Rail officials have awarded Nan Inc. — not Watts Constructors — the contract to build the final trio of stations along rail’s first 10 miles, even though Watts had submitted the lowest bid for that work.

A Nov. 17 bid-opening showed that Nan had bid $115.8 million to build what rail officials have dubbed the “Kamehameha Highway Stations Group,” including the Pearl Highlands, Pearlridge and Aloha Stadium stations. Watts bid $112.7 million. However, federal officials eventually found that the Watts bid did not comply with the required Buy American laws, according to a Federal Transit Administration letter to the firm Friday.

The FTA made that call because Watts had submitted documents that showed three of its subcontractors could not comply with those Buy American regulations for the work, according to the letter. Watts then told the FTA that those details about the subcontractors were “superfluous” to the bid, the letter stated. Representatives for Watts could not be reached late Tuesday.

Using Nan’s bid, it should cost about $250.8 million to build all nine stations along the transit line’s first 10 miles to Aloha Stadium, excluding any change orders. That’s significantly less than the $294 million low bid that the Honolulu Authority for Rapid Transportation received in 2014 to build all nine stations together, before the rail agency canceled that bid and broke the stations into groups to seek lower costs.

But the new price also represents about $50 million more than HART had originally budgeted to build those nine stations, back when it scrapped the first bids. Overall, the 20-mile, 21-station rail project faces an approximately $1.3 billion shortfall.

Nan, meanwhile, has had a complicated relationship with the rail transit construction project thus far.

The firm submitted the original $294 million bid back in 2014 to build all nine stations to Aloha Stadium. It initially challenged HART’s cancellation before relenting.

Earlier this year Nan challenged with state commerce officials the Hawaiian Dredging $78.9 million low bid to build three stations at Leeward Community College, Waipahu and West Loch. Those state commerce officials eventually denied Nan’s challenge.

This past summer Nan bid lowest and received a contract to build the second trio of stations in West Oahu. The company later tried to withdraw its $56.1 million bid due to errors in calculating prices for materials, according to a July 1 letter to the firm from HART. The agency denied Nan’s request to withdraw.