Attenuation natural

Van der Meer JR, C Werlen, SF Nishino, JC Spain (1998) Evolution of a pathway for chlorobenzene metabolism leads to natural attenuation in contaminated groundwater. Appl Environ Microbiol 64 4185-4193. 

Sturchio NC, JL Clausen, IJ Heraty, L Huang, BD Holt, TA Abrajano (1998) Chlorine isotope investigation of natural attenuation of trichloroethene in an aerobic aquifer. Environ Sci Technol 32 3037-3042. 

Bloom Y, R Aravena, D Hunkeler, E Edwards, SK Frape (2000) Carbon isotope fractionation during microbial dechlorination of trichlorothene, cw-l,2-dichloroethene, and vinyl chloride implications for assessment of natural attenuation. Environ Sci Technol 34 2768-2772. 

Natural attenuation relies on natural processes to clean up or attenuate pollution in soil and ground-water. Natural attenuation occurs at most polluted sites. However, the right conditions must exist underground to clean sites properly. If not, cleanup will not be quick enough or complete enough. Scientists monitor or test these conditions to make sure natural attenuation is working. This is called monitored natural attenuation (MNA)94-96... 

The U.S. EPA publishes natural attenuation reports94 96 that provide a general description on approaches to clean up contaminated waste sites. One U.S. EPA report lists five questions about each cleanup approach ... 

Other U.S. EPA reports explain what MNA means when the term is used to describe a potential strategy to remediate a contaminated site. They also describe the various physical, chemical, and biological processes of natural attenuation that may occur at a site. Other informational materials are in preparation and will provide more specific details and scientific depth for the evaluation of MNA as a remedy at specific sites. 

Surampalli, Ong, Seagren, and Nuno compiled and edited a book by the American Society of Civil Engineers (ASCE) called Natural Attenuation of Hazardous Wastes.97 In addition to a discussion of the regulatory framework, this book covers major pollutants and basic scientific principles on physical, chemical, and biological processes involved in natural attenuation. It also contains an extensive review of literature, examples of applications of natural attenuation, and site characterization and monitoring requirements and procedures. 

The primary action in this alte mative is capping of one or more contaminated areas (such as Areas 1 and 2 of Figure 16.21) and then natural attenuation of the contaminated groundwater. The cap would be consistent with the state RCRA (which is more stringent than the Federal requirement) landfill closure requirements. 

Two assumptions about the surface have been made to determine the effect of natural attenuation on the contaminated groundwater. First, despite the fractured nature of the bedrock, it has been assumed that the subsurface is homogeneous so as to facilitate the evaluation. Second, the potential for reduction in TCE concentrations has been assessed using a hydrogeologic model in which the fact that the cap would reduce existing leachate production by 75% is taken into account. This model is assumed to predict that the concentration of TCE in the groundwater would be reduced to an excess cancer risk level of 28 pg/L in 60 yr and an excess cancer risk level of 5 pg/L, approximately equal to the MCL, in approximately 100 yr. 

Alternative 2 achieves protection by preventing exposure through capping and natural attenuation of the contaminated groundwater. Alternative 3 combines treatment to reduce the risk from the TCE-contaminated soil and groundwater and capping of the lead area. Alternatives 4 and 5 reduce risks posed by all portions of the site through treatment. 

U.S. EPA, Monitored Natural Attenuation of Chlorinated Solvents, Technical Report EPA-600-F-98-022, U.S. EPA, Washington, 1998. 

ASCE, Natural Attenuation of Hazardous Wastes, American Society of Civil Engineers, Reston, VA, 2004, 256 p. 

U.S. EPA defines MNA as the reliance on natural processes, within the context of a carefully controlled and monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The natural processes include biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant concentrations, and reducing contaminant mobility and bioavailability. Other terms for natural attenuation in the literature include intrinsic remediation, intrinsic bio-remediation, passive bioremediation natural recovery, and natural assimilation. 30... 

U.S. EPA published a guide about the steps needed to understand the rate and extent to which natural processes are reducing contaminant concentrations.56 Although this guide is directed at sites contaminated by chlorinated solvents, some of the steps would also have relevance for sites contaminated by oxygenates like MTBE. The guide identifies parameters that are useful in the evaluation of natural attenuation and provides recommendations on how to analyze and interpret the data... 

U.S. EPA, Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites, OSWER Directive 9200-4.17P, United States Environmental Protection Agency, Washington, DC. April 1999. Available at www.epa.gov/oust/directiv/d9200417.pdf, 2009. 

Rittmann, B.E., Monitored natural attenuation of MTBE, in MTBE Remediation Handbook, Moyer, E.E. and Kostecki, P.T., Eds, Amherst Scientific Publishers, 2003. 

Schirmer, M., Butler, B., Barker, J., Church, C., and Schirmer, K., Evaluation of biodegradation and dispersion as natural attenuation processes of MTBE and benzene at the Borden field site, Physics and Chemistry of the Earth Part B Hydrology, Oceans and Atmosphere, 24 (6), 557-560, 1999. 

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... 

Downey D. and Hicks, J., Impact of landfill closure designs on long-term natural attenuation of chlorinated hydrocarbons, Proceedings of the 2003 AFCEE Technology Transfer Workshop, San Antonio, Texas, February 25, 2003. 

ESTCP, Impact of Landfill Closure Designs on Long-Term Natural Attenuation of Chlorinated Hydrocarbons, Prepared by Parsons Engineering for Environmental Security Technology Certification Program, Arlington, VA, March 2002. 

Palmer C.D., Puls R.W. Natural attenuation of hexavalent chromium in ground water and soils. EPA/540/S-94/505, 1994. 

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