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