Not sure about the NG, but when starting from scratch on wide gauge, we used to calculate that it takes about 1 ton of ballast for 8"-12" below the tie, per foot, to fill the cribs. That of course is a standard ballast section including 6" of of the end of tie. Ballast represents a huge cost in mainline rr construction, a cost which sometimes is lost or forgotten, in the initial estimates. How much has been used on the C&TS? Don't know, but I agree with your observation that it didn't seem to be there until fairly recently.