This sewer area is a very nice setting. The first piping doesn't make much sense as you have a ladder right next to it.

There's a certain... issue with the level design on the first stage. If the headless zombies fall down, which they tend to do since they like to take cover on the terrace over the pit, their corpses will alert the enemies below - which is fine. However, there's that technician there that really likes placing mines on the same place repeatedly. At first I didn't even notice as I was exploring the upper areas. Then it crashed the game for me. Rushing that area is irritating and the landmine count still gets too high. It seems you have to lure the enemies out of that mine pile.

This whole chain-reaction is quite consistent and I would look into ways of preventing it. To me, it doesn't seem that important to have that technician down there. I would just remove / replace it with another enemy. You could also place armed landmines of your own there instead.