Fact sheet: Landfarming

From: Public Services and Procurement Canada

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Description

Landfarming is an ex situ remediation technology involving a biological treatment by aerobic biodegradation of organic contaminants present in soils and sediments. This technology consists in excavating and spreading contaminated soils on large impermeable surfaces of small thickness in order to stimulate biodegradation reactions of non-volatile contaminants.

Periodic mixing of soils is then carried out using agricultural equipment to keep them in an aerobic condition (presence of oxygen), to preserve their moisture level, for the addition of nutrients and amendments and to make contaminants bioavailable. During mixing, amendments such as fertilizers can be added to stimulate the growth and activity of microorganisms. Structuring agents can also be added to improve and better control aeration and water content. In many cases, irrigation systems are also necessary to ensure sufficient moisture.

Sources:

Implementation of the technology

Landfarming may include:

  • mobilization, site access, and the establishment of temporary installations;
  • preparation of the treatment area (waterproofing, water and leachate management and treatment system, if applicable, vapour emissions management and treatment system, if applicable);
  • excavation of contaminated soils, including stripping of topsoil and its temporary storage, control of slope stability, dewatering of excavations, protection of structures to be saved;
  • loading and transport of soils to the treatment area;
  • soil mixing using specialized equipment;
  • the addition of fertilizers and/or additives;
  • backfilling and surface restoration (grading, paving, hydroseeding or planting).

Materials and Storage

On-site storage may include amendments, geomembranes, drainage pipes, fuels, lubricants and other site materials required for the operation of machinery or equipment for the process. Piles of treated soils may also be temporarily stored on site, awaiting replacement in the excavations.

On-site storage is generally limited to small quantities of fuel and lubricants (daily refuelling is often done from a mobile tank) and small quantities of various site supplies required during construction of the landfarming area.

Typically, a starting amount of fertilizer and/or bulking agent is plowed, mixed, or sifted into the soils. Fairly small amounts of fertilizer may be retained on site for addition to, for example, irrigation water over time.

The technique is performed using traditional methods and equipment readily available for civil engineering work (including excavators, bar screens, rotary screeners), using specialized equipment and/or agricultural equipment.

Treatment cells can use imported aggregates, overlay or protective geomembranes, perforated drainage pipes.

Soils can be amended with texture or swelling agents (such as alfalfa, wood chips, shredded cardboard, or rice hulls) and/or by controlling pH (usually with lime).

Residues and Discharges

Treated soils can be reused as backfill material if they meet site conditions and are therefore not considered waste. Materials such as geomembranes and other materials used to construct the treatment area should be managed at the end of the treatment.

Vapours, leachate and runoff may be generated during treatment. These releases are usually captured by appropriate management and treatment systems.

Dust transported by air, from excavations, soil treatment areas, or soil spread on the ground by equipment wheels or tracks, can also be deposited on surfaces located in the wind direction.

Recommended analyses for detailed characterization

Biological analysis

  • Enumeration of the total heterotrophic bacterial population and the specific bacterial population.

Chemical analysis

  • pH
  • Organic matter content
  • Contaminant concentrations present in the following phases:
    • adsorbed
  • Nutrient concentrations including:
    • nitrates
    • nitrites
    • total phosphorus
    • organic nitrogen
    • potassium
    • sulfates
    • carbonates
    • manganese
    • ferrous and ferric iron

Physical analysis

  • Soil water content
  • Soil granulometry
  • Assessment of biological conditions and ecological factors such as vegetation, water availability and biological diversity

Recommended trials for detailed characterization

Biological trials

  • Conducting laboratory tests to verify the efficiency of biodegradation
  • Small-scale nutrient and/or amendment addition tests (on-site or off-site) to determine optimal dosages

Physical trials

  • Soil mixing tests (on-site or off-site) to determine recurrence, equipment and optimal parameters for optimal aerobic treatment.
  • If structuring agents must be used, laboratory tests to establish the correct ratio may be required

Other information recommended for detailed characterization

Phase II

  • Detailed topography
  • Regional climatic conditions (precipitation, temperature, etc.)
  • Presence of potential environmental receptors
  • Presence of above and below ground infrastructure

Phase III

  • Volume of contaminated material to treat
  • Characterization of the hydrogeological system including:
    • the direction and speed of the groundwater flow
    • the hydraulic conductivity
    • the seasonal fluctuations
    • the hydraulic gradient
  • Hydraulic tests to evaluate dewatering flows, if necessary
  • Evaluation of discharge water quality (if pumping required)

Notes:

It may be necessary to validate the stability of the various chemical and physical products that could be used.

