Page 338 - gas transport in porous media

CHAPTER 21

GAS TRANSPORT ISSUES IN LANDMINE
DETECTION

JAMES M. PHELAN
Sandia National Laboratories, Albuquerque, NM, 87185, USA

Principles of gas and vapor transport have been applied to evaluate the processes
affecting the chemical signature from buried landmines. Due to the shallow burial
depth of landmines, environmental factors play a significant role in the chemical sig-
natureavailablefortracechemicaldetectionbysensorsoranimals. Figure21.1depicts
the complex interdependencies affecting landmine chemical transport in the soil.
Chemical vapors emanate from a buried landmine by permeation through the case
materials or leakage through seals and seams, and from surface contamination on the
case. Transport through the surrounding soil occurs in the liquid and gas phases by
diffusion and advection. Liquid phase advection is driven by precipitation and evapo-
ration of water from the soil, and gas advection can occur due to barometric pressure
changes. Partitioning among the phases is important for explosive compounds, which
tends to concentrate the explosives on the solid and in the liquid phase. The explosive
compounds are also subject to biodegradation.
Trace chemical detection of buried landmines is a challenging task due to the
extremely low concentrations available for sensing. Understanding the nature of the
trace chemical detection process has matured through evaluation of the individual
landmine-soil-atmosphere processes, and through evaluation of the interdependen-
cies among these individual processes using sophisticated computer simulation tools
(Phelan and Webb, 2002). Computational simulation models articulate the fundamen-
tal processes mathematically to provide a representation of the chemical signature
emissions from the buried landmine, movements through the soil, and vapor release
at the ground surface. Demonstration calculations have shown the dramatic impact
of surface weather conditions on the vapor emanations from soil that are available
for detection by technology or canines. Comparisons of simulation model predic-
tions to laboratory data (Phelan et al., 2000, 2001) provide confidence that the
model represents well the reality of certain situations. Simulations were extended

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C. Ho and S. Webb (eds.), Gas Transport in Porous Media, 339–352.
© 2006 Springer.