Here is the full list of all 20 The Brookhaven Experiment achievements.
Survive the seventh campaign level.
Acquire all guns and upgrades in campaign mode.
Survive the sixth campaign level.
Kill 1000 enemies.
Survive the fifth campaign level.
Kill four enemies at once with an explosive.
Survive the fourth campaign level.
Survive the third campaign level.
Survive the second campaign level.
Finish a nighttime campaign level without turning on the flashlight.
Kill 100 enemies.
Survive the first campaign level.
Survive the eight campaign level.
Survive the ninth campaign level.
Survive the final campaign level.
Blow the head off of something large and toothy.
Survive ten waves in a survival map.
Acquire all guns and upgrades in a survival game.
Acquire 200 throwables in campaign mode.
Survive a nighttime campaign level using only the knife.