Site-specific remedial objective

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... 

Developing remedial action objectives specifying the contaminant and media of interest, exposure pathways, and preliminarily remediation goals that permit a range of treatment and containment alternatives to be developed on the basis of chemical-specific ARARs when available, other available information, and site-specific, risk-... 

In the selection of a microbial system and bioremediation method, some examination of the degradation pathway is necessary. At a minimum, the final degradation products must be tested for toxicity and other regulatory demands for closure. Recent advances in the study of microbial metabolism of xenobiotics have identified potentially toxic intermediate products (Singleton, 1994). A regulatory agency sets treatment objectives for site remediation, and process analysis must determine whether bioremediation can meet these site objectives. Specific treatment objectives for some individual compounds have been established. In other cases total petroleum hydrocarbons total benzene, toluene, ethyl benzene, and xylene (BTEX) or total polynuclear aromatics objectives are set, while in yet others, a toxicology risk assessment must be performed. 

For each potential remedy identified for evaluation, the effectiveness must be evaluated in order to determine whether the remedy is capable of achieving all of the remedial action objectives. The evaluation of effectiveness for each remedial action should be made within the context of the conceptual site model (i.e., the contaminants, physical and hydrogeologic conditions, and other site-specific factors affecting technology effectiveness). A number of resources are available to assist with the evaluation of technical effectiveness of potential remedial actions ... 

Within each priority category, further refinement of the relative classification of sites may be necessary. The National Classification System is a screening tool only. Firm conclusions about the need for remedial action will still depend on a number of factors (including planned long-term use or redevelopment of the site, application of contaminated site criteria, and relevant/site-specific objectives of the jurisdiction in which the site is located, local issues, availability of technology, remediation costs, etc.). These factors are beyond the scope of this section, however, and are not meant to be addressed. 

Developing preliminary remedial action alternatives. This involves initiating limited field investigations if available data are inadequate to develop a conceptual site model and adequately scope the project, and identifying preliminary remedial action objectives and likely response actions for the specific project. 

We report here on the distributions of several chlorobiphenyls In samples of water, sediment and biota of the Acushnet River Estuary - New Bedford Harbor, Buzzards Bay, Massachusetts, U.S.A. Our general objective Is to gain Information of generic utility In addition to providing specific data and Interpretations of assistance to remedial action at this Superfund site. Our specific objectives In this paper are to 1) document the composition of Individual chlorobiphenyls In biota normally harvested by commercial and recreational fishermen and discuss factors which could lead to the observed distributions and potential Implications for public health standards for PCBs In fish and 11) to Investigate, In a preliminary manner, the adherence of bloconcentratlon of PCBs to predictions based on equilibrium assumptions and octanol/water (Kg ) partition coefficients (, 22). 

As the sampling sites with high responses of the test-battery are of most interest, the maximal elements are taken as priority elements, i.e. the equivalence classes 27, 33, 46, 47, 31, 95, 32, 9, 18. From this we conclude that a) the sites 27, 33, 46, 47, 31, 95, 32, 9, 18 are of specific importance, and b) the set of sites 27, 33, 46, 47 has the same profile of scores, thus, they may be remedied by the same methods, whereas the attribute profiles differ among all other priority objects. 

An effective conceptual site model is essential for the identification of risk-based and non-risk remedial action objectives. The conceptual model should identify source areas complete, potentially complete, and incomplete exposure pathways and receptors. In addition, the conceptual model should identify contaminants, affected environmental media, and specific areas within the affected environmental media to be addressed by the selected remedial action. Although a conceptual model should be developed prior to initiation of the risk-based remedy selection process, the conceptual model should be updated as needed during the remedy selection process to reflect any changes in the understanding of the site. ASTM (2003), Standard Guide for Developing Conceptual Site Models for Contaminated Sites, provides guidance for the development of an effective conceptual model. 

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