Mulberry Street in downtown Baltimore could be closed for weeks because of a growing sinkhole that may have developed undetected even as crews worked recently to replace a water main on the busy commuter thoroughfare.
On Tuesday, a city inspector who tumbled into the crater when the road gave way beneath him a day earlier was released from the hospital.
The hole initially spanned a single lane of the three-lane eastbound artery, but a day later stretched from one sidewalk to the other, between Paca and Greene streets.
Mulberry is the latest instance of failing infrastructure causing sinkholes in the area. A sewer main collapsed in Mount Vernon in April. Last month, a break in a city-owned water main caused a sinkhole in Cockeysville.
City transportation officials said they would release a traffic advisory Wednesday suggesting detours around Mulberry Street, a key west-to-east thoroughfare that carries U.S. 40 across downtown.
Crews are still investigating how the earth eroded beneath the busy street, which is paved with concrete. City officials believe a leak from a water pipe serving a single building is responsible.
Just feet south of that pipe, a narrow trench of fresh asphalt shows where a 20-inch water main was replaced about three weeks ago. But there was no sign of trouble during that excavation, officials said.
"There was no visible water," said Art Shapiro, chief of engineering and construction for the Department of Public Works.
A buckle in the road first appeared about a week ago, officials said.
They said they don't know how long the water pipe had been leaking. That's because the leak was contained under concrete — a material likely chosen to pave the heavily trafficked roadway because it is more durable than asphalt, officials said. But had asphalt been used instead, water may have come bubbling to the surface, offering a warning before causing the street to collapse, they said.
Sinkholes can develop when water erodes dirt underneath pavement. In some cases, such as a sinkhole that stretched across East Monument Street near Johns Hopkins Hospital for six months in 2012, rainwater is to blame.
But in others, leaks occur as old infrastructure fails and continue unmonitored because crews have no way of knowing about them until something goes visibly wrong.
The Public Works Department replaces 15 miles of water mains each year to prevent breaks and sinkholes, officials said.
In this case, that effort did not catch the leak because the faulty 8-inch-wide pipe was not as high a priority as the larger main nearby due to its small size, Shapiro said. The pipes underneath Mulberry Street date to the 1930s or 1940s, he estimated.
There were no signs that repairs to the roadway were needed, and officials do not believe water seeped through joints between concrete slabs, said Adrienne Barnes, a spokeswoman for the city transportation department. Even if the roadway had been paved with asphalt, she said, a sinkhole still would have happened.
Information was not immediately available about how recently the road was paved, when and where utility work required cuts into the concrete or how many motorists travel on it daily, Barnes said.
Public works officials said they will continue to investigate what led to the Mulberry Street leak and the sinkhole.
There were signs of damage to an 80-inch sewer main along the same stretch, and officials said one theory is that the main carried away dirt that eroded from beneath the roadway. Sewage is moving more slowly than normal through the main, Shapiro said.
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"What we have to determine is what was the cause and the effect," city public works spokesman Jeff Raymond said.
Public works crews don't know yet what repairs are needed to the underground infrastructure — and must address that before work to restore the roadway can begin. Shapiro said he expects work will include repairing what is likely a concrete sewage main and checking the integrity of the newly installed water main, which no longer has dirt supporting it. As a result, officials said, the damaged section of Mulberry Street is likely to be closed for weeks.
The incident comes about two months after a crater opened up on Centre Street in Mount Vernon because of a crumbling sewer main. Between Park Avenue and Charles Street, Centre Street — another west-to-east thoroughfare across the city — was closed for weeks. It is partially reopened, though repair work there is expected to continue for several weeks more.
In Cockeysville, a portion of York Road was closed for days after a water main ruptured June 20, washing away a lane of traffic near Thornton Mill Road and interrupting water service for thousands of residents. It took city crews two days to fix the main before the road could be repaired.