The water line is about 2 foot deep.
Can I Plant Arborvitaes Over a Water Line?
Arborvitae are not considered a species with invasive roots, and the plumbing should be safe. Make sure to consider mature size in selecting a variety. This article will tell you more about growing healthy and beautiful arborvitae: https://www.gardeningknowhow.com/ornamental/trees/arborvitae/growing-arborvitae-trees.htm