HR: 1340h
AN: H33A-0451    [Abstracts]
TI: Estimation of NAPL/Water Interfacial Areas in Well-Characterized Porous Media
AU: Dobson, R
EM: richard.dobson@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, ZH CH-8952 Switzerland
AU: * Schroth, M H
EM: martin.schroth@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, ZH CH-8952 Switzerland
AU: Oostrom, M
EM: mart.oostrom@pnl.gov
AF: Environmental Toxicology Division, Pacific Northwest National Laboratory, P.O. Box 999, MS K9-33, Richland, WA 99352 United States
AU: Zeyer, J
EM: josef.zeyer@env.ethz.ch
AF: Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Grabenstrasse 3, Schlieren, ZH CH-8952 Switzerland
AB: The NAPL/water interfacial area is an important parameter which affects the rate of NAPL dissolution in porous media. We generated a set of baseline data for specific interfacial area in a well-characterised laboratory system, and subsequently used these data to evaluate current models that seek to predict this parameter. The interfacial tracer technique was used to measure specific NAPL/water interfacial areas at residual NAPL-saturation in four grades of silica sand wet-packed into a 28cm-long, 3cm-i.d. column. The two-phase system contained water and hexadecane as NAPL. The first model tested distributes entrapped NAPL over the pore classes based on Land's algorithm and assumes spherical geometry for the resulting ganglia. The other model is thermodynamically based, assuming that reversible work done on the system results in an increase in the interfacial area, such that the area between drainage and imbibition curves can be related to the interfacial area. The interfacial tracer tests gave specific interfacial areas between 57 cm$^{-1}$ for the finest sand and 16 cm$^{-1}$ for the coarsest, compared to values between 33 cm$^{-1}$ and 7 cm$^{-1}$ for the first model and between 19 cm$^{-1}$ and 5cm$^{-1}$ for the thermodynamic model. The assumption of spherical geometry made by the first model serves to minimise the specific interfacial areas of the ganglia. Computed tomography (CT) scans of similar samples to those used in the column experiments showed that the geometry of the visible blobs was generally not spherical; hence it is reasonable to suggest that this may explain the underprediction by the first model. We believe the thermodynamic model underestimates the interfacial area because it assumes that entrapment occurs only within the largest pores. We also calculated a modified version of this model assuming entrapment across all pore classes; this yielded values between 64 cm$^{-1}$ and 14 cm$^{-1}$, suggesting that this may be a more appropriate method.
DE: 5112 Microstructure
DE: 5194 Instruments and techniques
DE: 3210 Modeling
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting