Wetlands Quests

For the achievement it is also required to solve the quest sequence af 26.9, 26.1 ending with Yorla Darksnare.

This was recently separated from the prior achievement Loch Modan & Wetlands Quests. It has its own individuality for the zone.
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You may have completed the prior and upon separation did not get credit for it such as myself. Open a ticket and Bug report for this. Some GMs may award it accordingly if you got one of the two and can provided screenshot with date. This isn't always the case. yMMv (Your mileage may vary).

New Achievement Titles:
Loch Modan Quests
Wetlands Quests

I thought the quests were reset like when Cataclysm happened upon implementing videos into a lot of quests which in return reset them in zones and in many dungeons. This is not the case here

This USED to be an individual achievement originally prior to merging them into one in 5.0.4 patch.

For the Slabchisel chain you also need to do the quests that Surveyor Thurdan gives http://www.wowhead.com/npc=41129/surveyor-thurdan