SAN FRANCISCO (BCN) — City building officials Thursday said they did not launch an investigation into structural problems in a South of Market high-rise that is sinking more than expected until after they began receiving media inquiries this summer, despite reports of excessive settlement dating back to 2009.

In a hearing at San Francisco City Hall Supervisor Aaron Peskin questioned officials with the Department of Building Inspection to determine “who knew what, when they knew it and what they did about it” with regards to the troubled Millennium Tower at 301 Mission St.

The 58-story building, which is built on landfill, has sunk as much as 16 inches so far and is leaning around 15 inches to the northwest at its peak. Current projections suggest it could ultimately sink more than 30

inches.

Peskin has previously said he believes city officials and the developer, Millennium Partners, were aware that the building was sinking more than expected as far back as 2009, but failed to notify buyers of the building’s more than 400 units.

Department officials Thursday acknowledged that engineer Raymond Lui sent Millennium Partners a letter in February of 2009 asking about reports of excessive settlement in the building.

The developer’s responses indicated that the building had sunk more than 8 inches by that time, beyond its expected lifetime settlement, but that the building was still considered safe.

However, officials were vague Thursday on whether that response was seen by anyone in the department other than Lui or whether any further action was taken. Final certificates allowing the building to be occupied were issued in September of 2009.

Department spokesman William Strawn said the department became aware of the current concerns about the building in July, when it began receiving media inquiries, and sent a team out to conduct a visual inspection. However, that team apparently found no cause for concern at that time.

Millennium Partners also forwarded a copy of a 2014 draft engineering report on the building’s settlement that month. The department plans to meet with the author of that report for an update in the near

future, Strawn said.

Media reports about the sinking building surfaced at the beginning of August, and a class action lawsuit representing property owners was announced on Aug. 9. U.S. Sen. Dianne Feinstein also sent a letter dated Aug. 10 to Mayor Ed Lee, expressing “increasing alarm” about the reports.

But the department did not take formal action until an anonymous complaint was called in to the city’s 311 line from a neighbor of the building on Aug. 16, according to Assistant Director Ron Tom and Director Tom

Hui. Building inspectors were sent out on Aug. 19 and a notice of correction was issued on Aug. 26 asking the building’s management to produce an updated engineering report.

Peskin expressed incredulity that the department did not act on Feinstein’s inquiry or media reports, but did respond to an anonymous complaint.

“I’m just asking, what does it take to get you guys to take something seriously that it might be a life and safety hazard?” Peskin asked.

Tom said code enforcement efforts are largely complaint driven, and the department does not have the resources to act in the absence of a complaint.

“Just in general, we are not monitoring the behavior and safety of every building in San Francisco,” Tom said.

Tom said the department is now working to determine if life safety systems including elevators and gas and water connections were threatened by the building’s settlement.

The sinking tower has become the subject of finger pointing, with developers blaming groundwater pumping at the neighboring Transbay Terminal construction site for the excessive settlement. The Transbay Joint Powers Authority in turn has said the building’s foundation design, which is not anchored into bedrock, is at fault.

City Attorney Dennis Herrera also issued subpoenas this week to Millennium Partners in an investigation into whether buyers received proper notification of potential structural issues.

Attorney Denis Shanagher, who is representing the homeowners association, Thursday said no homeowners had received such notifications to his knowledge.

Evette Davis, a spokeswoman for the association, Thursday said that homeowners planned to independently hire engineers to conduct an analysis of the building.

“As everyone knows, the homeowners of the Millennium Tower are in the unfortunate position of trying to go about their lives as if nothing has happened, while attorneys work to learn the facts and assign responsibility,” Davis said.

“Given the circumstances, the … Association cannot stand by and rely on others to interpret their own versions of the facts about the safety of the building,” Davis said.

Mayor Ed Lee Thursday said he has asked city officials to strengthen building codes and independent review processes for current and future high-rises, to amend the city’s 30-year earthquake safety plan to expedite the safety of high-rise buildings and to review failure mitigation measures for buildings in geographically hazardous areas.