The input file is "column1.in", the superfile is "hbgc123d.cl1".
This sample demonstrates the use of HBGC123D for a reactive transport problem with chemical but without microbiological reactions. The model domain represents the same laboratory column experiment that was presented in sample 1. The measurements of the cylindrical column are length = 14.5 cm and radius = 4.2 cm. This is represented by a one-dimensional mesh with 58 elements and 59 nodes. The porosity is 0.428, the bulk density of the soil is r = 1.428 kg/dm3.
Initially, the column contained no EDTA species. The inflow of CdEDTA began at the start of the experiment and lasted for 1826.5 h. The inflow concentration of CdEDTA is 1.9 mmol/l. Afterwards, a washout phase began and no EDTA flowed into the column anymore. Two flow interrupts were performed in the course of the experiment. The first one started at t = 1267.45 h and lasted until t = 1508.45 h. The second one started at t = 3155.5 h and lasted until t = 3342.5 h. During these flow interrupts, neither water nor solutes flowed into the column. During the remainder of the experiment the inflow rate into the column was q = 5 ml/h. This yields a Darcy velocity of v = 9.022*10-3 dm/h. The units used in the HBGC123D simulation are dm, h, mol. A time step size of Dt = 0.05 h was used in this simulation.
In order to simulate the various flow phases (flow and flow interrupts), KVI was set to -2 in Data Set 2. 10 data points were specified in Data Set 16 for both velocity and water content. The water content is constant during the entire experiment, so that these values are the same for all data points.
CdEDTA is adsorbed to the solid phase. Therefore, its breakthrough is retarded compared to bromide in sample 1. Ligand exchange with iron oxides results in the production of FeEDTA. Figure 1 shows the breakthrough curve (concentration in the effluent from the column in the experiment and concentration at node 59 in the simulation) for CdEDTA. Figure 2 shows the breakthrough curve of FeEDTA. There is fairly good agreement between the measured and the simulated data for the CdEDTA outflow concentration. However, the FeEDTA simulation data do not match the experimental data very well. The reaction parameters in the input file have not been fully optimized to reflect the experimental data.
Figure 1: Breakthrough curve for CdEDTA, comparison of simulated and measured data.
Figure 2: Breakthrough curve for FeEDTA, comparison of simulated and measured data.
Acknowledgement
The column data were provided by Philip Jardine and Melanie Mayes of the Environmental Sciences Divison of Oak Ridge National Laboratory. The experimental results will be published in Mayes et al. (1999).
Reference
Mayes, M. A., Jardine, P. M., Larsen, I. L., Brooks, S. C., and Fendorf, S. E. (1999): Multispecies contaminant transport in undisturbed columns of weathered, fractured saprolite". Submitted to Journal of Contaminant Hydrology, July 1999 (in review).