For a short time, we had a very weak regular ground wave in SE Michigan from WBMB 1060 West Branch. They got an FM, WBMI 105.5, and decided that they didn't need the AM and turned the license in. I used a tuned circuit in series between a long wire and a ground screw in a nearby outlet, and coupled it inductively with the coil of the tuned circuit next to the ferrite loop in a Sony Portable that was FAIRLY sensitive on AM, very sensitive on FM. I would say that WBMB was in the range of 25 uV/m at my RL. The FM is now on Silent STA. They had a Class D minimum efficiency of 282 mV/m, indicating a reduced input according to the Canadian Database.