2 min read•july 24, 2024
and mechanisms play a crucial role in how contaminants interact with soil. These processes determine whether pollutants stick to soil particles or get released back into the environment, affecting their spread and cleanup.
Contaminant transport and modeling help us understand how pollutants move through soil. By considering factors like water flow, spreading, and chemical reactions, we can predict where contaminants might end up and how to best clean them up.
Sorption attaches contaminants to soil particles through and
Adsorption accumulates contaminants on soil particle surfaces driven by physical (van der Waals forces) and chemical (covalent or ionic bonding) forces
Absorption incorporates contaminants into soil particle structure within pores or molecular structure
Ion exchange replaces ions on soil surfaces with contaminant ions measured by (CEC) for cations and (AEC) for anions
Desorption releases sorbed contaminants back into soil solution influenced by environmental changes (, )
Soil pH affects surface charge of particles and contaminants, influences ionization of organic contaminants, and impacts pH-dependent sorption of metals
increases sorption capacity for organic contaminants, forms metal ion complexes, and affects soil structure and water retention
varies in sorption capacities (kaolinite: low CEC, smectite: high CEC, illite: intermediate CEC)
impacts surface area for sorption (clay particles provide more sites than sand or silt)
influence metal contaminant speciation and mobility, affect organic contaminant degradation
Temperature generally increases desorption rates at higher levels, affects contaminant solubility and volatility
moves contaminants with flowing water, governed by Darcy's law, velocity depends on hydraulic conductivity and gradient
spreads contaminants due to velocity variations through mechanical (flow path tortuosity) and hydrodynamic (combination with ) processes
Diffusion moves contaminants from high to low concentration areas following Fick's laws, significant in low-permeability soils
slows contaminant movement relative to water flow due to sorption, quantified by (R)
enhances mobility through association with colloids or dissolved organic matter
rapidly moves contaminants through macropores or fractures, bypassing matrix flow
(ADE) models contaminant transport:
Retardation factor (R) calculated as:
models non-linear sorption:
assumes monolayer adsorption:
for biodegradable contaminants:
simulates water flow and solute transport in soils incorporating various processes
describe contaminant distribution: , for organic compounds normalized to organic carbon content