The county is not responsible to clean the mess for him, unless it's county employees doing this.  But if you can identify the dumpers, you can contact the police and they can be ticketed for the illegal dumping and/or trespassing; and/or sue them for any clean up costs (e.g. in small claims court). It is the person or business doing this dumping that can be held accountable for it. Installing security cameras to see who comes, goes, and dumps might be a good idea.