On the morning of November 18, a sinkhole opened up adjacent to Sleighton Park, a major recreational facility in Delaware County. Sunoco has been doing horizontal directional drilling there, and that work has triggered at least three other sinkholes along the pipeline right-of-way at the park in recent weeks.
This time, the sinkhole was right in Forge Road, one of the two main roads in the area. Sunoco brought in a series of cement trucks to fill the hole before it could be examined by officials. A county official who arrived on site while the hole was being filled was prevented by Sunoco security from observing the work from close at hand.
From drone images provided by a local resident, we know that the surface opening was not very big—perhaps a few feet in diameter. But the hole beneath must have been vast. As of 6 p.m., truckloads of cement were still being poured into the sinkhole and Forge Road remained closed. By some reports, two dozen truckloads had been poured into the hole. A void of that size implies that the two active Mariner East pipelines, both of which run through the same easement at that location, were almost certainly exposed and unsupported in the hole.
Is the cement itself a danger? The cement will presumably stabilize the pipes, but will the mass of tons of cement be adequately supported by the ground beneath? If there are huge voids near the surface, there could be deeper voids below the cement. If one of those deeper voids were to collapse, it could allow the cement to drop, pulling down the pipe with it.
This is exactly the kind of subsidence that occurred in the woods near Follansbee, WV, a few years ago, triggering a huge explosion. In that event, no one was hurt. The nearest house, almost half a mile away, was damaged but no one was home.
If that same accident happened near Sleighton Park, in a suburban neighborhood, dozens of people would potentially be in harm’s way (or hundreds, if the park’s soccer fields were in use).
The cement could also interfere with “cathodic protection”, the method Sunoco uses to prevent the pipeline from rusting. This technique requires that a constant small flow of electrical current is maintained between the pipeline and the surrounding soil.
These pipelines need to be shut down immediately until the stability of the underlying geology at this location is confirmed and the long-term integrity of the pipeline is assured.