MNA Frequent Question 3. What is meant by the term “natural attenuation?
“Natural attenuation” is the effect of natural processes (i.e., those which do not require human intervention such as engineered enhancements or controls) which reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater. When relying on natural attenuation processes for site remediation, EPA prefers those processes that degrade or destroy contaminants. Also, EPA generally expects that MNA will only be appropriate for sites that have a low potential for contaminant migration. “Natural attenuation” is passive in the sense that natural attenuation processes occur without human intervention, however, the use of “natural attenuation” at a site does not preclude the use of “active” remediation or the application of enhancers of biological activity (e.g., electron acceptors, nutrients, and electron donors). By definition, a remedy that includes the introduction of an enhancer of any type is no longer considered to be “natural” attenuation. EPA encoura
