I'm not an expert but I would start with what you know.

There are 2 splices covering 250? So, these must be 100' sections. Start at 100' from the upstream. If you find a splice and it's the wrong one go another 100' down. If you don't find a splice count 100' from the downstream end for the most likely spots. That said, the pipe could have been damaged literally anywhere during the backfill.