All types of biodegradation, both in situ or ex situ, can be considered to remediate soils: in situ bioremediation, bioventing, composting, controlled solid phase, or landfarming. Slurry phase biological treatment is also applicable but is less widely used. Treatability studies should be conducted to evaluate design parameters, such as degradation rates, supplemental organism addition, cleanup levels achievable, degradation intermediates, and nutrient/oxygen addition.
Biodegradation uses a process in which indigenous or inoculated microorganisms (e.g., fungi, bacteria, and other microbes) degrade (i.e., metabolize) organic contaminants found in soil and/or ground water. In the presence of sufficient oxygen (aerobic conditions), microorganisms will ultimately convert many organic contaminants to carbon dioxide, water, and microbial cell mass. In the absence of oxygen (anaerobic conditions), the contaminants will be ultimately metabolized to methane and carbon dioxide. Sometimes contaminants may not be completely degraded, but only transformed to intermediate products that may be less, equally, or more hazardous than the original contaminant.
In situ bioremediation of soil typically involves the percolation or injection of ground water or uncontaminated water containing dissolved oxygen and nutrients. Ex situ bioremediation typically uses tilling or continuously mixed slurries to apply oxygen and nutrients, and is performed in a prepared bed (liners and aeration) or reactor. Bioventing is also potentially applicable to some nonhalogenated SVOCs.
Incineration uses high temperatures, 870o to 1,200o C (1,400o to 2,200o F), to volatilize and combust (in the presence of oxygen) organic constituents in hazardous wastes. The destruction and removal efficiency (DRE) for properly operated incinerators exceeds the 99.99% requirement for hazardous waste.
Distinct incinerator designs available for solids are rotary kiln, fluidized bed, and infrared units. All three types have been used successfully at full scale.
Excavation, retrieval, and off-site disposal of contaminated soil (with or without stabilization) to a landfill have been performed extensively at many sites. Landfilling of hazardous materials, especially hazardous wastes, is becoming increasingly difficult and expensive as a result of growing regulatory control, and may be cost-prohibitive for sites with large volumes, greater depths, or complex hydrogeologic environments. Determining the feasibility of off-site disposal requires knowledge of land disposal restrictions and other regulations developed by state governments.