HR: 0800h
AN: H31D-0426    [Abstracts]
TI: Shape of gas flow paths causes power law tailing
AU: * Kawanishi, T
EM: kawanisi@t.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1992 Japan
AU: Sakami, A
EM: ayumu28@nihonkai.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1992 Japan
AU: Hayashi, Y
EM: yohayasi@server.t.kanazawa-u.ac.jp
AF: Kanazawa University, Kakuma-machi, Kanazawa, 920-1992 Japan
AB: In soil and/or groundwater remediation, we often see prolonged tailings: continuous outflow of low concentration pollutants for very long time, and in many cases power low behavior of late-time time-concentration curves. We considered that this kind of tailing can be caused by the shape of the gaseous flow introduced in saturated/unsaturated porous media. When gas is introduced to porous media, like air-sparging or soil vapor extraction, the shape of the gas flow path would be tree-like, or to some extent "fractal." So, there would be a distribution of the distance that a solute would have to travel by diffusion before getting to a gas/water interface, and we might expect that the distribution of this "diffusion distance" would be power-law-like. In order to see if tailing can be caused by this mechanism, simple column experiments were carried out. A column, 64 mm in inner diameter and 240 mm in height, was prepared and was packed with 1mm diameter glass beads. Nitrogen gas containing 5 % CO2 and 5% He was supplied from the bottom of the column, and after the water in the column is approximately saturated with CO2, the sparging gas was changed to pure nitrogen. The CO2 and He concentrations in the effluent gas was monitored and recorded. As the result, we saw tailing: the double-log plots of the concentration vs. time relationship was practically linear, and the absolute value of the slope in the double-log charts were 1.28, 0.95 and 0.83 according to the gas flow rates of 40, 80 and 120 ml/min, respectively. Slope less than 1.00 showed that these tailings cannot be explained by Freundlich-type adsorption behavior. Model analysis showed that this power low time-concentration behavior with the slope of approximately -1.0 can be explained by the power law distribution of diffusion distance \textit{a} with PDF p(\textit{a}) proportional to \textit{a}^{-1}.
DE: 1831 Groundwater quality
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting