Millennium builder fights back, says public agency caused sinking

The Millennium tower on the left, across the street from the location of a new proposed plaza tucked into the southwest corner of the intersection of Mission and Fremont Streets next to the new Salesforce Tower on the right in San Francisco , Calif., on Monday, August 29, 2016. less The Millennium tower on the left, across the street from the location of a new proposed plaza tucked into the southwest corner of the intersection of Mission and Fremont Streets next to the new Salesforce ... more Photo: Carlos Avila Gonzalez, The Chronicle Buy photo Photo: Carlos Avila Gonzalez, The Chronicle Image 1 of / 18 Caption Close Millennium builder fights back, says public agency caused sinking 1 / 18 Back to Gallery

The developer of the sinking Millennium Tower in downtown San Francisco went on the offensive Tuesday, charging the public agency building the new Transbay Transit Center with causing the structural issues by pumping hundreds of millions of gallons of water from the ground during construction.

At a news conference at the Four Seasons, also built by Millennium Partners, founder Christopher Jeffries said the water table under the condominium high-rise at 301 Mission St. dropped 20 feet during construction of the adjacent transit center. The dewatering caused the compression and weakening of the soil under the Millennium Tower’s foundation, he said.

“A pattern of reckless behavior by TJPA over the course of several years caused the settlement issues at 301 Mission,” he said. The Transbay Joint Powers Authority is building the new transit center, a replacement for the old Transbay Terminal that will be a hub for numerous bus services and could one day house a California high-speed rail station and an extension of Caltrain.

Since August, the question of what is causing the sinking and tilting of San Francisco’s most expensive and luxurious residential tower has prompted accusations among the developer, the joint powers authority, the condo owners and city politicians.

The Millennium has sunk 16 inches since opening in 2009, far more than the 6 inches the builder initially anticipated. In May, a geotechnical engineer hired by the homeowners association warned that the tower was still settling at a rate of about an inch a year. The building is also tilting 2 inches to the northwest at its base, according to engineer Patrick Shires.

Jeffries said the dangers of dewatering, and the need to track closely how the Transbay project was impacting the soil beneath surrounding properties, were the source of extensive negotiations between his company and the authority starting in 2009.

Millennium Partners raised the dewatering issue with the joint powers authority and the city Department of Building Inspection in 2009 after concluding that its own dewatering activity prior to 2008 was causing its tower to settle more than expected, Jeffries said.

Using sumps or wells, builders dewater sites to create dry and safe excavation conditions. But if not sealed off from adjoining properties, dewatering can have an adverse impact, lowering the water table and compressing the soil.

Those concerns were incorporated into an easement agreement between the authority and the developer that requires the public agency to monitor the water table and track the Millennium’s settlement.

A groundwater monitoring device called a piezometer, controlled by the authority, was installed in the basement of the Millennium. The agreement allowed the groundwater level to drop by 3 feet — any more than that and the authority was required to take measures to bring the level back up to prevent the building from sinking, according to the agreement. The piezometer was shut off in June 2015, according to a report done for the authority by the engineering firm Arup.

“We were promised zero impact on groundwater under our building,” said Jeffries. “They couldn’t affect our building. They knew it. Their engineers knew it.”

The joint powers authority has repeatedly said that the tower’s structural problems were in evidence prior to the start of construction of the transit center in 2012. In a statement released on Sept. 13, the authority said that the building’s “excessive movement is attributable to (Millennium Partners’) inadequate foundation, which does not reach bedrock.”

“The TJPA’s work is not the cause of the continued tilting and excessive settlement of the Millennium Tower,” the agency’s statement reads.

Jeffries scoffed at the idea Millennium Partners erred by driving 80-foot piles into dense sand rather than 200-foot piles into bedrock. Before the Millennium project, no building in downtown San Francisco had piles driven into bedrock, he said. Since then, four projects have broken ground with piles that reach bedrock — all are developments on joint powers authority land: 181 Fremont, the Salesforce Tower at 101 First St., Park Tower at 350 Howard St. and the Transbay Transit Center itself.

“The state of the art of foundation design in San Francisco has not been to go to bedrock,” he said. “The only buildings built to bedrock are these four. This represents a dramatic change in how buildings are designed in San Francisco, and it’s a standard that has all of a sudden been imposed in the press as what everyone should be doing in San Francisco.”

He added: “We did this building the right way.”

Also on Tuesday San Francisco City Attorney Dennis Herrera subpoenaed Millennium Partners. He wants to know if the developer disclosed the structural issues to buyers of condominiums in the building.

“I have serious concerns that the disclosures required by state law … did not contain information about the settling of the Property,” Herrera wrote to the developer.

Millennium says that the building sold out in 2013, before the issues of severe settling had emerged.

“We are a little surprised by the subpoena — we would have handed over the documents if they had called,” Millennium Partners founding director Philip Aarons said. “There has never been anything that we were hiding.”

Millennium executives also made a plea that the authority cooperate with their request for information about the dewatering.

“In order to fix and solve the problem we need to have the information, and we have not been able to get the information from the TJPA,” Jeffries said.

On Thursday, San Francisco Supervisor Aaron Peskin will hold a hearing on the Millennium Tower. He wants to know if city building inspectors were aware of structural flaws while the building was being planned and constructed.

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com

Twitter: @sfjkdineen