There's no quest giver, and the QA is open to anyone now. But, there's not much in the way of IC reasoning for why a lot of chars would hit the area, nor a potential for a reward. Lawful chars wouldn't go deciding to rob the place Evil chars robbing it, sure, but even though they're Duergars, if they've been tolerated for this long, why would there suddenly be a Team Good Gank Squad out to kill them, as opposed to calling a Watchman like they would if a PC had murdered someone?

Could we possibly have a quest giver at the Watch House or somewhere, saying they'd been supplying the Spellguard with food, and there were rumours of rebels being fed to the pigs during the Civil War?

I'm not really addressing the merit of the suggestion, but rather the spirit:

Just because some past government made the mistake of tolerating the duergar long enough for them to set up a farm doesn't mean Lawful Good characters can't take being Lawful Good unto themselves and see if these duergar, racially known for greed and other evils, have made themselves deserving of a righteous ass-kicking, especially in the aftermath of these turbulent times.

Ah right. A lynch-mob does work :).