An audit by NASA's inspector general questioned whether it was the best use of limited funds and urged the agency to re-examine its cleanup plans for the Santa Susana Field Laboratory, where the federal government and other parties conducted nuclear research and tested rocket engines for four decades.
Several of the site's former users, including NASA, are required by law to remove contaminated groundwater and soil from the site by 2017.
NASA estimated it would cost at least $200 million to reduce pollution to background levels at its portion of the 2,850-acre hilltop complex about 30 miles northwest of Los Angeles. The NASA section will be preserved as open space once it's decontaminated.
NASA "can ill afford to spend tens of millions of dollars to clean up an area beyond its risk level or expected land use," the report said.
The inspector general's office said Santa Susana is not NASA's only worry.
"Several other projects pose greater risks to human health and the environment than Santa Susana," the report said.
During the Cold War, workers at the sprawling site tested rockets and experimental nuclear reactors.
In 1959, one reactor's coolant channels became blocked, causing fuel rods to overheat and partially melt.
By the time the lab closed in late 1990s, decades of testing and several accidents after the partial meltdown contaminated the soil. Residents and environmentalists have criticized the slow pace of the cleanup.
In a response attached to the audit, NASA did not specifically address the concerns raised. The agency said it will continue to work with the state Department of Toxic Substances Control, which oversees the cleanup.
Along with NASA, the Energy Department and Boeing Co. are also responsible for returning the site to its natural state. The internal audit only dealt with cleanup efforts involving the NASA portion of the lab.