49.—(1) Any person served by the Agency with a notice under article 48 (removal of obstructions other than vessels) may, within 21 days of being served, serve a counter-notice on the Agency disputing the notice on any of the following grounds—
(a)that the item the Agency required to be marked, removed or modified is not an obstruction,
(b)that the item required to be marked, removed or modified is an obstruction which has occurred naturally and that to mark, remove or modify it is unreasonable,
(c)where the requirement is to remove the obstruction, that it would be adequate in all the circumstances of the case to mark or modify the obstruction, or
(d)where the requirement is to modify the obstruction, that it would be adequate in all the circumstances of the case to mark the obstruction.
(2) Any dispute under this article is to be determined in accordance with article 68 (arbitration).
(3) On the hearing of a dispute under this article the arbitrator may confirm, vary or set aside the requirement of the notice, as the case may be.