Any rules against it? There's tons of regs on what you can't do from the ground up but nothing I can find about below grade. Our engine failure options are getting grim, 30 foot wall if you sputter into the gravel pit. It's getting bigger every year, we're going to be an island.

Check out Duncan Airport in BC. They have been digging out the gravel for years and will eventually eat up the airport. This is the Google earth link. Duncan Airport, Langtry Road, Duncan, BC, Canada
This picture was 2004 and they have now started removing gravel on the other side of the runway. They have a wind sock at each end and traditionally when crossing midfield both little ends are pointing at each other.
KenW

Gravel pits inevitably fill with water. Now you have some nice waterfowl and gull habitat right off the end of your runway......perfect.

MTV

Oh boy I forgot about birds. I guess we should ask them to dig it big enough for floats.

KFWB has the same problem, for natural reasons. Built on a hilltop.

One of my favorite approaches in wisconsin is over a lake. A natural one full of birds.

Nothing can be done except to note that if we raise a stink about the gravel pit *we* will be the nimby's.