The Collaborative International Dictionary of English v.0.48:

Ballastage \Bal"last*age\, n. (Law)
   A toll paid for the privilege of taking up ballast in a port
   or harbor.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

BALLASTAGE, mar. law. A toll paid for the privilege, of taking up ballast
from the bottom of the port. This arises from the property in the soil. 2
Chit. Com. Law, 16.