Monitored Natural Attenuation
Contaminants in the environment are subject to a variety of physical, chemical, or biological processes that lead to their attenuation. The EPA recognizes that natural attenuation can be used as a remedy if certain criteria are met; including the effectiveness of the attenuating mechanisms to offset contaminant loading (Figure 1). In the EPA's Office of Solid Waste and Emergency Response (OSWER) Directive 9200.4-17, the natural attenuation processes have been identified as follows:
…a variety of physical, chemical, or biological processes that under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentrations of contaminants in soil or groundwater. These in-situ processes include biodegradation, dispersion, dilution, sorption, volatilization, radioactive decay, and chemical or biological stabilization, transformation, or destruction of contaminants.
In order to demonstrate that MNA is a viable remediation option, the physical, chemical, and biological processes and the rate and extent to which these natural processes attenuate (i.e. decrease) the mass, toxicity, mobility, volume, or concentration, must be demonstrated for the contaminants of interest under site-specific conditions.
Characterization of these complex processes is inherently an interdisciplinary problem. At PNNL, we are uniquely equipped with the necessary interdisciplinary expertise, facilities, and tools to conduct the required studies to complete these kinds of tasks. We have highly sophisticated experimental and analytical laboratories, modeling capabilities, and decision making tools, which place us in an exceptional position to conduct detailed investigations for identifying and quantifying the natural attenuation of contaminants in the environment.
Following is a list of PNNL MNA projects:
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- Member of a national working group on advancing Monitored Natural Attenuation
- Evaluating several Dept. of Energy waste sites for application of Monitored Natural Attenuation.
- TCE and TCA in groundwater at various semiconductor manufacturing facilities in the Silicon Valley of California.
- Natural attenuation in conjunction with active remediation of diesel fuel in a aquifer contaminated by a leaking tank at a construction company equipment yard in New Mexico.
- Fuel hydrocarbons and PCBs (sometimes in conjunction with active remediation) at a number of natural gas compressor stations located in New Mexico.
- TCE and chromate at an airport in Arizona.
- Sr-90 at the 100-N Area of the Hanford Site, Washington (DOE, Department of Energy).
- Chromate at a number of locations on the Hanford Site, Washington (DOE).
- Lead and arsenic at a former phosphate fertilizer facility in South Carolina.