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Toxic Acres 

The fill below Treasure Island is filled with dangerous toxins left by the Navy

Wednesday, May 24 2006
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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.

The firm responsible for the certification was Toft, de Nevers & Lee, engineers for the John Stewart Co. But a 1999 letter from C. Vincent de Nevers, one of the firm's partners, didn't sound like a ringing endorsement. "It continues to be my opinion that a significant seismic event could produce extensive structural and therefore economic damage [in the housing area] without resulting in material life safety impairment," de Nevers wrote. "Only in the unlikely event of a very major ground shift ... do I foresee the possibility of injury to occupants."

His assertion that the possibility of such a ground shift was "so remote that it constitutes an acceptable risk" even prompted a friendly corrective from Michael Cohen, in his then-capacity as a deputy city attorney. "I want to clarify that at no point in time has the city and county of San Francisco or the Treasure Island Development Authority (or anyone else that I am aware of) agreed that the possibility of a major seismic movement ... is so remote that it constitutes an acceptable risk," Cohen wrote. "To the contrary," he added, the city was relying on de Nevers' "written certifications" that the housing units met Federal Emergency Management Agency guidelines for "life safety."

No major seismic reinforcement around the perimeter dike has occurred in the 16 years since the Navy's consultants first raised the issue after the Loma Prieta quake. And none is anticipated until after construction of the hoped-for Treasure Island redevelopment project gets started, which, under the most optimistic scenario, may be at least three years away.

About The Author

Ron Russell


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