There are times when environmental consultants aren't exactly welcomed with open arms when they're in the field.
In any number of situations, you can find yourself working either right next to a hostile person's property, or in the steet in front of them. Or maybe you have to be on someone's property because of a court order. I know folks who have collected samples with a sheriff standing guard. Drillers have told me that they've been shot at before.
I haven't been personally attacked, maybe because I looked young and the locals assumed (wrongly) that the other person with me was in charge. But I've witnessed coworkers getting screamed at or having folks get in their face.
Sometimes environmental issues get contentious. Having a well in the street in front of your house may lower your home's resale value, even if the source of contamination is a mile or more away. An environmental site may be the focus of consolidation, causing contamination to be concentrated (although capped or otherwise stabilized). And libertarian types may be offended if the government appears to be imposing on property owners (or paying "my tax dollars" toward cleanup).
Just remember: the person who actually comes around to do the sampling is 90% of the time a consultant working for the property owner, the law firm, the government, or whatever. And we're pretty careful to make sure that we have all our legal issues worked out so that we're not trespassing.
The environmental folks coming to the site didn't cause the mess. And the person doing the sampling is almost never in any position to make a decision about the property - they're just doing a job. Abusing the person collecting the sample does nothing to hold back or otherwise change the course of a project. If you actually drive them off, chances are they'll be back and accompanied by law enforcement. If you disagree about the project, contact your local newspaper, government, or the property owner and register an official complaint.