By Erin Sherbert
By Erin Sherbert
By Leif Haven
By Erin Sherbert
By Chris Roberts
By Kate Conger
By Brian Rinker
By Rachel Swan
The same report yields new information about the Navy's handling of a radium spill in another area of the base in January 1950, in which at least five students and other personnel were exposed. In that incident, a capsule containing about 40 milligrams of the highly radioactive material was inadvertently dropped in a laboratory at Building No. 233, a long-vacant, two-story wooden structure near the southeast corner of the island. It is deemed to have been the most serious radiological breach at the former base for which there is a record.
In a summary of the incident, the Navy referred to surfaces inside the building that couldn't be decontaminated as part of the cleanup operation. Last year, Dale Smith, the restoration advisory panel member, sought to know what became of the materials. The reply: that more than 200 barrels of radioactive waste generated from the spill was stored aboard the USS Independence at Hunter's Point Naval Shipyard and later the report does not say when weighted with concrete and "sunk at sea."
After more than half a century, and despite Building No. 233's having been cleared for reuse within a year, the decrepit structure across the street from a little league ball field has recently come under renewed scrutiny as part of the Navy's overall cleanup of the island in preparation for its presumed transfer to the city of San Francisco. Barely a month ago, after years of open access, the Navy erected a fence around it.
As for Area 12, not only does it harbor some of the most troublesome environmental pollution yet to be dealt with as part of the Navy cleanup, it's also perhaps the most seismically vulnerable part of the 405-acre island. Originally conceived as a site for San Francisco's airport and home to the Golden Gate International Exposition that opened in 1939, the island was constructed in the 1930s by the U.S. Army Corps of Engineers. To build it, the engineers dredged 29 million cubic yards of material most of it sand from the bottom of the bay and entombed it behind a perimeter rock dike.
Like the Marina District and other areas of the city built on fill, the entire island during a severe earthquake is susceptible to liquefaction, a phenomenon in which ground-shaking causes porous soil to turn mushy and collapse. In addition, geotechnical studies show that the areas closest to the dike including much, if not all, of the housing area that hugs the northwest shoreline are vulnerable to lateral spreading, in which ground-failure along a slope, in this case the dike, could be expected to spread laterally toward the island's interior.
Both phenomena occurred on Treasure Island during the 1989 Loma Prieta earthquake. Damage assessments compiled for the Navy describe "sand boils" appearing in the northern part of the island, a tell-tale sign of liquefaction in the underlying soil, and huge cracks several feet long in parking lots. Lateral spreading was blamed for some 44 gas, sewage, and water line breaks that disrupted services on the then-still-occupied base for up to three days after the quake.
The Loma Prieta quake registered 7.1 on the Richter scale. U.S. Geological Survey data indicate that ground motion on Treasure Island was among the strongest recorded in the Bay Area, despite the island's being some 60 miles from the epicenter.
However, the 1990 report compiled for the Navy following the earthquake, and obtained by SF Weekly, suggests that what happened on the island in 1989 pales compared to what could happen there during a similar or more powerful quake along either the San Andreas or Hayward faults with an epicenter closer than Loma Prieta.
It warned that such a quake could cause "substantially more severe shaking" on the island; that "liquefaction [could be] expected to be widespread," and that lateral spreading accompanied by liquefaction poses "a significant risk of widespread distress to the perimeter areas of the island during future large earthquakes."
The document concluded that "unless remedial measures to the dikes are implemented," lateral spreading during a magnitude 8 quake on the San Andreas fault could extend "several hundred feet into the island and thus encompass large portions of the island's interior." In that scenario, the report said, buildings such as those that constitute much of the housing stock in Area 12 could be "severely damaged."
The lease provided to tenants by the John Stewart Co. is straightforward in disclosing the seismic issue. It quotes from a geotechnical report prepared for the city in 1995 that concluded that the island's soil is of "poor quality and [is] subject to liquefaction and soil displacement (spreading)" similar to that of the Marina District. "That same report established that the areas located within 500 feet of the perimeter island seawall (dike) will be subject to the greatest soil displacement and spreading, and would consequently be subject to the most serious damage in the event of major earthquake," the lease states.
City officials, meanwhile, have long insisted that the island's current residents do not face unacceptable seismic risks. "All of us in San Francisco live with the risk of earthquakes," says Michael Cohen, who heads the mayor's Office of Base Reuse and Development. Cohen says that consulting engineers took seismic issues into account before certifying that the former base housing meets federal standards for "life safety" before the units were opened as rentals in 1999.