The San Francisco Department of Building Inspection was notified that the Millennium Tower was sinking about the same time the first owners started moving into the luxury high-rise in 2009, documents obtained by NBC Bay Area show.
According to the documents released Friday, the engineering firm on the Millennium project alerted the city in early 2009 that the building had sunk 8.3 inches and could sink another four inches.
The findings were summarilzed in a Feb. 25, 2009 letter the Millennium project's engineering firm DeSimone Engineers sent to the city, according to documents obtained NBC Bay Area obtained under the state Public Records Act.
The issue of the extent of sinking had become an issue at this point with the transit project being next door by the public Transbay Joint Powers authority, an amalgam of public agencies.
The chief engineer for the authority, Brian Dykes, reminded the developer in a Jan. 14, 2010 about the fact that the findings DeSimone Engineers had told the city about the year before. The actual Feb. 25, 2008, letter the firm sent to the city, however, has not been disclosed.
According to Dykes, the soils firm Treadwell and Rollo's findings were included in that letter DeSimone sent to the city.
Dykes then pressed the builder further about the cause and nature of the sinking problem.
Treadwell and Rollo, according to Dykes, blamed the problem on too much dewatering of the foundation. The basement of the building routinely flooded with ground water. Such draining removes tiny particles that help hold clay together, and the drying can cause soil settlement, experts say.
According to Dykes' letter, the soils firm also cited the "limited effectiveness" of pre-drilling method used to install the piles that were driven 90 feet down to support the foundation. Pre-drilling is supposed to limit the disturbance to surrounding soils by the pile driving process. It is designed to assure that soil is not so disturbed that it can cling to the piles and hold them in place by friction.
While the transbay project authority released its letter to the builder, it did not provide the builder's response. Dykes was out of the office and not available for comment Friday. Treadwell and Rollo has declined comment on the matter.
A Department of Building Inspection spokesman said that the staff of the agency "had no recollection of any such notification."
William Strawn, in an email statement to NBC Bay Area, added: "We are still gathering all our records on this address - so it is theoretically possible that such a notification is among these records....I simply cannot say whether it exists or not at this time," Strawn said.
However, he said that "such a notification would receive immediately a demand that they provide the department with a detailed engineering report documenting their findings, and providing DBI with their proposed remedy to stabilize such settlement."
The burden is on the builder to notify the residents, he said. "They built the building and sold the units, not the City."
As to issuing certificates of occupancy for the building at the time, Strawn said that the agency would not issue them "unless all reviews have been completed and signed off by appropriate inspectors and special inspectors. The fact that we did issue these suggests to me we had no such notification, as alleged."
Charlie Goodyear, a spokesman for the Millennium Tower Association said the owners group "has recently been made aware of correspondence dating back to 2009 regarding settlement of the building."
The association is investigating to "determine whether information should have been made known to the Association and to owners within the building."
He said the owners have independent experts and is "assured that the building is safe."