Mesquite can send a tap root down something like 190' at least for one tree some university dug up to see. Caliche can be anywhere say in the 1' to 10' range and be thin to foot or two thick. In general caliche is not a continuous unbroken surface. I would never worry about caliche unless it's a known issue. Let the tree earn its keep and let it find the cracks it can send roots through. It's kind of like the drainage issue...if there's standing water the tree won't grow roots in that area and keep roots higher. As long as we're not talking about a bog the tree will probably find a way. A lot of these rules for planting stuff are the absolute best possible environment. But plants, like people, can handle a less than perfect world. I may have mentioned in another thread, this year I grew Mesquites from seed in a bucket with no drainage, watered everyday, so it was sitting in water. If you asked a 100 gardeners 99.9 of them would say that's impossible. Most of what you hear is just repeated from person to person, there's little actual testing or knowledge. A bit of common sense goes a long way when listening to advice.

orchidlily, I know of its effect on a banana farm. It causes the banana fruits to ripen in geometric proportions. However, here might be some information that you can use.

I've got a bit more info. 1) I looked at the GIS map for the land the hospital bought, and it's actually NOT the acreage directly behind our lot - it's actually another 1/3 - 1/2 mile further south - right off the highway exit. There are a couple other country roads with private property between our lot and the planned hospital lot. 2) Our lot is about 3/4ths of a mile from the main road, so even if a siren went by we most likely wouldn't hear it because our road is heavily tree'd and very private. 3) The posted plan for the hospital is a four-story building. I didn't see a helipad listed in the plans, but that doesn't mean they won't have one. But I'm not worried about it. I would think at most the helicopter would be used 1-2x a week, which is okay by me. 4) I'm now very excited about the hospital being built, if only because I can put in for a transfer when the time comes and try to lower my commute from 45 minutes each way to 5 minutes each way! *lol*

I see this thread is a few months old, but I'll throw in what I've found researching this very question. The generator manufacturers instructions will likely list a minimum clearance around the unit for maintenance and operational purposes, but not necessarily for safety. That's why they also will mention NFPA 37 "Installation and use of Stationary Combustion Engines and Gas Turbines", which I found at my local library. A key paragraph is 4.1.4 "Engines Located Outdoors" (2006 edition). It requires engines and their weatherproof housings to be 5' from openings in walls and also to be 5' from structures having combustible walls. Building codes would normally consider pretty much any wood frame construction to be combustible, even if it has a masonry veneer. The clearance may be reduced "where the following conditions exist." If the adjacent wall of the structure has a 1 hour fire rating, and if the weatherproof enclosure has been designed to contain a fire. The wording makes me think that both exceptions must be met before you can reduce the 5' minimum clearance. Its my understanding that Generac will not make the claim that their enclosures will contain a fire. Now that being said, I've yet to see any photographs of installations, including those from Generac or their dealers that show a generator offset that far from a wall. This may simply be a standard rarely enforced, or I may be fundamentally misunderstanding its application.