The sinkhole, which is about 20 feet in diameter and 10 feet deep, was reported around 5 p.m. Monday at Lake Street and Second Avenue, SFPUC spokesman Tyrone Jue said.
Investigators believe the sinkhole occurred when a 19-inch brick sewer line below the roadway ruptured, Jue said. Crews estimate that the line is at least 100 years old, he said.
"Once those things break or start to deteriorate, the roadway just starts to give way," he said.
Residents had recently reported a depression in the roadway, and crews came and laid out an additional asphalt base in the intersection, but "the break happened before we could even get our inspection crew out there," Jue said.
He said the investigation is expected to wrap up today, and crews will spend the next three days completing repairs.
"Hopefully by Friday we should be out of there," he said.
The sinkhole is "a classic example of what happens when you have an aging sewer infrastructure," Jue said. "As our system ages, we'll continue to see more and more of these, and that's why we're investing a lot of money into the infrastructure."
The Presidio Heights repairs are expected to cause minor traffic delays in the area this week, he said.
