There are several corridors and smaller rooms nearby. You won't have to explore all of them, but you should prevent enemy units from making surprise attacks. You'll encounter a group of enemy soldiers when you get to a new large room [#280]. Don't forget to use grenades - they'll be very effective in confined space.
Take interest in ammunition, as well as in a new medkit. Get ready to defend yourself against attacks of a second group of enemy units [#281]. Most of them will be standing on an upper balcony and you have to be ready to kill them when they try to hop over the railing. Keep pushing forward and leave no one behind.
Be on a look out for signs. They will help in getting to your current destination which is going to be a Pump Room. Watch out for upper balconies and eliminate additional enemy units when they arrive. A large group will be also waiting for you near the stairs [#282]. Kill them and take your time to find ammunition, as well as a new armor. Head over to a long balcony leading to a new section of the sewers.
Eventually you'll have to get to a large hole in the ground. Use the ladder to go further into the sewers. You'll see Keegan very soon, but you don't have to pursue him at all costs. Watch out for electrical discharges and go to your left. There's going to be a lever here [#283] and you must pull it in order to shut down power supply to this section of the sewers.
Get ready to defend yourself against new ghosts. Remember not to stay in one place for a longer period of time and to fire at the wraiths with short but controlled bursts. Your first objective will be to get down to an area where you saw the discharges [#284]. Go to your right and continue moving forward. Search for medical supplies, but sadly there aren't going to be a lot of them.
There's only one narrow passageway leading to your current destination, so you shouldn't get lost. Keep firing at the ghosts to scare them away, but you must acknowledge the fact that you'll probably lose a lot of health here. Eventually you'll get to a new carriage. Explore the area and you'll find a small stash [#285]. Take the ammunition and much needed syringes.
You may proceed towards a second carriage located in the distance. I'd strongly recommend that you take a peek inside, because you will find a new document [#286] - Line extension. You may finally head towards the stairs. Collect ammunition for your primary weapons along the way. Proceed to the end of the balcony and you'll find grenades and armor. Go back to a staircase and head down to a lower level.