Unknown chemical sprayed on my property

by Keith
(USA)

My 12 acres has a powerline that passes over a section that is part of the main water shed for the entire property. While I was at work today my wife called and said that two men who could not speak english and would not talk to her. They were spraying an unknown chemical under the powerlines.

I am in the process of setting up an Organic orchard and vegetable plot that was to use this watershed as a primary source of water. How should I deal with this setback?