Philly sinkhole Credit: Samuel Lieberman

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A garbage truck fell through my street last week. A full wheel cracked right through on its way through the 500 block of Mountain Street, and it sounded like an explosion. Then, the timeless South Philly sounds of arguing, from the recycling truck’s crew.

The rest of the day turned into a bizarre limbo, with the whole street gathered around the beached vehicle. We were waiting for it to be either sucked into the abyss or just gently pushed out of the hole by the Philadelphia Department of Streets.

Of course, Streets came and pushed the truck out. The next day, the gaping hole was filled with gravel and sand. We had lived through a sinkhole, a sign of the aging infrastructure of Philadelphia.

The problem

Our street experienced one of the 678 sinkholes that the Department of Streets has repaired so far this year. In 2014, they repaired a total of 1,839. Why? Geology. Pennsylvania is in an area known as “the Great Valley” which sits on a porous foundation of limestone. The limestone is particularly susceptible to being gutted by the groundwater, creating a void. This just leaves the top layer. This is usually just crusted in dirt and rock. In some cases, this can be extremely dramatic, even deadly.

Urban sinkholes work a little differently. Underneath the streets of Philadelphia, there is primarily dirt and soil brought in around sewage pipes. The way an urban sinkhole forms is, primarily, a leak in a sewage pipe that has wiped the dirt away from the area around it. There is no telling where these areas are. For all you know, as you are walking you could be on top of just a thin layer of asphalt and a bit of a plunge.

June Cantor, a spokesperson for the Department of Streets said in an email to Billy Penn, “The infrastructure is aging and more resources need to be dedicated to keep it in a state of good repair.”

Garbage truck, stuck in a rut (a sinkhole) right outside my house.

The different kinds of holes: pot or sink?

The Department of Streets distinguishes potholes from sinkholes like so: Potholes are just surface damage to the asphalt and a sinkhole is a problem with the foundation, what is under the street. Sinkhole repair becomes confusing as the Water Department, or sometimes the property owner, hires a plumber to come in and fix what, apparently, caused the sinkhole. The Department of Streets does not go too deep below the top layer.

The process of dealing with a sinkhole becomes an urban existential question of what defines “the street.” Is it just the top? Does it include what is underneath? “Ground” is obviously not just the top layer. Apparently the city’s rule is that the “ground” is the first six inches of surface, depth-wise.

The solution

The Department of Streets currently receives $125 million out of the almost-$4 billion Philadelphia annual budget. This year they were given an extra $20 million to fix the streets. Last year they received a $16 million increase for repairs and we are on track for significantly less sinkhole repairs this year.

Yet, Streets Commissioner Dave Perry told Billy Penn that these numbers don’t mean much. “The numbers can change drastically year to year and can have nothing to do with the amount of surface repair we do to the streets.”

He said there isn’t really anything the Streets Department can do to prevent sinkholes. A sinkhole is created by a “sewage lateral” (or pipe) that is the property of whoever owns the house it is connected to. He says that most of these pipes have just reached the end of their life span.

“I don’t know of any program or funding that would [or could] proactively replace them before they fail,” said Perry.

According to Streets, a pothole takes on average 90 seconds to repair (Please, somebody bust that myth). A sinkhole is repaired temporarily and can take weeks before a permanent repair is achieved.

The sinkhole on my block is currently still a sandbox. The abyss is filled, but not re-paved… so it’s still not comfortably a “street.”