You're looking for Raskalion, not Grundel. Grundel is the dead dude in the cul-de-sac where you found the writ.
Before you get too far, though...did you just agree to the "favor" from Scanthril, or did you ask him about a "job"? He has to give you the "Job" to kill Raskalion, or you'll never get credit for it.
That being said, Raskalion is way, way back in the mines; he's the hardest one to find. You have to switch both tracks around so that the east mine car goes down the track other than the one to the Burning Caverns.
Check out Xignal's site for detailed maps:
http://www.volberding.com/Whints/Mas...ames_Stout.htm
Hope this helps!
-Sazerac