18. Article 4 applies—
(a)to the deposit, on the site of dredging for aggregates or other minerals, of any substance or object taken from the sea in the course of such dredging (other than any of the aggregates or minerals being dredged);
(b)to the deposit of waters (whether by overflow or pumped discharge) from the hold of a vessel—
(i)in the normal course of dredging for aggregates or other minerals, or
(ii)at the site of such dredging following its completion or during the return journey of the vessel.