It likely has nothing to do with oil/gas drilling. Farm policies sometimes have coverage for farm related pollution release. (for example a tractor upsets and spills fuel or farm chemicals into a stream....that is pollution directly caused by farming) I know of one company that used to include the farm related pollution coverage for no charge but no longer does that. Sounds like you may have coverage with them.
Pollution caused by commercial companies doing oil and gas drilling on your land is not going to be covered by your home or farm insurance at all.
Someone told me that the State of Ohio holds the driller responsible for any pollution, but I wonder what the situation would be if the driller goes bankrupt and leaves the landowner with a mess.....who is responsible to pay for cleanup then?