Part 31

Return down the ramp and through the "SURFACE ACCESS" door. Enter the room with the first aid station to be knocked out and have your weapons taken. You will be dragged to section c2a3e.

Upon regaining control, quicksave. Run forward and jump onto the boxes, then carefully crouch-jump onto a side ledge to avoid the trash compactor.

Wait for the trash compactor to stop, quicksave, and quickrestore to ensure its halves are displayed correctly. Use the compactor halves to cross the room and grab the crowbar from the ledge.

Climb down the nearest ladder, use your flashlight to find a grating on the floor, bash it out, and drop into a large pipe to reach the "Residue Processing" chapter.

After falling into water, turn right and exit the water. Go through a short tunnel to a large outdoor area where two headcrabs will appear. Avoid them by running into the area, swerving left into the water, and then running/hopping across the water to a silo-like structure with a ladder.

Go to the right of the silo to find a valve wheel. Start turning it, then immediately run up the ladder. Quickly drop onto the lowering wooden platform inside the silo before it descends too far.

Ride the platform until it stops, then crouch-walk into the rusty pipe opening and move along until section c2a4a loads.

At the end of the pipe, bash out the grating. A security guard will kill some headcrabs. Follow him, and grab his pistol after he is eaten by barnacles. Collect the bullet clip on the floor in the curving hallway.

Use the crowbar to bash the three barnacles the guard leads you to. Use the first aid station on the wall past them if needed.

Go down the hallway to the left of the first aid station to find another bashable barnacle near the top of winding stairs. At the bottom of the stairs, find an HEV station, but beware of two headcrabs to the right.

Return to the room where you dropped from the pipe. Find the ladder on the side of the hazardous waste vat. Climb it and jump to the gunk chunk ahead, then take a running jump to the pipe entrance past it, crouching before landing.

Follow the pipe to a ledge in a room with waste vats and mashers. Jump onto the first masher as it rises from the sludge, then jump to the second masher before the first submerges. Immediately jump to the big pipe past the second masher.

Walk along the big pipe, turn right, and jump to the other nearby big pipe. Follow it to the waste mixing vat. Drop to the lower floor and use the first aid station. You can also go through a door to an area with two headcrabs and an HEV station. Defeat the headcrabs, then use the HEV and first aid stations to restore health and armor.

Climb the ladder back up next to the mixing vat. Jump to the center of the nearest mixer, then wait for the mixing arms to align to jump to the second mixer's center. After that, run forward to land on the open pipe's edge. Crouch-walk into it until section c2a4b loads.

In the room with conveyor belts, bash wooden crates for health and ammo. Ride the slanty conveyor down into the water. Turn around and enter the large underwater pipe marked "DANGER". Surface in the next room and get onto a side ledge.