This is on I-195 W just outside Trenton.
A few years ago the hill was excavated, "capped" with what appeared to be a black rubber sheet, then dirt.
Nothing much seems to grow there, even during the lush, rainy past two summers.
Sometimes geese can be seen grazing there (makes you wonder).
The 55-gallon drum - vent pipe contraptions likely allow venting of fermentation / decomposition gases.
Strangely, they seem to be inspired by the extraterrestrial craft depicted in "War of the Worlds"
(and Grover's Mill, NJ is just a few miles away).