A multimillion-dollar project is underway at the underground facility to install a new ventilation system so that full operations can resume, following a radiation leak in 2014 forced the repository's closure for nearly three years.
Operations after it reopened had to be throttled back because parts of the facility were contaminated and airflow was reduced.
Federal officials have said that the construction project will ensure that the repository can meet the Energy Department's needs for disposing of tons of Cold War-era waste left behind by decades of bomb making and nuclear research.
But the Government Accountability Office report stated that the Energy Department faces construction and regulatory risks that might delay its plans.
According to Energy Department documents, the ventilation project as of last fall was projected to cost about $486 million, nearly 70% more than originally planned. The project also is about three years behind schedule, with a new estimated completion date of January 2026.
The Energy Department had blamed significant cost overruns and delays on the contractor’s inexperience and difficulties in attracting workers to the area, an expansive desert that is also home to one of the most productive oilfields in the world.
While some corrective measures were taken, department officials told the Government Accountability Office that they have not updated an internal system that is meant to track risks and mitigation measures.
Without the updates, Energy Department officials may not be able to meet their waste disposal schedule, "which could in turn create shipping delays and cost increases for the sites that are generating the waste,” the accountability office's report said.
The report reiterated that the repository is running out of permitted space for waste and that the Energy Department has a large amount of “transuranic waste” — which typically consists of lab coats, rubber gloves, tools and debris contaminated with plutonium and other radioactive elements — at sites around the country that still requires disposal.
The repository was carved out of an ancient salt formation about a half-mile (0.8 kilometer) below the surface, with the idea that the shifting salt would eventually entomb the radioactive waste.
Its current footprint includes eight panels, which the Energy Department estimates will be filled in 2025. There are plans for two new panels in the short term, but the report noted that it's unclear whether the new space will be ready in time to prevent an interruption of disposal operations.
New Mexico regulators also have yet approve permit changes and other requests from the Energy Department, and it's unclear how long that will take.
Department officials in a response to the report agreed with the recommendations aimed at addressing the root causes of the cost increases and construction delays to ensure “that DOE projects benefit taxpayers while reducing the risk to human health and the environment.”
Nuclear watchdog groups have been critical of the Energy Department. They have raised concerns about the repository's future, citing the increase in defense-related waste that will need to be disposed of when production of key components for the country's nuclear arsenal ramps up at Los Alamos National Laboratory in New Mexico and the Savannah River Site in South Carolina.