A pre-War hazardous waste repository, now home to a variety of mutated enemies.
Entry is gained through the L'Enfant Plaza Metro tunnels. A hole in the tracks leads to the cave network below the subway tunnels. Another entrance is located at the southwest corner of the Mall, near the Lincoln Memorial. The L'Enfant Plaza entrance is a generic, large metro entrance behind the broken pyramid and next to a refrigerator. A number of super mutants occupy the area. The Mall entrance is signified by a large metro entrance near the Lincoln Memorial. No enemies repeatedly spawn in the vicinity of this metro entrance.
Near the L'Enfant Plaza entrance is a rigged baby carriage along the wall and a bed located in the corner by the collapsed hallway. The disposal site is home to one or two super mutants (near the L'Enfant Plaza exit), and a number of feral ghouls, ranging from basic ferals to glowing ones.
At higher levels, with the Broken Steel add-on, there will be several feral ghoul reavers, usually one in the main cavern and one in each of the three tunnels. In addition, with the add-on, one can be attacked by super mutant overlords at higher levels when exiting into L'Enfant Plaza from the Mall.
- The body of a dead wastelander is found in the caverns, with their fingers twitching. The body may be animated in sleep mode instead of being animated dead, but isn't actually alive and can be looted normally. Looking closely will reveal there's gas in the area, which causes a shimmering effect and makes it look like the fingers are moving. Any firearms will set off the gas.
- Neither of the metro exits leading to this location are consistent compared to their locations in the Capital Wasteland. The Mall Southwest metro exit faces directly northwest according to its exterior location, but once inside, the player is facing due south. Similarly, the exit to L'Enfant Plaza faces due east on the exterior, but directly north when inside. When looking through the grate doors separating the worldspaces, there is no visible bend suggesting a directional change.
Hazmat disposal site L5 appears only in Fallout 3.