LANDFILL GAS MODULE, PERFORMANCE-BASED SYSTEM FOR POST-CLOSURE CARE AT MSW LANDFILLS

摘要

A team of experts has been assembled from the landfill industry in an effort to develop a performance-based system for evaluating post-closure care (PCC) at municipal solid waste (MSW) landfills. This approach to PCC is being designed to address long-term stewardship of landfills by assessing current and future impacts to the environment in an effort to determine the most appropriate manner and time frame for implementation and monitoring of PCC. The four main aspects of landfill post-closure monitoring and maintenance required under Resource Conservation and Recovery Act (RCRA) Subtitle D (i.e., operation of a leachate collection system, landfill gas management, groundwater monitoring and protection, and cap maintenance) are considered within this system. The approach uses logic diagrams for each aspect of PCC whereby they can be evaluated sequentially by means of a modular system. The landfill gas (LFG) evaluations within this structure provide a series of steps to determine the best LFG management strategy to be implemented during PCC and when it is appropriate to reduce the level of LFG control and/or monitoring after closure. It is believed that this approach represents a more realistic and environmentally protective strategy for the management of closed landfills than the current time-based approach under Subtitle D. The approach enables the owner/operator to identify those operational and management practices that can best mitigate or reduce long-term environmental risks. The mam focus of this paper is to provide a detailed summary of the configuration of the LFG module within the larger PCC evaluation system. This summary includes a description of the procedures by which the impacts of LFG can be evaluated for RCRA Subtitle D compliance. These compliance issues include explosive concentrations of methane due to subsurface LFG migration, groundwater contamination from LFG, as well as odor/nuisance concerns. The LFG module is designed to assist the owner/operator in a determination of most appropriate method for LFG management based on site-specific conditions. Finally, in order to assist in the development of the LFG module, the paper summarizes recent LFG data, which serve to compare the decline in methane and non-methane organic compound (NMOC) generation rates over time. These data were derived from a study of several landfills throughout the country where NMOC concentrations in the LFG were determined for different ages of waste. These data are used to verify that both methane and NMOC impacts from LFG should diminish with time after the landfill enters the post-closure period and LFG generation begins to decrease.