It happened in the area of 29th and Bowers Street in the Eastlake Housing area around 10:45 a.m. Tuesday.
A spokesperson for Delmarva Power says a third party contractor, who was digging to put up a fence, hit the 4" main.
The gas line was secured about a half hour later, though repairs are expected to take until the early evening.
A total of 31 people had to be evacuated.