Toxic Substances Hydrology Program
Relying on Nature to Clean Up Contaminated Ground Water
The use of monitored natural attenuation as a remediation strategy at contaminated ground-water sites has dramatically increased in recent years. A January 30, 2001, article in EOS entitled "Natural Attenuation Strategy for Groundwater Cleanup Focuses on Demonstrating Cause and Effect" summarizes the current state-of-the-science with regard to monitored natural attenuation. The article highlights the findings of a National Research Council committee report entitled "Natural Attenuation for Groundwater Remediation." The report "concluded that the key to demonstrating the effectiveness of natural attenuation at a site is establishing the cause-and-effect relationship between loss of contaminant and the mechanisms responsible for the loss." The report, along with the EOS article, gives practitioners a detailed insight into the tools needed to conduct site investigations that help officials understand mechanisms such as ground-water flow and biogeochemical reactions responsible for naturally attenuating contaminants in the subsurface. This understanding is key to making regulatory decisions about the use of monitored natural attenuation at contaminated ground-water sites.
The EOS article also presents two case studies of natural attenuation that are based on two U.S. Geological Survey Toxic Substances Hydrology (Toxics) Program research sites (Crude Oil Contamination in the Shallow Subsurface, Bemidji, Minnesota, and Hard Rock Mining Contamination in Arid Southwest Alluvial Basins, Pinal Creek, Arizona). The Toxics Program's goal for these research sites is to provide scientific information on the behavior of toxic substances in the Nation's hydrologic environments. These two case studies are also examples of how the Toxics Program conducts long-term, multidisciplinary research geared not to answering site-specific questions but to developing tools and understanding that can be applied to solving contamination problems Nationwide. The long-term studies at these sites and other Toxics Program sites have been a key component of demonstrating the effectiveness of natural attenuation as an alternative to engineered remediation strategies.
The article concludes with a discussion of natural attenuation in the context of emerging research issues, such as the poorly understood environmental fate of several classes of chemical compounds, the uncertainty caused by heterogeneous hydraulic and chemical properties in the subsurface, and the long-term sustainability of monitored natural attenuation remedies.
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USGS Information on Natural Attenuation