Download Key words: fracture, x-rays, dissolution, NAPL, radioisotopes

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MEASURING MASS DEPLETION BY DISSOLUTION OF ENTRAPPED
NONAQUEOUS-PHASE LIQUIDS IN FRACTURED MEDIA WITH X-RAYS
1
Joseph J. McGahee and 2Tissa Illangasekare
1
Colorado School of Mines, 1012 14th Street, Golden, CO 80401; 1Phone: (303) 384-2237,
1
E-mail: jmcgahee@mines.edu; 2AMAX Professor, Division of Environmental Science and
Engineering, Colorado School of Mines, 1012 14th Street, Golden, CO 80401; 2Phone:
(303) 384-212, 2E-mail: tillanga@mines.edu.
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.
Key words: fracture, x-rays, dissolution, NAPL, radioisotopes