| Author | Prasong Wongvicha |
| Call Number | AIT RSPR no. EV-88-05 |
| Subject(s) | Soils--Trace element content--Mathematical models
|
| Note | A research study submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Research studies project report ; no. EV-88-05 |
| Abstract | Solute transport models were used to describe the movement of contaminants
through saturated and unsaturated soils. A comprehensive literature review is
given for solute transport modeling.
For saturated soils a two region physical non-equilibrium transport model
incorporating two regions, namely the mobile and immobile regions, originally
developed by Van Genutchen et al. (1976) was used. Freundlich's non-linear
adsorption isotherms were coupled with this transport model to account for the
adsorption phenomena. A CSMP III ( Continuous System Modeling Program)
program was written to solve this model numerically. The model was tested for 3
sets of experimental data having different soil and solute properties. The
experimental curves were fitted by varying 3 parameters. The model predicted
7 well only for fairly conservative solutes. To predict the movement of highly
adsorptive solutes such as cadmium, the . model needs further modification.
Effects of dispersion coefficient (D), mass transfer coefficient (a ), distribution
factor for adsorption sites in the mobile region (f), and the fraction of mobile
water content (!IS) on the breakthrough curves were studied. Considerable
influence was exerted by a and f but D and ยข showed little effect. Solute
concentration profiles for a semi- infinite column (as in the field situation) was
predicted for three different cases using this model and the penetration depths
were compared with those obtained from Green and Ampt profiles. Green and
profile was found to be a good approximation to find the penetration depths in
environmental impact assessment studies for mildly reactive solutes exhibiting
fairly sharp solute fronts. However for highly adsorptive solutes such as
cadmium this simple model does not seem appropriate and one has to go for more
accurate models.
For unsaturated soils, a non- linear equilibrium adsorption model by treating
all parameters such as water content (0), hydraulic conductivity (K), soilwater
diffusivity (D), dispersion coefficient (Ds) , pore velocity (v) as variables and the
latter four also as functions of e. A Fortran program using a first order finite
difference approximation was used to solve this model. Water content and solute
concentration profiles were predicted using this model for experimental
conditions used by Elrick et al. (1979) with KCl being the solute and Broolcston
clay loam as the soil. Good agreement was found with experimental and
predicted water content profiles although curve fitting was not used in this
case. For solute concentration profiles only one parameter >. (a constant used to
express Ds as a function of v and e) was varied to fit the experimental data.
The value of >. for best fit was found to be well within the acceptable limits.
Although only first order approximations were used the curves were ensured to
be fairly smooth by eliminating the effect of numerical dispersion using the
method adopted here. Fairly sharp fronts were obtained for the solute
concentration profile indicating low miscibility in the unsaturated case. |
| Year | 1988 |
| Corresponding Series Added Entry | Asian Institute of Technology. Research studies project report ; no. EV-88-05 |
| Type | Research Study Project Report (RSPR) |
| School | School of Environment, Resources, and Development |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Vigneswaran, S.; |
| Examination Committee(s) | Yamamoto, K. ;Kriengsak Udomsinrot; |
| Scholarship Donor(s) | The Royal Government of Denmark; |
| Degree | Research Studies Project Report (M. Eng.) - Asian Institute of Technology, 1988 |