to ATP.
Salt will poison the ground and take a very long time to dissipate. That will preclude being able to plant anything in that area.
You can use glysophate (Round-up) and coat the cut back plant, or use any of these alternative methods. Please be advised, it may take more than 1 application to totally eradicate the pampas grass.
1) use straight vinegar and drench the plant, cover with plastic
2) cover the plant with a tarp, stake in place and allow it to stay until the plant is dead (deprives water and sunlight)
3) One study found good results using an application called "ropewick treatment," which applies herbicide with a wick or sponge attached to a "well" of herbicide. None of the nurseries I contacted had heard of this device. It would permit the application of herbicide directly to the leaves of the plant, which can also be done (carefully) with a paintbrush. Using herbicide in either summer or fall is advised. One study recommended cutting back fronds/leaves in early summer; as new growth appears in late summer, use herbicide on the new growth. This method requires less herbicide. (from this link)
http://ucanr.edu/sites/MarinMG...
4)Trench around the plant, set fire to the crown (only after cutting the plant to the ground) then, treat any new growth with Glysophate/herbicide
Good Luck.