Former pest control guy here (I was an Orkin man for several summers to pay for university). No idea about the legal ramifications, but I have lots of info about ants.
Ideally you want to use bait with ants. Just spraying something that kills them tends to be very ineffective because you usually don't get the queen, and colonies can rebound quickly. It's also entirely possible that killing a large number of ants has caused the colony to split and relocate, so now you're going to want to do a very thorough search through your home.
Carpenter ants really like damp areas and decaying wood. Make sure that you get rid of any leaks, leaky taps, leaky windows, wood that gets wet from leaks from the roof, etc. If they're in one specific wall, you need to figure out why . . . and this may involve ripping up the wall. Once you remove the habitat they like, they'll be much less likely to come back. Spraying the perimeter of the house can help prevent immediate re-infestation, but if the underlying cause is still there they will eventually be back.
It's important that you clear the area near your house of things that could attract carpenter ants . . . any dead/rotting wood nearby should be removed. Old stumps half buried in the ground, firewood, etc. Carpenter ants will wander around a great distance, so if there's a colony near your house you'll probably find them in your house regularly.
A simple (and reasonably non-toxic) bait for carpenter ants is a tablespoon of borax (boric acid) mixed with a teaspoon of honey or peanut butter (put out both, depending on time of year ants will be attracted to different things). You want to place this along their trails. Don't overdo the borax part of this mix, you want them to take it back to the nest and kill off the queen.
A pest control guy will have access to better chemicals than you can buy (at least this is true in Ontario, not sure about Virginia). They should also do much more than spray chemicals . . . they should assess why the infestation happened in the first place and take steps / give guidance on how to prevent recurrence. A pest control guy should also have a better understanding of how to apply baits and mixing the perfect concentration.