Taxpayers may have to come up with an additional $3.8 million to help pay for Honolulu's rail line, if an investigation reveals rail officials overspent millions of dollars. 

"Of course I don't find this to be welcome news and I think it shows that they need stronger controls on this issue," Mayor Kirk Caldwell said. 

An internal review of the Honolulu Authority for Rapid Transportation's files found it may have overspent millions on relocating residences and businesses in the path of the rail line. 

The review found more than a dozen files showed inconsistent documentation and mathematical errors. 

Caldwell says the deficiencies are under investigation.  

"We now need to find out what went wrong and to make sure that it never happens again," he said.

As of January, HART spent more than $13 million on relocation. A portion of that was reimbursed by the Federal Transit Authority. 

Rail officials say the project will opt out of $3.8 million dollars from the FTA if the ongoing investigation finds over payments were made. 

On Thursday, HART sent a letter to the FTA and and the Inspector General for the U.S. Department of Transportation detailing deficiencies.  

"This is just one more example of trying to be ahead of the problem. In this case, we're not a head of the problem. The good news is they caught it before it continued because there's a lot more acquisitions to complete particularly in the city center, we want to make sure those acquisitions are properly so we don't have to revisit this a second time. And to be vigilant about other problems that may come up in a few," Caldwell said. 

HART's executive director released this statement saying:

While HART's focus is on ensuring compliance going forward, HART is committed to identifying and correcting any past non-compliant actions. For that reason, we are in the process of furthering our internal review. HART will work with the FTA on any further inquiries it may have and on developing appropriate corrective actions. 

Earlier this month crews started working near Aloha Stadium on the third phase of the $8.1 billion rail.

The 20 mile project running from Kapolei to Ala Moana is expected to be complete by 2025.