Phase II of the Silver Line is expected to open in 2020. (Jahi Chikwendiu/The Washington Post)

A contractor admitted Friday to falsifying concrete quality tests while working on stations for the Metro Silver Line extension to Dulles International Airport, part of a scheme that cast doubt on the durability of the $5.8 billion project.

“I falsified data recording for concrete testing for the air quality of the concrete, and I instructed others to do the same,” Andrew Nolan, 28, admitted in federal court in Alexandria.

Nolan pleaded guilty to conspiracy to commit wire fraud and faces up to five years in prison. He also owes $700,567 in restitution to the Metropolitan Washington Airports Authority, which is overseeing the project.

The concrete used for outdoor panels for stations on the extended rail line was consistently below the required 4 percent air content quality standards, Nolan said in court. The Justice Department is also suing Nolan’s employer, Universal Concrete, which manufactured the low-quality panels as part of a $6.1 million contract.

Issues with the concrete panels on the Silver Line project became public in April, when the executive director of the project announced that the lead contractors had identified problems with 1,500 precast panels installed at five of the six new stations that could lead to water seepage and premature deterioration of the station walls.

According to the lawsuit filed in July by the Justice Department and the state of Virginia, management at Universal Concrete learned that workers had falsified records that were intended to verify the quality and longevity of the panels that were being brought in for installation on the project. But those managers failed to bring those issues to light, the lawsuit said — and instead, supervisors fired a company official who had pushed for an internal audit to root out the wrongdoings.

The lawsuit alleges that the falsification of those records began before October 2015 and lasted until at least February 2017.

The Silver Line extension is being overseen by the Metropolitan Washington Airports Authority, and financed in part by $300 million in funding from the state of Virginia, along with $2 billion in loans from the federal government. The project will open six new Metro stations, bringing the rail line out to Dulles International Airport and into Loudoun County.

Although the timeline of the project has been delayed from original projections, it’s now expected to open in 2020 — and officials with the project say that the complications with the work done by Universal Concrete won’t prevent them from hitting that delivery date.

Capital Rail Constructors, which is overseeing the whole project, has said the panels can be reinforced with sealant and that construction can move forward on time and within budget.