A RISK BASED SYSTEM FOR POST-CLOSURE CARE ― REFORMING THE 30-YEAR TIME-BASED SYSTEM OF RCRA SUBTITLE D

摘要

In 1991, the U.S. EPA promulgated regulations governing the disposal of non-hazardous wastes in landfills under Subtitle D of the Resource Conservation and Recovery Act (RCRA). By 1996, there were approximately 3,100 permitted landfills, and landfills are projected to remain the dominant form of municipal solid waste (MSW) management in the U.S. for the foreseeable future. Once a landfill is closed, the site owner is required to monitor and maintain the site for what is referred to as the post-closure care period. Post-closure care activities include leachate collection and treatment, groundwater monitoring, inspection and maintenance of the final cover, and monitoring to insure that landfill gas does not migrate off site or into on-site buildings. Subtitle D specifies a 30-year post-closure care period unless this period is extended or shortened by the governing regulatory agency on a site-specific basis. The decision to extend or shorten the post-closure care period is based on whether the landfill is a threat to human health or the environment. Financial management practices of private landfill owners provide funds for maintaining the closed landfill through the required 30-year post-closure period. The implication of Subtitle D is that, by the end of the 30-year interval, the landfill will be allowed to cease post-closure care. However, federal regulations are unclear as to whether the post-closure period will actually end, and the regulations contain no procedure to define when a landfill no longer poses a threat to the environment other than referencing three risk assessment guidance documents for evaluating leachate management. Such criteria are needed to enable regulators to make defensible decisions on maintaining, extending, or reducing the 30-year post-closure care period. The objective of this paper is to present a new conceptual model to define when to end post-closure care. This paper describes processes that are needed and that will help reform the current 30 year time based system under Subtitle D. The new model addresses all aspects of landfill post-closure monitoring and maintenance including leachate collection and treatment, gas collection and treatment, monitoring, and maintenance of the final cover. The approach includes a series of decision points at which the source, point(s) of compliance, and potential environmental receptors are evaluated in a manner consistent with existing regulations. Rather than rely on a determination that post-closure monitoring is either complete or must be continued at the same level of intensity, the model evaluates each potential release and exposure mechanism individually and allows for the possibility that certain aspects of post-closure care could be discontinued before others. For example, it may be appropriate to discontinue active gas collection due to very low gas production rates or groundwater monitoring due to acceptable risk factors. At the same time, it may be entirely appropriate to continue cover inspections and maintenance to insure that cracks do not lead to increased leachate production. The conceptual approach presented in this paper represents a more realistic and environmentally protective strategy for the management of closed landfills than the current approach under Subtitle D. The approach would enable the owner/operator to identify those operational practices that can best mitigate environmental risk, and where practicable, implement certain practices at closed sites (e.g. leachate recirculation) to help reduce long-term risk to the environment. The authors believe that the proposed approach will result in increased protection of human health and the environment because assessments of environmental impact and potential risk posed by the source will be required before any aspect of post-closure care may be discontinued. Implementation and refinement of this approach will require discussions with regulators and demonstration of its appropriateness thro