A pedestrian bridge at Innovation Station, part of Phase 2 of Metro's Silver Line expansion, seen in July. (Katherine Frey/The Washington Post)

Metro officials will seek an independent assessment of more than 1,000 concrete panels installed at five rail stations being built as part of the Silver Line rail extension, following allegations the manufacturer used unapproved materials and instructed employees to cover up test results showing deficiencies.

The accusations were contained in a whistleblower lawsuit filed in U.S. District Court for the Eastern District of Virginia and unsealed Wednesday. The assertions by a former employee of Universal Concrete set off speculation about the fate of the $5.8 billion rail project, which already is 13 months behind schedule.

Officials from Universal Concrete, based in Stowe, Pa., have not responded to requests for comment on the lawsuit and its allegations.

Based on the unsealed lawsuit, “it’s necessary for Metro to look at this with our own independent contractor to ensure whatever remedies are applied to the concrete are ultimately safe for our passengers and our employees,” Paul J. Wiedefeld, Metro’s general manager, said in a statement Thursday.

Dan Stessel, a Metro spokesman, said it is not clear who will pay for the independent inspection or how long it will take to complete.

Construction of the Silver Line is overseen by the Metropolitan Washington Airports Authority, which hired Capital Rail Constructors (CRC), a joint venture between Clark Construction Group and Kiewit Infrastructure, to build it. But ultimately, it will be Metro’s responsibility to oversee and maintain the rail line, including a total of six new stations.

Wiedefeld said Metro would continue to collaborate with the airports authority. “But let me be clear,” he said. “Metro is committed to ensuring that any remedies are paid for by those responsible and that taxpayers and Metro customers are protected.”

As described in the lawsuit, the precast concrete did not meet specifications dealing with water content and air mixtures that could make it prone to problems with erosion and internal cracking.

The Silver Line is being built in two phases. The first phase included five stations that opened in July 2014, with four in Tysons Corner and one in Reston. The second phase, expected to open for passenger service in 2020, will include a stop at Dulles International Airport and extend Metro service into Loudoun County.

MWAA officials said Thursday their consultants would conduct their own review of the allegations, about flaws in the making of the precast concrete used on exterior walls at five of the six new stations being built in the median of the Dulles Toll Road and Dulles Greenway. The walls face the highways.

Some of the outside walls are designed to emulate bricks. The sealing that CRC plans to apply to the panels is designed to protect them from salt and water splatter from the adjacent roads.

Panels for the exterior walls at Dulles Airport station are being made by a different company.

“The Airport Authority welcomes this decision by [Metro] to have an independent contractor look into the conditions of the concrete panels,” officials said in an emailed statement. “MWAA, like [Metro], is committed to building a safe and durable Metrorail extension that serves rail customers and taxpayers.”

Officials at MWAA and CRC knew for nearly a year that there were problems with the panels after CRC inspectors uncovered some problems during a visit to the Universal plant, CRC has previously said. Issues with the concrete were noted in monthly project reports but in only vague detail and with no specifics on how many panels were affected.

It was not until earlier this month when news reports surfaced about problems that officials more fully acknowledged the issues.

And it was on Wednesday, hours before the lawsuit was unsealed, that CRC said roughly 20 percent — or just over 300 of the 1,569 panels — were flawed. Keith Couch, CRC’s project director, told MWAA’s board of directors that the company would deal with the issue by treating the panels every 10 years with a sealant to ensure materials meet the 100-year life span required in their contract.

MWAA and CRC had said the problems discovered with the concrete would not add to the project’s cost or delay its completion. But that was before the whistleblower complaint was unsealed, with allegations that problems could be more widespread.

On Thursday, officials from CRC reiterated a pledge to deliver the project on schedule and at budget.

“CRC is committed to providing a high-quality product that does not present any additional costs to the taxpayer and serves the community for decades to come,” Couch said.

The complaint against Universal was filed by Nathan Davidheiser, a former employee of the company. He filed it under the federal False Claims Act, which allows whistleblowers to receive a portion of any money the government recovers on behalf of defrauded taxpayers.

Davidheiser, who worked for Universal from July 2015 to February 2016, was responsible for testing the concrete for air content, a critical measure of the material because improper air ratios could cause water erosion, “weakening the integrity of the structure” and “potentially causing a collapse,” according to the suit.

According to court papers, Universal is a family-run company with 90 employees. The lawsuit said the company is owned by Donald Faust and that Davidheiser’s supervisor, Andrew Nolan, is Faust’s nephew.

The suit alleged Davidheiser and Nolan, lacked the certifications to properly carry out required testing in Virginia.

The Justice Department and the state of Virginia have joined the whistleblower lawsuit and said they will file a complaint in coming weeks.