More than 100 feet below Stockton Street in San Francisco’s Chinatown, crews are working to complete the future site of Muni’s Chinatown station as part of the 1.7 mile Central Subway.

Officials with the San Francisco Municipal Transportation Agency on Tuesday announced that the construction of the station hit a milestone, with crews completing the excavation of the 12-story deep structure.

While crews completed the excavation of the Chinatown station, the entire $1.6 billion project is still a year behind schedule, said transit officials.

Much of the delay stems from the method of construction chosen for the Chinatown station.

Albert Hoe, the acting project manager of the Central Subway, said method is called the “New Austrian Tunneling Method,” which has only been used in one other transit tunnel project in the United States in Seattle.

Hoe said construction crews are doing most of the work underground instead of above ground to minimize Chinatown businesses affected by the construction, but said the method was one of the most challenging parts of constructing the Chinatown station:

“It’s not typical. We learn as we go.”

Businesses owners have said the construction of the subway has played a role in lost revenue. The City did eventually step in to provide some funding relief to Chinatown merchants from the Office of Economic Workforce and Development while working the late Mayor Ed Lee and Supervisor Aaron Peskin, who represents Chinatown.

While other future stations such as one at Union Square and Yerba Buena/Moscone are further ahead in progress, there was some talk from the former project manager John Funghi on partially opening the Central Subway.

SFMTA Director of Transportation Ed Reiskin said that is a possibility but highly unlikely the transit agency will open the subway until the completion of the Chinatown station:

“It won’t benefit much and it may complicate getting the overall project done.”

Crews on Tuesday were waterproofing the station with a yellow PVC material, said Hoe. After the waterproofing is complete, crews will work on pouring the concrete followed by electrical work.

Mayor Mark Farrell joined transit officials on a tour of the future station. Farrell said to reporters: