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Natural Attenuation &

Monitored Natural Attenuation

Monitored natural attenuation is gaining popularity as a remedial option.   However, this approach may not actually save you money in the long run because of  prolonged sampling and reporting expenses.  Each site must be evaluated individually to determine if  Monitored Natural Attenuation is the best approach.

The Environmental Protection Agency (EPA) defines Natural Attenuation (NA) as “naturally occurring processes in soil and groundwater environments that act without human intervention to reduce mass, toxicity, mobility volume or concentration of contaminants in those media”.  These processes include “biodegradation, dispersion, dilution, adsorption, volatilization and chemical or biological stabilization or destruction of contaminants”  

Natural attenuation is also referred to as Monitored Natural Attenuation (MNA).  Before a site owner can even consider this approach the groundwater contaminate plume must be defined and permanent monitoring wells installed to track the movement and degradation of the contaminates.  After a period of monitoring, usually over a year of quarterly sampling,  the site should be evaluated to determine if natural degradation is actually occurring.    The EPA defines monitored natural attenuation as “the use of natural attenuation processes within the context of a carefully controlled and monitored site cleanup approach that will reduce contaminant concentrations to levels that are protective of human health and the environment within a reasonable time frame.”  Further, the EPA cites the monitored natural attenuation processes as being “those processes that degrade contaminants and expects that MNA will be most appropriate where plumes are stable. 

MNA is only appropriate with groundwater plumes that are well defined, stable and protective of  human health and the environment.   It is important to understand that Monitored Natural Attenuation  is not a "do nothing” option it involves:

  • Characterizing the fate and transport of the contaminants.  Evaluating the progress of natural attenuation by studying the plume concentrations and groundwater gradients.

  • Ensuring that the processes reduce the concentration, toxicity and or mobility of the contaminant.

  • Evaluation of the long term factors such as total migration and impact on other media

  • Monitoring of the plume concentrations at various points thought the use of monitoring wells and the installation of additional monitor wells as the need arises.

While monitored natural attenuation is an excellent choice in some instances the the overall cost of monitoring over a long period of time must be compared to the cost of accelerating the degradation and to other technologies.   Remember, as with all groundwater contaminate plumes,  the cleanup process and required time to achieve closure  is limited by the geology.   

Useful  links for monitored natural attenuation:

 

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