Research - Category III: Water Quality

Application of Acoustic Pressure Waves in Aquifer Remediation and Mobilization of Entrapped Organic Liquids
(Funded 2000-2001)

Principal Investigator: Constantinos V. Chrysikopoulos
Department of Civil & Environmental Engineering
UC Irvine
(949) 824-8661
cchrysik@uci.edu

Executive Summary:
Dense nonaqueous phase liquids (DNAPLs) entrapped in aquifers pose a long term threat to groundwater quality. DNAPLs are only slightly soluble in water and removing them from subsurface formations is not a trivial task. DNAPLs may penetrate the subsurface under density driven flow. Often DNAPLs in the form of ganglia and blobs may encounter small pore throats where the capillary pressure required for further NAPL migration is insufficient. Under these circumstances ganglia become immobile. Remediation of immobile ganglia is a time consuming and costly process that is usually performed by a pump-and-treat technology. Surfactants and/or cosolvents are often used to mobilize residual DNAPL by reducing both the surface tension and capillary pressure. Unfortunately, use of surfactants and cosolvents may lead to further contamination of the subsurface.

The proposed research is focusing on the development of anew and environmentally friendly aquifer remediation technology that seeks to determine if acoustic waves can mobilize trapped DNAPL blobs and ganglia. Acoustic pressure waves in saturated porous media can affect fluid pressure and should the capillary pressure be exceeded, DNAPL mobilization can occur. A unique feature of the proposed remediation technology is that an acoustical transducer can be lowered to any desired aquifer depth down a conventional groundwater well.

To determine the efficacy of acoustic pressure wave enhanced remediation of aquifers contaminated by residual DNAPLs, two sets of experiments will be performed. The first experimental design consists of a water saturated packed column and an hydrophone placed within a water reservoir section of the column. The multi-phase fluid as well as the solid matrix will be subjected to a range of acoustic wave amplitudes and frequencies under various interstitial fluid velocities. The degree of DNAPL dissolution enhancement caused by the acoustic waves will be determined by monitoring the effluent dissolved DNAPL concentrations. The second experimental design involves a two-dimensional tank filled with glass beads. DNAPL mobilization, both in the presence and absence of acoustic pressure waves, will be observed, recorded, and quantitatively analyzed. The pore scale effects of acoustic wave induced DNAPL mobilization will be evaluated and the acoustic wave attenuation as a function of distance from the transducer will be determined. Subsequently, mathematical models describing acoustic wave propagation through porous media saturated with a multi-phase fluids (i.e. water and DNAPL) will be developed.

The results of the proposed research will determine the viability of acoustic wave use in remediating DNAPL contaminated aquifers. Moreover, the data from the experimental investigations will assist in the development of the mathematical models and will add to the current understanding of NAPL mobilization in porous media. If the results of the proposed investigations lead to a promising aquifer remediation technology, more comprehensive experiments will be designed and additional funds will be requested from the National Science Foundation.