Update: June 25

  • Emergency repair work to fix a washed-out section of sewer infrastructure was completed earlier than expected: SEPTA reopened the road for the Route 34 trolley on Monday, June 24.
  • Tonight, Tues. June 25, PWD will offer a talk with historian Adam Levine about the local Mill Creek sewer, which began construction 150 years ago this year. 
  • The University of the Sciences will host the free public event, with doors opening at 6:15 p.m. at 600 S. 43rd St. 
  • The event will be taped and broadcast live: Mill Creek Talk Livestream

At the risk of quashing a blossoming and dedicated club of Mill Creek sewer infrastructure/sinkhole aficionados in West Philadelphia, we just have to say it:

It is not, technically, a sinkhole.

While most people call any hole in the street a “sinkhole,” those are natural, geological phenomena caused by limestone eroding and creating holes and caverns, or more generically, depressions where drainage collects.

And the site everyone is talking about? It isn’t actually THE infamous Mill Creek Sewer. Rather, what folks are seeing is a part of the system that feeds into what was once the creek.

FREE EVENT: Philadelphia Water Department in-house historian Adam Levine will offer his Mill Creek: Stream to Sewer presentation on Tuesday, June 25 at the University of the Sciences.

We will also present the latest information regarding the state of the repair work.

Tickets are recommended not but required.

Everyone OK?

Alright then, to the facts!

We are, of course, speaking of the much-covered and ogled construction site where an issue with a sewer—call it a wash-out or cave-in—eroded a copious amount of soil beneath Baltimore Avenue at 43rd Street.

That created a large gap between the road and the top of a smaller sewer that is not the Mill Creek Sewer.

“This is actually good news in some ways, considering that it would have been much worse if the actual Mill Creek sewer failed,” says our resident historian, Adam Levine. “If that had happened, it could have been a 40-foot deep hole the size of a house. We could have been out there for months and months.”

As it is, the hole that was excavated to make repairs—PWD work should be finished by the end of June—was about 12 feet deep (and 25 feet at the deepest point of excavation). Reports about a three-foot-wide hole began to come in on June 4, and the intersection was immediately closed:

An inspection revealed the large washed-out area beneath the street. With considerable help from a jackhammer-equipped backhoe, the cavernous maw that has since spawned everything from “Sinkhole Pizza Parties” to buttons that boast surviving “Sinkhole Summer 2019” was uncovered:

What's Next for the Neighborhood?

Once our sewer work is done, getting the intersection back open could take more time, as we coordinate with SEPTA to get the Route 34 Trolley tracks back in place. Route 34 riders can check on the status of the work in the Alerts box in the middle of SEPTA’s home page or view the current status on the SEPTA Realtime route page. (The route even has its own Twitter account.)

Residents of any neighborhood who see street or sidewalk depressions or holes in the street should report the exact location to the PWD hotline, (215) 685-6300, right away. 

The details: What happened to make this big hole?

PWD excavation revealed, among other things, a broken storm drain or inlet pipe leading to a wellhole, a vertical shaft that helps spread out pressure during high volume, wet weather days and can provide access for inspections and maintenance.
There was also a roughly 3.5-foot “egg-shaped” sewer. Built in 1888, its bottom layer of brick had been washed out. This smaller sewer runs east toward the Mill Creek Sewer, which is much deeper under the street and nearly 20 feet in diameter.

Here’s the difference in size:

At left is a PWD photo showing the 3.5-foot egg-shaped sewer that broke in 2019. At right: the 18-plus-foot main stem of the Mill Creek Sewer, as photographed by Joseph E. B. Elliott for his book Finding the Hidden City. The smaller sewer feeds stormwater runoff into the main sewer.

While our inspectors do not know precisely what caused the big wash-out below the pavement, heavy afternoon rainstorms likely washed water into the broken inlet pipe. That carried off the soil-fill under the avenue this spring and further damaged the sewer.

Repairs are being completed on a manhole, the smaller sewer, and the inlet pipe that allows stormwater from the street to flow into the sewer.

In addition to the fact that no one was hurt, a silver lining can be found in the fact that this area has a less dense network of pipes, wires, gas and other infrastructure that can make repairs in places like Center City take much longer.

Currently, we don’t anticipate any water shutoffs or other utility interruptions. Here's a shot of the site on June 18 with the hole filled and the new manhole's riser section peeking up.

Mark E. Waas, a P.E. and our Director of Field Operations, has worked in the industry for over 30 years and says the incident isn’t extremely uncommon — even if the local viral news response makes it seem that way.

“It certainly is not the norm, but large cave-ins of this type do happen occasionally,” says Waas. “This one just happens to be in a very public location and impacts the trolleys, which has made it a bigger story.”

Live in the area and want updates?

Signup for PWD email/text updates and include your ZIP code and we’ll send info out to nearby residents as the project wraps up.

Living On Top of Mill Creek

Creative responses are helping the community cope with the construction and inconvenience, but the world of buried streams and hidden hydrology has a more complicated, even deadly past. That will be covered in detail at our June 25 presentation about Mill Creek history, and our engineers are providing more information about the sewer system. 

You can learn more about how past failures and cave-ins damaged neighborhoods and left behind vacant lots in communities still coping with blight in this short film: The Buried River, by Anne Whiston Spirn.

For a quick crash-course on the environmental impacts that come with covering over 300 miles of Philly streams, check out our animated short — Welcome Back, Otter.