At another part of the mine, on Penlan-wen, water would have been in short supply; a siphon could have transferred water from the main aqueduct or one of its tanks, but remains unproven. The vein carries along the hill for some considerable distance, and has been trenched out. This method involved excavating the vein vertically down while keeping the top open. However, ventilation becomes a problem when fire-setting is used, so three long adits were driven in from the hillside to the north. They are much wider than normal galleries, suggesting that their primary purpose was to allow circulation of air through the trench and permit safe fire-setting. The upper two adits are still open to the trench, but the lowest one is currently blocked.