The Ministry of the Environment summarized the effects of decontamination projects, which involved approximately 33,000 facilities that were implemented by national and local governments by the end of August, 2013.
The latest information regarding decontamination is publicly available at The decontamination information site of the Ministry of the Environment.

Table 1　Effects of decontamination in decontamination projects implemented by national and local governments (major results)
(Ministry of the Environment, "FY2014 Decontamination Report").

Air dose rate※1,2 (measurement height: 1 m)	Before decontamination：0.36～0.93 µSv/h ↓ After decontamination：0.25～0.57 µSv/h
Reduction rate of air dose rate　(average)※2,3	Before decontamination : less than 1 µSv	Before decontamination : 1～3.8 µSv/h	Before decontamination : more than 3.8 µSv/h
	32％	43％	51％
Example of the reduction rate of surface concentration of contamination※4	Asphalt pavement of parking lots : 50％～70％ by washing, 30％～70％ by high-pressure washing Soil grounds : 80％～90％ by surface soil stripping

• ※1：Ranges between 25th and 75th percentile of air dose rate
• ※2：Data at a measurement height of 50 cm are not included in the living environment data for children at school, etc.
• ※3：Average reduction rate of air dose rate at each dose classification before decontamination (reduction rate (％) = (1 − air dose rate after decontamination/air dose rate before decontamination) × 100)）
• ※4：Publicized in a press release entitled “Regarding the release of ‘Effects of Decontamination Techniques in Decontamination Projects Implemented to Date by National and Local Governments’”on January 18, 2013.

• The air dose rate was reduced by decontamination by 30％～50％ on average.
• The reduction rate of the air dose rate in living environments for children such as schools and parks was roughly 50％～80％ and tended to be higher than that of the whole area (air dose rate at 1m).
• The air dose rate reduction features varied depending on the characteristics of the decontamination site, type of land use, and other factors. As a general trend, the reduction rate was relatively high in residential areas and relatively low in forests.

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Reference

1. 環境省, 平成26年度「除染に関する報告書」—これまでに環境省等が実施した生活環境の除染の経験等のとりまとめ−, 平成27年3月