Traditional methods for monitoring sites that may be contaminated with toxic chemicals can be expensive, time consuming, and misrepresentative of in-situ conditions. A novel microsensor system has been developed that can be used to monitor and characterize volatile organic contaminants in the subsurface. This system has been employed in a number of laboratory experiments in this study to evaluate diffusion of volatiles in porous media. The transient diffusion of water vapor and iso-octane vapor was monitored by the sensors in one-dimensional column experiments in air and in sand. Calibration data were used to convert sensor responses to vapor concentration, and results were plotted as a normalized concentration versus time to generate standard breakthrough curves. These were compared to theoretical predictions that were derived from the diffusion equation, with appropriate boundary conditions and parameters taken from the experimental conditions. A comparison of the experimental and theoretical results produced estimates of diffusion coefficients that were close to values reported in the literature. The results also provided an increased understanding of the behavior of the microsensors in porous media.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.