was highly influenced by
the cyclic variations on water flux, water content, evaporation, and influx concentrations. Concentrations of TNT and
other ERCs were further affected by vapor transport and sorptive and degradation processes.
The existence of explosive related chemicals (ERCs) near the soil-atmospheric and other surfaces depend
on their fate and transport characteristics within the environmental settings. Consequently, detection of
ERC in environmental matrices is influenced by conditions that affect their fate and transport. Experimental
work to study the fate and transport behavior of ERCs relies on proper temporal and spatial sampling
techniques. Because the low vapor pressure of these chemicals and their susceptibility to adsorption and
degradation, vapor concentrations in environmental matrices are very low. Depending on the environmental
conditions, the amount of samples that can be withdrawn for analysis is also limited. It is, therefore,
necessary to develop sampling technologies that can provide quantitative measures of ERC concentrations
in limited sampling environments.
This paper presents experimental work conducted to develop a sampling technique to quantify DNT and
TNT vapor concentrations of low vapor-pressure ERCs in environmental setting having limited sampling
volumes and large sample numbers. Two potential vapor sampling techniques, Solid phase Microextraction
(SPME) and Solid Phase Extraction (SPE), were developed and evaluated. SPME sampling techniques are
excellent to quantify for DNT and TNT at very low concentrations. Its passive sampling capabilities meet
the requirement for low-volume environmental sampling, but measured concentrations may be lagged in
time. SPMEs' requirements for immediate analysis after sampling limit the technique for continuous vapor
sampling.
SPE showed to be a sensitive and reproducible technique to determine vapor concentrations of TNT and
DNT in atmospheric and soil setting having limited sampling volumes and large sample numbers. Smallvolume
(600&mgr;L) air samples provide measurements in the &mgr;gL-1 concentration range using isoamyl acetate
and acetonitrile as the solvents. Small extraction volumes make this technique cost efficient and attractive.
Issues with extraction inefficiencies, however, were observed and are being investigated.
KEYWORDS: Head, Humidity, Visible radiation, Control systems, 3D modeling, Ultraviolet radiation, Temperature metrology, Lamps, Systems modeling, Soil science
This paper presents the development and testing of a three-dimensional laboratory-scale soil tank system for modeling ERC fate and transport under controlled, but variable environmental conditions in partially saturated soil. The system incorporates a rainfall simulator, variable light (visible and UV), temperature and relative humidity components, and a 3D SoilBed capable of simulating several boundary and initial conditions. Experimental work indicate that water and solute transport is highly influenced by interrelated environmental and boundary conditions. The presence of light and higher system temperatures induces greater water drainage and solute fluxes. During infiltration, hydraulic heads increase at faster rates under no light exposure suggesting greater water and solute retention. The spatial and temporal distribution of hydraulic heads during rainfall events is not uniform and flow patterns reflect preferential paths. Transport of conservative solutes closely follows water flow patterns, and reflects the influence of variable and interrelated environmental factors on spatial and temporal concentration distribution. These experiments show that interrelated environmental factors must be taken into account to accurately predict the distribution of chemicals near the soil-atmosphere surface. They demonstrate that non-reactive solutes are highly influenced by variation in hydraulic, advective, and dispersive processes induced by changes in environmental conditions. Greater impacts are expected for reactive and semi-volatile solutes such as ERCs. In such case, fate and transport will also be affected by variations in soptive, gas transport, and degradation processes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.