Ch. 6-4 Underground water plant -> better solution (?)

[Psyringe]

There are already two walkthroughs for this area - and undeniably a lot of work has gone into them -, but I'm wondering if there isn't a better solution. Both walkthroughs perform the steps in an order that would unnecessarily pump sewage into the big raw water pool and the big flocculation pool for a while. The game does not seem to care (it gives the repair notices anyway), but who knows which calculations are going on in the background. In any case, since the game encourages players to find optimal solutions rather than just "good enough" ones, here is mine. I'll also explain the process along the way, as there are probably people who would like to _understand_ what they are doing (which can be difficult with this puzzle), rather than just follow instructions.

If anyone wants to use any of my text or screenshots in their own guide, feel free. I probably won't maintain this after I've finished the game.

I'm assuming that you have found all keys and keycards, turned off the fire alarm (which is necessary to unlock certain doors), and have access to all areas. If that is not the case, please consult one of these two walkthroughs (search for "Reserve" to find the respective section):
https://steamcommunity.com/sharedfiles/filedetails/?id=1387770838
https://steamcommunity.com/sharedfiles/filedetails/?id=773226367

1. What we start with:

The underground water plant has 3 problems:
a) The main water source (the Bergmann tunnel) does not provide enough water any more (presumably the flow is inhibited due to the cave-ins).
b) The main flocculation pool (which is supposed to provide one step of the cleaning process) is not working correctly
c) There were traces of sewage found in the water after the cleaning process.

(a) and (b) are noted in a document in the control room, (c) is noted in a document in Tomas Balog's office. See screenshots of both below. The document in the control room also denotes the correct cleaning process: Coagulation -> Flocculation -> Sedimentation -> Filtration -> Disinfection.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926885902
https://steamcommunity.com/sharedfiles/filedetails/?id=1926885939

(Unnecessary side info - if you want to know how the plant is working, and why the order of steps is important, here's a very rough explanation:
1. Raw Water: water that has not been treated yet, so it contains particles that you want to remove, to make sure that it's safe for drinking
2. Coagulation: chemicals are added that make the unwanted particles clump together
3. Flocculation: further clumping, the unwanted particles now form flocs or flakes.
4. Sedimentation: the water is left still so that the flocs/flakes can sink to the ground due to their heavier weight
5. Filtration: Flocs/flakes that are too light to sink, are filtered out by passing the water through a substance that holds the unwanted particles back - usually sand
6. Disinfection: kills pathogenic microorganisms that survived the previous steps)

2. What we need to do:

On several screens in the area, we see the current state of the system as a flowchart:
https://steamcommunity.com/sharedfiles/filedetails/?id=1926885973

This display shows us what we need to do to solve the three problems:
a) On the top of the chart, we see a secondary raw water source from a reserve pool. By adding this water to the treatment system, we can make up for the reduced water flow from the Bergmann tunnel.
b) Switch from the problematic big flocculation pool (with the "low pH" message) to the two smaller secondary flocculation pools.
c) Make sure that the sewage (brown lines in the chart) gets drained properly and does not end up in any water pools.

While we do this, we also have to make sure that water is led through the different treatment steps in the order mentioned in the document in the control room.

I'll give detailed steps further below, but if you just want a quick list of instructions and already know where everything is, here it is:

1. In the crawlspace directly above the big flocculation pool, open Sewer Pipe 03 and close the "Flocculation Pool" pipe.
2. At the first sewer pipe junction, close the left valve ("Sewer Pipe 01 / Raw water pool") and open the right one ("Sewer Pipe 02 / Flocculation pool and sever pipe 03").
3. In the sewer pump shed, place a valve on the pipe, turn it to open the pipe, then start the pump by pressing the button behind you.
4. In the crawlspace below the hatch, open the right valve and leave the left one closed.
5. At "Sedimentation", open the one pipe that isn't already open.
6. At "Coagulation", open the "Raw Water / Coagulation" valve and leave the "Raw Water / Filtration" valve closed.
7. Activate the secondary flocculation pools by pushing the button on the machine next to them.
8. On the central railing in the main room, switch off all four pumps that put water in the main flocculation pool.

