Tree Huggers

I'm not sure if this is a good fit for this community, but I've read enough to know there are some very knowledgeable folks here, so I thought I'd give it a shot. Feel free to remove if it's off topic/too specific.

This umbrella pine has been here for around 60 years, and recently started having some trouble. I know a certain amount of yellowing and seasonal needle drop is common, but it seems like this one's been hit especially hard, and there's a companion tree on the other side of the house, same age, which is still deep green. I'd really really love to keep it going, and I'm hoping it's not too late.

We had a bad summer, unusually wet, and I think it stressed this tree - the other one is on top of a hill so it must get better drainage. There was also some construction somewhat nearby, and uphill, which might be causing more water to enter the yard - the basement flooded for the first time in awhile. Also a road crew cut some trees that might have been shading it occasionally, I'm not sure. They might have been too far away to make any difference.

I'm planning to improve on a drainage ditch which runs along the driveway between this tree and the wettest areas, hopefully before snowmelt. I guess my questions are is there anything else I can/should do? Soil test in case it needs something? Can this tree be saved? It's yellowing but it still has some deep green in places (mostly on the shady side).

I have some closeups too if that would help.