Here, in the Florida Keys, our Agricultural Extension Office will test soil for free. That might be an option for you up there. Even if they don't do it, they probably know a company that will do it for a nominal cost.
Again, here, we have trees that are very salt tolerant and others that are not. Any idea if Douglas Fir is salt tolerant? We have had a few storms that have pushed salt water over our islands and it is always interesting to see which trees it affects and when. After "Wilma", which pushed up to 10 feet of salt water over Marathon, we had Gumbo Limbo trees that looked good for about 3 years, then boom, on the ground they went. The root damage was obvious and then assumed it was from the 4 hours of salt water intrusion. (the water left the island in 4 hours) However, some Gumbos never have failed.
This past year, we had Irma which pushed a wall of salt water 12' over certain islands. Some trees went down with the 130 mile per hr winds lol, but it will be interesting to see, in a couple of years, which trees that were left standing were affected by the salt water.
Not sure if you have lived in that area long enough to know the answer to this, but are you seeing sea levels rising there? In my 20 years down here, I have seen it here. If I had not seen it with my own two eyes, you would not have been able to convince me that the sea level is rising.