S. Jeong and Werth, C. J., “Evaluation of methods to obtain geosorbent fractions enriched in carbonaceous materials that affect hydrophobic organic chemical sorption,” Environ. Sci. Technol., vol. 39, pp. 3279–3288, 2005.
T. Baumann and Werth, C. J., “Visualization of colloid transport through heterogeneous porous media using magnetic resonance imaging,” Colloids and Surfaces A., pp. 2–10, 2005.
C. E. Knutson, Werth, C. J., and Valocchi, A. J., “Pore-scale simulation of biomass growth along the transverse mixing zone of a model two-dimensional porous medium,” Water Resources Research, vol. 41, no. 7, 2005. Publisher's VersionAbstract
The success of in situ bioremediation projects depends on the mixing of contaminants and nutrients in the presence of microbes. In this work, a pore-scale model is developed to simulate biomass growth that is controlled by the mixing of an electron donor and acceptor. A homogeneous packing of cylinders representing solid grains is used as the model two-dimensional porous medium. The system is initially seeded with microbes in computational cells located at grain-water interfaces. The solutes enter the system completely unmixed; each solute is input over one half of the inlet boundary. Solute mixing is controlled by molecular diffusion transverse to the flow direction, and solutes are biotransformed according to dual Monod kinetics only where biomass is present. Simulation of biomass growth requires calculation of the water flow field as well as transport and reaction of solutes. The lattice Boltzmann method is used to obtain the flow field. Transport and reaction of the solutes is modeled by a finite volume discretization of the advection-diffusion-reaction equation. Biomass is allowed to grow and spread by means of a cellular automata algorithm. Model parameters are systematically varied to understand their effects on biomass development. Base case parameter values are obtained from batch experiments reported in the literature and are modified to achieve agreement between simulation results and previously reported micromodel experimental results. The most significant mechanisms that control biomass development are shear strength of new biomass and solute degradation rates. The biomass growth model achieves good qualitative agreement with experimental results.
T. Willingham, Werth, C. J., Valocchi, A. J., Krapac, I., Stark, T., and Daniel, D., “Evaluation of multi-dimensional transport through a field-scale compacted soil liner,” J. Geotech. Geoenviron. Eng., vol. 130, pp. 887–895, 2004.
Y. Chu, Werth, C. J., Valocchi, A. J., Yoon, H., and Webb, A. G., “Magnetic resonance imaging of nonaqueous phase liquid during soil vapor extraction in heterogeneous porous media,” J. Contam. Hydrol., vol. 73, pp. 15–37, 2004.
T. Baumann and Werth, C. J., “Visualisation and modelling of polystyrol colloid transport in a silicon micromodel,” Vadose Zone J., vol. 3, 2004.
A. J. Valocchi and Werth, C. J., “Web-based interactive simulation of groundwater pollutant fate and transport,” Computer Appl. Engineer. Education, vol. 12, pp. 75–84, 2004.
J. Li and Werth, C. J., “Slow desorption mechanisms of volatile organic chemical mixtures in soil and sediment micropores,” Environ. Sci. Technol., vol. 38, pp. 440–448, 2004.
H. Yoon, Valocchi, A. J., and Werth, C. J., “The influence of water content on soil vapor extraction,” Vadose Zone J., vol. 2, pp. 368–381, 2003.
I. Nambi, Werth, C. J., Sanford, R. A., and Valocchi, A. J., “Pore-scale analysis of anaerobic halorespiring bacterial growth along the transverse mixing zone of an etched silicon pore network,” Environ. Sci. Technol., vol. 37, pp. 5617–5624, 2003.
C. Chomsurin and Werth, C. J., “Analysis of pore-scale nonaqueous phase liquid dissolution in etched silicon pore networks,” Water Resources Research, vol. 39, no. 9, 2003. Publisher's VersionAbstract
Predicting the dissolution rate of nonaqueous phase liquids (NAPLs) in groundwater is difficult, as the effects of variable pore and NAPL blob geometry are poorly understood. To elucidate these effects, fluorescence microscopy and digital image analysis were used to quantify the size and location of variably distributed NAPL blobs during dissolution in homogeneous and heterogeneous pore networks etched into silicon wafers. Results show that the dissolution rate constant (expressed as the Sherwood number, Sh) is relatively constant regardless of pore and NAPL blob geometry when the average mass transfer length scale remains constant during dissolution. Results also show that Sh increases with Peclet (Pe) between 2 and 26 and then levels off. The limiting value of Sh reached depends on the average diffusion length scale; this length scale was directly calculated and found to vary depending on the pore and