The challenge of contaminated sites: remediation approaches in North America

Abstract

The pervasive occurrence of contaminated land has become a major issue facing society and involving enormous financial and social implications. Several problems arise at the interface between environmental science and public policy in dealing with future uses of such land. Contaminated sites need to have the nature and magnitude of the contamination identified. Such characterization must deal with the enormous complexity of many common wastes, the selection of appropriate analytical methods, and the heterogeneity of site conditions. Responses to these problems are limited by the capabilities of remediation technologies available. These may be categorized as containment/immobilization, mobilization, or destruction processes. In the last category, bioremediation has shown the most promise and general utility, but a number of specific requirements and constraints must be satisfied. For bioremediation to be feasible, the contaminants must be amenable to biological degradation, an appropriate and active microbial community must be provided, the contaminants must be accessible (bioavailable) to the microbial community, waste-specific constraints must be minimized, and appropriate environmental conditions must be provided for the microbial population. Cleanup criteria are fundamental to any decisions about contaminated sites. The U.S. Superfund approach has avoided developing generic contamination criteria, in contrast with the Canadian approach. Some common problems arise with either approach. There is a trend towards increasing reliance on risk assessment for site remediation decisions. Management challenges facing effective site remediation include the interdisciplinary nature of the issues, communication between laboratory and field personnel, and misrepresentation or inadequate attention to uncertainty. Constructive and positive advances to deal with these problems have been developed and include statistical sampling methods, tiered protocols, integrated toxicity testing procedures, multimedia partitioning models, and uncertainty analyses. Considering all the problems and challenges, there remains overwhelming evidence that prevention of contamination is vastly superior to remediation.Key words: waste characterization, analytical methods, cleanup technologies, bioremediation, cleanup criteria, risk management.