Remedial technologies natural attenuation

Leading new technologies include the landfill as a bioreactor,1 and the use of natural attenuation processes to enhance effectiveness of remediation at reduced cost by naturally renewable and continuing processes.2-3... 

Smith, G., Adams, T. V., and Jurka, V., 1998, Closing a DNAPL Site through Source Removal and Natural Attenuation In Physical, Chemical, and Thermal Technologies — Remediation of Chlorinated and Recalcitrant Compounds (edited by G. B. Wickramanayake and R. E. Hinchee), Battelle Press, Columbus, OH, pp. 97-102. 

Natural attenuation should not be perceived as a permanent remedy or as a means to achieve certain cleanup levels, but rather as (1) an interim measure until future technologies are developed, (2) a managerial tool for reducing site risks, and (3) a bridge from active engineering (i.e., pump-and-treat, vapor extraction, etc.) to no further action. 

Natural attenuation, often called intrinsic remediation, intrinsic bioremediation, bioattenuation, or monitored natural attenuation (MNA) is an in situ treatment technology for soil, sediment, or groundwater. The technology has been used for full-scale remediation of sites contaminated with volatile organic compounds (VOCs), total petroleum hydrocarbons (TPH), chlorinated solvents, explosives, inorganics, and metals. 

While the processes entailed in MNA take place without human intervention, the technology is not a do-nothing approach. Before MNA can be chosen as a site remedy, assessments are required to determine the risks at the site and to determine if MNA can be effective in reducing those risks to acceptable levels. Evaluations are required for factors that could influence natural attenuation processes over time. Also, long-term monitoring is required during MNA. 

Reisinger, H.J., Burris, D.R. and Hering, J.G. (2005) Remediating subsurface arsenic contamination with monitored natural attenuation. Environmental Science and Technology, 39(22), 458A-464A. 

Although it has long been known that the adsorbed Fe(II) can be an effective reductant, its potential role as a mediator of reductive transformations of contaminants only recently has gained widespread recognition. Of particular interest are its possible roles in "natural attenuation" (65) and remediation technologies where the bulk reductant is dithionite (79) or Fe° (66). 

NRC (2000) Natural Attenuation for Groundwater Remediation, Committee on Intrinsic Remediation, Water Science and Technology Board,. Board on Radioactive Waste Management, National Research Council, 292pp. 

Brown et al. (1998) commented that similar to organic contamination, metal-contaminated soils will go through three stages of evolution (1) a gross removal process, (2) an active in situ treatment, and (3) a risk-based closure and natural attenuation. They also comment that very little time or money has been spent on developing in situ approaches for metal contamination. It is nine years since Brown et al., published their work, but we have yet to progress to active in situ remediation of metal-contaminated soils, and only a few innovative technologies are currently available for remediation of metal-contaminated soils (U.S. EPA, 1997). 

Within a risk-based remedial action framework, any of these three types of technologies may be considered for selection provided that they are effective at protecting human health and ecological resources. For a complex site, a remedial action may consist of multiple technologies (e.g., clay soil cap or monitored natural attenuation) representing one or more classes of remedial action (i.e., removal, decontamination, or control) that are combined in order to achieve all of the remedial action objectives. The user must research the effectiveness of each potential remedial action in order to determine whether the remedial action is capable of achieving all of the risk-based remedial action objectives. 

Consideration of MNA as a remedy or remedy component is the result of a complex process including evaluation of MNA along with other remedial approaches and technologies. In particular, source control measures should be evaluated for all sites and implemented at most sites where practicable. These measures include the removal, treatment or containment of sources (US EPA 1999). If human action is involved to accelerate the attenuation processes the term Enhanced Natural Attenuation (ENA) is used. 

The removal of chlorinated compounds from soils has long been a challenging task. Conventional remediation technologies such as pump-and-treat and natural attenuation have failed to clean up most contaminated sites to desired levels. Therefore, innovative technologies such as electrokinetic remediation have been developed the latter has been considered for the removal of contaminants from the soils with low hydraulic permeability. 

Contamination Cleanup Natural Attenuation and Advanced Remediation Technologies... 

Remediation Technologies Development Forum, Natural Attenuation of Chlorinated Solvents in Groundwater Seminar, Class notes Ed., RTDF, 1997. 

After the site and exposure assessment is approved, a decision regarding the necessity of remediation is made. This decision typically results in one of three outcomes (1) there is no need for further action, (2) remediation must be implemented, or (3) the site should be monitored to determine whether or not natural attenuation processes (e.g., biodegradation) will remediate the site, with the potential for implementation of a more aggressive remediation technology some time in the future. 

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