Public Services and Procurement Canada
Landfarming is an ex situ remediation technique used for the biological treatment of soil contaminated with petroleum hydrocarbons and/or non-volatile organic compounds.
This technique consists of spreading excavated contaminated soil on the ground, in an approximately 30 cm to 45 cm thick layer. This layer of soil may be covered when it is important to control soil water content and/or runoff water. Depending on the characteristics of the underlying soils (soil particle size and permeability) and the depth to the water table, the contaminated soil may be spread directly on the ground surface or on a membrane with an upper-protective layer.
Mixing of the contaminated soil is normally required to maintain aerobic conditions (presence of oxygen), to blend nutrients and amendments, to distribute moisture and to enhance the bioavailability of contaminants. The soil is often tilled using equipment such as a harrow pulled by a farm tractor (hence the name landfarming). During the mixing, volatilization of contaminants into the atmosphere will occur but should be kept to a minimum. Fertilizers that will stimulate bacterial growth and activity, as well as structuring agents that will improve soil porosity and allow control over soil aeration and water content may be added during the soil mixing process.
During treatment, nitrogen compound concentrations, pH and water content must be periodically monitored to ensure optimal conditions for contaminant biodegradation. Contaminated soils must be well drained while maintaining a water content ranging between 50% to 80% of the total water holding capacity of the soil. Irrigation systems, runoff control and leachate collection and treatment systems may be required. The collected runoff water and/or leachate may be either re-used in the treatment process or disposed of. The collected runoff water and/or leachate might have to be treated prior to its disposal.
A cleared area (trees and/or other structures are removed) is excavated to predetermined or field-determined limits (or, less frequently, tilled in situ). A lift of contaminated soils is spread over in the landfarm area (usually 30 cm to 45 cm thick layer). Microbial activity (and less frequently, fungal activity) is stimulated with fertilizer, pH control, moisture control, temperature control, inoculation with seed material and/or soil texture improvements. The soils are tilled/mixed regularly to aerate and blend the nutrients into the soils. Biological activity degrades contaminants (some fraction of volatile contamination is discharged to the atmosphere). After a period of weeks to years, the soil is remediated and can be spread out or used as fill.
Conventional excavation equipment is used to physically remove or mix shallow contaminated soil for biological treatment. Landfarming activities may include:
If soil contaminants include volatile compounds, vapour/off-gas controls might be required. Depending on precipitations, contaminant characteristics and depth to groundwater, a leachate collection and treatment system may also be required.
A variety of proprietary slow-release fertilizers, admixtures (including emulsifiers and surfactants, such as lecithin) and microbial cultures are available. Indigenous microorganisms are typically used; sometimes exogenous cultures (with mixed results) are used.
Chlorobenzenes: suitable for chlorobenzene, dichlorobenzene and trichlorobenzene;
Phenolic compounds: suitable for cresol, pentachlorophenol and tetrachlorophenol.
Less volatile and more recalcitrant compounds may require up to two years of treatment. Readily degradable compounds may be remediated in weeks. High levels of treatment (contaminant reductions of 99% or more) typically require significantly more time than moderate contaminant reductions (70% to 90%).
Few to no long-term considerations exist at sites where treatment has met appropriate criteria, equipment/facilities have been decommissioned and the site has been cleaned up. Poor backfilling practices (backfill placed frozen, not compacted, etc.) can create geotechnical stability problems or differential settlement.
Few to none. The technique is predominantly used for fuel-range organics, which typically degrade to CO2 and water (or form biomass), thus doesn’t typically generate deleterious secondary by-products or metabolites.
An application example is available at this link:
Under optimal landfarming conditions, petroleum hydrocarbon contaminated soil, for example, is treated over a time period of 3 months to 2 years.
Unavailable for this fact sheet.
Composed by : Magalie Turgeon, National Research Council
Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada
Updated Date : March 1, 2015
Latest update provided by : Daniel Charette, P.Eng., eng., Jan McNicoll, M.Sc., P. Geo., exp Services Inc.
Updated Date : March 31, 2017