Passive remediation approach

Natural attenuation (NA) refers to the reduction of contaminant concentrations in environmental media by processes such as dilution, dispersion, sorption, volatilization, and biotic or abiotic transformations. As a passive remediation approach, NA is mostly applied in connection with organic contaminants which migrate from the source in groundwater. Naturally attenuating contaminant plumes show a decline in the dissolved contaminant mass as a function of time, and a decline in contaminant concentrations downgradient from the source. Before potential receptor exposure points are reached, natural attenuation is expected to reduce dissolved contaminant concentrations below regulatory standards (Wiedeme-ier et al. 1999). 

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... 

Permeable reactive barriers have significant advantages over the conventional approaches for groundwater remediation. The barriers are passive systems whose effectiveness can persist for several years to decades. Moreover, the reactive material can be adjusted to target specific contaminants from a mine site and the contaminants precipitated within the barrier are isolated from the surface-water environment and biota (Blowes et al., 2000). 

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