Here is the full list of all 16 Clandestinity of Elsie achievements.
Kill an Alchy.
Escape the Singed ambush.
Gather medical supplies at the hospital.
Kill 10 Singed.
Find the Blood Bag at the Troy Restaurant.
Find the pendant.
Activate the elevator at the Yorkshire Apartments.
Kill a Victim.
Save your game for the first time.
Went to the Cunningham home.
Kill a Thorn.
Leave the sewage plant.
Enter the sewers (again).
Return to Burnie's Garage.
You finally found Elsie.
Diverted the water flow.