This paper introduces the concepts of safety and peace of mind as they relate to controlled final disposal sites (landfills) as follows :
1) An absolute requirement for landfill safety is that waste and leachate should not be released off-site, leachate should be allowed to flow consistently following effluent standards; 2) Safety at landfills is defined by scientific indicators and risk management. The former is based on the three ordinance criteria and the latter is founded on environmental assessments; 3) Peace of mind at a landfill is based on the legal system and full confidence in business operators, which is founded on certainty regarding their legal compliance and on the financial base of operators. Operators must be responsible regarding execution of maintenance in accordance with legal systems and must relate to (profit ≫ income − expenses) according to business development outlooks; and 4) Future study is needed to clarify determination methods for stabilization and prediction methods on the period required for stabilization.

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This paper presents requirements for the safe and secure establishment and operation of landfills and divides them into three factors―target, reason, and requirement―from the viewpoint of developmental stages of waste disposal measures up to now. Requirements have changed over time beginning with the exclusion of waste from urban areas, then followed by efforts to control the public nuisance created by waste, and more recently the prevention of environmental contamination. Currently, the most pressing requirement demands that landfills are made sustainable for the next generation. When considering material flow, the final destination (“Sink”) of any substance is indispensable, and landfills will continue to play an important role in returning substances to nature for the future. It is necessary to fully consider the role of the landfill: Should landfills as temporary sink be allowed to release substances under control or should landfills be regarded as the final sink of substances? This must be considered based on the characteristics of the substance. In addition, further requirements for the safe and secure establishment and operation of landfills, along with early stabilization, are also discussed in the paper, with regard to least-controlled and controlled type landfills in Japan.

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History of legal changes regarding a containment strategy for landfilled solid waste is summarized in this paper. The containment of landfilled solid waste consists of leaching limitations, bottom liner systems, the intermediate cover soil, final cover systems (including capping), leachate treatment systems and groundwater monitoring.
　The functions of these containments are mentioned and viewpoints are discussed. We recognize anew that the aim of containment is groundwater protection so that leakage from the landfill site, when it passes through a bottom liner system that has permeability, must be controlled long after landfill closure has been completed. The flux control concept, which works from the landfill to the groundwater, is proposed here with the example of a radioactively contaminated waste landfill method whereby only the solute flux is controlled, rather than the leachate flux.

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Stabilization is an important factor in maintaining safety at a waste landfill. Various research techniques have been tried and developed at landfills, however investigation methods for stabilization have not yet been generalized. This paper presents an outline of research techniques and the results obtained using monitoring investigations since 2005 at an industrial-controlled landfill in Fukui Prefecture. Since stabilization is advanced by “washing out of salts”, “forming solid compounds” and “decomposition of organic matter”, it is important to estimate for salts and organic matter at any landfill. The general situation at landfills cannot be estimated solely by local investigation because it is not homogeneous, with various mixed wastes. Results from several different investigations must be combined with each other in order to result in correct evaluations. In addition, a periodic follow-up investigation is needed to estimate the long-term stabilization process.

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The findings of composition and flux for landfill gas can indirectly show stabilization of buried wastes and assure safety for the waste landfill site and its surroundings. Presenting reviews and investigations on landfill gas by the authors, this paper discusses some of the problems related to the evaluation of end-of-operation/aftercare and greenhouse gas emissions at waste landfill sites. “Hot spots,” where landfill gases may be leaking out through the surface of the landfill, may indicate the best points for operation and maintenance monitoring. Furthermore, in order to minimize day-to-day variations, the measurement of gas flux should be done over a longer period of time.
　The reason for investigating landfill gas composition is not only to gather and analyze information regarding the actual conditions in gas ventilation pipes, but also to observe gases in the waste layer using vertical gas monitoring pipes. In addition, measuring the pH of the leachate and any of the retained water enables for confirmation of acid gas release, such as hydrogen sulfide and carbon dioxide.

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Electrical resistivity survey is an up-and-coming technique that involves non-destructive, prompt on-site means for conducting surveys within a landfill site. This article presents several case studies where electrical resistivity surveys were implemented at landfills by the authors. Results revealed that the electrical resistivity survey is a useful technique in that it is able to record images of (1) perched water; (2) structures such as earth-fill dams or liner sheets and; (3) the condition of progress regarding stabilization inside the landfill. In addition, progressive techniques, such as the induced polarization survey and the three-dimensional survey, are expected to be useful new approaches for investigating inside landfills.

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Although measures are followed as outlined by standard ministerial orders and administrative guidelines, many problems have occurred at industrial waste final disposal sites in Chiba Prefecture. In light of this situation, a procedural manual for maintenance was developed with the aim of making operations at landfills in Chiba more stable, working toward the prevention of accidents and minimizing damages by referring to local features and reviewing reports on past accidents. This paper introduces the most important points found in the manual.

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