When engineers decided to explore the sewer to determine the cause of multiple sewer overflows in the area, they discovered the fatberg, DPW said. The walls of a 100-year-old, 24-inch wide pipe were caked with congealed fats, oils and grease. Up to 85 percent of the pipe was clogged with the congealed fat, blocking the flow of sewage.Raymond said there were other, smaller fatbergs throughout the city's pipes, but none as large as the one under Penn Station.