Gleason's Gielinor Guide

Arcenia root is a quest item used in the quest The Dig Site to make Chemical compound along with nitroglycerin, ammonium nitrate and ground charcoal to blow up bricks blocking the path below digsite. It is obtained from tunnels where players can only enter with the invitation letter. Entering the tunnels requires 10 Agility.

Spawns

Location	Members	Spawns	Map
Digsite Dungeon		4	Show map

Item		Members	Skills	XP	Materials
	Chemical compound		10	7.5	1 × Nitroglycerin 1 × Ammonium nitrate 1 × Ground charcoal 1 × Arcenia root
	Chemical compound		10	2.5	1 × Mixed chemicals (Step 2) 1 × Arcenia root

After destroying the bricks under the Digsite, the Arcenia root spawns seem to shift to different locations - one of which is obscured completely by the sloping ground but can still be picked up. This shows that the dungeon after the explosion is actually a separate copy of the dungeon, which seems to be a common solution Jagex uses for changes made in quest areas.
The model of the Arcenia root is the same as a Limpwurt root in 2005.