Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground level as possible.
Why aren't particle accelerators built on ground level? What is the shallowest depth at which particle accelerators can be feasibly built, and what are the equations such as synchrotron radiation or luminosity interference (or, at least, the phenomena, and not necessarily the equations behind them) that determine this?
Some situation (forgot where and when) in which a stray particle from an accelerator hit someone ended in them from the effects of being by a high-energy (hadron?). Also, a Fermilab researcher who taught one of my classes told us about one of the times in which some loose particles found their way out of the accelerator and shot an inches-wide hole through a steel beam in a fraction of a fraction of a second.
Now, I doubt the particle-accelerator engineers sat down in a conference and said 'we must build them below ground or else particles beams could tear through people' but this is the only drawback I know of that comes with a ground-level accelerator; it can accidentally release fairly high-energy particles that can hit things.
Solar radiation might also have notable effects, but I am not sure.