The Dreaded Septic bed

The Dreaded Septic bed

Hey guys, i have a quick question. I have a client who would like native materials planted around and over her bed, because they have already badly disturbed the forest to install it there. I am a city folk, so I don't know much about how a septic bed works. I am doing as they ask, which is do some research for them and test their soil, but when the septic bed is fully functional, won't the soil be very poor? Either way, I only want to recommend groundcovers for their bed, if any, though they have already been advised to only plant grass. What should I do? I want them to be happy with something, but with very shallow roots.
plant id.

plant id.

Newbie

Newbie

Autumn’s Place

Autumn’s Place

Please help identify this plant

Please help identify this plant

Helppp!

Helppp!

my room.

my room.