Document Type : Original Article
Authors
1 PhD Candidate, Water Engineering Department, University of Zabol, Zabol, Iran.
2 Associate Professor, Water Engineering Department, University of Zabol, Zabol, Iran.
3 PhD Graduate, Water Engineering Department, Bu-Ali Sina University, Hamedan, Iran.
Abstract
Despite differences in the physical characteristics of porous media, flow intensity and average velocity can be identical at various points within aquifers. Under such conditions, solute transport is influenced by pore-scale factors such as grain size and pore water velocity. Therefore, in order to better understand adsorption/desorption coefficients and solute transport processes, simulation is essential.
This study was conducted to investigate the effect of porous media grain size on solute transport under uniform hydraulic conditions using laboratory experiments and both equilibrium and nonequilibrium numerical simulation models. The laboratory columns were made of PVC, with a length of 25 cm and an internal diameter of 8 cm, and the porous media consisted of natural sand and gravel particles. Potassium nitrate was used as the tracer and injected into the soil columns in a pulse-input manner.
According to experimental results, the peak concentration (C/C₀) in fine, medium, and coarse-grained media was 0.50, 0.27, and 0.30, respectively, and their distribution coefficients (K_D) were 23.2, 1.8, and 2.1 L/kg, respectively. These results indicate greater dilution of solutes in coarse-grained media and increased retention in fine-grained media.
Simulation results showed that nonequilibrium dual-site (RMSE = 0.01) and single-site models (RMSE = 0.01–0.03) provided better accuracy compared to the equilibrium model (RMSE = 0.01–0.09), suggesting the presence of time-dependent kinetic processes in solute transport. Therefore, incorporating both kinetic and equilibrium-based models is recommended for simulating solute transport in porous media.
Keywords
Main Subjects
)