Photo/IllutrationThe construction site for a U.S. military base off the Henoko district of Nago, Okinawa Prefecture (Shinosuke Ito)

NAHA--Eight years over deadline with a final tab that comes to 2.5 trillion yen ($22.12 billion), 10 times more than initial Defense Ministry estimates.

That, according to Okinawan prefectural authorities, is what it will cost to finish relocating the U.S. Marine Corps Air Station Futenma within Okinawa Prefecture.

In releasing the figures, Okinawan officials also projected that it will take 13 years to complete the partially offshore base, eight years longer than planned, due in part to additional work to solidify the soft seabed.

It is the first time for the prefectural government to issue its own assessment of the cost and time required for the completion of the new facility off the Henoko district of Nago in northern Okinawa Prefecture.

The Futenma base is currently located in Ginowan.

Okinawa Governor Denny Tamaki shared the prefectural government’s estimate with Prime Minister Shinzo Abe when they met in Tokyo on Nov. 28.

The ministry projected total construction costs at approximately 231 billion yen when it announced its plan in 2013.

A year later, however, it notified prefectural officials that the figure had shot up by another 9.5 billion yen.

But that increase appears to be only a fraction of the project’s ballooning price tag, given an array of related project documents produced by the Defense Ministry.

For example, a document submitted to the transport minister when the Defense Ministry sought to repeal the Okinawa government’s revocation of its earlier approval for reclamation work off Henoko showed the value of contracts for the base project that had been concluded by the end of March came to 142.6 billion yen.

The figure accounts for nearly 60 percent of the ministry’s 2014 projection.

Of the 142.6 billion yen, approximately 92 billion yen had already been paid to contractors, according to the document.

The ministry’s original plan envisaged a total of 22 embankments.

But only six have been completed so far, and one is still under construction, according to the prefectural government.

Given the 92 billion yen that was already paid for the seven embankments, it means that construction of the seven embankments will cost 12 times more than the ministry’s initial projection of 7.8 billion yen.

Taking into account the project's progress, the prefectural authorities undertook their own trial calculations of the entire cost to complete all the work.

The projected 2.4 trillion yen price tag is based on a scenario that the tab for the remaining embankments and land reclamation will be 10 times more than the ministry’s initial estimate.

Work to pour earth and sand into the sea is expected to begin as early as Dec. 14.

The Okinawa government's estimate also included the cost and time for more work to stabilize the seabed to support the heavy infrastructure.

In response to a request for disclosure of information by a civic group, the Defense Ministry acknowledged the planned reclamation includes an area where the seabed is feared to be too soft.

Studying similar projects elsewhere, the prefectural government calculated that an additional 150 billion yen will be needed to solidify the foundations in waters off Henoko.

It also estimated the entire project will take eight years longer than the ministry's initial plan.

The ministry said the reclamation work would take five years.

But the prefectural government projected that work to strengthen the foundations will take another five years and the installation of facilities after reclamation three years.