Applications

Generally suitable for granular soils; highly cohesive soils require the use of structuring agents. Appropriate for use on soils with conditions favourable to biodegradation: soils should generally be between 10 °C and 45 °C, pH between 5 and 9, and moisture between 40% and 80%. 

Applications to sites in northern regions

  • The technology is achievable in northern sites, however, remote sites require greater mobilization, resulting in higher on-site supervision costs. In addition, equipment availability is limited and work windows are relatively short.
  • The cold climate will have an impact on the biodegradation processes of the contaminants. The treatment time will be longer compared to that in a temperate climate.
  • Uniform mixing of soils may be difficult if frost has penetrated deep into the soil to be treated;
  • Northern conditions may also limit the implementation of complementary soil mixing technologies.

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Applies
Biological
Applies
Chemical
Does not exist
Control
Does not exist
Dissolved contamination
Does not exist
Free Phase
Does not exist
Physical
Applies
Residual contamination
Applies
Resorption
Applies
Thermal
Does not exist

State of technology

State of technology
State of technologyExist or Does not exist
Testing
Does not exist
Commercialization
Exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
Does not apply
Chlorobenzenes
With restrictions
Explosives
Does not apply
Metals
Does not apply
Monocyclic aromatic hydrocarbons
With restrictions
Non metalic inorganic compounds
Does not apply
Pesticides
With restrictions
Petroleum hydrocarbons
With restrictions
Phenolic compounds
With restrictions
Policyclic aromatic hydrocarbons
With restrictions
Polychlorinated biphenyls
Does not apply

Notes:

Not appropriate for light petroleum hydrocarbons and volatile organic compounds, as they are more prone to volatilization than biodegradation.

Treatment time

Treatment time
Treatment timeApplies or Does not apply
Less than 1 year
Applies
1 to 3 years
Applies
3 to 5 years
Applies
More than 5 years
Does not apply

Notes:

Less volatile and more recalcitrant compounds may require several years of treatment. Easily degradable compounds can be degraded in weeks or months.

Long-term considerations (following remediation work)

This technology has limited long-term implications once the equipment and facilities are dismantled and the soil is considered treated.

Secondary by-products and/or metabolites

This technology is mainly used to treat organic compounds that generally do not generate toxic by-products as a result of their degradation. 

Limitations and Undesirable Effects of the Technology

  • Soils contaminated with volatile organic compounds must be pretreated to minimize the volatilization of these compounds during the installation and operation of the technology.
  • Dust released during soil mixing can be problematic.
  • When fertilizers and/or structuring agents are added, the volume of soil to treat can be considerably increased.
  • Soil manipulation costs can be high.
  • The sieving of the soils to treat may be necessary.
  • Treatment conditions are highly dependent on variations in weather conditions.
  • The treatment depth is limited to the plowed thickness (approximately 30 cm to 45 cm).
  • High concentrations of some contaminants may limit the effectiveness of the technology.
  • The technology may generate leachate that could seep into and contaminate groundwater if left uncontrolled. The generated leachate may also run off into a surface water body if not controlled.
  • The presence of heavy machinery, used for the works, can create temporary nuisances for the population. The concerns of neighbours and stakeholders are often related to dust, noise, odours, light (at night) and traffic problems.

Complementary technologies that improve treatment effectiveness

  • An air injection system to further stimulate the biodegradation of aerobic microorganisms.
  • An irrigation system to maintain soil moisture.
  • A physical operation such as sieving to reduce aggregates before processing.
  • Bioaugmentation can be used to increase the performance and efficiency of biodegradation processes.

Required secondary treatments

No secondary treatment is required.

Application examples

The following links present examples of applications:

Performance

Under optimal controlled application and environmental conditions, treatment efficiency of over 90% are possible. A high level of treatment, 99% or more reduction in contaminant levels, has already been achieved.

Measures to improve sustainability or promote ecological remediation

  • Use of renewable energy and energy-efficient equipment for the implementation of the technology.
  • Optimization of the schedule to promote resource sharing and reduce the number of mobilization days.
  • Priority use of recyclable reactive materials.
  • Recycling of leachate and/or runoff water within the soil treatment process.
  • The use of the TRIAD approach to planning and executing site characterization steps to optimize characterization efforts and reduce the environmental footprint of this work.
  • Technology implementation and site remediation that optimizes the protection of ecological habitats and/or improves the quality of these habitats.
  • Valorization of treated soils.
  • Use of locally produced fertilizers or amendments.

Potential impacts of the application of the technology on human health

Unavailable for this fact sheet.

References

Author and update

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 : Nathalie Arel ing., M.Sc., Frédéric Gagnon CPI., Sylvain Hains ing., M.Sc., Golder Associates Ltd.

Updated Date : March 24, 2022

Version:
1.2.6