Hundreds of cracks in concrete panels have been found on buildings at the rail yard being built near Dulles International Airport for the Silver Line, the latest in a growing list of construction problems that have plagued the multibillion-dollar rail project.

Officials at the Metropolitan Washington Airports Authority, which is overseeing construction of the next phase of the Silver Line, said cranes used to maintain the rail cars don’t meet “Buy America” requirements and will have to be replaced. And in another instance, a platform at a building where trains are parked had to be removed and rebuilt because it was built using the wrong dimensions.

Coming a week after The Washington Post reported that more than 400 concrete rail ties have flaws in them that can cause the tracks to tilt outward, the list of problems and concerns about oversight of the $5.8 billion rail project has forced project officials to concede that they may not make the August deadline they’ve set for completion of the rail line. The project is already 13 months behind schedule.

News of the cracked panels at the rail yard, first reported by NBC4, is the fourth major issue involving concrete to surface since construction of the Silver Line’s second phase began in 2015.

Previously reported problems, which included cracks in support girders, defective concrete paneling and flawed concrete rail ties, involve the portion of the project being built by Capital Rail Constructors, a joint venture between Bethesda-based Clark Construction and Kiewit Infrastructure.

CRC has pledged stricter oversight, particularly of its subcontractors, but problems have continued to mount.

This latest set of issues involves work by a different contractor, Hensel Phelps.

Charles Stark, executive director of the Silver Line rail project, blamed contractors for the problems.

“The only answer is the quality process is not being followed as vigorously as it needs to be,” he said. “We do have a quality assurance function, which is mainly to examine [our contractors’] paperwork and do quality audits to basically assure ourselves that the contractor is doing its job. Unfortunately, we don’t have the manpower to follow their folks around and to make sure they are doing their job.”

Hensel Phelps, a nationally known firm with offices in nine U.S. cities, has a contract worth more than $250 million to build the rail yard. William Thompson, vice president and district manager at the company, would not respond to specific questions about issues at the rail yard because the firm is in negotiations with the MWAA.

However, in a statement, the company downplayed the issue, characterizing the cracking as “minor.”

“The engineers and precast fabricator have determined that the issue is common in virtually all concrete that experiences heating and cooling cycles due to daytime heating and nighttime cooling.”

Stark said officials have received Hensel Phelps’s assessment but will conduct their own analysis before agreeing on a solution.

Project officials first discovered the cracks in July. In October, scans of the panels determined the cracking was not due to “missing or misplaced steel bars and changes in panel thickness.”

The cranes used to maintain trains were built in Germany and don’t meet “Buy America” requirements. They will have to be replaced, Stark said.

The rail yard was originally scheduled to open this month, but according to project documents, officials at Hensel Phelps said it would not be completed until May 2020 — a delay of 507 days. Project documents indicate that there have been schedule problems from the start and that company executives and officials from the MWAA have been at odds over the timing for months.

In its statement, the company said the delays were created by “circumstances outside of the control of Hensel Phelps, its design team and trade partners.”

Stark conceded that design changes did cause delays but said that Hensel Phelps shares some of the blame. Even so, he remained confident that despite the problems, the rail yard would be completed by next fall. In a statement Wednesday, Hensel Phelps concurred with that estimate.

The rail yard is a critical component of the Silver Line’s second phase. Metro already maintains four rail yards, including one at West Falls Church. But a yard near Dulles enables the agency to park and maintain the new trains it has added to its fleet and allows for more-efficient operations because it reduces the distance trains will have to travel to service the western end of the Silver Line.

The first phase of the Silver Line opened in 2014 and included four stops in Tysons Corner and one in Reston. The second phase will extend service to Dulles Airport and into eastern Loudoun County.

Metro officials said they are unwilling to accept the project unless both the rail line and the rail yard are completed as outlined in their agreement with the MWAA.

“The rail yard is a critical part of the project and necessary to support operations on the Silver Line extension,” said Sherri Ly, a Metro spokeswoman. “That’s why the extension and the yard get accepted at the same time. Metro will not be able to support rail service on the new segment without the yard.”

Problems with cracks in concrete panels have surfaced in other areas of the project, including at five of the six stations being built as part of the second phase of the rail line.

A whistleblower lawsuit unsealed earlier this year alleged that the panels were made from substandard material by a company that falsified test results. The company — different from the one that made the ties — began manufacturing the panels in 2015, but the problem was not discovered by CRC officials until last year. One person has pleaded guilty in connection with the case.

Those panels are scheduled to be treated with a special sealant to prevent further wear.