Remedial objectives

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... 

In 2002, changes were incorporated in the SPA. The major adjustment was to make remediation cheaper by the introduction of land-use-dependent remediation objectives (LRO Figure 9.3) (BEVER, 1999). Consequently, the multifunctional approach was abandoned. It is no longer necessary that each remediation project should end in soil with contamination levels below the target values. 

To trigger regulatory action and establishment of target remediation objectives, e.g. for dredged material. 

Both the risk reduction and the management objectives for the site as a whole may support a set of sub-objectives for zones on the site that have either a particular risk profile or a land management requirement. For larger sites, a number of different remedial objectives may have to be adopted for different site zones, so that the most effective and cost-efficient management option is implemented for the site as whole. 

Risk assessment procedures undertaken on any contaminated site will establish a range of contaminants (hazards), pathways and receptors, will identify possible linkages of concern and will determine a set of remediation objectives. Any remediation subsequently proposed for the site must then be capable of fulfilling these objectives. In general terms the primary aims of any remediation is to break the linkage between contaminant source and the receptor to achieve a reduction of actual or potential risk so that unacceptable risks are reduced to acceptable levels. 

However, more commonly, non-risk remedial action objectives are not directly tied to site contaminant concentrations and therefore do not include remedial action levels. Examples of non-numeric remedial objective include ... 

Each potential remedial action must be evaluated with respect to its ability to achieve each risk-based and non-risk remedial action objective and to prevent unsafe exposure at all times. The timeframe available to achieve the remedial objectives is likely to vary from site to site. For example, a remedy for contaminated drinking water must prevent shortterm exposure for users of the existing water supply. However, for a remedial action objective applying drinking water standards to groundwater not currently used for drinking water, the remedy must be within a timeframe based on the potential future use of this groundwater. 

In this way a remediation objective can be calculated such that the impact on the receiving water course is acceptable. 

Before investigation of potential remediation options begins, however, remediation objectives should be defined. The discussion below... 

May require longer time frame to achieve remediation objectives using natural attenuation relative to more aggressive remedial options, especially when a source zone exists. 

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