SAN FRANCISCO (KGO) -- City Attorney Dennis Herrera has formally subpoenaed Millennium Partners as part of his office's investigation into whether the developer complied with state law by disclosing known structural sinking issues to purchasers of more than 400 residential units in the Millennium Tower.
RELATED: SF skyscrapers to be examined following millennium tower tilting
The exclusive residential Millennium Tower sits at the corner of Mission and Fremont streets in San Francisco. The 58-story building is sinking and titling. The foundation of the tower is supported by piles deep into dense sand but not into bedrock like many other buildings here. It turns out, some of the city's best known skyscrapers are also built the same way including the Embarcardero Center, the SF MOMA and the Marriott and 101 California.
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WATCH VIDEO: Luxury skyscraper Millennium Tower sinking in downtown SF
The Millennium's Homeowners Association has launched its own investigation. ABC7 News has learned they've hired consultants, who'll begin seismic testing and sample drilling on their building September 26.
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Now the residential tower is sinking 16 inches and perhaps more concerning, its tilting almost two inches.
Click here to read the subpoena.
Click here for a look at more stories and videos about the Millennium Tower in San Francisco.