Contractor damaged property in NH

Hello all, I had the unfortunate experience of a contractor drilling into my well water pipe. The pipe runs through a utility easement in the woods behind my neighbors house. My neighbor was aware of the easement and notified the contractor of where it was. When I spoke to the contractor, after the fact, he said that is crew was told where to put in fence posts but they deviated from the route and into my easement. My question is that after digging up the water line it is only 18" deep in the ground. International plumbing code says that water piping shall not be less than 6" below the frost line. Where I live that line is 4' deep. Because the water pipe had to be fixed would the whole pipe need to be brought up to code, and would the contractor be liable for that? Thank you all in advance for any help!