depends on the type of contract - if area is actually loaned, above works.
If a lease, leased premises,etc.

this is an environmental term. The technical terms in Spanish are either canteras or zanjas de prestamo - where you take dirt or rock from to place elsewhere (as a quarry). I suppose you could call them borrow areas or zones. Usually, once you begin to dig you end up with a ditch or hole of some sort. good luck