None of these techniques are entirely satisfactory (Exner, 1995). Landfilling is a temporary solution that delays remediation. Furthermore, it has been discontinued in most countries. Incapsulation/solidification does not remove the contaminant from the soil thereby greatly limiting the value of the soil. Soil washing and flushing have been used extensively in Europe but only had limited use in the U.S. The process entails excavation of the contaminated soil, mechanical screening to remove various oversized materials, separation processes to generate coarse- and fine-grained fractions, treatment of those fractions, and management of the generated residuals. Soil washing performance is closely tied to three key physical soil characteristics: particle size distribution, contaminant distribution among the different size particles, and how strongly the soil binds the contaminant. In general, soil washing is most appropriate for soils that contain at least 50% sand and gravel, such as coastal sandy soils and soils with glacial deposits (Westinghouse Hanford Co., 1994).
Treatment technologies are based on processes addressed to removal, stabilization or destruction of contaminants.
- Removal may be attained by contaminant mobilization and/or accumulation processes (leaching, sorption), contaminant concentration and recovery processes (physical separation) or a combination of processes (accumulator plants).
- In-situ stabilization consists of the contaminant being made less mobile and therefore less toxic by a combination of physical, chemical and biological processes.
- Contaminant destruction by physical, chemical or biological degradation (e.g. thermic or microbiological treatments).