Mobilization of Residual NAPL by Seismic Waves

Project Abstract: Mobilization of Residual NAPL by Seismic Waves Conventional pump-and-treat technologies have proven to be ineffective in cleaning up aquifers that are contaminated by nonaqueous phase liquids (NAPL). One possible approach for enhancing the remediation of NAPL-contaminated aquifers consists of applying seismic waves. Little is known, however, about the mechanism leading to mobilization. We hypothesize that the mobilization of trapped NAPL blobs can be optimized by exploiting capillarity-induced resonance. We will perform experiments that visualize the response of NAPL blobs in porous media to oscillatory flow, which is one component of a seismic wave. Constant background flow in the surrounding aqueous phase will ensure that mobilized blobs are moved into a desired direction and hence simulate the combined action of pump-and-treat and seismic waves. Optical refractive index matching will allow for undisturbed view on the fluids in the flow cells. Illumination with a planar laser sheet and high speed photography will resolve the motion within an excitation cycle. Blobs will be excited (1) at their resonant frequency to enhance process understanding, and (2) in the form of appropriately parameterized frequency sweeps to account for the facts that a blob changes its resonant frequency as it moves through a pore space. A lattice-Boltzmann (LB) model will be developed that is used to guide the design of the experiments and as a simulation test bed. The importance of the formation of small, mobile droplets during excitation of the interfaces will also be measured and evaluated. Correlations for the resonant frequency of trapped blobs and intensities required to mobilize them will be inferred from physical experiments and LB simulations. Our research could improve the efficiency of both groundwater remediation techniques for NAPL contamination and enhanced oil recovery schemes that use seismic waves. We will in general elucidate how oscillatory flows effect the distribution of immiscible fluids in porous media. The proposed research will also help understanding the effects of oscillatory flow on mass transfer (dissolution) between immiscible fluids. Furthermore, NAPL blob resonance could be exploited to monitor the shrinking of a NAPL pool during a groundwater remediation, or even to locate NAPL pools. The project will provide research opportunities for one PhD student. Moreover, the project will enrich K-12 education at Baltimore City Neighborhood Schools. The PhD student will develop a teaching module on groundwater contamination.