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Abstract

Pump-and-treat, withdrawing contaminants from aquifers through wells to a ground treatment system for removal of contaminants, is today the most commonly-used technology to remediate groundwater pollution. Unfortunately, pump-and-treat does not always work effectively because some contaminants stick to soils or rocks due to capillary effect such that they cannot thus be easily removed.

Over the past years, a number of researches have been successfully conducted to demonstrate that seismic wave stimulation is emerging as a new technology to mobilize the movement of LNAPL (Light Non-Aqueous Phase Liquid) and DNAPL (Dense Non-Aqueous Phase Liquid) contaminants. In the current study, a series of experiments were carried out to investigate the effect of seismic wave stimulation on fluid flow rate enhancement in both saturated and unsaturated sands.

There are two drainage processes which were conducted, the multi-step and continuous drainage ones. In the multi-step drainage process, the height of the outflow tube is lowered at three different stages. The first stage of the multi-step drainage process tends to generate a higher increase in fluid flow rate induced by seismic wave stimulation even though the height of the outflow was lowered with the same value (-30 cm) at the second and third stages. The cumulative water outflow is able to be increased up to 14% during the first stage of the multi-step drainage process with seismic wave stimulation than that without seismic wave stimulation. This is because water head is different at every stage due to capillary pressure.

Seismic wave stimulation also causes obvious increases in water saturations over time (∂S/∂t) in the continuous drainage process. The water retention curve obtained with seismic wave stimulation moves upward as compared to that obtained without seismic wave stimulation. The upward shift of water retention curve due to seismic wave stimulation is clearly in line with the increase in cumulative water outflows.

Based on those results, it has shown that seismic wave stimulation is able to serve as an excitation source for providing consistent and controllable periodic stress-pulsing for enhancing fluid flows in a porous medium.

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