NAPL blob geometry. For example, the average diffusion length scale decreases (and Sh increases) as the pore throat width to grain diameter increases. Last, results show that the volumetric NAPL content (θn) is linearly related to the specific NAPL-water interfacial area (ait) over much of the dissolution process. However, this relationship depends on the pore and blob size distribution. For example, when multipore blobs control dissolution, the relationship between these parameters will change as smaller blobs dominate dissolution at low θn. These results are important because existing mass transfer correlations do not account for limiting values of Sh that can be obtained at high Pe for the effect of blob or pore geometry on the average diffusion length scale (and therefore on Sh) or for the effect of pore geometry and transient blob size distribution on the relationship between ait and θn.
C. Toupiol, Willingham, T., Valocchi, A. J., Werth, C. J., Krapac, I. G., Stark, T. D., and Daniel, D. E., “Long-Term Tritium Transport Through a Field-Scale Compacted Soil Liner,” J. Geotech. Geoenviron. Eng., vol. 128, pp. 640–650, 2002.
J. Li and Werth, C. J., “Modeling sorption isotherms of volatile organic chemical mixtures in model and natural solids,” Environ. Toxicol. Chem., vol. 21, pp. 1377–1383, 2002.
C. J. Werth and Hansen, K. M., “Modeling the effects of concentration history on the slow desorption of trichloroethene from a soil,” J. Contam. Hydrol., vol. 54, pp. 307–327, 2002.
C. Zhang, Werth, C. J., and Webb, A. G., “A Magnetic Resonance Imaging Study of Dense Nonaqueous Phase Liquid Dissolution from Angular Porous Media,” Environmental Science & Technology, vol. 36, no. 15, pp. 3310–3317, 2002. Publisher's VersionAbstract
Magnetic resonance imaging (MRI) was used to determine the effects of pore-scale heterogeneity on the dissolution of a nonaqueous phase liquid (NAPL) in water-saturated flow-through columns (1.2 cm in diameter) packed with either ∼500 or ∼1000 micron diameter angular silica gel (referred to as SG500 and SG1000, respectively). Columns were contaminated with 1,3,5-trifluorobenzene at residual saturation and then purged with water at a constant Darcy velocity of 1.83 m/day. Three-dimensional 19F images were acquired every 2−5 h at an imaging resolution of 59 × 234 × 234 μm3. Imaging results show that the specific NAPL surface area (at) is linearly related to the NAPL volumetric fraction (θn) and that the constant of proportionality between these parameters is determined by the blob size and geometry distribution. Overall (expressed as the modified Sherwood number, Sh') and intrinsic (expressed as the apparent Sherwood number, Shapt) mass transfer rate coefficients were calculated. Values of Sh' and Shapt for SG500 were approximately three times less than those for SG1000. For both solids, Sh' first increased or stayed the same and then decreased with decreasing θn, while Shapt generally increased with decreasing θn. These results suggest that during dissolution new flow paths were created (i.e., bypass zones were eliminated) as NAPL dissolved, decreasing the fraction of NAPL−water interfaces adjacent to pores filled with stagnant water and the average diffusion length scale. Since at for SG500 was dominated by less spherical multipore blobs (as opposed to more spherical singlets for SG1000), these results also suggest that the extent of flow bypassing (and the average diffusion length scale) increases in systems with more irregular blobs. These results are important because Sh' correlations and a “sphere” dissolution model do not account for transient changes in the fraction of NAPL surface area that contributes to dissolution or for the effect of initial blob size and geometry distribution on this fraction.
J. Li and Werth, C. J., “Evaluating competitive sorption mechanisms of volatile organic compounds in soils and sediments using polymers and zeolites,” Environ. Sci. Technol., vol. 35, pp. 568–574, 2001.
C. E. Knutson, Werth, C. J., and Valocchi, A. J., “Pore-scale modeling of dissolution from variably distributed nonaqueous phase liquid blobs,” Water Resour. Res., vol. 37, pp. 2951–2963, 2001.
B. K. Grens and Werth, C. J., “

Durability of wood-based versus coal-based granular activated carbon

,” Journal American Water Works Association, vol. 93, no. 4, pp. 175–181, 2001.
S. M. Vera, Werth, C. J., and Sanford, R. A., “

Evaluation of different polymeric organic materials for creating conditions that favor reductive processes in groundwater

,” Bioremediation Journal, vol. 53, no. 3, pp. 169-181, 2001.
C. E. Schaefer, Schuth, C., Werth, C. J., and Reinhard, M., “Binary desorption isotherms of TCE and PCE from silica gel and natural solids,” Environ. Sci. Technol., vol. 34, pp. 4341–4347, 2000.