I’m having underground electrical installed at my house, Southern California. The trench passes very close to a massive mature pine tree, roughly 3 ft trunk diameter, around 80 ft tall, with a very wide canopy.

The electrical conduit will be 3” in diameter and needs to be about 36” deep. The trench passes approximately 2–3 ft from the edge of the trunk.

I knew there were large roots in the area, and the contractor had been trying to work around/tunnel underneath them. After they finished for the day, the contractor told me that they weren’t able to tunnel under these roots and they’ll have to cut and trench through the concrete driveway, which I agree with. However, I inspected the excavation and realized several substantial roots had been cut, maybe about 10 percent of the exposed roots in the picture (most of the exposed roots they did not cut).

From what I can tell, approximately:  
Four \~2” diameter roots  
One \~3” root  
One \~4” root  
One \~5” root that appears partially cut/damaged

I’ve attached photos of the larger ones.  
The cuts are concentrated along the same general side of the tree. The tree otherwise appears healthy, but because it’s approximately 80 ft tall, stability would obviously be a major concern, especially since we regularly get 60 to 80 mph wind gusts in my area. It’s also close enough that it could potentially hit and significantly damage my neighbor’s house.

I’ve scheduled a certified arborist to inspect the tree and exposed roots tomorrow morning, and I’ve already informed my neighbor. No additional work will happen around the tree before the arborist sees it.

For the arborists/tree professionals here:  
How significant is this amount of root loss for a tree this large, particularly only 2–3 ft from the trunk?

I’m especially interested in whether this is more of a long-term tree-health issue or whether cutting roots of this size could meaningfully affect structural stability.

Also, assuming the arborist determines the tree is still generally stable, what would be a reasonable rule for the contractor going forward? For example, should I tell them not to cut anything greater than 2” without stopping and getting approval, or should essentially all roots this close to the trunk be preserved and tunneled around?

Contractor cut several 3-5" roots from a huge mature tree while trenching - how concerned should I be?