SAN FRANCISCO (KGO) -- There's a major milestone for a billion dollar transportation project in San Francisco.
RELATED: San Francisco Central Subway line opening delayed
Once completed in 2019, the Central Subway Project will extend Muni Metro service all the way into Chinatown. Now, one of the subway stations is getting its first pour of concrete.
Seventy cement mixers were lined up around Union Square for the big pour. It all happened deep below the earth.
"We reached the bottom, it's an all day pour," said project manager John Funghi.
Tons of cement were pumped down from Stockton Street to the ground level of the future Union Square Station on the Central Subway Line.
RELATED: Crews finish building tunnel for Central Subway Line
"Hundreds of people working underground," Funghi added. "You don't see it topside."
Crews poured 700 cubic yards of cement.
A dispute between the MTA and the contractor could delay the opening of the subway project by 10 months-- 2019, so it's now a game of catch up.
"We're working hard with the contractor to make up the time," said SFMTA spokesperson Paul Rose.
Those who work and shop in Union Square long for the day when Stockton St. is reopened.
"It's going to be great to get Stockton St. back, so many tourists are confused," said food vendor Kelsey McCormack. "I don't know where to go."
The $1.6 billion subway project will take riders from AT&T Park to Chinatown.
San Francisco Central Subway Project reaches milestone as concrete poured
CENTRAL SUBWAY PROJECT