More leats and tanks can be found below the line of the main aqueduct, some of which are shown on the map of the site. They surround the lip of the very large opencast and the tank shown at right is one which was built on the main aqueduct. It was successful in finding a vein, judging by the opencast below, but must have been modified later to feed a washing table built to the left-hand side (near the figure in the picture), probably to wash the crushed ore from the same opencast working. It is labelled Tank C in the schematic diagram. Similar tanks occur below as the Romans followed the large vein down to the road and the main opencast. Most of the opencast workings must therefore be Roman in origin, since one of the aqueducts has been confirmed by carbon 14 dating as to predate all modern workings. Just by the road itself the Carreg Pumsaint has been erected in the space beside a large mound, now thought to be a dump of waste material from mining activities.