Shepard drops out of the vent into an underground section of Black Mesa's Waste Processing Area 3. He can hear an odd roar in the distance, which upon entering the main toxic waste dumping room, Shepard comes across Race X's large monstrous Pit Worm blocking the path forward. Unfortunately, Shepard arrived too late as all the HECU soldiers fighting the Pit Worm are already dead. Shepard fights his way into the maintenance room, but is unable to flush the toxic waste until the room's valve and gearbox are turned on.
The corporal fights his way through the Xen and Race X aliens into a side section of the dumping room to turn on the gearbox, and avoids the Pit Worms attacks in order to turn on the valve. Shepard then returns to the maintenance room, and activates the waste dump, which flushes toxic waste into the room and kills the Pit Worm. The corporal then activates the bridge leading to the door that the Pit Worm was blocking, and heads off to the next area.
This Chapter contains examples of:
- Creator Cameo: Shepard activates the "Valve" and the "Gearbox" to kill the Pit Worm. Valve has overall control of the franchise while Gearbox is the studio that used Valve's resources to develop the Opposing Force expansion. The overall level is basically Gearbox's take on the "Blast Pit" level that Valve developed for the original game.
- Shout-Out: Some sections of the level bare a very strong similarity to the trash compactor room from A New Hope.
- Skippable Boss: It is possible to skip the Pit Worm by using the Barnacle to pull yourself up to one of the grappling points near the ceiling and then using the momentum to bounce yourself to the bridge behind the Worm (the same one that extends once the Worm is dead). It isn't really worth it, since there is some luck involved and the fall damage - as well as any hits you'll catch from the Pit Worm along the way - can easily kill you.
- Visual Pun: To defeat the Pit Worm, you have to first reactivate a Gear Box, and open a pressure Valve. Hmm... For a bonus, before activating the valve you have to use a Steam Vent. Since Opposing Force came out years before Steam, this one it's coincidental, but still pretty funny.
