The subterranean collapse of a 19th-century stormwater drain near Lake Montebello created a sinkhole that is also sucking in more and more taxpayer money.

What was once predicted to be a $10 million fix has ballooned to at least $30 million, according to financial documents from the city. And that cost could keep rising.

“Given the nature of our work, there could still be potential for adjustments based on unforeseen conditions encountered during the construction process,” Mary Stewart, a spokesperson for the Baltimore City Department of Public Works, said in an email. “We want to stress that this project was an emergency, which required immediate action to protect public health and safety.”

The sinkhole was caused by a collapsed drain — basically a giant pipe — that carries stormwater underground and dates to 1876.

The stormwater drain replaced Tiffany Run, a river that fed into Herring Run, effectively burying it underground and out of sight.

But Tiffany Run never went away, and when the drain started to collapse, the river found its revenge.

Officials realized that something was wrong in summer 2020 when a storm caused severe flooding nearby. By November 2022, a sinkhole became visible, the ground was unstable, and the problem could no longer be ignored.

Excavating tons of dirt and rock, replacing the collapsed stormwater drain, and reburying Tiffany Run has been complex and costly.

The sinkhole opened near Lake Montebello, a reservoir used by the nearby water filtration plant.

In February 2023, the Department of Public Works expected the fix to cost $10 million and last two months. Neither estimate was correct.

In July 2023 the department asked city officials to move $11 million into a fund specifically for this project.

Worked continued into 2025. Earlier this year, the Department of Public Works asked that an additional $19 million to be moved into the Tiffany Run project.

“What began as a sinkhole roughly the size of a basketball revealed the urgent need to overhaul century-old infrastructure beneath Lake Montebello,” Public Works Director Khalil Zaied said in a news release about the project.

This month, after more than two years and $30 million of work, the 1.3-mile path around Lake Montebello reopened.

But it won’t be open for long. After the Baltimore Running Festival in October, officials will shut down the loop for another overdue project: dredging Lake Montebello, which is expected to last two years.

The cost of that project is still unknown. Public works officials will ask the city’s spending board next week to reject all bids for the dredging work.

Banner reporters Clara Longo de Freitas and Adam Willis contributed to this story.