300 Kilometers of Japan’s Sewer Pipes Need Emergency Measures, Ministry Inspections Find

The Yomiuri Shimbun

16:32 JST, September 18, 2025

About 300 kilometers of sewer pipes — nearly half of priority pipes so far checked for such risks as corrosion and damage — require emergency measures within five years, according to interim results of special inspections conducted by the infrastructure ministry.

In the wake of a fatal road cave-in accident that occurred in Yashio, Saitama Prefecture, in January, the Land, Infrastructure, Transport and Tourism Ministry is currently conducting inspections of large sewer pipes installed more than 30 years ago nationwide.

The interim results released Wednesday showed that 12% of the pipes checked so far were in need of measures within one year. On the same day, the ministry sent a written request to municipalities that oversee such sewer pipes to take swift measures to prevent cave-in accidents.

The ministry launched the emergency inspections in March, targeting large sewer pipes more than 2 meters in diameter that were installed in or before fiscal 1994. The total length of these pipes is about 5,000 kilometers. The inspections give priority to 813 kilometers of sewer pipes at risk of extensive damage, including pipes that have ground conditions similar to those at the accident site in Yashio or have structures prone to corrosion. At the request of the ministry, local governments are checking for abnormalities using such methods as drone photography, visual inspections and tapping tests.

The interim findings were presented at a ministry expert panel meeting on Wednesday. An analysis of 621 kilometers for which the inspections had been finished by Aug. 8 showed that the total length of pipes requiring repair or reconstruction within five years due to such factors as exposed reinforcement bars, surface cracks or groundwater infiltration was 297 kilometers, accounting for 48% of the total checked so far. These pipes are located in all prefectures except Gunma, Fukui, Ehime, Saga, Nagasaki and Oita. Of these pipes, 72 kilometers in 35 prefectures, or 12% of the total, were found to need measures within one year.

In the inspections, six underground cavities were found near sewer pipes — one in Kitami, Hokkaido; two in Niigata City; and three in Tamana, Kumamoto Prefecture. One of the three found in Tamana reached nearly 1 meter in diameter. As these cavities have either been repaired or are slated for repair, the risk of road cave-ins is low, according to the ministry.

“The figures that came out are extremely serious,” Hitoshi Ieda, chair of the expert panel who is a senior professor at the National Graduate Institute for Policy Studies, told reporters after the meeting. “We hope repairs will be made as soon as possible.”

The ministry plans to advance the installation of parallel sewer pipes and the replacement of aging large pipes next fiscal year. To that end, it has included related expenses in its budget request for fiscal 2026.