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Natural Attenuation Services

Natural Attenuation

Natural Attenuation

Natural Attenuation (NA) of contaminants in groundwater has been the subject of much research and many field studies over the past 20-plus years. It is now increasingly recognized as a common phenomenon, particularly for hydrocarbons, but also for other contaminants such as chlorinated solvents.

Natural attenuation is the combination of naturally occurring processes that act without the need for human intervention or enhancement, and result in reduced risks posed by contamination in soil and groundwater. A good working definition is that of the US Environmental Protection Agency (EPA) Office of Solid Waste and Emergency Response:

"The 'natural attenuation processes' that are at work in such a remediation approach include a variety of physical, chemical, or biological processes that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater. These in-situ processes include biodegradation, dispersion, dilution, sorption, volatilization, and chemical or biological stabilization, transformation, or destruction of contaminants."

Natural attenuation is not a "do-nothing" approach. Rather, it is based on careful and extensive initial validation and appropriate follow-up monitoring designed to demonstrate that natural attenuation is occurring and that it will remain protective of both human health and the environment. Hence the term "monitored natural attenuation" is often used.

NA is an appropriate remedial option when risk-based site management is employed, and risk assessment demonstrates that it is protective of human health and the environment. This requires that NA is evaluated, implemented and monitored with at least the same rigor applied for other remedial technology. It is clear that appropriate monitoring is required to ensure that the performance of NA remains acceptable for the duration of the remedial process.

The potential for NA should generally be evaluated at any site because it may offer a less intrusive, efficient approach to protection of human health and the environment. It can be cost-effective, may result in less environmental impact than active remediation technologies, may be less disruptive to the site operations than other remediation technologies, and can enable a fuller understanding of contaminant fate and transport in the subsurface relevant to any other type of remedial measure.

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