Millennium Tower owners assure homeowners the building is still safe and seismically sound despite sinking and tilting. pic.twitter.com/miYYFrTddU— Vic Lee (@vicleeabc7) September 20, 2016
Millennium Partners held their news conference on the same day San Francisco City Attorney Dennis Herrera formally subpoenaed them 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.
The exclusive residential Millennium Tower sits at the corner of Mission and Fremont streets in San Francisco.
RELATED: SF skyscrapers to be examined following Millennium Tower tilting
The developers said they held their news conference to stop what they called rampant, reckless speculation and behavior by Transbay officials.
The developers of Millennium Tower revealed that it's groundwater level dropped by a staggering 20 feet when the Transbay Joint Powers Authority or TJPA built an underground buttress wall between the tower and its transit site.
Millennium Partners blames sinking of the Tower On Transbay Terminal excavations which they say caused as much as 20 foot groundwater drop. pic.twitter.com/3CcSD5ZtNy— Vic Lee (@vicleeabc7) September 20, 2016
Millennium Partner founder Chris Jeffries said that caused the skyscraper to tilt two inches and sink 16 inches, far more than they expected. "If you dig a 60-foot hole and dewater for six years and drop the water table by 20 feet on a major high rise structure, you're going to cause a problem," Jeffries said.
WATCH VIDEO: Luxury skyscraper Millennium Tower sinking in downtown SF
Whats more, Millennium Partners said it should have been no surprise to Transbay engineers. "TJPA knew well before they began work on the transit and their site that their construction and in particular their de-watering of their site could have a significant impact," Meier said.
"We were promised it would have zero impact on groundwater in our building," Jeffries said.
The developers said the environmental impact study for the transit site required TJPA to install devices to measure water levels at Millennium Tower.
The building's engineers began inquiring about the unexpected settlement last year. After that, the engineers say Transbay turned off the measuring devices.
San Francisco Supervisor Aaron Peskin said there's perhaps a more important question here. "We know that Millennium Partners knew and the city knew and Transbay knew as early as 2009 that the building was sinking yet we failed to disclose that to the public," Peskin said.
Transbay officials said they are working on a response, but they have said earlier that the settlement problem was caused because the tower's foundation is on piles of dense, deep sand and not on bedrock.
The developers counter by saying that most of the building's foundations in the area are the same as the tower.
Click here to read the subpoena.
Click here for a look at more stories and videos about the Millennium Tower in San Francisco.