A lot of 50-100 year ols water pipe is failing and many time a contractor for a utility may just leave in in the ground unless they haul it out.
If it's in the way of something and it needs to come out, then it certainly makes sense, to me at least, to scrap it. (Some contractors don't think that way though, so you could get lucky, if you ask.) That having been said though, the scrap value of old pipe in the ground most often isn't enough to make it worth the time and effort to chase it and remove it, because over and above the cost of digging, any hole that you dig needs to be properly backfilled and the surface restored to its previous condition.
As far as that goes, a lot of what I personally dig up comes out of old fill. It got buried because it wasn't worth the trouble of scrapping when they dug it up the last time.
Just like most anything else, call your yard to find out what they'll accept and what they'll pay, but in my experience, for cast iron, if you whack it hard enough with an excavator, or a sledge hammer, to break it into pieces you can manhandle, usually most of the mineral deposits on the inside will break loose. Corrosion isn't really that much of an issue.
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