(Detailed descriptions in the next post)

[Psyringe]

3. Fixing the sewage drain:

We'll fix the sewage drain first - the order doesn't seem to matter, but it's the easier task. Currently, the sewage is blocked off (as shown by the red X on the sewage source pipe at the bottom right of the flowchart). We'll work our way in reverse through the system, to make sure that all junctions are set up correctly by the time we turn the sewage pump back on.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886021

Start at the big "No fishing" sign at the center of the main hall (shown above), with the 4 pumps in your back and the office building to your right. Look over the railing across the big flocculation pool, and you'll see a ladder leading down. Go around the corner, take this ladder, follow the ledge, climb a different ladder, and you'll enter a room with two valves - shown below:

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886067

1. Open the left one ("Sewer Pipe 03") - it opens the pipe that will lead the sewage away from the facility. Close the right one ("Flocculation Pool") - it would lead the sewage into the pool where the water is supposed to get cleansed for drinking, we don't want it there.

Go back to our starting point, enter the office building, and take the door to the right of the 4 paintings at the back wall of floor 1. Walk forward through a gate, then through another gate at your right. You'll now see two valves that control sewage flow, shown below:

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886118

2. Close the left valve ("Sewer Pipe 01 / Raw water pool") - this closes the connection between the sewer pipes and the big raw water pool, we don't want sewage in our water. Open the right valve ("Sewer Pipe 02 / Flocculation pool and sever pipe 03") - this opens the connection from the sewer source (which is still closed) to the sewer junction we visited before.

Go back through the gate, turn left then immediately right, walk forward until you see a door to your right. Open it. You'll see a pipe, this is where the sewage is supposed to enter the facility. The valve is missing, you need to find one - walk back the path you just came from, enter the first gate to your right, and look for a well-hidden valve in a back corner of the room.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926923490

3. Place the valve on the pipe, turn it (this opens the sewage source), then press the button behind you. This will pump sewage through the system, which is safe now, because we closed off both connections to our water pools, and provided an exit at Sewer Pipe 03. You'll get the first "Successful Repair" notification.

Note: In reality, it is perfectly possible to clean sewage and turn it into potable water. It's a good option for areas that use more water than nature provides. But perhaps this facility does not have the equipment for that. The document in Balog's office mentions traces of sewage in the water after treatment, and the note on the sewage pump explicitly warns about draining it into the water pools. So let's be safe here.

4. Water sources and flocculation pools:

Step out of the room, turn right, then immediately left, then go a few steps forward until you see a hatch in the floor to the right. Open it and climb down.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886160

4. Turn the right valve ("Flocculation / Sedimentation"). This opens the connection from the secondary flocculation pools (that we will turn on later) to the sedimentation system, which is the correct sequence according to the document in the control room. Don't open the left valve, that one would skip sedimentation.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886230

5. Climb out of the hatch and turn around until you see a door on the opposite wall, with a sign reading "Sedimentation" on top of it. Go through that door, find the one pipe that shows a red light behind its valve, and turn that valve until the light turns green. Now all 4 pipes to the sedimentation system are open, so the sedimentation system is fully operational.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886284

6. Go back all the way to the "No fishing" sign we started from. Look straight at it and beyond, you'll see a door on the far wall at a high railing. Go there and turn the left valve on ("Raw Water / Coagulation"). This opens an additional water source (the "reserve") and leads the water into the first step of the cleaning process. Don't turn on the right-hand valve, that one would skip several cleaning steps.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886342

7. Go back to the "No fishing" sign. Turn around until you see the machine with the "D2 Flocculation" sign on the floor below. Go there and press the button. This will turn on the secondary flocculation pools.

https://steamcommunity.com/sharedfiles/filedetails/?id=1926886399

8. Now that we have a working flocculation system, we can turn the problematic big flocculation pool off. Go back to the "No fishing" sign and turn around until you see a row of 4 buttons for the 4 pumps below. Switch all of them off. At this point, you should get the second "Successful repair" notification. I would also expect the achievement to drop at this point, but could not verify this myself, as I already had it.

The flowchart should now look like this:
https://steamcommunity.com/sharedfiles/filedetails/?id=1926886438

Congratulations. :) You have improved the water quality without ever disrupting the service, or pumping sewage into any water pools.

[oku]

I'm getting ready to play through again for old times sake and I look forward to retracing your steps. Thanks for putting in the time and effort for this guide.

[cwsumner]

Interesting. I had most of it, I think. It's fun to read this. 8-)

[Tone]

Great guide, very descriptive. Thanks!

[Old Salt]

Yes ,it worked for me. Thank you for your guide!

[vBidon]

It helps, thanks. Very informative guide.

[SHADOW IN THE DARK]

Hi, i can't find Tomas Balog's office key, can somebody tell where is it?