Silent Hill Homecoming

The first opportunity you get to unlock this achievement is shortly after your encounter with Judge Holloway, upon your first return to Shepard's Glenn proceed through the small town until you trigger a short cutscene which introduces you to Judge Holloway, once the cutscene has ended you need to head east and enter the town hall, you'll know be in the main lobby, take the door to your right and head down the hall until you reach the first door on your right, this is where the first serum is located.

At the back of the room there are 2 tables, one of which has a briefcase resting on it, the first serum is located inside the briefcase, as soon you've collected it the achievement will unlock!