Fire in the Hole!

Blasted greenskins! Defilin' the mines that carry my father's father's good name. Comin' straight out of the tunnels like the bloody vermin they are! I kept saying we should have blown those tunnels shut years ago, but the need for Bitterstone is too great. Now look at the mess we're in! I'm here to set things right, |n, and you're going to lend a hand. I've got the powder set up. All you need to do is blow them tunnels. We'll see what them greenskins have to say after bein' buried by a ton of rock and stone!

From Goldbrow's Lament, work your way past the Squigs and enter one of the mineshafts of Stonemane's Junction. You should find a Plunger Box there; interact with it to blow one of the mineshafts shut. Return to Agmar Stonemane in Goldbrow's Lament when finished.