The U.S. Navy disclosed Tuesday that it recently uncovered a “basketball-sized” chunk of low-level radioactive dirt buried beneath the front door of a Treasure Island home.
The Navy did not specify when or where exactly it unearthed the contaminated find among the cluster of 650 two-story townhomes spread around the island’s northwest corner called Site 12—or if the home was occupied—but did note that the radioactive dirt was not discovered during a prior scan, according to military branch’s five-paragraph information bulletin.
The military branch said the site posed “no health risk to local residents or the public” based on the “results of [a] pre-excavation scan, which found no elevated radiation levels” as well as the later excavation work.
It remains unclear how the radioactive “basketball” escaped earlier detection efforts. Other earlier scans have turned up radioactive radium discs and flakes of metal or paint under as much as 10 inches of concrete in Treasure Island homes.
The Navy did not immediately respond to requests for comment.
Responsible for cleaning the polluted former base and future site of 8,000 housing units, the Navy said that the since-removed hot dirt posed no threat to the island’s 1,800 current residents. Still, the the discovery of more radioactivity in an area thought to be clean of such pollution will raise questions amid other concerns about the project’s long-term viability.
Comprised of 403 acres of dredged bay bottom surrounded by artificial rock reefs, Treasure Island, built for the 1939 Golden Gate International Exposition, was later used as an ammunition dump, airfield, and training center for Cold War-era radioactive “decontamination.”
Trash found in old Navy landfills—where Navy housing was later built—includes radioactive material like deck markers or other sources of radium, a radioactive element most often used to make dials, gauges, and other surfaces glow in the dark.
The Navy vacated the island in 1998. Old military housing was turned over to the city for low-income housing, including Section 8 recipients and formerly homeless and incarcerated people in supportive housing.
Treasure Island qualified as one of the country’s most polluted sites and a priority for federal cleanup.
But, as the public advocacy organization Public Employees for Environmental Responsibility (PEER) revealed on Tuesday, unlike the other former Navy base and shipyard at Hunters Point, Treasure Island was never named an EPA Superfund site.
The ongoing redevelopment at Hunters Point, where several hundred units are sold and occupied, is embroiled in lawsuits after the contractor hired by the Navy to remove radioactive soil there was found to have faked its work, according to federal prosecutors.
But at Treasure Island, some of the Navy-built low-income housing units, it was later discovered, were built on top of petroleum spills and on top of areas where Navy personnel burned toxic trash. These have since been vacated and in some cases demolished.
Early assessments of Treasure Island contamination downplayed the possibility that the area was polluted with radioactive elements. But in 2006, the Navy allowed that radioactive material, including items contaminated with radium and thorium, which was likely dumped in the trash heaps upon which homes were later built. Other areas were likely not “radiologically impacted,” the Navy said at the time—an assessment that would later be found to be off.
A series of contractors hired by the Navy tasked with removing contamination have steadily found more radioactive material in unexpected areas. According to a Reuters investigation published earlier this year, in February 2011, the Navy discovered radioactive items under a schoolyard, “an area it had vowed had no contaminants.”
Contamination present at Treasure Island includes chemicals like dioxin and petroleum byproducts. Past discoveries of radioactive material in occupied housing on Treasure Island have triggered outcries from members of the public and the occasional elected official, as well as a Navy effort to determine what other radioactive material may have been missed.
A transformation of the windswept artificial plain into a tightly-packed new neighborhood of upwards of 15,000 people—mostly in high-density residential mid-rises, with nearby parks, shops, and office space—is underway. Construction will begin in earnest next year.
In addition to a wider search for radioactive material approved last year, other ongoing work at Site 12 includes the excavation of chemical spills.
Some of the island’s current 1,800 residents have been promised they can stay, but their new homes and the roughly 1,400 other units of affordable housing planned for the island will require another $170 million in funding.
City officials have not immediately addressed the find. The city’s myriad of housing goals can’t be met without building on Treasure Island.