Head down into the sewer and turn to the North. Either head through the gas (if you have not turned it off) or use the side passage just next to it to bypass it. After the gas, follow the passage over to the right. Go through the first gate on that side. The gate is locked (Security Rating 2). Its code is 6122. This code can be found where the gas is in the sewer before this gate. There is a dead civilian with it on them.
Get through the gate and look forward. You will see a high ledge that is leading to where you want to go. It is electrified so you will need to take some damage to shut down the power. Against the back wall is a Breaker. Interact with it to shut down the electricity. This will allow easy access to the area beyond with minimal trouble.
Inside here, you will find a number of augmented people hiding out. Start by talking with the one you saved and then find find Little K. She is the older woman roaming about. Respond to her approach of the matter and then see about helping them relocate all the people who have gathered here. Exhaust all the dialogue options to make sure you know as much as you can about the situation.