I hooked up a hot tub today that a customer has buried in the ground (mostly). It is actually half hot tub and a half pool that generates a current so you can swim in place. It is about 12 feet long and about 5 feet wide divided into two separate sections. He buried it into a hill that slopes at a 45 degree angle so all sides are underground except for the side that has the electrical connections. Since this is now buried underground does it now need a copper conductor grid? There will be no concrete or pavers just dirt around the unit. I'm a little unsure of the perimeter surfaces section of article 680.