Recently water has been pooling on my lawn and spilling over into my neighbor's yard. I think it may be a leaking underground PVC drainage pipe. How can I fix this?

There's only one option for a broken sewer line and that's to dig it up and repair it. Good luck, Tom

I am responsible for repairs to the pipe or is WSSC?

It depends upon where the pipe's located. You are responsible for all the pipes that are on your property. Good luck, Tom