The discovery of contamination from an industrial solvent in a monitoring well near the Honolulu airport halted drilling for columns on a segment of the Honolulu rail project for more than three months, according to the rail authority.

That discovery of the solvent TCE, or trichloroethylene, triggered temporary layoffs of about 50 workers and is expected to cost the rail project “several million dollars,” said John Moore, east area construction manager for the Honolulu Authority for Rapid Transportation.

Monitoring wells were drilled in the area to determine whether there was any preexisting contamination in the construction area, and TCE was discovered underground Dec. 15 near the site of a former Army facility near the airport. “Some of the solvents that they used evidently got dumped on the ground and got into the water table in this area,” Moore said.

Moore told members of the HART Project Oversight Committee on Thursday that the state Department of Transportation Airports Division ordered that work stop in the area where the airport station is to be built, which idled two major drilling rigs that were working on that portion of the project.

Rail contractor Shimmick/Traylor/Granite JV then laid off more than 50 people because of the delay because they couldn’t do any work in that area, Moore said. Work on other portions of the rail guideway and stations continued, he said.

Environmental consultants for HART then developed a sampling plan for the area over the holidays that involved drilling more than a dozen monitoring wells in areas where shafts are to be drilled for the rail line and station supports, Moore said.

“The sampling found a contained area of contamination that will require special handling,” Moore said in a written response to questions. The test results showed contaminated water will affect construction operations on only four of the 227 drilled shafts for that portion of the project, he said.

“However, a great deal of time and effort was necessary to ensure the safety of all participants in the required work,” Moore said in a written statement.

After the test results were received in February, the state Department of Transportation allowed surface work to resume that included relocating utilities and building an access road, he said.

The state Department of Health finally authorized HART to resume work drilling for the rail columns last week, and the contractor STG is mobilizing to get crews back on the site, Moore said. However, “this is going to be a few million dollars in standby and delay costs because of this environmental issue,” he told board members.

Bill Brennan, spokesman for the rail project, said HART isn’t required to clean up the contamination at the airport, but is required to handle and dispose of any contaminated materials it might dig up in an “environmentally acceptable way.”

HART awarded Shimmick/Traylor/Granite JV a $874.7 million design- build contract in 2016 to build the rail guideway and stations from Aloha Stadium to Middle Street. That is known as the airport segment, one of four major segments of the 20-mile rail line.

Moore said the delay will not change the overall schedule of the project for the airport segment of the project, which is scheduled to be completed in May 2021.