Fallout 3/Project Impurity

Infect project purity's water supply, or not.) This quest activates once the final barrier to project purity is down.

At raven rock, you were given a vial of a modified FEV strain, which allegedly will cleanse the area from supermutants and other genetic impurities. However, you might not have the vial depending on the dialogue boxe

Jefferson Memorial
The Jefferson Memorial will be almost the same way you left it, although it is now occupied by the Enclave. The main gift section has about four enemy solders in their power armor.

When you reach the control room, you will encounter Colonel Autumn with an escort of two soldiers. This will be the final battle in the game, and should be easy with the other people around. One of the soldiers is wearing regular power armor, with the other wearing Tesla armor (resistant to energy weapons.)

It is possible to use a few speech checks to convince him to leave without fighting. Sentinel Lyons will comment about this based on your karma level, before heading to the control room.

Control room
At the control room, you have several options:
 * Do nothing and flee.
 * Convince Lyons to enter the control room.
 * Enter the control room yourself, activating the purifier to create clean water.
 * Enter the control room yourself, activating the purifier with the FEV virus.
 * If you have Broken Steel installed, you can also ask one of your companions to activate the purifier for you. The companions who can activate it are Fawkes, RL-3, and Charon, as they are all immune to radiation.

The combination to project purity is 2-1-6. You can learn this from the audio logs created by James, which point to the Book of Revelations, verse 21:6.

The radiation inside the control room is lethal. When using the Advanced Rad Suit and Rad-X, you will take approximately 1 rad/second until you successfully enter the code - at that point, a cutscene takes over and kills the player (unless Broken Steel is installed, in which case it merely knocks the player out).