Maybe someone can expain this to me.

I'm working with my plumber on a job. We are installing an underground water tank to use for a small coy pond and an irrigation system. The tank is fed from a small creek and has a submersible pump. I had all the wiring done and the well guy was wiring the pump in the tank and got shocked. They called me and asked me what the problem was. I'm thinking, oh crap, did I leave the disconnect on, did I wire it wrong, etc. The disconnect was off. Apparently I have got some stray voltage on the egc. He got a shock off the ground. When I go back to the panel and turn off the main I get 2v from the egc to earth ground. Is this a utility problem and how do I diagnose it? I wasn't there when he got popped but it was enough to make think about it.