Sewage pipes stretching about 1,600 kilometers through Tokyo's 23 wards, or about 10 percent of the capital's drainage system, have not been replaced or repaired despite the expiry of their average service life of 50 years, it has been learned.

The Construction and Transport Ministry stipulates that such pipes be replaced or refurbished every 50 years. According to the Tokyo metropolitan government, however, about 1,600 kilometers of sewage piping laid more than 50 years ago has not been renovated, and about 2,100 kilometers of piping will exceed its service life in next 10 years.

If old sewage pipes corrode and leak, it will become impossible for residents whose homes are served by the pipes to use toilets or baths. Road subsidence also can result from the failure of such pipes. But the metropolitan government's work to replace or refurbish old sewage pipes is not keeping up with the pace of deterioration of the pipe network, raising concerns among metropolitan government service officials.

Meanwhile, 2,075 kilometers of piping was laid between 1959 and 1968 and will exceed its service life in the next 10 years. Refurbishment work will have to be carried out on a total of 3,700 kilometers of piping, accounting for 23 percent of the entire network. The length is more than the distance between Tokyo and Manila.

Renovation of the network will cost 1.48 trillion yen, according to the metropolitan government.

The metropolitan government spends about 69 billion yen on refurbishing old sewage pipes each year. Even if pipes were laid more than 50 years ago, they need not be replaced if appropriate repairs are carried out. The metropolitan government, therefore, is trying to keep costs to a minimum through such measures as renovating old pipes without digging up roads.

Of the more than 200 kilometers of pipe that exceeds its service life each year on average, the metropolitan government is now able to replace or refurbish about 90 kilometers on average.

In Tokyo, the laying of sewage pipes was conducted rapidly around the time of the 1964 Tokyo Olympics, meaning that much more piping will have to be renovated or replaced in the near future.

"We haven't been able to refurbish pipes that have already become too old, and more and more piping will soon reach the end of its intended life," a bureau official said.

Delays in replacing or refurbishing sewage pipes could affect roads built over them.

In Tokyo's 23 wards, there were 19,000 cases of road subsidence, including minor ones, in the 15 years between fiscal 1993 to fiscal 2007, the period for which such data is available. This means that about 1,300 cases of road subsidence occurred each year. --The Yomiuri Shimbun, ANN