The Landfill Treatment and Disposal Study Group of the Japan Society of Material Cycles and Waste Management is in the process of revising its 2002 report, Survey and evaluation methods of aftercare completion criteria for closed landfills, after 23 years. The main issues in this revision work are the survey and evaluation method used for landfill gas and the measures to be taken for closed-type landfills. In addition to the original approach to the completion of aftercare of waste landfills, the enactment of regulations on Changes to the Form or Nature of Land Where Waste Is Underground in the Waste Management and Public Cleansing Act has modified the meaning of the assessment of the landfill gas at the time of aftercare completion. We have presented issues and considerations necessary for a reasonable and objective view of the assessment of landfill gas in terms of the completion of aftercare at waste landfills. We also refer to measures required to confirm long-term functional security of the structure, including the cover, in the completion of aftercare of closed-type waste landfills. Also introduced is the generation behavior and quality of the internally retained water and leachate due to changes in management methods, such as the suspension of artificial water sprinkling at the sites.

Due to advances in waste treatment technology and changes in environmental regulations, the evaluation criteria for final disposal sites are becoming more diverse. The release of pollutants from landfills of incinerator ash is different from that of landfills of food waste （decomposition of organic matter） and therefore requires new evaluation methods. Currently, the evaluation methods are being reviewed to reflect the actual conditions at disposal sites, and the judgment criteria for leachate quality are also scheduled to be revised. In this paper, we introduce the changes in leachate quality at final disposal sites over several decades to show that appropriate management and analysis of measurement data are beneficial to the efficiency of maintenance and management. In addition, as it is expected that the high pH of leachate at coastal disposal sites will continue for hundreds of years or more, we discuss the concept of the post-closure care period while comparing it with that of land disposal sites.

Because investigations of landfill gas are not included in engineering standards for maintenance of closed landfills, facility managers and contractors only have the opportunity to measure the gas emission when aftercare completion of closed landfills is implemented.

　The author has clarified the behavior of landfill gas based on more than 20 years of research, while organizing the concept of aftercare completion for closed landfills. A report which aims to generalize gas measurement methods for aftercare completion criteria to the extent possible was then compiled.

　Although this revision has not resolved everything, gas investigations for aftercare completion of closed landfills are likely to begin seriously. The accumulation of reported cases will lead to repeated identification and resolution of issues related to decisions of aftercare completion, and scientific understanding and academic advancements regarding landfills can also be anticipated.

In terms of aftercare completion of closed landfills, it is necessary to carry out surveys on various parameters stipulated in the landfill completion criteria. This paper introduces a case study in which landfill gas and temperatures were surveyed over a period of approximately 10 years at a closed landfill for general waste after closure. It shows trends in the changes over time and the distribution in the depth direction within the observation borehole, along with statistical indicators. Based on the survey results, we evaluated the landfill completion criteria and also showed that long-term surveys are necessary, taking into account the fluctuations of the composition and emission of landfill gas and temperature.

The concept of “measures to be taken for post-closure care of landfill sites” has changed significantly compared to what was first published in Survey and Evaluation Methods of Aftercare Completion Criteria for Landfills. In this report, we summarize our thoughts regarding publication of the first edition in 2002 and also summarize the subsequent amendments to the Act on Waste Management and Public Cleaning, which includes the establishment of a regulation for changes in the shape or nature of the land. In the revised edition for 2024, we summarize procedures required for completing post-closure care at landfill sites which have been established according to regulations for changes in the shape or nature of the land. We also explain other matters that must be addressed, such as storage and inheritance of maintenance and monitoring data, removal and management of equipment and structures, and response to emergencies from the end of the post-closure care period onwards. It is desirable that responses to these issues all be discussed in advance with the landowner, the person disposing of the landfill, and the site manager. In addition, we have summarized issues to be considered when using the site once post-closure care has been completed.

We have seen a wide range of diverse ways landfills can be reused, including parks, sports facilities, solar power generation facilities, and civic farms. Normally, maintenance of a landfill ends when its postclosure care has been finally discontinued and actual reuse of the landfill can begin. In recent years, however, there have been reports of explosions caused by flammable gases while site is being used for other purposes. This makes investigation and evaluation of the waste stabilization status crucial. Landfill gas, leachate quality, and internal temperature have been evaluated to determine decommissioning, but there is a need for multifaceted evaluation to be conducted beyond these particular indicators. A report issued in 2002 introduced follow-up indicators following post-closure care completion but in reality, these are not actively being followed. Rather than introducing follow-up indicators for post-closure care, the 2024 Report: Survey and Evaluation Methods of Aftercare Completion Criteria for Closed Landfills introduces indicators for evaluating completion of aftercare, along with updated information on existing evaluation indicators（postend of aftercare follow-up indicators）, and additional follow-up indicators that evaluate the stabilization status of currently authorized wastes. This paper describes the specific items that have been newly added.