MEASURING MASS DEPLETION BY DISSOLUTION OF ENTRAPPED NONAQUEOUS-PHASE LIQUIDS IN FRACTURED MEDIA WITH X-RAYS
1Joseph J. McGahee and 2Tissa Illangasekare
1Colorado School of Mines, 1012 14th Street, Golden, CO 80401; 1Phone: (303) 384-2237, 1E-mail: ; 2AMAX Professor, Division of Environmental Science and Engineering, Colorado School of Mines, 1012 14th Street, Golden, CO 80401; 2Phone: (303) 384-212, 2E-mail: .
Nonaqueous-phase liquids (NAPLs) pose a potential risk to humans when released into the environment. Once a NAPL is released into the environment, it could have the ability to contaminate the groundwater and nearby bodies of water. With this in mind, the dissolution of NAPLs needs to be better understood in order to adequately predict the impact of these contaminants in the subsurface, as well as for determining the best remediation process for removing the NAPL.
The ability to detect spatial differences and to monitor changes in the various phases within a porous medium is vital to enhancing the information extracted from multi-phase flow and transport experiments. Radiation attenuation techniques have been productively used in multi-phase research at Colorado School of Mines and elsewhere with the use of radioisotopes (gamma rays). X-ray generators can theoretically offer advantages as a radiation source in the nondestructive measurement of phase fractions in porous media as compared with radioisotopes emitting photons of similar energy. This is true because x-ray generators can produce a photon flux two to three orders of magnitude greater than radioisotopes, thus allowing the time necessary to take a measurement to be reduced. Also, photon energies can be optimized to yield the best measurement precision for a given experiment by choosing the voltage setting on the x-ray generator and by filtering the emitted radiation spectrum with filters. X-ray generators have been shown to have enough flexibility in photon-energy settings to allow accurate and precise measurements, and sufficient photon flux and detector throughput to perform these measurements in short durations.
Currently, gamma rays are being used in the laboratory at Colorado School of Mines to measure the location and dissolution of NAPLs in porous media. With the use of x-rays, better resolution and accuracy will be obtained in measurements compared to the use of gamma rays. Once the x-ray generator is assembled, experiments will be performed to measure the dissolution of NAPLs in fractured media, as well as various other experiments. This x-ray system will also be used in conjunction with the gamma system in order to better understand and determine the behavior of NAPLs in porous media.