From: Public Services and Procurement Canada
Monitored Natural Attenuation is an environmental management approach that uses a natural process, or combination of natural processes, that results in the reduction of the mass, toxicity, mobility, volume, or concentration of contaminants and their degradation products in the environment.
Monitored Natural Attenuation processes include a range of physical, chemical, or biological processes that, under favourable conditions, act without human intervention. These in situ processes include: biodegradation; dispersion; dilution; sorption; volatilization; radioactive decay and stabilization; transformation or chemical or biological destruction of contaminants.
Sources:
Implementation of this environmental management approach may include:
Controlled natural attenuation is a management approach. It does not require materials or storage on site.
Controlled natural attenuation produces no residues or discharges other than those generated by natural processes. Drill cuttings could be generated during the installation of the follow-up wells.
Notes:
Tests examining the effect of temperature change on hydraulic conductivity and establishing the zone of freezing with a pilot scale tubing system are recommended to properly design the full-scale containment system.
Natural attenuation applies to all contaminants for which effectiveness has been demonstrated, primarily organic contaminants. MNA has a greater potential for success based on the following key characteristics:
Depending on-site-specific characteristics, the time required for treatment can be years or even decades.
If natural attenuation meets remediation goals, there will be little or no long-term considerations.
The biodegradation of monocyclic aromatic hydrocarbons as well as petroleum hydrocarbons does not generally generate by-products or metabolites more toxic than the original compound. It generates harmless products such as carbon dioxide and water.
Biodegradation of some chlorinated aliphatic hydrocarbons can generate more toxic metabolites. For example, the biological transformation of dichloroethene forms vinyl chloride.
Biodegradation processes can alter the geochemical conditions of groundwater and promote the mobilization of certain substances such as metals. For example, a change in redox potential in groundwater, caused by biodegradation processes, can increase the solubility of some metals.
Controlled natural attenuation is rarely used as the sole remediation strategy. It is combined with other source area treatment technologies. Examples are numerous and could include:
The following links provide application examples:
Controlled natural attenuation is a management option that is generally inexpensive compared to active or intrusive treatment technologies. However, it takes several years to complete, does not always achieve the remediation goal, and may limit the reuse of the land for other types of activities.
Unavailable for this fact sheet
Composed by : Magalie Turgeon, National Research Council
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : March 1, 2009
Latest update provided by : Nathalie Arel ing., M.Sc., Frédéric Gagnon CPI., Sylvain Hains ing., M.Sc., Golder Associates Ltd.
Updated Date : March 21, 2022