Here is the full list of all 16 Clandestinity of Elsie achievements.
You finally found Elsie.
Return to Burnie's Garage.
Enter the sewers (again).
Kill a Thorn.
Leave the sewage plant.
Diverted the water flow.
Kill an Alchy.
Kill 10 Singed.
Escape the Singed ambush.
Gather medical supplies at the hospital.
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.